CMV and Other Herpes-virus Infections After Stem Cell Transplantation
42nd Annual Meeting of the American Society of Hematology
[Hematology-Oncology Conference Summaries - © 2000 Medscape, Inc.
As part of the 42nd Annual Meeting of the American Society of Hematology, Dr. John Zaia, of the City of Hope National Medical Center in Duarte, California, chaired an educational program that addressed the current issues surrounding cytomegalovirus (CMV) infection after stem cell transplantation (SCT). This article will summarize these proceedings as well as a number of presentations on human herpesviruses that were discussed elsewhere at the meeting.
Cytomegalovirus Infection After SCT
The Impact of Late Cytomegalovirus Disease
Dr. Zaia began by discussing the problems that remain in the current era of effective pre-emptive antiviral therapy. Historically, CMV has been one of the most feared infectious complications of allogeneic SCT. Reactivation of CMV occurs in approximately 80% of patients who are seropositive before transplantation, and about one third of seronegative patients with seropositive marrow donors develop primary CMV infection. Before the introduction of specific prophylaxis, the risk for CMV disease was approximately 20% to 35% among seropositive SCT recipients.[3,4]
CMV can cause multiorgan disease after SCT, including pneumonia, gastroenteritis, hepatitis, retinitis, and encephalitis; pneumonia and gastrointestinal disease are the most common. CMV has also been associated with posttransplant marrow failure. Indeed, a presentation by Dr. Beverly Torok-Storb and colleagues, of the Fred Hutchinson Cancer Research Center, Seattle, Washington, suggested that certain CMV genotypes may be associated with cases of aplastic anemia as well.
In the preganciclovir era, the peak incidence of CMV disease after SCT was between days 45 and 60. With current antiviral strategies, however, CMV disease now more commonly occurs late (> 100 days after transplant).[6,7] This most likely is a result, at least in part, of the effective suppression of CMV replication, which does not allow the patient to mount an adequate immune response to CMV.[8,9] Incomplete T-cell reconstitution as well as acute and chronic graft-versus-host disease (GVHD), which is particularly associated with unrelated and mismatched grafts, may be the underlying mechanisms of this phenomenon.[9,10] Indeed, in a recently completed natural history study of late CMV disease conducted at the Fred Hutchinson Cancer Research Center, the incidence of disease after day 100 in CMV-seropositive allogeneic recipients was 17%; the presence of any GVHD at day 95 after transplantation was predictive of this outcome (M. Boeckh, MD, unpublished data, 2000).
The Age of Adoptive Immunotherapy?
Our current understanding of CMV immunopathogenesis was discussed by Dr. J.G. Patrick Sissons, of the University of Cambridge Clinical School, Cambridge, United Kingdom. CMV is characterized by persistence and latency of infection, with notable repression of immediate early (IE) genes in undifferentiated cells. Host immune surveillance is intense, requiring CD8+ T-cell control with CD4+ T-cell support (and, possibly, the activity of natural killer [NK] cells). CD8+ T cells recognize CMV proteins in the context of MHC class I; specific immunodominant peptides have been identified for several human lymphocyte antigen (HLA) types.
To date, viral tegument proteins such as pp65 and pp150 have been most frequently identified as targets of immune surveillance and are recognized early after primary infection. Since the tegument enters the host cell along with the viral genome, the proteins can be presented in the context of MHC class 1 without intracellular viral replication or translation. Later, T-cell reactivity decreases due to viral protein (US2, US3, US6, US11) blockade of MHC class-I presentation of antigen. Nevertheless, state-of-the-art molecular assays have shown that as much as 1% to 4% of CD8+ T cells in the circulation of most immunocompetent hosts are directed against a single CMV peptide.
Dr. Stanley Riddell, of the Fred Hutchinson Cancer Research Center, Seattle, Washington, discussed his experience with adoptive immunotherapy for the prevention of CMV disease in SCT recipients. Murine models of CMV infection show the importance of CD4+ cytokine help for CD8+ cells to optimize cytotoxic function. In patients status after SCT, the recovery of CMV-specific CD4 and CD8 T cells was correlated with protection from CMV disease, although cause and effect were not yet proven. Dr. Riddell thus began adoptive transfer experiments of CD8+ clones that were directed against CMV structural proteins, aimed at preventing CMV disease in patients at risk.
Previously reported phase 1 studies of SCT recipients showed little toxicity, but among patients who failed to independently demonstrate CD4+ responses, the CD8+ clones were short-lived. Phase 2 studies therefore included CMV-specific CD8+ and CD4+ infusions. In this study, a strong, persistent CD4 and CD8 response was demonstrated; the cumulative incidence of viremia was cut in half when compared with historical controls. The problems encountered surrounded steroid therapy for GVHD, which decreased T-cell survival and interferon production in vitro, even though cytotoxic activity was retained. Almost all cases of viremia occurred in those with GVHD receiving 2 or more mg/kg of corticosteroids.
Dr. Riddell concluded by stating that adoptive immunotherapy for CMV infection appears safe, but may be more useful in T-cell depleted allograft recipients because of their reduced need for steroid therapy for GVHD.
Given the toxicity associated with current antiviral agents and the cost and implementation difficulties associated with adoptive T-cell immunotherapy, vaccination is an extremely attractive option. Dr. Don J. Diamond, of the City of Hope National Medical Center, Duarte, California, identified a number of immunodominant CMV peptides that elicit both CD4 and CD8 responses when coupled with adjuvant long-chain fatty acids.
Most of these CMV-specific peptides are based upon pp65 and pp150, with a different immunodominant peptide used for each HLA type. Unfortunately, this adds a layer of complexity to the strategy, as multiple peptides must be included in the product. Alternatively, testing of the recipient's HLA type could be performed in order to identify the proper vaccine. Furthermore, immunizing with a single peptide raises the possibility that single mutations in viral proteins would allow immune evasion. This was demonstrated by Dr. Zaia and colleagues, who showed that immune escape, at least in the case of 1 peptide epitope, was indeed rare.
Other approaches that are under investigation include DNA vaccines, live attenuated viral vaccines, and viral vector constructs that express CMV antigens. Allogeneic SCT recipients would be prime candidates for the latter approach, given their risk of symptomatic CMV disease, but vaccination of the patient before transplant would not be efficacious because of the immunoablation that occurs with transplantation. Vaccination of the stem cell donor prior to stem cell harvest is therefore being evaluated by Dr. Diamond, with the hopes of boosting an immunity that would be transferred to the stem cell recipient. Clinical trials of this strategy are scheduled to begin in 2001.
Human Herpesvirus Infections After SCT
The Role of Underlying Immunosuppression
One recurrent theme at the meeting was the role of the immunosuppressive regimen in determining the incidence and severity of CMV infection after SCT. Previously, several lines of evidence have indicated that T-cell-depleted allogeneic transplant recipients have a higher incidence of CMV viremia and disease.[15,16] For the autologous SCT recipient, Dr. Leona Holmberg and colleagues, of the Fred Hutchinson Cancer Research Center, Seattle, Washington, have shown that CD34 selection, which effectively depletes the stem cell product T cells, B cells, antigen-presenting cells, and NK cells, is associated with a large increase in the risk of symptomatic CMV disease.
New approaches, such as the use of nonmyeloablative regimens followed by SCT, the so-called mini-transplants, have further changed the scope of CMV prevention. For example, Dr. Christian Junghanss and colleagues, of the Fred Hutchinson Cancer Research Center, Seattle, Washington, performed a matched-case control study that compared the incidence of CMV infection and disease between conventional myeloablative and nonmyeloablative regimens. Although the incidence of CMV antigenemia, viremia, and disease were not different between the groups, both viremia and CMV disease were significantly delayed among nonmyeloablative SCT recipients. Dr. Vijay Reddy and colleagues, of the University of Florida College of Medicine, Gainesville, Florida, presented similar findings.
Nonmyeloablative regimens, however, differ greatly in the degree of immunosuppression that they achieve. Dr. Suparno Chakrabarti and colleagues, of the Heartlands Hospital, Birmingham, United Kingdom, reported an extremely high incidence of early and late CMV infection that was associated with delayed CD4 reconstitution in their nonmyeloablative allogeneic transplant recipients; it is important to note that this regimen included in vivo T-cell depletion with Campath, an anti-CD52 antibody.
Another potential cause of distinction in viral load outcome is the graft source. Amy Pazzalia and colleagues, of the University of Florida College of Medicine, Gainesville, Florida, compared patients who either received stem cells via bone marrow transplant (BMT) or via peripheral blood (PB) SCT in a nonrandomized fashion. The incidence of CMV antigenemia was similar between groups, but more patients had recurrent antigenemia in the BMT group, which translated into longer and repeated courses of ganciclovir therapy. Because PBSCT recipients engraft quicker, this finding is likely due to delayed immune reconstitution in the BMT group.
One potential therapeutic outcome of this trial is that PBSCT recipients, who presumably reconstitute their CMV-specific immunity earlier than their BMT counterparts, could be treated with less intensive antiviral therapy. Dr. Ravi Vij and colleagues, of the Washington University School of Medicine, St. Louis, Missouri, looked at whether low-dose ganciclovir (5 mg/kg intravenously daily for 21 days) as pre-emptive therapy for CMV shell vial positivity is adequate in these patients. The vast majority of patients cleared viremia with this approach; early CMV disease occurred in only 2.1% of the cohort. Of importance, no patient required granulocyte-colony stimulating factor for ganciclovir-induced neutropenia.
In non-T-cell depleted patients, the use of oral, as opposed to intravenous, ganciclovir as maintenance therapy in a pre-emptive strategy may even be sufficient. In a phase 2 study that evaluated 5 weeks of oral ganciclovir after 1 week of intravenous induction in patients with evidence of CMV replication, Dr. Ricardo Spielberger and colleagues, of the City of Hope National Medical Center, Duarte, California, reported no cases of CMV disease on therapy and no discontinuations for rising viral load.
Ganciclovir has very low oral bioavailability, yet in this study, levels for the oral ganciclovir group, who were dosed 3 times daily, were higher than for those treated daily with intravenous medication. Almost half of the patients required dose modifications for toxicity, but the effects were manageable and were not associated with a higher rate of viral reactivation on therapy. While oral therapy is certainly preferable to long courses of intravenous therapy, we believe that careful risk assessment should be done before this approach is entertained. Appropriate candidates may include recipients of unmanipulated grafts as well as those without GVHD and therefore not in need of high-dose corticosteroid therapy.
T-cell depletion, either in vivo or ex vivo, was a significant predictor for CMV complications in several studies. Dr. H. Hebart and colleagues, of the University Hospital, Tuebingen, Germany, showed that in vivo T-cell depletion with antithymocyte globulin (ATG) after allogeneic SCT, but not CD34 selection, was associated with more frequent viral reactivation, longer time to CMV clearance with antiviral therapy, and a slight increase in the incidence of CMV disease. By contrast, Dr. Rodrigo Martino and colleagues, of the Hospital de Sant Pau, Barcelona, Spain, showed that the probability of CMV reactivation, but not disease, as well as disseminated varicella-zoster virus infections was higher in patients receiving CD34 selected allogeneic SCT when compared with unmanipulated grafts.
The most profound immunosuppression, however, generally occurs in patients receiving haploidentical SCT, which requires stringent T- and B-cell depletion of the graft to prevent fatal GVHD. In this setting, reactivation of latent human herpesviruses is the rule, not the rarity. Dr. Amelia Langston and colleagues, of Emory University, Atlanta, Georgia, reported on a series of 9 adults with hematologic malignancies who received CD34-selected haploidentical allografts after conditioning with total body irradiation, fludarabine, and ATG.
Even though these patients received acyclovir (ACV) prophylaxis until engraftment and exhibited no posttransplant immunosuppression, reactivation of herpes simplex virus (HSV) occurred in 4 of 5 HSV-seropositive patients. All patients failed to respond to ACV and were shown to have ACV-resistant isolates. Surprisingly, no serious CMV infections occurred in the cohort. Nevertheless, resistant human herpesvirus infections can be anticipated to occur whenever prolonged, incomplete suppression occurs in the presence of antiviral therapy. These haploidentical transplant recipients, who failed to reconstitute robust T-cell immunity even 100 days after transplant, are prime candidates for this type of complication.
Epstein-Barr Virus-Related Posttransplant Lymphoproliferative Disorder: Prediction and Therapy
Epstein-Barr virus (EBV)-related posttransplant lymphoproliferative disorder (PTLD) is a serious complication of SCT. Caused by an unregulated expansion of B cells, it carries a high mortality without therapy. Previous work has shown that the incidence of PTLD is highest in T-cell depleted allogeneic SCT, and may be preceded by increasing levels of EBV DNA in the blood that can be detected by polymerase chain reaction. Although decreasing levels of immunosuppression can occasionally induce remissions, this approach is ineffective in most cases.
EBV PTLD is usually considered the domain of allogeneic SCT. Nevertheless, Dr. Richard Nash and colleagues, of the Fred Hutchinson Cancer Research Center, Seattle, Washington, presented 2 fatal cases of EBV PTLD that occurred after CD34-selected autologous transplantation. The transplant indication for these 2 patients was severe autoimmune disease (ie, systemic sclerosis and multiple sclerosis). In addition, both patients received full courses of rabbit ATG due to positive skin tests against horse ATG. Among 34 patients treated on the same protocol with horse ATG, no cases of EBV PTLD occurred. As a result of these findings, patients now treated on protocol in this institution with reactions to horse ATG do not receive alternative antibody therapy.
Even the dose of ATG used for in vivo T-cell depletion may have an effect on viral infections. Dr. Michel Duval and colleagues, of the Hôpital Robert-Debré, Paris, France, showed that higher doses of ATG used in the allogeneic conditioning regimen were associated with a higher incidence of viral infections, including EBV PTLD, as well as a lower probability for disease-free survival. By contrast, Dr. Juliet Barker and colleagues, of the University of Minnesota Medical School, Minneapolis, Minnesota, showed that there was an extremely low incidence of EBV PTLD after unrelated umbilical cord blood transplantation. This finding was somewhat unexpected, since the transfused T-cell dose is often low, neonatal T-cell immune surveillance is likely to be incomplete, and antigen mismatch often prompts the use of ATG in the conditioning regimen.
Therapy with anti-CD20 antibody (rituximab) has been previously shown to induce remissions in many patients with EBV PTLD. Case reports presented here again demonstrated the efficacy of rituximab with or without[29,31] donor lymphocyte infusions for the treatment of EBV PTLD. Dr. Diane George and colleagues, of the Memorial Sloan-Kettering Cancer Center, New York, noted serious pulmonary complications in nearly one fourth of patients treated, which resulted in respiratory failure in 2 patients. Nevertheless, Dr. J. Cornelissen and colleagues, of the University Hospital Rotterdam, The Netherlands, reported success with a pre-emptive strategy for T-cell depleted allogeneic transplant recipients. In this study, rituximab administered for EBV DNA viral loads of more than 1000 genome equivalents/mL prevented progression to PTLD in 11/12 patients, with 1 patient responding to a second infusion and donor lymphocyte infusion after PTLD developed. This result compared quite favorably with the 32% PTLD-related mortality associated with this level of EBV DNA in a retrospective study conducted at the same center.
Summary: Implications for Clinical Practice
In the era of effective prophylactic and pre-emptive therapy against CMV, late disease poses the greatest risk; the logistics of management of these patients will continue to prove challenging. Different transplantation modalities are associated with different degrees of immunosuppression, and thus different attack rates from human herpesviruses. Prophylactic and pre-emptive strategies must therefore be modified according to risk category.
The risk for CMV viremia and disease may be lower among nonmyeloablative SCT recipients, but studies thus far have been too small to draw definitive conclusions. Onset does, however, seems to be delayed. Whether short-course pre-emptive therapy would be effective in this setting requires further study. New approaches for pre-emptive therapy against CMV, such as short-course intravenous or oral maintenance ganciclovir, seem promising in patients at low risk for progression to CMV disease. Rituximab offers hope for the treatment of patients with EBV PTLD, although pulmonary complications may become a limiting factor.
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- Pazzalia AD, Leather HL, Lucas L et al. A comparison of persistent or recurrent cytomegalovirus antigenemia in recipients of peripheral blood stem cell transplant versus bone marrow transplant (Abstract 809). Blood 2000;96(suppl 1):189a.
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- Spielberger R, Zaia J, Nelson RA, et al. Use of oral ganciclovir for the preemptive treatment of CMV following allogeneic HCT: safety and feasibility results. Blood 2000;96(suppl 1):586a. Abstract 2516.
- Hebart H, Brugger W, Grigoleit U, et al. Risk for CMV disease in patients receiving PCR-based preemptive antiviral therapy after allogeneic stem cell transplantation depends on transplantation modality. Blood. 2000;96(suppl 1):190a. Abstract 814.
- Martino R, Rovira M, Carreras E, et al. Severe infections after allogeneic peripheral blood stem cell transplantation: a matched-pair analysis of unmanipulated and CD34 cell selected transplantation. Blood. 2000;96(suppl 1):785a. Abstract 3393.
- Langston A, Redei I, Bucur S, et al. Acyclovir resistant herpes simplex virus after T and B-cell depleted haploidentical stem cell transplantation. Blood. 2000;96(suppl 1):193a. Abstract 826.
- Nash RA, Dansey R, Storek J, et al. EBV-associated PTLD after high-dose immunosuppressive therapy and autologous CD34-selected stem cell transplantation for severe autoimmune diseases. Blood. 2000;96(suppl 1):406a. Abstract 1747.
- Duval M, Pedron B, Legrand F, et al. Higher dosage of pre-graft antithymocyte globulin may negatively influence immune reconstitution and survival after stem cell transplantation. Blood. 2000;96(suppl 1):788a. Abstract 3408.
- Barker JN, Martin PL, Defor T, et al. Low incidence of Epstein-Barr Virus associated PTLD in 263 unrelated donor umbilical cord blood transplant recipients. Blood. 2000;96(suppl 1):206a. Abstract 880.
- Macheta MP, Stevens RF, Will AM, et al. Successful treatment of EBV-associated PTLD with donor T-cell infusions and monoclonal anti-CD20 antibody (Abstract 823). Blood 2000;96(suppl 1):192a.
- George D, Small TN, Boulad F, et al. Rituximab for the treatment of EBV-associated lymphoproliferative disorders. Blood. 2000;96(suppl 1):405a. Abstract 1745.
- Cornelissen JJ, van Esser JWJ, van der Holt B, et al. Pre-emptive anti B cell immunotherapy guided by quantitative PCR effectively reduces the incidence and mortality of EBV-lymphoproliferative disease after allogeneic T-cell depleted stem cell transplantation. Blood 2000;96(suppl 1):507a. Abstract 2182.
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