Umbilical cord blood transplantation in adults using myeloablative and nonmyeloablative preparative regimens

Article Outline

• Abstract
• Introduction
• UCBT using myeloablative preparative regimens
• Clinical results in adult patients
• Comparative analysis of unrelated UCBT in children and adults
  • Hematopoietic recovery and engraftment
  • Graft-versus-host disease
  • Toxicity and transplant-related mortality
  • Disease relapse
  • Survival and outcome
  • Summary
• NM stem cell transplantation
  • NM transplantation with UCB progenitor cells
  • The Duke university experience
  • NM UCBT—results from other transplant centers
• Immune reconstitution
  • Immune reconstitution in myeloablative UCBT patients
  • Differences in UCB immune reconstitution between myeloablative and NM regimens
• Ex vivo expansion and transplantation of multiple units of UCB
• Remaining questions and future directions for UCBT in adults
  • What is the optimal UCB cell dose required for adult patients?
  • What is the difference in overall efficacy between myeloablative and NST UCBT?
  • Is the incidence of GVHD similar in ablative versus NST regimens?
  • Is the incidence of infection similar in ablative versus NST regimens?
  • What is the optimal NST conditioning regimen and GVHD prophylaxis?
• Conclusion
• References
• Copyright

Abstract 

Unrelated umbilical cord blood (UCB) transplantation has recently been explored in an increasing number of adult patients. The relative ease of procurement and the lower-than-anticipated risk of severe acute graft-versus-host disease has made UCB transplantation an appealing alternative to bone marrow-derived hematopoietic stem cells. The use of reduced-intensity or nonmyeloablative preparative regimens to allow engraftment of UCB broadens the scope of patients who may benefit from allogeneic immunotherapy, including elderly and medically infirm patients with no matched sibling donor. This review summarizes the available data on the use of UCB as an alternative source of hematopoietic stem cell transplantation in adult patients.

Keywords:  Umbilical cord blood transplantation, Hematopoietic stem cell transplantation, Nonmyeloablative preparative regimen

Back to Article Outline

Introduction 

The success of the first allogeneic umbilical cord blood (UCB) transplantation in October 1988 in a child with Fanconi anemia [1] opened the way to an entire new field in the domain of allogeneic hematopoietic stem cell transplantation (HSCT). After this successful transplantation procedure, it is estimated that more than 2000 UCB transplantations (UCBT) have been performed worldwide from both related and unrelated donors (UD) [2], although many of these transplantations have not been reported in refereed publications for evaluation. UCB has now been accepted as an alternative source for HSCT in children. The rapid expansion in the use of UCB for transplantation is the culmination of several factors, most of which are to address the limitations encountered in the use of HLA-matched related hematopoietic stem cells: these include (1) a lack of suitable HLA-matched donors; (2) complications of graft-versus-host disease (GVHD) associated with HLA disparities, particularly if bone marrow from an HLA-matched UD is used 3, 4; and (3) the cumbersome process of identifying, typing, and harvesting from an UD, with a median time interval between initiation of a search and donation of marrow of approximately 4 months [5].

Unrelated UCB offers many practical advantages as an alternative source of stem cells, including (1) the relative ease of procurement and the fact that stem cells are available considerably faster than are unrelated bone marrow grafts [6]; (2) the absence of risk for mothers and donors; (3) the reduced likelihood of transmitting infections, particularly cytomegalovirus (CMV); (4) the ability to store fully tested and HLA-typed cord blood (CB), in the frozen state, available for immediate use [7]; (5) potential reduced risk of GVHD [8]; (6) less stringent criteria for HLA matching for donor/recipient selection; and (7) absence of donor attrition.

The past 12 years have witnessed an explosion of advances leading to an increased understanding of the biological characteristics of UCB, in parallel with its applications in clinical transplantations. UCB banks have been established for related and unrelated UCBT, and more than 30 000 units are currently available [9]. Although CB transplantation from both related donors and UDs has demonstrated encouraging results in pediatric patients with hematologic malignancies or marrow failure syndromes, there is still limited applicability in adults. The lower number of hematopoietic stem cells in CB compared with bone marrow, together with preliminary data showing the importance of cell dose for the outcome of UCBT, has been a cause for caution with its use in adult patients 10, 11. Also, most UCBT involved the use of myeloablative preparative regimens that are known to be associated with considerable morbidity and mortality. Despite having suitable UCB donors, many older patients and patients with comorbidities will be prevented from receiving UCBT because of the unacceptable toxicities from the standard conditioning regimens.

Recently, older recipients of allogeneic HSCT have been treated successfully after a variety of less intense nonmyeloablative (NM) conditioning regimens 12, 13, 14. These encouraging observations were a result of selective ablation of the lymphoid cells by using lymphotoxic agents, large progenitor cell doses, and drugs to prevent host-versus-graft disease, as well as GVHD. On the basis of these encouraging observations, it has been hypothesized that a reduced-intensity preparative regimen would allow engraftment of the UCB stem cells. Although the total numbers of mononuclear cells are limited, the progenitor content and the proliferative potential of CB cells are high. Therefore, these CB cells could establish full donor chimerism with a lower risk of transplantation-related morbidity in older patients and in patients who are deemed unfit to undergo transplantation with conventional myeloablative preparative regimens. UCB, with its unique cellular characteristics as listed previously, can potentially overcome the problem of limited availability of suitable related and unrelated stem cell donors and thereby broaden the scope of patients who may benefit from NM HSCT.

This review summarizes the available data on the use of UCB as an alternative source of hematopoietic stem cells for allogeneic transplantation in adult patients, with an overview of the current knowledge on some areas of interest, including a comparative analysis in clinical outcome between adult and pediatric patients, the difference between myeloablative and NM approaches, and several areas of uncertainty on the NM approach.

Back to Article Outline

UCBT using myeloablative preparative regimens 

UCBT in adults and children from related donors and UDs after myeloablative preparative regimens has been shown to produce successful engraftment in both children and adults with hematologic malignancies, marrow failure syndrome, and immune deficiencies. The results of several large series have been reported in the peer-reviewed literature over the past 7 years 8, 9, 10, 11, 15, 16, 17, 18, 19, 20, 21, 22. The myeloablative preparative regimens used in these studies were either total body irradiation (TBI) based or chemotherapy based, with inclusion of antithymocyte globulin in some of the patients. The data from these UCBT registries, in which most recipients are children, point to a significant delay in the time of neutrophil recovery, with the median time to an absolute neutrophil count (ANC) >500/μL ranging between 22 and 30 days. The overall probability of engraftment was in the range of 80% to 90%. Despite a higher degree of HLA disparity, grade II to IV GVHD in those unrelated UCB recipients was lower than in recipients of unrelated bone marrow or peripheral blood grafts from adult donors. It is important to note that the number of nucleated cells in the infused UCB influences the speed of recovery of neutrophils and platelets. In a recently published study, Wagner et al. [20] demonstrated the importance of CD34 cell dose in determining the outcome after unrelated UCBT. Patients receiving a CD34 cell dose <1.7 × 10⁵/kg body weight have a slower neutrophil recovery at a median of 34 days (range, 17–54 days), an inferior likelihood of engraftment, and a higher incidence of treatment-related mortality.

Back to Article Outline

Clinical results in adult patients 

In comparison to the published studies on pediatric patients, the clinical data on the use of UCBT in adult patients is relatively limited: 3 in peer-reviewed published articles 9, 21, 22 and the remaining either in abstract form 23, 24, 25, 26, 27 or integrated into the studies that have been conducted in predominantly pediatric populations 10, 11, 20, 28. The clinical results of the studies that were conducted exclusively in adult patients are summarized in the following paragraphs and in Table 1.

Table 1. Studies of Unrelated Umbilical Cord Blood Transplantation in Adults

NA indicates not available; TRM, treatment-related mortality; NC, nucleated cell dose; TAI, thoracoabdominal radiation; Ara-C, cytarabine arabinoside; Thio, thiotepa; ATG, antithymocyte globulin; Bu, busulfan; Flu, fludarabine; Cy, cyclophosphamide; Mel, melphalan; Pred, prednisolone; FK506, tacrolimus; MDS, myelodysplastic syndrome.

Laughlin et al. [21] published one of the first multicenter studies of 68 adults with life-threatening hematologic disorders (79% hematological malignancies; 21% bone marrow failure syndrome or inborn error of metabolism) who were receiving HLA-mismatched unrelated UCBT. Approximately one third of the patients had advanced or refractory hematologic malignancies before transplantation. The median age of the patients was 31.4 years (range, 17.6–58.1 years), and the median weight was 69.2 kg (range, 40.9–115.5 kg). More than two third of the patients received grafts that were mismatched for ≥2 HLA antigens. The probability of neutrophil recovery during the first 42 days after transplantation was 90%. The median time required for an ANC ≥500/μL and platelets ≥20 000/μL was 27 days (range, 13–59 days) and 58 days (range, 35–142 days), respectively. As in children, rapid recovery occurred in patients who received the highest number of nucleated cells in UCB before freezing and CD34⁺ cells after thawing. Despite HLA mismatches in more than two thirds of the patients, the incidence of GVHD was low. Only 11 (20%) of the 55 evaluable patients developed grade III or IV GVHD within the first 100 days after transplantation. With a median follow-up of 22 months (range, 11–51 months), 19 (28%) of the 68 patients were alive, and 18 were disease free. The event-free survival (EFS) at 40 months was 26%. Notably, the presence of a higher CD34⁺ cell dose—>1.2 × 10⁵/kg—was associated with improved EFS.

Sanz et al. [22] reported the results of unrelated UCBT after a standardized preparative and GVHD regimen in a series of 22 adult patients with hematologic malignancies. The median age was 29 years (range, 18–46 years), and the median weight was 69.5 kg (range, 41–85 kg). HLA matching was 6 of 6 in 1 case, 5 of 6 in 13 cases, and 4 of 6 in 8 cases. The median number of nucleated cells infused was 1.71 × 10⁷/kg (range, 1.01–4.96 × 10⁷/kg). All 20 patients who survived for >30 days experienced myeloid engraftment. The median time to reach an ANC >0.5 × 10⁹/L and platelets >20 × 10⁹/L was 22 days and 69 days, respectively. All patients except 1 developed acute GVHD. Seven patients developed acute GVHD above grade II, and 9 of 10 patients at risk developed chronic GVHD. Disease-free survival (DFS) at 1 year was 53%. Patients younger than 30 years had a better DFS than the older age group. Of note, a greater proportion of patients in this series presented with more favorable disease status at transplantation as compared with most other adult series; 13 (59%) patients had either chronic myeloid leukemia (CML) in first chronic phase or acute leukemia in first remission.

Gluckman [9] analyzed the outcomes of 108 adults who received unrelated UCBT and who were reported to the Eurocord registry [23]. The median age was 26 years (range, 15–53 years) for the entire group of patients, of which most had leukemia or lymphoma. The median weight was 60 kg (range, 35–110 kg). With a median infused nucleated cell dose of 1.7 × 10⁷/kg, the probability of 81% myeloid engraftment at day 60 was attained. The median time for ANC to exceed 500/μL and platelets to exceed 20 000/μL was 32 days (range, 13–57 days) and 129 days (range, 26–176 days), respectively. The overall 1-year survival was 27%, and more favorable outcomes were seen among patients with chronic disease or leukemia in remission. The estimated transplant-related mortality at day 100 was 54%. Disease in the chronic phase or remission, an infused nucleated cell dose ≥2.0 × 10⁷/kg, and transplantation performed after January 1998 were identified as factors that were associated with lower treatment-related mortality (TRM) within the first 100 days.

Goldberg et al. [24] performed 19 unrelated UCBT in adult patients with hematologic malignancies or myelodysplastic syndrome, and several patients had high-risk diseases or had experienced treatment failure with prior autologous transplantation. The median age was 48 years (range, 20–59 years), and the median weight was 69 kg (range, 52–126 kg). The degree of HLA matching of the UCB units was 6 of 6 in 4, 5 of 6 in 8, and 4 of 6 in 7 patients. The median infused cell total nucleated dose was 1.8 × 10⁷/kg. Ten patients in this study group received ex vivo expanded UCB units. The median time to ANC >500/μL was 28 days, and the median time to platelets >20 000/μL was 56 days. The 100-day overall survival was 32%. One-year overall survival was 20% in good-risk and 21% in poor-risk patients.

The Cord Blood Transplantation Study Group recently updated the results of their National Heart, Lung, and Blood Institute-sponsored, prospectively conducted pilot study on the use of unrelated UCBT in patients requiring allogeneic transplantation [26]. The 34 adult patients in the study, most of whom had poor-risk hematologic malignancies, were at a median age of 34.5 years (range, 18.2–55 years). Most subjects (n = 23) were matched at 4 of 6 HLA alleles; 10 subjects were matched at 5 of 6 alleles and 1 at 6 of 6 alleles. The conditioning regimen was TBI/cyclophosphamide for 27 patients and busulfan/melphalan for 7 patients. The median nucleated cell dose infused was 1.73 × 10⁷/kg (range, 11.1–37.5 × 10⁷/kg). Primary graft failure was seen in 8 (28%) of the evaluable patients. Engraftment occurred in 22 of the 29 evaluable subjects, with a cumulative incidence of 72% achieved by day 60. Grade II to IV acute GVHD and grade III to IV GVHD was seen in 11 (38%) and 6 (21%) of the 29 evaluable patients, respectively. Four patients were alive between 373 and 743 days after transplantation. Kaplan-Meier survival estimates, excluding the 4 early deaths, were 47% and 30% at 100 and 180 days, respectively. Notably, overall survival was not influenced by age stratification, degree of matching, or cell dose. The poor survival outcome in this cohort of patients reflects the poor-risk subjects enrolled onto the study.

Iseki et al. [29] reported one of the largest series of adult unrelated UCB recipients outside North America and European transplant centers. In their series of 30 Japanese patients with hematologic malignancies or myelodysplastic syndrome, the median age, weight, and infused nucleated doses were 38 years, 52 kg, and 2.39 × 10⁷/kg, respectively. The median time for neutrophil recovery (ANC ≥500/μL) and platelet recovery (≥50 000/μL) was 22 days and 38 days, respectively. Early death occurred in 3 patients. Eight patients developed acute GVHD grade II, and 1 patient developed grade III GVHD. The overall survival was 36% at 3 years.

In another Japanese series reported by Ooi et al. [30], 13 patients with advanced myelodysplastic syndrome received 1 to 3 HLA antigen-mismatched unrelated UCB infusion after a myeloablative preparative regimen containing granulocyte colony- stimulating factor (G-CSF) and cytosine arabinoside in combination with the standard TBI and cyclophosphamide regimen. The median age of the patients was 40 years (range, 21–50 years), the median weight was 51 kg (range, 43–68 kg), and the median cell dose was 2.43 × 10⁷/kg of nucleated cells. Of note, before transplantation, 8 of the 13 patients did not receive induction therapy, and 4 of the 5 patients who received induction therapy could not achieve complete remission. Myeloid reconstitution occurred in 12 patients (92%), and the median time for neutrophil recovery (ANC ≥500/μL) and self-sustained platelet recovery (≥50 000/μL) was 22.5 days and 49 days, respectively. The probability of DFS at 2 years was 76.2%.

At Duke University, 57 patients with both malignant and nonmalignant hematologic diseases underwent unrelated UCBT between January 1996 and January 2002. Nineteen of these patients were included in the multicenter study published in 2001 [21]. The follow-up on surviving patients has been extended from that study by 22 months, with an additional 38 patients included for analysis. The median age was 31 years (range, 18–58 years), and the median weight was 70 kg (range, 46–110 kg). HLA matching between donor and recipient was 3 of 6 in 3 patients, 4 of 6 in 44 patients, 5 of 6 in 8 patients, and 6 of 6 in 2 patients. The median infused nucleated cell dose was 1.50 × 10⁷/kg (range, 0.54–2.78 × 10⁷/kg), and the median infused CD34⁺ cell dose was 1.37 × 10⁵/kg (range, 0.02–12.45 × 10⁵/kg). Forty-one of the 57 patients had evidence of neutrophil engraftment, reaching an ANC of ≥500/μL at a median of 26 days (range, 12–55 days) with an untransfused platelet count of 20 000/μL at a median of 84 days (range, 35–167 days). The number of CD34⁺ cells correlated with the rate of platelet recovery. Acute GVHD of grade III or IV developed in 9 of 41 evaluable patients. Chronic GVHD was seen in 8 patients who survived >100 days. With a median follow-up of 1670 days (range, 67–2251 days) for the surviving patients (n = 11), the overall survival and EFS at 3 years were 19% and 15%, respectively. Notably, patients who were 31 years or younger had a significantly better EFS than those who were older.

Back to Article Outline

Comparative analysis of unrelated UCBT in children and adults 

Hematopoietic recovery and engraftment 

Comparative studies by Eurocord in pediatric patients have suggested that as compared with allogeneic marrow transplant recipients, UCBT recipients have a lower engraftment rate and more delayed hematopoietic recovery 8, 31. The median times for neutrophil recovery to ANC recovery and platelet recovery (>20 000/μL) in unrelated UCB recipients were significantly delayed: 32 days (range, 11–56 days) and 81 days (range, 16–159 days), respectively, for unrelated UCBT recipients as compared with 18 days (range, 10–40 days) and 29 days (range, 8–141 days) for unrelated marrow recipients [31]. The higher risk of graft failure and the delay in hematopoietic recovery may be related to several factors, including the lower nucleated cell and CD34⁺ cell doses with the UCB grafts as compared with the marrow allografts 32, 33, 34; factors such as immaturity of stem cells, which might need more cell divisions before differentiation to marrow progenitors; and the lack of subpopulations to facilitate engraftment [35]. However, a study performed by the University of Minnesota reported a different outcome in terms of engraftment. In their matched-pair analysis comparing twenty-six 0 to 3 HLA-mismatched unrelated UCB recipients with 26 matched unrelated unmanipulated marrow recipients, neutrophil recovery was significantly delayed in the unrelated UCB recipients, but there was no significant difference in terms of the overall engraftment rate at day 45 and platelet recovery.

The important correlation between nucleated cell dose and rate of engraftment in unrelated UCBT patients has been demonstrated by the data from New York Blood Bank and the Eurocord registry 10, 11. A recent study published by investigators from the University of Minnesota has shown that recipients of UCB grafts containing CD34⁺ cells >1.7 × 10⁵/kg had a incidence of engraftment similar to that observed in unrelated marrow allograft recipients [20].

The concern of limited cell doses leading to a higher risk of primary graft failure in adults is related to the disproportionate difference between the number of nucleated cells in the UCB graft and the adult body weight, giving rise to relatively fewer infused cells per kilogram of the recipient body weight, especially in heavier patients. However, the available data on adult recipients of unrelated UCBT thus far have shown that UCB contained sufficient numbers of hematopoietic stem cells to achieve engraftment. The observed primary graft failure rate was approximately 10% to 20%, the median day to neutrophil engraftment (ANC >500/μL) ranged between 22 and 32 days, and the probability of engraftment by day 60 ranged between 70% and 100%. These results seem comparable to those observed in the pediatric series, in which the median time for neutrophil engraftment ranged between 25 and 32 days and the probability of myeloid engraftment ranged between 80% and 90% 10, 11, 28, 31, 36. Similar to pediatric patients, the neutrophil and platelet recovery in adult UCB recipients were significantly delayed compared with the marrow allograft recipients.

In 2 of the largest adult series, the nucleated cell dose was associated with the rate of neutrophil and platelet recovery 9, 21. In the multicenter study by Laughlin et al. [21], neutrophil engraftment was faster in adult patients who underwent transplantation with a cryopreserved nucleated cell dose >1.87 × 10⁷/kg. In the Eurocord analysis, an infused nucleated cell dose of >1.7 × 10⁷/kg was associated with more rapid neutrophil recovery [23].

Ooi et al. [37], in a non-matched-pair analysis, performed a clinical comparison of 8 unrelated UCBT recipients with 8 unrelated marrow transplant recipients. All patients in both groups were adult patients with acute leukemia in complete remission who received the same conditioning regimen, GVHD prophylaxis, and supportive treatment. The median times to ANC >0.5 × 10⁹/L (33 days of UCBT versus 20.5 days of bone marrow transplantation [BMT]; P < .05) and platelets to >50 × 10⁹/L (48 days of UCBT versus 25.5 days of BMT; P < .05) were significantly longer in the UCBT group.

The correlation between CD34⁺ cell dose and engraftment has also been evaluated. In the Duke University series, patients who received >1.37 × 10⁵/kg CD34⁺ cells had more rapid platelet recovery. No correlation between CD34⁺ cell dose and engraftment was discerned in the multicenter study by Laughlin et al. [21], although in that study, EFS was improved in patients who received >1.2 × 10⁵ CD34⁺ cells per kilogram.

The optimal nucleated cell dose and CD34⁺ cell dose in UCB grafts remain to be determined. In the context of pediatric patients, the recommended nucleated cell doses include 1.0 × 10⁷/kg, 1.5 × 10⁷/kg, and 2.0 × 10⁷/kg 28, 38, 39. A CD34⁺ cell dose of 1.7 × 10⁵/kg has been established as the threshold dose for patients at the University of Minnesota [20]. On the basis of the clinical data available so far for adult unrelated UCBT 21, 23, it is not unreasonable to suggest that UCB should contain a cryopreserved cell dose of at least 1.8 × 10⁷ nucleated cells per kilogram and 1.2 × 10⁵ CD34⁺ cells per kilogram.

Graft-versus-host disease 

Published data from most of the CB registries 10, 11, 17, 18, 20, 32 have shown that despite the infusion of HLA class I and II disparate grafts, the incidence and severity of acute and chronic GVHD among unrelated UCB recipients have thus far been lower than previously reported in recipients of matched UD marrow or partially matched family member marrow allografts 40, 41, 42, 43, 44. In these series of UCBT recipients, most of whom are children, the overall incidence of grade II to IV acute GVHD and grade III to IV acute GVHD were in the range of 30% to 50% and 10% to 20%, respectively.

Barker et al. [36], in a matched-pair analysis, demonstrated a similar rate of acute and chronic GVHD between pediatric recipients of 0 to 3 HLA antigen-mismatched UD UCB grafts and those who received HLA-matched UD marrow grafts. Another comparative study by Rocha et al. [31] has demonstrated a lower incidence of acute GVHD (hazard ratio, 0.50) and chronic GVHD (hazard ratio, 0.24) in a cohort of pediatric patients who received mismatched unrelated UCB grafts compared with unrelated, unmanipulated bone marrow recipients. The association between HLA disparity and the risk of GVHD in unrelated UCB recipients remains unclear; most studies demonstrate no correlation 10, 16, 17, 20, 28. However, in an updated multivariate analysis of data from the largest series published so far, Rubinstein and Steven [45] have shown a significant association between acute GVHD and HLA disparity. The incidence of grade III to IV acute GVHD in patients with no mismatch, 1-antigen HLA mismatch, and ≥2-antigen mismatch were 8%, 19%, and 28%, respectively (P = .006).

To date, no matched-pair comparative study has been performed in the adult patient population to compare the incidence of GVHD between unrelated UCBT and UD marrow transplantation. The reported series in adults have shown 40% to 60% and 20% to 22% incidences of grade II to IV and grade III to IV acute GVHD, respectively, and a 26% to 90% incidence of chronic GVHD (Table 1). Given the increased patient age in these adult patients (age is recognized as a risk factor for GVHD 46, 47), the incidence of acute and chronic GVHD among these adult patients is considered acceptable as compared with the pediatric unrelated UCBT series, which have reported 33% to 44% and 11% to 22% incidences of grade II to IV and grade III to IV GVHD, respectively, and a 0% to 25% incidence of chronic GVHD 10, 11, 20, 31. Also, with many of these patients receiving HLA-mismatched UCB grafts, the incidence of grade III to IV acute GVHD in these unrelated UCB recipients compares favorably to the 35% to 55% incidence reported in recipients of HLA-matched bone marrow from adult UDs who received standard prophylaxis against GVHD 41, 42, 43, 44, 48. It is noteworthy that the reported incidence of chronic GVHD showed a wide range from 26% to 90%. In comparison, chronic GVHD develops in 55% to 75% of patients who receive HLA-matched BMT from UDs 41, 42, 43, 44, 48. The variability in the reported rate of GVHD may be attributed to the following factors: (1) differences in conditioning regimens and GVHD prophylaxis regimens used by different centers, (2) differences in supportive care, (3) transplant center effect [49], (4) the disease and disease status of the patients, and (5) subjective elements and inconsistency involved in the grading of GVHD by different teams. The association between HLA mismatch and GVHD has not been addressed in these adult series except in the report by Laughlin et al. [21], which did not observe any influence of histocompatibility on the severity of acute GVHD.

Toxicity and transplant-related mortality 

Several series with predominantly pediatric patients receiving unrelated UCB grafts have reported 100-day and 1-year TRM in the range of 27% to 39% and 30% to 44%, respectively 16, 20, 31, 36. Infection and acute GVHD were the main causes of death within the first day after transplantation. Rocha et al. [31] reported in their pediatric studies that the incidence of 100-day TRM in the unrelated marrow recipients was significantly higher as compared with the unrelated UCB recipients. However, no such difference was detected in another series reported by the group from the University of Minnesota [36]. The University of Minnesota series, which consisted predominantly of children, has shown the important association between TRM and CD34 dose, recipient’s age, and development of grade III to IV acute GVHD. However, no correlation could be discerned between HLA and TRM [20].

A relatively higher incidence of TRM at 100 days has been observed in the adult series, ranging between 43% to 56%. The high nonrelapse mortality in these series is partially attributable to the high-risk nature of the patient population. Several prognostic factors have been found to predict higher TRM. The Eurocord data, which showed a higher 180-day TRM in adult unrelated UCB (56%) as compared with the pediatric patients (32%), found a lower 100-day TRM among patients with disease in chronic phase or remission, number of nucleated cells infused ≥2.0 × 10⁷/kg, and transplantation performed after January 1998 9, 39. In the Laughlin et al. [21] series, the TRM for the first 100 days was 50%, and nearly half of the deaths were due to infection. Notably, improved EFS was seen among patients who received UCB grafts with CD34⁺ cells >1.2 × 10⁵/kg [21]. A study from a Spanish center on 27 adult recipients of unrelated UCB has shown a 100% incidence of infectious episodes, a 55% incidence of bacteremia, a 58% incidence of CMV antigenemia, and an 11% incidence of fungal infections. In that study, the reported TRM at day 100 was 37%, and 80% of the deaths were related to infections. It is important to note that the study observed more than half of the infections occurring after myeloid recovery [50].

The increased risk of infection within the first 100 days after transplantation may be related to delayed engraftment, GVHD, or impaired immune recovery 11, 21. With the data from the University of Minnesota showing the profound influence of CD34 cell dose on the rate of engraftment, TRM, and survival and also the observation that most recipients of UCB with an adequate cell dose do not die of infection [20], it is believed that prolonged neutropenia is the main contributory cause of increased risk of infection. However, the Spanish experience [50], which showed a high incidence of infection after myeloid recovery, certainly suggests the influence of impaired immune recovery and GVHD in causing infections.

Organ toxicity associated with the intensive treatment administered to patients before UCBT is another leading cause of nonrelapse mortality in adult UCB recipients. In the Laughlin et al. [21] series, 35% of the deaths were related to the preparative regimen. Because of toxicities from the intensive conditioning regimens to nonmarrow organs, such as gut, liver, lung, and heart, UCBT with myeloablative preparative regimens has been restricted to patients younger than 50–55 years of age; none of the series reported thus far has included patients older than 60 years of age. Such restrictions based on age are problematic in that many hematologic malignancies typically present after the age of 50 years [51], thus making many patients ineligible for UCBT despite having suitably matched unrelated UCB grafts with adequate cell doses. These limitations have given an impetus for exploring the use of NM regimens for UCBT, as will be discussed later in this article.

Finally, given the heterogeneity of the patient population and the conditioning and GVHD prophylaxis regimens used, as well as the supportive care rendered at the different centers, it is difficult to have a reliable evaluation of the possible effect of different pretransplantation variables on TRM. However, among all the different prognostic variables that have been evaluated, the cell dose of the UCB graft seems to be the only one that can be manipulated [20]. Future efforts in decreasing TRM should therefore focus not only on improving transplant methodology and supportive care, but also on improving the UCB cell dose.

Disease relapse 

As with UD BMT, relapse is another common cause of death after UCBT. Concerns raised about the possibility of an increased risk of leukemia recurrence in UCBT recipients are derived from the following considerations: (1) there is a close association of graft-versus-leukemia (GVL) with GVHD in allograft recipients, such that patients who develop either acute or chronic GVHD experience a much lower risk of relapse 52, 53; (2) the incidence and severity of both acute and chronic GVHD seemed to be less after transplantation of CB progenitors than after marrow transplantation 10, 11, 17, 18, 20, 31; and (3) immaturity and diminished cytotoxicity of infused CB lymphocytes 54, 55 could further impair the immune-mediated anti malignancy effect. However, 3 previous reports comparing UCBT and unmanipulated BMT from HLA-identical siblings [8] and from UDs 31, 36 among children with leukemia have shown a similar risk of relapse. The 2-year incidence of relapse in children receiving unrelated UCBT ranges between 37% and 40%, and disease status at transplantation is the predominant risk factor 16, 20, 31.

In comparison with the pediatric series, the data on the adult patient population are scanty and inconclusive because of a smaller number of patients, shorter duration of follow-up, and difference in patient selection. The reported incidence of relapse as the cause of death has ranged widely between 6% 21, 24 and 35% [26]. The variability in the relapse rate is likely due to heterogeneity in patient selection.

Survival and outcome 

Two comparative studies in pediatric patients have shown no difference in survival between patients receiving UD UCBT and UD BMT 31, 36. Most of the studies, which mainly involved children with UD UCBT, have reported 1- and 2-year overall survival in the range of 29% to 58% and 35% to 53%, respectively 10, 20, 28, 31, 36. The prognostic factors that have been found to influence survival include (1) disease status at transplantation 9, 16, (2) HLA match 11, 20, (3) infused nucleated cell dose per kilogram of recipient’s weight 10, 11, 28, (4) CD34 cell dose per kilogram of recipient’s weight 20, 28, (5) age of recipient 11, 28, (6) grade III to IV GVHD [20], and (7) CMV status of recipient [10].

In contrast to the series in children, it is difficult to have a reliable evaluation of the possible effect of various pretransplantation variables on the survival of the adult UCB recipients because of the heterogeneity of the patient population and the limitations of small patient numbers and a short duration of follow-up. The available series thus far have reported a survival outcome with a wide range, from 19% to 76% for 3-year overall survival and from 21% to 53% for 1-year EFS. In the Laughlin et al. [21] series, the presence of a higher CD 34⁺ cell dose in the UCB graft was associated with improved EFS. In both the Duke University series and the Spanish series [22], age at transplantation had a significant effect on survival. The Eurocord data have shown that a good risk status at transplantation and an infused nucleated dose of >1 × 10⁷/kg are favorable factors for survival [23]. The superior survival of a small group of Japanese patients with high-risk myelodysplastic syndrome has provided further evidence that an adequate cell dose has a critical effect on survival [30]. Of note, none of these studies has demonstrated any association between HLA disparity and survival. However, in a recent review with 861 unrelated UCBT recipients from the placental blood program of the New York Blood Center, which included 181 (21%) patients aged ≥18 years and 170 patients (20%) weighing ≥60 kg, Rubinstein and Steven [45] demonstrated in a multivariate analysis that HLA match was an independent predictor of EFS in the subset of patients with acute lymphoblastic leukemia (ALL), acute myeloid leukemia, or CML.

A study from the St. Louis Cord Blood bank, reported in abstract form, compared the outcome of 23 adults (with median age of 39 years [range, 17–66 years] and a median weight 66 kg [range, 41–131 kg]) with that of 83 children (with a median age of 7 years [range, 1–16 years] and a median weight of 25 kg [range, 6–78 kg]) [56]. The adult patients received a significantly lower cell dose, with a median total nucleated cell dose of 2.7 × 10⁷/kg (range, 1.1–5.3 × 10⁷/kg) and a median CD34 cell dose of 1.4 × 10⁵/kg (range, 0.2–4.4 × 10⁵/kg), as compared with the children, who had a median total nucleated cell dose of 5.8 × 10⁷/kg (range, 1.3–24.8 × 10⁷/kg) and a median CD34 cell dose of 3.3 × 10⁵/kg (range, 0.5–20.8 × 10⁵/kg). The times to neutrophil and platelet recovery were similar between the 2 groups. The estimated 1-year survival was comparable between the adults and the children (64% for adults; 60% for children). Taken together, these results suggest that UCB should be considered as an alternative stem cell source for adults, especially when an unrelated marrow donor is not available in a timely fashion.

Summary 

UCB contained a sufficient number of HSCs to achieve engraftment in adult patients with a lower-than-anticipated risk of severe acute GVHD, even when HLA-disparate grafts were infused. The use of UCB as a source of stem cells allows allografting to be offered to more patients, many of whom do not have a matched sibling or UD, to allow allogeneic therapy as the only chance to cure the underlying disease. The results thus far suggest that UD UCBT can result in long-term DFS in many of these patients. Similar to the pediatric series, clinical experience in the adult patients has also documented the importance of graft cell dose in determining engraftment and survival. The critical threshold dose below which engraftment and survival become significantly inferior remains to be defined in a larger study with a longer follow-up. On the basis of current results, it seems that the UCB graft, which contains at least 1.8 × 10⁷ nucleated cells per kilogram and 1.2 × 10⁵ CD34⁺ cells per kilogram, is acceptable for adult recipients. It is hoped that the advantage of a lower GVHD incidence without any apparent increase in relapse in UCBT will offset any adverse effect of reduced cell dose on survival. As in the pediatric setting, TRM remains the main obstacle for successful UCBT in adults. With the profound influence of UCB cell dose (both nucleated cell dose and CD34⁺ cell dose) on engraftment, survival and, probably, TRM in the adult setting, future research should also focus on increasing the cell dose of the UCB graft.

Back to Article Outline

NM stem cell transplantation 

NM stem cell transplantation (NST) or transplantation with reduced-intensity conditioning was proposed initially on the basis of the rationale that the therapeutic benefit of an allogeneic transplantation is partially related to the crucial immune-mediated graft-versus-malignancy effect. The concept of graft-versus-malignancy as the pivotal therapeutic component of allogeneic transplantation is supported by the observations from clinical studies that (1) patients with acute and chronic GVHD have a reduced risk of relapse 52, 53; (2) patients with syngeneic BMT and after T cell-depleted allotransplantation have a higher incidence of relapse compared with other allogeneic donors 53, 57; and (3) patients with a relapsed malignancy after allogeneic transplantation can be reinduced into complete remission without any chemotherapy by donor lymphocyte infusion 58, 59, 60.

NST, with its reduced-intensity preparative regimens, makes allogeneic transplantation applicable to patients with relative contraindications to myeloablative regimens. This dose-reduced conditioning nourished the hope that patients would experience less transplant-related mortality with fewer infections and less GVHD. This approach was based on the hypothesis that the attenuated conditioning regimens would (1) decrease the mucosal and tissue damage, (2) minimize the release of inflammatory cytokines, (3) decrease the incidence of infections, (4) reduce the incidence of GVHD, and (5) ultimately allow powerful alloimmune responses to eradicate disease processes while minimizing the initial treatment-related morbidity and mortality. The development of the strategy with the NST preparative regimen not only revolutionizes but also overturns some of the long-held dogmas in clinical stem cell transplantation. First, it is no longer correct to assume that myeloablative chemoradiotherapy is required to “create space” for donor cell engraftment or to ensure leukemia cure. This approach relies more on the creation of “immunologic space” for engraftment rather than the more traditional approach of creating “physical space” by the intensive chemoradiotherapy. Second, responses in renal cell cancer challenge the assumption that solid tumors are unsuitable targets for graft-versus-tumor effects because tumor bulk and chemoresistance render them beyond the reach of stem cell allograft approaches [61].

The clinical outcomes of patients undergoing allogeneic transplantation with this novel reduced-intensity preparative regimen have been published by several groups 13, 14, 62, 63, 64, 65. Most of these patients represent a poor prognostic group, with either relapsed chemoresistant or primary refractory hematologic diseases. The most frequently reported diseases treated with this modality include chronic hematologic malignancies such as chronic lymphocytic leukemia, low-grade non-Hodgkin lymphoma, and multiple myeloma, followed less frequently by refractory and more aggressive diseases, including acute leukemias, lymphoma, and solid tumors. The early results are encouraging, with lower treatment-related mortality and mortality. However, the median follow-up for most of these studies is short; hence, the evidence for a sustained antitumor effect is very limited, and the long-term survival benefit remains to be established. Although these reduced-intensity preparative regimens have decreased immediate procedural mortality, they have not resulted in a low incidence of GVHD, as expected in preclinical studies. GVHD remains the predominant cause of death after such transplantations 12, 13, 61. It is apparent that NST and subsequent donor lymphocyte infusion are changing the time frames in which acute and chronic GVHD manifest; hence, the standard GVHD definitions may be less applicable. Furthermore, because the preparative regimen does not contribute significantly to the antimalignancy effect, the risk of disease progression after transplantation remains higher compared with the myeloablative approach. It has been shown that NST is more applicable for more indolent malignancies, for which there is less urgency for immediate treatment, or for diseases that are susceptible to graft-versus-malignancy effects. The clinical outcome is disappointing in active, aggressive malignancies, in which the rapidity of tumor growth outpaces the development of the graft-versus-malignancy effect [62].

NM transplantation with UCB progenitor cells 

Given the excellent tolerance of these nonmyeloablative (NM) regimens and the high rate of alloengraftment, there has been considerable interest in these transplantation strategies by using UCB as a source of hematopoietic stem cell support after NM preparative regimens. NST with UCB provides an opportunity for immunotherapy for older patients, sicker patients, and patients without suitable donors, who are not eligible for this potentially curative approach. However, there is increased concern about graft rejection with this approach. In NST with adult related donor or UD stem cells, the infusion of cytokine-mobilized peripheral blood progenitor cells with a higher cell dose may overcome the major HLA barrier 66, 67, with resultant stable donor cell recovery over the autologous recovery. This may not be feasible in the setting of UCBT with NM conditioning therapy because there are on average 2 log fewer cells infused than would be considered standard for matched sibling or UD transplantation. The clinical outcome of 2 patients with malignant lymphoma by using this novel approach was first reported by investigators at Duke University [68]. In their study, 2 patients with relapsed lymphoma who had no matched siblings, partially matched family members, or matched UDs successfully underwent NM conditioning therapy followed by infusion of 4 of 6 matched UD UCB cells at the nucleated cell dose of 2.9 and 6.5 × 10⁷/kg. The conditioning regimens consisted of fludarabine 30 mg/m² and cyclophosphamide 500 mg/m² daily for 4 days with antithymocyte globulin 30 mg/kg/d for 3 days. Cyclosporin A (CyA) and prednisolone were given for acute GVHD prophylaxis. Both patients had 100% donor engraftment by the third month after transplantation and remained in remission 6 and 12 months after transplantation. The favorable outcome demonstrates the feasibility of the mismatched unrelated UCB cells, even with the NM preparative regimens.

The Duke university experience 

Between November 2000 and September 2002, 10 patients underwent NST with UCB at Duke University Medical Center. The median age of these patients was 51 years (range, 19–62 years), their median weight was 65.7 kg (range, 49.1–99 kg), and the median number of nucleated cells per kilogram infused was 2.07 × 10⁷/kg (range, 1.07–5.53 × 10⁷/kg). The diagnoses included relapsed mantle cell lymphoma (n = 2), myelodysplastic syndrome (n = 2), metastatic melanoma (n = 1), relapsed high-grade lymphoma (n = 1), high-risk ALL (n = 2), relapsed acute myeloid leukemia (n = 1), and CML (n = 1). Eight patients received grafts disparate at 2 HLA loci, and the other 2 had 1 HLA locus-disparate graft.

All patients received fludarabine 30 mg/m² and cyclophosphamide 500 mg/m² daily for 4 days (days −5 to −2) with antithymocyte globulin 30 mg/kg/d for 3 days (days −3 to −1). Acute GVHD prophylaxis consisted of CyA and methylprednisolone for all patients except 2, who were given CyA and mycophenolate mofetil (MMF). All patients received subcutaneous 5 μg/kg of G-CSF or granulocyte-macrophage colony-stimulating factor until neutrophil engraftment.

Six (60%) of the 10 patients demonstrated donor chimerism between 4 weeks and 6 months. Three patients became fully donor, whereas 3 patients had transient low levels of detectable donor cells, but these cells did not persist. The remaining 4 (40%) patients never demonstrated any evidence of donor engraftment. The median time to neutrophil recovery with ANC ≥500/μL for all 10 patients was 8 days (range, 0–32 days), and the median time to platelet recovery with a platelet count exceeding 20 000/μL was 3 days (range, 0–61 days). Three patients never had a nadir ANC <500/μL, whereas 5 patients never had a nadir platelet count <20 000/μL. Five of the 7 patients who did not engraft experienced transient grade 4 cytopenia before autologous hematopoietic reconstitution.

Of the 3 patients who achieved full donor chimerism, 1 developed grade 3 steroid-refractory acute GVHD of the gut at 4 months after transplantation; the other patient developed chronic GVHD 9 months after transplantation. One patient subsequently died of disseminated aspergillosis and 1 of complications from and debilitation after cerebral infarction. With a median follow-up of 7 months (range, 2–24 months), 5 (50%) patients have died: 3 from disease progression or relapse without evidence of engraftment, 1 from fungal infections in the sixth month, and 1 to a cerebral infarction 13 months after transplantation while in complete remission and with full donor chimerism. Five (50%) patients were alive at the last follow-up. Only 2 of the surviving patients were in complete remission: one patient sustained full donor chimerism at 2 years after transplantation, and the other patient had a low donor signal at 8 months after transplantation. The estimated overall survival and EFS at 2 years for this high-risk group were 36% (95% confidence interval, 16%-55%) and 27% (95% confidence interval, 12%–42%), respectively. It is important to note that no treatment-related mortality was observed within the first 100 days after transplantation.

NM UCBT—results from other transplant centers 

A similar approach has also been reported by investigators at the University of Colorado Health Sciences Center (Table 2). McSweeney et al. [69] reported on 4 patients with advanced hematologic malignancies (age, 25–78 years) who received 5 of 6 or 6 of 6 HLA-matched UCB after being conditioned with fludarabine 30 mg/m² × 3 and TBI 200 cGy. CyA and MMF were used as postgrafting immunosuppression. The ranges of nucleated cell doses and CD34⁺ cells were 0.75 to 1.3 × 10⁷/kg and 1.0 to 4.0 × 10⁴/kg, respectively. Two of the 3 evaluable patients had stable engraftment. Mild biopsy-proven skin GVHD developed in 1 patient but resolved spontaneously.

Table 2. Summary of Results of Nonmyeloablative Unrelated Umbilical Cord Blood Transplantation

aGVHD indicates acute graft-versus-host disease; cGVHD, chronic graft-versus-host disease; NC, nucleated cell; ANC, absolute neutrophil count; NHL, non-Hodgkin lymphoma; MDS, myelodysplastic syndrome; AML, acute myeloid leukemia; MEL, melanoma; ALL, acute lymphoblastic leukemia; HD, Hodgkin disease; CLL, chronic lymphocytic leukemia; THAL, thalassemia; WAS, Wiskott-Aldrich syndrome; NBL, neuroblastoma; HM, hematologic malignancies; F, fludarabine; ATG, antithymocyte globulin; C, cyclophosphamide; TBI, total body irradiation; Bu, busulphan; CyA, cyclosporin A; MMF, mycophenolate mofetil; PDN, prednisolone; FK506, tracrolimus; NA, not available; CI, cumulative incidence; PR, partial remission; OS, overall survival; DFS, disease-free survival

Cairo et al. [70] demonstrated the feasibility of reduced-intensity allogeneic transplantation by using 1- to 2-antigen-mismatched UCB with a median nucleated cell dose of 5 × 10⁷/kg (range, 0.22–9.5 × 10⁷/kg) and a median CD34⁺ cell dose of 1.95 × 10⁵/kg (range, 0.11–3.7 × 10⁷/kg) on 6 children and adolescent patients with both malignant and nonmalignant diseases. All patients were <21 years old and were conditioned with a fludarabine-based regimen. Engraftment occurred in all patients except 1, and a survival of >50% was attained.

Transplantation with reduced-intensity conditioning was also evaluated by investigators from the University of Minnesota in a cohort of high-risk patients with hematologic malignancies [71]. In their study, unrelated UCB grafts with a median nucleated cell dose of 3.7 × 10⁷/kg (range, 1.6–6.0 × 10⁷ /kg) were infused into 43 patients (median age of 49.5 years [range, 22–65 years]) after they received 2 types of NM conditioning regimens: fludarabine 200 mg/m², TBI 200 cGy, and busulphan 8 mg/kg (Flu/Bu/TBI) for the initial 21 subjects and fludarabine 200 mg/m², TBI 200 cGy, and cyclophosphamide 50 mg/kg (Flu/Cy/TBI) for the subsequent 22 subjects. All patients received GVHD prophylaxis with CyA and MMF. The median time to neutrophil recovery of >0.5 × 10⁹/L was 26 days (range, 12–30 days) for the Flu/Bu/TBI recipients but was only 9.5 days (range, 5–28 days) for the Flu/Cy/TBI recipients. The cumulative incidence of engraftment for Flu/Bu/TBI and Flu/Cy/TBI recipients was 76% and 94%, respectively. Despite the use 1 to 2 HLA-antigen mismatched grafts in 93% of the recipients, the cumulative incidence of grade II to IV GVHD and grade III to IV GVHD for the entire cohort of patients was 44% and 9%, respectively. The DFS of these high-risk subjects was also favorable: 24% at 1 year for Flu/Bu/TBI recipients and 41% at 1 year for Flu/Cy/TBI recipients.

In the experience reported by Ballen et al. [72], 6 patients with solid tumors and 1 patient with lymphoma, who did not have family matched donors, received unrelated UCBT after conditioning with 100 cGy of TBI. No GVHD prophylaxis was given to any of these patients. The median number of CD34⁺ and CD3⁺ cells per kilogram was 3.1 × 10⁴/kg (range, 1.1–10.7 × 10⁴/kg) and 1.7 × 10⁶/kg (range, 0.5–3.7 × 10⁶/kg), respectively. However, none of these patients achieved a tumor response or evidence of donor chimerism.

Back to Article Outline

Immune reconstitution 

Immune reconstitution in myeloablative UCBT patients 

Immune reconstitution after allogeneic BMT has been studied extensively 73, 74, 75, 76. However, only a few reports, all of which enrolled a limited number of patients, addressed the immune reconstitution of UCBT recipients after myeloablative regimens 77, 78, 79, 80, 81, 82. The lower number of lymphocytes infused in the UCB and their immaturity presents a potential problem for immune recovery and T-cell reconstitution after UCBT. This issue is of paramount importance with respect to the occurrence of relapse, GVHD, and infectious complications. Moretta et al. [78] showed that immune recovery after either related or unrelated UCBT was similar to that after matched related or unrelated BMT. Niehues et al. [81] demonstrated that the median time to both CD3⁺ and CD4⁺ cell reconstitution was 11.7 months, whereas the median time of CD8⁺ cell reconstitution was 7.9 months. The characteristic inversion of the CD4/CD8 ratio, as observed after BMT [73], was not seen after UCBT 80, 81, 82. Recovery of natural killer (NK) cells and B cells occurred quickly, taking a median of 3 and 6 months, respectively.

A similar study on immune reconstitution, but also including functional immune recovery, was undertaken by investigators at the Indiana School of Medicine [80]. The T-cell response to mitogen stimulation recovered between 6 and 9 months; B-cell function, as assessed by immunoglobulin production, remained in the normal range after transplantation, with nadirs between 1 and 3 months; and NK cell lytic function recovered at 1 month. There was no relationship between the time to recovery of T-, B-, or NK-cell numbers and nucleated cells per kilogram or CD34⁺ cells per kilogram. Neither was there a correlation between either numerical or functional immune recovery and the incidence or grade of infectious complications. However, there was a weak association between the recovery of the response to phytohemagglutinin and pokeweed mitogen and nucleated cells per kilogram infused.

Investigators at Duke University Medical Center analyzed the immunologic reconstitution after myeloablative unrelated UCBT in adults and children to determine the source of the regenerated T-cell pool [79]. UCB is phenotypically naive but T-cell replete, allowing for T-cell reconstitution through either central or peripheral mechanisms. Reconstitution of immunity after UCB occurred over 2 to 3 years for both adult and pediatric recipients. Both patient groups eventually demonstrated a normal lymphocyte count with a quantitatively normal distribution of B cells, T cells, and NK cells. The sources of T cells, however, seem strikingly different. Pediatric patients demonstrated significant numbers of signal-joint T-cell receptor excision circle (TREC)-containing T cells starting within 1 year after transplantation, indicating that the T cells were recent thymic emigrants. In contrast, adult recipients did not demonstrate any signal-joint TREC-containing T cells until 1.5 to 2 years after transplantation, and then only at relatively low levels. These results suggest that adult recipients of CB had a very slow recovery of T-cell numbers and functions. By using a complementarity-determining region 3 repertoire to measure the changes in T-cell receptor diversity occurring with restoration of thymic function, skewing of T-cell repertoires was demonstrated in adults and children at 12 to 18 months after transplantation. However, this recovered to near-normal diversity at 2 to 3 years after transplantation. The T-cell repertoire seemed more diverse earlier in children (at 1 to 2 years after transplantation) than in adults (at 3 to 4 years after transplantation). The analysis provides evidence that early T-cell recovery after UCBT occurs primarily through the peripheral expansion of adoptively transferred donor T cells and results in skewing of the T-cell repertoire. These data also underscore the importance of preserving the integrity of thymic function, thus allowing the rapid recovery of T cells with a complex diversity. NM conditioning regimens in this respect, with their decreased toxicity, may afford the advantages of enhancing the ability of the recipient thymus to support differentiation of de novo-derived T cells of donor origin compared with the more toxic regimens, which may produce more substantial thymic injury.

Differences in UCB immune reconstitution between myeloablative and NM regimens 

Comparison of immune reconstitution between myeloablative and NST recipients has been performed by several groups on adult hematopoietic stem cells (peripheral blood progenitor cells and bone marrow). When comparing allogeneic peripheral blood stem cell recipients after an NST regimen versus after a myeloablative regimen, Morecki et al. [83] observed a decrease in the absolute number of CD4⁺ cells, which was accompanied by an increase in CD8⁺ cells; this led to an inverted CD4/CD8 cell ratio. The NM conditioning regimen was found to result in early reconstitution of immune responses in vitro, and this benefit may translate into faster development of effective immune responses against residual host-type malignant and abnormal nonmalignant hematopoietic cells. On the basis of complementarity-determining region 3 size spectratype analysis, Friedman et al. [84] demonstrated that patients who received NST conditioning together with either bone marrow or peripheral blood stem cells exhibited more rapid reconstitution of T-cell repertoire complexity [85].

Limited data are currently available on immune reconstitution of UCB recipients after NST preparative regimens. Immune recovery in 5 recipients of UCBT after an NST regimen was compared with recovery in adults recipients of UCB after a myeloablative regimen by investigators at Duke University [85]. The absolute lymphocyte count reached normal levels in adults 6 to 12 months after NST transplantation with UCB, in contrast to 24 months in adults who received a myeloablative regimen [79]. At 12 months after transplantation, the numbers of phenotypically naive (CD45RA⁺) T cells were higher in those who received the NST regimen. The rapidly expanding naive population outnumbered the memory cells in the recipients of NST regimen. The T-cell repertoire in UCB recipients treated with an NST regimen was markedly more diverse and robust compared with the repertoire in those who received the myeloablative regimen at similar time points. TRECs, which are generated within the thymus and identify new thymic emigrants and those that have not divided, were detected 12 months after transplantation in the NST recipients. This compared favorably to the delayed detection of TRECs at 18 to 24 months among recipients of myeloablative regimens. Thus, in adults who received an NST preparatory regimen, the quantitative and qualitative recovery of T cells occurs through rapid peripheral expansion. The ability of patients receiving NST transplantation to recover within a few months suggests that the peripheral niches in which T cells can proliferate are preserved in these patients compared with those who receive myeloablative regimens. Moreover, the presence of TREC-positive cells within 1 year suggests that thymic recovery is likewise accelerated in recipients of NST compared with myeloablative regimens. The favorable results of T-cell recovery after NST suggest that it may be possible to have an excellent outcome with an unrelated mismatched UCBT in adult patients. Patients have a rapid recovery of T cells with a complex diversity. The primary difference between recipients of ablative and nonablative regimens was the extent of physiologic damage caused by the preparatory regimen. When the damage is relatively mild, as in the NM regimen, the donor T cells are able to expand effectively in the periphery, and the development of new T cells through the thymus is also accelerated compared with the rate of development in those who receive ablative regimens. Alternatively, the lower incidence of GVHD in NST may also play an important role in preservation of the peripheral and central niches for T-cell development.

Back to Article Outline

Ex vivo expansion and transplantation of multiple units of UCB 

One of the major limitations of using UCB as the source of stem cells for transplantation is the low cell dose, which not only adversely affects both the rate of hematopoietic recovery and the probability of survival 10, 11, 86, but also results in a higher risk of graft failure as compared with BMT. In addition, data from the University of Minnesota have demonstrated the profound importance of the CD34 cell dose on the rate of engraftment, treatment-related mortality, and survival in patients receiving UD UCBT [71]. The risk of engraftment failure is substantially higher and ranges from 10% to 25% in series with adult patients (>18 years old, >40 kg, or both) 21, 24, 25. In addition, the lack of available donor immune effector cells for adoptive cellular immunotherapy is the other major limitation associated with using unrelated UCB.

To circumvent these limitations after UCBT, studies have been performed to investigate the possibility of expanding the UCB progenitors ex vivo to improve engraftment. This area of investigation is particularly interesting because in vitro studies have shown that expansion can be increased in UCB compared with bone marrow cells. The use of cytokine cocktails, including stem cell factor, G-CSF, and megakaryocyte growth and differentiation factor, is effective in preclinical studies [87]. In a report from the University of Colorado, the infusion of UCB that was expanded ex vivo in conjunction with the unexpanded fraction in adults (weighing 54–116 kg) and pediatric patients with high-risk malignancies after myeloablative therapy resulted in a low incidence of engraftment failure and equivalent times to engraftment of neutrophils and platelets as reported for smaller pediatric patients [88]. Of note, the protocols used in this study consisted of both an expanded fraction and an unexpanded fraction. The unexpanded fraction was included because of the concern that ex vivo expansion may exhaust long-term engrafting cells. The same group of investigators has also addressed this issue of the short- and long-term engrafting potential of ex vivo expanded CB by performing an experiment with a fetal sheep xenogeneic transplantation model. In that study, the ex vivo expanded cells was be able to provide rapid short-term engraftment, but the long-term potential of expanded cells may be compromised. It is for this reason that transplantation of the unexpanded CB products was included in the studies to ensure durable long-term donor engraftment [89]. The overall benefit of this strategy has not been fully determined and deserves further investigation.

Another avenue of research is the possibility of using several CB units to increase the stem cell yield. In a sheep xenograft model of human hematopoiesis, a combination of human UCB units enhanced the short-term, but not long term, repopulating capacity of human UCB cells [90]. Barker et al. [91] first reported successful transplantation of 2 partially HLA-matched units of UCB into a 53-year-old, 83-kg woman with an accelerated phase of chronic myelogenous leukemia and no bone marrow donor. A double chimera with both units contributing to hematopoiesis was attained on the basis of a restriction fragment length polymorphism analysis performed 60 days after transplantation. The same group of investigators recently updated the clinical outcome of 23 high-risk adult patients (median age, 47 years; range, 18–60 years]) with hematologic malignancies [92]. Using both myeloablative and NM conditioning regimens, they demonstrated a high incidence of engraftment (94%) without an increase in severe GVHD (the cumulative incidences of grade II-IV and grade III-IV acute GVHD were 47% and 10%, respectively). The data support the principle that transplantation of 2 immunologically distinct UCB units is not associated with crossed immunologic rejection. These observations provide the most compelling argument for focusing future investigations on evaluating the efficacy of ex vivo expansion of ≥2 units of UCB in larger clinical trials and also for exploring the potential advantages of the transplantation of multiple units of UCB after NM preparative regimens [92].

Back to Article Outline

Remaining questions and future directions for UCBT in adults 

UCB from UDs has been increasingly used as an alternative source of hematopoietic stem cells in adults with hematologic diseases that can be cured only with allogeneic stem cell transplantation. The ability to achieve stable mixed or full donor chimerism by using reduced-intensity preparative regimens, with successful eradication of primary disease in the absence of severe treatment-related toxicity in preliminary clinical studies, signifies another advancement in the field of transplantation and immunobiolology. However, there are several unresolved issues and remaining questions regarding the utility of this novel strategy.

What is the optimal UCB cell dose required for adult patients? 

Most of the series on unrelated UCBT have emphasized the paramount importance of nucleated cell dose in engraftment and survival, and HLA disparity has a less convincing effect 10, 11, 16, 45. Two of the studies have indicated that a higher CD34 cell dose partially overcomes the negative effect of HLA for each level of HLA disparity 20, 93. Transplantation of a UCB graft containing >1.5 × 10⁷ nucleated cells per kilogram or >1.7 × 10⁷ CD34⁺ cells per kilogram of recipient weight has been suggested to be the minimum cell dose required for pediatric patients 20, 28. The optimal cell dose for unrelated UCBT in adults is yet to be determined. As noted previously, 2 previous studies have demonstrated the threshold for more favorable engraftment among adult recipients to be a nucleated cell dose of >1.7 × 10⁷/kg and 1.87 × 10⁷/kg 9, 21, 23. However, very little is known about the minimal cell dose for durable engraftment in the context of UCBT after an NST conditioning regimen. With NST conditioning and mismatched UDs, the concern over rejection of UCB is increased. The underlying diseases for which the transplantation was performed also affect the risk of engraftment failure, with a trend toward greater risk of graft failure in recipients with a history of a bone marrow failure syndrome, CML, hemoglobinopathy, or storage disease 10, 11, 94, 95.

With a median nucleated cell dose of >2.07 × 10⁷/kg recipient body weight infused, durable engraftment occurred in 3 of the 10 patients from the Duke University series. As for the University of Minnesota series, a median nucleated dose of 3.7 × 10⁷/kg recipient body weight resulted in a 76% to 94% probability of engraftment [71]. Potential strategies to overcome the risk of graft rejection include the use of a graft with a higher cell dose, a graft that has been expanded ex vivo, combinations of multiple CB units, and the use of modified protocol that conveys a higher degree of pretransplantation immunosuppression to overcome transfusion-induced sensitization in patients with bone marrow failure syndromes and hemoglobinopathies. Optimizing postgrafting immunosuppression, such as including the use of MMF and modifying the duration of GVHD prophylaxis, might be another promising approach in the context of allogeneic transplantation after an NST preparative regimen 14, 96, 97.

What is the difference in overall efficacy between myeloablative and NST UCBT? 

In contrast to UCBT with a myeloablative conditioning regimen, the published series on NST with UCB have involved either primarily a small cohort of patients with refractory hematologic malignancies or patients who were otherwise poor candidates for a conventional transplantation approach. The follow-up period is usually too short and the data are too scanty to determine the overall benefit of NST with UCB as the source of stem cells. Furthermore, because most NSTs are performed in situations in which standard transplantations would not be considered, no comparative studies between myeloablative regimens and NST would be, or would be likely to be, performed in the near future.

The indications for NST versus a myeloablative preparative regimen need to be carefully defined. The benefit of reduced toxicity with NST regimens may be offset by the loss of cytoreduction of the tumor cells induced by high-dose chemotherapy. The use of NST has generally been more successful in patients with indolent lymphoid malignancies or malignancies that are susceptible to GVL effects, such as CML. It is less successful in patients with aggressive malignancies or malignancies that seem relatively insensitive to GVL effects, such as ALL and high-grade lymphoma. The rapid proliferation of these malignancies may outpace the developing immune response. Given the limitation of the cell dose of UCB and the logistic problem in donor recall, NST with UCB does not afford the same advantage as in NST with adult hematopoietic stem cells, in which the transplant provides a platform for repeated delivery of adoptive cellular immunotherapy with donor lymphocyte infusion. In the case of an aggressive malignancy in which the delayed graft-versus-malignancy effect cannot be relied on, it may be more beneficial to use a preparative regimen (reduced-toxicity ablative regimen) that provides some disease control 12, 98 and also facilitates engraftment.

One important issue that deserves attention is the potential of NST with UCB to minimize the inpatient stay and improve the quality of life in the peritransplantation period while reducing cost. All patients in the Duke University series had transplantation performed largely in the outpatient setting. The median time for hematopoietic recovery is shorter than with conventional UCBT. Longer follow-up with more patients will be needed to determine the incidence of chronic GVHD and the quality of life of such recipients.

Is the incidence of GVHD similar in ablative versus NST regimens? 

UCBT has been associated with a reduced risk of developing severe GVHD in children and adults 8, 21, even when cells from partially HLA-mismatched donors are used. NST was introduced with the hope that patients would experience less GVHD after reduced-intensity conditioning regimens 61, 99. This was based on the hypotheses that (1) less tissue injury would occur because of the lower dose of cytotoxic agents and (2) the induction of mixed chimerism could reduce the incidence of GVHD 100, 101. However, GVHD remains the most significant cause of morbidity and mortality after NST conditioning. Previously published reports on NST have shown a 38% to 60% incidence of grade II to IV acute GVHD 13, 14, 62, 63, 65, 102. It remains to be seen whether unrelated UCB used in the NST regimen can result in an incidence of grade II to IV lower than the range of 40% to 60%, as reported in previous adult series receiving myeloablative unrelated UCBT 21, 22, 25, 27. Barker et al. [71] have demonstrated in their cohort of 43 adult patients that the incidence of grade III to IV acute GVHD was low (9%). This is encouraging given the fact that 1 to 2 HLA antigen-mismatched UCB grafts were used in 93% of their patients.

In addition, studies on immune recovery have produced optimism that patients undergoing NST with UCB may experience less GVHD. These studies on immune reconstitution among patients receiving UCBT or BMT 79, 84, 85, 103 have demonstrated the potential benefit of minimizing thymic damage through an NST conditioning regimen. The early restoration of thymic function will allow early dominance of the thymus-dependent phase and thus prevent the exclusive expansion of peripheral T-cell clones. In addition, the increased level of T-cell repertoire complexity observed in patients receiving NST regimens may lead to increased numbers of alloreactive immunoregulatory cells, such as those marked by CD4⁺ CD25⁺ expression, and thereby suppress GVHD 104, 105. Nevertheless, determining whether the incidence and severity of GVHD related to NST with UCB are lower than with myeloablative UCBT will require clinical trials in comparable groups of patients.

Is the incidence of infection similar in ablative versus NST regimens? 

Adult UCBT recipients are at risk for opportunistic infections for at least 2 to 3 years after transplantation. Infection may account for half of all treatment-related deaths after UCBT after an ablative regimen [11]. Apart from the prolonged neutropenia associated with myeloablative UCBT, the risk of infection may be an intrinsic property of UCB, because UCB has been shown to be phenotypically naive [106], to expand slowly in response to antigen stimulation, to have a higher threshold for cytokine stimulation, and to possess a lower effective cytotoxicity relative to adult donor T-cell controls 106, 107. Moreover, thymic production of new T cells is substantially delayed and remains limited in adult recipients of UCB after an ablative preparative regimen.

Patients who receive UCBT after a nonablative preparative regimen have a shorter period of neutropenia and more rapid immune reconstitution with a more diverse T-cell repertoire [85]. Whether the more favorable immune recovery can be translated into faster development of effective immune responses against opportunistic infections and, therefore, improved transplantation outcome remains to be determined in clinical trials.

Data from previous studies suggest that recipients of NM HSCT may have different, but not necessarily decreased, risks for invasive bacterial, viral, and fungal infections [108]. One of the main reasons is due to the use of differing NM or reduced-intensity regimens, and each of these regimens varies in its hematologic and nonhematologic toxicities. The risk of infection in both myeloablative and allogeneic NST recipients is dependent on the degree of immunoablation/myeloablation, the severity of GVHD and its immunosuppressive therapies, and the rate of immune reconstitution. Preliminary results suggest that NM conditioning regimens may decrease the risk of bacterial infections associated with mucosal damage and persistent neutropenia; however, risks for late viral and fungal infections persist during severe GVHD [108]. It is currently unclear whether the incidence of GVHD is similar between ablative and NM UCBT recipients. Because previous reports have not shown a lower incidence of GVHD in NM HSCT recipients, it is not surprising to see infectious complications emerging as a major contributory cause of nonrelapse mortality in NM UCBT recipients.

As opposed to the data that have been gathered regarding CMV infections after BMT, the knowledge regarding the risk of CMV infection after myeloablative and NM UCBT is sparse. Rubinstein et al. [11] showed that CMV infection after unrelated UCBT occurred in 23% of seropositive recipients and 3% of seronegative patients. CMV seropositivity has been identified to be associated with a higher risk of GVHD, higher treatment-related mortality, and poorer survival outcome in the studies by the Eurocord Transplant Group and the group from the University of Minnesota 10, 20. Saavedra et al. [50] reported a 41% incidence of CMV reactivation within the first 100 days after transplantation in 27 adult patients receiving unrelated UCB grafts after a myeloablative preparative regimen. CMV disease occurred in only 1 patient, and there was no CMV-related mortality. In a Japanese single-institutional study of 28 adult UCBT recipients, the use of UCB units from UDs containing serologically and genetically multiple mismatches in the HLA loci was associated with a high probability of CMV reactivation [109].

In patients receiving BMT, it is thought that the loss of immunocompetent host cells after the myeloablative regimen and the delayed recovery of donor graft-derived immunity contributes to the risk of CMV infections. The risk is further potentiated by the presence of acute GVHD [110], whereby the recovery of the CMV-specific T-cell response is further impaired. In NM HSCT, it was hypothesized that the incomplete eradication of host T cells and the prolonged presence of host immunity after NST might provide some protection against early infection as compared with conventional myeloablative transplantation. However, clinical studies have shown that this immunologic advantage did not confer any superior outcome in terms of CMV infections. Investigators from Seattle have shown that the risk of CMV-associated disease does not seem to be lower with NM regimens. It is important to note that the time of onset of CMV disease was significantly delayed in the NM compared with the myeloablative HSCT recipients; most cases occurred after day 100 [111]. These data are in contrast to 2 other studies. Chakrabarti et al. [112] found a 90% incidence of CMV infections within 35 days after transplantation by using an alemtuzumab (Campath-1H) and fludarabine-based NM preparative regimen. In another study involving 21 NM transplant recipients given a preparative regimen that contained fludarabine and antithymocyte globulin, Mohty et al. [113] found a high incidence (65%) of CMV infection before day 50. These apparently conflicting findings may be explained by the difference in the intensity of immunosuppression of the preparative regimens and the GVHD prophylaxis schedule. The inclusion of fludarabine, a highly immunosuppressive agent, in most NM regimens may result in a higher incidence of CMV infection [114]. A higher risk of CMV infection may also be attributed to the use of a CyA and MMF combination as GVHD prophylaxis in many NST recipients, because this regimen has been found to have synergistic and more profound immunosuppressive effects on T cells as compared with the CyA and MTX combinations 112, 115. It is important that investigators be aware of these pitfalls, which may secondarily increase transplant toxicity. Further studies are needed to define appropriate preventive, surveillance, and therapeutic strategies. With several NM conditioning regimens with differing immunosuppressive potentials being explored at different centers, the timing of infections may differ, and it is therefore imperative to determine the risk for early and late viral infections for each regimen. For patients receiving NM unrelated UCBT, the effect of favorable immunologic recovery on the risks of CMV infections remains to be determined in multiple larger studies, especially considering the substantial variation between conditioning regimens.

What is the optimal NST conditioning regimen and GVHD prophylaxis? 

The optimal intensity of preparative regimens is uncertain, and several factors must be considered, including the aggressiveness of the underlying disease, the age of the patient, the immunocompetence of the recipients, and the genetic disparity between the donor and recipient. A wide range of NST conditioning regimens has been used. These regimens are designed not to eradicate the underlying malignancy but to provide sufficient immunosuppression to facilitate engraftment. The question posed is how immunosuppressed the patients need to be to overcome the risk of graft rejection. The benefit of reduced toxicity with NST regimens may be offset by the loss of cytoreduction induced by high-dose chemotherapy. As noted previously, the use of NST has generally been less successful in aggressive malignancies, which are likely to recur rapidly and outpace immune reconstitution. Given the increasing indication of applying NST in older patients with refractory malignancies, future efforts may focus on the development of a more tolerable regimen that has broad-spectrum antineoplastic and immunosuppressive activity that not only facilitates engraftment, but also provides some disease control. The challenge becomes greater when mismatched UCBT is used, where HLA disparity and a lower cell dose is associated with a higher risk of graft rejection. Further studies are necessary to define the best regimen that reduces the risk of rejection without increasing the risk of relapse and regimen-related toxicity.

GVHD remains the leading cause of death among patients receiving NST, and optimizing the GVHD prophylaxis regimen is of paramount importance in improving the transplantation outcome. Although acute GVHD tends to be less severe after an NST preparative regimen, it frequently occurs after the early termination of immunosuppressive therapy [116]. Inclusion of Campath-1H has recently been reported to produce a low rate of GVHD [117]. The use of Campath-1H or any other maneuver that effectively results in T-cell depletion of the graft may have adverse effects, including slow immune reconstitution resulting in an increased risk of viral infection [112] and stable mixed chimerism that could abrogate the GVL effect of the allograft and lead to relapse of the underlying malignancy. Longer-term follow-up will be required to assess whether these potential disadvantages will overweigh the lower GVHD-related morbidity and mortality.

Back to Article Outline

Conclusion 

UCB is a viable alternative to bone marrow and peripheral blood as a source of stem cells capable of hematopoietic reconstitution for adults when an unrelated marrow donor is not available. UCBT after an NST preparative regimen is an exciting new approach that provides an option for patients who are otherwise excluded from conventional HSCT, including elderly or medically infirm patients with no matched sibling donor. Preliminary results have shown that such an approach can be associated with timely engraftment with full donor chimerism. Comparison between myeloablative and NST approaches will be needed before this therapy can be considered for younger patients eligible for myeloablative transplantation. At the moment, the use of NST UCBT cannot be encouraged outside of clinical trials or selected patients. The future challenge will be to develop strategies to optimize the chance of early and durable engraftment, as well as to minimize the risk of GVHD and transplant-related death.

Back to Article Outline

References 

1. Gluckman E, Broxmeyer HA, Auerbach AD, et al.  Hematopoietic reconstitution in a patient with Fanconi’s anemia by means of umbilical-cord blood from an HLA-identical sibling. N Engl J Med. 1989;321:1174–1178
   • View In Article
   • MEDLINE
   • CrossRef
2. Barker JN, Wagner JE. Umbilical cord blood transplantation (current state of the art). Curr Opin Oncol. 2002;14:160–164
   • View In Article
   • MEDLINE
   • CrossRef
3. Kernan NA, Bartsch G, Ash RC, et al.  Analysis of 462 transplantations from unrelated donors facilitated by the National Marrow Donor Program. N Engl J Med. 1993;328:593–602
   • View In Article
   • MEDLINE
   • CrossRef
4. Beatty PG, Clift RA, Mickelson EM, et al.  Marrow transplantation from related donors other than HLA-identical siblings. N Engl J Med. 1985;313:765–771
   • View In Article
   • MEDLINE
   • CrossRef
5. Howe CWS, Radde-Stepaniak T. Hematopoietic cell donor registries. In:  Thomas ED,  Blume KG,  Forman SJ editor. Hematopoietic Cell Transplantation. Second Edition. Malden, MA: Blackwell Science; 1999;p. 503–512
   • View In Article
6. Barker JN, Krepski TP, DeFor TE, et al.  Searching for unrelated donor hematopoietic stem cells (availability and speed of umbilical cord blood versus bone marrow). Biol Blood Marrow Transplant. 2002;8:257–260
   • View In Article
   • Abstract
   • Full-Text PDF (107 KB)
   • CrossRef
7. Gluckman E, Rocha V, Chevret S. Results of unrelated umbilical cord blood transplantation. Rev Clin Exp Hematol. 2001;5:87–89
   • View In Article
   • MEDLINE
   • CrossRef
8. Rocha V, Wagner JE, Sobocinkski KA, et al.  Graft-versus-host disease in children who have received a cord blood or bone marrow transplant from an HLA-identical sibling. N Engl J Med. 2000;342:1846–1854
   • View In Article
   • MEDLINE
   • CrossRef
9. Gluckman E. Current status of umbilical cord blood hematopoietic stem cell transplantation. Exp Hematol. 2000;28:1197–1205
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (109 KB)
   • CrossRef
10. Gluckman E, Rocha V, Boyer-Chammard A, et al.  Outcome of cord-blood transplantation from related and unrelated donors. N Engl J Med. 1997;337:373–381
    • View In Article
    • MEDLINE
    • CrossRef
11. Rubinstein P, Carrier C, Scaradavou A, et al.  Outcomes among 562 recipients of placental-blood transplants from unrelated donors. N Engl J Med. 1998;339:1565–1577
    • View In Article
    • MEDLINE
    • CrossRef
12. Giralt S, Thall PF, Khouri I, et al.  Melphalan and purine analog-containing preparative regimens (reduced-intensity conditioning for patients with hematologic malignancies undergoing allogeneic progenitor cell transplantation). Blood. 2001;97:631–637
    • View In Article
    • MEDLINE
    • CrossRef
13. Slavin S, Nagler A, Naparstek E, et al.  Nonmyeloablative stem cell transplantation and cell therapy as an alternative to conventional bone marrow transplantation with lethal cytoreduction for the treatment of malignant and nonmalignant hematologic diseases. Blood. 1998;91:756–763
    • View In Article
    • MEDLINE
14. McSweeney PA, Niederwieser D, Shizuru JA, et al.  Hematopoietic cell transplantation in older patients with hematologic malignancies (replacing high-dose cytotoxic therapy with graft-versus-tumor effects). Blood. 2001;97:3390–3400
    • View In Article
    • MEDLINE
    • CrossRef
15. Wagner JE, Kernan NA, Steinbuch M, et al.  Allogeneic sibling umbilical-cord-blood transplantation in children with malignant and non-malignant disease. Lancet. 1995;346:214–219
    • View In Article
    • Abstract
    • CrossRef
16. Locatelli F, Rocha V, Chastang C, et al.  Factors associated with outcome after cord blood transplantation in children with acute leukemia. Blood. 1999;93:3662–3671
    • View In Article
    • MEDLINE
17. Kurtzberg J, Laughlin M, Graham ML, et al.  Placental blood as a source of hematopoietic stem cells for transplantation into unrelated recipients. N Engl J Med. 1996;335:157–166
    • View In Article
    • MEDLINE
    • CrossRef
18. Wagner JE, Rosenthal J, Sweetman R, et al.  Successful transplantation of HLA-matched and HLA-mismatched umbilical cord blood from unrelated donors (analysis of engraftment and acute graft-versus-host disease). Blood. 1996;88:795–802
    • View In Article
    • MEDLINE
19. Cairo MS, Wagner JE. Placental and/or umbilical cord blood (an alternative source of hematopoietic stem cells for transplantation). Blood. 1997;90:4665–4678
    • View In Article
    • MEDLINE
20. Wagner JE, Barker JN, DeFor TE, et al.  Transplantation of unrelated donor umbilical cord blood in 102 patients with malignant and nonmalignant diseases (influence of CD34 cell dose and HLA disparity on treatment-related mortality and survival). Blood. 2002;100:1611–1618
    • View In Article
    • MEDLINE
21. Laughlin MJ, Barker J, Bambach B, et al.  Hematopoietic engraftment and survival in adult recipients of umbilical-cord blood from unrelated donors. N Engl J Med. 2001;344:1815–1822
    • View In Article
    • MEDLINE
    • CrossRef
22. Sanz GF, Saavedra S, Planelles D, et al.  Standardized, unrelated donor cord blood transplantation in adults with hematologic malignancies. Blood. 2001;98:2332–2338
    • View In Article
    • MEDLINE
    • CrossRef
23. Rocha V, Arcese W, Sanz G, et al.  Prognostic factors of outcome after unrelated cord blood transplant (UCBT) in adults with haematologic malignancies. Blood. 2000;96:587a; (abstr.)
    • View In Article
24. Goldberg SL, Chedid S, Jennis AA, Preti RA. Unrelated cord blood transplantation in adults (a single institution experience). Blood. 2000;96:208a; (abstr.)
    • View In Article
25. Long G, Madan B, Kurtzberg J, et al.  Unrelated umbilical cord blood transplants in adult patients (PTS) with hematological malignancies or genetic disorders. Blood. 1999;94:570a; (abstr.)
    • View In Article
26. Cornetta K, Laughlin M, Carter S, et al.  Umbilical cord blood transplantation in adults (results of a prospective, multi-institutional, NHBLI sponsored trial). Blood. 2002;100:42a; (abstr.)
    • View In Article
27. Iseki T, Ooi J, Tomonari A, et al.  Unrelated cord blood transplantation in adults with hematological malignancy (a single institution experience). Blood. 2001;98:665a; (abstr.)
    • View In Article
28. Ballen K, Broxmeyer HE, McCullough J, et al.  Current status of cord blood banking and transplantation in the United States and Europe. Biol Blood Marrow Transplant. 2001;7:635–645
    • View In Article
    • Abstract
    • Full-Text PDF (153 KB)
    • CrossRef
29. Iseki T, Ooi J, Tomonari A, et al.  Unrelated cord blood transplantation in adults with hematological malignancy (a single institution experience). Blood. 2001;98:665a; (abstr.)
    • View In Article
30. Ooi J, Iseki T, Takahashi S, et al.  Unrelated cord blood transplantation for adult patients with advanced myelodysplastic syndrome. Blood. 2003;101:4711–4713
    • View In Article
    • MEDLINE
    • CrossRef
31. Rocha V, Cornish J, Sievers EL, et al.  Comparison of outcomes of unrelated bone marrow and umbilical cord blood transplants in children with acute leukemia. Blood. 2001;97:2962–2971
    • View In Article
    • MEDLINE
    • CrossRef
32. Mavroudis D, Read E, Cottler-Fox M, et al.  CD34+ cell dose predicts survival, posttransplant morbidity, and rate of hematologic recovery after allogeneic marrow transplants for hematologic malignancies. Blood. 1996;88:3223–3229
    • View In Article
    • MEDLINE
33. Sierra J, Storer B, Hansen JA, et al.  Transplantation of marrow cells from unrelated donors for treatment of high-risk acute leukemia (the effect of leukemic burden, donor HLA-matching, and marrow cell dose). Blood. 1997;89:4226–4235
    • View In Article
    • MEDLINE
34. Bender JG, Unverzagt K, Walker DE, et al.  Phenotypic analysis and characterization of CD34+ cells from normal human bone marrow, cord blood, peripheral blood, and mobilized peripheral blood from patients undergoing autologous stem cell transplantation. Clin Immunol Immunopathol. 1994;70:10–18
    • View In Article
    • MEDLINE
    • CrossRef
35. Martin PJ, Akatsuka Y, Hahne M, Sale G. Involvement of donor T-cell cytotoxic effector mechanisms in preventing allogeneic marrow graft rejection. Blood. 1998;92:2177–2181
    • View In Article
    • MEDLINE
36. Barker JN, Davies SM, DeFor T, et al.  Survival after transplantation of unrelated donor umbilical cord blood is comparable to that of human leukocyte antigen-matched unrelated donor bone marrow (results of a matched-pair analysis). Blood. 2001;97:2957–2961
    • View In Article
    • MEDLINE
    • CrossRef
37. Ooi J, Iseki T, Takahashi S, et al.  A clinical comparison of unrelated cord blood transplantation and unrelated bone marrow transplantation for adult patients with acute leukaemia in complete remission. Br J Haematol. 2002;118:140–143
    • View In Article
    • MEDLINE
    • CrossRef
38. Wagner JE, Kurtzberg J. Allogeneic umbilical cord blood transplantation. In:  Broxmeyer HE editors. Cellular Characteristics of Cord Blood and Cord Blood Transplantation. Bethesda, MD: AABB Press; 1998;p. 113–146
    • View In Article
39. Gluckman E. Hematopoietic stem-cell transplants using umbilical-cord blood. N Engl J Med. 2001;344:1860–1861
    • View In Article
    • MEDLINE
    • CrossRef
40. Beatty PG, Hansen JA, Longton GM, et al.  Marrow transplantation from HLA-matched unrelated donors for treatment of hematologic malignancies. Transplantation. 1991;51:443–447
    • View In Article
    • MEDLINE
    • CrossRef
41. Kernan NA, Bartsch G, Ash RC, et al.  Analysis of 462 transplantations from unrelated donors facilitated by the National Marrow Donor Program. N Engl J Med. 1993;328:593–602
    • View In Article
    • MEDLINE
    • CrossRef
42. Hansen JA, Gooley TA, Martin PJ, et al.  Bone marrow transplants from unrelated donors for patients with chronic myeloid leukemia. N Engl J Med. 1998;338:962–968
    • View In Article
    • MEDLINE
    • CrossRef
43. McGlave PB, Shu XO, Wen W, et al.  Unrelated donor marrow transplantation for chronic myelogenous leukemia (9 years’ experience of the national marrow donor program). Blood. 2000;95:2219–2225
    • View In Article
    • MEDLINE
44. Szydlo R, Goldman JM, Klein JP, et al.  Results of allogeneic bone marrow transplants for leukemia using donors other than HLA-identical siblings. J Clin Oncol. 1997;15:1767–1777
    • View In Article
    • MEDLINE
45. Rubinstein P, Steven CE. Placental blood for bone marrow replacement (the New York Blood Center’s program and clinical results). Baillieres Best Pract Res Clin Haematol. 2000;13:565–584
    • View In Article
46. Nash RA, Pepe MS, Storb R, et al.  Acute graft-versus-host disease (analysis of risk factors after allogeneic marrow transplantation and prophylaxis with cyclosporine and methotrexate). Blood. 1992;80:1838–1845
    • View In Article
    • MEDLINE
47. Anasetti C, Beatty PG, Storb R, et al.  Effect of HLA incompatibility on graft-versus-host disease, relapse, and survival after marrow transplantation for patients with leukemia or lymphoma. Hum Immunol. 1990;29:79–91
    • View In Article
    • MEDLINE
    • CrossRef
48. Schiller G, Feig SA, Territo M, et al.  Treatment of advanced acute leukaemia with allogeneic bone marrow transplantation from unrelated donors. Br J Haematol. 1994;88:72–78
    • View In Article
    • MEDLINE
    • CrossRef
49. Frassoni F, Labopin M, Powles R, et al.  Effect of centre on outcome of bone-marrow transplantation for acute myeloid leukaemia (Acute Leukaemia Working Party of the European Group for Blood and Marrow Transplantation). Lancet. 2000;355:1393–1398
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (91 KB)
    • CrossRef
50. Saavedra S, Sanz GF, Jarque I, et al.  Early infections in adult patients undergoing unrelated donor cord blood transplantation. Bone Marrow Transplant. 2002;30:937–943
    • View In Article
    • MEDLINE
    • CrossRef
51. Deisseroth AB, Kantarjian J, Andreeff M. Chronic leukemias. In:  De Vita V,  Hellman S,  Rosenberg SA editor. Cancer (Principles and Practice of Oncology). (Fifth Edition). Philadelphia, PA: Lippincott-Raven; 1997;p. 2321–2338
    • View In Article
52. Weiden PL, Flournoy N, Thomas ED, et al.  Antileukemic effect of graft-versus-host disease in human recipients of allogeneic-marrow grafts. N Engl J Med. 1979;300:1068–1073
    • View In Article
    • MEDLINE
    • CrossRef
53. Horowitz MM, Gale RP, Sondel PM, et al.  Graft-versus-leukemia reactions after bone marrow transplantation. Blood. 1990;75:555–562
    • View In Article
    • MEDLINE
54. Risdon G, Gaddy J, Stehman FB, Broxmeyer HE. Proliferative and cytotoxic responses of human cord blood T lymphocytes following allogeneic stimulation. Cell Immunol. 1994;154:14–24
    • View In Article
    • MEDLINE
    • CrossRef
55. Harris DT, Schumacher MJ, Locascio J, et al.  Phenotypic and functional immaturity of human umbilical cord blood T lymphocytes. Proc Natl Acad Sci USA. 1992;89:10006–10010
    • View In Article
56. Wall DA, Oliver DA, Alonso MJ, et al.  Adult recipients of unrelated donor cord blood transplants for treatment of leukemia have a similar engraftment and survival compared to children (St Louis Cord Blood Bank experience). Blood. 2001;98:666a; (abstr.)
    • View In Article
57. Gale RP, Horowitz MM, Ash RC, et al.  Identical-twin bone marrow transplants for leukemia. Ann Intern Med. 1994;120:646–652
    • View In Article
    • MEDLINE
58. Kolb HJ, Mittermuller J, Clemm C, et al.  Donor leukocyte transfusions for treatment of recurrent chronic myelogenous leukemia in marrow transplant patients. Blood. 1990;76:2462–2465
    • View In Article
    • MEDLINE
59. Cullis JO, Jiang YZ, Schwarer AP, et al.  Donor leukocyte infusions for chronic myeloid leukemia in relapse after allogeneic bone marrow transplantation. Blood. 1992;79:1379–1381
    • View In Article
    • MEDLINE
60. Kolb HJ, Schattenberg A, Goldman JM, et al.  Graft-versus-leukemia effect of donor lymphocyte transfusions in marrow grafted patients. Blood. 1995;86:2041–2050
    • View In Article
    • MEDLINE
61. Barrett J, Childs R. Non-myeloablative stem cell transplants. Br J Haematol. 2000;111:6–17
    • View In Article
    • MEDLINE
    • CrossRef
62. Giralt S, Estey E, Albitar M, et al.  Engraftment of allogeneic hematopoietic progenitor cells with purine analog-containing chemotherapy (harnessing graft-versus-leukemia without myeloablative therapy). Blood. 1997;89:4531–4536
    • View In Article
    • MEDLINE
63. Khouri IF, Keating M, Korbling M, et al.  Transplant-lite (induction of graft-versus-malignancy using fludarabine-based nonablative chemotherapy and allogeneic blood progenitor-cell transplantation as treatment for lymphoid malignancies). J Clin Oncol. 1998;16:2817–2824
    • View In Article
    • MEDLINE
64. Nagler A, Slavin S, Varadi G, et al.  Allogeneic peripheral blood stem cell transplantation using a fludarabine-based low intensity conditioning regimen for malignant lymphoma. Bone Marrow Transplant. 2000;25:1021–1028
    • View In Article
    • MEDLINE
    • CrossRef
65. Childs R, Chernoff A, Contentin N, et al.  Regression of metastatic renal-cell carcinoma after nonmyeloablative allogeneic peripheral-blood stem-cell transplantation. N Engl J Med. 2000;343:750–758
    • View In Article
    • MEDLINE
    • CrossRef
66. Reisner Y, Martelli ME. Stem cell escalation enables HLA-disparate haematopoietic transplant patients in leukemia patients. Immunol Today. 1999;20:343–347
    • View In Article
    • MEDLINE
    • CrossRef
67. Reisner Y, Martelli MF. Transplantation tolerance induced by ‘mega dose’ CD34+ cell transplants. Exp Haematol. 2000;28:119–127
    • View In Article
68. Rizzieri DA, Long GD, Vredenburgh JJ, et al.  Successful allogeneic engraftment of mismatched unrelated cord blood following a nonmyeloablative preparative regimen. Blood. 2001;98:3486–3488
    • View In Article
    • MEDLINE
    • CrossRef
69. McSweeney PA, Bearman SI, Jones RB, et al.  Nonmyeloablative hematopoietic cell transplant using cord blood. Blood. 2001;98:666a; (abstr.)
    • View In Article
70. Cairo M, Harrison L, Wolownik K, et al.  Reduced intensity (RI) allogenic stem cell transplantation (AlloSCT) from related and unrelated donors in children and adolescents with malignant and non-malignant disease. Exp Hematol. 2002;30(suppl):74
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (177 KB)
    • CrossRef
71. Barker JN, Weisdorf DJ, DeFor TE, et al.  Rapid and complete donor chimerism in adult recipients of unrelated donor umbilical cord blood transplantation after reduced-intensity conditioning. Blood. 2003;102:1915–1919
    • View In Article
    • MEDLINE
    • CrossRef
72. Ballen KK, Becker PS, Emmons RV, et al.  Low-dose total body irradiation followed by allogeneic lymphocyte infusion may induce remission in patients with refractory hematologic malignancy. Blood. 2002;100:442–450
    • View In Article
    • MEDLINE
    • CrossRef
73. Lum LG. The kinetics of immune reconstitution after human marrow transplantation. Blood. 1987;69:369–380
    • View In Article
    • MEDLINE
74. Atkinson K. Reconstruction of the haemopoietic and immune systems after marrow transplantation. Bone Marrow Transplant. 1990;5:209–226
    • View In Article
    • MEDLINE
75. Arnold R, Schmeiser T, Heit W, et al.  Hemopoietic reconstitution after bone marrow transplantation. Exp Hematol. 1986;14:271–277
    • View In Article
    • MEDLINE
76. Small TN, Papadopoulos EB, Boulad F, et al.  Comparison of immune reconstitution after unrelated and related T-cell-depleted bone marrow transplantation (effect of patient age and donor leukocyte infusions). Blood. 1999;93:467–480
    • View In Article
    • MEDLINE
77. Locatelli F, Maccario R, Comoli P, et al.  Hematopoietic and immune recovery after transplantation of cord blood progenitor cells in children. Bone Marrow Transplant. 1996;18:1095–1101
    • View In Article
    • MEDLINE
78. Moretta A, Maccario R, Fagioli F, et al.  Analysis of immune reconstitution in children undergoing cord blood transplantation. Exp Hematol. 2001;29:371–379
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (230 KB)
    • CrossRef
79. Klein AK, Patel DD, Gooding ME, et al.  T-cell recovery in adults and children following umbilical cord blood transplantation. Biol Blood Marrow Transplant. 2001;7:454–466
    • View In Article
    • Abstract
    • Full-Text PDF (1193 KB)
    • CrossRef
80. Thompson BG, Robertson KA, Gowan D, et al.  Analysis of engraftment, graft-versus-host disease, and immune recovery following unrelated cord donor blood transplantation. Blood. 2000;86:2703–2711
    • View In Article
81. Niehues T, Rocha V, Filipovich AH, et al.  Factors affecting lymphocyte subset reconstitution after either related or unrelated cord blood transplantation in children—a Eurocord analysis. Br J Haematol. 2001;114:42–48
    • View In Article
    • MEDLINE
    • CrossRef
82. Abu-Ghosh A, Goldman S, Slone V, et al.  Immunological reconstitution and correlation of circulating serum inflammatory mediators/cytokines with the incidence of acute graft-versus-host disease during the first 100 days following unrelated umbilical cord blood transplantation. Bone Marrow Transplant. 1999;24:535–544
    • View In Article
    • MEDLINE
83. Morecki S, Gelfand Y, Nagler A, et al.  Immune reconstitution following allogeneic stem cell transplantation in recipients conditioned by low intensity vs myeloablative regimen. Bone Marrow Transplant. 2001;28:243–249
    • View In Article
    • MEDLINE
    • CrossRef
84. Friedman TM, Varadi G, Hopely DD, et al.  Nonmyeloablative conditioning allows for more rapid T-cell repertoire reconstitution following allogeneic matched unrelated bone marrow transplantation compared to myeloablative approaches. Biol Blood Marrow Transplant. 2001;7:656–664
    • View In Article
    • Abstract
    • Full-Text PDF (142 KB)
    • CrossRef
85. Chao NJ, Liu CX, Rooney B, et al.  Nonmyeloablative regimen preserves ‘niches’ allowing for peripheral expansion of donor T cells. Biol Blood Marrow Transplant. 2002;8:249–256
    • View In Article
    • Abstract
    • Full-Text PDF (221 KB)
    • CrossRef
86. Wagner JE, DeFor T, Rubinstein P, Kurtzbeg J. Transplantation of unrelated donor umbilical cord blood (UCB) (outcome and analysis of risk factors). Blood. 1997;90:398a; (abstr.)
    • View In Article
87. Gehling UM, Ryder JW, Hogan CJ, et al.  Ex vivo expansion of megakaryocyte progenitors (effect of various growth factor combinations on CD34+ progenitor cells from bone marrow and G-CSF-mobilized peripheral blood). Exp Hematol. 1997;25:1125–1139
    • View In Article
    • MEDLINE
88. Shpall EJ, Quinones R, Giller R, et al.  Transplantation of ex vivo expanded cord blood. Biol Blood Marrow Transplant. 2002;8:368–376
    • View In Article
    • Abstract
    • Full-Text PDF (165 KB)
    • CrossRef
89. McNiece IK, Almeida-Porada G, Shpall EJ, Zanjani E. Ex vivo expanded cord blood cells provide rapid engraftment in fetal sheep but lack long term engraftment potential. Exp Hematol. 2002;30:612–616
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (77 KB)
    • CrossRef
90. Zanjani E, Almeida-Porada G, Hangoc G, Broxmeyer HE. Enhanced short term engraftment of human cells in sheep transplanted with multiple cord bloods (implications for transplantation of adults). Blood. 2000;96:552a; (abstr.)
    • View In Article
91. Barker JN, Weisdorf DJ, Wagner JE. Creation of a double chimera after the transplantation of umbilical-cord blood from two partially matched unrelated donors. N Engl J Med. 2001;344:1870–1871
    • View In Article
    • MEDLINE
    • CrossRef
92. Barker JN, Weisdorf DJ, Defor TE, et al.  Multiple unit unrelated donor umbilical cord blood transplantation in high risk adults with hematologic malignancies (impact on engraftment and chimerism). Blood. 2002;100:41a; (abstr.)
    • View In Article
93. Rubinstein P, Carrier C, Carpenter C, et al.  Graft selection in unrelated placental/umbilical cord blood (PCB) transplantation (influence and weight of HLA match and cell dose on engraftment ands survival). Blood. 2000;96:588a; (abstr)
    • View In Article
94. Wagner JE, Kurtzberg J. Allogeneic umbilical cord blood transplantation. In:  Broxmeyer HE editors. Cellular Characteristics of Cord Blood and Cord Blood Transplantation. Bethesda, MD: AABB Press; 1998;p. 113–146
    • View In Article
95. Gluckman E. Cord blood banking and transplantation in Europe. In:  Broxmeyer HE editors. Cellular Characteristics of Cord Blood and Cord Blood Transplantation. Bethesda, MD: AABB Press; 1998;p. 147–164
    • View In Article
96. Niederwieser N, Maris M, Shizuru JA, et al.  Low-dose total body irradiation (TBI) and fludarabine followed by hematopoietic cell transplantation (HCT) from HLA-matched or mismatched unrelated donor and postgrafting immunosuppression with cyclosporin and mycophenolate mofetil (MMF) can induce durable complete chimerism and sustained remissions in patients with hematological diseases. Blood. 2003;101:1620–1629
    • View In Article
    • MEDLINE
    • CrossRef
97. Zaucha JM, Yu C, Zellmer E, et al.  Effects of extending the duration of postgrafting immunosuppression and substituting granulocyte-colony-stimulating factor-mobilized peripheral blood mononuclear cells for marrow in allogeneic engraftment in a nonmyeloablative canine transplantation model. Biol Blood Marrow Transplant. 2001;7:513–516
    • View In Article
    • Abstract
    • Full-Text PDF (223 KB)
    • CrossRef
98. Champlin R, Khouri I, Kornblau S, et al.  Reinventing bone marrow transplantation (reducing toxicity using nonmyeloablative, preparative regimens and induction of graft-versus-malignancy). Curr Opin Oncol. 1999;11:87–95
    • View In Article
    • MEDLINE
    • CrossRef
99. Champlin R, Khouri I, Shimoni A, et al.  Harnessing graft-versus-malignancy (non-myeloablative preparative regimens for allogeneic haematopoietic transplantation, an evolving strategy for adoptive immunotherapy). Br J Haematol. 2000;111:18–29
    • View In Article
    • MEDLINE
    • CrossRef
100. Storb R, Yu C, Wagner JL, et al.  Stable mixed hematopoietic chimerism in DLA-identical littermate dogs given sublethal total body irradiation before and pharmacological immunosuppression after marrow transplantation. Blood. 1997;89:3048–3054
     • View In Article
     • MEDLINE
101. Hill RS, Petersen FB, Storb R, et al.  Mixed hematologic chimerism after allogeneic marrow transplantation for severe aplastic anemia is associated with a higher risk of graft rejection and a lessened incidence of acute graft-versus-host disease. Blood. 1986;67:811–816
     • View In Article
     • MEDLINE
102. Schetelig J, Kroger N, Held TK, et al.  Allogeneic transplantation after reduced conditioning in high risk patients is complicated by a high incidence of acute and chronic graft-versus-host disease. Haematologica. 2002;87:299–305
     • View In Article
     • MEDLINE
103. Garderet L, Dulphy N, Douay C, et al.  The umbilical cord blood αβ T-cell repertoire (characteristics of a polyclonal and naı̈ve but completely formed repertoire). Blood. 1998;91:340–346
     • View In Article
     • MEDLINE
104. Kuniyasu Y, Takahashi T, Itoh M, et al.  Naturally anergic and suppressive CD25(+)CD4(+) T cells as a functionally and phenotypically distinct immunoregulatory T cell subpopulation. Int Immunol. 2000;12:1145–1155
     • View In Article
     • MEDLINE
     • CrossRef
105. Stephens LA, Mottet C, Mason D, Powrie F. Human CD4(+)CD25(+) thymocytes and peripheral T cells have immune suppressive activity in vitro. Eur J Immunol. 2001;31:1247–1254
     • View In Article
     • MEDLINE
     • CrossRef
106. Han P, Hodge G, Story C, Xu X. Phenotypic analysis of functional T-lymphocyte subtypes and natural killer cells in human cord blood (relevance to umbilical cord blood transplantation). Br J Haematol. 1995;89:733–740
     • View In Article
     • MEDLINE
     • CrossRef
107. Risdon G, Gaddy J, Stehman FB, Broxmeyer HE. Proliferative and cytotoxic responses of human cord blood T lymphocytes following allogeneic stimulation. Cell Immunol. 1994;154:14–24
     • View In Article
     • MEDLINE
     • CrossRef
108. Junghanss C, Marr KA. Infectious risks and outcomes after stem cell transplantation (are nonmyeloablative transplants changing the picture?). Curr Opin Infect Dis. 2002;15:347–353
     • View In Article
     • MEDLINE
     • CrossRef
109. Tomonari A, Iseki T, Ooi J, et al.  Cytomegalovirus infection following unrelated cord blood transplantation for adult patients (a single institute experience in Japan). Br J Haematol. 2003;121:304–311
     • View In Article
     • MEDLINE
     • CrossRef
110. Miller W, Flynn P, McCullough J, et al.  Cytomegalovirus infection after bone marrow transplantation (an association with acute graft-v-host disease). Blood. 1986;67:1162–1167
     • View In Article
     • MEDLINE
111. Junghanss C, Boeckh M, Carter RA, et al.  Incidence and outcome of cytomegalovirus infections following nonmyeloablative compared with myeloablative allogeneic stem cell transplantation, a matched control study. Blood. 2002;99:1978–1985
     • View In Article
     • MEDLINE
     • CrossRef
112. Chakrabarti S, Mackinnon S, Chopra R, et al.  High incidence of cytomegalovirus infection after nonmyeloablative stem cell transplantation (potential role of Campath-1H in delaying immune reconstitution). Blood. 2002;99:4357–4363
     • View In Article
     • MEDLINE
     • CrossRef
113. Mohty M, Faucher C, Vey N, et al.  High rate of secondary viral and bacterial infections in patients undergoing allogeneic bone marrow mini-transplantation. Bone Marrow Transplant. 2000;26:251–255
     • View In Article
     • MEDLINE
     • CrossRef
114. Bainton RD, Byrne JL, Davy BJ, Russell NH. CMV infection following nonmyeloablative allogeneic stem cell transplantation using Campath. Blood. 2002;100:3843–3844
     • View In Article
     • MEDLINE
     • CrossRef
115. Yu C, Seidel K, Nash RA, et al.  Synergism between mycophenolate mofetil and cyclosporine in preventing graft-versus-host disease among lethally irradiated dogs given DLA-nonidentical unrelated marrow grafts. Blood. 1998;91:2581–2587
     • View In Article
     • MEDLINE
116. Storb RF, Champlin R, Riddell SR, et al.  Non-myeloablative transplants for malignant disease. Hematology (Am Soc Hematol Educ Program). 2001;375–391
     • View In Article
117. Kottaridis PD, Milligan DW, Chopra R, et al.  In vivo Campath-1H prevents graft-versus-host disease following nonmyeloablative stem cell transplantation. Blood. 2000;96:2419–2425
     • View In Article
     • MEDLINE