Antibody-dependent cell-mediated cytotoxicity overcomes NK cell resistance in MLL-rearranged leukemia expressing inhibitory KIR ligands but not activating ligands

Targeting MYC in combination with epigenetic regulators induces synergistic anti-leukemic effects in MLLr leukemia and simultaneously improves immunity

MLL rearranged (MLLr) leukemias are associated with a poor prognosis and a limited response to conventional therapies. Moreover, chemotherapies result in severe side effects with significant impairment of the immune system. Therefore, the identification of novel treatment strategies is mandatory. Recently, we developed a human MLLr leukemia model by inducing chromosomal rearrangements in CD34+ cells using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9. This MLLr model authentically mimics patient leukemic cells and can be used as a platform for novel treatment strategies. RNA sequencing of our model revealed MYC as one of the most important key drivers to promote oncogenesis. However, in clinical trials the BRD4 inhibitor JQ-1 leading to indirect blocking of the MYC pathway shows only modest activity. We and others previously reported that epigenetic drugs targeting MAT2A or PRMT5 promote cell death in MLLr cells. Therefore, we use these drugs in combination with JQ-1 leading to augmented anti-leukemic effects. Moreover, we found activation of T, NK and iNKT cells, release of immunomodulatory cytokines and downregulation of the PD-1/PD-L1 axis upon inhibitor treatment leading to improved cytotoxicity. In summary, the inhibition of MYC and MAT2A or PRMT5 drives robust synergistic anti-leukemic activity in MLLr leukemia. Moreover, the immune system is concomitantly activated upon combinatorial inhibitor treatment, hereby further augmenting the therapeutic efficiency.

Inhibitory receptors for HLA class I as immune checkpoints for natural killer cell-mediated antibody-dependent cellular cytotoxicity in cancer immunotherapy

Natural killer (NK) cells mediate potent anti-tumor responses, which makes them attractive targets for immunotherapy. The anti-tumor response of endogenous- or allogeneic NK cells can be enhanced through clinically available monoclonal antibodies that mediate antibody-dependent cellular cytotoxicity (ADCC). NK cell activation is regulated by interaction of inhibitory receptors with classical- and non-classical human leukocyte antigens (HLA) class I molecules. Inhibitory receptors of the killer immunoglobulin-like receptor (KIR) family interact with HLA-A, -B or -C epitopes, while NKG2A interacts with the non-classical HLA-E molecule. Both types of inhibitory interactions may influence the strength of the ADCC response. In the present review, we provide an overview of the effect of inhibitory KIRs and NKG2A on NK cell-mediated ADCC, which highlights the rationale for combination strategies with ADCC triggering antibodies and interference with the NK cell relevant inhibitory immune checkpoints, such as KIR and NKG2A.

Ruxolitinib does not completely abrogate the functional capabilities of TLR4/9 ligand-activated NK cells

Introduction

Natural killer (NK) cells are lymphocytes from the innate immune system part of the first defense barrier against infected and transformed cells, representing 5%-15% of peripheral blood lymphocytes. The cytotoxic capacity of NK cells is controlled by a balance between inhibitory and activating NK receptors expressed on their surface, which recognize and interact with the ligands on stressed cells. The cytokines involved in NK cell activation, proliferation, survival, and cytotoxicity are signaled mainly through the Janus kinase and signal transducer and activator of transcription proteins (JAK/STAT) pathway. NK cells are also activated in response to pathogens through Toll-like receptors (TLRs) expressed on their surface. Ruxolitinib is a specific JAK1/2 inhibitor approved for treating myelofibrosis and for steroid-refractory acute and chronic graft-versus-host disease (SR-GvHD).

Methods

Purified NK cells from healthy donors were stimulated with two TOLL-like receptor ligands, LPS and CpG, in the presence of different concentrations of Ruxolitinib.

Results

This study showed the effects of ruxolitinib on TLR4 and TLR9 ligand-activated NK cells from healthy donors. Ruxolitinib did not completely inhibit STAT3 phosphorylation and had a moderate effect on NK cell cytokine activation via the TLR pathway. Only the highest doses of ruxolitinib led to a decrease in the pro-inflammatory cytokines tumor necrosis factor α, interferon-γ, interleukin-6, and interleukin-1β. The cytotoxic capacity of stimulated NK cells versus K562, SEM, and MV-4-11 cell lines was reduced by increasing doses of ruxolitinib, but it was not completely abolished and we observed no major changes in degranulation capacity. Phenotypic changes were observed in activated NK cells in the presence of ruxolitinib. In a small cohort of pediatric patients treated with ruxolitinib for SR-GvHD, we observed no decrease in NK cell counts; however, further prospective studies with larger cohorts are necessary to confirm this finding.

Discussion

In summary, our results showed that the functional capabilities and phenotype of NK cells activated through TLR4/9 agonists were not completely abolished by the inhibition of the JAK-STAT pathway by ruxolitinib.

Immunotherapeutic Targeting of Mesothelin Positive Pediatric AML Using Bispecific T Cell Engaging Antibodies

Simple Summary

Immunotherapy development in pediatric AML has been slow due to the paucity of validated AML-specific targets. We recently identified mesothelin (MSLN) as a therapeutic target in pediatric AML. Mice receiving T cell engaging bispecific antibodies (BsAbs) targeting MSLN and CD3 achieved complete remission and durable responses in two MSLN-positive patient-derived xenograft (PDX) models. This is a first report showing MSLN-targeting BsAbs are a viable immunotherapy for MSLN-positive pediatric AML.

Abstract

Advances in the treatment of pediatric AML have been modest over the past four decades. Despite maximally intensive therapy, approximately 40% of patients will relapse. Novel targeted therapies are needed to improve outcomes. We identified mesothelin (MSLN), a well-validated target overexpressed in some adult malignancies, to be highly expressed on the leukemic cell surface in a subset of pediatric AML patients. The lack of expression on normal bone marrow cells makes MSLN a viable target for immunotherapies such as T-cell engaging bispecific antibodies (BsAbs) that combine two distinct antibody-variable regions into a single molecule targeting a cancer-specific antigen and the T-cell co-receptor CD3. Using antibody single-chain variable region (scFv) sequences derived from amatuximab-recognizing MSLN, and from either blinatumomab or AMG330 targeting CD3, we engineered and expressed two MSLN/CD3-targeting BsAbs: MSLN^AMA-CD3^L2K and MSLN^AMA-CD3^AMG, respectively. Both BsAbs promoted T-cell activation and reduced leukemic burden in MV4;11:MSLN xenografted mice, but not in those transplanted with MSLN-negative parental MV4;11 cells. MSLN^AMA-CD3^AMG induced complete remission in NTPL-146 and DF-5 patient-derived xenograft models. These data validate the in vivo efficacy and specificity of MSLN-targeting BsAbs. Because prior MSLN-directed therapies appeared safe in humans, MSLN-targeting BsAbs could be ideal immunotherapies for MSLN-positive pediatric AML patients.

Harnessing CD16-Mediated NK Cell Functions to Enhance Therapeutic Efficacy of Tumor-Targeting mAbs

Simple Summary

Natural Killer (NK) cells play a major role in cancer immunotherapy based on tumor-targeting mAbs. NK cell-mediated tumor cell killing and cytokine secretion are powerfully stimulated upon interaction with IgG-opsonized tumor cells, through the aggregation of FcγRIIIA/CD16 IgG receptor. Advances in basic and translational NK cell biology have led to the development of strategies that, by improving mAb-dependent antitumor responses, may overcome the current limitations of antibody therapy attributable to tolerance, immunosuppressive microenvironment, and genotypic factors. This review provides an overview of the immunotherapeutic strategies being pursued to improve the efficacy of mAb-induced NK antitumor activity. The exploitation of antibody combinations, antibody-based molecules, used alone or combined with adoptive NK cell therapy, will be uncovered. Within the landscape of NK cell heterogeneity, we stress the role of memory NK cells as promising effectors in the next generation of immunotherapy with the aim to obtain long-lasting tumor control.

Abstract

Natural killer (NK) cells hold a pivotal role in tumor-targeting monoclonal antibody (mAb)-based activity due to the expression of CD16, the low-affinity receptor for IgG. Indeed, beyond exerting cytotoxic function, activated NK cells also produce an array of cytokines and chemokines, through which they interface with and potentiate adaptive immune responses. Thus, CD16-activated NK cells can concur to mAb-dependent “vaccinal effect”, i.e., the development of antigen-specific responses, which may be highly relevant in maintaining long-term protection of treated patients. On this basis, the review will focus on strategies aimed at potentiating NK cell-mediated antitumor functions in tumor-targeting mAb-based regimens, represented by (a) mAb manipulation strategies, aimed at augmenting recruitment and efficacy of NK cells, such as Fc-engineering, and the design of bi- or trispecific NK cell engagers and (b) the possible exploitation of memory NK cells, whose distinctive characteristics (enhanced responsiveness to CD16 engagement, longevity, and intrinsic resistance to the immunosuppressive microenvironment) may maximize therapeutic mAb antitumor efficacy.

Natural killer cell-based immunotherapy for acute myeloid leukemia

Despite considerable progress has been achieved in the treatment of acute myeloid leukemia over the past decades, relapse remains a major problem. Novel therapeutic options aimed at attaining minimal residual disease-negative complete remission are expected to reduce the incidence of relapse and prolong survival. Natural killer cell-based immunotherapy is put forward as an option to tackle the unmet clinical needs. There have been an increasing number of therapeutic dimensions ranging from adoptive NK cell transfer, chimeric antigen receptor-modified NK cells, antibodies, cytokines to immunomodulatory drugs. In this review, we will summarize different forms of NK cell-based immunotherapy for AML based on preclinical investigations and clinical trials.

Increased Relapse Risk of Acute Lymphoid Leukemia in Homozygous HLA-C1 Patients after HLA-Matched Allogeneic Transplantation: A Japanese National Registry Study

Natural killer (NK) cells expressing killer cell immunoglobulin-like receptors (KIRs) can recognize specific HLA class I molecules as their ligands. By studying a large Japanese transplant registry, we compared transplant outcomes between patients heterozygous for HLA-C^Asn80/C^Lys80 (HLA-C1/C2) and those homozygous for HLA-C1 (HLA-C1/C1) among patients who had undergone HLA-matched hematopoietic stem cell transplantation (HSCT). A high frequency of KIR2DL1 with strong HLA-C2 binding capacity and a low frequency of HLA-C2 and KIR haplotype B are characteristic of the Japanese population. In our previous report, HLA-C1/C1 patients with myeloid leukemia were less likely to relapse than HLA-C1/C2 patients. We newly assessed 2884 patients with acute lymphoblastic leukemia (ALL) who received HLA-matched allogeneic HSCT and analyzed their leukemia relapses by using adjusted competing-risk methods. HLA-C1/C1 patients with ALL experienced significantly higher relapse rates than HLA-C1/C2 patients (hazard ratio [HR] = 1.55, P = .003), contrary to our results in patients with myeloid leukemia. We allocated patients with ALL to several subgroups and found a higher frequency of relapse (HR >1.8) in the HLA-C1/C1 group than in the HLA-C1/C2 group among patients with Ph-negative ALL, those who had no cytomegalovirus reactivation, those who received transplants from donors who were aged 41 years or older, and those who experienced acute graft-versus-host disease, especially if it required systemic treatment. One interpretation of our results is that KIR2DL1-positive NK cells disrupt T cells, antigen-presenting cells, or both from working efficiently in transplant immunity in HLA-C1/C1 patients with ALL. Another is that KIR2DS1-positive NK cells directly attack HLA-C2-positive ALL blasts in HLA-C1/C2 patients. Whether HLA-C2 can cause recurrence to decrease or increase in patients depending on the disease (ALL or myeloid leukemia) will be a very important finding. We hope that our results will provide clues to the real mechanisms behind relapse after transplantation in patients with different HLA profiles.

Natural Killer Cells in Myeloid Malignancies: Immune Surveillance, NK Cell Dysfunction, and Pharmacological Opportunities to Bolster the Endogenous NK Cells

Natural killer (NK) cells are large granular lymphocytes involved in our defense against certain virus-infected and malignant cells. In contrast to T cells, NK cells elicit rapid anti-tumor responses based on signals from activating and inhibitory cell surface receptors. They also lyse target cells via antibody-dependent cellular cytotoxicity, a critical mode of action of several therapeutic antibodies used to treat cancer. A body of evidence shows that NK cells can exhibit potent anti-tumor activity against chronic myeloid leukemia (CML), acute myeloid leukemia (AML), and myelodysplastic syndromes (MDS). However, disease-associated mechanisms often restrain the proper functions of endogenous NK cells, leading to inadequate tumor control and risk for disease progression. Although allogeneic NK cells can prevent leukemia relapse in certain settings of stem cell transplantation, not all patients are eligible for this type of therapy. Moreover, remissions induced by adoptively infused NK cells are only transient and require subsequent therapy to maintain durable responses. Hence, new strategies are needed to trigger full and durable anti-leukemia responses by NK cells in patients with myeloid malignancies. To achieve this, we need to better understand the interplay between the malignant cells, their microenvironment, and the NK cells. This review focuses on mechanisms that are involved in suppressing NK cells in patients with myeloid leukemia and MDS, and means to restore their full anti-tumor potential. It also discusses novel molecular targets and approaches, such as bi- and tri-specific antibodies and immune checkpoint inhibitors, to redirect and/or unleash the NK cells against the leukemic cells.

Role of ADAM17 as a regulatory checkpoint of CD16A in NK cells and as a potential target for cancer immunotherapy

Human NK cell antitumor activities involve Ab-dependent cell-mediated cytotoxicity (ADCC), which is a key mechanism of action for several clinically successful tumor-targeting therapeutic mAbs. Human NK cells exclusively recognize these Abs by the Fcγ receptor CD16A (FcγRIIIA), one of their most potent activating receptors. Unlike other activating receptors on NK cells, CD16A undergoes a rapid down-regulation in expression by a proteolytic process following NK cell activation with various stimuli. In this review, the role of a disintegrin and metalloproteinase-17 (ADAM17) in CD16A cleavage and as a regulatory checkpoint is discussed. Several studies have examined the effects of inhibiting ADAM17 or CD16A cleavage directly during NK cell engagement of Ab-coated tumor cells, which resulted in strengthened Ab tethering, decreased tumor cell detachment, and enhanced CD16A signaling and cytokine production. However, the effects of either manipulation on ADCC have varied between studies, which may be due to dissimilar assays and the contribution of different killing processes by NK cells. Of importance is that NK cells under various circumstances, including in the tumor microenvironment of patients, down-regulate CD16A and this appears to impair their function. Considerable progress has been made in the development of ADAM17 inhibitors, including human mAbs that have advantages of high specificity and increased half-life in vivo. These inhibitors may provide a therapeutic means of increasing ADCC potency and/or antitumor cytokine production by NK cells in an immunosuppressive tumor microenvironment, and if used in combination with tumor-targeting Abs or NK cell-based adoptive immunotherapies may improve their efficacy.

Anti-CD105 Antibody Eliminates Tumor Microenvironment Cells and Enhances Anti-GD2 Antibody Immunotherapy of Neuroblastoma with Activated Natural Killer Cells

PURPOSE

We determined whether elimination of CD105⁺ cells in the tumor microenvironment (TME) with anti-CD105 antibodies enhanced anti-disialoganglioside (GD2) antibody dinutuximab therapy of neuroblastoma when combined with activated natural killer (aNK) cells.

EXPERIMENTAL DESIGN

The effect of MSCs and monocytes on antibody-dependent cellular cytotoxicity (ADCC) mediated by dinutuximab with aNK cells against neuroblastoma cells was determined in vitro. ADCC with anti-CD105 mAb TRC105 and aNK cells against MSCs, monocytes, and endothelial cells, which express CD105, was evaluated. Anti-neuroblastoma activity in immunodeficient NSG mice of dinutuximab with aNK cells without or with anti-CD105 mAbs was determined using neuroblastoma cell lines and a patient-derived xenograft.

RESULTS

ADCC mediated by dinutuximab with aNK cells against neuroblastoma cells in vitro was suppressed by addition of MSCs and monocytes, and dinutuximab with aNK cells was less effective against neuroblastomas formed with coinjected MSCs and monocytes in NSG mice than against those formed by tumor cells alone. Anti-CD105 antibody TRC105 with aNK cells mediated ADCC against MSCs, monocytes, and endothelial cells. Neuroblastomas formed in NSG mice by two neuroblastoma cell lines or a patient-derived xenograft coinjected with MSCs and monocytes were most effectively treated with dinutuximab and aNK cells when anti-human (TRC105) and anti-mouse (M1043) CD105 antibodies were added, which depleted human MSCs and murine endothelial cells and macrophages from the TME.

CONCLUSIONS

Immunotherapy of neuroblastoma with anti-GD2 antibody dinutuximab and aNK cells is suppressed by CD105⁺ cells in the TME, but suppression is overcome by adding anti-CD105 antibodies to eliminate CD105⁺ cells.

161533 TriKE stimulates NK-cell function to overcome myeloid-derived suppressor cells in MDS

Myelodysplastic syndrome (MDS) is a clonal heterogeneous stem cell disorder driven by multiple genetic and epigenetic alterations resulting in ineffective hematopoiesis. MDS has a high frequency of immune suppressors, including myeloid-derived suppressor cells (MDSCs), that collectively result in a poor immune response. MDSCs in MDS patients express CD155 that ligates the T-cell immunoreceptor with immunoglobulin and ITIM domain (TIGIT) and delivers an inhibitory signal to natural killer (NK) cells. To mediate a productive immune response against MDS, negative regulatory checkpoints, like TIGIT, expressed on MDS NK cells must be overcome. NK cells can be directed to lyse MDS cells by bispecific killer engagers (BiKEs) that ligate CD16 on NK cells and CD33 on MDS cells. However, such CD16 × CD33 (1633) BiKEs do not induce the proliferative response in MDS NK cells needed to sustain their function. Here, we show that the addition of an NK stimulatory cytokine, interleukin-15 (IL-15), into the BiKE platform leads to productive IL-15 signaling without TIGIT upregulation on NK cells from MDS patients. Lower TIGIT expression allowed NK cells to resist MDSC inhibition. When compared with 1633 BiKE, 161533 trispecific killer engager (TriKE)-treated NK cells demonstrated superior killing kinetics associated with increased STAT5 phosphorylation. Furthermore, 161533 TriKE-treated MDS NK cells had higher proliferation and enhanced NK-cell function than 1633 BiKE-treated cells without the IL-15 linker. Collectively, our data demonstrate novel characteristics of the 161533 TriKE that support its application as an immunotherapeutic agent for MDS patients.

Immunosenescence and Immunotherapy in Elderly Acute Myeloid Leukemia Patients: Time for a Biology-Driven Approach

Acute myeloid leukemia (AML) is a disease, which mainly affects the elderly population. Unfortunately, the prognosis of patients aged >65 years is dismal, with 1-year overall survival approaching 10% with conventional therapies. The hypothesis of harnessing the immune system against cancer, including leukemia, has been postulated for a long time, and several clinical attempts have been made in this field. In the last years, we increased our knowledge about the interplay between AML and immune cells, but no major improvement has been translated, up to now, from bench to bedside. However, the outstanding results coming from the modern immuno-oncology trials with new drugs have granted a new interest for immunotherapy in AML. Accordingly, the elderly population represents an ideal target, given the low percentage of patients eligible for allogeneic stem cell transplant. With that in mind, in the era of immunotherapy, we consider immunosenescence as the optimal background to start investigating a biology-driven approach to AML therapy in the elderly. By taking into account the physiological age-related changes of immune response, more personalized and tailored use of the new drugs and strategies harnessing the immune system against AML, has the potential to increase their efficacy and impact on clinical outcomes.

Investigational CD33-targeted therapeutics for acute myeloid leukemia

INTRODUCTION

There is long-standing interest in drugs targeting the myeloid differentiation antigen CD33 in acute myeloid leukemia (AML). Positive results from randomized trials with the antibody-drug conjugate (ADC) gemtuzumab ozogamicin (GO) validate this approach. Partly stimulated by the success of GO, several CD33-targeted therapeutics are currently in early phase testing.

AREAS COVERED

CD33-targeted therapeutics in clinical development include Fc-engineered unconjugated antibodies (BI 836858 [mAb 33.1]), ADCs (SGN-CD33A [vadastuximab talirine], IMGN779), radioimmunoconjugates (²²⁵Ac-lintuzumab), bi- and trispecific antibodies (AMG 330, AMG 673, AMV564, 161533 TriKE fusion protein), and chimeric antigen receptor (CAR)-modified immune effector cells. Besides limited data on ²²⁵Ac-lintuzumab showing modest single-agent activity, clinical data are so far primarily available for SGN-CD33A. SGN-CD33A has single-agent activity and has shown encouraging results when combined with an azanucleoside or standard chemotherapeutics. However, concerns about toxicity to the liver and normal hematopoietic cells - the latter leading to early termination of a phase 3 trial - have derailed the development of SGN-CD33A, and its future is uncertain.

EXPERT OPINION

Early results from a new generation of CD33-targeted therapeutics are anticipated in the next 2-3 years. Undoubtedly, re-approval of GO in 2017 has changed the landscape and rendered clinical development for these agents more challenging.

Tumor immunotherapy: New aspects of natural killer cells

A group of impressive immunotherapies for cancer treatment, including immune checkpoint-blocking antibodies, gene therapy and immune cell adoptive cellular immunotherapy, have been established, providing new weapons to fight cancer. Natural killer (NK) cells are a component of the first line of defense against tumors and virus infections. Studies have shown dysfunctional NK cells in patients with cancer. Thus, restoring NK cell antitumor functionality could be a promising therapeutic strategy. NK cells that are activated and expanded ex vivo can supplement malfunctional NK cells in tumor patients. Therapeutic antibodies, chimeric antigen receptor (CAR), or bispecific proteins can all retarget NK cells precisely to tumor cells. Therapeutic antibody blockade of the immune checkpoints of NK cells has been suggested to overcome the immunosuppressive signals delivered to NK cells. Oncolytic virotherapy provokes antitumor activity of NK cells by triggering antiviral immune responses. Herein, we review the current immunotherapeutic approaches employed to restore NK cell antitumor functionality for the treatment of cancer.

Adoptive cell therapy in multiple Myeloma

INTRODUCTION

Recent breakthrough advances in Multiple Myeloma (MM) immunotherapy have been achieved with the approval of the first two monoclonal antibodies, elotuzumab and daratumumab. Adoptive cell therapy (ACT) represents yet another, maybe the most powerful modality of immunotherapy, in which allogeneic or autologous effector cells are expanded and activated ex vivo followed by their re-infusion back into patients. Infused effector cells belong to two categories: naturally occurring, non-engineered cells (donor lymphocyte infusion, myeloma infiltrating lymphocytes, deltagamma T cells) or genetically- engineered antigen-specific cells (chimeric antigen receptor T or NK cells, TCR-engineered cells). Areas covered: This review article summarizes our up-to-date knowledge on ACT in MM, its promises, and upcoming strategies to both overcome its toxicity and to integrate it into future treatment paradigms. Expert opinion: Early results of clinical studies using CAR T cells or TCR- engineered T cells in relapsed and refractory MM are particularly exciting, indicating the potential of long-term disease control or even cure. Despite several caveats including toxicity, costs and restricted availability in particular, these forms of immunotherapy are likely to once more revolutionize MM therapy.

Efficacy of an Fc-modified anti-CD123 antibody (CSL362) combined with chemotherapy in xenograft models of acute myelogenous leukemia in immunodeficient mice

The prognosis of older patients with acute myelogenous leukemia is generally poor. The interleukin-3 receptor α-chain (CD123) is highly expressed on the surface of acute leukemia cells compared with normal hematopoietic stem cells. CSL362 is a fully humanized, CD123-neutralizing monoclonal antibody containing a modified Fc structure, which enhances human natural killer cell antibody-dependent cell-mediated cytotoxicity. Six continuous acute myelogenous leukemia xenografts established from patient explants and characterized by cell and molecular criteria, produced progressively lethal disease 42-202 days after transplantation. CSL362 alone reduced engraftment of one of four and three of four acute myelogenous leukemia xenografts in the bone marrow and peripheral organs, respectively. A cytarabine and daunorubicin regimen was optimized using this model to identify potentially synergistic interactions with CSL362. Cytarabine/daunorubicin improved the survival of mice engrafted with four of four acute myelogenous leukemia xenografts by 31-41 days. Moreover, CSL362 extended the survival of cytarabine/daunorubicin-treated mice for two of two acute myelogenous leukemia xenografts, while augmentation of natural killer cell-deficient NSG mice with adoptively transferred human natural killer cells improved survival against a single xenograft. Interestingly, this enhanced CSL362 efficacy was lost in the absence of chemotherapy. This study shows that acute myelogenous leukemia xenografts provide a platform for the evaluation of new therapeutics, simulating complex in vivo interactions, and that the in vivo efficacy of CSL362 supports continued clinical development of this drug.

Natural killer cell therapy in children with relapsed leukemia

BACKGROUND

Novel therapies are needed for children with relapsed or refractory leukemia. We therefore tested the safety and feasibility of haploidentical natural killer cell therapy in this patient population.

PROCEDURE

Twenty-nine children who had relapsed or refractory leukemia were treated with chemotherapy followed by the infusion of haploidentical NK cells. Cohort 1 included 14 children who had not undergone prior allogeneic hematopoietic cell transplantation (HCT), whereas Cohort 2 included 15 children with leukemia that had relapsed after HCT.

RESULTS

Twenty-six (90%) NK donors were KIR mismatched (14 with one KIR and 12 with 2 KIRs). The peak NK chimerism levels were >10% donor in 87% of the evaluable recipients. In Cohort 1, 10 had responsive disease and 12 proceeded to HCT thereafter. Currently, 5 (36%) are alive without leukemia. In Cohort 2, 10 had responsive disease after NK therapy and successfully proceeded to second HCT. At present, 4 (27%) are alive and leukemia-free. The NK cell infusions and the IL-2 injections were well-tolerated.

CONCLUSIONS

NK cell therapy is safe, feasible, and should be further investigated in patients with chemotherapy-resistant leukemia.

Natural killer (NK) cells and anti-tumor therapeutic mAb: unexplored interactions

Tumor-targeting mAb are widely used in the treatment of a variety of solid and hematopoietic tumors and represent the first immunotherapeutic approach successfully arrived to the clinic. Nevertheless, the role of distinct immune mechanisms in contributing to their therapeutic efficacy is not completely understood and may vary depending on tumor- or antigen/antibody-dependent characteristics. Availability of next-generation, engineered, tumor-targeting mAb, optimized in their capability to recruit selected immune effectors, re-enforces the need for a deeper understanding of the mechanisms underlying anti-tumor mAb functionality. NK cells participate with a major role to innate anti-tumor responses, by exerting cytotoxic activity and producing a vast array of cytokines. As the CD16 (low-affinity FcγRIIIA)-activating receptor is expressed on the majority of NK cells, its effector functions can be ideally recruited against therapeutic mAb-opsonized tumor cells. The exact role of NK cells in determining therapeutic efficacy of tumor-targeting mAb is still unclear and much sought after. This knowledge will be instrumental to design innovative combination schemes with newly validated immunomodulatory agents. We will summarize what is known about the role of NK cells in therapeutic anti-tumor mAb therapy, with particular emphasis on RTX chimeric anti-CD20 mAb, the first one used in clinical practice for treating B cell malignancies.

Leukemogenic rearrangements at the mixed lineage leukemia gene (MLL)-multiple rather than a single mechanism

Despite manifold efforts to achieve reduced-intensity and -toxicity regimens, secondary leukemia has remained the most severe side effect of chemotherapeutic cancer treatment. Rearrangements involving a short telomeric <1 kb region of the mixed lineage leukemia (MLL) gene are the most frequently observed molecular changes in secondary as well as infant acute leukemia. Due to the mode-of-action of epipodophyllotoxins and anthracyclines, which have widely been used in cancer therapy, and support from in vitro experiments, cleavage of this MLL breakpoint cluster hotspot by poisoned topoisomerase II was proposed to trigger the molecular events leading to malignant transformation. Later on, clinical patient data and cell-based studies addressing a wider spectrum of stimuli identified cellular stress signaling pathways, which create secondary DNA structures, provide chromatin accessibility, and activate nucleases other than topoisomerase II at the MLL. The MLL destabilizing signaling pathways under discussion, namely early apoptotic DNA fragmentation, transcription stalling, and replication stalling, may all act in concert upon infection-, transplantation-, or therapy-induced cell cycle entry of hematopoietic stem and progenitor cells (HSPCs), to permit misguided cleavage and error-prone DNA repair in the cell-of-leukemia-origin.

New approaches for the immunotherapy of acute myeloid leukemia

Acute myeloid leukemia (AML) is a set of related diseases characterized by the immortalization and uncontrolled expansion of myeloid precursor cells. Core therapy for AML has remained unchanged for nearly 30 years, and survival rates remain unsatisfactory. However, advances in the immunotherapy of AML have created opportunities for improved outcomes. Enforcing a tumor-specific immune response through the re-direction of the adaptive immune system, which links remarkable specificity with potent cytotoxic effector functions, has proven particularly compelling. This may be coupled with immune checkpoint blockade and conventional therapies for optimal effect. Engineered antibodies are currently in use in AML and the repertoire of available therapeutics will expand. NK cells have shown effectiveness in this disease. New methods to optimize their activation and the targeting of AML show potential. Most significantly, adoptive immunotherapy with tumor-specific T cells, and particularly T cells re-directed using genetically introduced TCR or chimeric antigen receptors, have demonstrated promise. Each of these approaches has unique benefits and challenges that we explore in this review.

Chimeric antigen receptor-redirected CD45RA-negative T cells have potent antileukemia and pathogen memory response without graft-versus-host activity

Chimeric antigen receptor (CAR)-redirected cellular therapy is an attractive modality for cancer treatment. We hypothesized that allogeneic CAR-engineered CD45RA-negative T cells can control cancer and infection without the risk of graft-versus-host disease (GVHD). We used CD19(+) MLL-rearranged leukemia as prototype because it is an aggressive and generally drug-resistant malignancy. CD45RA(-) cells that were transduced with anti-CD19 CAR containing 4-1BB and CD3ζ signaling domains effectively lysed MLL-rearranged leukemia cell lines and primary blasts in vitro. In a disseminated leukemia mouse model, CAR(+)CD45RA(-) cells significantly reduced leukemia burdens and prolonged overall survival without GVHD. CAR(+) cells were sustainable in blood, and all the treated mice remained leukemia-free even after they were re-challenged with leukemia cells. Despite the transduction process, CD45RA(-) cells retained recall activity both in vitro and in vivo against human pathogens commonly found in cancer patients. In comparison with CD45RA(+) cells, CD45RA(-) cells showed less allogeneic activity in mixed leukocyte reactions and in mouse models. Thus, the use of CAR(+)CD45RA(-) cells can separate GVHD from graft-versus-malignancy effect and infection control. These cells should also be useful in nontransplant settings and may be administered as off-the-shelf third-party cells.

Ex vivo-expanded natural killer cells demonstrate robust proliferation in vivo in high-risk relapsed multiple myeloma patients

Highly activated/expanded natural killer (NK) cells can be generated by stimulation with the human leukocyte antigen-deficient cell line K562, genetically modified to express 41BB-ligand and membrane-bound interleukin (IL)15. We tested the safety, persistence, and activity of expanded NK cells generated from myeloma patients (auto-NK) or haploidentical family donors (allo-NK) in heavily pretreated patients with high-risk relapsing myeloma. The preparative regimen comprised bortezomib only or bortezomib and immunosuppression with cyclophosphamide, dexamethasone, and fludarabine. NK cells were shipped overnight either cryopreserved or fresh. In 8 patients, up to 1×10⁸ NK cells/kg were infused on day 0 and followed by daily administrations of IL2. Significant in vivo expansion was observed only in the 5 patients receiving fresh products, peaking at or near day 7, with the highest NK-cell counts in 2 subjects who received cells produced in a high concentration of IL2 (500 U/mL). Seven days after infusion, donor NK cells comprised >90% of circulating leukocytes in fresh allo-NK cell recipients, and cytolytic activity against allogeneic myeloma targets was retained in vitro. Among the 7 evaluable patients, there were no serious adverse events that could be related to NK-cell infusion. One patient had a partial response and in another the tempo of disease progression decreased; neither patient required further therapy for 6 months. In the 5 remaining patients, disease progression was not affected by NK-cell infusion. In conclusion, infusion of large numbers of expanded NK cells was feasible and safe; infusing fresh cells was critical to their expansion in vivo.

γδ T Cell-Mediated Antibody-Dependent Cellular Cytotoxicity with CD19 Antibodies Assessed by an Impedance-Based Label-Free Real-Time Cytotoxicity Assay

γδ T cells are not MHC restricted, elicit cytotoxicity against various malignancies, are present in early post-transplant phases in novel stem cell transplantation strategies and have been shown to mediate antibody-dependent cellular cytotoxicity (ADCC) with monoclonal antibodies (mAbs). These features make γδ T cells promising effector cells for antibody-based immunotherapy in pediatric patients with B-lineage acute lymphoblastic leukemia (ALL). To evaluate combination of human γδ T cells with CD19 antibodies for immunotherapy of B-lineage ALL, γδ T cells were expanded after a GMP-compliant protocol and ADCC of both primary and expanded γδ T cells with an Fc-optimized CD19 antibody (4G7SDIE) and a bi-specific antibody with the specificities CD19 and CD16 (N19-C16) was evaluated in CD107a-degranulation assays and intracellular cytokine staining. CD107a, TNFα, and IFNγ expression of primary γδ T cells were significantly increased and correlated with CD16-expression of γδ T cells. γδ T cells highly expressed CD107a after expansion and no further increased expression by 4G7SDIE and N19-C16 was measured. Cytotoxicity of purified expanded γδ T cells targeting CD19-expressing cells was assessed in both europium-TDA release and in an impedance-based label-free method (using the xCELLigence system) measuring γδ T cell lysis in real-time. Albeit in the 2 h end-point europium-TDA release assay no increased lysis was observed, in real-time xCELLigence assays both significant antibody-independent cytotoxicity and ADCC of γδ T cells were observed. The xCELLigence system outperformed the end-point europium-TDA release assay in sensitivity and allows drawing of conclusions to lysis kinetics of γδ T cells over prolonged periods of time periods. Combination of CD19 antibodies with primary as well as expanded γδ T cells exhibits a promising approach, which may enhance clinical outcome of patients with pediatric B-lineage ALL and requires clinical evaluation.

Antibody Fc engineering improves frequency and promotes kinetic boosting of serial killing mediated by NK cells

The efficacy of most therapeutic monoclonal antibodies (mAbs) targeting tumor antigens results primarily from their ability to elicit potent cytotoxicity through effector-mediated functions. We have engineered the fragment crystallizable (Fc) region of the immunoglobulin G (IgG) mAb, HuM195, targeting the leukemic antigen CD33, by introducing the triple mutation Ser293Asp/Ala330Leu/Ile332Glu (DLE), and developed Time-lapse Imaging Microscopy in Nanowell Grids to analyze antibody-dependent cell-mediated cytotoxicity kinetics of thousands of individual natural killer (NK) cells and mAb-coated target cells. We demonstrate that the DLE-HuM195 antibody increases both the quality and the quantity of NK cell-mediated antibody-dependent cytotoxicity by endowing more NK cells to participate in cytotoxicity via accrued CD16-mediated signaling and by increasing serial killing of target cells. NK cells encountering targets coated with DLE-HuM195 induce rapid target cell apoptosis by promoting simultaneous conjugates to multiple target cells and induce apoptosis in twice the number of target cells within the same period as the wild-type mAb. Enhanced target killing was also associated with increased frequency of NK cells undergoing apoptosis, but this effect was donor-dependent. Antibody-based therapies targeting tumor antigens will benefit from a better understanding of cell-mediated tumor elimination, and our work opens further opportunities for the therapeutic targeting of CD33 in the treatment of acute myeloid leukemia.

Genetic diversity of the KIR/HLA system and outcome of patients with metastatic colorectal cancer treated with chemotherapy

OBJECTIVE

To explore genes of the killer-cell immunoglobulin-like receptor (KIR) and of the HLA ligand and their relationship with the outcome of metastatic colorectal cancer (mCRC) patients treated with first-line 5-fluorouracil, leucovorin, and irinotecan (FOLFIRI).

METHODS

A total of 224 mCRC patients were screened for KIR/HLA typing. The determination of the KIR/HLA combinations was based upon the gene content and variants. Genetic associations with complete response (CR), time to progression (TTP) and overall survival (OS) were evaluated by calculating odds and hazard ratios. Multivariate modeling with prognostic covariates was also performed.

RESULTS

For CR, the presence of KIR2DL5A, 2DS5, 2DS1, 3DS1, and KIR3DS1/HLA-Bw4-I80 was associated with increased CR rates, with median ORs ranging from 2.1 to 4.3, while the absence of KIR2DS4 and 3DL1 was associated with increased CR rates (OR 3.1). After univariate analysis, patients that underwent resective surgery of tumor, absence of KIR2DS5, and presence of KIR3DL1/HLA-Bw4-I80 showed a significant better OS (HR 1.5 to 2.8). Multivariate analysis identified as parameters independently related to OS the type of treatment (surgery; HR 2.0) and KIR3DL1/HLA-Bw4-I80 genotype (HR for T-I80 2.7 and for no functional KIR/HLA interaction 1.8). For TTP, no association with KIR/HLA genes was observed.

CONCLUSION

This study, for the first time, evidences that the genotyping for KIR-HLA pairs are found predictive markers associated with complete response and improves overall survival prediction of FOLFIRI treatment response in metastatic colorectal cancer. These results suggest a role of the KIR/HLA system in patient outcome, and guide new research on the immunogenetics of mCRC through mechanistic studies and clinical validation.

Modulation of NKG2D ligand expression and metastasis in tumors by spironolactone via RXRγ activation

The diuretic drug spironolactone up-regulates NKG2D ligand expression in colon cancer cells via activation of the ATM–Chk2–mediated checkpoint pathway to enhance the antitumor function of NK cells.

Tumor metastasis and lack of NKG2D ligand (NKG2DL) expression are associated with poor prognosis in patients with colon cancer. Here, we found that spironolactone (SPIR), an FDA-approved diuretic drug with a long-term safety profile, can up-regulate NKG2DL expression in multiple colon cancer cell lines by activating the ATM–Chk2-mediated checkpoint pathway, which in turn enhances tumor elimination by natural killer cells. SPIR can also up-regulate the expression of metastasis-suppressor genes TIMP2 and TIMP3, thereby reducing tumor cell invasiveness. Although SPIR is an aldosterone antagonist, its antitumor effects are independent of the mineralocorticoid receptor pathway. By screening the human nuclear hormone receptor siRNA library, we identified retinoid X receptor γ (RXRγ) instead as being indispensable for the antitumor functions of SPIR. Collectively, our results strongly support the use of SPIR or other RXRγ agonists with minimal side effects for colon cancer prevention and therapy.

Natural killer cell mediated antibody-dependent cellular cytotoxicity in tumor immunotherapy with therapeutic antibodies

In the last decade several therapeutic antibodies have been Federal Drug Administration (FDA) and European Medicines Agency (EMEA) approved. Although their mechanisms of action in vivo is not fully elucidated, antibody-dependent cellular cytotoxicity (ADCC) mediated by natural killer (NK) cells is presumed to be a key effector function. A substantial role of ADCC has been demonstrated in vitro and in mouse tumor models. However, a direct in vivo effect of ADCC in tumor reactivity in humans remains to be shown. Several studies revealed a predictive value of FcγRIIIa-V158F polymorphism in monoclonal antibody treatment, indicating a potential effect of ADCC on outcome for certain indications. Furthermore, the use of therapeutic antibodies after allogeneic hematopoietic stem cell transplantation is an interesting option. Studying the role of the FcγRIIIa-V158F polymorphism and the influence of Killer-cell Immunoglobuline-like Receptor (KIR) receptor ligand incompatibility on ADCC in this approach may contribute to future transplantation strategies. Despite the success of approved second-generation antibodies in the treatment of several malignancies, efforts are made to further augment ADCC in vivo by antibody engineering. Here, we review currently used therapeutic antibodies for which ADCC has been suggested as effector function.