Volume 9, Issue 9, Pages 543-558 (September 2003)

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Cytomegalovirus in hematopoietic stem cell transplant recipients: current status, known challenges, and future strategies

Received 17 July 2003; accepted 1 August 2003.

Abstract

Cytomegalovirus (CMV) infection is a major cause of morbidity and mortality after hematopoietic stem cell transplantation. Significant progress has been made in the prevention of CMV disease over the past decade, but prevention of late CMV disease continues to be a challenge in selected high-risk populations. The pretransplantation CMV serostatus of the donor and/or recipient remains an important risk factor for posttransplantation outcome despite the use of antiviral prophylaxis and preemptive therapy; CMV-seropositive recipients of T cell-depleted grafts in particular continue to have a survival disadvantage compared with seronegative recipients with seronegative donors. The risk of developing antiviral drug resistance remains low in most patients; however, in a setting of intense immunosuppression (eg, after transplantation from a haploidentical donor), the incidence may be as high as 8%. Primary CMV infection via blood transfusion can be reduced by the provision of seronegative or leukocyte-depleted blood products; however, a small risk of 1% to 2% of CMV disease remains. Surveillance and preemptive therapy are effective in preventing the sequelae of transfusion-related CMV infection. Indirect immunomodulatory effects of CMV are increasingly recognized in hematopoietic stem cell transplant recipients. Strategies currently being investigated include long-term suppression of CMV with valganciclovir for the prevention of late CMV infection and disease, adoptive transfer of CMV-specific T cells, and donor and recipient vaccination strategies.

Keywords: CMV, Herpes virus, Hematopoietic stem cell, Transplantation, Immunosuppression, Resistance

Article Outline

• Abstract

• Introduction

• Effect of CMV in hematopoietic sct

• Effect of CMV serostatus in the era of preemptive therapy and prophylaxis

• Effect of source of stem cells and CD34 selection

• Effect of the conditioning regimen

• Effect of posttransplantation immunosuppression

• Late CMV disease in the era of preemptive therapy

• Clinical manifestations of CMV disease

• CMV infection diagnosis and surveillance

• Current prevention and treatment strategies

• Prevention of primary CMV infection

• Prophylaxis strategies

• Immune globulin and antibody therapy

• Acyclovir and valacyclovir

• Ganciclovir

• Foscarnet

• Preemptive strategies

• Ganciclovir and foscarnet

• Oral ganciclovir and valganciclovir

• Cidofovir

• Initiation and duration of preemptive therapy and viral monitoring

• Effect of drug-resistant cmv strains

• Future pharmacologic and immune therapies

• Conclusions

• Acknowledgment

• References

• Further reading

• Copyright

Introduction

Historically, untreated cytomegalovirus (CMV) infection and disease were associated with significant morbidity in the early period after transplantation and led to mortality in nearly 25% of seropositive patients undergoing allogeneic hematopoietic stem cell transplantation (SCT) 1, 2, 3. Despite the introduction of effective antiviral therapies during the last 2 decades, the mortality from late CMV disease and the indirect effects of CMV remain deterrents to successful long-term outcomes 4, 5. Furthermore, as hematopoietic SCT has evolved, less toxic nonmyeloablative conditioning regimens coupled with intensive postengraftment immunosuppressive therapies have enabled the use of less selective transplant matches and have enabled older patients to undergo transplantation, with increasing risks for subsequent opportunistic and reactivated infections requiring further intervention.

Although significant progress has been made in diagnostic and prevention strategies, hematopoietic SCT recipients exist in a dynamic environment and require constant surveillance and reassessment of viral challenge. In particular, those high-risk recipients characterized by treatment with high-dose corticosteroids, mycophenolate mofetil, and T-cell depletion or anti-T-cell strategies are most vulnerable to CMV infection. Also, long-term outpatient management poses a more practical concern in some areas. During this review of our current knowledge of CMV, risk factors, prevention and treatment strategies, the potential threat of CMV drug resistance, and unresolved issues in our current prophylactic and therapeutic approaches will be discussed.

Effect of CMV in hematopoietic sct

Regardless of currently available antiviral strategies, hematopoietic SCT recipients remain at risk for CMV infection not only during the early posttransplantation period (<100 days), but also later (>100 days) in the posttransplantation course. Before the introduction of ganciclovir, the vast majority of CMV infections occurred in the time period between engraftment and day 100 after hematopoietic SCT, with sporadic occurrences before engraftment [6] (Figure 1). However, whereas the prevalence of early CMV disease has declined to 3% to 6% with intense antiviral drug use, the risk of late CMV disease has increased over the past few years, with up to 18% of recipients developing disease even when no prevention is administered 7, 8, 9, 10, 11, 12.

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Figure 1. Incidence of early (before day 100) versus late (after day 100) cytomegalovirus (CMV) disease by year of hematopoietic stem cell transplantation in seropositive allogeneic recipients (n = 1458). Reprinted with permission [6].

Effect of CMV serostatus in the era of preemptive therapy and prophylaxis

The issue of CMV serostatus in the ganciclovir era is complex and continues as an area of active study 13, 14, 15, 16, 17, 18, 19, 20, 21 (Table 1). Despite almost complete prevention of CMV disease in most of these studies, positive CMV serostatus of the recipient remains a poor prognostic factor, especially in recipients of T cell-depleted marrow or stem cells. An association of CMV with graft-versus-host disease (GVHD) and nonviral infections or sepsis has been suggested as a possible mechanism 13, 18. A large study by Ljungman et al. [16] demonstrated the importance of donor serostatus among CMV-seropositive recipients of unrelated grafts, possibly as a result of transferred CMV-specific immunity from the donor to the recipient. In an analysis of a large cohort of T cell-replete SCT recipients, both donor-positive/recipient-positive and donor-positive/recipient-negative recipients had a higher risk of mortality [18]. After controlling for neutropenia and CMV disease, only donor-positive/recipient-negative recipients had a higher risk of mortality. The authors attributed this outcome to indirect immunomodulatory effects of CMV because there was an excess mortality due to bacterial and fungal infections when compared with donor-negative/recipient-negative recipients [18]. Collectively, these studies of the effect of CMV serostatus in the ganciclovir era suggest that CMV infection before transplantation remains an important factor leading to poor outcome after transplantation, especially in recipients of T cell-depleted transplants.

Table 1.

Results of Selected Studies of Cytomegalovirus (CMV) Serostatus and Patient Outcomes


Study	No. Patients	T-Cell Depletion	Effect of CMV Serostatus on Mortality	Specific Outcomes
Broers [13]	115	Yes (n = 109) No (n = 6)	Yes (recipient)	5-y survival significantly better for CMV-seronegative than CMV-seropositive recipients, primarily because of treatment-related mortality: 64% versus 40% (P = .01)
McGlave [21]	1423	Yes	Yes (recipient)	CMV-seronegative recipients had a lower risk of death or relapse (hazard ratio, 0.80; P = .02)
Cornelissen [20]	127	Yes	Yes (recipient)	CMV-seronegative recipients had longer disease-free survival (P = .05) and lower transplant-related mortality (P = .08)
Craddock [15]	106	Yes	Yes (recipient)	5-y survival significantly better for CMV-seronegative than for CMV-seropositive recipients: 60% versus 42% (P = .006)
Kroger [19]	125	Yes	Yes (recipient)	CMV-positive serostatus of recipient associated with higher mortality (P = .014) and transplant-related mortality (P = .02)
Ljungman [16]	7018	No	Yes (donor)∗	For HLA-identical siblings, donor CMV serostatus had no effect on outcomes in a univariate analysis
				For unrelated donor transplants, recipients of CMV-seropositive donor transplants had significantly improved survival (P = .006) and treatment-related mortality (P < .001) compared with recipients of CMV-seronegative donor transplants
Castro-Malaspina [14]	510	Yes (n = 389) No (n = 121)	Yes (recipient)	CMV-negative recipient serostatus was associated with significantly better overall survival (P = .002), reduced treatment-related mortality (P = .004), and higher cancerfree survival (P = .001)
Meijer [17]	253	Yes	Yes (recipient)	For recipients from matched, related donors, CMV seropositivity of either donor or recipient was not associated with survival or treatment-related mortality
				For recipients from matched, unrelated donors, recipient CMV seropositivity was associated with poorer survival (P = .013) and treatment-related mortality (P = .0070)
Nichols [18]	1750	No	Yes (recipient, donor)	Highest mortality associated with CMV-seropositive donor and CMV-seronegative recipient paining (P = .04) or CMV-seropositive donor and CMV-seropositive recipient paining (P = .03)

∗

This study examined the impact of donor CMV status among seropositive recipients. Effect of recipient serostatus was not evaluated.

Effect of source of stem cells and CD34 selection

Recipients of transplants from unrelated or mismatched related donors in some analyses show an increased risk of CMV disease, CMV-associated death, and transplant-associated mortality [23]. Whereas altering the cellular components of the hematopoietic SCT through CD34 depletion is theoretically advantageous in reducing contaminating tumor cells, T cell-depleting the graft or CD34 selection in both allogeneic 24, 25 and autologous hematopoietic SCT after myeloablative conditioning has shown a notable increase in CMV disease and CMV-associated deaths [26]. Investigation of the effect of the source of stem cells on CMV infection provides conflicting results. Emergence of CMV infection and disease after either unmodified peripheral blood SCT or bone marrow transplantation was evaluated in 2 studies. One nonrandomized study (n = 158) showed that the incidences of CMV antigenemia (P = .01) and CMV interstitial pneumonia (P = .04) were significantly reduced in the peripheral blood SCT recipients compared with the bone marrow transplant recipients [26]. However, results from a randomized trial (n = 172) showed a higher incidence of CMV infection (P = .04) and a trend toward more CMV disease (P = .06) in unmodified peripheral blood SCT recipients when compared with bone marrow transplant recipients [27].

Effect of the conditioning regimen

Data are accumulating on the effect of the pretransplantation conditioning regimen on CMV incidence and outcome. Myeloablative conditioning regimens seek to destroy the existing cells, allowing for replacement with the graft cells. With nonmyeloablative regimens, a mixed chimerism occurs, with coexistence of host and donor cells until the replacement graft material prevails. Because myeloablative conditioning regimens destroy host T cells (including the cytotoxic T cells specific for CMV), the question has been raised whether nonmyeloablative regimens would result in less early CMV infection, a shorter duration of neutropenia, reduced regimen-related toxicity, and a longer duration of host immunocompetence when compared with myeloablative regimens. To date, several nonmyeloablative and reduced-toxicity conditioning regimens have been reported (Figure 2), although the corresponding level of immunosuppression varies. In a study of mostly HLA-matched sibling transplant recipients with hematologic malignancies undergoing either nonmyeloablative (total body irradiation; 2 Gy) or conventional hematopoietic SCT, CMV disease was significantly delayed in the nonmyeloablative group compared with the myeloablative group (P = .02) [28]. However, the overall incidence of CMV disease at 1 year was similar between the 2 conditioning regimens in recipients at high risk (Figure 3). Notably, the incidence and onset of CMV antigenemia, as well as the time to antigenemia clearance, were also comparable [28]. There was a trend toward more CMV infection and disease arising in unrelated donor transplant recipients [29]. However, a reduced-toxicity conditioning regimen of alemtuzumab-1H (immunoglobulin G1 humanized monoclonal anti-CD52) showed a high incidence of CMV infection with very early reactivation of virus in 50% of patients at a median of 27 days after engraftment [30]. The results of these studies suggest that the choice of conditioning regimens affects the time of CMV reactivation and disease, but the overall risks have not been substantially reduced in the nonmyeloablative SCT recipient.

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Figure 2. Continuum of intensity from nonmyeloablative to myeloablative hematopoietic stem cell transplant-conditioning regimens. ATG indicates antithymocyte globulin; TBI, total body irradiation; MP, melphalan.

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Figure 3. Incidence of cytomegalovirus disease in high-risk hematopoietic stem cell transplant recipients after nonmyeloablative and myeloablative conditioning regimens. Incidence at day 100, P = .08; incidence at day 365, P = 87; day of onset, P = .02. Reprinted with permission [28].

Effect of posttransplantation immunosuppression

The immunosuppressive regimens that allow the recipient to retain the graft and avoid the complications of GVHD also play a role in CMV epidemiology. The net state of immunosuppression experienced by the recipient is modulated by factors such as pharmacologic therapies (type, timing, duration, and sequence), immunogenetic characteristics (HLA match), the presence or absence of immunomodulating viruses, and metabolic abnormalities [31]. Hematopoietic SCT recipients treated with high-dose corticosteroids (>1 mg/kg/d), mycophenolate mofetil, T cell-depleted autografts or allografts, and certain anti-T-cell strategies (eg, antithymocyte globulin) are considered at high risk for CMV disease. In one study, an increased risk of CMV disease or CMV-related complications in allogeneic stem cell recipients was associated with mycophenolate mofetil treatment, which seems to upregulate CMV [5]. In another study of allogeneic hematopoietic SCT recipients receiving intense immunosuppression and preemptive therapy, based on 2 positive DNA polymerase chain reaction (PCR) assays, the strategy failed because of the rapid rate of viral load increase [32]. In this population, treatment at a lower viral threshold is necessary and should not be delayed to obtain a second positive diagnostic test.

What emerges from these studies is that highly immunosuppressed recipients have delayed or reduced immune reconstitution, which has a direct effect on the viral replication dynamics in vivo [33]. Contrary to widely held beliefs that CMV is a slowly replicating virus (based on its time to clinical manifestations and its slow growth in fibroblast tissue cultures), the in vivo increase of viral load progresses with a doubling time of approximately 1 day in SCT recipients. The likelihood of subsequent CMV disease development is independently predicted by both the initial viral burden and the rate of viral burden increase. Therefore, measurement of these viral characteristics supports identification of recipients at immediate risk of CMV disease 33, 34. Overall, recipients with a higher viral burden are more prone to manifest CMV disease during both the early and the late transplantation periods 7, 35. The time frame for progression from viral detection to overt disease with a rapidly increasing viral load is compressed in highly immunosuppressed patients (eg, those taking >1 mg/kg/d of corticosteroids or those who are T-cell depleted) such that any positive test should trigger immediate treatment in these patients.

The same factors influence the viral load kinetics in patients receiving antiviral treatment. Nichols et al. [36] showed that viral load may increase in highly immunosuppressed individuals receiving ganciclovir. These viral load increases were seen in patients receiving high doses of corticosteroids.

Late CMV disease in the era of preemptive therapy

Although preemptive ganciclovir therapy administered in response to pp65 antigenemia [8] or PCR detection of CMV DNA [9] has dramatically reduced early CMV disease after allogeneic hematopoietic SCT, with concurrent improved survival in certain high-risk recipients 9, 37, the resulting increase in the occurrence of late CMV disease has emerged as a threat to long-term survival. A recent prospective study explored the incidence and risk factors for late CMV infection in seropositive allogeneic hematopoietic SCT recipients receiving ganciclovir prophylaxis either at engraftment or preemptively in response to pp65 antigenemia, where routine antiviral drug use terminated after 3 months (Figure 4) [7]. Of the 146 patients followed up, 17.8% developed late CMV disease at a median of 169 days after engraftment. CMV disease was associated not only with a mortality rate of 46%, but also with recurrence in 38% of survivors [7]. Risk factors for late mortality and CMV disease are shown in Table 2. Other studies have confirmed that chronic GVHD (P = .0017) and prior use of antiviral therapy for longer than 4 weeks (P = .0073) are risk factors for late CMV disease [10]. The authors of both studies recommended continued monitoring for CMV with rapid, sensitive techniques and prompt application of preemptive therapy, especially for high-risk recipients, in the late period after hematopoietic SCT.

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Figure 4. Cumulative incidence of late CMV disease in patients with the presence and absence of risk factors present at 3 months. Right, graft-versus-host disease (GVHD; grade 2–4 or clinical chronic). Left: Any pp65 antigenemia (AG) before day 95 and CD4 count <50 cells per cubic millimeter. Reprinted with permission [7].

Table 2.

Risk Factors Associated with Late CMV Disease and Mortality in High-Risk Allogeneic Hematopoietic Stem Cell Transplant Recipients∗


Variable	Relative Risk (95% Confidence Interval)	P Value
Risk factors present by month 3 after transplantation associated with mortality†
Absolute lymphocytopenia after day 40 (≤100 cells/mm3)	1.8 (1.1–3.0)	≤.05
CD4 count (≤50 cells/mm3)	1.9 (1.1–3.1)	≤.05
CD8 count (≤50 cells/mm3)	2.5 (1.5–4.2)	≤.01
CMV pp65 antigenemia (any level positive)	1.8 (1.0–3.1)	≤.01
Surveillance risk factors present after day 95 after transplantation associated with late CMV disease‡
Lymphocytopenia (<300 cells/mm3)	9.4 (3.8–23.5)	≤.01
CMV DNA (plasma)
>1000 copies/mL	6.2 (1.0–39.2)	<.05
>10 000 copies/mL	12.3 (1.8–85.1)	≤.01
CMV pp65 antigenemia (any level positive)	5.3 (1.5–19.1)	≤.01
Risk factors present after day 95 after transplantation associated with mortality‡
CMV disease	2.3 (1.2–4.2)	≤.01
Lymphocytopenia (<300 cells/mm3)	3.6 (1.9–6.7)	≤.01

∗

Adapted with permission [7].

†

Univariate analysis.

‡

Multivariate analysis.

Practically, the effectiveness of the preemptive strategy depends on compliance with testing. Although no randomized trials have been performed, cohort studies suggest that viral monitoring should occur weekly 28, 38. Thus, the logistics of frequent testing must be arranged with the patient (especially in the rural community setting). Although this has not been well studied, the frequency of monitoring may be reduced in patients receiving low doses of immunosuppression (ie, tapering doses of corticosteroids at <0.5 mg/kg/d) and in those without evidence of viral reactivation for 4 weeks [7] (Boeckh and Nichols, 2003, unpublished data).

Clinical manifestations of CMV disease

The direct clinical manifestations of CMV disease vary slightly for early compared with late disease. The most common manifestations are pneumonia and gastrointestinal disease, which can occur from the esophagus to the colon [39]. After day 100, manifestations other than pneumonia and gastrointestinal disease are sometimes observed, including CMV retinitis 40, 41 and central nervous system disease 13, 42. Standardization of definitions for use in clinical studies of CMV infection and disease in immunocompromised patients has allowed more accurate assessments [43].

The indirect effects associated with CMV include graft rejection, accelerated atherosclerosis, and bacterial or fungal superinfections; these have been primarily documented in solid organ transplantation 44, 45, 46, 47. Early studies with acyclovir prophylaxis for CMV infection after bone marrow transplantation provided preliminary indications of indirect CMV effects [48]. More recently, the indirect effects of primary CMV infection were implicated in the higher incidence of bacterial and fungal infection in a large cohort of seronegative recipients of hematopoietic SCTs from seropositive donors [18]. Efforts to elucidate and ameliorate these indirect effects have stimulated an impressive body of research from clinical trials, as well as basic research. Inclusion of indirect effects as valuable end points (especially in clinical trials of drug therapies) should help assess these effects 31, 43.

CMV infection diagnosis and surveillance

CMV disseminates through the blood during active infection, and the presence of viremia is recognized as the major virologic risk factor for progression to clinical disease. Older techniques, such as culture-based assays, failed to provide the rapid, sensitive, and efficient detection and quantitation required for prediction of outcomes or initiation (or changes) of antiviral treatments [3]. In the era of preemptive antiviral treatment strategies, the most universally applicable clinical assays are CMV DNA detection methods and the pp65 antigenemia assay. Recently, the pp67 messenger RNA (mRNA) assay has been shown to be an alternative to these methods [49]. In general, use of PCR technology with either in-house or commercially available assays to detect CMV DNA has proven an excellent guide to trigger preemptive therapy. However, the individual assays vary in sensitivity, specificity, and predictive value. Although plasma was long considered a poor source for PCR-driven assays, improvement of these assays through sophisticated technology provides sensitivity similar to that of cell-based sources 50, 51. Another practical issue concerns assay variability. All quantitative measurements have a certain coefficient of variation, so the general guideline for a true increase or decrease in viral load is 0.5 log10—approximately a 3-fold difference. Although the pp65 antigenemia assay, the pp67 mRNA assay, and most DNA PCR assays perform well in clinical practice [39] (Table 3), assay sensitivity and low variability of quantitation become especially critical for highly immunosuppressed recipients, in whom the viral load can increase rapidly [53]. For these recipients, monitoring by quantitative PCR with immediate antiviral therapy at low levels without waiting for a second positive test may affect CMV-related outcomes 8, 32, 54, 55.

Table 3.

Results of PCR-, pp67 mRNA-, and pp65 Antigenemia-Guided Preemptive Treatment Studies∗


Study∗∗	Surveillance	Control Group	Treatment Regimen (Start/End)	N	Incidence of CMV Disease (day 100) (%)
Randomized trials
Einsele [9]	PCR CMV DNA	Rapid culture-guided ganciclovir	Ganciclovir and CMV Ig for 2 consecutive positive PCR results; discontinuation after 2 wk or when PCR negative; repeated treatment if PCR positivity recurred	26†	7.7
Boeckh [8]	pp65 AG	Ganciclovir prophylaxis	Ganciclovir for pp65 AG (≥2 positive cells per 150 000 PBL; discontinuation after 3 wk or 6 d after negative pp65 AG assay; repeated treatment if positive AG recurred	114†‡	14.1§
Moretti [109]	pp65 AG	Preemptive foscarnet or ganciclovir	Ganciclovir or foscarnet for 15 d for pp65 AG (1 to 4 positive cells per 200 000 PBL)	19‖	10.5
Humar [110]	pp65 AG	Day 35 BAL	Positive pp65 AG: ganciclovir 5 mg/kg twice daily for at least 2 wk or until negative AG; repeated treatment if necessary	60	0
			Positive BAL: ganciclovir 5 mg/kg twice daily for 2 wk followed by 8 wk of 5 mg/kg/d, 5 d/wk
Reusser [78]	pp65 AG, PCR CMV DNA	Preemptive ganciclovir or foscarnet for positive AG or PCR	Ganciclovir: 14 d of 5 mg/kg twice daily	110 (FSC)	3.3 (both groups combined)¶
			Foscarnet: 14 d of 60 mg/kg twice daily	103 (GCV)
			Continued maintenance therapy if persistent positive screening test at 2 wk
Gerna [49]	pp67 mRNA	pp65 AG	Ganciclovir 5 mg/kg twice daily until 2 negative tests	41 (pp67 mRNA)#	0 (both groups)
Nonrandomized trials
Ljungman [89]	PCR CMV DNA	Historical	Ganciclovir for 2 consecutive positive results DNA	39 (pp65 AG)# 58	6.0
Gerna [111]	pp65 AG	None	Ganciclovir for pp65 AG (≥2 positive cells per 200 000 PBL); discontinuation after 2 wk; maintenance for 7 to 14 d in patients with GVHD; repeated treatment if pp65 AG recurred	30#	6.6
Boeckh [112]	pp65 AG	Historical	Ganciclovir for pp65 AG at any level until day 100	102‡	3.8
Einsele [10]	PCR CMV DNA	None	Ganciclovir for 2 consecutive positive PCR results for 14 d; if still positive, foscarnet until PCR negative	86	3.5

Reprinted with permission [39].

CMV indicates cytomegalovirus; PCR, polymerase chain reaction; Ig, immunoglobulin; AG, antigenemia; PBL, peripheral blood leukocyte; BAL, bronchoaveolar lavage; FSC, foscarnet; GCV, ganciclovir; GVHD, graft-versus-host disease.

∗

Data refer to the incidence of CMV disease in seropositive recipients or seronegative recipients with seropositive donors.

†

Incidence among engrafted patients.

‡

Study includes only seropositive recipients.

Disease before or after AG of 2 positive cells per slide, 8.8%; disease shortly after discontinuation of ganciclovir on the basis of a negative test, 5.3%.

‖

Only disease after AG was reported; 1 patient was seronegative with a seronegative donor.

There was no difference in the incidence of CMV disease between the 2 groups. Incidence figures refer to the time after the start of study drug rather than the entire first 100 days.

Pediatric patients only.

∗∗

Additional studies have been reported without data provided for day 100 27, 52.

Current prevention and treatment strategies

Prevention of primary CMV infection

For CMV-seronegative hematopoietic SCT recipients, prevention focuses on use of seronegative donors and blood products or use of leukocyte-reduced blood products. However, the rate of CMV disease with leukocyte-reduced blood products can be up to 2.4% [56]. In a follow-up study of 807 patients receiving leukocyte-reduced or seronegative blood products, filtered red blood cell units (but not apheresis platelet products) from CMV-positive donors were associated with a significant 32% increase in the odds for transfusion-transmitted CMV (P = .006). These results underscore that CMV-seronegative products should remain a critical resource for high-risk patients [57]. Although posttransplant surveillance and preemptive therapy are currently not uniformly advocated 58, 59, their use is highly effective in eliminating complications of transfusion-related CMV infection [57].

Prophylaxis strategies

Immune globulin and antibody therapy

The use of CMV-specific intravenous immune globulin (IVIG) for viral prophylaxis has been assessed in 2 separate randomized, controlled trials of treatment of seronegative recipients of allogeneic bone marrow transplants from seropositive donors, and these studies showed no difference in disease incidence 60, 61. Other studies of IVIG or CMV immunoglobulin have failed to show either consistent positive results for CMV-related complications or survival benefits 62, 63, 64, 65. A trial with a highly neutralizing monoclonal antibody (MSL-109) specific to the CMV glycoprotein H also failed to show a benefit in seropositive hematopoietic SCT recipients [66]. Overall, antibody treatments are not currently recommended for CMV prophylaxis [58], and uncertainty remains over the usefulness of IVIG or hyperimmune globulin for the prevention of non-CMV complications.

Acyclovir and valacyclovir

The first trial of antiviral prophylaxis used acyclovir (500 mg/m2) intravenously (IV) every 8 hours from 5 days before engraftment to 30 days after transplantation in seropositive allogeneic bone marrow transplant recipients [67]. This prospective, nonrandomized study showed that high-dose acyclovir therapy reduced the risk of CMV infection and invasive disease, as well as mortality, in the first 100 days after transplantation. With the apparent success of acyclovir, a more extensive prospective, double-blind trial showed a survival advantage for the IV acyclovir/oral acyclovir group compared with the controls (low-dose oral acyclovir/placebo group). There was no difference in the incidence of CMV pneumonia or other CMV diseases between the treatment groups. The survival benefit of 19% was maintained through 1 year of follow-up. In addition, there seemed to be fewer deaths related to bacterial and fungal infections 48, 68.

The development of a valine-ester prodrug of acyclovir, valacyclovir, allowed investigators to explore 2 issues limiting acyclovir use as CMV prophylaxis: (1) poor oral bioavailability of the parent acyclovir and (2) potential to expand dosage and the duration of treatment with an improved oral formulation. One large study randomized 727 seropositive (recipient-positive or donor-positive) allogeneic bone marrow transplant recipients to either oral valacyclovir (2000 mg) or oral acyclovir (800 mg) 4 times per day for 18 weeks after transplantation after prophylactic IV acyclovir therapy (500 mg/m2 IV every 8 hours from 5 days before engraftment to 28 days after transplantation) [69]. Treatment with valacyclovir significantly reduced the risk of CMV viremia compared with high-dose oral acyclovir (28% versus 40%, respectively; P < .0001) during the approximately 160 days of follow-up. Preemptive treatment with ganciclovir guided by either PCR or antigenemia detection of CMV resulted in a low incidence of CMV disease in the valacyclovir group (3.6%) and in the acyclovir group (5.6%). Survival did not differ between treatment groups. Tolerability was also similar for the 2 drugs [69]. In a subset analysis, the effect of valacyclovir was seen mainly in low-risk patients, whereas little effect was shown in recipients of unrelated donor grafts. A small randomized trial of valacylovir versus intravenous ganciclovir showed no statistically significant difference in CMV disease, neutropenia, and survival [70].

Ganciclovir

Results of early prophylaxis with ganciclovir in seropositive allogeneic bone marrow transplant recipients have been reported from 3 randomized, double-blind studies with slightly different protocols 8, 71, 72. Although all studies demonstrated a significant (P < .001) reduction of CMV infection or disease during the first 100 days after engraftment, 2 studies also showed a significant (P < .001 and P = .002, respectively) and near-total prevention of CMV disease during ganciclovir therapy [8,70]. No survival advantage was demonstrated, and severe neutropenia was observed in all studies and was potentially linked to greater risks of fungal or bacterial infections 8, 71, 72. However, none of these studies had a sufficiently large sample size to evaluate survival as a study end point. Thus, there was no detectable survival benefit with early prophylaxis in these 3 studies, whereas analyses of large high-risk cohorts, such as unrelated donor transplant recipients [37] and randomized studies of preemptive therapy performed in high-risk individuals, did show an effect of ganciclovir on survival 9, 73. Studies listed in Table 1 indicate that there are now important subsets of patients in whom the use of ganciclovir prophylaxis or preemptive therapy leads to the elimination of the survival disadvantage associated with pretransplantation CMV serostatus.

Foscarnet

Only small uncontrolled studies of foscarnet in hematopoietic SCT recipients have been conducted for CMV prophylaxis. Renal toxicity has limited widespread prophylactic use of this agent 74, 75.

Preemptive strategies

Preemptive therapy in hematopoietic SCT recipients refers to identification of at-risk recipients by using timely CMV detection with PCR techniques or with quantitative pp65 antigenemia, followed by immediate implementation of antiviral treatment on viral detection (Figure 5). The premises of preemptive therapy are that CMV viremia predicts disease development and that viral load is a critical factor in pathogenesis 3, 35. Therefore, this approach requires access to reliable and rapid early diagnostic tests, strict monitoring (at least weekly), and appropriate sample selection [3]. Another risk-adapted strategy (sometimes called selected prophylaxis) uses immunologic and virologic risk factors (eg, antithymocyte globulin therapy, CMV antigenemia, or GVHD) to adjudicate administration of a short course of ganciclovir. However, although this is reasonable in high-risk situations, studies on this approach are sparse, and general applicability remains untested 76, 77.

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Figure 5. Approximate time of CMV infection after allogeneic hematopoietic stem cell transplantation during the era of preemptive treatment strategies with ganciclovir. GCV indicates ganciclovir; FSC, foscarnet; IP, interstitial pneumonia; BMT, bone marrow transplantation.

Ganciclovir and foscarnet

Currently, preemptive therapy with IV ganciclovir has decreased the cumulative incidence of CMV disease to rates ranging from 3.3% to 10.5% before day 100 after engraftment (Table 3). Although most data are available for ganciclovir regimens, both ganciclovir and foscarnet are used in preemptive therapy. In a large randomized trial of 213 SCT recipients, preemptive therapy with foscarnet was compared with that with ganciclovir; the incidence of CMV disease was <5% in both groups [78]. Neutropenia was more frequently reported in the ganciclovir arm, whereas impaired renal function and electrolyte abnormalities were more frequent in the foscarnet arm [78]. Despite the higher incidence of neutropenia, the composite end point of CMV disease-free survival was not different between the groups. A small study of reduced-dose ganciclovir and foscarnet combinations did not show a reduction in viral load or treatment-related toxicities [79].

Oral ganciclovir and valganciclovir

Pharmacokinetic evaluations of an oral ganciclovir formulation in a phase I/II study showed that the presence of acute GVHD of the gastrointestinal tract did not seem to limit drug absorption, and, thus, the bioavailability of the drug seemed appropriate for hematopoietic SCT recipients. Gastrointestinal intolerance and neutropenia in the early postengraftment period (before day 60) seemed to be impediments to the use of this formulation [80]. Use of the oral ganciclovir formulation later in the transplantation course after IV treatment provided acceptable tolerability and efficacy in another study [81].

Valganciclovir is a valine-ester prodrug of ganciclovir that, in solid organ transplant recipients [82] and human immunodeficiency virus-infected patients [83], has improved bioavailability, resulting in an area under the curve similar to that of IV ganciclovir. If the early reports of drug usefulness are supported by currently ongoing clinical trials in hematopoietic SCT, valganciclovir may become an alternative to IV ganciclovir for some indications 84, 85.

Cidofovir

Although randomized clinical trials have not yet been performed, small, uncontrolled studies of cidofovir in allogeneic hematopoietic SCT recipients indicate that it may be effective as second-line therapy in patients with CMV disease whose traditional antiviral treatments have failed [86] or in low-risk patients after low-intensity conditioning regimens [87]. However, treatment-related toxicities (ie, renal and marrow impairments) and reports of cidofovir failures prohibit its use as front-line preemptive therapy before comparative studies are conducted 85, 87, 88.

Initiation and duration of preemptive therapy and viral monitoring

The definitive threshold for triggering antiviral preemptive therapy remains undecided, and centers continue to base their regimens primarily on local experience and patient characteristics. In general, initiation of therapy triggered by 2 consecutive positive results with either DNA PCR-guided or any positive pp65 antigenemia test result is effective in allogeneic recipients receiving standard immunosuppression 9, 54. In cases of highly immunosuppressed recipients, the faster increase in CMV levels warrants therapy initiation at very low levels of virus detection [32].

Various durations of antiviral treatment within preemptive therapy have been explored. The original studies continued any initiated ganciclovir therapy until day 100 after engraftment (approximately 6 to 8 weeks in the average recipient). Studies from the mid 1990s of shorter ganciclovir courses based on negative PCR assays at the end of therapy with a 3-week mean [9] or a 2-week mean [89] were generally effective; however, resumption of preemptive therapy was necessary in approximately 30% of patients (Figure 5). Most centers now continue antiviral treatment until the designated viral marker is negative. If less sensitive markers, such as the pp65 antigenemia assay or pp67 mRNA assay, are used, then preemptive therapy should be continued until 2 negative assays are obtained [69]. Induction dosing should continue until a decline of viral load has been demonstrated [55].

If either the recipient or donor is seropositive, weekly CMV surveillance is recommended until day 100 after engraftment. After day 100, weekly surveillance should be continued in recipients at high risk for disease on the basis of early patient characteristics [39] (Table 4). Because 80% of CMV cases are documented before day 270 after engraftment [7], surveillance should be performed during this period; the duration and frequency of CMV monitoring in the later transplantation periods have not been determined. Nonetheless, a surveillance strategy should include considerations of the net immunosuppression of the recipient (including corticosteroid treatments for GVHD) and history of CMV reactivation. Thus, selected patients with continued intense immunosuppression may benefit from surveillance after day 270 after transplantation.

Table 4.

Management of CMV Infection after Hematopoietic Stem Cell Transplantation: Recommendations [39]


Indication	Strategy	Comment
Prevention
Allogeneic transplantation (myeloablative and nonmyeloablative)	Antigenemia- or PCR-guided early ganciclovir treatment: 5 mg/kg BID for minimum of 7 d or until viral load decreases (whichever comes later), followed by 5 mg/kg/d until day 100 or until serial negative PCR or antigenemia∗	Some cases of CMV disease may occur shortly after discontinuation based on negative PCR or antigenemia; thus, 2 negative tests are required in high-risk settings
	or
Seropositive recipient	Ganciclovir prophylaxis at engraftment: 5 mg/kg BID for 5 d followed by 5 mg/kg/d on 5–6 dy/wk until day 100	Recommended if neither PCR no antigenemia testing is available
Seronegative recipient/seropositive donor	Antigenemia- or PCR-guided early ganciclovir treatment: 5 mg/kg BID for 7 d or until viral load decreases, followed by 5 mg/kg/d until day 100 (or until negative PCR or antigenemia)∗	Prophylaxis at engraftment not recommended because of low incidence of posttransplantation infection
	and
	Seronegative or leukocyte-reduced blood products
Seronegative recipient/seronegative donor	Seronegative or leukocyte-reduced blood products	Breakthrough disease of up to 2.3%; virologic monitoring and preemptive therapy effective in reducing breakthrough rates but not uniformly advocated
Autologous transplantation, seropositive recipient	Antigenemia- or PCR-guided early ganciclovir treatment: 5 mg/kg ganciclovir BID for 7 d or until viral load decreases, followed by 5 mg/kg/d for 14 to 21 d	Monitoring not uniformly advocated because of very low risk in some settings (absence of corticosteroids, TBI, CD34 selection); CD34-depleted recipients represent a special population that should be monitored similarly to allogeneic recipients
Seronegative recipient	Seronegative or leukocyte-reduced blood products	Breakthrough disease of up to 2.3%; virologic monitoring and preemptive therapy effective in reducing breakthrough rates but not uniformly advocated
Treatment of disease
CMV pneumonia	Ganciclovir 5 mg/kg BID for 14 to 21 d (or until declining viral load) followed by 5 mg/kg/d for at least 3 to 4 wk plus IVIG 500 mg/kg or CMV Ig 150 mg/kg every other day for 2 wk, then weekly	Extended maintenance throughout the period of severe immunosuppression (ie, GVHD treatment) may be considered
Gastrointestinal disease	Ganciclovir 5 mg/kg BID for 14 to 21 d (or until declining viral load) followed by 5 mg/kg/d for at least 3 to 4 wk	If deep ulcerations are present, longer maintenance may be required
Marrow failure	Foscarnet 90 mg/kg BID for 14 d followed by 90 mg/kg/d for 2 wk plus G-CSF	Ganciclovir plus IVIG has also been used
Retinitis	Ganciclovir 5 mg/kg BID for 14 to 21 d followed by 5 mg/kg/d for at least 3 to 4 wk	Extended maintenance may be required; ophthalmologic monitoring is required

TBI indicates total body irradiation; IVIG, intravenous immune globulin; Ig, immunoglobulin; G-CSE, granulocyte colony-stimulating factor; BID, twice daily.

∗

Foscarnet has been shown to be equivalent with regard to efficacy in 1 randomized trial [78].

Effect of drug-resistant cmv strains

Overall, ganciclovir resistance remains a rare occurrence in hematopoietic SCT recipients 36, 42, 90, 91, 92, 93 (Table 5). Most reports of ganciclovir resistance in transplant recipients suggest that children with immunodeficiency syndromes or those who receive transplants from haploidentical donors with T cell-depleted allografts are at higher risk for development of CMV strains resistant to ganciclovir (multidrug resistance to foscarnet and cidofovir also occur) [93]. Although children seem at higher risk in the early period (days 44 to 95 after allogeneic engraftment with T cell-depleted material) before recovery of immune competence, ganciclovir resistance does not always correlate with delayed immune recovery [94]. Ganciclovir resistance emerged in 2 adult haploidentical hematopoietic SCT recipients after prolonged preemptive therapy [42]. One case involved central nervous system manifestations linked to mixed wild-type and UL97 mutant viral populations in the cerebrospinal fluid. The second case resulted from a resistant variant in the lung [42]. The incidence of ganciclovir resistance in hematopoietic SCT continues to be monitored through clinical response assessments and identification of resistance-associated mutations.

Table 5.

Studies Documenting Ganciclovir Resistance in Hematopoietic Stem Cell Transplant Recipients


Study	Setting	N	Incidence (%)
CMV disease
Slavin [90]	CMV interstitial pneumonia	12	8.3
CMV infection
Erice [91]	CMV infection	15	6.7
Nichols [36]	pp65 antigenemia (all)	119	0.8
	Increasing pp65 antigenemia (subset)	15	6.7
Boivin [92]	pp65 antigenemia	34	0
All patients
Eckle [93]	Unrelated donor/haploidentical	79	3.8
Wolf [42]	Allogeneic/haploidentical (all)	138	1.4
	Haploidentical (subset)	26	7.6

Resistance to ganciclovir results from mutations in the viral DNA polymerase gene (UL54) and the viral phosphotransferase gene (UL97), with mutations in UL97 emerging first (resulting in low-level resistance), followed by the more severe resistance associated with UL54 mutations 91, 95. The development of ganciclovir resistance is linked to the degree of immunosuppression, the kinetics of viral replication, the presence of mutant viral strains at the onset of drug therapy, and the effectiveness and duration of antiviral therapy. Situations in which prolonged subclinical reactivation occurs in the presence of antiviral drug predispose patients to development of drug resistance. With quantitative virologic monitoring, increases in viral load for >2 weeks on induction doses of antivirals may be suggestive of viral resistance. Although switching antiviral drug therapy to foscarnet or cidofovir (which are not affected by the UL97 mutation) has shown benefit, some cross-resistance has been reported 93, 95, 96. Use of the prodrug valganciclovir in solid organ transplant recipients has suggested that lower rates of resistance may occur when compared with those seen with oral ganciclovir, but data are not yet available for hematopoietic SCT recipients [97].

Future pharmacologic and immune therapies

Clinical trials are under way with valganciclovir. The drug is well absorbed, with proven efficacy as induction therapy in human immunodeficiency virus-infected patients with new CMV retinitis, and preemptive studies are ongoing [84]. However, absorption in SCT recipients with gastrointestinal GVHD has not been studied. In hematopoietic SCT, randomized studies are ongoing to determine the role of valganciclovir in preemptive therapy and for long-term prophylaxis of late CMV infection and disease. Initial uncontrolled reports show no breakthrough disease in a small cohort of hematopoietic SCT recipients receiving preemptive therapy [98]. Additional drugs are in preclinical and clinical development 99, 100.

The profound and prolonged immunodeficiency engendered by the processes necessary for hematopoietic SCT provides the opportunity for CMV reactivation. Current immunotherapy approaches involve 2 strategies: (1) early restoration of recipient CMV-specific immunity with adoptive transfer of expanded T-cell clones from donor material 101, 102, 103 and (2) vaccination of stem cell donors with or without recipient vaccination. For the adoptive transfer approach, research interest has centered on restoration of CMV-specific CD8+ cytotoxic T cells, because initial studies showed that these cells were capable of preventing the development of CMV-associated disease in the early postengraftment time frame [104]. More than a decade ago, the potential of adoptive transfer of CMV-specific CD8+ T-cell clones propagated in vitro was reported in allogeneic hematopoietic SCT recipients [105]. More recently, adoptive transfer of cloned or expanded CMV-specific CD8+ T cells from the blood of their CMV-seropositive donors was successfully accomplished in allogeneic hematopoietic SCT recipients, with resultant substantial increases in anti-CMV cytotoxic activity and no treatment-related side effects [101]. However, this study also highlighted the need for concurrent transfer of CD4+ helper T cells. Another recent study reported infusion of CMV-specific T cells for the treatment of CMV infection not responding to antiviral chemotherapy [106].

A number of strategies to produce sufficient quantities of T cells appropriate for adoptive immunotherapy have been explored; major technical issues include maximizing comprehensive and efficient antigen presentation and selection of the T-cell subsets most likely to avoid the risk of GVHD. For expansion of T-cell clones through presentation of exogenously provided antigen, the choice of antigen-presenting cells includes monocytes, dendritic cells, and B-lymphocyte cell lines. Techniques for presentation of endogenously provided antigens have used a variety of antigen-presenting cells, transduction versus transfection approaches, different vectors, and different antigens. Approaches for selection of the most favorable lymphocyte subset involve boosting cell numbers and identifying and retrieving the cells [107]. Host factors and immunosuppressive or treatment-related drugs are likely to influence the success of immune reconstitution after hematopoietic SCT. In particular, use of high-dose corticosteroids (>1 mg/kg/d) has already been identified as predicting poorer recovery of competent T-cell immunity during the first 3 months after transplantation [108]. The major issues with clinical application of adoptive immunotherapy include technical and time-dependent challenges, lack of appropriate donor material, further characterization of host and regimen effects, and the expense of this treatment approach.

Extensive literature exists on CMV-directed vaccines using material derived from attenuated live virus, recombinant live virus, viral DNA sequences, whole CMV proteins, and peptides. However, these approaches will be successful only in the recipient with adequate postengraftment immune reconstitution, especially for the CMV-specific T cells. Vaccine-based approaches for the immunosuppressed host are still hindered by the major obstacle of producing an effective vaccine based on products other than live virus. Even if such a vaccine were available, the best approach for its application remains to be defined. Should seropositive donors be boosted, or should seronegative donors be vaccinated, with or without subsequent stem cell recipient vaccination [103]? Although immunotherapy seems to be the most comprehensive approach in theory, practical clinical application requires more intensive investigation.

Conclusions

Although many of the problematic issues of CMV infection and disease in hematopoietic SCT recipients remain active areas of investigation, significant progress has been made in reducing the clinical effects of infection in recipients at low to average risk. However, the highly immunosuppressed recipient remains at high risk for infection and subsequent late CMV disease manifestations, as well as indirect effects of CMV. Major advances in prevention of CMV infection occurred with the introduction of the antiviral agent ganciclovir and the more widespread use of sophisticated viral diagnostics. These advances, combined with identification of at-risk recipients, resulted in effective application of the preemptive therapy approach to minimizing early viral infection. One surprising finding is that the preemptive approach, although highly effective in preventing CMV disease (Table 3), has not eliminated the survival disadvantage associated with CMV seropositivity in highly immunosuppressed patients, such as recipients of T cell-depleted grafts (Table 1). This may be due to indirect effects of CMV not covered by preemptive therapy; thus, prophylaxis using highly effective antivirals may be warranted in these situations. However, drug toxicity remains a major impediment with currently available drugs. New anti-CMV drugs with improved tolerability are needed. Meanwhile, prophylactic approaches with intensified supportive measures (eg, ganciclovir or valganciclovir with the administration of granulocyte colony-stimulating factor) may be studied to examine whether preventing the effects of neutropenia results in improved overall outcomes in high-risk CMV-seropositive recipients. The increased incidence of late CMV infection and disease is another practical concern, because many recipients are no longer under the care of the specialty oncology center when reactivation occurs. The emerging issue of drug-resistant viral mutations presents new challenges for successful patient outcomes. Efforts to eliminate the effects of CMV infection require the development of improved antiviral agents and basic research on more fundamental immunotherapy approaches.

Acknowledgements

This paper originated from a roundtable discussion on recent aspects of CMV in hematopoietic SCT recipients, supported by an unrestricted grant from Roche Laboratories Inc., Nutley, NJ. Opinions expressed in the article are those of the authors. Additional participants of the round table were Dr. Richard Champlin, MD Anderson Cancer Center, Tx, and Dr. Finn Petersen, University of Utah, UT.

The authors report having received consulting fees and/or lecture fees from Bayer AG, Glaxo-Smith-Kline, MedImmune, Roche Laboratories, Vical Inc., Viropharma (Dr. Boeckh); Roche Laboratories and Vical Inc. (Dr. Nichols); Roche Laboratories, Pfizer, Merck (Dr. Rubin); Roche Laboratories (Dr. Wingard); Gemini Science Inc., Roche Laboratories, Vical Inc (Dr. Zaia).

References

1. 1 Bueno J, Ramil C, Green M. Current management strategies for the prevention and treatment of cytomegalovirus infection in pediatric transplant recipients. Paediatr Drugs. 2002;4:279–290. MEDLINE | CrossRef

2. 2 Ljungman P. Beta-herpes virus challenges in the transplant recipient. J Infect Dis. 2002;186:S99–S109. CrossRef

3. 3 Boeckh M, Boivin G. Quantitation of cytomegalovirus (methodologic aspects and clinical applications). Clin Microbiol Rev. 1998;11:533–554. MEDLINE

4. 4 Boeckh M, Nichols WG, Marr KA. Long-term care after hematopoietic-cell transplantation in adults. N Engl J Med. 2002;347:1625–1626. CrossRef

5. 5 Hambach L, Stadler M, Dammann E, Ganser A, Hertenstein B. Increased risk of complicated CMV infection with the use of mycophenolate mofetil in allogeneic stem cell transplantation. Bone Marrow Transplant. 2002;29:903–906. MEDLINE | CrossRef

6. 6 Armstrong D, Cohen J. Infectious Diseases. Philadelphia, PA: Mosby; 1999;.

7. 7 Boeckh M, Leisenring W, Riddell SR, et al. Late cytomegalovirus disease and mortality in recipients of allogeneic hematopoietic stem cell transplants (importance of viral load and T-cell immunity). Blood. 2003;101:407–414. MEDLINE | CrossRef

8. 8 Boeckh M, Gooley TA, Myerson D, Cunningham T, Schoch G, Bowden RA. Cytomegalovirus pp65 antigenemia-guided early treatment with ganciclovir versus ganciclovir at engraftment after allogeneic marrow transplantation (a randomized double-blind study). Blood. 1996;88:4063–4071. MEDLINE

9. 9 Einsele H, Ehninger G, Hebart H, et al. Polymerase chain reaction monitoring reduces the incidence of cytomegalovirus disease and the duration and side effects of antiviral therapy after bone marrow transplantation. Blood. 1995;86:2815–2820. MEDLINE

10. 10 Einsele H, Hebart H, Kauffmann-Schneider C, et al. Risk factors for treatment failures in patients receiving PCR-based preemptive therapy for CMV infection. Bone Marrow Transplant. 2000;25:757–763. MEDLINE | CrossRef

11. 11 Nguyen Q, Champlin R, Giralt S, et al. Late cytomegalovirus pneumonia in adult allogeneic blood and marrow transplant recipients. Clin Infect Dis. 1999;28:618–623. MEDLINE

12. 12 Zaia JA, Schmidt GM, Chao NJ, et al. Preemptive ganciclovir administration based solely on asymptomatic pulmonary cytomegalovirus infection in allogeneic bone marrow transplant recipients (long-term follow-up). Biol Blood Marrow Transplant. 1995;1:88–93. MEDLINE

13. 13 Broers AE, van Der Holt R, van Esser JW, et al. Increased transplant-related morbidity and mortality in CMV-seropositive patients despite highly effective prevention of CMV disease after allogeneic T-cell-depleted stem cell transplantation. Blood. 2000;95:2240–2245. MEDLINE

14. 14 Castro-Malaspina H, Harris RE, Gajewski J, et al. Unrelated donor marrow transplantation for myelodysplastic syndromes (outcome analysis in 510 transplants facilitated by the National Marrow Donor Program). Blood. 2002;99:1943–1951. MEDLINE | CrossRef

15. 15 Craddock C, Szydlo RM, Dazzi F, et al. Cytomegalovirus seropositivity adversely influences outcome after T-depleted unrelated donor transplant in patients with chronic myeloid leukaemia (the case for tailored graft-versus-host disease prophylaxis). Br J Haematol. 2001;112:228–236. MEDLINE | CrossRef

16. 16 Ljungman PT, Brand R, Einsele H, Frassoni F, Niederwieser D, Cordonnier C. Donor CMV serological status and outcome of CMV seropositive recipients after unrelated donor stem cell transplantation: an EBMT megafile analysis. Blood. In press.

17. 17 Meijer E, Dekker AW, Rozenberg-Arska M, Weersink AJ, Verdonck LF. Influence of cytomegalovirus seropositivity on outcome after T cell-depleted bone marrow transplantation (contrasting results between recipients of grafts from related and unrelated donors). Clin Infect Dis. 2002;35:703–712. CrossRef

18. 18 Nichols WG, Corey L, Gooley T, Davis C, Boeckh M. High risk of death due to bacterial and fungal infection among cytomegalovirus (CMV)-seronegative recipients of stem cell transplants from seropositive donors (evidence for indirect effects of primary CMV infection). J Infect Dis. 2002;185:273–282. MEDLINE | CrossRef

19. 19 Kroger N, Zabelina T, Kruger W, et al. Patient cytomegalovirus seropositivity with or without reactivation is the most important prognostic factor for survival and treatment-related mortality in stem cell transplantation from unrelated donors using pretransplant in vivo T-cell depletion with anti-thymocyte globulin. Br J Haematol. 2001;113:1060–1071. MEDLINE | CrossRef

20. 20 Cornelissen JJ, Carston M, Kollman C, et al. Unrelated marrow transplantation for adult patients with poor-risk acute lymphoblastic leukemia (strong graft-versus-leukemia effect and risk factors determining outcome). Blood. 2001;97:1572–1577. MEDLINE | CrossRef

21. 21 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. MEDLINE

23. 23 Ljungman P, Aschan J, Lewensohn-Fuchs I, et al. Results of different strategies for reducing cytomegalovirus-associated mortality in allogeneic stem cell transplant recipients. Transplantation. 1998;66:1330–1334. MEDLINE | CrossRef

24. 24 Boeckh M, Storer B, Bensinger W, Blume K. CMV infection and disease after marrow vs. PBSC transplantation (results from a randomized trial). Blood. 2001;98: (abstr. 2006).

25. 25 Burt RK, Drobyski W, Seregina T, et al. Anti-tumor effectiveness of herpes simplex thymidine kinase gene transduced donor lymphocyte infusions for relapsed hematologic malignancies following allogeneic hematopoietic stem cell transplantation. Blood. 2001;98: (abstr. 2917).

26. 26 Holmberg LA, Boeckh M, Hooper H, et al. Increased incidence of cytomegalovirus disease after autologous CD34-selected peripheral blood stem cell transplantation. Blood. 1999;94:4029–4035. MEDLINE

27. 27 Trenschel R, Ross S, Husing J, et al. Reduced risk of persisting cytomegalovirus pp65 antigenemia and cytomegalovirus interstitial pneumonia following allogeneic PBSCT. Bone Marrow Transplant. 2000;25:665–672. MEDLINE | CrossRef

28. 28 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. MEDLINE | CrossRef

29. 29 Junghanss C, Storb R, Maris MB, et al. Impact of unrelated donor status on the incidence and outcome of CMV infection after nonmyeloablative allogeneic stem cell transplantation. Br J Haematol. In press.

30. 30 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. MEDLINE | CrossRef

31. 31 Rubin RH. Clinical approach to infection in the compromised host. In: Rubin RH, Young LS editor. Infection in the Organ Transplant Recipient. New York, NY: Kluwer Academic Press; 2002;p. 573–679.

32. 32 Hebart H, Brugger W, Grigoleit U, et al. Risk for cytomegalovirus disease in patients receiving polymerase chain reaction-based preemptive antiviral therapy after allogeneic stem cell transplantation depends on transplantation modality. Blood. 2001;97:2183–2185. MEDLINE | CrossRef

33. 33 Emery VC, Sabin CA, Cope AV, Gor D, Hassan-Walker AF, Griffiths PD. Application of viral-load kinetics to identify patients who develop cytomegalovirus disease after transplantation. Lancet. 2000;355:2032–2036. Abstract | Full Text | Full-Text PDF (95 KB) | CrossRef

34. 34 Emery VC, Cope AV, Bowen EF, Gor D, Griffiths PD. The dynamics of human cytomegalovirus replication in vivo. J Exp Med. 1999;190:177–182. MEDLINE | CrossRef

35. 35 Gor D, Sabin C, Prentice HG, et al. Longitudinal fluctuations in cytomegalovirus load in bone marrow transplant patients (relationship between peak virus load, donor/recipient serostatus, acute GVHD and CMV disease). Bone Marrow Transplant. 1998;21:597–605. MEDLINE

36. 36 Nichols WG, Corey L, Gooley T, et al. Rising pp65 antigenemia during preemptive anticytomegalovirus therapy after allogeneic hematopoietic stem cell transplantation (risk factors, correlation with DNA load, and outcomes). Blood. 2001;97:867–874. MEDLINE | CrossRef

37. 37 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. MEDLINE | CrossRef

38. 38 Peggs KS, Preiser W, Kottaridis PD, et al. Extended routine polymerase chain reaction surveillance and pre-emptive antiviral therapy for cytomegalovirus after allogeneic transplantation. Br J Haematol. 2000;111:782–790. MEDLINE | CrossRef

39. 39 Boeckh M, Ljungman P. Cytomegalovirus infection after BMT. In: Bowden RA, Ljungman P editor. Transplant Infection. Philadelphia: Lippincott Williams & Wilkins; 1998;p. 215–227.

40. 40 Crippa F, Corey L, Chuang EL, Sale G, Boeckh M. Virological, clinical, and ophthalmologic features of cytomegalovirus retinitis after hematopoietic stem cell transplantation. Clin Infect Dis. 2001;32:214–219. MEDLINE | CrossRef

41. 41 Ljungman P, Larsson K, Kumlien G, et al. Leukocyte depleted, unscreened blood products give a low risk for CMV infection and disease in CMV seronegative allogeneic stem cell transplant recipients with seronegative stem cell donors. Scand J Infect Dis. 2002;34:347–350. MEDLINE | CrossRef

42. 42 Wolf DG, Lurain NS, Zuckerman T, et al. Emergence of late cytomegalovirus central nervous system disease in hematopoietic stem cell transplant recipients. Blood. 2003;101:463–465. MEDLINE | CrossRef

43. 43 Ljungman P, Griffiths P, Paya C. Definitions of cytomegalovirus infection and disease in transplant recipients. Clin Infect Dis. 2002;34:1094–1097. CrossRef

44. 44 Lowance D, Neumayer HH, Legendre CM, et al. Valacyclovir for the prevention of cytomegalovirus disease after renal transplantation. International Valacyclovir Cytomegalovirus Prophylaxis Transplantation Study Group. N Engl J Med. 1999;340:1462–1470. MEDLINE | CrossRef

45. 45 Valantine HA, Gao SZ, Menon SG, et al. Impact of prophylactic immediate posttransplant ganciclovir on development of transplant atherosclerosis (a post hoc analysis of a randomized, placebo-controlled study). Circulation. 1999;100:61–66.

46. 46 Nichols WG, Boeckh M, Carter RA, Wald A, Corey L. Transferred herpes simplex virus immunity after stem-cell transplantation (clinical implications). J Infect Dis. 2003;187:801–808. MEDLINE | CrossRef

47. 47 George MJ, Snydman DR, Werner BG, et al. The independent role of cytomegalovirus as a risk factor for invasive fungal disease in orthotopic liver transplant recipients. Boston Center for Liver Transplantation CMVIG-Study Group. Cytogam, MedImmune, Inc. Gaithersburg, Maryland. Am J Med. 1997;103:106–113. Abstract | Full Text | Full-Text PDF (192 KB) | CrossRef

48. 48 Prentice HG, Gluckman E, Powles RL, et al. Impact of long-term acyclovir on cytomegalovirus infection and survival after allogeneic bone marrow transplantation. European Acyclovir for CMV Prophylaxis Study Group. Lancet. 1994;343:749–753. Abstract | CrossRef

49. 49 Gerna G, Lilleri D, Baldanti F, et al. Human cytomegalovirus immediate early-mRNAemia vs pp65-antigenemia for guiding pre-emptive therapy in children and young adults given hematopoietic stem cell transplantation (a prospective, randomized, open-label trial). Blood. 2003;101:5053–5060. MEDLINE | CrossRef

50. 50 Boeckh M, Huang ML, Ferrenberg J, et al. Optimization of quantitative detection of cytomegalovirus DNA in plasma by real-time PCR. J Clin Microbiol. In press.

51. 51 Kaiser L, Perrin L, Chapuis B, et al. Improved monitoring of cytomegalovirus infection after allogeneic hematopoietic stem cell transplantation by an ultrasensitive plasma DNA PCR assay. J Clin Microbiol. 2002;40:4251–4255. MEDLINE | CrossRef

52. 52 Machado CM, Dulley FL, Boas LS, et al. CMV pneumonia in allogeneic BMT recipients undergoing early treatment of pre-emptive ganciclovir therapy. Bone Marrow Transplant. 2000;26:413–417. MEDLINE | CrossRef

53. 53 Emery VC, Hassan-Walker AF, Burroughs AK, Griffiths PD. Human cytomegalovirus (HCMV) replication dynamics in HCMV-naive and -experienced immunocompromised hosts. J Infect Dis. 2002;185:1723–1728. MEDLINE | CrossRef

54. 54 Boeckh M, Bowden RA, Gooley T, Myerson D, Corey L. Successful modification of a pp65 antigenemia-based early treatment strategy for prevention of cytomegalovirus disease in allogeneic marrow transplant recipients. Blood. 1999;93:1781–1782. MEDLINE

55. 55 Nichols WG, Boeckh M. Recent advances in the therapy and prevention of CMV infections. J Clin Virol. 2000;16:25–40. Abstract | Full Text | Full-Text PDF (120 KB) | CrossRef

56. 56 Bowden RA, Slichter SJ, Sayers M, et al. A comparison of filtered leukocyte-reduced and cytomegalovirus (CMV) seronegative blood products for the prevention of transfusion-associated CMV infection after marrow transplant. Blood. 1995;86:3598–3603. MEDLINE

57. 57 Nichols WG, Price TH, Gooley T, Corey L, Boeckh M. Transfusion-transmitted cytomegalovirus infection after receipt of leukoreduced blood products. Blood. 2003;101:4195–4200. MEDLINE | CrossRef

58. 58 Centers for Disease Control and Prevention Infectious Diseases Society of America American Society of Blood and Marrow Transplantation . Guidelines for preventing opportunistic infections among hematopoietic stem cell transplant recipients. Biol Blood Marrow Transplant. 2000;6:659–713. MEDLINE

59. 59 Zaia JA. Prevention of cytomegalovirus disease in hematopoietic stem cell transplantation. Clin Infect Dis. 2002;35:999–1004. CrossRef

60. 60 Bowden RA, Fisher LD, Rogers K, Cays M, Meyers JD. Cytomegalovirus (CMV)-specific intravenous immunoglobulin for the prevention of primary CMV infection and disease after marrow transplant. J Infect Dis. 1991;164:483–487. MEDLINE

61. 61 Ruutu T, Ljungman P, Brinch L, et al. No prevention of cytomegalovirus infection by anti-cytomegalovirus hyperimmune globulin in seronegative bone marrow transplant recipients. The Nordic BMT Group. Bone Marrow Transplant. 1997;19:233–236. MEDLINE

62. 62 Bass EB, Powe NR, Goodman SN, et al. Efficacy of immune globulin in preventing complications of bone marrow transplantation (a meta-analysis). Bone Marrow Transplant. 1993;12:273–282. MEDLINE

63. 63 Guglielmo BJ, Wong-Beringer A, Linker CA. Immune globulin therapy in allogeneic bone marrow transplant (a critical review). Bone Marrow Transplant. 1994;13:499–510. MEDLINE

64. 64 Messori A, Rampazzo R, Scroccaro G, Martini N. Efficacy of hyperimmune anti-cytomegalovirus immunoglobulins for the prevention of cytomegalovirus infection in recipients of allogeneic bone marrow transplantation (a meta-analysis). Bone Marrow Transplant. 1994;13:163–167. MEDLINE

65. 65 Zikos P, Van Lint MT, Lamparelli T, et al. A randomized trial of high dose polyvalent intravenous immunoglobulin (HDIgG) vs. cytomegalovirus (CMV) hyperimmune IgG in allogeneic hemopoietic stem cell transplants (HSCT). Haematologica. 1998;83:132–137. MEDLINE

66. 66 Boeckh M, Bowden RA, Storer B, et al. Randomized, placebo-controlled, double-blind study of a cytomegalovirus-specific monoclonal antibody (MSL-109) for prevention of cytomegalovirus infection after allogeneic hematopoietic stem cell transplantation. Biol Blood Marrow Transplant. 2001;7:343–351. Abstract | Full-Text PDF (956 KB) | CrossRef

67. 67 Meyers JD. Prevention and treatment of cytomegalovirus infection after marrow transplantation. Bone Marrow Transplant. 1988;3:95–104. MEDLINE

68. 68 Prentice HG, Gluckman E, Powles RL, et al. Long-term survival in allogeneic bone marrow transplant recipients following acyclovir prophylaxis for CMV infection. The European Acyclovir for CMV Prophylaxis Study Group. Bone Marrow Transplant. 1997;19:129–133. MEDLINE

69. 69 Ljungman P, de La Camara R, Milpied N, et al. Randomized study of valacyclovir as prophylaxis against cytomegalovirus reactivation in recipients of allogeneic bone marrow transplants. Blood. 2002;99:3050–3056. MEDLINE | CrossRef

70. 70 Winston DJ, Yeager AM, Chandrasekar PH, et al. Randomized comparison of oral vancyclovir and intravenous ganciclovir for prevention of cytomegalovirus disease after allogeneic bone marrow transplantation. Clin Infect Dis. 2003;36:749–758. CrossRef

71. 71 Goodrich JM, Bowden RA, Fisher L, Keller C, Schoch G, Meyers JD. Ganciclovir prophylaxis to prevent cytomegalovirus disease after allogeneic marrow transplant. Ann Intern Med. 1993;118:173–178. MEDLINE

72. 72 Winston DJ, Ho WG, Bartoni K, et al. Ganciclovir prophylaxis of cytomegalovirus infection and disease in allogeneic bone marrow transplant recipients. Results of a placebo-controlled, double-blind trial. Ann Intern Med. 1993;118:179–184. MEDLINE

73. 73 Goodrich JM, Mori M, Gleaves CA, et al. Early treatment with ganciclovir to prevent cytomegalovirus disease after allogeneic bone marrow transplantation. N Engl J Med. 1991;325:1601–1607. MEDLINE | CrossRef

74. 74 Reusser P, Gambertoglio JG, Lilleby K, Meyers JD. Phase I-II trial of foscarnet for prevention of cytomegalovirus infection in autologous and allogeneic marrow transplant recipients. J Infect Dis. 1992;166:473–479. MEDLINE

75. 75 Bregante S, Bertilson S, Tedone E, et al. Foscarnet prophylaxis of cytomegalovirus infections in patients undergoing allogeneic bone marrow transplantation (BMT) (a dose-finding study). Bone Marrow Transplant. 2000;26:23–29. MEDLINE | CrossRef

76. 76 Verdonck LF, Dekker AW, Rozenberg-Arska M, van den Hoek MR. A risk-adapted approach with a short course of ganciclovir to prevent cytomegalovirus (CMV) pneumonia in CMV-seropositive recipients of allogeneic bone marrow transplants. Clin Infect Dis. 1997;24:901–907. MEDLINE

77. 77 Mori T, Okamoto S, Matsuoka S, et al. Risk-adapted pre-emptive therapy for cytomegalovirus disease in patients undergoing allogeneic bone marrow transplantation. Bone Marrow Transplant. 2000;25:765–769. MEDLINE | CrossRef

78. 78 Reusser P, Einsele H, Lee J, et al. Randomized multicenter trial of foscarnet versus ganciclovir for preemptive therapy of cytomegalovirus infection after allogeneic stem cell transplantation. Blood. 2002;99:1159–1164. MEDLINE | CrossRef

79. 79 Mattes FM, Hainsworth E, Murdin-Geretti AM, et al. A randomized, controlled trial comparing ganciclovir or ganciclovir plus foscarnet (each half dose) for preemptive therapy of cytomegalovirus infection in transplant recipients. Paper presented at the 41st Interscience Conference on Antimicrobial Agents and Chemotherapy. 2001; Chicago, IL.

80. 80 Boeckh M, Zaia JA, Jung D, Skettino S, Chauncey TR, Bowden RA. A study of the pharmacokinetics, antiviral activity, and tolerability of oral ganciclovir for CMV prophylaxis in marrow transplantation. Biol Blood Marrow Transplant. 1998;4:13–19. MEDLINE

81. 81 Spielberger R, Zaia J, Nelson RA, et al. Use of oral ganciclovir for the preventive treatment of CMV following allogeneic HCT (safety and feasibility results). Blood. 2000;96: (abstr. 586).

82. 82 Pescovitz MD. Oral ganciclovir and pharmacokinetics of valganciclovir in liver transplant recipients. Transpl Infect Dis. 1999;1:31–34.

83. 83 Brown F, Banken L, Saywell K, Arum I. Pharmacokinetics of valganciclovir and ganciclovir following multiple oral dosages of valganciclovir in HIV- and CMV-seropositive volunteers. Clin Pharmacokinet. 1999;37:167–176. MEDLINE | CrossRef

84. 84 Pescovitz MD, Rabkin J, Merion RM, et al. Valganciclovir results in improved oral absorption of ganciclovir in liver transplant recipients. Antimicrob Agents Chemother. 2000;44:2811–2815. MEDLINE | CrossRef

85. 85 Antin JH. Clinical practice. Long-term care after hematopoietic-cell transplantation in adults. N Engl J Med. 2002;347:36–42. CrossRef

85. 85 Ljungman P, Deliliers GL, Platzbecker U, et al. Cidofovir for cytomegalovirus infection and disease in allogeneic stem cell transplant recipients. The Infectious Diseases Working Party of the European Group for Blood and Marrow Transplantation. Blood. 2001;97:388–392. MEDLINE | CrossRef

87. 87 Platzbecker U, Bandt D, Thiede C, et al. Successful preemptive cidofovir treatment for CMV antigenemia after dose-reduced conditioning and allogeneic blood stem cell transplantation. Transplantation. 2001;71:880–885. MEDLINE | CrossRef

88. 88 Chakrabarti S, Collingham KE, Osman H, Fegan CD, Milligan DW. Cidofovir as primary pre-emptive therapy for post-transplant cytomegalovirus infections. Bone Marrow Transplant. 2001;28:879–881. MEDLINE | CrossRef

89. 89 Ljungman P, Lore K, Aschan J, et al. Use of a semi-quantitative PCR for cytomegalovirus DNA as a basis for pre-emptive antiviral therapy in allogeneic bone marrow transplant patients. Bone Marrow Transplant. 1996;17:583–587. MEDLINE

90. 90 Slavin MA, Bindra RR, Gleaves CA, Pettinger MB, Bowden RA. Ganciclovir sensitivity of cytomegalovirus at diagnosis and during treatment of cytomegalovirus pneumonia in marrow transplant recipients. Antimicrob Agents Chemother. 1993;37:1360–1363. MEDLINE

91. 91 Erice A. Resistance of human cytomegalovirus to antiviral drugs. Clin Microbiol Rev. 1999;12:286–297. MEDLINE

92. 92 Boivin G, Gilbert C, Gaudreau A, Greenfield I, Sudlow R, Roberts NA. Rate of emergence of cytomegalovirus (CMV) mutations in leukocytes of patients with acquired immunodeficiency syndrome who are receiving valganciclovir as induction and maintenance therapy for CMV retinitis. J Infect Dis. 2001;184:1598–1602. MEDLINE | CrossRef

93. 93 Eckle T, Prix L, Jahn G, et al. Drug-resistant human cytomegalovirus infection in children after allogeneic stem cell transplantation may have different clinical outcomes. Blood. 2000;96:3286–3289. MEDLINE

94. 94 Eckle T, Lang P, Prix L, et al. Rapid development of ganciclovir-resistant cytomegalovirus infection in children after allogeneic stem cell transplantation in the early phase of immune cell recovery. Bone Marrow Transplant. 2002;30:433–439. MEDLINE | CrossRef

95. 95 Emery VC, Griffiths PD. Prediction of cytomegalovirus load and resistance patterns after antiviral chemotherapy. Proc Natl Acad Sci U S A. 2000;97:8039–8044. MEDLINE | CrossRef

96. 96 Limaye AP, Corey L, Koelle DM, Davis CL, Boeckh M. Emergence of ganciclovir-resistant cytomegalovirus disease among recipients of solid-organ transplants. Lancet. 2000;356:645–649. Abstract | Full Text | Full-Text PDF (83 KB) | CrossRef

97. 97 Boivin G, Goyette N, Gilbert C, Roberts N, Tansley R, Covington E. Low frequency of emergence of cytomegalovirus UL97 mutations associated with ganciclovir resistance in solid organ transplant patients receiving valganciclovir or oral ganciclovir prophylaxis. Paper presented at the 42nd Interscience Conference on Antimicrobial Agents and Chemotherapy. 2002; San Diego, CA.

98. 98 Leather HL, Meyer CL, Wingard JR. Oral valganciclovir for preemptive therapy of cytomegalovirus antigenemia in hematopoietic stem cell transplant recipients. Biol Blood Marrow Transplant. 2003;9:132; (abstr. 238). CrossRef

99. 99 Wang LH, Peck RW, Yin Y, Allanson J, Wiggs R, Wire MB. Phase 1 safety and pharmacokinetic trials of 1263W94, a novel oral anti-human cytomegalovirus agent, in healthy and human immunodificiency virus-infected subjects. Antimicrob Agents Chemother. 2003;47:1334–1342. MEDLINE | CrossRef

100. 100 McSharry JJ, McDonough A, Olson B, et al. Susceptibilities of human cytomegalovirus clinical isolates to BAY38–4766, BAY43–9695, and ganciclovir. Antimicrob Agents Chemother. 2001;45:2925–2927. MEDLINE | CrossRef

101. 101 Walter EA, Greenberg PD, Gilbert MJ, et al. Reconstitution of cellular immunity against cytomegalovirus in recipients of allogeneic bone marrow by transfer of T-cell clones from the donor. N Engl J Med. 1995;333:1038–1044. MEDLINE | CrossRef

102. 102 Peggs KS, Verfuerth S, Mackinnon S. Induction of cytomegalovirus (CMV)-specific T-cell responses using dendritic cells pulsed with CMV antigen (a novel culture system free of live CMV virions). Blood. 2001;97:994–1000. MEDLINE | CrossRef

103. 103 Zaia JA, Sissons JG, Riddell S, et al. Status of cytomegalovirus prevention and treatment in 2000. Hematology. 2000;339–355.

104. 104 Reusser P, Riddell SR, Meyers JD, Greenberg PD. Cytotoxic T-lymphocyte response to cytomegalovirus after human allogeneic bone marrow transplantation (pattern of recovery and correlation with cytomegalovirus infection and disease). Blood. 1991;78:1373–1380. MEDLINE

105. 105 Greenberg PD, Reusser P, Goodrich JM, Riddell SR. Development of a treatment regimen for human cytomegalovirus (CMV) infection in bone marrow transplantation recipients by adoptive transfer of donor-derived CMV-specific T cell clones expanded in vitro. Ann N Y Acad Sci. 1991;636:184–195. MEDLINE | CrossRef

106. 106 Einsele H, Roosnek E, Rufer N, et al. Infusion of cytomegalovirus (CMV)-specific T cells for the treatment of CMV infection not responding to antiviral chemotherapy. Blood. 2002;99:3916–3922. MEDLINE | CrossRef

107. 107 Peggs KS, Mackinnon S. Clinical trials with CMV-specific T cells. Cytotherapy. 2002;4:21–28. MEDLINE | CrossRef

108. 108 Hakki M, Riddell SR, Storek J, et al. Immune reconstitution to cytomegalovirus after allogeneic hematopoietic stem cell transplantation: impact of host factors, drug therapy, and subclinical reactivation. Blood. In press.