Comparison between antithymocyte globulin and alemtuzumab and the possible impact of KIR-ligand mismatch after dose-reduced conditioning and unrelated stem cell transplantation in patients with multiple myeloma

The Evolution Of Immune Dysfunction In Multiple Myeloma

OBJECTIVES

This review discusses the role of immune dysfunction at the different stages of MM.

METHODS

Narrative review RESULTS: Multiple myeloma (MM) is a complex disease and immune dysfunction has been known to play an important role in disease pathogenesis, progression, and drug resistance. MM is known to be preceded by asymptomatic precursor states and progression from the precursor states to MM is likely related to a progressive impairment of the immune system.

CONCLUSIONS

An understanding of the role of the immune system in the progression of MM is important to guide the development of immunotherapeutic strategies for this disease.

Blocking the PCNA/NKp44 Checkpoint to Stimulate NK Cell Responses to Multiple Myeloma

Simple Summary

Membrane-associated PCNA is expressed on the surface of human MM cell lines and primary MM cells. Mab 14-25-9 interacts with membrane-associated PCNA and blocks its binding to NK-expressed NKp44, thus activating NK function. We showed that mAb 14-25-9 can serve as an immune checkpoint blocker, enhancing the function of NK cells on target human MM cell lines and primary cells.

Abstract

Multiple Myeloma (MM) is a devastating malignancy that evades immune destruction using multiple mechanisms. The NKp44 receptor interacts with PCNA (Proliferating Cell Nuclear Antigen) and may inhibit NK cells’ functions. Here we studied in vitro the expression and function of PCNA on MM cells. First, we show that PCNA is present on the cell membrane of five out of six MM cell lines, using novel anti-PCNA mAb developed to recognize membrane-associated PCNA. Next, we stained primary bone marrow (BM) mononuclear cells from MM patients and showed significant staining of membrane-associated PCNA in the fraction of CD38⁺CD138⁺ BM cells that contain the MM cells. Importantly, blocking of the membrane PCNA on MM cells enhanced the activity of NK cells, including IFN-γ-secretion and degranulation. Our results highlight the possible blocking of the NKp44-PCNA immune checkpoint by the mAb 14-25-9 antibody to enhance NK cell responses against MM, providing a novel treatment option.

Role and Modulation of NK Cells in Multiple Myeloma

Myeloma tumor cells are particularly dependent on their microenvironment and sensitive to cellular antitumor immune response, including natural killer (NK) cells. These later are essential innate lymphocytes implicated in the control of viral infections and cancers. Their cytotoxic activity is regulated by a balance between activating and inhibitory signals resulting from the complex interaction of surface receptors and their respective ligands. Myeloma disease evolution is associated with a progressive alteration of NK cell number, phenotype and cytotoxic functions. We review here the different therapeutic approaches that could restore or enhance NK cell functions in multiple myeloma. First, conventional treatments (immunomodulatory drugs-IMids and proteasome inhibitors) can enhance NK killing of tumor cells by modulating the expression of NK receptors and their corresponding ligands on NK and myeloma cells, respectively. Because of their ability to kill by antibody-dependent cell cytotoxicity, NK cells are important effectors involved in the efficacy of anti-myeloma monoclonal antibodies targeting the tumor antigens CD38, CS1 or BCMA. These complementary mechanisms support the more recent therapeutic combination of IMids or proteasome inhibitors to monoclonal antibodies. We finally discuss the ongoing development of new NK cell-based immunotherapies, such as ex vivo expanded killer cell immunoglobulin-like receptors (KIR)-mismatched NK cells, chimeric antigen receptors (CAR)-NK cells, check point and KIR inhibitors.

Haploidentical transplantation in patients with multiple myeloma making use of natural killer cell alloreactive donors

Disease relapse is an important problem after allogeneic stem cell transplantations in multiple myeloma (MM). To test the hypothesis that natural killer (NK) cell alloreactivity in the setting of a haploidentical stem cell transplantation (haploSCT) can reduce the risk of myeloma relapse, we performed a small prospective phase 2 study in which we transplanted poor-risk MM patients using a killer cell immunoglobulin-like receptor (KIR)-ligand mismatched haploidentical donor. Patients received bone marrow grafts after reduced-intensity conditioning, with post-transplantation cyclophosphamide (PTCY) graft-versus-host-disease (GVHD) prophylaxis. The primary endpoint was 1.5-year progression-free survival (PFS); stopping rules were installed in case interim results made a benefit of 50% PFS at 1.5 years unlikely. After inclusion of 12 patients, of which 9 were evaluable for the primary endpoint, all patients relapsed within a median time of 90 days. All except 1 patient showed engraftment, with a median time to neutrophil recovery of 18 (12–30) days. The study was prematurely terminated based on the predefined stopping rules after the inclusion of 12 patients. With this small study, we show that in chemo-resistant myeloma patients, NK cell KIR-mismatch is not superior to conventional alloSCT. This strategy, however, can serve as a platform for new treatment concepts.

Clinical Trial Registry: NCT02519114

Long-Term Follow-up of CALGB (Alliance) 100001: Autologous Followed by Nonmyeloablative Allogeneic Transplant for Multiple Myeloma

CALGB (Alliance) 100001 was a phase II study evaluating autologous stem cell transplant (ASCT) followed by nonmyeloablative allogeneic stem cell transplant (alloSCT) in patients with multiple myeloma who had received no more than 18 months of prior therapy and had experienced no more than 1 prior progression event. Conditioning for ASCT was with high-dose melphalan (200 mg/m²). The alloSCT reduced-intensity conditioning (RIC) regimen consisted of fludarabine (30 mg/m²/d i.v. on days -7 through -3) and cyclophosphamide (1 g/m²/d i.v. on days -4 through -3). The primary objective was to determine the 6-month post-alloSCT treatment-related mortality (TRM) rate. Additional objectives included determining the proportion of patients who could complete this tandem ASCT-alloSCT approach in a cooperative group setting, overall response rates, rates of donor chimerism, rates of graft-versus-host disease (GVHD), disease-free survival, and overall survival (OS). Sixty patients were enrolled, of whom 57 (95%) completed ASCT and 49 (82%) completed tandem ASCT-alloSCT. The TRM rate was 2% (1/49; 90% confidence interval, 0.10% to 9.3%). Moderate to severe (grades 2 to 3) acute GVHD was observed in 13 of 49 alloSCT patients (27%). One patient died due to GVHD within 9 months of alloSCT. Twenty-seven of the 49 patients (55%) who underwent alloSCT reported chronic GVHD as either limited (15/49; 31%) or extensive (12/49; 24%) in the first year post-alloSCT and prior to the start of nonprotocol therapy for progressive disease. With a median follow-up for survival of 11 years, the median OS time is 6.6 years and the median time to disease progression is 3.6 years. Similar to other studies, this study confirmed that tandem ASCT/alloSCT is associated with durable disease control in a subset of patients. This study demonstrated the feasibility of performing tandem ASCT/alloSCT in a cooperative group setting and determined that a fludarabine/cyclophosphamide RIC regimen is associated with a very low TRM rate.

Presence of donor-encoded centromeric KIR B content increases the risk of infectious mortality in recipients of myeloablative, T-cell deplete, HLA-matched HCT to treat AML

The reported influence of donor Killer-cell Immunoglobulin-like Receptor (KIR) genes on the outcomes of haematopoietic cell transplantation (HCT) are contradictory, in part due to diversity of disease, donor sources, era and conditioning regimens within and between different studies. Here, we describe the results of a retrospective clinical analysis establishing the effect of donor KIR motifs on the outcomes of 119 HLA-matched, unrelated donor HCT for adult acute myeloid leukaemia (AML) using myeloablative conditioning (MAC) in a predominantly T-cell deplete (TCD) cohort. We observed that HCT involving donors with at least one KIR B haplotype were more likely to result in non-relapse mortality (NRM) than HCT involving donors with two KIR A haplotypes (p = 0.019). Upon separation of KIR haplotypes into their centromeric (Cen) and telomeric (Tel) motif structures, we demonstrated that the Cen-B motif was largely responsible for this effect (p = 0.001). When the cause of NRM was investigated further, infection was the dominant cause of death (p = 0.006). No evidence correlating donor KIR B haplotype with relapse risk was observed. The results from this analysis confirm previous findings in the unrelated, TCD, MAC transplant setting and imply a protective role for donor-encoded Cen-A motifs against infection in allogeneic HCT recipients.

Tuning Natural Killer Cell Anti-multiple Myeloma Reactivity by Targeting Inhibitory Signaling via KIR and NKG2A

Natural killer (NK) cells are attractive candidates for allogeneic cell-based immunotherapy due to their potent antitumor effector function and good safety profile. NK cells express killer immunoglobulin-like receptors (KIRs) and the NKG2A receptor important for NK cells education as well as providing inhibitory signals upon encountering HLA-expressing target cells. Multiple myeloma (MM) is an example of a tumor expressing relatively high levels of HLA molecules. In this review, we discuss the functional relevance of inhibitory KIRs and NKG2A for NK cells anti-MM response and strategies to lower these inhibitory signaling to enhance clinical efficacy of allogeneic NK cells in MM.

Mechanisms of NK Cell Activation and Clinical Activity of the Therapeutic SLAMF7 Antibody, Elotuzumab in Multiple Myeloma

Multiple myeloma (MM) is a bone marrow plasma cell neoplasm and is the second most-common hematologic malignancy. Despite advances in therapy, MM remains largely incurable. Elotuzumab is a humanized IgG1 monoclonal antibody targeting SLAMF7, which is highly expressed on myeloma cells, and the antibody is approved for the treatment of relapsed and/or refractory (RR) MM in combination with lenalidomide and dexamethasone. Elotuzumab can stimulate robust antibody-dependent cellular cytotoxicity (ADCC) through engaging with FcγRIIIA (CD16) on NK cells and antibody-dependent cellular phagocytosis (ADCP) by macrophages. Interestingly, SLAMF7 is also expressed on cytolytic NK cells, which also express the requisite adaptor protein, EAT-2, to mediate activation signaling. Accumulating evidence indicates that antibody crosslinking of SLAMF7 on human and mouse NK cells can stimulate EAT-2-dependent activation of PLCγ, ERK, and intracellular calcium mobilization. The binding of SLAMF7 by elotuzumab can directly induce signal transduction in human NK cells, including co-stimulation of the calcium signaling triggered through other surface receptors, such as NKp46 and NKG2D. In RRMM patients, elotuzumab monotherapy did not produce objective responses, but did enhance the activity of approved standard of care therapies, including lenalidomide or bortezomib, which are known to enhance anti-tumor responses by NK cells. Taken together, these preclinical results and accumulating experience in the clinic provide compelling evidence that the mechanism of action of elotuzumab in MM patients involves the activation of NK cells through both CD16-mediated ADCC and direct co-stimulation via engagement with SLAMF7, as well as promoting ADCP by macrophages. We review the current understanding of how elotuzumab utilizes multiple mechanisms to facilitate immune-mediated attack of myeloma cells, as well as outline goals for future research.

Translating the anti-myeloma activity of Natural Killer cells into clinical application

Natural Killer cells (NK) are innate effector cells with a critical role in immunosurveillance against different kinds of cancer cells, including Multiple Myeloma (MM). However, the number and/or function of these lymphocytes are strongly reduced during MM progression and in advanced clinical stages. A better understanding of the mechanisms controlling both MM and NK cell biology have greatly contributed to develop novel and combined therapeutic strategies in the treatment of this incurable hematologic malignancy. These include approaches to reverse the immunosuppressive MM microenvironment or potentiate the natural or antibody-dependent cellular cytotoxicity (ADCC) of NK cells. Moreover, chemotherapeutic drugs or specific monoclonal antibodies (mAbs) can render cancer cells more susceptible to NK cell-mediated recognition and lysis; direct enhancement of NK cell function can be obtained by means of immunomodulatory drugs, cytokines and blocking mAbs targeting NK cell inhibitory receptors. Finally, adoptive transfer of ex-vivo expanded and genetically manipulated NK cells is also a promising therapeutic tool for MM. Here, we review current knowledge on complex mechanisms affecting NK cell activity during MM progression. We also discuss recent advances on innovative approaches aimed at boosting the functions of these cytotoxic innate lymphocytes. In particular, we focus our attention on recent preclinical and clinical studies addressing the therapeutic potential of different NK cell-based strategies for the management of MM.

Cytomegalovirus: an unlikely ally in the fight against blood cancers?

Cytomegalovirus (CMV) infection is a potentially fatal complication in patients receiving haematopoietic stem cell transplantation (HSCT), but recent evidence indicates that CMV has strong anti-leukaemia effects due in part to shifts in the composition of natural killer (NK) cell subsets. NK cells are the primary mediators of the anti-leukaemia effect of allogeneic HSCT, and infusion of allogeneic NK cells has shown promise as a means of inducing remission and preventing relapse of several different haematological malignancies. The effectiveness of these treatments is limited, however, when tumours express human leucocyte antigen (HLA)-E, a ligand for the inhibitory receptor NKG2A, which is expressed by the vast majority of post-transplant reconstituted and ex-vivo expanded NK cells. It is possible to enhance NK cell cytotoxicity against HLA-Epos malignancies by increasing the proportion of NK cells expressing NKG2C (the activating receptor for HLA-E) and lacking the corresponding inhibitory receptor NKG2A. The proportion of NKG2Cpos /NKG2Aneg NK cells is typically low in healthy adults, but it can be increased by CMV infection or ex-vivo expansion of NK cells using HLA-E-transfected feeder cells and interleukin (IL)-15. In this review, we will discuss the role of CMV-driven NKG2Cpos /NKG2Aneg NK cell expansion on anti-tumour cytotoxicity and disease progression in the context of haematological malignancies, and explore the possibility of harnessing NKG2Cpos /NKG2Aneg NK cells for cancer immunotherapy.

Anti-thymocyte globulin improves survival free from relapse and graft-versus-host disease after allogeneic peripheral blood stem cell transplantation in patients with Philadelphia-negative acute lymphoblastic leukemia: An analysis by the Acute Leukemia Working Party of the EBMT

BACKGROUND

Mobilized peripheral blood stem cells are currently the predominant source of grafts for allogeneic transplantation (allogeneic peripheral blood stem cell transplantation [allo-PBSCT]), although, in comparison with bone marrow, their use is associated with an increased risk of chronic graft-versus-host disease (cGVHD). Attempts to reduce the incidence of cGVHD include the addition of anti-thymocyte globulin (ATG) to the pretransplant conditioning regimen.

METHODS

The goal of this retrospective study was to analyze the effect of ATG on allo-PBSCT outcomes for adults with Philadelphia-negative acute lymphoblastic leukemia (Ph-neg ALL). The primary endpoint was survival free from relapse, grade 3 to 4 acute graft-versus-host disease (aGVHD), and cGVHD (ie, graft-versus-host disease-free/relapse-free survival [GRFS]). Nine-hundred twenty-four patients who underwent unmanipulated allo-PBSCT in their first complete remission between 2007 and 2016 were included. ATG was used in 97 of the 494 transplants from matched sibling donors (20%) and in 307 of the 430 transplants from human leukocyte antigen-matched (8 of 8 loci) unrelated donors (71%).

RESULTS

The use of ATG was an independent factor for an improved chance of GRFS (hazard ratio [HR], 0.70; P = .0009). Furthermore, it was associated with a reduced risk of both grade 2 to 4 (HR, 0.66; P = .005) and grade 3 to 4 aGVHD (HR, 0.58; P = .03). Similarly, its addition reduced the incidence of both total (HR, 0.45; P < 10^-5 ) and extensive cGVHD (HR, 0.30; P < 10^-5 ) as well as nonrelapse mortality (HR, 0.58; P = .01). No significant effect was found with respect to leukemia-free or overall survival. However, an increased risk of relapse was noted for those who received ATG (HR, 1.40; P = .04).

CONCLUSIONS

Patients with Ph-neg ALL treated with allo-PBSCT benefit from the use of ATG in terms of improved GRFS. Its use may, therefore, be considered in this setting. Cancer 2018;124:2523-33. © 2018 American Cancer Society.

No indication of increased infection rates using low-dose alemtuzumab instead of anti-thymocyte globulin as graft-versus-host disease prophylaxis before allogeneic stem cell transplantation

BACKGROUND

Alemtuzumab as part of the conditioning protocol is effective in reducing graft-versus-host disease (GvHD), but may be associated with increased infection rates, especially when using high doses (ie, 100 mg).

METHODS

We performed a retrospective, single-center, case-control study analyzing the rates of neutropenic fever, cytomegalovirus (CMV) reactivation, Epstein-Barr virus (EBV) reactivation, clinical manifest toxoplasmosis, and clinical manifest human herpesvirus-6 (HHV6) infection using low-dose alemtuzumab in comparison with anti-thymocyte globulin (ATG) as GvHD prophylaxis before allogeneic stem cell transplantation. Forty-four patients transplanted from unrelated donors between 2001 and 2012 were matched by age, diagnosis, and conditioning regimen and treated either with alemtuzumab 10 mg at day -2 (respectively, 20 mg in case of mismatch transplantation) or ATG. ATG Fresenius (10 mg/kg for 3 days) or Thymoglobulin (2 mg/kg for 3 days) were used.

RESULTS

Rates of CMV reactivation, EBV reactivation, and clinical manifest HHV6 infection or toxoplasmosis did not differ significantly between both groups until 2 years after transplantation. No case of post-transplant lymphoproliferative disorder was observed. Also, rates of neutropenic fever during inpatient treatment after transplantation did not differ significantly in both groups.

CONCLUSION

We saw no indication of increased infections rates when using low-dose alemtuzumab as GvHD prophylaxis before allogeneic stem cell transplantation in this retrospective analysis.

Allograft for Myeloma: Examining Pieces of the Jigsaw Puzzle

Multiple myeloma (MM) cure remains elusive despite the availability of newer anti-myeloma agents. Patients with high-risk disease often suffer from early relapse and short survival. Allogeneic hematopoietic cell transplantation (allo-HCT) is an “immune-based” therapy that has the potential to offer long-term remission in a subgroup of patients, at the expense of high rates of transplant-related morbidity and mortality. Donor lymphocyte infusion (DLI) upon disease relapse after allo-HCT is able to generate an anti-myeloma response suggestive of a graft-versus-myeloma effect. Allo-HCT provides a robust platform for additional immune-based therapy upon relapse including DLI and, maintenance with immunomodulatory drugs and immunosuppressive therapy. There have been conflicting findings from randomized prospective trials questioning the role of allo-HCT. However, to this date, allo-HCT remains the only potential curable treatment for MM and its therapeutic role needs to be better defined especially for patients with high-risk disease. This review examines different aspects of this treatment and summarizes ongoing attempts at improving its therapeutic index.

Restoring Natural Killer Cell Immunity against Multiple Myeloma in the Era of New Drugs

Transformed plasma cells in multiple myeloma (MM) are susceptible to natural killer (NK) cell-mediated killing via engagement of tumor ligands for NK activating receptors or “missing-self” recognition. Similar to other cancers, MM targets may elude NK cell immunosurveillance by reprogramming tumor microenvironment and editing cell surface antigen repertoire. Along disease continuum, these effects collectively result in a progressive decline of NK cell immunity, a phenomenon increasingly recognized as a critical determinant of MM progression. In recent years, unprecedented efforts in drug development and experimental research have brought about emergence of novel therapeutic interventions with the potential to override MM-induced NK cell immunosuppression. These NK-cell enhancing treatment strategies may be identified in two major groups: (1) immunomodulatory biologics and small molecules, namely, immune checkpoint inhibitors, therapeutic antibodies, lenalidomide, and indoleamine 2,3-dioxygenase inhibitors and (2) NK cell therapy, namely, adoptive transfer of unmanipulated and chimeric antigen receptor-engineered NK cells. Here, we summarize the mechanisms responsible for NK cell functional suppression in the context of cancer and, specifically, myeloma. Subsequently, contemporary strategies potentially able to reverse NK dysfunction in MM are discussed.

NK-92 cell, another ideal carrier for chimeric antigen receptor

The remarkable clinical outcomes of the treatment for B-cell malignancies through the application of CD19 chimeric antigen receptor T (CAR-T) cells have made adoptive immunotherapy with genetically modified immune effector cells a hotspot in the field of antitumor. However, numerous toxicities of CAR-T cells have been identified. Thus, some studies have resorted to another cytotoxic cell, NK-92 cell, to reach for better efficacy with minimal toxicity. Preclinical studies have confirmed the safety and feasibility of the genetically modified NK-92 cells with highly specific cytotoxicity in vitro and in vivo. Therefore, it is expected that NK-92 cell becomes another ideal carrier for CAR for its unique advantages over primary NK cells, parental NK-92 cells and autologous T cells.

Possible Impact of Cytomegalovirus-Specific CD8+ T Cells on Immune Reconstitution and Conversion to Complete Donor Chimerism after Allogeneic Stem Cell Transplantation

Complete donor chimerism is strongly associated with complete remission after allogeneic stem cell transplantation (allo-SCT) in patients with hematologic malignancies. Donor-derived allo-immune responses eliminate the residual host hematopoiesis and thereby mediate the conversion to complete donor chimerism. Recently, cytomegalovirus (CMV) reactivation was described to enhance overall T cell reconstitution, to increase graft-versus-host disease incidence, and to reduce the leukemia relapse risk. However, the link between CMV and allo-immune responses is still unclear. Here, we studied the relationship between CMV-specific immunity, overall T cell reconstitution, and residual host chimerism in 106 CMV-seropositive patients transplanted after reduced-intensity conditioning including antithymocyte globulin. In accordance with previous reports, the recovery of CMV-specific cytotoxic T cells (CMV-CTLs) was more frequent in CMV-seropositive recipients (R) transplanted from CMV-seropositive than from seronegative donors (D). However, once CMV-CTLs were detectable, the reconstitution of CMV-specific CTLs was comparable in CMV R+/D- and R+/D+ patients. CD3⁺ and CD8⁺ T cell reconstitution was significantly faster in patients with CMV-CTLs than in patients without CMV-CTLs both in the CMV R+/D- and R+/D+ setting. Moreover, CMV-CTL numbers correlated with CD3⁺ and CD8⁺ T cell numbers in both settings. Finally, presence of CMV-CTLs was associated with low host chimerism levels 3 months after allo-SCT. In conclusion, our data provide a first indication that CMV-CTLs in CMV-seropositive patients might trigger the reconstitution of T cells and allo-immune responses reflected by the conversion to complete donor chimerism.

Impact of in vivo T cell depletion in HLA-identical allogeneic stem cell transplantation for acute myeloid leukemia in first complete remission conditioned with a fludarabine iv-busulfan myeloablative regimen: a report from the EBMT Acute Leukemia Working Party

Background

The impact of the use of anti-thymocyte globulin (ATG) in allogeneic stem cell transplantation performed with HLA-identical sibling donors following fludarabine and 4 days intravenous busulfan myeloablative conditioning regimen has been poorly explored.

Methods

We retrospectively analyzed 566 patients who underwent a first HLA-identical allogeneic stem cell transplantation with this conditioning regimen for acute myeloid leukemia in first complete remission between 2006 and 2013 and compared the outcomes of 145 (25.6%) patients who received ATG (ATG group) to 421 (74.4%) who did not (no-ATG group). The Kaplan-Meier estimator, the cumulative incidence function, and Cox proportional hazards regression models were used where appropriate.

Results

Patients in the ATG group were older, received more frequently peripheral blood stem cell grafts from older donors, and were transplanted more recently. With a median follow-up of 19 months, patients in the ATG group had reduced 2-year cumulative incidence of chronic graft-versus-host disease (GVHD) (31 vs. 52%, p = 0.0002) and of its extensive form (8 vs. 26%, p < 0.0001) but similar relapse incidence (22 vs. 27%, p = 0.23) leading to improved GVHD and relapse-free survival (GRFS) (60 vs. 40%, p = 0.0001). In multivariate analyses, the addition of ATG was independently associated with lower chronic GVHD (HR = 0.46, p = 0.0001), improved leukemia-free survival (HR = 0.67, p = 0.027), overall survival (HR = 0.65, p = 0.027), and GRFS (HR = 0.51, p = 4 × 10⁻⁵). Recipient age above 50 years was the only other factor associated with worse survivals.

Conclusions

These results suggest that the use of ATG with fludarabine and 4 days intravenous busulfan followed by HLA-identical sibling donor allogeneic stem cell transplantation for acute myeloid leukemia improves overall transplant outcomes due to reduced incidence of chronic GVHD without increased relapse risk.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0389-4) contains supplementary material, which is available to authorized users.

Checkpoint inhibition in myeloma

Historically, attempts at cancer immunotherapy have emphasized strategies designed to stimulate or augment the immune system into action. In the past decade, a complementary approach has developed, that of releasing immune cells from inhibitory restraint. Discoveries in the fundamental biology of how immunity is regulated, how the immune system interfaces with malignancy, and how cancer cells may exploit these processes to evade detection have all been translated into the rapidly growing field of therapeutic immune checkpoint inhibition for cancer. Myeloma is a malignancy associated with significant immune dysfunction imparted both by the disease itself as well as by many of the immunosuppressive therapies that have been used in the past. The growing body of preclinical data regarding immunoregulatory mechanisms that appear active in myeloma has begun to be translated to clinical trials targeting these signaling axes. This review will attempt to summarize the current understanding of the basic biology of several immune checkpoint pathways that may be important in myeloma and provide an up-to-date overview of recent and ongoing clinical trials of immune checkpoint inhibitors in myeloma. Finally, several current challenges and possible future directions of immune checkpoint blockade in myeloma will be reviewed.

Checkpoint Inhibition of KIR2D with the Monoclonal Antibody IPH2101 Induces Contraction and Hyporesponsiveness of NK Cells in Patients with Myeloma

PURPOSE

Immune checkpoint inhibitors have recently revolutionized cancer immunotherapy. On the basis of data showing KIR-ligand mismatched natural killer (NK) cells reduce the risk of leukemia and multiple myeloma relapse following allogeneic hematopoietic stem cell transplantation, investigators have developed a checkpoint inhibition antibody that blocks KIR on NK cells. Although in vitro studies suggest the KIR2D-specific antibody IPH2101 induces KIR-ligand mismatched tumor killing by NK cells, our single-arm phase II clinical trial in patients with smoldering multiple myeloma was prematurely terminated due to lack of clinical efficacy. This study aimed at unveiling the underlying mechanisms behind the lack of clinical efficacy.

EXPERIMENTAL DESIGN

Treatment-naïve patients received an intravenous infusion of 1 mg/kg IPH2101 every other month for up to a year. Peripheral blood was collected at baseline and 24 hours after first infusion, followed by weekly samples for the first month and monthly samples thereafter. NK cell phenotype and function was analyzed using high-resolution flow cytometry.

RESULTS

Unexpectedly, infusion of IPH2101 resulted in rapid reduction in both NK cell responsiveness and KIR2D expression on the NK cell surface. In vitro assays revealed KIR2D molecules are removed from the surface of IPH2101-treated NK cells by trogocytosis, with reductions in NK cell function directly correlating with loss of free KIR2D surface molecules. Although IPH2101 marginally augmented the antimyeloma cytotoxicity of remaining KIR2D^dull patient NK cells, the overall response was diminished by significant contraction and reduced function of KIR2D-expressing NK cells.

CONCLUSIONS

These data raise concerns that the unexpected biological events reported in this study could compromise antibody-based strategies designed at augmenting NK cell tumor killing via checkpoint inhibition. Clin Cancer Res; 22(21); 5211-22. ©2016 AACRSee related commentary by Felices and Miller, p. 5161.

Decreased CD161 activating and increased CD158a inhibitory receptor expression on NK cells underlies impaired NK cell cytotoxicity in patients with multiple myeloma

AIM

As innate immune cells natural killer (NK), NK-like T and CTLγδ are important in antitumour response in multiple myeloma (MM), the aim of this study was to investigate some functional and phenotypical characteristics of these cells in MM.

METHODS

29 patients with MM prior to therapy, in clinical stage I-III and 15 healthy controls (HCs) were investigated. Percent of immune cells in peripheral blood, NK cell activity, expression of activating (CD161) and inhibitory (CD158a, CD158b) NK cell receptors on CD3-CD16+ NK cells were evaluated using 51-chromium-release assay and by flow cytometry. Production of interleukin (IL) 2 and tumour necrosis factor (TNF)α was analysed in supernatants from in vitro activated peripheral blood mononuclear cells.

RESULTS

In patients with MM the percent of NK cells and their two subsets did not differ from controls, while NK-like T and CTLγδ cells were significantly decreased. Significant impairment of NK cell cytotoxicity, CD107a expression and interferon γ intracellular level was also shown. There was a significant decrease in CD161 and an increase in CD158a receptor expression on NK cells in these patients. Also IL-2 production was lowest in clinical stage III. However, TNF-α production did not differ between patients and HCs.

CONCLUSIONS

Altered expression of CD161 activating and CD158a KIR inhibitory receptor is responsible for impaired antitumour activity of NK cells in MM patients. These new biomarkers may be helpful for patient selection for immunotherapy with cytokines, and novel KIR blocking monoclonal antibodies that enhance NK cell antimyeloma activity and provide clinical benefit.

Immune responses in multiple myeloma: role of the natural immune surveillance and potential of immunotherapies

Multiple myeloma (MM) is a tumor of terminally differentiated B cells that arises in the bone marrow. Immune interactions appear as key determinants of MM progression. While myeloid cells foster myeloma-promoting inflammation, Natural Killer cells and T lymphocytes mediate protective anti-myeloma responses. The profound immune deregulation occurring in MM patients may be involved in the transition from a premalignant to a malignant stage of the disease. In the last decades, the advent of stem cell transplantation and new therapeutic agents including proteasome inhibitors and immunoregulatory drugs has dramatically improved patient outcomes, suggesting potentially key roles for innate and adaptive immunity in disease control. Nevertheless, MM remains largely incurable for the vast majority of patients. A better understanding of the complex interplay between myeloma cells and their immune environment should pave the way for designing better immunotherapies with the potential of very long term disease control. Here, we review the immunological microenvironment in myeloma. We discuss the role of naturally arising anti-myeloma immune responses and their potential corruption in MM patients. Finally, we detail the numerous promising immune-targeting strategies approved or in clinical trials for the treatment of MM.

Reduced platelet transfusions and earlier platelet engraftment using alemtuzumab-based conditioning regimen in allogeneic stem cell transplantation

PURPOSE

In patients undergoing allogeneic stem cell transplantation, conditioning regimens containing alemtuzumab instead of anti-thymocyte globulin (ATG) may result in an earlier platelet engraftment and a reduced number of platelet transfusions.

METHODS

We performed a retrospective, single-center, case-control study analyzing time to engraftment and transfusion needs using alemtuzumab in comparison with ATG as part of conditioning protocol.

RESULTS

Median values for time to platelet engraftment, number of transfused platelet concentrates and number of transfused red cell concentrates were 12 versus 19.5 days (p < 0.001), 2 versus 14 (p < 0.001) and 6 versus 14.5 (p = 0.003) in the alemtuzumab and ATG group. Time to leukocyte engraftment did not differ with median 15 days in both groups. Patients in the ATG group showed a significant higher decrease in platelet count during conditioning (68 vs. 29 %, p = 0.001), leading to significant lower median platelet counts at the day of stem cell infusion (38 vs. 95.5 Gpt/l, p = 0.008), and higher values for median C-reactive protein after first antibody infusion (69.0 vs. 43.6 mg/l, p = 0.001) compared with alemtuzumab group. Test for significance was done by using Wilcoxon rank-sum test. Subgroup analysis considering the type of ATG used (Thymoglobulin vs. ATG Fresenius) revealed that differences between alemtuzumab and ATG group were more due to effects of ATG Fresenius than Thymoglobulin.

CONCLUSIONS

The use of alemtuzumab in comparison with ATG as part of the conditioning regimen may be an approach to reduce the number of transfused platelet and red cell concentrates after allogeneic stem cell transplantation.

Optimal selection of natural killer cells to kill myeloma: the role of HLA-E and NKG2A

Immunotherapy with allogeneic natural killer (NK) cells offers therapeutic perspectives for multiple myeloma patients. Here, we aimed to refine NK cell therapy by evaluation of the relevance of HLA-class I and HLA-E for NK anti-myeloma reactivity. We show that HLA-class I was strongly expressed on the surface of patient-derived myeloma cells and on myeloma cell lines. HLA-E was highly expressed by primary myeloma cells but only marginally by cell lines. HLA-E(low) expression on U266 cells observed in vitro was strongly upregulated after in vivo (bone marrow) growth in RAG-2(-/-) γc(-/-) mice, suggesting that in vitro HLA-E levels poorly predict the in vivo situation. Concurrent analysis of inhibitory receptors (KIR2DL1, KIR2DL2/3, KIR3DL1 and NKG2A) and NK cell degranulation upon co-culture with myeloma cells revealed that KIR-ligand-mismatched NK cells degranulate more than matched subsets and that HLA-E abrogates degranulation of NKG2A+ subsets. Inhibition by HLA-class I and HLA-E was also observed with IL-2-activated NK cells and at low oxygen levels (0.6 %) mimicking hypoxic bone marrow niches where myeloma cells preferentially reside. Our study demonstrates that NKG2A-negative, KIR-ligand-mismatched NK cells are the most potent subset for clinical application. We envision that infusion of high numbers of this subclass will enhance clinical efficacy.

Inhibitory killer cell immunoglobulin-like receptor (iKIR) mismatches improve survival after T-cell-repleted haploidentical transplantation

Alloreactivity triggered by interaction between killer cell immunoglobulin-like receptors (KIRs) and natural killer (NK) cells plays a role in the graft-versus-tumor effect after hematopoietic stem cell transplantation (SCT). Our aim in this study was to evaluate this role in the setting of T-cell-repleted haploidentical SCT with postinfusion high-dose cyclophosphamide (PT-Cy). We included 33 patients. Among patient-donor pairs with at least 1 inhibitory KIR (iKIR) gene mismatch, event-free survival (EFS) and cumulative incidence of relapse 1 year after transplant were significantly better (85% vs. 37% [P = 0.008] and 18% vs. 46% [P = 0.041], respectively). A subanalysis in 12 patients with Hodgkin's lymphoma (HL) showed an improvement in EFS 1 year after transplant in those patients with KIR ligand mismatch (100% vs. 25%, P = 0.012), although overall survival (OS) was not affected (85% vs. 80%, P = 0.2). Eight of 12 patient-donors pairs presented iKIR mismatches. Of note, this outcome was better in the small subgroup, both for EFS (100% vs. 25%, P = 0.012) and for OS (100% vs. 37%, P = 0.004). Our data suggest that in the setting of T-cell-repleted haploidentical SCT with PT-Cy, iKIR mismatch is associated with improved survival, with particularly good results for both iKIR and KIR ligand mismatches in patients with HL.

A Phase I Trial of the Anti-KIR Antibody IPH2101 and Lenalidomide in Patients with Relapsed/Refractory Multiple Myeloma

PURPOSE

Natural killer (NK) cells may play an important role in the immune response to multiple myeloma; however, multiple myeloma cells express killer immunoglobulin-like receptor (KIR) ligands to prevent NK cell cytotoxicity. Lenalidomide can expand and activate NK cells in parallel with its direct effects against multiple myeloma; however, dexamethasone may impair these favorable immunomodulatory properties. IPH2101, a first-in-class antiinhibitory KIR antibody, has acceptable safety and tolerability in multiple myeloma as a single agent. The present work sought to characterize lenalidomide and IPH2101 as a novel, steroid-sparing, dual immune therapy for multiple myeloma.

EXPERIMENTAL DESIGN

A phase I trial enrolled 15 patients in three cohorts. Lenalidomide was administered per os at 10 mg on cohort 1 and 25 mg on cohorts 2 and 3 days 1 to 21 on a 28-day cycle with IPH2101 given intravenously on day 1 of each cycle at 0.2 mg/kg in cohort 1, 1 mg/kg in cohort 2, and 2 mg/kg in cohort 3. No corticosteroids were utilized. The primary endpoint was safety, and secondary endpoints included clinical activity, pharmacokinetics (PK), and pharmacodynamics (PD).

RESULTS

The biologic endpoint of full KIR occupancy was achieved across the IPH2101 dosing interval. PD and PK of IPH2101 with lenalidomide were similar to data from a prior single-agent IPH2101 trial. Five serious adverse events (SAE) were reported. Five objective responses occurred. No autoimmunity was seen.

CONCLUSIONS

These findings suggest that lenalidomide in combination with antiinhibitory KIR therapy warrants further investigation in multiple myeloma as a steroid-sparing, dual immune therapy. This trial was registered at www.clinicaltrials.gov (reference: NCT01217203).

Current and future immunotherapeutic approaches to multiple myeloma therapy

SUMMARY 

Multiple myeloma (MM) is a hematologic malignancy associated with heterogeneous treatment and survival outcomes due in part to the ability of MM to evade and suppress the immune system. Research has focused on finding ways to modulate and enhance immunity while targeting the bone marrow microenvironment. Contemporary therapies include immunomodulatory drugs, proteasome inhibitors and autologous and allogeneic stem cell transplant and have improved outcomes for patients with MM. Future therapies, including monoclonal antibodies, chimeric antigen receptor cells and MM vaccines, show promise to further improved outcomes, particularly when used in combination with existing therapies. This review covers the mechanism of action of currently available and future therapies and explores ways in which treatment may be more specifically directed in the future.

Opportunities and limitations of natural killer cells as adoptive therapy for malignant disease

Although natural killer (NK) cells can be readily generated for adoptive therapy with current techniques, their optimal application to treat malignant diseases requires an appreciation of the dynamic balance between signals that either synergize with or antagonize each other. Individuals display wide differences in NK function that determine their therapeutic efficacy. The ability of NK cells to kill target cells or produce cytokines depends on the balance between signals from activating and inhibitory cell-surface receptors. The selection of NK cells with a predominant activating profile is critical for delivering successful anti-tumor activity. This can be achieved through selection of killer immunoglobulin-like receptor-mismatched NK donors and by use of blocking molecules against inhibitory pathways. Optimum NK cytotoxicity may require licensing or priming with tumor cells. Recent discoveries in the molecular and cellular biology of NK cells inform in the design of new strategies, including adjuvant therapies, to maximize the cytotoxic potential of NK cells for adoptive transfer to treat human malignancies.

Genetic modification of T cells redirected toward CS1 enhances eradication of myeloma cells

PURPOSE

Our goal is to test whether CS1 could be targeted by chimeric antigen receptor (CAR) T cells to treat multiple myeloma (MM).

EXPERIMENTAL DESIGN

We generated a retroviral construct of a CS1-specific CAR and engineered primary human T cells expressing the CAR. We then tested the capacity of CS1-CAR T cells to eradicate human MM tumor cells in vitro, ex vivo, and in vivo using orthotopic MM xenograft mouse models.

RESULTS

In vitro, compared with mock-transduced T cells, upon recognizing CS1-positive MM cells, CS1-CAR-transduced T cells secreted more IFN-γ as well as interleukin (IL)-2, expressed higher levels of the activation marker CD69, showed higher capacity for degranulation, and displayed enhanced cytotoxicity. Ectopically forced expression of CS1 in MM cells with low CS1 expression enhanced recognition and killing by CAR T cells. Ex vivo, CS1-CAR T cells also showed similarly enhanced activities when responding to primary MM cells. More importantly, in orthotopic MM xenograft mouse models, adoptive transfer of human primary T cells expressing CS1-CAR efficiently suppressed the growth of human MM.1S and IM9 myeloma cells and significantly prolonged mouse survival.

CONCLUSIONS

CS1 is a promising antigen that can be targeted by CAR-expressing T cells for treatment of MM.

Improving the outcome of leukemia by natural killer cell-based immunotherapeutic strategies

Blurring the boundary between innate and adaptive immune system, natural killer (NK) cells are widely recognized as potent anti-leukemia mediators. Alloreactive donor NK cells have been shown to improve the outcome of allogeneic stem-cell transplantation for leukemia. In addition, in vivo transfer of NK cells may soon reveal an important therapeutic tool for leukemia, if tolerance to NK-mediated anti-leukemia effects is overcome. This will require, at a minimum, the ex vivo generation of a clinically safe NK cell product containing adequate numbers of NK cells with robust anti-leukemia potential. Ideally, ex vivo generated NK cells should also have similar anti-leukemia potential in different patients, and be easy to obtain for convenient clinical scale-up. Moreover, optimal clinical protocols for NK therapy in leukemia and other cancers are still lacking. These and other issues are being currently addressed by multiple research groups. This review will first describe current laboratory NK cell expansion and differentiation techniques by separately addressing different NK cell sources. Subsequently, it will address the mechanisms known to be responsible for NK cell alloreactivity, as well as their clinical impact in the hematopoietic stem cells transplantation setting. Finally, it will briefly provide insight on past NK-based clinical trials.

Killer immunoglobulin-like receptors and tumor immunity

were originally named for their capacity to elicit potent cytotoxicity against tumor cells independent of prior sensitization or gene rearrangement. This process is facilitated through the expression of activating and inhibitory receptors that provide for NK cell "education" and a subsequent ability to survey, recognize, and lyse infected or transformed cells, especially those lacking or possessing mutated MHC class I expression. Since these original observations were made, how NK cells recognize candidate target cells continues to be the topic of ongoing investigation. It is now appreciated that NK cells express a diverse repertoire of activating and inhibitory receptors of which killer immunoglobulin-like receptors (KIR) appear to play a critical role in mediating self-tolerance as well as facilitating cytotoxicity against infected or transformed cells. In addition, in the presence of an activating signal, the absence or mismatch of MHC class I molecules on such targets (which serve as inhibitory KIR ligands) promotes NK cell–mediated lysis. An increasing understanding of the complexities of KIR biology has provided recent opportunities to leverage the NK cell versus tumor effect as a novel avenue of immunotherapy for cancer. The present review summarizes the current understanding of KIR expression and function and highlights ongoing efforts to translate these discoveries into novel NK cell–mediated immunotherapies for cancer.

CS1-specific chimeric antigen receptor (CAR)-engineered natural killer cells enhance in vitro and in vivo antitumor activity against human multiple myeloma

Multiple myeloma (MM) is an incurable hematological malignancy. Chimeric antigen receptor (CAR)-expressing T cells have been demonstrated successful in the clinic to treat B-lymphoid malignancies. However, the potential utility of antigen-specific CAR-engineered natural killer (NK) cells to treat MM has not been explored. In this study, we determined whether CS1, a surface protein that is highly expressed on MM cells, can be targeted by CAR NK cells to treat MM. We successfully generated a viral construct of a CS1-specific CAR and expressed it in human NK cells. In vitro, CS1-CAR NK cells displayed enhanced MM cytolysis and IFN-γ production, and showed a specific CS1-dependent recognition of MM cells. Ex vivo, CS1-CAR NK cells also showed similarly enhanced activities when responding to primary MM tumor cells. More importantly, in an aggressive orthotopic MM xenograft mouse model, adoptive transfer of NK-92 cells expressing CS1-CAR efficiently suppressed the growth of human IM9 MM cells and also significantly prolonged mouse survival. Thus, CS1 represents a viable target for CAR-expressing immune cells, and autologous or allogeneic transplantation of CS1-specific CAR NK cells may be a promising strategy to treat MM.

Natural killer cell alloreactivity 10 years later

PURPOSE OF REVIEW

This article reviews the impact of natural killer (NK) cell alloreactivity on hematopoietic cell transplantation since it was first observed in haploidentical transplant recipients 10 years ago.

RECENT FINDINGS

Research has established 'missing self-recognition' as the mechanism underlying NK cell-mediated graft-versus-leukemia effects in T-cell-depleted haploidentical hematopoietic cell transplantation and has clarified optimal transplantation protocols to harness NK cell alloreactivity.

SUMMARY

In the past decade, clinical studies have shown that the benefits of donor-versus-recipient NK cell alloreactivity in haploidentical transplantation are triggered by specific human leukocyte antigen (HLA) class I mismatches. Donor HLA is crucial for driving NK cell education so that reconstituting NK cells mature as donor-tolerant and recipient-alloreactive. Transplantation of large doses of extensively T-cell-depleted hematopoietic grafts with no posttransplant immune suppression was found to be essential for development of NK cell alloreactivity. Clinical trials demonstrated that donor-versus-recipient NK cell alloreactivity is a key therapeutic element in haploidentical transplants for acute myeloblastic leukemia in adults and acute lymphoblastic leukemia in children. Moreover, in pilot studies, mature haploidentical NK cells were transiently transferred into lymphoablated patients with acute leukemia in remission. The results showed NK cell therapy may be a promising strategy for consolidating leukemia remission. In line with the notion that NK cell function is regulated by a balance between activating and inhibitory receptors, in the matched transplant setting, transplantation from donors possessing certain activating NK receptors (activating killer cell immunoglobulin-like receptors) appeared to protect from relapse and improved survival.

Low-dose alemtuzumab vs. standard policy for prevention of graft-versus-host disease in unrelated and related allogeneic stem cell transplantation-a matched pair analysis

Antibody-mediated in vivo T cell depletion is common prior to unrelated (URD) or mismatched allogeneic stem cell transplantation (alloSCT) and optional in HLA-identical sibling (FAM) alloSCT. While anti-thymocyte globulin (ATG) is the current standard, alemtuzumab is an alternative. The optimal dose of alemtuzumab has not been defined. This retrospective analysis compares low-dose alemtuzumab with ATG in URD alloSCT and with no antibody in FAM alloSCT. Twenty-eight patients treated with alemtuzumab (10 mg; HLA mismatch, 20 mg) were matched to 28 patients who have either received ATG (URD) or no antibody (noAB) according to disease, disease stage, age, transplant type and risk state. Both groups were compared for engraftment, outcome, disease-free (DFS) and overall survival (OS), graft-versus-host disease (GvHD), freedom from GvHD (ffGvHD) and transplant-related mortality (TRM). No significant differences were found between the groups for leukocyte engraftment, GvHD, ffGvHD, TRM, DFS and OS. There was a trend for reduction of cGvHD by alemtuzumab (p = 0.05). A transplant-type stratified subanalysis consolidated equivalency of alemtuzumab and ATG in URD-SCT and indicates possible superiority of low-dose alemtuzumab compared to noAB in FAM-SCT. Low-dose alemtuzumab, as part of conditioning regimen prior to alloSCT, is safe and comparable to standard ATG. Prospective trials, particularly comparing alemtuzumab vs. noAB in FAM alloSCT, should be conducted.

The TNF receptor-ligands 4-1BB-4-1BBL and GITR-GITRL in NK cell responses

Interactions between several tumor necrosis factor (TNF)-TNF receptor (TNFR) superfamily members that are expressed by T cells and natural killer (NK) cells and various other cell types modulate immune responses. This review summarizes the current understanding of how the TNF ligand-TNFR interactions 4-1BBL with 4-1BB, and GITRL with glucocorticoid-induced TNFR-related (GITR) regulate NK cell mediated antitumor responses and discuss its therapeutic implications.

Role of killer immunoglobulin-like receptor and ligand matching in donor selection

Despite all efforts to improve HLA typing and immunosuppression, it is still impossible to prevent severe graft versus host disease (GVHD) which can be fatal. GVHD is not always associated with graft versus malignancy and can prevent stem cell transplantation from reaching its goals. Overall T-cell alloreactivity is not the sole mechanism modulating the immune defense. Innate immune system has its own antigens, ligands, and mediators. The bridge between HLA and natural killer (NK) cell-mediated reactions is becoming better understood in the context of stem cell transplantation. Killer immunoglobulin-like receptors (KIRs) constitute a wide range of alleles/antigens segregated independently from the HLA alleles and classified into two major haplotypes which imprints the person's ability to suppress or to amplify T-cell alloreactivity. This paper will summarize the impact of both activating and inhibitory KIRs and their ligands on stem cell transplantation outcome. The ultimate goal is to develop algorithms based on KIR profiles to select donors with maximum antileukemic and minimum antihost effects.

Postallograft lenalidomide induces strong NK cell-mediated antimyeloma activity and risk for T cell-mediated GvHD: Results from a phase I/II dose-finding study

Lenalidomide may prevent relapses after allogeneic stem cell transplantation by promoting the immune-mediated graft-versus-tumor effect. We performed a prospective phase I/II study to define the dose-limiting toxicity and the immunologic effects of lenalidomide given early (day 100-180) after allograft for four cycles in patients with multiple myeloma. According to the Fibonacci design, 24 patients with a median age of 53 years were included. Dose-limiting toxicity was organ toxicity owing to graft-versus-host disease, and the maximum tolerable dose was 5 mg. The incidence of graft-versus-host disease after lenalidomide was 38%, occurring after a median of 22 days, and was beside organ toxicity, a leading cause to discontinue the study in 29% of the patients. Immune monitoring revealed a significant increase in peripheral γ-interferon-secreting CD4(+) and CD8(+) T cells within the first week of lenalidomide treatment followed by a delayed increase in T regulatory cells. Furthermore, natural killer (NK) cells isolated from the peripheral blood of patients evidenced a significantly improved antimyeloma activity after lenalidomide treatment. The immune effect might have contributed to the increased CR rate from 24-42% after lenalidomide treatment because nonresponding patients showed significantly less natural killer and T cell activation. (Study registered under: NCT 00778752.).

A phase 1 trial of the anti-KIR antibody IPH2101 in patients with relapsed/refractory multiple myeloma

Natural killer (NK) cells elicit cytotoxicity against multiple myeloma (MM); however, MM cells express HLA class I molecules as ligands to NK cell inhibitory killer immunoglobulin-like receptors (KIRs) as a means of immunoevasion. KIR-ligand mismatch may improve outcomes in allogeneic transplantation for MM. Extrapolating on this concept, we conducted a phase 1 trial of IPH2101, an anti-KIR antibody, in patients with relapsed/refractory MM. IPH2101 was administered intravenously every 28 days in 7 dose-escalated cohorts (0.0003-3 mg/kg) for up to 4 cycles. Pharmacokinetic, pharmacodynamic, and correlative immunologic studies were completed. A total of 32 patients were enrolled. The biologic endpoint of full KIR2D occupancy across the dosing cycle was achieved without dose-limiting toxicity or maximally tolerated dose. One severe adverse event was noted. Pharmacokinetic and pharmacodynamic findings approximated preclinical predictions, and IPH2101 enhanced ex vivo patient-derived NK cell cytotoxicity against MM. No objective responses were seen. No evidence of autoimmunity was observed. These findings suggest that IPH2101 is safe and tolerable at doses that achieve full inhibitory KIR saturation, and this approach warrants further development in MM. This trial was registered at www.clinicaltrials.gov as #NCT00552396.

The role of natural killer cells in immunity against multiple myeloma

Multiple myeloma (MM) is an essentially incurable malignancy associated with profound immune dysregulation. Despite the advent of novel therapies and improvements in survival over the last 10 years, death from progressive disease and infection remains a common outcome. Natural killer (NK) cells are CD56(+)CD3(-) large granular lymphocytes that constitute a key cellular subset of the innate immune system. For over 30 years, the relationship between NK cells and MM has been described in the clinical setting and characterized in the laboratory. Data suggest that NK cells may play a role in the immune response to MM; however, this effect is lost due to immunoevasive strategies utilized by MM. Nevertheless, progress in the understanding of the mechanisms perpetuating this effect have led to new opportunities to recover or augment NK cell function therapeutically in MM. In fact, the novel agents thalidomide, lenalidomide and bortezomib all confer anti-MM effects, in part, through enhancement of NK cell function. Currently, the development of therapies designed specifically to increase NK cell cytotoxicity against MM is under way. The present review summarizes the current understanding of the NK cell versus MM effect and characterizes therapeutic interventions that exert anti-MM efficacy via NK cell function against the disease.

Targeting natural killer cells and natural killer T cells in cancer

Natural killer (NK) cells and natural killer T (NKT) cells are subsets of lymphocytes that share some phenotypical and functional similarities. Both cell types can rapidly respond to the presence of tumour cells and participate in antitumour immune responses. This has prompted interest in the development of innovative cancer therapies that are based on the manipulation of NK and NKT cells. Recent studies have highlighted how the immune reactivity of NK and NKT cells is shaped by the environment in which they develop. The rational use of these cells in cancer immunotherapies awaits a better understanding of their effector functions, migratory patterns and survival properties in humans.

NK cell MHC class I specific receptors (KIR): from biology to clinical intervention

The natural killer (NK) cell effector response towards infected cells or tumoural cells is guided by the integration of activating and inhibitory signals sensed by NK cell surface receptors. Major histocompatibility complex class I specific inhibitory receptors expressed by NK cells have two distinct roles: while allowing self tolerance, they are also needed for the acquisition of NK cell functional competence, a process termed education. In the context of allotransplantation, NK cell alloreactivity, arising from the expression on donor NK cells of inhibitory killer Ig-like receptors (KIRs) that do not recognize human leukocyte antigen from the patient, has shown clinical benefit for leukaemia patients. Based on these genetic studies, a blocking antibody directed against KIRs, as well as allogeneic NK cell infusions are now tested in clinical trials in various oncology indications. They offer promising immunotherapeutic approaches for the treatment of cancer patients.

IPH2101, a novel anti-inhibitory KIR antibody, and lenalidomide combine to enhance the natural killer cell versus multiple myeloma effect

Multiple myeloma (MM) patients who receive killer cell Ig-like receptor (KIR) ligand-mismatched, T cell-depleted, allogeneic transplantation may have a reduced risk of relapse compared with patients who receive KIR ligand-matched grafts, suggesting the importance of this signaling axis in the natural killer (NK) cell-versus-MM effect. Expanding on this concept, IPH2101 (1-7F9), an anti-inhibitory KIR mAb, enhances NK-cell function against autologous MM cells by blocking the engagement of inhibitory KIR with cognate ligands, promoting immune complex formation and NK-cell cytotoxicity specifically against MM cell targets but not normal cells. IPH2101 prevents negative regulatory signals by inhibitory KIR, whereas lenalidomide augments NK-cell function and also appears to up-regulate ligands for activating NK-cell receptors on MM cells. Lenalidomide and a murine anti-inhibitory NK-cell receptor Ab mediate in vivo rejection of a lenalidomide-resistant tumor. These mechanistic, preclinical data support the use of a combination of IPH2101 and lenalidomide in a phase 2 trial for MM.

Bone marrow may be the preferable graft source in recipients homozygous for HLA-C group 2 ligands for inhibitory killer Ig-like receptors

HLA class I molecules participate in natural killer cell regulation by acting as ligands for inhibitory killer cell Ig-like receptors (KIRs). One individual may express one or more inhibitory KIR lacking the corresponding HLA ligand. The role of this 'missing KIR ligand' constellation in hematopoietic SCT (HSCT) remains controversial and depends on incompletely defined transplant variables. We have retrospectively analyzed the effects of missing HLA-C group 1/2 and Bw4 KIR ligands in the recipients on the outcome in 382 HSCT, comparing 118 BMT to 264 PBSC transplants (PBSCT). In the multivariate Cox analysis of PBSCT, poor PFS was observed in homozygous HLA-C group 2 (C2/2) recipients (risk ratio (RR), 1.59; P=0.026). In contrast, C2 homozygosity was not unfavorable after BMT (RR, 0.68; P=0.16). C2 homozygous recipients (n=68) had better PFS after BMT than after PBSCT (RR, 0.17; P=0.001), due to fewer relapses (RR, 0.27; P=0.018). Missing Bw4 favorably influenced PFS after BMT (RR, 0.56; P=0.04), but not after PBSCT. These data suggest opposite effects of missing KIR ligands in BMT vs PBSCT. Larger studies are required to reassess whether BMT should be preferred to PBSCT as an option for C2/C2 recipients.

Use of NK cell activity in cure by transplant

Analogous to T cells, Natural Killer (NK) cells may facilitate engraftment, combat infection, and control cancer in bone marrow or haematopoietic stem cell transplantation (HSCT); however, NK cells do not cause graft-versus-host disease. Killer immunoglobulin-like receptors (KIRs) regulate NK cell function, and recent data suggest that KIR is as important as its ligand (human leucocyte antigen; HLA) in HSCT for both malignant and non-malignant conditions. Because there is substantial variability in KIR gene content, allelic polymorphism, and cell-surface expression among people, careful selection of donors based on HLA and KIR is essential to optimize HSCT outcomes. Furthermore, NK cells may be used for adoptive immunotherapy after HSCT in place of conventional donor lymphocyte infusion, as part of pre-transplant cytoreductive therapy, or as an independent therapeutic agent in high-risk leukaemia in place of sibling donor HSCT.

Alemtuzumab in allogeneic hematopoetic stem cell transplantation

INTRODUCTION

With the use of reduced-intensity conditioning (RIC), early toxicity of allogeneic stem cell transplantation (SCT) has been much reduced. Graft-versus-host disease (GvHD) causes morbidities and mortality. Alemtuzumab is a mAb directed against CD52. When administered prior to transplant, it leads to T-cell depletion. Incorporation of alemtuzumab in RIC results in low rates of GvHD and treatment-related mortality (TRM) in haematological diseases, even in the setting of mismatched-donor transplantation.

AREAS COVERED

The use of alemtuzumab for GvHD prophylaxis in SCT. The benefit of alemtuzumab-based conditioning is partially offset by increased disease relapse due to impaired graft-versus-tumor effect (GvT) and by slower immune reconstitution, necessitating special precautions. While GvHD is prevented with alemtuzumab, post-SCT interventions are often required. Most studies find that alemtuzumab-based conditioning results in decreased chronic GvHD and TRM, but also in decreased progression-free survival. Overall survival after 3 - 5 years is usually equivalent and quality of life may be improved because of a lower incidence of sequelae of chronic GvHD. Many aspects of alemtuzumab treatment are under investigation.

EXPERT OPINION

Alemtuzumab reduces GvHD and TRM after SCT. Use of alemtuzumab requires awareness and strict management of the risk of opportunistic infections and of an increased risk of disease recurrence.