Bone Marrow Stromal Cell-Derived IL-8 Upregulates PVR Expression on Multiple Myeloma Cells via NF-kB Transcription Factor

SOCS1 Inhibits IL-6-Induced CD155 Overexpression in Lung Adenocarcinoma

CD155, also known as the poliovirus receptor (PVR), is a crucial molecule in the development and progression of cancer, as its overexpression favors immune evasion and resistance to immunotherapy. However, little is known about the mechanisms that regulate its overexpression. Proinflammatory factors produced by various cellular components of the tumor microenvironment (TME) have been associated with CD155 expression. We analyzed the effect of interleukin (IL)-6 on CD155 expression in lung adenocarcinoma. We found a positive relationship between mRNA and protein levels. This correlation was also observed in bioinformatics analysis and in biopsies and serum from patients with lung adenocarcinoma. Interestingly, lung adenocarcinoma cell lines expressing suppressor of cytokine signaling 1 (SOCS1) did not show increased CD155 levels upon IL-6 stimulation, and SOCS1 silencing reverted this effect. IL-6 and SOCS1 are critical regulators of CD155 expression in lung adenocarcinoma. Further basic and clinical studies are needed to define the role of these molecules during tumor development and to improve their clinical impact as biomarkers and targets for predicting the efficacy of immunotherapies. This study deepens the understanding of the intricate regulation of the immune checkpoints mediated by soluble factors and allows us to devise new ways to combine conventional treatments with the most innovative anticancer options.

Increased PVR Expression on Bone Marrow Macrophages May Promote Resistance to TIGIT Blockade in Multiple Myeloma

PURPOSE

TIGIT blockade in our ex vivo model of bone marrow (BM) reduced the number of malignant plasma cells (PC) in only half of patients with multiple myeloma. Here, we wanted to investigate whether increased expression of TIGIT ligands may inhibit T-cell immune response promoting resistance to TIGIT blockade.

EXPERIMENTAL DESIGN

We first characterized the number and phenotype of BM macrophages in different stages of the disease by multiparameter flow cytometry. We assessed the effect of TIGIT ligands on PC survival by performing experiments in the ex vivo BM model and analyzed changes in gene expression by using NanoString technology and real-time PCR.

RESULTS

The frequency of BM macrophages was significantly decreased in multiple myeloma, which was accompanied by changes in their immunophenotype. Moreover, we found a higher number of malignant PC in ex vivo BM cells cultured onto the poliovirus receptor (PVR) and nectin-2 compared with control, suggesting that both ligands may support PC survival. In addition, the presence of PVR, but not nectin-2, overcame the therapeutic effect of TIGIT blockade or exogenous IL2. Furthermore, exogenous IL2 increased TIGIT expression on both CD4+ and CD8+ T cells and, indirectly, PVR on BM macrophages. Consistently, PVR reduced the number of cytotoxic T cells and promoted a gene signature with reduced effector molecules.

CONCLUSIONS

IL2 induced TIGIT on T cells in the BM, in which increased PVR expression resulted in cytotoxic T-cell inhibition, promoting PC survival and resistance to TIGIT blockade.

Multi-Niche Human Bone Marrow On-A-Chip for Studying the Interactions of Adoptive CAR-T Cell Therapies with Multiple Myeloma

Multiple myeloma (MM), a cancer of bone marrow plasma cells, is the second-most common hematological malignancy. However, despite immunotherapies like chimeric antigen receptor (CAR)-T cells, relapse is nearly universal. The bone marrow (BM) microenvironment influences how MM cells survive, proliferate, and resist treatment. Yet, it is unclear which BM niches give rise to MM pathophysiology. Here, we present a 3D microvascularized culture system, which models the endosteal and perivascular bone marrow niches, allowing us to study MM-stroma interactions in the BM niche and model responses to therapeutic CAR-T cells. We demonstrated the prolonged survival of cell line-based and patient-derived multiple myeloma cells within our in vitro system and successfully flowed in donor-matched CAR-T cells. We then measured T cell survival, differentiation, and cytotoxicity against MM cells using a variety of analysis techniques. Our MM-on-a-chip system could elucidate the role of the BM microenvironment in MM survival and therapeutic evasion and inform the rational design of next-generation therapeutics.

TEASER

A multiple myeloma model can study why the disease is still challenging to treat despite options that work well in other cancers.

Natural killer cells affect the natural course, drug resistance, and prognosis of multiple myeloma

Multiple myeloma (MM), a stage-developed plasma cell malignancy, evolves from monoclonal gammopathy of undetermined significance (MGUS) or smoldering MM (SMM). Emerging therapies including immunomodulatory drugs, proteasome inhibitors, monoclonal antibodies, chimeric antigen-T/natural killer (NK) cells, bispecific T-cell engagers, selective inhibitors of nuclear export, and small-molecule targeted therapy have considerably improved patient survival. However, MM remains incurable owing to inevitable drug resistance and post-relapse rapid progression. NK cells with germline-encoded receptors are involved in the natural evolution of MGUS/SMM to active MM. NK cells actively recognize aberrant plasma cells undergoing malignant transformation but are yet to proliferate during the elimination phase, a process that has not been revealed in the immune editing theory. They are potential effector cells that have been neglected in the therapeutic process. Herein, we characterized changes in NK cells regarding disease evolution and elucidated its role in the early clinical monitoring of MM. Additionally, we systematically explored dynamic changes in NK cells from treated patients who are in remission or relapse to explore future combination therapy strategies to overcome drug resistance.

CD155 and its receptors in cancer immune escape and immunotherapy

In recent years, there have been multiple breakthroughs in cancer immunotherapy, with immune checkpoint inhibitors becoming the most promising treatment strategy. However, available drugs are not always effective. As an emerging immune checkpoint molecule, CD155 has become an important target for immunotherapy. This review describes the structure and function of CD155, its receptors TIGIT, CD96, and CD226, and summarizes that CD155 expressed by tumor cells can upregulate its expression through the DNA damage response pathway and Ras-Raf-MEK-ERK signaling pathway. This review also elaborates the mechanism of immune escape after binding CD155 to its receptors TIGIT, CD96, and CD226, and summarizes the current progress of immunotherapy research regarding CD155 and its receptors. Besides, it also discusses the future direction of checkpoint immunotherapy.

Dysregulation of DNAM-1-Mediated NK Cell Anti-Cancer Responses in the Tumor Microenvironment

NK cells play a pivotal role in anti-cancer immune responses, thanks to the expression of a wide array of inhibitory and activating receptors that regulate their cytotoxicity against transformed cells while preserving healthy cells from lysis. However, NK cells exhibit severe dysfunction in the tumor microenvironment, mainly due to the reduction of activating receptors and the induction or increased expression of inhibitory checkpoint receptors. An activating receptor that plays a central role in tumor recognition is the DNAM-1 receptor. It recognizes PVR and Nectin2 adhesion molecules, which are frequently overexpressed on the surface of cancerous cells. These ligands are also able to trigger inhibitory signals via immune checkpoint receptors that are upregulated in the tumor microenvironment and can counteract DNAM-1 activation. Among them, TIGIT has recently gained significant attention, since its targeting results in improved anti-tumor immune responses. This review aims to summarize how the recognition of PVR and Nectin2 by paired co-stimulatory/inhibitory receptors regulates NK cell-mediated clearance of transformed cells. Therapeutic approaches with the potential to reverse DNAM-1 dysfunction in the tumor microenvironment will be also discussed.

CD155 and Its Receptors as Targets for Cancer Therapy

CD155, also known as the poliovirus receptor, is an adhesion molecule often overexpressed in tumors of different origins where it promotes cell migration and proliferation. In addition to this pro-tumorigenic function, CD155 plays an immunomodulatory role during tumor progression since it is a ligand for both the activating receptor DNAM-1 and the inhibitory receptor TIGIT, expressed on cytotoxic innate and adaptative lymphocytes. DNAM-1 is a well-recognized receptor involved in anti-tumor immune surveillance. However, in advanced tumor stages, TIGIT is up-regulated and acts as an immune checkpoint receptor, counterbalancing DNAM-1-mediated cancer cell clearance. Pre-clinical studies have proposed the direct targeting of CD155 on tumor cells as well as the enhancement of DNAM-1-mediated anti-tumor functions as promising therapeutic approaches. Moreover, immunotherapeutic use of anti-TIGIT blocking antibody alone or in combined therapy has already been included in clinical trials. The aim of this review is to summarize all these potential therapies, highlighting the still controversial role of CD155 during tumor progression.

Role of NF-κB Signaling in the Interplay between Multiple Myeloma and Mesenchymal Stromal Cells

Nuclear factor-κB (NF-κB) transcription factors play a key role in the pathogenesis of multiple myeloma (MM). The survival, proliferation and chemoresistance of malignant plasma cells largely rely on the activation of canonical and noncanonical NF-κB pathways. They are triggered by cancer-associated mutations or by the autocrine and paracrine production of cytokines and growth factors as well as direct interaction with cellular and noncellular components of bone marrow microenvironment (BM). In this context, NF-κB also significantly affects the activity of noncancerous cells, including mesenchymal stromal cells (MSCs), which have a critical role in disease progression. Indeed, NF-κB transcription factors are involved in inflammatory signaling that alters the functional properties of these cells to support cancer evolution. Moreover, they act as regulators and/or effectors of pathways involved in the interplay between MSCs and MM cells. The aim of this review is to analyze the role of NF-κB in this hematologic cancer, focusing on NF-κB-dependent mechanisms in tumor cells, MSCs and myeloma-mesenchymal stromal cell crosstalk.

A Hyaluronan and Proteoglycan Link Protein 1 Matrikine: Role of Matrix Metalloproteinase 2 in Multiple Myeloma NF-κB Activation and Drug Resistance

The NF-κB signaling pathway plays key roles in inflammation and the pathogenesis of many solid and hematologic malignancies, including multiple myeloma, a malignancy of the plasma cells. While proteasome inhibitors, such as bortezomib, employed in multiple myeloma treatments may inhibit NF-κB signaling pathways, multiple myeloma cells often become drug resistant in part due to non-cell autonomous mechanism(s) from the multiple myeloma tumor microenvironment. We previously found that fragments of, but not full-length, hyaluronan and proteoglycan link protein 1 (HAPLN1), produced by multiple myeloma bone marrow stromal cells (BMSC), activate an atypical bortezomib-resistant NF-κB pathway in multiple myeloma cells. In our current study, we found that multiple myeloma cells promote HAPLN1 expression and matrix metalloproteinase 2 (MMP2) activity in cocultured BMSCs and MMP2 activity is higher in BMSCs established from multiple myeloma patients' BM aspirates relative to normal equivalents. Moreover, MMP2 cleaves HAPLN1 into forms similar in size to those previously observed in patients with multiple myeloma with progressive disease. Both HAPLN1 and MMP2 in BMSCs were required to enhance NF-κB activation and resistance to bortezomib-induced cell death in cocultured multiple myeloma cells. We propose that MMP2-processing of HAPLN1 produces a matrikine that induces NF-κB activation and promotes bortezomib resistance in multiple myeloma cells.

IMPLICATIONS

HAPLN1 and MMP2 produced by BMSCs obtained from patients with multiple myeloma promote NF-κB activity and resistance to bortezomib toxicity in multiple myeloma cells, uncovering their potential as biomarkers or therapeutic targets to address bortezomib resistance in patients with multiple myeloma.

GAS6/TAM signaling pathway controls MICA expression in multiple myeloma cells

NKG2D ligands play a relevant role in Natural Killer (NK) cell -mediated immune surveillance of multiple myeloma (MM). Different levels of regulation control the expression of these molecules at cell surface. A number of oncogenic proteins and miRNAs act as negative regulators of NKG2D ligand transcription and translation, but the molecular mechanisms sustaining their basal expression in MM cells remain poorly understood. Here, we evaluated the role of the growth arrest specific 6 (GAS6)/TAM signaling pathway in the regulation of NKG2D ligand expression and MM recognition by NK cells. Our data showed that GAS6 as well as MERTK and AXL depletion in MM cells results in MICA downregulation and inhibition of NKG2D-mediated NK cell degranulation. Noteworthy, GAS6 derived from bone marrow stromal cells (BMSCs) also increases MICA expression at both protein and mRNA level in human MM cell lines and in primary malignant plasma cells. NF-kB activation is required for these regulatory mechanisms since deletion of a site responsive for this transcription factor compromises the induction of mica promoter by BMSCs. Accordingly, knockdown of GAS6 reduces the capability of BMSCs to activate NF-kB pathway as well as to enhance MICA expression in MM cells. Taken together, these results shed light on molecular mechanism underlying NKG2D ligand regulation and identify GAS6 protein as a novel autocrine and paracrine regulator of basal expression of MICA in human MM cells.

Significance of a tumor microenvironment-mediated P65-miR-30a-5p-BCL2L11 amplification loop in multiple myeloma

Despite significant progress in the treatment of myeloma, multiple myeloma (MM) remains an incurable hematological malignancy due to cell adhesion-mediated drug resistance (CAM-DR) phenotype. However, data on the molecular mechanisms underlying the CAM-DR remains scanty. Here, we identified a miRNA-mRNA regulatory network in myeloma cells that are directly adherent to bone marrow stromal cells (BMSCs). Our data showed that the BMSCs up-regulated miR-30a-5p and down-regulated BCL2L11 at both mRNA and protein level in the myeloma cells. Besides, luciferase reporter genes demonstrated direct interaction between miR-30a-5p and BCL2L11 gene. Moreover, the BMSCs activated NF-ΚB signaling pathway in myeloma cells and the NF-κB P65 was shown to directly bind the miR-30a-5p promoter region. Moreover, suppression of the miR-30a-5p or upregulation of the BCL2L11 promoted apoptosis of the myeloma cells independent of the BMSCs, thus suggesting clinical significance of miR-30a-5p inhibitor and PLBCL2L11 plasmid in CAM-DR. Together, our data demonstrated the role of P65-miR-30a-5p-BCL2L11 loop in CAM-DR myeloma cells. These findings give new insights into the role of tumor microenvironment in the treatment of patients with myeloma.

Natural Killer Cells in the Malignant Niche of Multiple Myeloma

Natural killer (NK) cells represent a subset of CD3- CD7+ CD56+/dim lymphocytes with cytotoxic and suppressor activity against virus-infected cells and cancer cells. The overall potential of NK cells has brought them to the spotlight of targeted immunotherapy in solid and hematological malignancies, including multiple myeloma (MM). Nonetheless, NK cells are subjected to a variety of cancer defense mechanisms, leading to impaired maturation, chemotaxis, target recognition, and killing. This review aims to summarize the available and most current knowledge about cancer-related impairment of NK cell function occurring in MM.

Mesenchymal Stem Cell Immunomodulation: A Novel Intervention Mechanism in Cardiovascular Disease

Mesenchymal stem cells (MSCs) are the member of multipotency stem cells, which possess the capacity for self-renewal and multi-directional differentiation, and have several characteristics, including multi-lineage differentiation potential and immune regulation, which make them a promising source for cell therapy in inflammation, immune diseases, and organ transplantation. In recent years, MSCs have been described as a novel therapeutic strategy for the treatment of cardiovascular diseases because they are potent modulators of immune system with the ability to modulating immune cell subsets, coordinating local and systemic innate and adaptive immune responses, thereby enabling the formation of a stable inflammatory microenvironment in damaged cardiac tissues. In this review, the immunoregulatory characteristics and potential mechanisms of MSCs are sorted out, the effect of these MSCs on immune cells is emphasized, and finally the application of this mechanism in the treatment of cardiovascular diseases is described to provide help for clinical application.

Immunomodulatory effect of NEDD8-activating enzyme inhibition in Multiple Myeloma: upregulation of NKG2D ligands and sensitization to Natural Killer cell recognition

Multiple Myeloma (MM) is an incurable hematologic malignancy of terminally differentiated plasma cells (PCs), where immune interactions play a key role in the control of cancer cell growth and survival. In particular, MM is characterized by a highly immunosuppressive bone marrow microenvironment where the anticancer/cytotoxic activity of Natural Killer (NK) cells is impaired. This study is focused on understanding whether modulation of neddylation can regulate NK cell-activating ligands expression and sensitize MM to NK cell killing. Neddylation is a post-translational modification that adds a ubiquitin-like protein, NEDD8, to selected substrate proteins, affecting their stability, conformation, subcellular localization, and function. We found that pharmacologic inhibition of neddylation using a small-molecule inhibitor, MLN4924/Pevonedistat, increases the expression of the NK cell-activating receptor NKG2D ligands MICA and MICB on the plasma membrane of different MM cell lines and patient-derived PCs, leading to enhanced NK cell degranulation. Mechanistically, MICA expression is upregulated at mRNA level, and this is the result of an increased promoter activity after the inhibition of IRF4 and IKZF3, two transcriptional repressors of this gene. Differently, MLN4924/Pevonedistat induced accumulation of MICB on the plasma membrane with no change of its mRNA levels, indicating a post-translational regulatory mechanism. Moreover, inhibition of neddylation can cooperate with immunomodulatory drugs (IMiDs) in upregulating MICA surface levels in MM cells due to increased expression of CRBN, the cellular target of these drugs. In summary, MLN4924/Pevonedistat sensitizes MM to NK cell recognition, adding novel information on the anticancer activity of neddylation inhibition.

Role of whole-body diffusion-weighted imaging in evaluation of multiple myeloma

The evaluation of bone disease in multiple myeloma (MM) is an important topic in imaging. This study retrospectively investigated whole-body diffusion-weighted imaging (WB-DWI) in the evaluation of bone marrow infiltration and treatment response in MM.A total of 126 patients with MM who underwent WB-DWI between January 2016 and December 2020 were enrolled. All the patients received 4-course induction chemotherapy. WB-DWI was performed before and after chemotherapy to measure the apparent diffusion coefficient (ADC) values. According to gender and Revised International Staging System (RISS) staging groups, the relationship between ADC value and bone marrow plasma cell infiltration ratio before treatment were explored using Spearman and Pearson correlation coefficients. Comparison of ADC values before and after treatment according to different chemotherapy regimens and treatment response was performed by 2-independent samples non-parametric tests and t test.There was a negative correlation between the ADC value and the degree of bone marrow infiltration and this was statistically significant (r = -0.843, P < .001). In different gender and RISS groups, ADC value before treatment was negatively correlated with the proportion of plasma cell infiltration (male, r = -0.849; female, r = -0.836; Stage I, r = -0.659; Stage II, r = -0.870; Stage III, r = -0.745; all P < .001). The ADC values of all subjects increased to varying degrees after 4-course induction chemotherapy, including different chemotherapy regimens and treatment responses (all P < .05 except for progressive disease group).The ADC value was negatively correlated with the degree of bone marrow infiltration in different gender and RISS stages. The ADC value increased after treatment, but it was not consistent with progressive disease group. The increase of ADC value may indicate the disease burden and outcome of MM induced chemotherapy.

Enhancement of Neuroblastoma NK-Cell-Mediated Lysis through NF-kB p65 Subunit-Induced Expression of FAS and PVR, the Loss of Which Is Associated with Poor Patient Outcome

Simple Summary

Neuroblastoma (NB) cells adopt several molecular strategies to evade the Natural Killer (NK)-mediated response. Herein, we found that the overexpression of the NF-kB p65 subunit in NB cell lines upregulates the expression of both the death receptor FAS and the activating ligand PVR, thus rendering NB cells more susceptible to NK-cell-mediated apoptosis, recognition, and killing. These data could provide a clue for a novel NK-cell-based immunotherapy of NB. In addition, array CGH analysis performed in our cohort of NB patients showed that loss of both the FAS and PVR genes correlated with low survival, thus revealing a novel biomarker predicting the outcome of NB patients.

Abstract

High-risk neuroblastoma (NB) is a rare childhood cancer whose aggressiveness is due to a variety of chromosomal genetic aberrations, including those conferring immune evasion. Indeed, NB cells adopt several molecular strategies to evade recognition by the immune system, including the downregulation of ligands for NK-cell-activating receptors. To date, while molecular strategies aimed at enhancing the expression of ligands for NKG2D- and DNAM-1-activating receptors have been explored, no evidence has been reported on the immunomodulatory mechanisms acting on the expression of death receptors such as Fas in NB cells. Here, we demonstrated that transient overexpression of the NF-kB p65 subunit upregulates the surface expression of Fas and PVR, the ligand of DNAM-1, thus making NB cell lines significantly more susceptible to NK-cell-mediated apoptosis, recognition, and killing. In contrast, IFNγ and TNFα treatment, although it induced the upregulation of FAS in NB cells and consequently enhanced NK-cell-mediated apoptosis, triggered immune evasion processes, including the strong upregulation of MHC class I and IDO1, both of which are involved in mechanisms leading to the impairment of a proper NK-cell-mediated killing of NB. In addition, high-resolution array CGH analysis performed in our cohort of NB patients revealed that the loss of FAS and/or PVR genes correlated with low survival independently of the disease stage. Our data identify the status of the FAS and PVR genes as prognostic biomarkers of NB that may predict the efficacy of NK-cell-based immunotherapy of NB. Overall, restoration of surface expression of Fas and PVR, through transient upregulation of NF-kB, may be a clue to a novel NK-cell-based immunotherapy of NB.

Cereblon regulates NK cell cytotoxicity and migration via Rac1 activation

Rearrangement of the actin cytoskeleton is critical for cytotoxic and immunoregulatory functions as well as migration of natural killer (NK) cells. However, dynamic reorganization of actin is a complex process, which remains largely unknown. Here, we investigated the role of the protein Cereblon (CRBN), an E3 ubiquitin ligase complex co‐receptor and the primary target of the immunomodulatory drugs, in NK cells. We observed that CRBN partially colocalizes with F‐actin in chemokine‐treated NK cells and is recruited to the immunological synapse, thus suggesting a role for this protein in cytoskeleton reorganization. Accordingly, silencing of CRBN in NK cells results in a reduced cytotoxicity that correlates with a defect in conjugate and lytic synapse formation. Moreover, CRBN depletion significantly impairs the ability of NK cells to migrate and reduces the enhancing effect of lenalidomide on NK cell migration. Finally, we provided evidence that CRBN is required for activation of the small GTPase Rac1, a critical mediator of cytoskeleton dynamics. Indeed, in CRBN‐depleted NK cells, chemokine‐mediated or target cell–mediated Rac1 activation is significantly reduced. Altogether our data identify a critical role for CRBN in regulating NK cell functions and suggest that this protein may mediate the stimulatory effect of lenalidomide on NK cells.

Next-Generation Biomarkers in Multiple Myeloma: Understanding the Molecular Basis for Potential Use in Diagnosis and Prognosis

Multiple myeloma (MM) is considered to be the second most common blood malignancy and it is characterized by abnormal proliferation and an accumulation of malignant plasma cells in the bone marrow. Although the currently utilized markers in the diagnosis and assessment of MM are showing promising results, the incidence and mortality rate of the disease are still high. Therefore, exploring and developing better diagnostic or prognostic biomarkers have drawn global interest. In the present review, we highlight some of the recently reported and investigated novel biomarkers that have great potentials as diagnostic and/or prognostic tools in MM. These biomarkers include angiogenic markers, miRNAs as well as proteomic and immunological biomarkers. Moreover, we present some of the advanced methodologies that could be utilized in the early and competent diagnosis of MM. The present review also focuses on understanding the molecular concepts and pathways involved in these biomarkers in order to validate and efficiently utilize them. The present review may also help in identifying areas of improvement for better diagnosis and superior outcomes of MM.

Activation of NF-κB signaling via cytosolic mitochondrial RNA sensing in kerotocytes with mitochondrial DNA common deletion

Scar formation as a result of corneal wound healing is a leading cause of blindness. It is a challenge to understand why scar formation is more likely to occur in the central part of the cornea as compared to the peripheral part. The purpose of this study was to unravel the underlying mechanisms. We applied RNA-seq to uncover the differences of expression profile in keratocytes in the central/peripheral part of the cornea. The relative quantity of mitochondrial RNA was measured by multiplex qPCR. The characterization of mitochondrial RNA in the cytoplasm was confirmed by immunofluoresence microscope and biochemical approach. Gene expression was analyzed by western blot and RT qPCR. We demonstrate that the occurrence of mitochondrial DNA common deletion is greater in keratocytes from the central cornea as compared to those of the peripheral part. The keratocytes with CD have elevated oxidative stress levels, which leads to the leakage of mitochondrial double-stranded RNA into the cytoplasm. The cytoplasmic mitochondrial double-stranded RNA is sensed by MDA5, which induces NF-κB activation. The NF-κB activation thereafter induces fibrosis-like extracellular matrix expressions and IL-8 mRNA transcription. These results provide a novel explanation of the different clinical outcome in different regions of the cornea during wound healing.

Targeting NK Cell Inhibitory Receptors for Precision Multiple Myeloma Immunotherapy

Innate immune surveillance of cancer involves multiple types of immune cells including the innate lymphoid cells (ILCs). Natural killer (NK) cells are considered the most active ILC subset for tumor elimination because of their ability to target infected and malignant cells without prior sensitization. NK cells are equipped with an array of activating and inhibitory receptors (IRs); hence NK cell activity is controlled by balanced signals between the activating and IRs. Multiple myeloma (MM) is a hematological malignancy that is known for its altered immune landscape. Despite improvements in therapeutic options for MM, this disease remains incurable. An emerging trend to improve clinical outcomes in MM involves harnessing the inherent ability of NK cells to kill malignant cells by recruiting NK cells and enhancing their cytotoxicity toward the malignant MM cells. Following the clinical success of blocking T cell IRs in multiple cancers, targeting NK cell IRs is drawing increasing attention. Relevant NK cell IRs that are attractive candidates for checkpoint blockades include KIRs, NKG2A, LAG-3, TIGIT, PD-1, and TIM-3 receptors. Investigating these NK cell IRs as pathogenic agents and therapeutic targets could lead to promising applications in MM therapy. This review describes the critical role of enhancing NK cell activity in MM and discusses the potential of blocking NK cell IRs as a future MM therapy.