The requirement for DNAM-1, NKG2D, and NKp46 in the natural killer cell-mediated killing of myeloma cells

Phenotype and Function of Activated Natural Killer Cells From Patients With Prostate Cancer: Patient-Dependent Responses to Priming and IL-2 Activation

Background: Although immunotherapy has emerged as the “next generation” of cancer treatments, it has not yet been shown to be successful in the treatment of patients with prostate cancer, for whom therapeutic options remain limited to radiotherapy and androgen (hormone) deprivation therapy. Previous studies have shown that priming natural killer (NK) cells isolated from healthy individuals via co-incubation with CTV-1 cells derived from an acute lymphoblastic leukemia (ALL) enhances their cytotoxicity against human DU145 (metastatic) prostate cancer cells, but it remains unknown to what extent NK cells from patients with prostate cancer can be triggered to kill. Herein, we explore the phenotype of peripheral blood NK cells in patients with prostate cancer and compare the capacity of CTV-1 cell-mediated priming and IL-2 stimulation to trigger NK cell-mediated killing of the human PC3 (metastatic) prostate cancer cell line.

Methods: The phenotype of resting, primed (co-incubation with CTV-1 cells for 17 h) and IL-2 activated (100 IU/ml IL-2 for 17 h) NK cells isolated from frozen-thawed peripheral blood mononuclear cell (PBMC) preparations from patients with benign disease (n = 6) and prostate cancer (n = 18) and their cytotoxicity against PC3 and K562 cells was determined by flow cytometry. Relationship(s) between NK cell phenotypic features and cytotoxic potential were interrogated using Spearman Rank correlation matrices.

Results and Conclusions: NK cell priming and IL-2 activation of patient-derived NK cells resulted in similar levels of cytotoxicity, but distinct NK cell phenotypes. Importantly, the capacity of priming and IL-2 stimulation to trigger cytotoxicity was patient-dependent and mutually exclusive, in that NK cells from ~50% of patients preferentially responded to priming whereas NK cells from the remaining patients preferentially responded to cytokine stimulation. In addition to providing more insight into the biology of primed and cytokine-stimulated NK cells, this study supports the use of autologous NK cell-based immunotherapies for the treatment of prostate cancer. However, our findings also indicate that patients will need to be stratified according to their potential responsiveness to individual therapeutic approaches.

Monitoring TIGIT/DNAM-1 and PVR/PVRL2 Immune Checkpoint Expression Levels in Allogeneic Stem Cell Transplantation for Acute Myeloid Leukemia

After allogeneic stem cell transplantation (alloSCT), several immune checkpoints play an important role in the antileukemic immune response in the bone marrow (BM) microenvironment. However, immune checkpoint expression levels in the BM have not been reported after alloSCT in patients with acute myeloid leukemia (AML). We investigated the clinical impact of immune checkpoint expression in BM samples after alloSCT for AML. Higher expression of T cell immunoreceptor with Ig and ITIM domains (TIGIT) was associated with a decreased incidence of acute graft-versus-host disease (P = .048) and poor overall (P = .046) and progression-free survival (P = 0.024). In addition, higher expression of TIGIT at engraftment after alloSCT was correlated with a decreased number of natural killer cells in BM (P = .019). Monitoring TIGIT expression in the BM could be useful for predicting outcome after alloSCT for AML. Our findings raise the possibility that blockade of TIGIT would improve survival.

Targeting PVR (CD155) and its receptors in anti-tumor therapy

Poliovirus receptor (PVR, CD155) has recently been gaining scientific interest as a therapeutic target in the field of tumor immunology due to its prominent endogenous and immune functions. In contrast to healthy tissues, PVR is expressed at high levels in several human malignancies and seems to have protumorigenic and therapeutically attractive properties that are currently being investigated in the field of recombinant oncolytic virotherapy. More intriguingly, PVR participates in a considerable number of immunoregulatory functions through its interactions with activating and inhibitory immune cell receptors. These functions are often modified in the tumor microenvironment, contributing to tumor immunosuppression. Indeed, increasing evidence supports the rationale for developing strategies targeting these interactions, either in terms of checkpoint therapy (i.e., targeting inhibitory receptors) or in adoptive cell therapy, which targets PVR as a tumor marker.

Natural killer cels in immunotherapy for cancer

Cancer is the second leading cause of death worldwide behind cardiovascular diseases. Late stage of cancer at diagnosis and low efficacy of traditional cancer treatments result in low survival rate in cancer patients. Modern techniques to kill tumor cells are therefore needed. Over the last decade novel anticancer treatments have emerged from advances in our understanding of tumor cell biology, and a number of molecular and biologic targets have been identified. Chimeric antigen receptor T cell (CAR-T cell) therapy is a novel adoptive immunotherapy, which is used predominantly in the treatment of hematological malignancies. Moreover, it has been evidenced that cells of the innate immune system are key players at initiating and regulating adaptive immune responses. Studies focusing on innate immune cells for cancer immunotherapy show promising results. In this review, we describe functions of natural killer cells and analyze the rationale for using natural killer cells in cancer therapy.

Key Role of the CD56lowCD16low Natural Killer Cell Subset in the Recognition and Killing of Multiple Myeloma Cells

Natural Killer (NK) cells play a pivotal role in the immunosurveillance of Multiple Myeloma (MM), but it is still undefined whether the NK cell functional properties underlying their protective activity against MM are confined to distinct NK cell populations. Interestingly, herein we report that the CD56^lowCD16^low NK cell subset displayed higher cytolytic activity compared to the other NK cell subsets (i.e., CD56^highCD16^+/−, CD56^lowCD16^high) against MM cells and its activity was impaired in MM patients. Decreased DNAM-1 expression levels were observed on the CD56^lowCD16^low NK cells during MM progression. Evaluating NK cell subset frequency after autologous hematopoietic stem cell transplantation, we found that CD56^lowCD16^low NK cells recovered earlier after transplantation. Overall, our data denote a key role of CD56^lowCD16^low subpopulation in the killing of MM cells and suggest that the reconstitution of CD56^lowCD16^low subpopulation after HSCT could be a useful approach of adoptive immunotherapy in the treatment of relapsed/refractory MM patients.

Enhancing the Activation and Releasing the Brakes: A Double Hit Strategy to Improve NK Cell Cytotoxicity Against Multiple Myeloma

Natural killer (NK) cells are innate lymphocytes with a strong antitumor ability. In tumor patients, such as multiple myeloma (MM) patients, an elevated number of NK cells after stem cell transplantation (SCT) has been reported to be correlated with a higher overall survival rate. With the aim of improving NK cell use for adoptive cell therapy, we also addressed the cytotoxicity of patient-derived, cytokine-stimulated NK cells against MM cells at specific time points: at diagnosis and before and after autologous stem cell transplantation. Remarkably, after cytokine stimulation, the patients' NK cells did not significantly differ from those of healthy donors. In a small cohort of MM patients, we were able to isolate autologous tumor cells, and we could demonstrate that IL-2/15 stimulated autologous NK cells were able to significantly improve their killing capacity of autologous tumor cells. With the aim to further improve the NK cell killing capacity against MM cells, we investigated the potential use of NK specific check point inhibitors with focus on NKG2A because this inhibitory NK cell receptor was upregulated following ex vivo cytokine stimulation and MM cells showed HLA-E expression that could even be increased by exposure to IFN-γ. Importantly, blocking of NKG2A resulted in a significant increase in the NK cell-mediated lysis of different MM target cells. Finally, these results let suggest that combining cytokine induced NK cell activation and the specific check point inhibition of the NKG2A-mediated pathways can be an effective strategy to optimize NK cell therapeutic approaches for treatment of multiple myeloma.

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.

Myeloma Bone Disease: Update on Pathogenesis and Novel Treatment Strategies

Bone disease, including osteolytic lesions and/or osteoporosis, is a common feature of multiple myeloma (MM). The consequences of skeletal involvement are severe pain, spinal cord compressions, and bone fractures, which have a dramatic impact on patients’ quality of life and, ultimately, survival. During the past few years, several landmark studies significantly enhanced our insight into MM bone disease (MBD) by identifying molecular mechanisms leading to increased bone resorption due to osteoclast activation, and decreased bone formation by osteoblast inhibition. Bisphosphonates were the mainstay to prevent skeletal-related events in MM for almost two decades. Excitingly, the most recent approval of the receptor activator of NF-kappa B ligand (RANKL) inhibitor, denosumab, expanded treatment options for MBD, for patients with compromised renal function, in particular. In addition, several other bone-targeting agents, including bone anabolic drugs, are currently in preclinical and early clinical assessment. This review summarizes our up-to-date knowledge on the pathogenesis of MBD and discusses novel state-of-the-art treatment strategies that are likely to enter clinical practice in the near future.

The challenges of checkpoint inhibition in the treatment of multiple myeloma

Despite significant improvements in the overall survival of patients with multiple myeloma (MM) over the past 15 years, the disease remains incurable. Treatment options are limited for patients who have relapsed or are refractory to immunomodulatory drugs (IMiDs), proteasome inhibitors, and monoclonal antibodies. In these patients, immunotherapies such as checkpoint inhibitors, oncolytic vaccines, and chimeric antigen receptor (CAR) T cells provide a potentially effective alternative treatment. While checkpoint inhibitors are effective in prolonging overall survival in some patients with advanced solid cancers and Hodgkin lymphoma, they have not demonstrated significant activity as a single agent in MM. In fact the combination of checkpoint inhibitors with IMiDs was recently found to increase the risk of death in myeloma patients. These challenges highlight the need for a better understanding of immune dysregulation in myeloma patients, and the mechanisms of action of- and resistance to- checkpoint inhibitors. In this review, we summarize immune dysfunction in patients with MM, and review the preclinical and clinical data regarding checkpoint inhibitors in myeloma. We conclude by proposing strategies to improve the efficacy and safety of checkpoint inhibitors in this population.

Selective DNAM-1 expression on small peritoneal macrophages contributes to CD4+ T cell costimulation

Mouse peritoneal macrophages consist of two subsets: large peritoneal macrophages (LPMs) and small peritoneal macrophages (SPMs), defined as CD11b^hiF4/80^hi and CD11b⁺F4/80^lo cells, respectively. We reveal that SPMs, but not LPMs, have the ability to present antigens to naïve CD4⁺ T cells. Coculture of SPMs with naïve ovalbumin (OVA) specific CD4⁺ T cells (OT-II) in the presence of OVA peptide effectively induced CD4⁺ T cells priming. SPMs, but not LPMs, strongly express DNAM-1, an activating immunoreceptor. Although antigen uptake and processing were comparable between WT and DNAM-1-deficient SPMs, deficiency of DNAM-1 on SPMs or blockade of DNAM-1 and its ligand interaction impaired CD4⁺ T cells priming by SPMs. Furthermore, T and B cell responses in mediastinal lymph nodes of mice intraperitoneally immunized with trinitrophenyl (TNP)–OVA protein in Alum adjuvant were enhanced by intraperitoneally transferred wild-type, but not DNAM-1-deficient, SPMs. We propose that SPMs are functionally distinct from LPMs, and DNAM-1 plays a costimulatory role in antigen presentation by SPMs.

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.

Myeloma escape after stem cell transplantation is a consequence of T-cell exhaustion and is prevented by TIGIT blockade

Autologous stem cell transplantation (SCT) remains a standard of care for multiple myeloma (MM) patients and prolongs progression-free survival. A small cohort of patients achieve long-term control of disease, but the majority of patients ultimately relapse, and the mechanisms permitting disease progression remain unclear. In this study, we used a preclinical model of autologous SCT for myeloma where the disease either progressed (MM relapsed) or was controlled. In the bone marrow (BM), inhibitory receptor expression on CD8⁺ T cells correlated strongly with myeloma progression after transplant. In conjunction, the costimulatory/adhesion receptor CD226 (DNAM-1) was markedly downregulated. Interestingly, DNAM-1^- CD8⁺ T cells in MM-relapsed mice had an exhausted phenotype, characterized by upregulation of multiple inhibitory receptors, including T-cell immunoglobulin and ITIM domains (TIGIT) and programmed cell death protein 1 (PD-1) with decreased T-bet and increased eomesodermin expression. Immune checkpoint blockade using monoclonal antibodies against PD-1 or TIGIT significantly prolonged myeloma control after SCT. Furthermore, CD8⁺ T cells from MM-relapsed mice exhibited high interleukin-10 (IL-10) secretion that was associated with increased TIGIT and PD-1 expression. However, while donor-derived IL-10 inhibited myeloma control post-SCT, this was independent of IL-10 secretion by or signaling to T cells. Instead, the donor myeloid compartment, including colony-stimulating factor 1 receptor-dependent macrophages and an IL-10-secreting dendritic cell population in the BM, promoted myeloma progression. Our findings highlight PD-1 or TIGIT blockade in conjunction with SCT as a potent combination therapy in the treatment of myeloma.

Interaction of PVR/PVRL2 with TIGIT/DNAM-1 as a novel immune checkpoint axis and therapeutic target in cancer

Avoiding immune surveillance and inducing a tumor-promoting inflammatory milieu found entry into the new generation of the hallmarks of cancer. Cancer cells hijack immune mechanisms which physiologically protect the body from the development of autoimmune diseases and excessive tissue damage during inflammation by downregulating immune responses. This is frequently achieved by upregulation of immune checkpoints. Therefore, the blocking of immune checkpoint ligand-receptor interactions can reinstall the immune systems capability to fight cancer cells as shown for CTLA4 and PD-1 inhibitors in a clinical setting. Newly described checkpoint antigens are currently under investigation in cancer immunotherapy. Preclinical data emphasize the immune checkpoint axis TIGIT-PVR/PVRL2 as very promising target. This axis includes additional receptors such as DNAM-1, CD96, and CD112R. In this review, we discuss the recent findings of the relevance of this complex receptor ligand system in hematologic and solid cancers. Emphasis is also laid on the discussion of potential combinations with other immunotherapeutic approaches.

TIGIT immune checkpoint blockade restores CD8+ T-cell immunity against multiple myeloma

Immune-based therapies hold promise for the treatment of multiple myeloma (MM), but so far, immune checkpoint blockade targeting programmed cell death protein 1 has not proven effective as single agent in this disease. T-cell immunoglobulin and ITIM domains (TIGIT) is another immune checkpoint receptor known to negatively regulate T-cell functions. In this study, we investigated the therapeutic potential of TIGIT blockade to unleash immune responses against MM. We observed that, in both mice and humans, MM progression was associated with high levels of TIGIT expression on CD8⁺ T cells. TIGIT⁺ CD8⁺ T cells from MM patients exhibited a dysfunctional phenotype characterized by decreased proliferation and inability to produce cytokines in response to anti-CD3/CD28/CD2 or myeloma antigen stimulation. Moreover, when challenged with Vk*MYC mouse MM cells, TIGIT-deficient mice showed decreased serum monoclonal immunoglobulin protein levels associated with reduced tumor burden and prolonged survival, indicating that TIGIT limits antimyeloma immune responses. Importantly, blocking TIGIT using monoclonal antibodies increased the effector function of MM patient CD8⁺ T cells and suppressed MM development. Altogether our data provide evidence for an immune-inhibitory role of TIGIT in MM and support the development of TIGIT-blocking strategies for the treatment of MM patients.

Coming of Age: CD96 Emerges as Modulator of Immune Responses

CD96 represents a type I transmembrane glycoprotein belonging to the immunoglobulin superfamily. CD96 is expressed mainly by cells of hematopoietic origin, in particular on T and NK cells. Upon interaction with CD155 present on target cells, CD96 was found to inhibit mouse NK cells, and absence of this interaction either by blocking with antibody or knockout of CD96 showed profound beneficial effects in containment of tumors and metastatic spread in murine model systems. However, our knowledge regarding CD96 functions remains fragmentary. In this review, we will discuss structural features of CD96 and their putative impact on function as well as some unresolved issues such as a potential activation that may be conferred by human but not mouse CD96. This is of importance for translation into human cancer therapy. We will also address CD96 activities in the context of the immune regulatory network that consists of CD155, CD96, CD226, and TIGIT.

A CS1-NKG2D Bispecific Antibody Collectively Activates Cytolytic Immune Cells against Multiple Myeloma

Multiple myeloma (MM) is an incurable hematologic malignancy of plasma cells, with an estimated 30,000 new cases diagnosed each year in the United States, signifying the need for new therapeutic approaches. We hypothesized that targeting MM using a bispecific antibody (biAb) to simultaneously engage both innate and adaptive cytolytic immune cells could present potent antitumor activity. We engineered a biAb by fusing an anti-CS1 single-chain variable fragment (scFv) and an anti-NKG2D scFv (CS1-NKG2D biAb). Although NKG2D is a potent activation receptor ubiquitously expressed on mostly cytolytic immune cells including NK cells, CD8⁺ T cells, γδ T cells, and NKT cells, the CS1 tumor-associated antigen on MM represents a promising target. CS1-NKG2D biAb engaged human MM cell lines and NKG2D⁺ immune cells, forming immune synapses. In effector cells, CS1-NKG2D biAb triggered the phosphorylation of AKT, a downstream protein kinase of the activated NKG2D-DAP10 complex. The EC₅₀ values of CS1-NKG2D biAb for CS1^high and for CS1^low MM cell lines with effector PBMCs were 10^-12 and 10^-9 mol/L, respectively. CS1-NKG2D biAb acted through multiple types of immune cells, and this induced cytotoxicity was both CS1- and NKG2D-specific. In vivo, survival was significantly prolonged using CS1-NKG2D biAb in a xenograft NOD-SCID^IL2γc-/- (NSG) mouse model engrafted with both human PBMCs and MM cell lines. Collectively, we demonstrated that the CS1-NKG2D biAb facilitated an enhanced immune synapse between CS1⁺ MM cells and NKG2D⁺ cytolytic innate and antigen-specific effector cells, which, in turn, activated these immune cells for improved clearance of MM. Cancer Immunol Res; 6(7); 776-87. ©2018 AACR.

The combination of ionizing radiation and proteasomal inhibition by bortezomib enhances the expression of NKG2D ligands in multiple myeloma cells

Bortezomib, which is a potent proteasome inhibitor, has been used as a first-line drugs to treat multiple myeloma for a few decades, and radiotherapy has frequently been applied to manage acute bone lesions in the patients. Therefore, it was necessary to investigate what the benefits might be if the two therapies were applied simultaneously in the treatment of multiple myeloma. Since it was known that radiotherapy and proteasome inhibitors could increase the expression of NKG2D ligands through induction of protein synthesis and suppression of protein degradation of NKG2D ligands, respectively, we supposed that the combined treatment might further enhance the expression of NKG2D ligands. In this study, we analyzed the expression level of NKG2D ligands using multiplex PCR and flow cytometry after treatment of IM-9 and RPMI-8226 myeloma cells with bortezomib and ionizing radiation; we then assayed the susceptibility to NK-92 cells. Although the expression of only some kinds of NKG2D ligands were increased by treatment with bortezomib alone, five kinds of NKG2D ligands that we assayed were further induced at the surface protein level after combined treatment with ionizing radiation and bortezomib. Furthermore, combined treatment made myeloma cells more susceptible to NK-92 cells, compared with treatment with bortezomib alone. In conclusion, the combination therapy of ionizing radiation plus the proteasome inhibitor bortezomib is a promising therapeutical strategy for enhancing NK cell-mediated anticancer immune responses.

One-Year Follow-Up of Natural Killer Cell Activity in Multiple Myeloma Patients Treated With Adjuvant Lenalidomide Therapy

Multiple myeloma (MM) is a proliferation of tumoral plasma B cells that is still incurable. Natural killer (NK) cells can recognize and kill MM cells in vitro and can limit MM growth in vivo. Previous reports have shown that NK cell function is impaired during MM progression and suggested that treatment with immunomodulatory drugs (IMIDs) such as lenalidomide (LEN) could enhance it. However, the effects of IMIDs on NK cells have been tested mostly in vitro or in preclinical models and supporting evidence of their effect in vivo in patients is lacking. Here, we monitored NK cell activity in blood samples from 10 MM patients starting after frontline induction chemotherapy (CTX) consisting either of association of bortezomib–lenalidomide–dexamethasone (Velcade Revlimid Dexamethasone) or autologous stem-cell transplantation (SCT). We also monitored NK cell activity longitudinally each month during 1 year, after maintenance therapy with LEN. Following frontline chemotherapy, peripheral NK cells displayed a very immature phenotype and retained poor reactivity toward target cells ex vivo. Upon maintenance treatment with LEN, we observed a progressive normalization of NK cell maturation, likely caused by discontinuation of chemotherapy. However, LEN treatment neither activated NK cells nor improved their capacity to degranulate or to secrete IFN-γ or MIP1-β following stimulation with MHC-I-deficient or antibody-coated target cells. Upon LEN discontinuation, there was no reduction of NK cell effector function either. These results caution against the use of LEN as single therapy to improve NK cell activity in patients with cancer and call for more preclinical assessments of the potential of IMIDs in NK cell activation.

NK cells and multiple myeloma-associated endothelial cells: molecular interactions and influence of IL-27

Angiogenesis represents a hallmark of tumor progression in Multiple Myeloma (MM), a still incurable malignancy. Here we analyzed the activity of cytokine-stimulated NK cells against tumor-associated endothelial cells isolated from bone marrow aspirates of MM patients with active disease (MMECs). We show that NK cells activated with optimal doses of IL-15 killed MMECs thanks to the concerted action of multiple activating receptors. In particular, according to the high expression of PVR and Nectin-2 on MMECs, DNAM-1 actively participated in target recognition. Interestingly, in MMECs the surface density of PVR was significantly higher than that detected in endothelium from patients with MM in complete remission or with monoclonal gammopathy of undetermined significance (MGUS). Importantly, IL-27, which unlike IL-15 does not display pro-angiogenic properties, maintained or increased the NK cell functions induced by suboptimal concentrations of IL-15. NK cell properties included killing of MMECs, IFN-γ production as well as a peculiar increase of NKp46 expression on NK cell surface. Finally, IL-27 showed a striking capability of up-regulating the expression of PD-L2 and HLA-I on tumor endothelium, whereas it did not modify that of PD-L1 and HLA-II.

Our results suggest that cytokine-activated endogenous or adoptively transferred NK cells might support conventional therapies improving the outcome of MM patients.

Elotuzumab for the Treatment of Relapsed or Refractory Multiple Myeloma, with Special Reference to its Modes of Action and SLAMF7 Signaling

Elotuzumab, targeting signaling lymphocytic activation molecule family 7 (SLAMF7), has been approved in combination with lenalidomide and dexamethasone (ELd) for relapsed/refractory multiple myeloma (MM) based on the findings of the phase III randomized trial ELOQUENT-2 (NCT01239797). Four-year follow-up analyses of ELOQUENT-2 have demonstrated that progression-free survival was 21% in ELd versus 14% in Ld. Elotuzumab binds a unique epitope on the membrane IgC2 domain of SLAMF7, exhibiting a dual mechanism of action: natural killer (NK) cell-mediated antibody-dependent cellular cytotoxicity (ADCC) and enhancement of NK cell activity. The ADCC is mediated through engagement between Fc portion of elotuzumab and FcgRIIIa/CD16 on NK cells. Enhanced NK cell cytotoxicity results from phosphorylation of the immunoreceptor tyrosine-based switch motif (ITSM) that is induced via elotuzumab binding and recruits the SLAM-associated adaptor protein EAT-2. The coupling of EAT-2 to the phospholipase Cg enzymes SH2 domain leads to enhanced Ca²⁺ influx and MAPK/Erk pathway activation, resulting in granule polarization and enhanced exocytosis in NK cells. Elotuzumab does not stimulate the proliferation of MM cells due to a lack of EAT-2. The inhibitory effects of elotuzumab on MM cell growth are not induced by the lack of CD45, even though SHP-2, SHP-1, SHIP-1, and Csk may be recruited to phosphorylated ITSM of SLAMF7. ELd improves PFS in patients with high-risk cytogenetics, i.e. t(4;14), del(17p), and 1q21 gain/amplification. Since the immune state is paralytic in advanced MM, the efficacy of ELd with minimal toxicity may bring forward for consideration of its use in the early stages of the disease.

Abnormal populations and functions of natural killer cells in patients with myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are clonal stem cell disorders characterized by ineffective hematopoiesis that lead to leukemia. Disorders of the immune system serve important functions in the pathophysiology and progression of this disease. Different levels or mechanisms of natural killer (NK) cells in patients with MDS have been measured in previous studies, making it challenging to understand the pathogenesis of NK cytotoxicity. The present study investigated the frequency of NK cell-mediated antibody-dependent cellular cytotoxicity and explored the function of NK cells by their activating receptors, inhibition signals, degranulation and cytotoxicity factors. In the present study, levels of cluster of differentiation (CD)3^-CD56⁺ NK cells, CD16⁺-expressing NK cells and subset CD56^dim NK cells were decreased in the peripheral blood of patients with MDS. Altered expression of NK protein 44, NK group 2 member D, killer cell immunoglobulin-like receptor 2DL1 (KIR2DL1) and KIR2DL3 on NK cell effector signaling pathways may trigger tumor cell lysis in patients with MDS. The weak cellular adhesion and decreased cytotoxicity of NK cells may lead to ineffective antitumor activity in MDS. These observations suggested that NK cells may serve as immunological determinants in MDS and may permit the development of NK cell-based immunotherapy for the treatment of patients with MDS.

Altered expression of CD226 and CD96 on natural killer cells in patients with pancreatic cancer

The progression of pancreatic cancer (PC) is significantly associated with tumor immune escape, which may be associated with nature killer (NK) cell dysfunction. CD226, CD96, and TIGIT, which share the ligand CD155, play important roles in the regulation of NK cell function. The present study was conducted to investigate the roles of these molecules in NK cells from PC patients. Expression of these molecules on NK cells was detected from samples of 92 pancreatic cancer patients and 40 healthy controls. The expression of CD155 was also evaluated by immunohistochemistry in 88 pancreatic cancer tissues. The percentage of CD226⁺ and CD96⁺ NK cells was significantly lower in PC patients than in the healthy controls; however, the mean fluorescence intensity of CD226 and CD96 was not significantly different between the two groups. TIGIT expression on NK cells from PC patients was similar to that in the healthy controls. Additionally, the expression of CD226 was positively correlated with CD96. Further analysis demonstrated that the decrease in the percentage of CD226⁺ and CD96⁺ NK cells was associated with tumor histological grade and lymph node metastasis. Moreover, the CD155 levels in PC tissues were significantly higher than those in adjacent tissues. Our results suggest that a lower percentage of CD226⁺ and CD96⁺ NK cells may contribute to tumor immune escape in PC patients; moreover, the use of NK cells with high CD226 and CD96 expression to treat PC cells with high CD155 expression may have potential and should be explored in the future.

Immunopathogenesis and immunotherapy of multiple myeloma

Despite the advent of novel therapies and improvements in survival, multiple myeloma (MM) remains an incurable disease. Thus, new treatment strategies including immunotherapies are needed for MM patients with stable disease after induction chemotherapy as well as for disease control in patients with advanced disease. However, profound immune dysregulation not only of B cells, but also of other immune cells such as natural killer cells, T cells, and dendritic cells and increase in the number of immunosuppressive cells, i.e., regulatory T and B cells and myeloid-derived suppressor cells, have been demonstrated in advanced MM patients, which may be involved in disease progression. Because of immune dysfunction, immunotherapies have not shown clinical efficacy in MM patients. It is therefore crucial to resolve immunosuppressive mechanisms and improve immune responses, especially in advanced MM patients. Recently, excellent clinical efficacy of new immunotherapeutic strategies such as immunomodulatory drug-intensified monoclonal antibody treatment, immune checkpoint inhibitors, and chimeric antigen receptor T-cell therapy targeting B cell maturation antigen has been reported in advanced-stage MM patients. Those new treatments or their combination will improve prognosis and possibly point toward a cure for myeloma.

Hematologic Malignancies: Plasma Cell Disorders

Multiple myeloma (MM) is a plasma cell malignancy characterized by the growth of tumor cells in the bone marrow. Properties of the tumor microenvironment provide both potential tumor-promoting and tumor-restricting properties. Targeting underlying immune triggers for evolution of tumors as well as direct attack of malignant plasma cells is an emerging focus of therapy for MM. The monoclonal antibodies daratumumab and elotuzumab, which target the plasma cell surface proteins CD38 and SLAMF7/CS1, respectively, particularly when used in combination with immunomodulatory agents and proteasome inhibitors, have resulted in high response rates and improved survival for patients with relapsed and refractory MM. A number of other monoclonal antibodies are in various stages of clinical development, including those targeting MM cell surface antigens, the bone marrow microenvironment, and immune effector T cells such as antiprogrammed cell death protein 1 antibodies. Bispecific preparations seek to simultaneously target MM cells and activate endogenous T cells to enhance efficacy. Cellular immunotherapy seeks to overcome the limitations of the endogenous antimyeloma immune response through adoptive transfer of immune effector cells with MM specificity. Allogeneic donor lymphocyte infusion can be effective but can cause graft-versus-host disease. The most promising approach appears to be genetically modified cellular therapy, in which T cells are given novel antigen specificity through expression of transgenic T-cell receptors (TCRs) or chimeric antigen receptors (CARs). CAR T cells against several different targets are under investigation in MM. Infusion of CD19-targeted CAR T cells following salvage autologous stem cell transplantation (SCT) was safe and extended remission duration in a subset of patients with relapsed/refractory MM. CAR T cells targeting B-cell maturation antigen (BCMA) appear most promising, with dramatic remissions seen in patients with highly refractory disease in three ongoing trials. Responses are associated with degree of CAR T-cell expansion/persistence and often toxicity, including cytokine release syndrome (CRS) and neurotoxicity. Ongoing and future studies are exploring correlates of response, ways to mitigate toxicity, and "universal" CAR T cells.

Boosting Natural Killer Cell-Based Immunotherapy with Anticancer Drugs: a Perspective

Natural killer (NK) cells efficiently recognize and kill tumor cells through several mechanisms including the expression of ligands for NK cell-activating receptors on target cells. Different clinical trials indicate that NK cell-based immunotherapy represents a promising antitumor treatment. However, tumors develop immune-evasion strategies, including downregulation of ligands for NK cell-activating receptors, that can negatively affect antitumor activity of NK cells, which either reside endogenously, or are adoptively transferred. Thus, restoration of the expression of NK cell-activating ligands on tumor cells represents a strategic therapeutic goal. As discussed here, various anticancer drugs can fulfill this task via different mechanisms. We envision that the combination of selected chemotherapeutic agents with NK cell adoptive transfer may represent a novel strategy for cancer immunotherapy.

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.

Activation of NK cells and disruption of PD-L1/PD-1 axis: two different ways for lenalidomide to block myeloma progression

Natural Killer (NK) cells play a critical role against tumor cells in hematological malignancies. Their activating receptors are essential in tumor cell killing. In Multiple Myeloma (MM) patients, NK cell differentiation, activation and cytotoxic potential are strongly impaired leading to MM escape from immune surveillance in tissues and bone marrow. Mechanisms used by MM to affect NK cell functions are mediated by the release of soluble factors, the expression of activating and inhibitory NK cell ligands, and the expression of immune check-point inhibitors. Lenalidomide represents an efficient clinical approach in MM treatment to improve patients' survival. Lenalidomide does not only promotes tumor apoptosis, but also stimulates T and NK cells, thereby facilitating NK-mediated tumor recognition and killing. This occurs since Lenalidomide acts on several critical points: stimulates T cell proliferation and cytokine secretion; decreases the expression of the immune check-point inhibitor Programmed Death-1 (PD-1) on both T and NK cells in MM patients; decreases the expression of both PD-1 and PD-L1 on MM cells; promotes MM cell death and abrogates MM/stromal microenvironment cross-talk, a process known to promote the MM cell survival and proliferation. This leads to the inhibition of the negative signal induced by PD-1/PD-L1 axis on NK cells, restoring NK cell cytotoxic functions. Given the importance of an effective immune response to counteract the MM progression and the promising approaches using anti-PD-1/PD-L1 strategies, we will discuss in this review how Lenalidomide could represent an adequate approach to re-establish the recognition against MM by exhausted NK cell.

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.

Natural killer cell-mediated immunosurveillance of human cancer

The contribution of natural killer (NK) cells to immunosurveillance of human cancer remains debatable. Here, we discuss advances in several areas of human NK cell research, many of which support the ability of NK cells to prevent cancer development and avoid relapse following adoptive immunotherapy. We describe the molecular basis for NK cell recognition of human tumor cells and provide evidence for NK cell-mediated killing of human primary tumor cells ex vivo. Subsequently, we highlight studies demonstrating the ability of NK cells to migrate to, and reside in, the human tumor microenvironment where selection of tumor escape variants from NK cells can occur. Indirect evidence for NK cell immunosurveillance against human malignancies is provided by the reduced incidence of cancer in individuals with high levels of NK cell cytotoxicity, and the significant clinical responses observed following infusion of human NK cells into cancer patients. Finally, we describe studies showing enhanced tumor progression, or increased cancer incidence, in patients with inherited and acquired defects in cellular cytotoxicity. All these observations have in common that they, either indirectly or directly, suggest a role for NK cells in mediating immunosurveillance against human cancer. This opens up for exciting possibilities with respect to further exploring NK cells in settings of adoptive immunotherapy in human cancer.

Innate immune activating ligand SUMOylation affects tumor cell recognition by NK cells

Natural Killer cells are innate lymphocytes involved in tumor immunosurveillance. They express activating receptors able to recognize self-molecules poorly expressed on healthy cells but up-regulated upon stress conditions, including transformation. Regulation of ligand expression in tumor cells mainly relays on transcriptional mechanisms, while the involvement of ubiquitin or ubiquitin-like modifiers remains largely unexplored. Here, we focused on the SUMO pathway and demonstrated that the ligand of DNAM1 activating receptor, PVR, undergoes SUMOylation in multiple myeloma. Concurrently, we found that PVR is preferentially located in intracellular compartments in human multiple myeloma cell lines and malignant plasma cells and that inhibition of the SUMO pathway promotes its translocation to the cell surface, increasing tumor cell susceptibility to NK cell-mediated cytolysis. Our findings provide the first evidence of an innate immune activating ligand regulated by SUMOylation, and confer to this modification a novel role in impairing recognition and killing of tumor cells.

CD155, an onco-immunologic molecule in human tumors

CD155 is the fifth member in the nectin‐like molecule family, and functions as the receptor of poliovirus; therefore, CD155 is also referred to as necl‐5, or PVR. As an immunoglobulin‐like adhesion molecule, CD155 is involved in cell motility, and natural killer and T cell‐mediated immunity. CD155 is barely or weakly expressed in various normal human tissues, but frequently overexpressed in human malignant tumors. CD155 overexpression promotes tumor cell invasion and migration, and is associated with tumor progression and poor prognosis. As the ligand for both costimulatory receptor CD226 and coinhibitory receptor TIGIT and CD96 on natural killer and T cells, CD155 seems to play a dual role in oncoimmunity. However, some recent studies indicate that CD155 overexpression may induce tumor immune escape. Taken together, CD155 may be considered as a target for the treatment of tumors with CD155 overexpression.

Regulation of NKG2D-Dependent NK Cell Functions: The Yin and the Yang of Receptor Endocytosis

Natural-killer receptor group 2, member D (NKG2D) is a well characterized natural killer (NK) cell activating receptor that recognizes several ligands poorly expressed on healthy cells but up-regulated upon stressing stimuli in the context of cancer or viral infection. Although NKG2D ligands represent danger signals that render target cells more susceptible to NK cell lysis, accumulating evidence demonstrates that persistent exposure to ligand-expressing cells causes the decrease of NKG2D surface expression leading to a functional impairment of NKG2D-dependent NK cell functions. Upon ligand binding, NKG2D is internalized from the plasma membrane and sorted to lysosomes for degradation. However, receptor endocytosis is not only a mechanism of receptor clearance from the cell surface, but is also required for the proper activation of signalling events leading to the functional program of NK cells. This review is aimed at providing a summary of current literature relevant to the molecular mechanisms leading to NKG2D down-modulation with particular emphasis given to the role of NKG2D endocytosis in both receptor degradation and signal propagation. Examples of chronic ligand-induced down-regulation of NK cell activating receptors other than NKG2D, including natural cytotoxicity receptors (NCRs), DNAX accessory molecule-1 (DNAM1) and CD16, will be also discussed.

Engineering Natural Killer Cells for Cancer Immunotherapy

The past several years have seen tremendous advances in the engineering of immune effector cells as therapy for cancer. While chimeric antigen receptors (CARs) have been used extensively to redirect the specificity of autologous T cells against hematological malignancies with striking clinical results, studies of CAR-modified natural killer (NK) cells have been largely preclinical. In this review, we focus on recent advances in NK cell engineering, particularly on preclinical evidence suggesting that NK cells may be as effective as T cells in recognizing and killing targets after genetic modification. We will discuss strategies to introduce CARs into both primary NK cells and NK cell lines in an effort to provide antigen specificity, the challenges of manufacturing engineered NK cells, and evidence supporting the effectiveness of this approach from preclinical and early-phase clinical studies using CAR-engineered NK cells. CAR-NK cells hold great promise as a novel cellular immunotherapy against refractory malignancies. Notably, NK cells can provide an "off-the-shelf" product, eliminating the need for a personalized and patient-specific product that plagues current CAR-T cell therapies. The ability to more potently direct NK cell-mediated cytotoxicity against refractory tumors through the expression of CAR is likely to contribute to the recent paradigm shift in cancer treatment.

TIGIT and CD96: new checkpoint receptor targets for cancer immunotherapy

While therapies targeting the co-inhibitory or immune checkpoint receptors PD-1 and CTLA-4 have shown remarkable success in many cancers, not all patients benefit from these therapies. This has catalyzed enormous interest in the targeting of other immune checkpoint receptors. In this regard, TIGIT and CD96 have recently entered the limelight as novel immune checkpoint receptor targets. TIGIT and CD96 together with the co-stimulatory receptor CD226 form a pathway that is analogous to the CD28/CTLA-4 pathway, in which shared ligands and differential receptor:ligand affinities fine-tune the immune response. Although the roles of TIGIT and CD96 as immune checkpoint receptors in T cell and natural killer cell biology are just beginning to be uncovered, accumulating data support the targeting of these receptors for improving anti-tumor immune responses. A clear understanding of the immune cell populations regulated by TIGIT and CD96 is key to the design of immunotherapies that target these receptors in combination with other existing immune checkpoint blockade therapies.

Cd226-/- natural killer cells fail to establish stable contacts with cancer cells and show impaired control of tumor metastasis in vivo

CD226 is an activating receptor expressed on natural killer (NK) cells, CD8⁺ T cells, and other immune cells. Upon binding to its ligands expressed on target cells, CD226 activates intracellular signaling that triggers cytokine production and degranulation in NK cells. However, the role of CD226 in contact dynamics between NK and cancer cells has remained unclear. Our time-lapse images showed that individual wild-type CD226⁺ NK cells contacted B16F10 melanoma cells for 23.7 min, but Cd226^-/- NK cells only for 12.8 min, although both NK cell subsets showed equal contact frequency over 4 h. On the surface of B16F10 cells, CD226⁺ cells stayed at the same site with oscillating movement (named stable contact), while Cd226^-/- NK cells moved around at a velocity of 4 μm/min (named unstable contact). Consequently, Cd226^-/- NK cells did not kill B16F10 cells in vitro and did not inhibit their metastasis into the lung in vivo. Taken together, our data demonstrate that CD226 enables prolonged stable interaction between NK and cancer cells, which is needed for efficient killing of cancer cells.

The anti-SLAMF7 antibody elotuzumab mediates NK cell activation through both CD16-dependent and -independent mechanisms

Elotuzumab is a humanized therapeutic monoclonal antibody directed to the surface glycoprotein SLAMF7 (CS1, CRACC, CD319), which is highly expressed on multiple myeloma (MM) tumor cells. Improved clinical outcomes have been observed following treatment of MM patients with elotuzumab in combination with lenalidomide or bortezomib. Previous work showed that elotuzumab stimulates NK cell-mediated antibody-dependent cellular cytotoxicity (ADCC), via Fc-domain engagement with FcγRIIIa (CD16). SLAMF7 is also expressed on NK cells, where it can transmit stimulatory signals. We tested whether elotuzumab can directly activate NK cells via ligation with SLAMF7 on NK cells in addition to targeting ADCC through CD16. We show that elotuzumab strongly promoted degranulation and activation of NK cells in a CD16-dependent manner, and a non-fucosylated form of elotuzumab with higher affinity to CD16 exhibited enhanced potency. Using F(ab')₂ or Fc-mutant forms of the antibody, the direct binding of elotuzumab to SLAMF7 alone could not stimulate measurable CD69 expression or degranulation of NK cells. However, the addition of soluble elotuzumab could costimulate calcium signaling responses triggered by multimeric engagement of NKp46 and NKG2D in a CD16-independent manner. Thus, while elotuzumab primarily stimulates NK cells through CD16, it can also transduce effective "trans"-costimulatory signals upon direct engagement with SLAMF7, since these responses did not require direct co-engagement with the activating receptors. Trans-costimulation by elotuzumab has potential to reduce activation thresholds of other NK cell receptors engaging with their ligands on myeloma target cell surfaces, thereby potentially further increasing NK cell responsiveness in patients.

Natural Killer Cells Response to IL-2 Stimulation Is Distinct between Ascites with the Presence or Absence of Malignant Cells in Ovarian Cancer Patients

Peritoneal ascites are a distinguishable feature of patients with advanced epithelial ovarian cancer (EOC). The presence of different lymphocyte subsets has been reported in EOC-associated ascites, which also can or not contain malignant cells. The goal of this study was to analyze the functional characteristics of natural killer (NK) cells from EOC-associated ascites in terms of their expression of activating receptors and ascites’ contents of lymphocyte subtypes, cytokine profile and presence of EOC cells. NK cell function was evaluated by the expression of the degranulation marker CD107a in resting and interleukin (IL)-2 stimulated NK cells from ascites and blood. Degranulation of NK cells from EOC cell-free ascites was significantly (p < 0.05) higher than all the other groups, either in their resting state or after IL-2 stimulation, suggesting a previous local stimulation. In contrast, treatment with IL-2 had no effect on NK cells from ascites with EOC cells. The amount of regulatory T cells was significantly higher in ascites with EOC cells compared to EOC cell-free ascites. Ascites with EOC cells also had higher levels of tumor necrosis factor (TNF)-α, suggesting inflammation related to the malignancy. In conclusion, the functional performance of NK cells was distinct between EOC cell-free ascites and ascites with EOC cells. The impairment of NK cell response to IL-2 in ascites with EOC cells was consistent with an immunosuppressive tumor microenvironment.

Phase I study of cord blood-derived natural killer cells combined with autologous stem cell transplantation in multiple myeloma

Multiple myeloma (MM) is a disease with known immune dysregulation. Natural killer (NK) cells have shown preclinical activity in MM. We conducted a first-in-human study of umbilical cord blood-derived (CB) NK cells for MM patients undergoing high dose chemotherapy and autologous haematopoietic stem cell transplantation (auto-HCT). Patients received lenalidomide (10 mg) on days -8 to -2, melphalan 200 mg/m2 on day -7, CB-NK cells on day -5 and auto-HCT on day 0. Twelve patients were enrolled, three on each of four CB-NK cell dose levels: 5 × 106 , 1 × 107 , 5 × 107 and 1 × 108 CB-NK cells/kg. Ten patients had either high-risk chromosomal changes or a history of relapsed/progressed disease. There were no infusional toxicities and no graft-versus-host disease. One patient failed to engraft due to poor autologous graft quality and was rescued with a back-up autologous graft. Overall, 10 patients achieved at least a very good partial response as their best response, including eight with near complete response or better. With a median follow-up of 21 months, four patients have progressed or relapsed, two of whom have died. CB-NK cells were detected in vivo in six patients, with an activated phenotype (NKG2D+ /NKp30+ ). These data warrant further development of this novel cellular therapy.

Multiple myeloma patients in long-term complete response after autologous stem cell transplantation express a particular immune signature with potential prognostic implication

The proportion of multiple myeloma patients in long-term complete response (LTCR-MM) for more than 6 years after autologous stem cell transplantation (ASCT) is small. To evaluate whether this LTCR is associated with a particular immune signature, peripheral blood samples from 13 LTCR-MM after ASCT and healthy blood donors (HBD) were analysed. Subpopulations of T-cells (naïve, effector, central memory and regulatory), B-cells (naïve, marginal zone-like, class-switched memory, transitional and plasmablasts) and NK-cells expressing inhibitory and activating receptors were quantified by multiparametric flow cytometry (MFC). Heavy/light chains (HLC) were quantified by nephelometry. The percentage of CD4⁺ T-cells was lower in patients, whereas an increment in the percentage of CD4⁺ and CD8⁺ effector memory T-cells was associated with the LTCR. Regulatory T-cells and NK-cells were similar in both groups but a particular redistribution of inhibitory and activating receptors in NK-cells were found in patients. Regarding B-cells, an increase in naïve cells and a corresponding reduction in marginal zone-like and class-switched memory B-cells was observed. The HLC values were normal. Our results suggest that LTCR-MM patients express a particular immune signature, which probably reflects a 'high quality' immune reconstitution that could exert a competent anti-tumor immunological surveillance along with a recovery of the humoral immunity.

Natural Killer Group 2, Member D/NKG2D Ligands in Hematopoietic Cell Transplantation

Natural killer group 2, member D (NKG2D) is an invariant activatory receptor present on subsets of natural killer and T lymphocytes. It stimulates the cytolytic effector response upon engagement of its various stress-induced ligands NKG2D ligands (NKG2DL). Malignant transformation and conditioning treatment prior to hematopoietic cell transplantation (HCT) are stress factors leading to the activation of the NKG2D/NKG2DL signaling in clinical settings. In the context of HCT, NKG2D-bearing cells can kill both tumor and healthy cells expressing NKG2DL. The NKG2D/NKG2DL engagement has therefore a key role in the regulation of one of the most salient issues in allogeneic HCT, i.e., maintaining a balance between graft-vs.-leukemia effect and graft-vs.-host disease. The present review summarizes the current state of our knowledge pertaining to the role of the NKG2D and NKG2DL in HCT.

Role of Distinct Natural Killer Cell Subsets in Anticancer Response

Natural killer (NK) cells, the prototypic member of innate lymphoid cells, are important effectors of anticancer immune response. These cells can survey and control tumor initiation due to their capability to recognize and kill malignant cells and to regulate the adaptive immune response via cytokines and chemokines release. However, several studies have shown that tumor-infiltrating NK cells associated with advanced disease can have profound functional defects and display protumor activity. This evidence indicates that NK cell behavior undergoes crucial alterations during cancer progression. Moreover, a further level of complexity is due to the extensive heterogeneity and plasticity of these lymphocytes, implying that different NK cell subsets, endowed with specific phenotypic and functional features, may be involved and play distinct roles in the tumor context. Accordingly, many studies reported the enrichment of selective NK cell subsets within tumor tissue, whereas the underlying mechanisms are not fully elucidated. A malignant microenvironment can significantly impact NK cell activity, by recruiting specific subpopulations and/or influencing their developmental programming or the acquisition of a mature phenotype; in particular, neoplastic, stroma and immune cells, or tumor-derived factors take part in these processes. In this review, we will summarize and discuss the recently acquired knowledge on the possible contribution of distinct NK cell subsets in the control and/or progression of solid and hematological malignancies. Moreover, we will address emerging evidence regarding the role of different components of tumor microenvironment on shaping NK cell response.

MGUS to myeloma: a mysterious gammopathy of underexplored significance

All cases of multiple myeloma (MM) are preceded by precursor states termed monoclonal gammopathy of undetermined significance (MGUS) or smoldering myeloma (SMM). Genetic analyses of MGUS cells have provided evidence that it is a genetically advanced lesion, wherein tumor cells carry many of the genetic changes found in MM cells. Intraclonal heterogeneity is also established early during the MGUS phase. Although the genetic features of MGUS or SMM cells at baseline may predict disease risk, transition to MM involves altered growth of preexisting clones. Recent advances in mouse modeling of MGUS suggest that the clinical dormancy of the clone may be regulated in part by growth controls extrinsic to the tumor cells. Interactions of MGUS cells with immune cells, bone cells, and others in the bone marrow niche may be key regulators of malignant transformation. These interactions involve a bidirectional crosstalk leading to both growth-supporting and inhibitory signals. Because MGUS is already a genetically complex lesion, application of new tools for earlier detection should allow delineation of earlier stages, which we term as pre-MGUS Analyses of populations at increased risk of MGUS also suggest the possible existence of a polyclonal phase preceding the development of MGUS. Monoclonal gammopathy in several patients may have potential clinical significance in spite of low risk of malignancy. Understanding the entire spectrum of these disorders may have broader implications beyond prevention of clinical malignancy.

TRAIL-mediated killing of acute lymphoblastic leukemia by plasmacytoid dendritic cell-activated natural killer cells

Acute lymphoblastic leukemia (ALL) still frequently recurs after hematopoietic stem cell transplantation (HSCT), underscoring the need to improve the graft-versus-leukemia (GvL) effect. Natural killer (NK) cells reconstitute in the first months following HSCT when leukemia burden is at its lowest, but ALL cells have been shown to be resistant to NK cell-mediated killing. We show here that this resistance is overcome by NK cell stimulation with TLR-9-activated plasmacytoid dendritic cells (pDCs). NK cell priming with activated pDCs resulted in TRAIL and CD69 up-regulation on NK cells and IFN-γ production. NK cell activation was dependent on IFN-α produced by pDCs, but was not reproduced by IFN-α alone. ALL killing was further enhanced by inhibition of KIR engagement. We showed that ALL lysis was mainly mediated by TRAIL engagement, while the release of cytolytic granules was involved when ALL expressed NK cell activating receptor ligands. Finally, adoptive transfers of activated-pDCs in ALL-bearing humanized mice delayed the leukemia onset and cure 30% of mice. Our data therefore demonstrate that TLR-9 activated pDCs are a powerful tool to overcome ALL resistance to NK cell-mediated killing and to reinforce the GvL effect of HSCT. These results open new therapeutic avenues to prevent relapse in children with ALL.

Natural killer cell recognition of in vivo drug-induced senescent multiple myeloma cells

Recognition of tumor cells by the immune system is a key step in cancer eradication. Melphalan is an alkylating agent routinely used in the treatment of patients with multiple myeloma (MM), but at therapeutic doses it leads to an immunosuppressive state due to lymphopenia. Here, we used a mouse model of MM to investigate the ability of in vivo treatment with low doses of melphalan to modulate natural killer (NK) cell activity, which have been shown to play a major role in the control of MM growth. Melphalan treatment was able to enhance the surface expression of the stress-induced NKG2D ligands RAE-1 and MULT-1, and of the DNAM-1 ligand PVR (CD155) on MM cells, leading to better tumor cell recognition and killing by NK cells, as highlighted by NK cell increased degranulation triggered by melphalan-treated tumor cells. Remarkably, NK cell population was not affected by the melphalan dose used, but rather displayed activation features as indicated by CD107a and CD69 expression. Furthermore, we showed that low doses of melphalan fail to induce tumor cell apoptosis, but promote the in vivo establishment of a senescent tumor cell population, harboring high levels of the stress-induced ligands RAE-1 and PVR. Taken together our data support the concept of using chemotherapy in order to boost antitumor innate immune responses and report the possibility to induce cellular senescence of tumor cells in vivo.