T-cell--depleted allogeneic bone marrow transplantation followed by donor lymphocyte infusion in patients with multiple myeloma: induction of graft-versus-myeloma effect

Role of allogeneic transplantation in multiple myeloma in the era of new drugs

High-dose melphalan with autologous stem cell rescue has been regarded as the standard of care for patients with newly diagnosed myeloma up to the age of 65–70 years. The recent development of agents with potent anti-tumor activity such as thalidomide, lenalidomide and bortezomib has further improved overall survival and response rates. However, relapse is a continuous risk.

Allografting is a potentially curative treatment for a subset of multiple myeloma patients for its well documented graft-vs-myeloma effects. However, its role has been hotly debated. Even though molecular remissions have been reported up to 50% after high-dose myeloablative conditionings, their applications, given the high toxicity, have been for long limited to younger relapsed/refractory patients. These limitations have greatly been reduced through the introduction of non-myeloablative/reduced-intensity conditionings.

The introduction of new drugs, characterised by low risks of early mortality, indeed requires to define role and timing of an allograft to capture the subset of patients who may most benefit from graft-vs-myeloma effects.

Ultimately, new drugs should not be viewed as mutually exclusive with an allograft. They may be employed to achieve profound cytoreduction before and enhance graft-versus-myeloma effects as consolidation/maintenance therapy after an allograft. However, this combination should be explored only in well-designed clinical trials.

NCI First International Workshop on the Biology, Prevention, and Treatment of Relapse after Allogeneic Hematopoietic Stem Cell Transplantation: report from the Committee on the Epidemiology and Natural History of Relapse following Allogeneic Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (alloHSCT) is increasingly being used for treatment of hematologic malignancies, and the immunologic graft-versus-tumor effect (GVT) provides its therapeutic effectiveness. Disease relapse remains a cause of treatment failure in a significant proportion of patients undergoing alloHSCT without improvements over the last 2-3 decades. We summarize here current data and outline future research regarding the epidemiology, risk factors, and outcomes of relapse after alloHSCT. Although some factors (eg, disease status at alloHSCT or graft-versus-host disease [GVHD] effects) are common, other disease-specific factors may be unique. The impact of reduced-intensity regimens on relapse and survival still need to be assessed using contemporary supportive care and comparable patient populations. The outcome of patients relapsing after an alloHSCT generally remains poor even though interventions including donor leukocyte infusions can benefit some patients. Trials examining targeted therapies along with improved safety of alloHSCT may result in improved outcomes, yet selection bias necessitates prospective assessment to gauge the real contribution of any new therapies. Ongoing chronic GVHD (cGVHD) or other residual post-alloHSCT morbidities may limit the applicability of new therapies. Developing strategies to promptly identify patients as alloHSCT candidates, while malignancy is in a more treatable stage, could decrease relapses rates after alloHSCT. Better understanding and monitoring of minimal residual disease posttransplant could lead to novel preemptive treatments of relapse. Analyses of larger cohorts through multicenter collaborations or registries remain essential to probe questions not amenable to single center or prospective studies. Studies need to provide data with detail on disease status, prior treatments, biologic markers, and posttransplant events. Stringent statistical methods to study relapse remain an important area of research. The opportunities for improvement in prevention and management of post-alloHSCT relapse are apparent, but clinical discipline in their careful study remains important.

Role of donor lymphocyte infusions in relapsed hematological malignancies after stem cell transplantation revisited

BACKGROUND

Treatment of relapsed hematological malignancies after an allogeneic peripheral blood stem cell transplant (SCT) is challenging. Donor lymphocyte infusion (DLI) from the stem cell donor is an attractive clinical option to salvage this group of patients.

METHODS

We reviewed the important studies looking at donor lymphocyte infusion as a therapy for the treatment of hematological disorders that are either refractory to or have relapsed after allogeneic SCT.

RESULTS

The response to DLI is dependent upon type of disease, dose of infused lymphocytes, and the development of graft vs. host disease (GvHD). The best response rates are seen in patients with chronic myeloid leukemia (CML) followed by patients with lymphomas, multiple myeloma and acute leukemias, respectively. The responses in patients with CML are durable whereas durable responses in other diseases are rare.

CONCLUSIONS

Given the development of new drugs to treat some hematological diseases, DLI has taken a backseat. New modalities to target the infused cells to the tumor and new approaches to reduce GvHD that will augment the graft vs. leukemia/lymphoma (GvL) effect and decrease the injury to normal host tissues need to be developed. Understanding the factors and mechanisms that differentiate the GvL effect from GvHD will help in the development of newer treatment modalities.

Phase I study of high-stringency CD8 depletion of donor leukocyte infusions after allogeneic hematopoietic stem cell transplantation

BACKGROUND

Donor leukocyte infusions (DLI) are given after hematopoietic stem-cell transplantation to eradicate persistent tumor or correct mixed chimerism (MC). The drawback of DLI is the risk of graft-versus-host disease (GVHD). In this phase I study, we examined the potential of highly extensive CD8 depletion of DLI as a means of improving its safety profile.

METHODS

High-stringency immunomagnetic CD8 depletion of DLI was performed after steady state donor apheresis. Patients with persistent disease or MC received escalated dose CD8-depleted DLI at 3-month intervals starting from 6 months posttransplantation. The starting dose was 1 x 10(6) CD4 cells/kg in recipients of unrelated and 3 x 10(6) CD4 cells/kg in recipients of related donor transplantations.

RESULTS

Twenty-eight patients received CD8-depleted DLI (n=16 unrelated or mismatched, n=12 human leukocyte antigen-identical sibling). Median CD8 depletion was more than 4 log. The median overall dose of CD4+ cells/kg given was 4 x 10(6) (range 1 x 10(6)-43 x 10(6)). Conversion from MC to full donor chimerism was observed in 8 of 16 evaluable patients, and disease responses occurred in 5 of 11 patients (complete response in four and partial response in one). Five of 28 patients developed severe acute pattern (grade II-IV) GVHD. Two patients died as a result of complications relating to GVHD.

CONCLUSIONS

Graft-versus-tumor effects can be observed after high-stringency CD8-depleted DLI, although the major toxicity remains GVHD in this high-risk patient group. The safety and efficacy profile of this approach will require testing in a randomized controlled study.

Graft-versus-leukemia effect of nonmyeloablative stem cell transplantation

Nonmyeloablative stem cell transplantation (NST) is increasingly used with beneficial effects because it can be applied to older patients with hematological malignancies and those with various complications who are not suitable for conventional myeloablative stem cell transplantation (CST). Various conditioning regimens differ in their myeloablative and immunosuppressive intensity. Regardless of the type of conditioning regimen, graft-versus- host disease (GVHD) in NST occurs almost equally in CST, although a slightly delayed development of acute GVHD is observed in NST. Although graft-versus-hematological malignancy effects (i.e., graft-versus-leukemia effect, graft-versus-lymphoma effect, and graft-versus-myeloma effect) also occur in NST, completely eradicating residual malignant cells through allogeneic immune responses is insufficient in cases with rapidly growing disease or uncontrolled progressive disease. Donor lymphocyte infusion (DLI) is sometimes combined to support engraftment and to augment the graft-versus-hematological malignancy effect, such as the graft-versus-leukemia effect. DLI is especially effective for controlling relapse in the chronic phase of chronic myelogenous leukemia, but not so effective against other diseases. Indeed, NST is a beneficial procedure for expanding the opportunity of allogeneic hematopoietic stem cell transplantation to many patients with hematological malignancies. However, a more sophisticated improvement in separating graft-versus-hematological malignancy effects from GVHD is required in the future.

Graft vs. Host Disease and Graft vs. Myeloma Effect after Non-myeloablative Allogeneic Transplantation

For many years progress in event free and overall survival in patients diagnosed with multiple myeloma have been modest, however recently newer therapeutic options have become available and, for a small but increasing subset of patients, an "operational cure" can be offered. Although autologous transplantation is associated with a prolongation in event free and overall survival as compared to conventional chemotherapy, there is no plateau in the survival curves. By contrast, the use of allogeneic hematopoietic stem cells provides a tumor-free stem cell source and graft-vs.-myeloma activity leading to a higher frequency of long term survivors in molecular remission. Unfortunately, allogeneic transplantation has been associated with high transplant-related mortality (TRM). Non-myeloablative or reduced intensity conditioning (RIC) regimens, designed to be immunosuppressive rather than myeloablative, in an effort to reduce the toxicity and TRM associated with high dose chemotherapy, but maintaining the GVM effect, have been developed showing up to 90% overall response rate and low TRM. Interestingly, in a significant proportion of patients disease response is preceded by GVHD, suggesting a clear relationship between GVHD and graft vs. myeloma effect. Nevertheless these patients are at risk of developing life threatening complications and, on the contrary, some patients who reach disease control after GVHD and respond to GVHD therapy may finally relapse. Thus, efforts to separate GVM and GVHD are still required in order to improve the outcome of myeloma patients receiving allogeneic transplantation.

Role of allogeneic stem cell transplantation in multiple myeloma

High-dose chemotherapy with autologous stem cell rescue has been regarded as the standard of care for young newly diagnosed myeloma patients. Moreover, the development of new agents with potent anti-tumor activity has further improved survival. However, relapse is a continuous risk primarily due to the inability of current therapies to eradicate all myeloma cells. Allografting is the only potentially curative treatment at least for a subset of multiple myeloma patients due to its well documented graft-versus-myeloma effects. Given the high transplant mortality of the high-dose myeloablative conditionings used until recently, allografting has for a long time been limited to younger relapsed/refractory patients. These limitations have been reduced significantly by the use of reduced-intensity conditionings. Although results of recent trials are encouraging, the subset of patients who may benefit most from an allograft remains to be determined. An overview of the clinical outcomes obtained with allografting and possible future developments are reported.

Poorex vivoinduction of T-cell responses to idiotype or tumor cell lysate-pulsed autologous dendritic cells in advanced pre-treated multiple myeloma

This study evaluated the feasibility of using dendritic cells (DCs) to generate, ex vivo, anti-tumor cytotoxic T lymphocytes (CTL) in patients with stage III multiple myeloma (MM). Nucleated cells from eight patients who had received chemotherapy (three of whom had undergone autologous hemopoeitic stem cell transplantation) were collected by apheresis. Their monocytes were enriched using counter-current centrifugation, differentiated into DCs which were further co-cultured with autologous CD8 lymphocytes to induce CTL. The DCs were pulsed either with the idiotypic paraprotein (regarded as a tumor-specific antigen) or with autologous MM cell lysate before co-culture. Specific T-cell responses were measured in IFNgamma enzyme-linked immunospot and chromium release assays of autologous plasmocyte targets. A slight increase in IFNgamma secretion by T-cells was observed for two patients (DCs pulsed with idiotypic paraprotein for one, MM cell lysate for the other). No or weak specific lysis of plasmocyte targets was observed in the chromium release assays. In conclusion, the T-cell response to pulsed DCs was very weak or absent. There are clinical and technical reasons that could explain, in part, this lack of response.

Rapid immune recovery and graft-versus-host disease-like engraftment syndrome following adoptive transfer of Costimulated autologous T cells

PURPOSE

Previously, we showed that adoptive transfer of in vivo vaccine-primed and ex vivo (anti-CD3/anti-CD28) costimulated autologous T cells (ex-T) at day +12 after transplant increased CD4 and CD8 T-cell counts at day +42 and augmented vaccine-specific immune responses in patients with myeloma. Here, we investigated the safety and kinetics of T-cell recovery after infusing ex-T at day +2 after transplant.

EXPERIMENTAL DESIGN

In this phase I/II two-arm clinical trial, 50 patients with myeloma received autografts after high-dose melphalan followed by infusions of ex-T at day +2 after transplant. Patients also received pretransplant and posttransplant immunizations using a pneumococcal conjugate vaccine only (arm B; n = 24) or the pneumococcal conjugate vaccine plus an HLA-A2-restricted microltipeptide vaccine for HLA-A2(+) patients (arm A; n = 26).

RESULTS

The mean number of T cells infused was 4.26 x 10(10) (range, 1.59-5.0). At day 14 after transplant, the median CD3, CD4, and CD8 counts were 4,198, 1,545, and 2,858 cells/microL, respectively. Interleukin (IL)-6 and IL-15 levels increased early after transplant and IL-15 levels correlated significantly to day 14 T-cell counts. Robust vaccine-specific B- and T-cell responses were generated. T-cell infusions were well tolerated with no effect on hematopoietic recovery. Eight patients (16%) developed a T-cell "engraftment syndrome" characterized by diarrhea and fever that was clinically and histopathologically indistinguishable from grade 1 to 3 acute graft-versus-host disease (GVHD) of the gastrointestinal tract (seven patients) and/or grade 1 to 2 cutaneous GVHD (four patients).

CONCLUSIONS

Adoptive T-cell transfers achieve robust T-cell recovery early after transplant and induce moderate-to-severe autologous GVHD in a subset of patients.

Post-transplant immunotherapy with donor-lymphocyte infusion and novel agents to upgrade partial into complete and molecular remission in allografted patients with multiple myeloma

OBJECTIVE

To investigate post-transplant immunotherapy with escalating donor-lymphocyte infusions (DLI) and novel agents (thalidomide, bortezomib, and lenalidomide) to target complete remission (CR).

MATERIALS AND METHODS

Thirty-two patients with multiple myeloma who achieved only partial remission after allogeneic stem cell transplantation were treated with DLI. If no CR was achieved, one of the novel agents was added to target CR.

RESULTS

CR defined either by European Group for Blood and Marrow Transplantation criteria, flow cytometry, or molecular methods as assessed by patient-specific immunoglobulin H-polymerase chain reaction or plasma cell chimerism polymerase chain reaction was accomplished in 59%, 63%, and 50% of patients, respectively. Achievement of CR resulted in improved 5-year progressive-free and overall survival, according to European Group for Blood and Marrow Transplantation criteria (53% vs 35%; p=0.03 and 90% vs 62%; p=0.06), flow cytometry (74% vs 15%; p=0.001 and 100% vs 52%; p=0.1), or molecular methods (84% vs 38%; p=0.001 and 100% vs 71%; p=0.03).

CONCLUSIONS

Our finding demonstrates the clinical relevance of posttransplantation therapies to upgrade remission, and of remission's depth for long-term survival in myeloma patients.

Emerging therapies for multiple myeloma

Multiple myeloma (MM) is a clonal plasma cell malignancy clinically characterized by osteolytic lesions, immunodeficiency, and renal disease. There are an estimated 750,000 people diagnosed with MM worldwide, with a median overall survival of 3 - 5 years. Besides chromosomal aberrations, translocations, and mutations in essential growth and tumor-suppressor genes, accumulating data strongly highlight the pathophysiologic role of the bone marrow (BM) microenvironment in MM pathogenesis. Based on this knowledge, several novel agents have been identified, and treatment options in MM have fundamentally changed during the last decade. Thalidomide, bortezomib, and lenalidomide have been incorporated into conventional cytotoxic and transplantation regimens, first in relapsed and refractory and now also in newly diagnosed MM. Despite these significant advances, there remains an urgent need for more efficacious and tolerable drugs. Indeed, a plethora of preclinical agents awaits translation from the bench to the bedside. This article reviews the scientific rationale of new therapy regimens and newly identified therapeutic agents - small molecules as well as therapeutic antibodies - that hold promise to further improve outcome in MM.

Haploidentical stem cell transplantation after a reduced-intensity conditioning regimen for the treatment of advanced hematologic malignancies: posttransplantation CD8-depleted donor lymphocyte infusions contribute to improve T-cell recovery

Haploidentical hematopoietic stem cell transplantation provides an option for patients with advanced hematologic malignancies lacking a compatible donor. In this prospective phase 1/2 trial, we evaluated the role of reduced-intensity conditioning (RIC) followed by early add-backs of CD8-depleted donor lymphocyte infusions (DLIs). The RIC regimen consisted of thiotepa, fludarabine, cyclophosphamide, and 2 Gy total body irradiation. Twenty-eight patients with advanced lymphoproliferative diseases (n = 24) or acute myeloid leukemia (n = 4) were enrolled. Ex vivo and in vivo T-cell depletion was carried out by CD34(+) cell selection and alemtuzumab treatment. The 2-year cumulative incidence of nonrelapse mortality was 26% and the 2-year overall survival (OS) was 44%, with a better outcome for patients with chemosensitive disease (OS, 75%). Overall, 54 CD8-depleted DLIs were administered to 23 patients (82%) at 3 different dose levels without loss of engraftment or acute toxicities. Overall, 6 of 23 patients (26%) developed grade II-IV graft-versus-host disease, mainly at dose level 2. In conclusion, our RIC regimen allowed a stable engraftment with a rather low nonrelapse mortality in poor-risk patients; OS is encouraging with some long-term remissions in lymphoid malignancies. CD8-depleted DLIs are feasible and promote the immune reconstitution.

Graft-versus-leukemia effects of transplantation and donor lymphocytes

Allogeneic transplantation of hematopoietic cells is an effective treatment of leukemia, even in advanced stages. Allogeneic lymphocytes produce a strong graft-versus-leukemia (GVL) effect, but the beneficial effect is limited by graft-versus-host disease (GVHD). Depletion of T cells abrogates GVHD and GVL effects. Delayed transfusion of donor lymphocytes into chimeras after T cell-depleted stem cell transplantation produces a GVL effect without necessarily producing GVHD. Chimerism and tolerance provide a platform for immunotherapy using donor lymphocytes. The allogeneic GVL effects vary from one disease to another, the stage of the disease, donor histocompatibility, the degree of chimerism, and additional treatment. Immunosuppressive therapy before donor lymphocyte transfusions may augment the effect as well as concomitant cytokine treatment. Possible target antigens are histocompatibility antigens and tumor-associated antigens. Immune escape of tumor cells and changes in the reactivity of T cells are to be considered. Durable responses may be the result of the elimination of leukemia stem cells or the establishment of a durable immune control on their progeny. Recently, we have learned from adoptive immunotherapy of viral diseases and HLA-haploidentical stem cell transplantation that T-cell memory may be essential for the effective treatment of leukemia and other malignancies.

Donor lymphocyte infusions: the long and winding road: how should it be traveled?

Donor lymphocyte infusions (DLI) often are used after allo-SCT to augment the graft-versus-tumor effect. Timing of infusion varies according to indication, for example to treat tumor recurrence, as a planned strategy to prevent disease relapse in the setting of T-cell-depleted grafts or non-myeloablative conditioning regimens, or as a method to convert mixed to full donor chimerism. The optimal strategy of timing, use of cytotoxic conditioning, cell dose and cell product composition, and so on, for DLI administration remains unclear. Despite varied techniques, DLI may lead to 3-year disease-free survivals (DFS) in excess of 60% for all CML patients and approach 90% in patients with only molecular or cytogenetic relapse. Other hematologic malignancies appear much less responsive, as less than 50% of patients respond and provide, at best, 3-year DFS rates of 20-50%. Multiple myeloma patients have overall response rates of 40-45% after DLI, suggesting benefit in relapsed disease, but limited experiences for diseases such as Hodgkin's lymphoma, myelodysplasia and ALL preclude recommendations for use of DLI at this time. Regardless of the indication, treatment-related mortality after DLI is 5-20% and more than one-third of patients will develop acute and/or chronic GVHD after DLI. The risks of these complications appear related, in part, to donor source, cell dose and therapy prior to DLI. Although there are no definitive answers, the information gleaned from published literature suggests that DLI should be administered early after relapse or as a prophylactic strategy in patients receiving T-cell-depleted grafts, and patients with bulky or aggressive disease may benefit from disease reduction prior to DLI.

The allogeneic dilemma

The place of allogeneic SCT in the management of multiple myeloma remains controversial. Although it may induce long-term clinical and molecular remissions, the very high transplant-related toxicity after a myeloablative preparative regimen has limited its role to younger patients as first-line treatment option. Even with this limited indication, toxic death rate related to infections and GVHD is considered too high and this strategy has been almost abandoned. Reduced intensity conditioning (RIC) regimens look promising, as the transplant-related mortality is low even with matched unrelated donors and can be considered for older patients up to the age of 65 years. However when used in patients with a high tumor burden or with chemo-resistant disease, the immunologic effect of the graft is not sufficient to avoid relapses. Therefore, RIC allotransplantation is currently used after tumor mass reduction with high-dose therapy followed by autologous SCT. A recently published Italian study shows that this strategy induces better event-free survival than double autologous SCT due to a reduced relapse rate. The questions raised by this encouraging result are discussed in this paper.

Hematopoietic Stem Cell Transplantation in Multiple Myeloma

High-dose therapy and autologous hematopoietic stem cell transplantation are standard early treatment of patients with multiple myeloma. Tandem transplantation appears to provide additional benefit, particularly in patients with limited response to initial transplantation. Myeloablative allogeneic transplantation provides the only potential for cure, but has been largely abandoned because of high mortality rates. Newer and better induction regimens, rigorous analysis of results with autologous and allogeneic transplantation, and the development of risk-adapted stratification provide the impetus for this critical evaluation of the role of hematopoietic stem cell transplantation in multiple myeloma.

Plasma cells from multiple myeloma patients express B7-H1 (PD-L1) and increase expression after stimulation with IFN-γ and TLR ligands via a MyD88-, TRAF6-, and MEK-dependent pathway

Multiple myeloma (MM) cells inhibit certain T-cell functions. We examined the expression of B7-H1 (PD-L1), a B7-related protein that inhibits T-cell responses, in CD138-purified plasma cells isolated from MM patients, monoclonal gammopathy of undetermined significance patients, and healthy donors. We observed that B7-H1 was expressed in most MM plasma cells, but not cells isolated from monoclonal gammopathy of undetermined significance or healthy donors. This expression was increased or induced by IFN-γ and Toll-like receptor (TLR) ligands in isolated MM plasma cells. Blocking the MEK/ERK pathway inhibited IFN-γ–mediated and TLR-mediated expression of B7-H1. Inhibition of the MyD88 and TRAF6 adaptor proteins of the TLR pathway blocked not only B7-H1 expression induced by TLR ligands but also that mediated by IFN-γ. IFN-γ–induced STAT1 activation, via MEK/ERK and MyD88/TRAF6, and inhibition of STAT1 reduced B7-H1 expression. MM plasma cells stimulated with IFN-γ or TLR ligands inhibited cytotoxic T lymphocytes (CTLs) generation and this immunosuppressive effect was inhibited by preincubation with an anti-B7-H1 antibody, the UO126 MEK inhibitor, or by transfection of a dominant-negative mutant of MyD88. Thus, B7-H1 expression by MM cells represents a possible immune escape mechanism that could be targeted therapeutically through inhibition of MyD88/TRAF6 and MEK/ERK/STAT1.

Mini-Midi-Maxi? How to harness the graft-versus-myeloma effect and target molecular remission after allogeneic stem cell transplantation

Allogeneic stem cell transplantation in multiple myeloma after standard myeloablative conditioning induces a high rate of complete remissions, but long-term freedom from disease is achieved in 30-40% of the cases only. The therapeutic effect of allogeneic stem cell transplantation is due to cytotoxicity of high-dose chemotherapy and immune-mediated graft-versus-myeloma effect by donor T cells. Retrospective studies clearly suggest that both (a) reducing the intensity of high-dose chemotherapy by using reduced-intensity or non-myeloablative conditioning regimen or (b) reducing the immunotherapy of donor T cells by using T-cell depletion result in lower treatment-related morbidity and mortality, but also in higher rate of relapse. Therefore, this review will focus on potential strategies of how treatment-related morbidity and mortality might be kept low without an increased risk of relapse and how remission status after transplantation can be enhanced by using the newly established donor immunosystems after allografting as a platform for post-transplant treatment strategies with new drugs (thalidomide, lenalidomide, bortezomib) or immunotherapy (donor lymphocyte infusion, vaccination, tumor-specific T cells) in order to achieve remission on a molecular level, which seems to be a 'conditio sine qua non' to cure myeloma patients.

Multiple myeloma patients receiving pre-emptive donor lymphocyte infusion after partial T-cell-depleted allogeneic stem cell transplantation show a long progression-free survival

The purpose of this study was to determine the role of pre-emptive donor lymphocyte infusion (pDLI) after partial T-cell-depleted allogeneic SCT in patients with multiple myeloma (MM). A cohort of 24 MM patients was treated with partial T-cell-depleted myeloablative SCT between December 1997 and April 2002. These patients were intended to receive pDLI after SCT. The overall response rate after SCT was 83% (20 of 24 patients) with 10 patients (42%) in complete remission (CR). Transplant-related mortality within 1 year after SCT was 29%. Thirteen patients (54%) received pDLI and four patients in partial remission reached CR. GVHD>grade I after pDLI developed in 4 out of 13 patients (30%). Four patients received therapeutic DLI, without preceding pDLI. Eleven patients (46%) are alive, with a median follow-up of 67 months (range, 48-100 months). Seven of these patients (29%) are in continuous CR (CCR), which was confirmed by a negative patient-specific IgH PCR in four patients. All seven patients in CCR received pDLI. Although myeloablative SCT in MM induces high toxicity, we show that the concept of T-cell depletion followed by pDLI is promising and needs to be investigated in a reduced-intensity conditioning setting.

Novel approaches in allogeneic stem cell transplantation

Allogeneic transplantation remains an integral part of the management of hematologic malignancies. However, transplant-related mortality, graft-versus-host disease, and disease recurrence continue to be major limitations to successful transplant outcomes and challenges to investigators in the field. Newer approaches have focused on reduction of the intensity of the conditioning regimens, harnessing the antitumor effects of the allograft, and development of adoptive immunotherapy strategies to circumvent the limitations. These developments provide physicians with the ability to tailor transplants to specific patients and their diseases.

Reduced-Intensity Stem Cell Transplantation

The recognition that the immune system can play a major role in the control and cure of transplantable disorders led to the development of reduced-intensity allogeneic transplantation. The notion is that a compromise can be made between the intensity of conditioning and the fostering of graft-versus-host disease/ graft-versus-leukemia (GVHD/GVL), allowing the use of less intense conditioning with concomitantly less intense immediate toxicity. Reduced-intensity conditioning regimens have allowed the application of transplantation to older patients and to patients with underlying medical problems that preclude full-dose transplantation. Clearly, in some settings in which dose intensity is important, reduced-intensity regimens are less useful. However, for diseases that are either indolent, highly susceptible to GVL, or under good control before entering transplantation, this approach appears to have substantial benefits. Although the therapy appears to be valuable, concerns about delayed immune reconstitution and GVHD remain.

Stem cell transplantation in multiple myeloma

Multiple myeloma (MM) is one of the key hematologic malignancies in which the impact of dose intensity has been demonstrated. Consequently, in 2005, MM was the most common disease for which autologous stem cell transplantation (ASCT) was indicated both in Europe and in the U.S. However, ASCT is not curative, and most patients relapse within a median of 3 years. Novel agents such as thalidomide (Thalidomid), bortezomib (Velcade), or lenalidomide (Revlimid) have been introduced to improve high-dose therapy, and promising results have been reported. Conversely, results from myeloablative allogeneic stem cell transplantation remain disappointing due to high transplantation-related mortality, justifying the exploration of strategies such as reduced-intensity conditioning, which have been shown to be feasible but for which proof of efficacy requires continued study.

Graft-versus-host reactions and the effectiveness of donor lymphocyte infusions

We retrospectively analyzed 83 consecutive recipients of donor lymphocyte infusions (DLI) after allogeneic transplantation for factors associated with disease response and graft-versus-host disease (GVHD). DLI was highly effective in relapsed chronic phase chronic myeloid leukemia (CML), with 71% of patients achieving durable complete remissions (CR). In relapsed acute myeloid leukemia, DLI led to durable CRs in 31% of patients; the rate was <20% in all other diseases. Achieving full donor chimerism and GVHD were predictive of CR. Grade II or higher acute or chronic GVHD occurred in 36 (43%) patients and contributed to death in 13 (16%). Even more patients, 33 (40%), died of their underlying malignancy, including 10 who developed active GVHD. In relapsed CML, most durable CRs occurred without clinically apparent GVHD, yet all responders achieved full donor chimerism, including 6 with coincident normal host hematopoiesis at the time of DLI. Thus, in CML, potent lymphohematopoietic graft-versus-host reactions occurred even in the absence of clinically apparent GVHD; this confirms the ability to dissociate these processes and argues against a leukemia-specific immunologic effect. DLI clearly has efficacy in the treatment of relapsed disease after allogeneic transplantation. However, with the exception of CML, most patients die of their underlying disease because of insufficient antitumor activity even with active GVHD.

Differential epitope mapping of antibodies to PDC-E2 in patients with hematologic malignancies after allogeneic hematopoietic stem cell transplantation and primary biliary cirrhosis

A unique characteristic of the autoimmune liver disease primary biliary cirrhosis (PBC) is the presence of high-titer and extremely specific autoantibodies to the E2 component of the pyruvate dehydrogenase complex (PDC-E2). Autoantibodies to PDC-E2 antigen have only been detected in patients with disease or in those who subsequently develop PBC. One exception has been a subgroup of patients with multiple myeloma (MM) who underwent allogeneic hematopoietic stem cell transplantation (HSCT) and received donor lymphocyte infusions (DLIs) after transplantation. These patients developed high-titer antibodies to a variety of myeloma-associated antigens, including PDC-E2, coincident with rejection of myeloma cells in vivo. To examine the specificity of autoantibodies to PDC in these patients, we screened sera from patients with MM, chronic leukemias, monoclonal gammopathy of unknown significance (MGUS), PBC, and healthy donors. Three of 11 patients with MM (27%) and 2 of 6 patients with chronic leukemias (33%) developed anti-PDC-E2 antibodies in association with DLI response; 2 of 12 (17%) patients in the MGUS pretreatment control population also had detectable anti-PDC responses. Interestingly, the epitope specificity of these PDC-E2 autoantibodies was distinctive, suggesting that the mechanisms leading to loss of tolerance in the transplantation patients are distinct from PBC.

Prophylactic transfer of CD8-depleted donor lymphocytes after T-cell-depleted reduced-intensity transplantation

Allogeneic hematopoietic stem cell transplantation (SCT) regimens incorporating the lymphocytotoxic CD52 antibody alemtuzumab demonstrate efficient engraftment and reduced graft-versus-host disease (GVHD). However, these protocols substantially impair posttransplantation antiviral and antitumor immunity. To accelerate immune reconstitution after alemtuzumab-based reduced-intensity SCT, we administered prophylactic CD8-depleted donor lymphocyte infusions (DLIs) starting on days 60 and 120 after transplantation. DLIs were processed in an immunomagnetic good manufacturing practice depletion procedure resulting in a 2.5- to 6-log reduction in CD8 T cells. Of 23 high-risk patients with hematologic malignancies, 11 received a total of 21 CD8-depleted DLIs. Five patients developed transient grade I acute GVHD following transfer. Only 2 patients with HLA-C-mismatched donors showed grade II and III acute GVHD and subsequently progressed to limited chronic GVHD. Following DLIs, 4 patients with declining hematopoietic donor chimerism converted to full chimeras. A 2.1-fold median increase of circulating CD4 T cells was observed within 2 weeks after infusion. Non-DLI patients did not show a comparable rise in CD4 counts. Four patients demonstrated enhanced frequencies of cytomegalovirus-specific CD4 and CD8 T cells following transfer. Our results suggest that prophylactic CD8-depleted DLIs accelerate immune reconstitution after lymphodepleted HLA-matched SCT and carry a low risk of inducing severe GVHD.

Allogeneic haematopoietic cell transplantation for multiple myeloma: reducing transplant-related mortality while harnessing the graft-versus-myeloma effect

Allogeneic haematopoietic cell transplantation (allo-HCT) provides effective therapy for patients with various haematological malignancies. In multiple myeloma (MM) this approach can induce response rates in 35-75% of patients. However, the outcome is hampered by high rates of treatment-related mortality (TRM). Reduced intensity conditioning to lower TRM has been successfully applied. The fact that previous clinical reports have documented graft-versus-myeloma (GVM) activity without graft-versus-host disease (GVHD) suggests that at least two distinct immunocompetent cell populations mediating GVHD and/or GVM may exist. Further characterization of effectors after allo-HCT and their targets may help to clarify the immune response that mediates the GVM effect. This review considers the clinical results with myeloablative and reduced intensity conditioning prior to allo-HCT for MM, with emphasis on attempts to prevent GVHD while preserving the GVM effect. Strategies including donor lymphocyte infusions as part of the allogeneic protocol and antigenic targets for GVM effect are reviewed.

Targeting signalling pathways for the treatment of multiple myeloma

Multiple myeloma (MM) is characterised by the expansion of monoclonal immunoglobulin-secreting plasma cells. Despite recent advances in systemic and supportive therapy, it remains incurable, with a median survival of about three years. Development of MM is a multistep process associated with an increasing frequency of chromosomal abnormalities and complex translocations, which induce mutations in several proto-oncogenes and tumour suppressor genes. Furthermore, differentiation, maintenance, expansion and drug resistance of MM cells are dependent on multiple growth factors, cytokines, and chemokines, secreted by tumour cells, bone marrow stromal cells, and non-haematopoietic organs; as well as on direct tumour cell-stromal cell contact. Therefore, signalling pathways initiated by both mutated genes in MM cells as well as signals originating in the bone marrow microenvironment represent potential targets for intervention. Close collaboration between basic researchers and clinicians will be required to further improve our knowledge of MM pathophysiologically in order to translate advances from the bench to the bedside and improve patient outcome.

Graft-versus-host disease and graft-versus-leukemia after donor leukocyte infusion

Although dramatically effective for relapsed chronic myelogenous leukemia (CML), successful donor leukocyte infusion (DLI) remains limited primarily by inadequate responses for patients with diseases other than CML and by toxicity related to graft-versus-host disease (GVHD). Acute GVHD grades 2 to 4 follows 34% to 47% of infusions and chronic GVHD occurs in 33% to 61% of cases. Strategies to reduce the incidence and severity of GVHD while preserving the graft-versus-leukemia (GVL) effect, such as low-dose DLI, depletion of GVHD effector cells, and tumor-specific DLI, are reviewed.

HLA class II restricted T-cell receptor gene transfer generates CD4+ T cells with helper activity as well as cytotoxic capacity

Both cytotoxic T cells and helper T cells are important in immune responses against pathogens and malignant cells. In hematological malignancies which express HLA class II molecules, immunotherapy may be directed to HLA class II restricted antigens. We investigated whether it is possible to engineer HLA class II restricted T cells with both antigen-specific cytolytic activity and the capacity to produce high amounts of cytokines. CD4+ and CD8+ peripheral-blood-derived T cells were retrovirally transduced with the HLA class II restricted minor histocompatibility antigen dead box RNA helicase Y (DBY)-specific TCR. The TCR-transduced CD4+ T cells exerted DBY-specific cytolytic activity, produced Th0, Th1, or Th2 cytokines, and proliferated upon DBY-specific stimulation. TCR-transduced CD8+ T cells exerted cytolytic activity which equaled the level of cytolytic activity of the TCR-transferred CD4+ T cells. Cotransfer of CD4 enhanced the cytolytic activity of the TCR-transduced CD8+ T cells, but introduction of CD4 was not sufficient to generate DBY-specific CD8+ T cells with the capacity to produce high amounts of cytokines. In this study, we demonstrated the feasibility to engineer T cells with antigen-specific cytolytic activity, as well as the ability to produce significant amounts of cytokines, by TCR transfer to CD4+ T cells.

Current therapeutic uses of lenalidomide in multiple myeloma

Thalidomide has demonstrated a broad spectrum of pharmacological and immunological effects, with potential therapeutic applications that span a wide spectrum of diseases: cancer and related conditions; infectious diseases; autoimmune diseases; dermatological diseases; and other disorders such as sarcoidosis, macular degeneration and diabetic retinopathy. Immunomodulatory derivative lenalidomide has more potent antitumour and anti-inflammatory effects. The molecular mechanisms of antitumour activity of lenalidomide have been extensively studied in multiple myeloma (MM). It directly induces growth arrest and/or apoptosis of even drug-resistant MM cells; inhibits binding of MM cells to bone marrow extracellular matrix proteins and stromal cells; modulates cytokine secretion and inhibits angiogenesis in the bone marrow milieu; and augments host antitumour immunity. Importantly, lenalidomide induces significant clinical responses even in patients with relapsed/refractory MM. Therefore, lenalidomide represents a new class of antitumour agents that is useful in the treatment of MM. Lenalidomide has received fast track designation from the FDA for the treatment of MM and myelodysplastic syndromes.

Clonal cytogenetic changes and myeloma relapse after reduced intensity conditioning allogeneic transplantation

To identify a correlation between metaphase cytogenetics and relapse after reduced intensity conditioning (RIC) allotransplant for patients with multiple myeloma, data on 60 patients (median age 52) who received grafts from a sibling (n = 49) or unrelated donor (n = 11) were analyzed. Fifty-three patients (88%) showed chromosomal abnormalities (CA) before the allotransplant, including 42 with abnormalities involving 13q (CA13). Twenty-two patients (41%) relapsed post-allotransplant at a median of 165 days. Of these, 11 patients showed abnormal cytogenetics at the time of post-allotransplant relapse at a median of 167 days. Of 54 patients who developed graft-versus-host disease, relapse occurred in 19 of 48 patients (43%) with CA present before RCI allotransplant, versus 1 of 6 without CA (17%) (P = 0.06). Loss of CA before RIC allotransplant and disease status > PR after RIC allotransplant were significantly associated with a lower risk of post-allotransplant relapse with cytogenetic abnormalities; 5.2 vs 36%, and 18 vs 53%, (both P < 0.05), respectively. The current data suggests that myeloma associated with persistent clonal cytogenetic abnormalities is an entity which most likely escapes the effects of a graft versus myeloma activity, maybe because of acquisition of resistance to immunologic manipulations.

Stem-cell transplantation in multiple myeloma

In patient with newly diagnosed multiple myeloma (MM), randomized studies have shown that autologous stem-cell transplantation (ASCT) is superior to conventional chemotherapy, and ASCT is now standard care, at least for younger patients. The best conditioning regimen is melphalan 200 mg/m2, and the best stem-cell source is unselected peripheral progenitor cells. Recent results of the IFM94 trial show that double ASCT is superior to single ASCT, at least in patients who do not achieve a 90% response after one transplant. By combining biologic markers (beta2-microglobulin, albumin) and genetic markers (hypodiploidy, chromosome 13 deletion) it is possible to accurately predict prognosis after ASCT. The results of allogeneic SCT remain disappointing due to a high transplant mortality. Strategies combining ASCT and reduced-intensity allogeneic SCT are currently being studied.

Current treatment options for myeloma

In most cases multiple myeloma is an incurable plasma cell malignancy. Despite the use of conventional therapy or high-dose chemotherapy with autologous stem cell transplantation (ASCT), patients continue to relapse at a constant rate. A small minority of patients are cured by allogeneic transplantation. Novel drugs targeting not only the myeloma cell but also its interactions with the malignant microenvironment have recently been used in patients with relapsed/refractory disease. So far, ASCT has been the treatment of choice for eligible myeloma patients. However, many questions regarding the management of myeloma patients remain unanswered. How safe is ASCT in elderly patients? Is there a role for non-myeloablative allogeneic transplantation in multiple myeloma? What is the role of novel agents, such as thalidomide, its analogues and bortezomib, in the treatment of newly diagnosed patients or as maintenance post-ASCT? This review summarises all available data for the current treatment options for myeloma providing a useful algorithm for its management.

Capillary electrophoresis for chimerism monitoring by PCR amplification of microsatellite markers after allogeneic hematopoietic cell transplantation

BACKGROUND

Hematopoietic chimerism has been demonstrated to be relevant for donor cell engraftment and detection of minimal residual disease after allogeneic hematopoietic cell transplantation (aHCT). In the light of increasing numbers of non-myeloablative aHCT as a treatment modality sensitive, rapid, and accurate chimerism monitoring techniques acquire novel relevance.

METHODS

We evaluated the informativeness of five microsatellite markers in 376 donor/recipient pairs and evaluated the ability of capillary electrophoresis to detect mixed chimerism after aHCT. The sensitivity for capillary electrophoresis with respect to different markers was determined by limiting dilution assays with mixed chimerism samples containing defined amounts of cells or DNA. Furthermore, capillary electrophoresis was applied in 17 retrospectively selected patients with a mixed chimerism detected previously by gel electrophoresis, having undergone aHCT for different hematologic diseases and initially achieving a complete donor chimerism.

RESULTS

In 163 of 165 (98%) of all related and 210 of 211 (99%) unrelated transplants the microsatellites identified informative alleles. The sensitivity and accuracy was higher with capillary electrophoresis when compared with gel electrophoresis with three of five microsatellites. Potential pitfalls with the application of capillary electrophoresis was preferential amplification and the occurrence of stutter peaks in the representative area. Investigation of the selected patient samples demonstrated that detection of a mixed chimerism was earlier with capillary electrophoresis when compared with gel electrophoresis. The detected recipient genotype by capillary electrophoresis examination, despite a negative gel electrophoresis result, ranged from 0.7 to 7.1%.

CONCLUSIONS

We conclude that chimerism assessment with our five microsatellites identified informative alleles in 99% of all donor/recipient pairs and may therefore be of use when establishing an institutional chimerism testing procedure. Capillary electrophoresis displayed a high sensitivity and accuracy for detecting a mixed chimerism in vitro and in vivo.

Partial CD8+ T-cell depletion of allogeneic peripheral blood stem cell transplantation is insufficient to prevent graft-versus-host disease

Prior studies suggest that depletion of CD8+ T cells from donor bone marrow or donor lymphocyte infusions can reduce graft-versus-host disease (GVHD) without compromising graft-versus-leukemia. We explored CD8 depletion in patients undergoing matched related donor (MRD, n=25) and unrelated donor (URD, n=16) peripheral blood stem cell transplantation following myeloablative conditioning with cyclophosphamide (60 mg/kg/day i.v. x 2) and total body irradiation (200 cGy x 7 fractions). Ex vivo incubation of mobilized donor peripheral blood cells with anti-CD8 antibody coated high-density microparticles removed 99% of CD8+ cells. The median number of CD8+ cells infused was 3.9 x 10(5) cells/kg (2.2 x 10(5) in MRD, and 8.1 x 10(5) in URD patients). Post transplant immune suppression included tacrolimus in the MRD cohort, and tacrolimus plus mini-methotrexate (5 mg/m2 days +1, 3, 6, 11) in the URD cohort. All 41 patients engrafted. Grade 2-4 acute GVHD incidence was 61% (44% MRD, 88% URD). Chronic GVHD incidence was 50% (48% MRD, 55% URD). Relapse incidence was 4.9%. Estimated event-free and overall survival rates were 65 and 63%, respectively, at 1 year and 56 and 57%, respectively, at 2 years. There was no correlation between CD8+ number and GVHD or survival. A 2-log depletion of CD8+ cells from PBSC is insufficient to prevent GVHD.

Donor lymphocyte infusions for multiple myeloma: clinical results and novel perspectives

Donor lymphocyte infusions (DLIs) provide effective therapy for patients with various hematological malignancies who have relapsed after allogeneic hematopoietic stem cell transplantation (HSCT). In patients with multiple myeloma (MM), DLIs can induce response rates of 40-52%. DLIs were employed as treatment for MM relapse or as prophylaxis for relapse in MM patients undergoing allo-HSCT. The clinically most relevant treatment-related morbidity with DLIs is the occurrence of graft-versus-host disease (GVHD). Secondly, graft failure and the immune escape of extramedullary plasmocytoma have been reported. The fact that previous clinical reports have documented graft-versus-myeloma (GVM) activity without GVHD suggests that at least two distinct immunocompetent cell populations mediating GVHD and/or GVM may exist. Further characterization of the effector cells such as T cells and/or NK cells and their targets may help to clarify the immune response that mediates the GVM effect. This review considers the results of clinical approaches with DLI for MM, with emphasis on strategies to prevent GVHD while preserving the GVM effect. Furthermore, currently investigated molecular antigenic targets for the GVM effect such as MM-specific idiotypic determinant of immunoglobulin variable regions, several PRAME epitopes and antigenic structures encoded by cancer germline-specific genes as candidates for immunotherapy trials are discussed.

Graft-versus-tumor response in patients with multiple myeloma is associated with antibody response to BCMA, a plasma-cell membrane receptor

Donor lymphocyte infusions (DLIs) induce effective graft-versus-tumor responses in patients with multiple myeloma who relapse after allogeneic hematopoietic stem-cell transplantation. The graft-versus-myeloma response is presumably mediated primarily by donor T cells, but recent studies have also demonstrated the presence of antibodies specific for a variety of myeloma-associated antigens in patients who achieve complete remission after DLI. One of the B-cell antigens identified in these studies was B-cell maturation antigen (BCMA), a transmembrane receptor of the tumor necrosis factor (TNF) superfamily that is selectively expressed by mature B cells. The present studies were undertaken to characterize the functional significance of antibodies to BCMA in vivo. Using transfected cells expressing BCMA, antibodies in patient serum were found to react with the cell-surface domain of BCMA. Post-DLI patient serum was able to induce complement-mediated lysis and antibody-dependent cellular cytotoxicity (ADCC) of transfected cells and primary myeloma cells expressing BCMA. BCMA antibodies were only found in post-DLI responders and not in other allogeneic transplant patients or healthy donors. These results demonstrate that BCMA is a target of donor B-cell immunity in patients with myeloma who respond to DLI. Antibody responses to cell-surface BCMA may contribute directly to tumor rejection in vivo.

Molecular mechanisms whereby immunomodulatory drugs activate natural killer cells: clinical application

Thalidomide and immunomodulatory drugs (IMiDs), which target multiple myeloma (MM) cells and the bone marrow microenvironment, can overcome drug resistance. These agents also have immunomodulatory effects. Specifically, we have reported that thalidomide increased serum interleukin-2 (IL-2) levels and natural killer (NK) cell numbers in the peripheral blood of responding MM patients. In this study, we investigated the mechanisms whereby IMiDs augment NK cell cytotoxicity. NK cytotoxicity and antibody-dependent cell-mediated cytotoxicity (ADCC) of peripheral blood mononuclear cells cultured with IMiDs were examined in the presence or absence of anti-IL-2 antibody, ciclosporin A or depletion of CD56-positive cells. IMiDs-induced signalling pathways, triggering IL-2 transcription in T cells, were also delineated. IMiDs facilitated the nuclear translocation of nuclear factor of activated T cells-2 and activator protein-1 via activation of phosphoinositide-3 kinase signalling, with resultant IL-2 secretion. IMiDs enhanced both NK cell cytotoxicity and ADCC induced by triggering IL-2 production from T cells. These studies defined the mechanisms whereby IMiDs trigger NK cell-mediated tumour-cell lysis, further supporting their therapeutic use in MM.

CD34 cell selection of peripheral blood progenitor cells using the CliniMACS device for allogeneic transplantation: clinical results in 102 patients

The present study investigated the effects of CD34(+) cell selection in 102 patients using the CliniMACS device. Patients were at high risk for the development of graft versus host disease (GvHD) because of age, or the use of a haploidentical, mismatched or unrelated donor (UD). The median age of the patients was 44 years. The CliniMACS procedure yielded 8.0 x 10(6) CD34(+) cells/kg and the number of residual T cells was 1.3 x 10(4)/kg (median). The median follow up was 20.6 months. The probability of graft failure was 7%. The rate of acute GvHD was low (compatible family donors 10%, UDs 17%, and haploidentical donors 26%) with no patient enduring more than grade II disease. The cumulative incidence of chronic GvHD at the median follow up after transplant was 15% for the compatible family donor group, 40% for the UD group and 78% in the group transplanted from a haploidentical donor Treatment failure was mainly because of transplant-related mortality, especially aspergillus infection, and not due to relapse. The probability of disease-free survival, stratified for the risk of treatment failure, was 27% for the high risk, 46% for the intermediate risk and 83% for the low risk group.

Molecular monitoring of minimal residual disease in patients with multiple myeloma

Improvement of transplantation strategies and a multitude of emerging novel therapies result in a better treatment outcome in patients with multiple myeloma (MM). This gives rise to the need for sensitive methods to detect minimal residual disease (MRD) in MM. Qualitative molecular monitoring using allele-specific oligonucleotide PCR for the immunoglobulin heavy chain (IgH) is well established to detect clonotypic cells after therapy or in stem cell harvests. Recently, real-time IgH PCR or limiting dilution based PCR assays offer the possibility to quantify the amount of residual tumour cells. In this review, different qualitative and quantitative IgH PCR techniques will be discussed as well as the current clinical role of molecular monitoring of MRD in patients with MM.

Stem cell transplantation-harnessing of graft-versus-malignancy

PURPOSE OF REVIEW

Allogeneic transplantation can cure a number of hematologic malignancies; however, the cost in morbidity and mortality is high. Much of the toxicity is a direct consequence of the intensity of the conditioning regimen. It has gradually been recognized that the conditioning regimen is important but not critical for the success of transplantation, particularly in the less aggressive hematologic malignancies. The graft-versus-malignancy effect, that is, the recognition of residual cancer cells by the T cells of the donor, is a critical component of the transplantation process.

RECENT FINDINGS

This effect has been emphasized over high-dose therapy by using less intensive, and therefore less toxic conditioning regimens, thus allowing the graft-versus-malignancy effect to predominate. Reduced-intensity conditioning regimens have allowed the application of transplantation to older patients and to patients with underlying medical problems that preclude full-dose transplantation.

SUMMARY

Although the long-term results of this type of approach have not yet been defined, it appears to be effective in diseases such as chronic myelogenous leukemia, chronic lymphocytic leukemia, and low-grade lymphomas that are not intrinsically very aggressive. Although the therapy appears to be valuable, concerns about delayed immune reconstitution and graft-versus-host disease remain.