Evidence of a graft-versus-leukemia effect in chronic lymphocytic leukemia after reduced-intensity conditioning and allogeneic stem-cell transplantation: the Cooperative German Transplant Study Group

Cellular Therapy in Chronic Lymphocytic Leukemia: Have We Advanced in the Last Decade?

BACKGROUND

Chronic lymphocytic leukemia (CLL) is a heterogeneous B-cell malignancy, affecting mainly older adults. Despite the recent introduction of multiple targeted agents, CLL remains an incurable disease. Cellular therapy is a promptly evolving area that has developed over the last decades from such standard of care as hematopoietic cell transplantation (HCT) to the novel treatment modalities employing genetically engineered immune cells.

SUMMARY

Tailoring the proper treatment for each patient is warranted and should take into account the disease biology, patient characteristics, and the available treatment modalities. Nowadays, the most broadly applied cellular therapies for CLL management are HCT and chimeric antigen receptor-T (CAR-T) cells. However, CAR-T cell therapy is currently not yet approved in CLL, and the appropriate sequencing for the administration of these agents remains to be clarified.

KEY MESSAGES

The current review will discuss various available cellular treatment options, their advances and limitations, as well as the optimal timing for the employment of such therapies in CLL patients.

Cellular Therapy in High-Risk Relapsed/Refractory Chronic Lymphocytic Leukemia and Richter Syndrome

Despite the development of highly effective, targeted inhibitors of B-cell proliferation and anti-apoptotic pathways in chronic lymphocytic leukemia (CLL), these treatments are not curative, and many patients will develop either intolerance or resistance to these treatments. Transformation of CLL to high-grade lymphoma—the so-called Richter syndrome (RS)—remains a highly chemoimmunotherapy-resistant disease, with the transformation occurring following targeted inhibitors for CLL treatment being particularly adverse. In light of this, cellular therapy in the form of allogenic stem cell transplantation and chimeric antigen receptor T-cell therapy continues to be explored in these entities. We reviewed the current literature assessing these treatment modalities in both high-risk CLL and RS. We also discussed their current limitations and place in treatment algorithms.

Cell therapy of chronic lymphocytic leukaemia: Transplants and chimeric antigen receptor (CAR)-T cells

There is substantial progress in the therapy of chronic lymphocytic leukaemia (CLL), much of it the result of new drug development. As such the definition of high-risk CLL is changing. Nevertheless, few persons with CLL are cured with current therapy. Two types of cell therapies of CLL are currently being evaluated or re-evaluated in the context of these advances: haematopoietic cell transplants and chimeric antigen receptor (CAR)-T-cells. We discuss the potential role of these cell therapies in the context of the evolving therapy topography of CLL including how these therapies work and who, if anyone, is an appropriate candidate for cell therapy.

Will New Drugs Replace Transplants for Chronic Lymphocytic Leukaemia?

Transplants have been used to treat chronic lymphocytic leukemia (CLL) for more than 35 years. Use has been restricted to <1 percent of highly selected persons typically failing concurrent conventional therapies. As therapies of CLL have evolved, so have indications for transplantation and transplant techniques. The data that we review indicate that transplants can result in long-term leukemia-free survival in some persons but are associated with substantial transplant-related morbidity and mortality. We discuss the mechanisms underlying the anti-leukemia effects of transplants including drugs, ionizing radiations, immune-mediated mechanisms and/or a combination. We discuss prognostic and predicative covariates for transplant outcomes. Importantly, we consider whether there is presently a role of transplants in CLL and who, if anyone, is an appropriate candidate in the context of new drugs.

Allogeneic stem cell transplantation for chronic lymphocytic leukemia in the era of novel agents

Although novel agents (NAs) have improved outcomes for patients with chronic lymphocytic leukemia (CLL), a subset will progress through all available NAs. Understanding outcomes for potentially curative modalities including allogeneic hematopoietic stem cell transplantation (alloHCT) following NA therapy is critical while devising treatment sequences aimed at long-term disease control. In this multicenter, retrospective cohort study, we examined 65 patients with CLL who underwent alloHCT following exposure to ≥1 NA, including baseline disease and transplant characteristics, treatment preceding alloHCT, transplant outcomes, treatment following alloHCT, and survival outcomes. Univariable and multivariable analyses evaluated associations between pre-alloHCT factors and progression-free survival (PFS). Twenty-four-month PFS, overall survival (OS), nonrelapse mortality, and relapse incidence were 63%, 81%, 13%, and 27% among patients transplanted for CLL. Day +100 cumulative incidence of grade III-IV acute graft-vs-host disease (GVHD) was 24%; moderate-severe GVHD developed in 27%. Poor-risk disease characteristics, prior NA exposure, complete vs partial remission, and transplant characteristics were not independently associated with PFS. Hematopoietic cell transplantation-specific comorbidity index independently predicts PFS. PFS and OS were not impacted by having received NAs vs both NAs and chemoimmunotherapy, 1 vs ≥2 NAs, or ibrutinib vs venetoclax as the line of therapy immediately pre-alloHCT. AlloHCT remains a viable long-term disease control strategy that overcomes adverse CLL characteristics. Prior NAs do not appear to impact the safety of alloHCT, and survival outcomes are similar regardless of number of NAs received, prior chemoimmunotherapy exposure, or NA immediately preceding alloHCT. Decisions about proceeding to alloHCT should consider comorbidities and anticipated response to remaining therapeutic options.

Relapsed Chronic Lymphocytic Leukaemia with Concomitant Extensive Chronic Graft versus Host Disease after Allogeneic Haematopoietic Stem Cell Transplantation Successfully Treated with Oral Venetoclax

A middle-aged gentleman who was diagnosed with high-risk chronic lymphocytic leukaemia (CLL), Rai stage IV, Binet C with del(17p) and del(13q) underwent allogeneic haematopoeitic stem cell transplantation (allo-HSCT) from a human leukocyte antigen (HLA) identical sister. The patient developed extensive skin, oral, and liver chronic graft versus host disease (GVHD) required tacrolimus, mycophenolate mofetil (MMF), and prednisolone. At seventh month after allo-HSCT, the patient presented with systemic symptoms, right cervical lymphadenopathy, splenomegaly, marked pancytopaenia, and elevated lactate dehydrogenase (LDH). Bone marrow study, immunophenotyping (IP), chromosome analysis, and PET-CT scan confirmed relapsed CLL with no evidence of Richter's transformation or posttransplant lymphoproliferative disease (PTLD). Withdrawal of immunosuppressant (IS) worsened cutaneous and liver GVHD. Chemotherapy was not a suitable treatment option in view of immunodeficiency. The patient underwent extracorporeal photopheresis (ECP) therapy eventually for extensive chronic GVHD, and the IS were gradually tapered to the minimal effective dose. The relapsed CLL was treated successfully with oral venetoclax accessible via a compassionate drug program. This case highlights challenges in managing relapsed CLL and loss of graft-versus-leukaemia (GVL) effect despite extensive chronic GVHD. Venetoclax is an effective and well-tolerated oral novel agent for relapsed CLL after allo-HSCT.

An autologous tumor vaccine for CLL

Chronic Lymphocytic Leukemia B cells (CLL) are malignant cells which retain at least some functions of normal B cells. Paramount amongst the latter is that when such cells are appropriately stimulated, they are able to present antigens, including any potential tumor antigens, making them excellent choices as a candidate tumor vaccine. We show that following stimulation of CLL cells with Phorbol myristic acetate, IL-2, the TLR7 agonist imiquimod (P2I) and ionomycin (P2Iio), markedly increased expression of CD54 and CD83 was seen, indicative of B cell activation and a transition to antigen-presenting cells. However, this occurred in the context of augmented expression of the known immunoregulatory molecule, CD200. Accordingly we explored the effect of stimulation of CLL cells with P2Iio, followed by coating of cells with a non-depleting anti-CD200mAb, on the ability of those cells to immunize PBL in vitro to become cytotoxic to CLL cells, or to protect NOD-SCIDγc^null (NSG) mice from subsequent CLL tumor challenge. Our data indicate that this protocol is effective in inducing CD8⁺ CTL able to lyse CLL cells in vitro, and decrease tumor burden in vivo in spleen and marrow of mice injected with CLL cells. Pre-treatment of mice with a CD8 depleting antibody before vaccination with P2Iio/anti-CD200 coated cells abolished any protection seen. These data suggest a potential role for blockade of CD200 expression on CLL cells as a component of a tumor vaccination strategy.

Outcomes of haploidentical stem cell transplantation for chronic lymphocytic leukemia: a retrospective study on behalf of the chronic malignancies working party of the EBMT

Allogeneic hematopoietic stem cell transplantation (HCT) may result in long-term disease control in high-risk chronic lymphocytic leukemia (CLL). Recently, haploidentical HCT is gaining interest because of better outcomes with post-transplantation cyclophosphamide (PTCY). We analyzed patients with CLL who received an allogeneic HCT with a haploidentical donor and whose data were available in the EBMT registry. In total 117 patients (74% males) were included; 38% received PTCY as GVHD prophylaxis. For the whole study cohort OS at 2 and 5 yrs was 48 and 38%, respectively. PFS at 2 and 5 yrs was 38 and 31%, respectively. Cumulative incidence (CI) of NRM in the whole group at 2 and 5 years were 40 and 44%, respectively. CI of relapse at 2 and 5 yrs were 22 and 26%, respectively. All outcomes were not statistically different in patients who received PTCY compared to other types of GVHD prophylaxis. In conclusion, results of haploidentical HCT in CLL seem almost identical to those with HLA-matched donors. Thereby, haploidentical HCT is an appropriate alternative in high risk CLL patients with a transplant indication but no available HLA-matched donor. Despite the use of PTCY, the CI of relapse seems not higher than observed after HLA-matched HCT.

Reduced intensity is preferred over myeloablative conditioning allogeneic HCT in chronic lymphocytic leukemia whenever indicated: A systematic review/meta-analysis

Despite availability of new and more effective therapies for chronic lymphocytic leukemia, presently this disease remains incurable unless eligible patients are offered an allogeneic hematopoietic cell transplant. Recent published clinical practice recommendations on behalf of the American Society for Blood and Marrow Transplantation relegated the role of for allogeneic hematopoietic cell transplantation to later stages of the disease. To our knowledge, no randomized controlled trial has been performed to date comparing myeloablative versus reduced intensity conditioning regimens in chronic lymphocytic leukemia patients eligible for the procedure. We performed a systematic review/meta-analysis to assess the efficacy of allogeneic hematopoietic cell transplantation when using myeloablative or reduced intensity conditioning regimens. We report the results in accordance to the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines. Based on lower non-relapse mortality and slightly better overall survival rates, reduced intensity conditioning regimens appear to be the most desirable choice whenever the procedure is indicated for this disease. It appears highly unlikely that a RCT will be ever performed comparing reduced intensity vs. myeloablative allogeneic hematopoietic cell transplantation in chronic lymphocytic leukemia. In the absence of such a study, results of this systematic review/meta-analysis represent the best available evidence supporting this recommendation whenever indicated in patients with chronic lymphocytic leukemia.

[Allogeneic haematopoietic cell transplantation for indolent lymphomas: Guidelines from the Francophone Society Bone Marrow Transplantation and Cellular Therapy (SFGM-TC)]

Despite great improvements in the outcome of patients with lymphoma, some may still relapse or present with primary refractory disease. In these situations, allogeneic hematopoietic cell transplantation is a potentially curative option, this is true particularly the case of relapse after autologous stem cell transplantation. Recently, novel agents such as anti-PD1 and BTK inhibitors have started to challenge the use of allogeneic hematopoietic cell transplantation for relapsed or refractory lymphoma. During the 2016 annual workshop of the Francophone Society of Bone Marrow Transplantation and Cellular Therapy (SFGM-TC), we performed a comprehensive review of the literature published in the last 10 years and established guidelines to clarify the indications and transplant modalities in this setting. This paper specifically reports on our conclusions regarding indolent lymphomas, mainly follicular lymphoma and chronic lymphocytic leukemia.

Assessment of Impact of HLA Type on Outcomes of Allogeneic Hematopoietic Stem Cell Transplantation for Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a common hematologic malignancy with many highly effective therapies. Chemorefractory disease, often characterized by deletion of chromosome 17p, has historically been associated with very poor outcomes, leading to the application of allogeneic hematopoietic stem cell transplantation (allo-HCT) for medically fit patients. Although the use of allo-HCT has declined since the introduction of novel targeted therapy for the treatment of CLL, there remains significant interest in understanding factors that may influence the efficacy of allo-HCT, the only known curative treatment for CLL. The potential benefit of transplantation is most likely due to the presence of alloreactive donor T cells that mediate the graft-versus-leukemia (GVL) effect. The recognition of potentially tumor-specific antigens in the context of class I and II major histocompatibility complex on malignant B lymphocytes by donor T cells may be influenced by subtle differences in the highly polymorphic HLA locus. Given previous reports of specific HLA alleles impacting the incidence of CLL and the clinical outcomes of allo-HCT for CLL, we sought to study the overall survival and progression-free survival of a large cohort of patients with CLL who underwent allo-HCT from fully HLA-matched related and unrelated donors at Center for International Blood and Marrow Transplant Research transplantation centers. We found no statistically significant association of allo-HCT outcomes in CLL based on previously reported HLA combinations. Additional study is needed to further define the immunologic features that portend a more favorable GVL effect after allo-HCT for CLL.

Flow cytometry minimal residual disease after allogeneic transplant for chronic lymphocytic leukemia

OBJECTIVES

This study investigates whether achieving complete remission (CR) with undetectable minimal residual disease (MRD) after allogeneic stem cell transplantation (allo-SCT) for chronic lymphocytic leukemia (CLL) affects outcome.

METHODS

We retrospectively studied 46 patients transplanted for CLL and evaluated for post-transplant MRD by flow cytometry.

RESULTS

At transplant time, 43% of the patients were in CR, including one with undetectable MRD, 46% were in partial response, and 11% had refractory disease. After transplant, 61% of the patients achieved CR with undetectable MRD status. By multivariate analysis, reaching CR with undetectable MRD 12 months after transplant was the only factor associated with better progression-free survival (P = 0.02) and attaining undetectable MRD, independently of the time of negativity, was the only factor that correlated with better overall survival (P = 0.04).

CONCLUSION

Thus, achieving undetectable MRD status after allo-SCT for CLL is a major goal to improve post-transplant outcome.

Durable responses to ibrutinib in patients with relapsed CLL after allogeneic stem cell transplantation

Ibrutinib, a recently approved inhibitor of Bruton's tyrosine kinase (BTK), has shown great efficacy in patients with high-risk CLL. Nevertheless, there are few data regarding its use in patients who relapsed after allogeneic stem cell transplantation (alloSCT). We report clinical data from five CLL patients treated with ibrutinib for relapse after first or even second allogeneic transplantation. Additionally, we performed analyses on cytokine levels and direct measuring of CD4 Th1 and CD4 Th2 cells to evaluate possible clinically relevant immunomodulatory effects of ibrutinib. All patients achieved partial responses including one minimal residual disease (MRD)-negative remission. Within 1 year of follow-up, no relapse was observed. One patient died of severe pneumonia while on ibrutinib treatment. Beside this, no unexpected adverse events were observed. Flow cytometry and analyses of T cell-mediated cytokine levels (IL10 and TNFα) did not reveal substantial changes in T-cell distribution in favor of a CD4 Th1 T-cell shift in our patients. No acute exacerbation of GvHD was reported. In conclusion, these results support further evaluation of ibrutinib in CLL patients relapsing after alloSCT.

Effect of immune modulation in relapsed peripheral T-cell lymphomas after post-allogeneic stem cell transplantation: a study by the Société Française de Greffe de Moelle et de Thérapie Cellulaire (SFGM-TC)

Peripheral T-cell lymphoma carries a poor prognosis. To document a possible graft-versus-lymphoma effect in this setting, we evaluated the impact of immunomodulation in 63 patients with peripheral T-cell lymphoma who relapsed after allogeneic transplant in 27 SFGM-TC centers. Relapse occurred after a median of 2.8 months. Patients were then treated with non-immunologic strategies (chemotherapy, radiotherapy) and/or immune modulation (donor lymphocyte infusions (DLI) and/or discontinuation of immunosuppressive therapy). Median overall survival (OS) after relapse was 6.1 months (DLI group: 23.6 months, non-DLI group: 3.6 months). Among the 14 patients who received DLI, 9 responded and 2 had stable disease. Among the remaining 49 patients, a complete response accompanied by extensive chronic GvHD was achieved in two patients after tapering of immunosuppressive drugs. Thirty patients received radio-chemotherapy, with an overall response rate of 50%. In multivariate analysis, chronic GvHD (odds ratio: 11.25 (2.68-48.21), P=0.0009) and skin relapse (odds ratio: 4.15 (1.04-16.50), P=0.043) were associated with a better response to treatment at relapse. In a time-dependent analysis, the only factor predictive of OS was the time from transplantation to relapse (hazards ratio: 0.33 (0.17-0.640), P=0.0009). This large series provides encouraging evidence of a true GvL effect in this disease.

A drive through cellular therapy for CLL in 2015: allogeneic cell transplantation and CARs

Over the past decade the development of safer reduced-intensity conditioning regimens, expanded donor pools, advances in supportive care, and prevention/management of graft-versus-host disease have expanded stem cell transplantation (SCT) availability for chronic lymphocytic leukemia (CLL) patients. However, there are now increasingly active treatment options available for CLL patients with favorable toxicity profiles and convenient administration schedules. This raises the critical issue of whether or not attainment of cure remains a necessary goal. It is now less clear that treatment with curative intention and with significant toxicity is required for long-term survival in CLL. In addition, the demonstrated safety and activity of genetically modified chimeric antigen receptor (CAR) T cells present the opportunity of harnessing the power of the immune system to kill CLL cells without the need for SCT. We attempt to define the role of SCT in the era of targeted therapies and discuss questions that remain to be answered. Furthermore, we highlight the potential for exciting new cellular therapy using genetically modified anti-CD19 CAR T cells and discuss its potential to alter treatment paradigms for CLL.

Non-myeloablative allogeneic hematopoietic stem cell transplantation for adults with relapsed and refractory mantle cell lymphoma: a single-center analysis in the rituximab era

Relapsed and refractory (rel/ref) mantle cell lymphoma (MCL) portends a dismal prognosis. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) represents the only potentially curative therapy in this setting. We analyzed survival outcomes of 29 recipients of non-myeloablative allo-HSCT for rel/ref MCL, and studied possible prognostic factors in this setting. The cumulative incidence of disease progression and non-relapse mortality at 3 years were 28% (95% confidence interval [CI]: 13-46%) and 29% (95%CI: 13-47%), respectively. The cumulative incidence of grade II-IV acute graft-versus-host disease (GVHD) at days +100 and +180 were 34% (95%CI: 18-52%) and 45% (95%CI: 26-62%), respectively. With a median follow-up in survivors of 53 (range 24-83) months, the 3-year overall survival (OS) and progression-free survival (PFS) were 54% (95%CI: 38-76%) and 41% (95%CI: 26-64%), respectively. In vivo T-cell depletion with alemtuzumab (n=6) was associated with inferior 3-year PFS (0% vs. 51%, p=0.007) and OS (17% vs. 64%, p=0.014). Conversely, a second line international prognostic index (sIPI) at transplantation equal to 0 (no risk factors) was associated with an improved 3-year PFS (52% vs. 22%, p=0.020) and OS (71% vs. 22%, p=0.006) compared to sIPI ≥1. Performing an allo-HSCT before 2007 was associated with a decreased 3-year OS (25% vs. 76%, p=0.015) but not with a significantly inferior PFS (17% vs. 59%, p=0.058). In this single center series, we report encouraging results with allo-HSCT for patients with rel/ref MCL. High alemtuzumab doses should probably be avoided in this context.

Outcomes of Cord Blood Transplantation Using Reduced-Intensity Conditioning for Chronic Lymphocytic Leukemia: A Study on Behalf of Eurocord and Cord Blood Committee of Cellular Therapy and Immunobiology Working Party, Chronic Malignancies Working Party of the European Society for Blood and Marrow Transplantation, and the Societé Française de Greffe de Moelle et Therapie Cellulaire

Outcomes after umbilical cord blood transplantation (UCBT) for chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) are unknown. We analyzed outcomes of 68 patients with poor-risk CLL/SLL who underwent reduced-intensity (RIC) UCBT from 2004 to 2012. The median age was 57 years and median follow-up 36 months; 17 patients had del 17p/p53mutation, 19 patients had fludarabine-refractory disease, 11 relapsed after autologous stem cell transplantation, 8 had diagnosis of prolymphocytic leukemia, 4 had Richter syndrome, and 8 underwent transplantation with progressive or refractory disease. The most common RIC used was cyclophosphamide, fludarabine, and total body irradiation (TBI) in 82%; 15 patients received antithymocyte globulin. Most of the cord blood grafts were HLA mismatched and 76% received a double UCBT. Median total nucleated cells collected was 4.7 × 10(7)/kg. The cumulative incidences (CI) of neutrophil and platelet engraftment were 84% and 72% at 60 and 180 days respectively; day 100 graft-versus-host disease (GVHD) (grade II to IV) was 43% and 3-year chronic GVHD was 32%. The CI of relapse, nonrelapse mortality, overall survival, and progression-free survival (PFS) at 3 years were 16%, 39%, 54%, and 45%, respectively. Fludarabine-sensitive disease at transplantation and use of low-dose TBI regimens were associated with acceptable PFS. In conclusion, use of RIC-UCBT seems to be feasible in patients with poor-risk CLL/SLL and improved outcomes were observed in patients with fludarabine-sensitive disease who received low-dose TBI regimens.

The impact of graft-versus-host disease prophylaxis in reduced-intensity conditioning allogeneic stem cell transplant in acute myeloid leukemia: a study from the Acute Leukemia Working Party of the European Group for Blood and Marrow Transplantation

The impact of the intensity of graft-versus-host-disease immunoprophylaxis on transplantation outcomes in patients undergoing transplantation following reduced-intensity conditioning is unclear. This study addresses this issue in 228 adult patients above 50 years of age with acute myeloid leukemia in first complete remission given peripheral blood stem cells from HLA-identical siblings after fludarabine and 2 days of intravenous busulfan reduced-intensity conditioning. A total of 152 patients received anti-thymocyte globulin, either in combination with cyclosporine A in 86 patients (group 1), or with cyclosporine A and mycophenolate mofetil or short course methotrexate in 66 patients (group 2). The remaining 76 patients did not receive anti-thymocyte globulin but were given cyclosporine A and methotrexate or mycophenolate mofetil (group 3). Incidences of grade II-IV acute graft-versus-host-disease were comparable in the three groups (16.5%, 29.5% and 19.5% in groups 1, 2 and 3, respectively, P=0.15). In multivariate analysis, the absence of anti-thymocyte globulin was the only factor associated with a higher risk of chronic graft-versus-host-disease (P=0.005), while the use of triple immunosuppression (group 3) was associated with an increased risk of relapse (P=0.003). In comparison to anti-thymocyte globulin and cyclosporine A alone, the other two strategies of graft-versus-host-disease prophylaxis were associated with reduced leukemia-free survival and overall survival (P=0.001 for each parameter), independently of the dose of anti-thymocyte globulin. These data suggest that fine tuning of the intensity of this prophylaxis can affect the outcome of transplantation and that anti-thymocyte globulin and cyclosporine A alone should be the preferred combination with the fludarabine-busulfan reduced-intensity conditioning regimen and sibling donors.

Prognosis and therapy of chronic lymphocytic leukemia and small lymphocytic lymphoma

Chronic lymphocytic leukemia (CLL) is characterized by a highly variable clinical course that has guided treatment principles in as much as anti-leukemic therapy is reserved for patients with active disease. This heterogeneity is somewhat dissected by prognostic markers, many of which represent pathogenic mechanisms. Recently, the introduction of highly active targeted agents and maturing data on predictive markers may lead to more individualized therapeutic approaches. In this chapter, we review key prognostic markers, current and emerging therapy, and will attempt to outline a future "where the two may connect".

Predictors of outcome in reduced intensity allogeneic hematopoietic cell transplantation for chronic lymphocytic leukemia: summarizing the evidence and highlighting the limitations

Several studies have reported the prognostic significance of various clinical, genetic, biologic and molecular markers on postallogeneic hematopoietic cell transplantation outcomes such as nonrelapse mortality, relapse and survival. Notwithstanding limitations, existence of refractory/progressive disease at allografting yields worse nonrelapse mortality, more relapse and inferior overall survival. Advanced age results in higher nonrelapse mortality and increased relapse risk. Presence of poor-risk cytogenetics increases post-transplant relapse risk, but its impact on overall survival appears controversial. Developing prognostic models using large multicenter data could help better understand the effect of these and other variables on post-transplant outcomes. Newly discovered mutations as well as response (or not) to new potent therapies, such as ibrutinib or others, would likely be incorporated in such models.

Managing high-risk CLL during transition to a new treatment era: stem cell transplantation or novel agents?

Allogeneic hematopoietic stem cell transplantation (HSCT) has been considered as the treatment of choice for patients with high-risk chronic lymphocytic leukemia (HR-CLL; ie, refractory to purine analogs, short response [<24 months] to chemoimmunotherapy, and/or presence of del[17p]/TP53 mutations). Currently, treatment algorithms for HR-CLL are being challenged by the introduction of novel classes of drugs. Among them, BCR signal inhibitors (BCRi) and B-cell lymphoma 2 antagonists (BCL2a) appear particularly promising. As a result of the growing body of favorable outcome data reported for BCRi/BCL2a, uncertainty is emerging on how to advise patients with HR-CLL about indication for and timing of HSCT. This article provides an overview of currently available evidence and theoretical considerations to guide this difficult decision process. Until the risks and benefits of different treatment strategies are settled, all patients with HR-CLL should be considered for treatment with BCRi/BCL2a. For patients who respond to these agents, there are 2 treatment possibilities: (1) performing an HSCT or (2) continuing treatment with the novel drug. Individual disease-specific and transplant-related risk factors, along with patient's preferences, should be taken into account when recommending one of these treatments over the other.

Paradigm shifts in the management of poor-risk chronic lymphocytic leukemia

With the growing complexity of treatment options for chronic lymphocytic leukemia (CLL) and variables that influence the underlying biology of this disease, providing allogeneic stem cell transplant (alloSCT) to appropriate candidates poses a challenge for transplant physicians. Novel small molecule inhibitors hold unprecedented promise for poor-risk subgroups, which will likely alter decision-making and referral patterns for transplant. In this review, we analyze what is known and may still remain true about indications for transplant based on outcomes reported in the literature recently and over the last decade.

Role of allogeneic transplantation in patients with chronic lymphocytic leukemia in the era of novel therapies: a review

Chronic lymphocytic leukemia (CLL) is the most common form of adult leukemia and is characterized by a highly variable clinical course. In the past decade, several prognostic risk factors have been identified facilitating the classification of CLL into various risk groups. Patients with poor risk disease, such as poor cytogenetics or relapsing after purine-based analogues, had limited therapeutic options, with allogeneic hematopoietic cell transplantation (allo-SCT) the only known therapy with curative potential. More recently, the introduction of novel agents inhibiting the B-cell receptor pathway, and the early success with chimeric antigen receptor T cells offers an effective and relatively safe option for this poor prognostic group which holds promise in the future. Alternatively, the use of reduced intensity conditioning regimens in the allo-SCT setting has led to a significant decrease in nonrelapse mortality to 16-23%, making it an attractive therapeutic option. No recent guidelines have been developed since these novel therapies became available regarding the optimal time to allo-SCT in this patient population. The advent of these novel and highly active therapeutic agents, therefore, warrants a reappraisal of the role and timing of allo-SCT in patients with CLL. In this article, we summarize the literature regarding the novel therapeutic agents available today as well as focus on the efficacy and safety of allo-SCT.

Transplantation in chronic lymphocytic leukemia: does it still matter in the era of novel targeted therapies?

Allogeneic stem cell transplantation (HSCT) offers the only potentially curative approach in chronic lymphocytic leukemia (CLL). However, this applies only to a minority of patients, and is associated with significant treatment-related mortality and morbidity. HSCT must therefore always be considered in view of other, potentially less toxic therapies. Several new agents demonstrate impressive and durable responses in high-risk patients who might be candidates for HSCT. Therefore the choice of HSCT versus a novel agent is one that must be gauged on a patient-by-patient basis; this will change as data mature on the use of these novel agents in CLL.

Outcomes of human leukocyte antigen-matched sibling donor hematopoietic cell transplantation in chronic lymphocytic leukemia: myeloablative versus reduced-intensity conditioning regimens

Allogeneic hematopoietic cell transplantation (HCT) can cure some chronic lymphocytic leukemia (CLL) subjects. This study compared outcomes of myeloablative (MA) and reduced-intensity conditioning (RIC) transplants from HLA-matched sibling donors (MSD) for CLL. From 1995 to 2007, information regarding 297 CLL subjects was reported to the Center of International Blood and Marrow Transplant Research; of these, 163 underwent MA and 134 underwent RIC MSD HCT. The MA subjects underwent transplantation less often after 2000 and less commonly received antithymocyte globulin (4% versus 13%, P = .004) or prior antibody therapy (14% versus 53%; P < .001). RIC was associated with a greater likelihood of platelet recovery and less grade 2 to 4 acute graft-versus-host disease compared with MA conditioning. One- and 5-year treatment-related mortality (TRM) were 24% (95% confidence intervals [CI], 16% to 33%) versus 37% (95% CI, 30% to 45%; P = .023), and 40% (95% CI, 29% to 51%) versus 54% (95% CI, 46% to 62%; P = .036), respectively, and the relapse/progression rates at 1 and 5 years were 21% (95% CI, 14% to 29%) versus 10% (95% CI, 6% to 15%; P = .020), and 35% (95% CI, 26% to 46%) versus 17% (95% CI, 12% to 24%; P = .003), respectively. MA conditioning was associated with better progression-free (PFS) (relative risk, .60; 95% CI, .37 to .97; P = .038) and 3-year survival in transplantations before 2001, but for subsequent years, RIC was associated with better PFS and survival (relative risk, 1.49 [95% CI, .92 to 2.42]; P = .10; and relative risk, 1.86 [95% CI, 1.11 to 3.13]; P = .019). Pretransplantation disease status was the most important predictor of relapse (P = .003) and PFS (P = .0007) for both forms of transplantation conditioning. MA and RIC MSD transplantations are effective for CLL. Future strategies to decrease TRM and reduce relapses are warranted.

The impact of allogeneic stem cell transplantation on the natural course of poor-risk chronic lymphocytic leukemia as defined by the EBMT consensus criteria: a retrospective donor versus no donor comparison

BACKGROUND

In a single-center retrospective donor versus no-donor comparison, we investigated if allogeneic stem cell transplantation (alloSCT) can improve the dismal course of poor-risk chronic lymphocytic leukemia (CLL).

PATIENTS AND METHODS

All patients with CLL who were referred for evaluation of alloSCT within a 7-year time frame and had a donor search indication according to the EBMT criteria or because of Richter's transformation were included. Patients for whom a matched donor could be found within 3 months (matches) were compared with patients without such a donor (controls). Primary end point was overall survival measured from the 3-month landmark after search initiation.

RESULTS

Of 105 patients with donor search, 97 (matches 83; controls 14) were assessable at the 3-month landmark. Matches and controls were comparable for age, gender, time from diagnosis, number of previous regimens, and remission status. Disregarding if alloSCT was actually carried out or not, survival from the 3-month landmark was significantly better in matches versus controls [hazard ratio 0.38, 95% confidence interval (CI) 0.17-0.85; P = 0.014]. The survival benefit of matches remained significant on multivariate analysis.

CONCLUSION

This study provides first comparative evidence that alloSCT may have the potential to improve the natural course of poor-risk CLL as defined by the EBMT criteria.

Boosting leukemia-specific T cell responses in patients following stem cell transplantation

Whole tumor cell-based vaccines administered within the first 2 to 3 months after allogeneic stem cell transplantation stand out as a promising approach to enhance graft-vs.-leukemia responses. Herein, the implications of this finding for the development of strategies to improve the outcome of patients subjected to allogeneic stem cell transplantation are discussed.

Low tumor burden is associated with early B-cell reconstitution and is a predictor of favorable outcome after non-myeloablative stem cell transplant for chronic lymphocytic leukemia

Abstract Reconstitution, engraftment kinetics and tumor cell clearance were analyzed after reduced intensity conditioning hematopoietic cell transplant (RIC-HCT) in patients with chronic lymphocytic leukemia (CLL). Patients were transplanted from unrelated (n = 40) or related (n = 10) donors after fludarabine and 2 Gy total body irradiation followed by cyclosporine and mycophenolate mofetil. The vast majority of patients (96%) engrafted with absolute neutrophil count (ANC) > 0.5 × 10(9)/L at day + 22. CLL cells decreased (median 2%, range 0-69%) within 28 days, but disappeared by day + 180 after HCT. Donor T-cell chimerism increased to > 95% at day 56 and donor B-cell chimerism to 94% at day + 360. Overall survival was 51 ± 8%, incidence of progression 37 ± 7% and non-relapse related mortality (NRM) 30 ± 7% at 4 years. The most common causes of NRM were graft-versus-host disease (GvHD) (14%) and sepsis (6%). Disease status at HCT was significantly associated with early B-cell reconstitution (p = 0.04) and with increased risk of relapse/progression in univariate and multivariate analysis (p = 0.022). Tumor cells were undetectable by day + 180, although B-cell reconstitution did not occur until 1.5 years after RIC-HCT. The best predictors for progression-free survival (PFS) and overall survival (OS) were complete response (CR) or first partial response (PR1) and the absence of bulky disease at transplant, respectively.

Understanding the immunodeficiency in chronic lymphocytic leukemia: potential clinical implications

Chronic lymphocytic leukemia (CLL) is the most common leukemia in adults. Although significant advances have been made in the treatment of CLL in the last decade, it remains incurable. Treatments may be too toxic for some elderly patients, who constitute most of the individuals with this disease, and there remain subgroups of patients for which this therapy has minimal activity. This article summarizes the current understanding of the immune defects in CLL. It also examines the potential clinical implications of these findings.

Reduced-intensity conditioning allogeneic stem cell transplantation in malignant lymphoma: current status

Allogeneic stem cell transplantation (allo-SCT) is a potential cure for patients with malignant lymphoma that is based on the graft-versus-lymphoma (GVL) effect. Myeloablative conditioning allo-SCT is associated with high mortality and morbidity, particularly in patients older than 45 years, heavily pretreated patients (prior hematopoietic stem cell transplantation or more than two lines of conventional chemotherapy) or patients affected by other comorbidities. Therefore, conventional allo-SCT is restricted to younger patients (<50 to 55 years) in good physical condition. Over the last decade, allo-SCT with reduced-intensity conditioning (RIC-allo-SCT) has been increasingly used to treat patients with lymphoma. This treatment is associated with lower toxicity and substantial decrease in the incidence of transplant-related mortality, and has the potential to lead to long-term remissions. Therefore, patients who are not suitable to undergo conventional allo-SCT can benefit from the potentially curative GVL effects of allo-SCT. Although RIC-allo-SCT has improved the survival of lymphoma patients, high post-transplant relapse rates or disease progression mainly results in treatment failure. Thus, further improvement is clearly needed. The role and timing of RIC-allo-SCT in the treatment of lymphoma remains unclear. Therefore, more prospective studies should clarify the effectiveness of this method. In this article, we review the recent literature on RIC-allo-SCT as a treatment for major lymphoma subtypes. Areas that require further investigation in the context of clinical trials are also highlighted.

Cellular therapy following allogeneic stem-cell transplantation

Allogeneic hematopoietic stem-cell transplantation (HSCT) is the most effective approach for many patients with hematologic malignancies. Unfortunately, relapse remains the most common cause of death after allogeneic HSCT, and the prognosis of relapsed disease is poor for most patients. Induction of a graft-versus-leukemia (GVL), or graft-versus-tumor, effect through the use of donor leukocyte infusion (DLI), or donor lymphocyte infusion, has been remarkably successful for relapsed chronic myelogenous leukemia. Unfortunately, response to DLI in other hematologic malignancies is much less common and depends on many factors including histology, pace and extent of relapse, and time from HSCT to relapse. Furthermore, graft-versus-host disease (GVHD) is common after DLI and often limits successful immunotherapy. Ultimately, manipulations to minimize GVHD while preserving or enhancing GVL are necessary to improve outcomes for relapse after allogeneic HSCT.

Chronic lymphocytic leukemia: inception to cure: are we there?

There have been remarkable advances in our understanding of the biology and therapeutics of chronic lymphocytic leukemia. B cell receptor signaling and micro-environment in CLL biology have been the most modern areas of research. In CLL therapeutics, we have come a long way from alkylating agents to chemo-immunotherapy. Despite this there remain significant lacunae in the disease biology that has hindered our quest to achieve the ultimate in CLL: Cure. This review aims to summarize the past, present and future in the biology and treatment of CLL.

Risk-stratified adoptive cellular therapy following allogeneic hematopoietic stem cell transplantation for advanced chronic lymphocytic leukaemia

Following reduced intensity-conditioned allogeneic stem cell transplantation (RIC allo-SCT) for chronic lymphocytic leukaemia (CLL), there is an inverse relationship between relapse and extensive chronic graft-versus-host disease (GVHD). We evaluated outcomes in 50 consecutive patients with CLL using the approach of alemtuzumab-based RIC allo-SCT and pre-emptive donor lymphocyte infusions (DLI) for mixed chimerism or minimal residual disease (MRD), with the intention of reducing the risk of GVHD. Forty two patients had high-risk disease, including 30% with 17p deletion (17p-). Of patients who were not in complete remission (CR) entering transplant, 83% subsequently achieved MRD-negative CR. Both MRD detection and uncorrected mixed chimerism were associated with greater risks of treatment failure. Nine of sixteen patients receiving DLI for persistent or relapsed disease subsequently attained MRD-negative CR. With a median follow-up of 4.3 years, 4-year current progression-free survival was 65% and overall survival was 75% (60% and 61% in respectively, patients with 17p-). DLI was associated with a 29% cumulative incidence of severe GVHD and mortality of 6.4%. At last follow-up, 83% of patients in CR were off all immunosuppressive treatment. In conclusion, the directed delivery of allogeneic cellular therapy has the potential to induce durable remissions in high-risk CLL without incurring excessive GVHD.

Immunotherapies in CLL

Chronic lymphocytic leukemia (CLL) is the most frequently diagnosed leukemia in the Western world, yet remains essentially incurable. Although initial chemotherapy response rates are high, patients invariably relapse and subsequently develop resistance to chemotherapy. For the moment, allogeneic hematopoietic stem cell transplant (allo-HSCT) remains the only potentially curative treatment for patients with CLL, but it is associated with high rates of treatment-related mortality. Immune-based treatment strategies to augment the cytotoxic potential of T cells offer exciting new treatment options for patients with CLL, and provide a unique and powerful spectrum of tools distinct from traditional chemotherapy. Among the most novel and promising of these approaches are chimeric antigen receptor (CAR)-based cell therapies that combine advances in genetic engineering and adoptive immunotherapy.

[Conventional therapeutic strategies for relapsed chronic lymphocytic leukemia]

The choice of salvage therapy for patients presenting relapsed chronic lymphocytic leukemia (CLL) has to take into account some factors influencing tumor resistance and comorbidities. Since 2010, new drugs targeting the tumor cells' signaling have been proposed for CLL patients. Waiting the results of various clinical trials evaluating these treatments, there is a need to describe the state-of-the-art concerning approved treatments such as chemotherapy and monoclonal antibodies.

Two days of antithymocyte globulin are associated with a reduced incidence of acute and chronic graft-versus-host disease in reduced-intensity conditioning transplantation for hematologic diseases

BACKGROUND

The optimal combination of fludarabine, busulfan, and antithymocyte globulin (ATG) for reduced-intensity conditioning (RIC) transplantation has not been established. ATG plays a pivotal role in the prevention of graft-versus-host disease (GvHD), but it is associated with a higher relapse rate and an elevated incidence of infections when high doses are used.

METHODS

The authors retrospectively compared 2 different doses of ATG combined with fludarabine and busulfan in 229 adult patients who underwent transplantation at their institution. ATG was administered over 1 day (FBA1) or over 2 days (FBA2) at a daily dose of 2.5 mg/kg.

RESULTS

There were 124 patients in the FBA2 cohort and 105 patients in the FBA2 cohorts. Patients in the FBA2 cohort were older and more frequently underwent transplantation from an unrelated donor; 93% of patients in the FBA2 cohort received intravenous busulfan versus only 5% in the FBA1 cohort. The incidence of grade 2 through 4 acute GvHD was 23% in the FBA2 cohort versus 42% in the FBA1 cohort (P = .002); the incidence of grade 3 through 4 acute GvHD was 10% versus 23%, respectively (P = .006); and the incidence of chronic GvHD was 35% versus 69%, respectively (P < .0001). The 2-year rates of overall survival, nonrelapse mortality, and relapse/progression for the FBA1 and FBA2 cohorts were 65% versus 67%, respectively (P = .99), 20% versus 19%, respectively (P = .61), and 30% versus 19%, respectively (P = .09). The results were confirmed in multivariate analysis.

CONCLUSIONS

The use of ATG at a dose of 5 mg/kg was correlated significantly with reduced incidence and severity of GvHD without impairing disease control. Taken together, the current results suggest that this conditioning represents a step forward in the optimization of RIC.

Autologous and Allogeneic Stem-Cell Transplantation for Transformed Chronic Lymphocytic Leukemia (Richter's Syndrome): A Retrospective Analysis From the Chronic Lymphocytic Leukemia Subcommittee of the Chronic Leukemia Working Party and Lymphoma Working Party of the European Group for Blood and Marrow Transplantation

Purpose

Patients with Richter's syndrome (RS) have a poor prognosis with conventional chemotherapy. The aim of this study was to evaluate the outcome after autologous stem-cell transplantation (autoSCT) or allogeneic stem-cell transplantation (alloSCT) in RS.

Patients and Methods

A survey was sent to all European Group for Blood and Marrow Transplantation centers assessing transplantations performed for RS. Eligibility criteria included a diagnosis of RS or secondary lymphoma before SCT, age ≥ 18 years, and SCT performed from 1997 to 2007. Data were analyzed by descriptive statistics and methods from survival analysis.

Results

Fifty-nine patients were registered. Thirty-four patients had received autoSCT, mostly because of chemotherapy-sensitive disease, and 25 had received alloSCT, with 36% being refractory to chemotherapy at SCT. In 18 allograft recipients (72%), reduced-intensity conditioning (RIC) was used. Three-year estimates of the probabilities of overall survival and relapse-free survival (RFS) and the cumulative incidences of relapse and nonrelapse mortality were 36%, 27%, 47%, and 26% for alloSCT and 59%, 45%, 43%, and 12% for autoSCT, respectively. Taking into account the limitations set by the low number of events and age younger than 60 years, chemotherapy-sensitive disease and RIC were found to be associated with superior RFS after alloSCT in multivariate analysis. Factors with a significant impact on autoSCT could not be identified.

Conclusion

Patients with RS who are sensitive to induction chemotherapy appear to benefit from consolidation with transplantation strategies, and prolonged survival was observed in a proportion of patients.

Primary B-CLL resistance to NK cell cytotoxicity can be overcome in vitro and in vivo by priming NK cells and monoclonal antibody therapy

Despite recent advances with monoclonal antibody therapy, chronic lymphocytic leukemia (CLL) remains incurable. Natural killer (NK) cells are potent antitumoral effectors, particularly against hematological malignancies. Defective recognition of B-CLL leukemic cells by NK cells has been previously described. Here, we deciphered the mechanisms that hamper NK cell-mediated clearance of B-CLL and evaluated the potential of NK cells as therapeutic tools for treatment of CLL. First of all, leukemic B cells resemble to normal B cells with a weak expression of ligands for NK receptors. Conversely, NK cells from B-CLL patients were functionally and phenotypically competent, despite a decrease of expression of the activating receptor NKp30. Consequently, resting allogeneic NK cells were unable to kill leukemic B cells in vitro. These data suggest that patients' NK cells cannot initiate a proper immune reaction due to a lack of leukemic cell recognition. We next set up a xenotransplantation mouse model to study NK-CLL cell interactions. Together with our in vitro studies, in vivo data revealed that activation of NK cells is required in order to control B-CLL and that activated NK cells synergize to enhance rituximab effect on tumor load. This study points out the requirements for immune system manipulation for treatment of B-CLL in combination with monoclonal antibody therapy.