Haploidentical stem cell transplantation with purified CD34⁺ cells after a chemotherapy-alone conditioning regimen

Article Outline

• Abstract
• Introduction
• Methods
  • Patients
  • HLA typing and donors
  • Stem cell mobilization, collection, and processing
  • Conditioning regimen
  • Infection prophylaxis, growth factor administration, and prevention of hepatic veno-occlusive disease
  • Assessment of engraftment and immunologic studies
  • Administration of donor leukocytes after transplantation and GVHD
  • Assessment of survival and statistical analysis
• Results
  • Patients
  • Stem cell mobilization, collection, and processing
  • Engraftment and toxicity of the conditioning regimen
  • Administration of donor leukocytes after transplantation and GVHD
  • Immunologic reconstitution
  • Posttransplantation infections
  • Survival and disease relapse
• Discussion
• Acknowledgements
• References
• Further reading
• Copyright

Abstract 

We investigated whether a novel chemotherapy-alone conditioning regimen would permit durable engraftment of standard doses of CD34⁺ purified stem cell grafts from full-haplotype mismatched related donors. We also examined the role of infusing limited doses of donor leukocytes for prevention of leukemia relapse. Our conditioning regimen consisted of thiotepa, fludarabine, rabbit antithymocyte globulin, melphalan, cyclosporin, and prednisolone. Since October 1998, 14 patients with high-risk leukemia were treated; 13 donor-patient pairs shared 3 of 6 HLA antigens, and 1 pair shared 5 of 6 HLA antigens. A median of 5.4 × 10⁶ CD34⁺ cells per kilogram, 1.62 × 10⁴ CD3⁺ cells per kilogram, and 9.32 × 10⁴ CD19⁺ cells per kilogram were infused. T-cell depletion was the only graft-versus-host disease (GVHD) prophylaxis. All patients had prompt engraftment, and no late graft rejections were observed. All surviving patients received at least 1 infusion of donor whole blood containing 5, 7, 10, 25, or 50 × 10³ CD3⁺ cells per kilogram between days 25 and 95 after transplantation, after which 8 developed acute GVHD (3 grade I, 2 grade II, 2 grade III, and 1 grade IV) and 2 developed a bronchiolitis obliterans-like syndrome. After attaining complete remission, 5 patients relapsed and died with active leukemia. The estimated relapse-related mortality at 4 years is 38.1%. As of June 15, 2003, 6 of 14 patients have survived a median of 43.5 months after transplantation with 100% donor cells. All 6 surviving patients developed acute GVHD and had a natural killer cell mismatch with their donors in the direction of graft versus host. The estimated overall survival and event-free survival for the 14 patients at 4 years is 41.7% ± 13.5%.

Keywords:  Haploidentical stem cell transplantation, Purified CD34⁺ cells, Chemotherapy-alone conditioning regimen, Hematologic malignancies

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Introduction 

Allogeneic stem cell transplantation is curative for a significant number of patients with hematologic malignancies [1]. Although the ideal donor is a genotypically HLA-matched sibling, most patients in need of such a procedure do not have a suitable donor in the family. This has led in past decades to a steady increment in the use of phenotypically HLA-matched volunteer donors from the international registries 2, 3.

The odds of finding a matched unrelated donor range from 60% to 70% for white populations to less than 15% in ethnic minorities [4]. Another potential alternative donor is a genotypically haploidentical family member; such a member is readily available for more than 90% of patients. Other advantages in favor of such a donor are the possibility to select for sex, age, and cytomegalovirus (CMV) status and to have continued access to donor cells for further immunologic initiatives. This strategy has been used with success in children with severe combined immunodeficiency and, more recently, in patients with hematologic malignancies 5, 6, 7, 8, 9, 10. Historical barriers to the successful outcome of these patients have been severe graft-versus-host disease (GVHD) in non-T cell-depleted grafts, delayed immune reconstitution, and graft rejection and disease relapse in T cell-depleted grafts. With the recent availability of automated devices for CD34 cell selection, it has become possible to T-cell deplete with a fairly simple technology. This has allowed the infusion of a dose of T cells below the threshold for acute GVHD in the haploidentical setting. The risk of graft rejection has been decreased by the use of highly immunosuppressive total body irradiation-including conditioning regimens, as well as by the infusion of megadoses of donor CD34⁺ cells 7, 8, 10, 11.

This study was designed to offer a potentially curative transplantation for patients with high-risk leukemia who lacked a suitable donor in the family and in the international registries. To develop a process that is more widely applicable worldwide, we have developed a non-TBI-containing preparative regimen for haploidentical transplantation [12]. We also investigated whether standard doses of purified CD34⁺ cells would induce durable donor engraftment in this setting. Finally, we wanted to examine whether the infusion of a controlled number of donor leukocytes after transplantation would decrease leukemia relapse.

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Methods 

Patients 

Between October 1998 and August 2002, 14 patients with poor-prognosis acute myeloid leukemia (AML) or chronic myeloid leukemia (Table 1) were treated at our center with an allogeneic stem cell transplant from a family donor sharing only 1 haplotype with the patient. These patients did not have a related or unrelated donor available. Written, informed consent was obtained both from the patients and the donors.

Table 1. Patient Characteristics

M indicates male; F, female; AML, acute myeloid leukemia; CML, chronic myeloid leukemia; CR, complete remission.

HLA typing and donors 

Patients and potential donors were studied by single-strand polymorphism DNA polymerase chain reaction for HLA class I and II alleles. Mixed lymphocyte cultures were not performed. Of the 14 patient-donor pairs, 13 were a full 1-haplotype mismatch, and 1 patient shared 5 of 6 HLA antigens with his donor. The donors were the father in 7 cases, the mother in 1 case, a sibling in 3 cases, and a son or daughter in 3 cases. None of the patients or donors was homozygous for HLA-A, -B, and -DR; therefore, all patient-donor pairs were mismatched both in the direction of graft versus host and of host versus graft. The donors were not selected according to potential natural killer (NK) cell alloreactivity against the host; the degree of mismatch between donor killer immunoglobulin-like receptors (KIRs) and host HLA class I alleles (HLA-A, -Bw4, and -C) was ascertained only at the time of evaluation of disease relapse and survival.

Stem cell mobilization, collection, and processing 

Peripheral blood stem cells were mobilized with granulocyte colony-stimulating factor (G-CSF) 10 to 12 μg/kg/d subcutaneously, divided into 2 administrations, for 5 days. Standard-volume leukaphereses, processing 2 total blood volumes, were performed via peripheral vein by using a CS3000 Plus continuous flow cell separator (Baxter, Deerfield, IL) on days 4 and 5 of G-CSF administration. Each leukapheresis was immediately processed, and the CD34 cell selection was performed with the automated CliniMacs device (Miltenyi Biotec, Bergisch-Gladbach, Germany). Thereafter, the CD34⁺ population was analyzed and cryopreserved. For the CD34 cell selection, the instructions of the manufacturer were followed with the exception of the addition of 250 mg of immunoglobulin (Octapharma, Wien, Austria) before the addition of the anti-CD34 monoclonal antibody to prevent nonspecific binding of B cells to the antibody. Because of a low CD34 cell count after the first mobilization, 1 donor had a third leukapheresis after a second stimulation with G-CSF. Our aim was to collect at least 5 × 10⁶ donor CD34⁺ cells per kilogram of the recipient’s body weight. On the day of transplantation, the CD34⁺ cells were gently thawed and immediately administered to the patient without further fluorescence-activated cell sorter (FACS) analysis.

Conditioning regimen 

Our conditioning regimen consisted of thiotepa 5 mg/kg/d on day −9 and day −8, fludarabine 40 mg/m²/d on day −9 to day −5, rabbit antithymocyte globulin (ATG; Thymoglobulin; IMTIX Pasteur Mérieux Connaught, Paris, France) 5 mg/kg/d on day −7 to day −3 as a 12- to 24-hour infusion, melphalan 60 mg/m²/d on day −4 and day −3, cyclosporin 3 mg/kg/d on day −10 to day −2, and prednisolone 2 mg/kg/d on day −7 to day −3 (1 mg/kg before the administration of ATG and 1 mg/kg with ATG). A schema of the conditioning regimen is depicted in Figure 1.

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• Figure 1. 

  Schema of the conditioning regimen. Thio. indicates thiotepa; Mel., melphalan. The doses of each drug are specified in Methods. The arrow indicates the infusion of the graft. The abscissa represents the days before transplantation.

Infection prophylaxis, growth factor administration, and prevention of hepatic veno-occlusive disease 

All patients were isolated in high-efficiency particulate air-filtered positive-pressure air-flow rooms from day −9 until the third day of neutrophils >1000/μL. They all received ciprofloxacin 500 mg orally twice daily from day −10 to the initiation of broad-spectrum intravenous antibiotics due to neutropenic fever, itraconazole 200 mg orally twice daily from day −10 until the eventual institution of liposomal amphotericin B or until discharge, acyclovir 500 mg/m² every 8 hours intravenously from day −10 and switched to 800 mg orally every 12 hours after day 21 to day 30, and trimethoprim sulfamethoxazole 960 mg orally twice daily from day −10 to day −4. After discharge, all patients continued to receive, at least until 18 months after transplantation, amoxicillin 500 mg orally twice daily, acyclovir 200 mg orally twice daily, itraconazole 200 mg orally twice daily, and trimethoprim sulfamethoxazole 960 mg orally twice daily 3 days per week. Despite the positivity for CMV immunoglobulin G in 13 of 14 patients, no specific prophylaxis with ganciclovir or foscarnet was performed. All patients received irradiated, leukocyte-depleted blood products, which were not analyzed for CMV status. All patients received intravenous immunoglobulin (Octapharma) 500 mg/kg weekly from day −10 until 3 months after transplantation, after which it was administered twice per month until day 180 and then once per month until 1 year after transplantation.

All patients received G-CSF 10 μg/kg/d intravenously from day 1 until consistent neutrophil engraftment. All patients also received prostaglandin E₁ 0.5 mg/d by continuous infusion as prophylaxis for hepatic veno-occlusive disease. This is a standard procedure at our center for patients receiving myeloablative conditioning regimens.

Assessment of engraftment and immunologic studies 

Engraftment was documented conventionally. Chimerism analysis of unseparated peripheral blood leukocytes was assessed monthly until day 180 and every 2 to 3 months thereafter by polymerase chain reaction amplification of hypervariable tandem repeat regions with different DNA polymorphisms, as described elsewhere [13].

With the frequency described for the chimerism studies, peripheral blood lymphocytes were also studied by flow cytometry (Scalibur FACS Scan; Becton Dickinson, Franklin Lakes, NJ) for a number of T-cell, B-cell, and NK-cell antigens, including CD2, CD3, CD4, CD5, CD7, CD8, CD19, CD20, CD56, CD25, CD69, HLA-DR, T-cell receptor (TCR) α/β, TCR γ/δ, CD45RO, and CD45RA, all purchased from Becton Dickinson, by following a methodology previously published [14].

Administration of donor leukocytes after transplantation and GVHD 

All patients received at least 1 infusion of donor whole blood between day 25 and day 95 after transplantation with the intent of hastening immune recovery and decreasing the risk of relapse (Table 2). Five patients received 5 × 10³ donor CD3⁺ cells per kilogram, 1 patient received 7 × 10³ donor CD3⁺ cells per kilogram, 3 patients received 1 × 10⁴ donor CD3⁺ cells per kilogram, 2 patients received 2.5 × 10⁴ donor CD3⁺ cells per kilogram, and 3 patients received 5 × 10⁴ donor CD3⁺ cells per kilogram. After the first administration, 1 patient who received 2.5 × 10⁴ donor CD3⁺ cells per kilogram on day 58 was infused with 4.5 × 10⁴ donor CD3⁺ cells per kilogram on day 72 because of persistent pancytopenia not responsive to growth factor administration, and another patient who received 7 × 10³ donor CD3⁺ cells per kilogram on day 31 received a second administration of 2 × 10⁴ donor CD3⁺ cells per kilogram on day 83. Other patients received higher doses of donor leukocytes because of leukemia relapse (discussed in more detail in Results). The diagnosis and degree of acute and chronic GVHD were assessed according to established criteria published in detail elsewhere 15, 16.

Table 2. Posttransplant Donor Cell Infusions, GVHD, NK Cell Alloreactvity of Donor versus Host, and Outcome

Assessment of survival and statistical analysis 

All patient details were routinely introduced and analyzed with the StemSoft software database (Stem Cell Technologies Inc, Vancouver, BC, Canada). The probabilities of overall and event-free survival from the time of transplantation were calculated according to the Kaplan-Meier method [17]. The events considered for the event-free survival analysis were time from the on-study date to relapse, evidence of disease progression, or death from any cause. The date of the first event was used in calculating event-free survival. Groups were compared by using the 2-sided log-rank test 18, 19. Differences were considered significant if the P value was <.05. Follow-up was updated to June 15, 2003.

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Results 

Patients 

A total of 14 patients (8 males and 6 females) underwent transplantation (Table 1). Their median age was 25 years (range, 13–45 years), and only 1 patient was younger than 18 years old. All the patients had high-risk leukemia, and, according to the judgment of the attending physicians, none had a significant chance for long-term survival without this therapeutic approach. The median time from diagnosis to transplantation was 12.5 months (range, 3–48 months). Of the 14 patients treated, 9 had chemoresistant blastic primary disease or relapse; 4 patients had relapsed after a myeloablative autologous bone marrow transplant. Five of the 9 patients with resistant disease received low-dose intravenous cytarabine, VP-16, or both in the 2 weeks before the conditioning regimen for control of blast counts. Of the 5 patients who received transplants in remission, only the patient with acute biphenotypic leukemia was in first complete remission. One patient with AML was in second complete remission, and the other 3 patients, also with AML, were in third complete remission.

Stem cell mobilization, collection, and processing 

No significant adverse events occurred during stem cell mobilization and collection. The patients received a median of 5.4 × 10⁶ (range, 2.9–13.8 × 10⁶) CD34⁺ cells per kilogram, 1.62 × 10⁴ (range, 0.33–5.96 × 10⁴) CD3⁺ cells per kilogram, and 9.32 × 10⁴ (range, 5.5–12.55 × 10⁴) CD19⁺ cells per kilogram. These cell counts were obtained at the time of cryopreservation; FACS analysis was not performed after thawing (the viability of the thawed cells by trypan blue exclusion was >90% in all patients). With the CD34⁺ cell selection, a 4.5 to 5 log₁₀ T-cell depletion was achieved. T-cell depletion was the only prophylaxis for GVHD.

Engraftment and toxicity of the conditioning regimen 

All 14 patients had primary and durable engraftment after a median of 10 days of severe pancytopenia. The median day of neutrophils >500/μL and 1000/μL was day 11 (range, day 9 to day 20) and day 12 (range, day 9 to day 22), respectively. Twelve of the 14 patients had a neutrophil count of 500/μL between days 9 and 12 after transplantation. The median day of platelets >20 000/μL and 50 000/μL was day 19 (range, day 11 to never reached) and day 38 (range, day 15 to never reached), respectively. Two patients never had platelet recovery: 1 experienced early relapse, and 1 died with CMV pneumonia. The latter patient, who had late engraftment (neutrophils >500/μL on day 20), developed interstitial pneumonia on day 5 and was treated with intravenous ganciclovir and trimethoprim sulfamethoxazole. All but 1 patient had 100% donor cell engraftment confirmed by DNA chimerism studies between days 21 and 30 after transplantation. One patient with primary resistant AML had 92% donor cells on day 21. He had a full relapse shortly thereafter. On subsequent engraftment analysis, all surviving patients were confirmed to have durable full donor engraftment. No late graft rejections were observed.

The toxicity of the conditioning regimen was minimal; 1 patient died within the first 100 days after transplantation (the patient with accelerated chronic myeloid leukemia who died of CMV pneumonia on day 96). No instance of hepatic veno-occlusive disease was observed.

Administration of donor leukocytes after transplantation and GVHD 

All patients received at least 1 infusion of the donor’s whole blood containing the number of CD3⁺ cells specified in Table 2. Most patients received a relatively low dose of donor T cells, which was estimated to have a low potential of inducing GVHD. Of the 11 evaluable patients, 8 developed acute GVHD (3 grade I, 2 grade II, 2 grade III, and 1 grade IV), and 2 patients developed chronic GVHD de novo (both patients with bronchiolitis obliterans-organizing pneumonia [BOOP]-like syndrome: 1 moderate and 1 severe). The median number of days between donor leukocyte infusion and development of acute GVHD was 30 days (range, 21–101 days). Five of the 8 patients with acute GVHD had a complete resolution of this syndrome with cyclosporin A plus steroids (n = 1), cyclosporine plus mycophenolate mofetil and steroids (n = 1), mycophenolate mofetil plus steroids (n = 1), or steroids alone (n = 2). One patient who developed grade III acute GVHD is still receiving mycophenolate mofetil and prednisolone 11 months after the transplantation.

The 2 patients with clinical BOOP-like syndrome developed this syndrome 21 and 88 days after donor leukocyte infusion. One of these patients had a prolonged immunodeficiency and significant pancytopenia requiring weekly platelet transfusions. He received two boosts of purified CD34⁺ from his donor (which required 2 additional stimulations with G-CSF) with, unfortunately, limited success. He never had circulating CD4⁺ cells and died 20 months after transplantation with an invasive Candida species lung infection. The second patient died with interstitial pneumonia, possibly due to CMV. None of these patients had developed acute GVHD.

One patient (Al 222) with primary resistant AML and a complex karyotype {45,XX, t(3;3)(q21;q26), −7[13]/45,XX, t(1;17)(p35;q12), t(3;3)(q21;q26), −7[2]}, who received a transplant from a full-haplotype mismatched donor, developed a mild skin rash on day 120 after the infusion of limited doses of donor leukocytes on days 38 and 107. Concomitantly with relapse, she presented at 3 months with 1256 × 10⁶/L CD3⁺, 559 × 10⁶/L CD4⁺, and 516 × 10⁶/L CD4⁺CD45RA⁺ cells, which were the highest of the group at this early time after transplantation. Although the rash was suggestive of acute GVHD, it was not treated and waned 2 days later. Subsequently, on day 124, she presented with peripheral blood blasts, and bone marrow relapse was confirmed. This patient had circulating myeloblasts for 3 months, with a bone marrow infiltration that ranged between 2% and 50% of total marrow cellularity. For this reason, she received increasing doses of donor leukocytes (Table 2), but developed extensive skin GVHD only after blast reduction with a total dose of 25 mg of anti-CD33 monoclonal antibody conjugated with calicheamicin (Mylotarg; Wyeth Ayerst, Collegeville, PA). The skin GVHD was not treated, and the patient attained a brief hematologic remission, but blast cells reappeared immediately thereafter, and the patient died with interstitial pneumonia. It is interesting to note that there was a KIR ligand incompatibility in the graft-versus-host direction in this case (donor HLA-Cw8 and patient HLA-Cw4), not controlling the leukemic clone.

Immunologic reconstitution 

All patients had a significant impairment in the reconstitution of peripheral blood lymphocyte subsets. Typically, very few CD3⁺ cells were detected in the complete blood count before the administration of donor leukocytes after transplantation and the development of GVHD. As depicted in Figure 2, the median count of CD3⁺ and CD4⁺ cells was quite low until more than 12 months after transplantation. The emergence of naı̈ve CD4⁺CD45RA⁺ cells was even slower. Only 1 patient had more CD4⁺ cells than CD8⁺ cells at 1 year after transplantation, and only 2 patients had more CD4⁺ cells than CD8⁺ cells at 2 years after transplantation. Higher levels of NK cells were detected within the first 3 months after transplantation. Functional studies were not performed.

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• Figure 2. 

  Median absolute number of CD3⁺, CD4⁺, CD8⁺, CD56⁺, CD4⁺CD45RA⁺, and CD19⁺ cells at the indicated timing after transplantation. M indicates months.

Posttransplantation infections 

Of the 14 patients, 7 had positive blood cultures for gram-positive or gram-negative bacteria in the first month after transplantation. All of these episodes were successfully treated. Four patients had Candida albicans isolated; 2 of these cases had invasive infection (1 esophageal and pulmonary and 1 pulmonary alone), which ultimately contributed to their death. One of these patients had primary resistant AML, and the other had severe chronic GVHD.

The major infectious complication after transplantation was due to CMV reactivation, which occurred in 10 of the 14 cases. To treat this, most patients received prolonged courses of intravenous ganciclovir, foscarnet, and immunoglobulin in our adult day hospital. CMV may have been a secondary contributor to the death of 4 patients with AML who relapsed after transplantation and was the cause of death in 1 patient who developed interstitial pneumonia on day 5 and in 1 of the patients with a BOOP-like syndrome. Finally, 4 patients developed transitory polyomavirus or adenovirus virurias.

Survival and disease relapse 

As of June 15, 2003, 6 of 14 patients remain alive with a median follow-up of 1331 days. All surviving patients received a full 1-haplotype mismatched transplant. Of the 14 patients who underwent transplantation, 9 had evidence of active leukemia before transplantation. After the transplantation, all patients attained remission, and only the first patient (Al 164) relapsed within 2 months. Of the 6 surviving patients, 4 were in remission at the time of transplantation. The Kaplan-Meier estimate of the proportion of patients alive (overall survival) and event free (event-free survival) at 4 years was, in both cases, 41.7% ± 13.5% (Figure 3A and 3B).

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• Figure 3. 

  The overall survival (A) and event-free survival (B) for the entire group at 4 years after transplantation was 41.7%.

All surviving patients developed acute GVHD, and 5 of these 6 patients survive disease free more than 2 years after transplantation, with a Karnofsky score of 100, without chronic GVHD, and off treatment (1 of these 5 patients had grade III and 1 had grade IV acute GVHD; Table 2). None of the 4 patients without GVHD was alive at 6 months after transplantation (their median survival time was 109 days), whereas 58.3% ± 16.1% of the 10 patients who developed GVHD are estimated to be alive at 4 years after transplantation, with the median survival time not reached (P < .0001).

We analyzed only NK cell alloreactivity of the donor against the recipient for the analysis of the results. Following the observations of other groups, all patients and donors were retyped for the HLA-C locus 20, 21. Of the 14 donor-recipient pairs, 9 had the following KIR ligand incompatibility in the graft-versus-host direction: 5 pairs were mismatched at the HLA-C locus, 2 pairs were mismatched for the HLA-Bw4 group, 1 pair was mismatched at the HLA-A3 level, and 1 pair was mismatched for the HLA-A3, -Bw4, and -C groups (Table 2). Six of these 9 patients survive disease free. All of these 6 patients also developed GVHD after the infusion of donor cells after transplantation. Of the 9 pairs with donor NK cell alloreactivity against the patient, 66.7% ± 15.7% are estimated to be alive at 4 years, with the median survival time not reached, whereas the 5 patients without NK cell alloreactivity all died with a median survival time of 186 days after transplantation. Three of these 5 patients died in relapse. Two patients with NK cell incompatibility in the direction of graft versus host, both at the level of the HLA-C locus, also died in relapse.

In 5 cases, death was due to leukemia relapse. Three of these patients had primary resistant AML, and the other 2 had chemotherapy-resistant relapse. Two of these 5 patients had a period of complete hematologic and cytogenetic remission that lasted 4 to 6 months. The relapse-related mortality for the whole group at 4 years in all patients was 38.1% (Figure 4).

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• Figure 4. 

  Relapse-related mortality for the entire group at 4 years after transplantation was 38.1%.

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Discussion 

Most conditioning regimens in haplotype-disparate transplantations have included total body irradiation, which is highly immunosuppressive, because of the significant risk of graft failure after the infusion of T cell-depleted grafts [22]. Our conditioning regimen was composed of chemotherapy alone. It used ATG, fludarabine, and thiotepa, administered at the same doses as in the Perugia regimen 7, 8. To prevent ATG infusion-related toxicity, we included prednisolone 2 mg/kg/d on the days of ATG infusion (1 mg/kg before ATG and 1 mg/kg with ATG) [23]. Other groups have been reluctant to use steroids in this setting because of apprehension with the development of donor Epstein-Barr virus (EBV)-induced B-cell lymphoproliferative disorders 7, 8. To replace total body irradiation, we gave melphalan at a dose of 120 mg/m² equally divided between days −4 and −3. From our analysis of the literature, we believed that this regimen, although fairly intensive and possibly myeloablative, would have acceptable toxicity. In fact, only 1 patient died within 100 days of transplantation, and none developed hepatic veno-occlusive disease (however, all patients received prophylaxis with prostaglandin E₁).

We were also interested in investigating whether a standard dose of purified CD34⁺ cells would consistently induce sustained engraftment in the setting of a chemotherapy-alone conditioning regimen for haploidentical transplantation. With the exception of 1 patient, all the others received CD34⁺ cells collected in 2 standard-volume leukaphereses, which is a highly feasible collection procedure. Because these cells were selected immediately after the procedure, analyzed, and cryopreserved, the number of cells infused to the patient was likely lower than that recorded. We cryopreserved a median of 5.4 × 10⁶ CD34⁺ cells per kilogram, which is approximately 50% of the number of cells administered by the Perugia group and 25% of the dose infused by the Tübingen group 7, 8, 10. With the CliniMacs system, a CD34⁺ cell purity higher than 97% was achieved, with minimal B- and T-cell contamination. Although our patients were conditioned with a chemotherapy-alone regimen, consistent donor engraftment was confirmed in all patients by DNA analysis of hypervariable tandem repeat regions, and no late graft failures occurred. In the selection procedure, we incubated the leukapheresed cells with human immunoglobulin to prevent nonspecific binding of the anti-CD34 monoclonal antibody to B cells, further decreasing the B-cell content of the graft. This was a relevant issue, because we were concerned that if the number of B cells in the graft were higher, together with the profound immunosuppression of the conditioning regimen and the anticipated delayed immune recovery, the risk of donor EBV-induced B-cell lymphoproliferative disorders after transplantation could be high 24, 25. None of patients developed this complication, suggesting that the number of donor EBV⁺ B cells in the graft was very low. The patients were not monitored for EBV replication in the posttransplantation period.

We also wanted to investigate whether the infusion of a limited dose of donor leukocytes after transplantation would hasten immune recovery and prevent disease relapse. This was clearly a risky procedure, but we hypothesized that the infusion of very low numbers of donor T cells could probably be of benefit without a significant risk of severe GVHD. Initially, our protocol was designed to infuse 2.5 to 5 × 10⁴ donor CD3⁺ cells per kilogram between days 30 and 45 after transplantation, but, with the development of GVHD in the second, third, and fourth patients, this number was decreased to 5 to 10 × 10³ CD3⁺ cells per kilogram. After the infusion of donor cells after transplantation, most patients developed GVHD. Because this complication emerged early after transplantation, we cannot distinguish the relative contribution of donor T cells infused with the CD34⁺ cells and those administered after transplantation for the development of GVHD. Typically, patients acquired peripheral blood lymphocytes >1 × 10⁹/L only after the development of clinical GVHD. Even though we observed a significant increase in CD3⁺ cells and their subsets after the infusion of donor leukocytes, we cannot determine whether this was beneficial clinically, because functional assays were not performed. Given the high rate of GVHD, even with the posttransplantation infusion of as little as 5 × 10³ donor CD3⁺ cells per kilogram (which corresponds in most donors to <0.3 mL of whole blood), it is unclear whether this strategy should be pursued. Even though the 6 patients alive developed GVHD, eventually suggesting a T cell-mediated graft-versus-leukemia effect, we cannot determine whether this was relevant for long-term disease control, because all of these donor-recipient pairs also had a KIR ligand incompatibility in the direction of graft versus host. It is of interest that 6 of 9 NK cell-incompatible donor-recipient pairs developed grade II to IV acute or chronic GVHD after the posttransplantation infusion of donor leukocytes, whereas only 1 of 5 pairs without NK-cell incompatibility developed this complication.

The association of GVHD and NK cell alloreactivity in haploidentical transplantation contrasts with the study in mice by Ruggeri et al. [21], who observed a protection against T cell-mediated GVHD in animals who underwent transplantation with haploidentical grafts possessing NK cell alloreactvity against the host, apparently because of donor NK cell lysis of host antigen-presenting cells capable of initiating GVHD. Also in contrast with these investigators 20, 21, we observed leukemia relapse in 2 patients with KIR ligand incompatibility in the direction of graft versus host, suggesting that other factors may also play a role in the attainment of long-term disease-free survival in patients with high-risk AML. In fact, both patients had highly resistant leukemias with multiple cytogenetic abnormalities. Alternatively, it may also be important to transplant a higher CD34⁺ cell dose than we administered to induce a more potent NK cell response against leukemia. Finally, it is unclear whether patients with such refractory diseases should be eligible for this type of transplantation, because the risk of leukemia relapse is so high. As suggested by the consensus recommendations reached at the Perugia and Chicago meetings, protocols using haplotype-disparate T cell-depleted grafts can be justified for patients in better condition with high-risk leukemia in first or second complete remission [26].

The significant immunosuppression observed after transplantation was likely determined by the infusion of a haplotype-disparate T cell-depleted graft. The use of G-CSF after transplantation might also have contributed to the delayed immune recovery, because it has been shown to block interleukin-12 production by the antigen-presenting cells [27]. However, we were concerned that without G-CSF, engraftment might be compromised because of the number of CD34⁺ cells transplanted [28]. We also recognize that a higher number of CD34⁺ cells may be desirable because cells within the CD34⁺ compartment possess potent veto activity, neutralizing cytotoxic T-lymphocyte precursors and thereby facilitating the induction of tolerance [29]. As reported by other groups, NK cells emerged early after transplantation in our patients 7, 8, 30. In contrast, CD3 cells and their subsets were quite low until >1 year after transplantation. In the patients who developed acute GVHD, a major increase in CD3⁺, CD4⁺, and CD8⁺ cells expressing TCR α/β was noted, suggesting that they were alloreactive. Both the Perugia and the Tübingen groups reported faster emergence of these subsets of cells after transplantation; this may be due to the higher CD34 cell count infused and to their avoidance of G-CSF 7, 8, 10, 30.

The main infectious complication associated with this prolonged immunosuppression was persistent CMV reactivation. In most patients this was asymptomatic, but it necessitated prolonged courses of intravenous ganciclovir, foscarnet, and immunoglobulin. This infection clearly represents a major challenge in the Portuguese population of patients submitted to this type of transplantation because most adults are CMV immunoglobulin G positive. Methods of adoptive immunotherapy with donor CMV-specific T-cell clones would be highly valuable in this setting [31]. One patient developed interstitial pneumonia almost 2 years after transplantation, with full recovery after intravenous ganciclovir, clarithromycin, and trimethoprim sulfamethoxazole. The etiology of this infection is uncertain. He was always negative for CMV during this episode. This event further demonstrates that these patients remain severely immunocompromised until late after transplantation.

With a projected overall and event-free survival of 41.7% at 4 years in a group of patients—13 adults and 1 child—with very high risk leukemia (9 of the 14 patients had primary or secondary resistant disease) who received transplants from a full 1-haplotype mismatched donor in all but 1 case, we believe that these results are encouraging and that the technique should be further developed. In the future, patients with a clear indication for an allogeneic stem cell transplantation in earlier remission and who lack an HLA-matched donor should probably be included in programs of haplotype-disparate stem cell transplantation.

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Acknowledgements 

The authors would like to thank Dr. Richard J. O’Reilly for critical review of the manuscript.

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Further reading 

12. Lacerda JF, Carmo JA, Martins C, et al.  Durable donor engraftment in haplo-identical stem cell transplantation with standard dose purified CD34+ cells after a chemotherapy alone conditioning regimen. Blood. 2001;98:478; (abstr.)