NKG2D/NKG2-Ligand Pathway Offers New Opportunities in Cancer Treatment

Absence of ATM leads to altered NK cell function in mice

Ataxia-telangiectasia (A-T) is a rare disorder caused by genetic defects of A-T mutated (ATM) kinase, a key regulator of stress response, and characterized by neurodegeneration, immunodeficiency, and high incidence of cancer. Here we investigated NK cells in a mouse model of A-T (Atm-/-) showing that they are strongly impaired at killing tumor cells due to a block of early signaling events. On the other hand, in Atm-/- littermates with thymic lymphoma NK cell cytotoxicity is enhanced as compared with ATM-proficient mice, possibly via tumor-produced TNF-α. Results also suggest that expansion of exhausted NKG2D+ NK cells in Atm-/- mice is driven by low-level expression of stress-inducible NKG2D ligands, whereas development of thymoma expressing the high-affinity MULT1 ligand is associated with NKG2D down-regulation on NK cells. These results expand our understanding of immunodeficiency in A-T and encourage exploring NK cell biology in A-T patients in the attempt to identify cancer predictive biomarkers and novel therapeutic targets.

A novel MICA/B-targeted chimeric antigen receptor augments the cytotoxicity of NK cells against tumor cells

Chimeric antigen receptor (CAR)-modified immune cells have emerged as a promising approach for cancer treatment, but single-target CAR therapy in solid tumors is limited by immune escape caused by tumor antigen heterogeneity and shedding. Natural killer group 2D (NKG2D) is an activating receptor expressed in human NK cells, and its ligands, such as MICA and MICB (MICA/B), are widely expressed in malignant cells and typically absent from healthy tissue. NKG2D plays an important role in anti-tumor immunity, recognizing tumor cells and initiating an anti-tumor response. Therefore, NKG2D-based CAR is a promising CAR candidate. Nevertheless, the shedding of MICA/B hinders the therapeutic efficacy of NKG2D-CARs. Here, we designed a novel CAR by engineering an anti-MICA/B shedding antibody 1D5 into the CAR construct. The engineered NK cells exhibited significantly enhanced cytotoxicity against various MICA/B-expressing tumor cells and were not inhibited by NKG2D antibody or NKG2D-Fc fusion protein, indicating no interference with NKG2D-MICA/B binding. Therefore, the developed 1D5-CAR could be combined with NKG2D-CAR to further improve the obstacles caused by MICA/B shedding.

Natural Killer Cells Reprogram Myeloid-Derived Suppressor Cells to Induce TNF-α Release via NKG2D-Ligand Interaction after Cryo-Thermal Therapy

In our previous studies, a novel cryothermal therapy (CTT) was developed to induce systemic long-term anti-tumor immunity. Natural killer (NK) cells were found to play an important role in CTT-induced long-term immune-mediated tumor control at the late stage after CTT, but the underlying mechanism is unclear. Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells that have potent immunosuppressive effects on T cells and weaken the long-term benefits of immunotherapy. Consequently, overcoming MDSC immunosuppression is essential for maintaining the long-term efficacy of immunotherapy. In this study, we revealed that NK cells considerably diminish MDSC accumulation at the late stage after CTT, boost T cell production, increase T cell activation, and promote MDSC maturation, culminating in Th1-dominant CD4+ T cell differentiation and enhancing NK and CD8+ T cell cytotoxicity. Additionally, NK cells activate ERK signaling in MDSCs through NKG2D-ligand interaction to increase the activity of tumor necrosis factor (TNF)-α converting enzyme (TACE)-cleaved membrane TNF-α. Furthermore, Increased TACE activity releases more soluble TNF-α from MDSCs to promote MDSC maturation. In our studies, we propose a novel mechanism by which NK cells can overcome MDSC-induced immunosuppression and maintain CTT-induced persistent anti-tumor immunity, providing a prospective therapeutic option to improve the performance of cancer immunotherapy.

Novel and multiple targets for chimeric antigen receptor-based therapies in lymphoma

Chimeric antigen receptor (CAR) T-cell therapy targeting CD19 in B-cell non-Hodgkin lymphoma (NHL) validates the utility of CAR-based therapy for lymphomatous malignancies. Despite the success, treatment failure due to CD19 antigen loss, mutation, or down-regulation remains the main obstacle to cure. On-target, off-tumor effect of CD19-CAR T leads to side effects such as prolonged B-cell aplasia, limiting the application of therapy in indolent diseases such as chronic lymphocytic leukemia (CLL). Alternative CAR targets and multi-specific CAR are potential solutions to improving cellular therapy outcomes in B-NHL. For Hodgkin lymphoma and T-cell lymphoma, several cell surface antigens have been studied as CAR targets, some of which already showed promising results in clinical trials. Some antigens are expressed by different lymphomas and could be used for designing tumor-agnostic CAR. Here, we reviewed the antigens that have been studied for novel CAR-based therapies, as well as CARs designed to target two or more antigens in the treatment of lymphoma.

The Human Soluble NKG2D Ligand Differentially Impacts Tumorigenicity and Progression in Temporal and Model-Dependent Modes

NKG2D is an activating receptor expressed by all human NK cells and CD8 T cells. Harnessing the NKG2D/NKG2D ligand axis has emerged as a viable avenue for cancer immunotherapy. However, there is a long-standing controversy over whether soluble NKG2D ligands are immunosuppressive or immunostimulatory, originating from conflicting data generated from different scopes of pre-clinical investigations. Using multiple pre-clinical tumor models, we demonstrated that the impact of the most characterized human solid tumor-associated soluble NKG2D ligand, the soluble MHC I chain-related molecule (sMIC), on tumorigenesis depended on the tumor model being studied and whether the tumor cells possessed stemness-like properties. We demonstrated that the potential of tumor formation or establishment depended upon tumor cell stem-like properties irrespective of tumor cells secreting the soluble NKG2D ligand sMIC. Specifically, tumor formation was delayed or failed if sMIC-expressing tumor cells expressed low stem-cell markers; tumor formation was rapid if sMIC-expressing tumor cells expressed high stem-like cell markers. However, once tumors were formed, overexpression of sMIC unequivocally suppressed tumoral NK and CD8 T cell immunity and facilitated tumor growth. Our study distinguished the differential impacts of soluble NKG2D ligands in tumor formation and tumor progression, cleared the outstanding controversy over soluble NKG2D ligands in modulating tumor immunity, and re-enforced the viability of targeting soluble NKG2D ligands for cancer immunotherapy for established tumors.

Ginsenoside Rh2 enhances immune surveillance of natural killer (NK) cells via inhibition of ERp5 in breast cancer

BACKGROUND

One critical component of the immune system that prevents breast cancer cells from forming distant metastasis is natural killer (NK) cells participating in immune responses to tumors. Ginsenoside Rh2 (GRh2) as one of the major active ingredients of ginseng has been employed in treatment of cancers, but the function of GRh2 in modulating the development of breast cancer remains elusive.

PURPOSE

This study was to dissect the effect of GRh2 against breast cancer and its potential mechanisms associated with NK cells, both in vitro and in vivo.

METHODS

MDA-MB-231 and 4T1 cells were used to establish in situ and hematogenous mouse models. MDA-MB-231 and MCF-7 were respectively co-cultured with NK92MI cells or primary NK cells in vitro. Anti-tumor efficacy of GRh2 was verified by immunohistochemistry (IHC), Cell Counting Kit-8 (CCK8), high resolution micro-computed tomography (micro-CT) scanning of lungs and hematoxylin and eosin (H&E) staining. Lactate dehydrogenase (LDH) cytotoxicity assay, flow cytometry, in vivo depletion of NK cells, enzyme-linked immunosorbent assay (ELISA), western blot, quantitative reverse transcription polymerase chain reaction (qRT-PCR), immunofluorescence and cell transfection were performed for investigating the anti-tumor mechanisms of GRh2. Molecular docking, microscale thermophoresis (MST) and cellular thermal shift assay (CETSA) were employed to determine the binding between endoplasmic reticulum protein 5 (ERp5) and GRh2.

RESULTS

We demonstrated that GRh2 exerted prominent impacts on retarding the growth and metastasis of breast cancer through boosting the cytotoxic function of NK cells, as validated by the elevated release of perforin, granzyme B and interferon-γ (IFN-γ). Mechanistical studies revealed that GRh2 was capable of diminishing the expression of ERp5 and GRh2 directly bound to ERp5 in MDA-MB-231 cells as well as on a recombinant protein level. GRh2 prevented the formation of soluble MICA (sMICA) and upregulated the expression level of MICA in vivo and in vitro. Importantly, the reduced lung metastasis of breast cancer by GRh2 was almost abolished upon the depletion of NK cells. Moreover, GRh2 was able to insert into the binding pocket of ERp5 directly.

CONCLUSION

We firstly demonstrated that GRh2 played a pivotal role in augmenting NK cell activity by virtue of modulating the NKG2D-MICA signaling axis via directly binding to ERp5, and may be further optimized to a therapeutic agent for the treatment of breast cancer.

Current status and future challenges of CAR-T cell therapy for osteosarcoma

Osteosarcoma, the most common bone malignancy in children and adolescents, poses considerable challenges in terms of prognosis, especially for patients with metastatic or recurrent disease. While surgical intervention and adjuvant chemotherapy have improved survival rates, limitations such as impractical tumor removal or chemotherapy resistance hinder the treatment outcomes. Chimeric antigen receptor (CAR)-T cell therapy, an innovative immunotherapy approach that involves targeting tumor antigens and releasing immune factors, has shown significant advancements in the treatment of hematological malignancies. However, its application in solid tumors, including osteosarcoma, is constrained by factors such as low antigen specificity, limited persistence, and the complex tumor microenvironment. Research on osteosarcoma is ongoing, and some targets have shown promising results in pre-clinical studies. This review summarizes the current status of research on CAR-T cell therapy for osteosarcoma by compiling recent literature. It also proposes future research directions to enhance the treatment of osteosarcoma.

The Role of NKG2D and Its Ligands in Autoimmune Diseases: New Targets for Immunotherapy

Natural killer (NK) cells and CD8+ T cells can clear infected and transformed cells and generate tolerance to themselves, which also prevents autoimmune diseases. Natural killer group 2 member D (NKG2D) is an important activating immune receptor that is expressed on NK cells, CD8+ T cells, γδ T cells, and a very small percentage of CD4+ T cells. In contrast, the NKG2D ligand (NKG2D-L) is generally not expressed on normal cells but is overexpressed under stress. Thus, the inappropriate expression of NKG2D-L leads to the activation of self-reactive effector cells, which can trigger or exacerbate autoimmunity. In this review, we discuss the role of NKG2D and NKG2D-L in systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), multiple sclerosis (MS), type I diabetes (T1DM), inflammatory bowel disease (IBD), and celiac disease (CeD). The data suggest that NKG2D and NKG2D-L play a pathogenic role in some autoimmune diseases. Therefore, the development of strategies to block the interaction of NKG2D and NKG2D-L may have therapeutic effects in some autoimmune diseases.

Potentiation of natural killer cells to overcome cancer resistance to NK cell-based therapy and to enhance antibody-based immunotherapy

Natural killer (NK) cells are cellular components of the innate immune system that can recognize and suppress the proliferation of cancer cells. NK cells can eliminate cancer cells through direct lysis, by secreting perforin and granzymes, or through antibody-dependent cell-mediated cytotoxicity (ADCC). ADCC involves the binding of the Fc gamma receptor IIIa (CD16), present on NK cells, to the constant region of an antibody already bound to cancer cells. Cancer cells use several mechanisms to evade antitumor activity of NK cells, including the accumulation of inhibitory cytokines, recruitment and expansion of immune suppressor cells such as myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs), modulation of ligands for NK cells receptors. Several strategies have been developed to enhance the antitumor activity of NK cells with the goal of overcoming cancer cells resistance to NK cells. The three main strategies to engineer and boost NK cells cytotoxicity include boosting NK cells with modulatory cytokines, adoptive NK cell therapy, and the employment of engineered NK cells to enhance antibody-based immunotherapy. Although the first two strategies improved the efficacy of NK cell-based therapy, there are still some limitations, including immune-related adverse events, induction of immune-suppressive cells and further cancer resistance to NK cell killing. One strategy to overcome these issues is the combination of monoclonal antibodies (mAbs) that mediate ADCC and engineered NK cells with potentiated anti-cancer activity. The advantage of using mAbs with ADCC activity is that they can activate NK cells, but also favor the accumulation of immune effector cells to the tumor microenvironment (TME). Several clinical trials reported that combining engineered NK cells with mAbs with ADCC activity can result in a superior clinical response compared to mAbs alone. Next generation of clinical trials, employing engineered NK cells with mAbs with higher affinity for CD16 expressed on NK cells, will provide more effective and higher-quality treatments to cancer patients.

T cells with split CARs specific for NKG2D ligands and PD-L1 exhibit improved selectivity towards monocyte-derived cells while effective in eliminating acute myeloid leukaemia in vivo

PURPOSE

The expression of NKG2D ligands and PD-L1 has been detected on acute myeloid leukaemia (AML) cells, as well as normal cells of the myeloid lineage. To target leukemic cells while minimizing collateral damage to normal cells, we constructed a split dual CAR system based on the AND-gate logic.

METHODS

The NKG2D extracellular domain linked with DAP12 without a co-stimulatory signal was used for the basal activation of T cells, and used together with the PD-L1-specific chimeric costimulatory receptor containing the 4-1BB activating domain for co-stimulatory signal 2 input. This dual CAR displayed cell-type specificity and activity similar as a 2nd generation NKG2D ligand-specific CAR.

RESULTS

When compared to CD64 and PD-L1-specific 2nd generation CARs, we observed that the split dual CAR offered an improved myeloid cell type selectivity. For example, PD-L1-specific CAR-T cells lysed all tested myeloid cell types that expressed PD-L1, including M0 macrophages (Mø0), LPS-polarized Mø1, IFN-γ polarized Mø1, IL-4 polarized Mø2, monocytes, immature dendritic cells (imDCs), mature DCs, as well as KG-1 AML cells, while the dual CAR-T cells displaying killing activity only towards LPS polarized Mø1, mature DCs and KG-1 cells that expressed both NKG2D ligands and PD-L1. In a mouse liquid tumor model, the dual CAR-T cells were effective in eradicating established KG-1 AML xenografts.

CONCLUSION

The improved cell type specificity offered by our split dual CAR-T cell system targeting paired antigens would favour the reduction of the on-target off-tumor toxicity towards normal myeloid cells during the treatment of myeloid leukaemia.

Intrinsic and extrinsic factors determining natural killer cell fate: Phenotype and function

Natural killer (NK) cells are derived from hematopoietic stem cells. They belong to the innate lymphoid cell family, which is an important part of innate immunity. This family plays a role in the body mainly through the release of perforin, granzyme, and various cytokines and is involved in cytotoxicity and cytokine-mediated immune regulation. NK cells involved in normal immune regulation and the tumor microenvironment (TME) can exhibit completely different states. Here, we discuss the growth, development, and function of NK cells in regard to intrinsic and extrinsic factors. Intrinsic factors are those that influence NK cells to promote cell maturation and exert their effector functions under the control of internal metabolism and self-related genes. Extrinsic factors include the metabolism of the TME and the influence of related proteins on the "fate" of NK cells. This review targets the potential of NK cell metabolism, cellular molecules, regulatory genes, and other mechanisms involved in immune regulation. We further discuss immune-mediated tumor therapy, which is the trend of current research.

Natural killer cell therapy targeting cancer stem cells: Old wine in a new bottle

A small proportion of cancer cells that have stem cell-like properties are known as cancer stem cells (CSCs). They can be used to identify malignant tumor phenotypes and patients with poor prognosis. Targeting these cells has been shown to improve the effectiveness of cancer therapies. Owing to the nature of CSCs, they are resistant to conventional treatment methods such as radio- and chemotherapy. Therefore, more effective anti-CSC therapies are required. Immunotherapy, including natural killer (NK) and T cell therapy, has demonstrated the ability to eliminate CSCs. NK cells have demonstrated superior anti-CSC capabilities compared to T cells in recognizing low levels of major histocompatibility complex (MHC) class I expression. However, CSC escape also occurs during NK cell therapy. It is important to determine CSC-specific immune evasion mechanisms and find out potential solutions to optimize NK cell function. Therefore, this review discusses promising strategies that can improve the efficiency of NK cell therapy in treating CSCs, and aims to provide a reference for future research.

The diagnostic effectiveness of serum sialic acid predicts both qualitative and quantitative prostate cancer in patients with prostate-specific antigen between 4 and 20 ng/mL

Introduction

This study aimed to evaluate the predictive value of the serum biochemical index, including alkaline phosphatase (AKP), lactate dehydrogenase (LDH), α-L-fucosidase (AFU), serum sialic acid (SA), and fibrinogen (FIB), for prostate cancer (PCa) and clinically significant prostate cancer (CSPCa) in patients with a prostate-specific antigen (PSA) value between 4 and 20 ng/mL.

Patients and methods

This study retrospectively examined the clinical data of 408 eligible patients who underwent prostate biopsies in our hospital between March 2015 and July 2022. CSPCa was defined as a "Gleason grade group of≥2". For analyzing the association between PCa/CSPCa and serum biochemical index, univariable logistic regression and multivariable logistic regression were conducted. Based on the multivariable logistic regression model, we constructed models and compared the area under the curve (AUC). We generated the nomogram, the ROC curve, the DCA curve, and the calibration curve for PCa.

Results

Overall, we studied 271 patients with PCa (including 155 patients with CSPCa) and 137 non-PCa patients. Patients with PCa were more likely to consume alcohol, have higher total PSA (TPSA) values, and have lower free PSA (FPSA) and free/total PSA (f/T) values. There were higher TPSA values and lower f/T values in the CSPCa group when compared with the non-CSPCa group. The univariate logistic regression analyses did not show significant results. However, AKP, AFU, SA, TPSA, and FPSA all retain significant significance when all factors are included in multifactor logistic regression analysis. This finding suggests that the exposure factor exhibited an independent effect on the outcome after controlling for other factors, including the potential confounding effects that may have been underestimated. Through ROC curves, we found that SA and TPSA levels are more powerful predictors. In contrast, there is a lack of excellent predictive value for PCA and CSPCa using Age, AFU, FIB, and FPSA.

Conclusion

In our study, serum biochemical index is a potential prediction tool for PCa and CSPCa for patients with PSA values between 4 and 20 ng/mL. Additionally, the new serum biochemical index SA is also useful when diagnosing PCa and CSPCa, as we conclude in our study.

Biomarkers as targets for CAR-T/NK cell therapy in AML

The most common kind of acute leukemia in adults is acute myeloid leukemia (AML), which is often treated with induction chemotherapy regimens followed by consolidation or allogeneic hematopoietic stem cell transplantation (HSCT). However, some patients continue to develop relapsed or refractory AML (R/R-AML). Small molecular targeted drugs require long-time administration. Not all the patients hold molecular targets. Novel medicines are therefore needed to enhance treatment outcomes. T cells and natural killer (NK) cells engineered with chimeric antigen receptors (CARs) that target antigens associated with AML have recently been produced and are currently being tested in both pre-clinical and clinical settings. This review provides an overview of CAR-T/NK treatments for AML.

Today's Kaposi sarcoma is not the same as it was 40 years ago, or is it?

This review will provide an overview of the notion that Kaposi sarcoma (KS) is a disease that manifests under diverse and divergent circumstances. We begin with a historical introduction of KS and KS-associated herpesvirus (KSHV), highlight the diversity of clinical presentations of KS, summarize what we know about the cell of origin for this tumor, explore KSHV viral load as a potential biomarker for acute KSHV infections and KS-associated complications, and discuss immune modulators that impact KSHV infection, KSHV persistence, and KS disease.

Human lymphocytes mobilized with exercise have an anti-tumor transcriptomic profile and exert enhanced graft-versus-leukemia effects in xenogeneic mice

Background

Every bout of exercise mobilizes and redistributes large numbers of effector lymphocytes with a cytotoxic and tissue migration phenotype. The frequent redistribution of these cells is purported to increase immune surveillance and play a mechanistic role in reducing cancer risk and slowing tumor progression in physically active cancer survivors. Our aim was to provide the first detailed single cell transcriptomic analysis of exercise-mobilized lymphocytes and test their effectiveness as a donor lymphocyte infusion (DLI) in xenogeneic mice engrafted with human leukemia.

Methods

Peripheral blood mononuclear cells (PBMCs) were collected from healthy volunteers at rest and at the end of an acute bout of cycling exercise. Flow cytometry and single-cell RNA sequencing was performed to identify phenotypic and transcriptomic differences between resting and exercise-mobilized cells using a targeted gene expression panel curated for human immunology. PBMCs were injected into the tail vein of xenogeneic NSG-IL-15 mice and subsequently challenged with a luciferase tagged chronic myelogenous leukemia cell line (K562). Tumor growth (bioluminescence) and xenogeneic graft-versus-host disease (GvHD) were monitored bi-weekly for 40-days.

Results

Exercise preferentially mobilized NK-cell, CD8+ T-cell and monocyte subtypes with a differentiated and effector phenotype, without significantly mobilizing CD4+ regulatory T-cells. Mobilized effector lymphocytes, particularly effector-memory CD8+ T-cells and NK-cells, displayed differentially expressed genes and enriched gene sets associated with anti-tumor activity, including cytotoxicity, migration/chemotaxis, antigen binding, cytokine responsiveness and alloreactivity (e.g. graft-versus-host/leukemia). Mice receiving exercise-mobilized PBMCs had lower tumor burden and higher overall survival (4.14E+08 photons/s and 47%, respectively) at day 40 compared to mice receiving resting PBMCs (12.1E+08 photons/s and 22%, respectively) from the same donors (p<0.05). Human immune cell engraftment was similar for resting and exercise-mobilized DLI. However, when compared to non-tumor bearing mice, K562 increased the expansion of NK-cell and CD3+/CD4-/CD8- T-cells in mice receiving exercise-mobilized but not resting lymphocytes, 1-2 weeks after DLI. No differences in GvHD or GvHD-free survival was observed between groups either with or without K562 challenge.

Conclusion

Exercise in humans mobilizes effector lymphocytes with an anti-tumor transcriptomic profile and their use as DLI extends survival and enhances the graft-versus-leukemia (GvL) effect without exacerbating GvHD in human leukemia bearing xenogeneic mice. Exercise may serve as an effective and economical adjuvant to increase the GvL effects of allogeneic cell therapies without intensifying GvHD.

Involvement of ILC1-like innate lymphocytes in human autoimmunity, lessons from alopecia areata

Here, we have explored the involvement of innate lymphoid cells-type 1 (ILC1) in the pathogenesis of alopecia areata (AA), because we found them to be significantly increased around lesional and non-lesional HFs of AA patients. To further explore these unexpected findings, we first co-cultured autologous circulating ILC1-like cells (ILC1lc) with healthy, but stressed, organ-cultured human scalp hair follicles (HFs). ILClc induced all hallmarks of AA ex vivo: they significantly promoted premature, apoptosis-driven HF regression (catagen), HF cytotoxicity/dystrophy, and most important for AA pathogenesis, the collapse of the HFs physiological immune privilege. NKG2D-blocking or IFNγ-neutralizing antibodies antagonized this. In vivo, intradermal injection of autologous activated, NKG2D+/IFNγ-secreting ILC1lc into healthy human scalp skin xenotransplanted onto SCID/beige mice sufficed to rapidly induce characteristic AA lesions. This provides the first evidence that ILC1lc, which are positive for the ILC1 phenotype and negative for the classical NK markers, suffice to induce AA in previously healthy human HFs ex vivo and in vivo, and further questions the conventional wisdom that AA is always an autoantigen-dependent, CD8 +T cell-driven autoimmune disease.

NKG2D Fine-Tunes the Local Inflammatory Response in Colorectal Cancer

Treating colorectal cancer (CRC) is a major challenge due to the heterogeneous immunological, clinical and pathological landscapes. Immunotherapy has so far only proven effective in a very limited subgroup of CRC patients. To better define the immune landscape, we examined the immune gene expression profile in various subsets of CRC patients and used a mouse model of intestinal tumors to dissect immune functions. We found that the NK cell receptor, natural-killer group 2 member D (NKG2D, encoded by KLRK1) and NKG2D ligand gene expression is elevated in the most immunogenic subset of CRC patients. High level of KLRK1 positively correlated with the mRNA expression of IFNG and associated with a poor survival of CRC patients. We further show that NKG2D deficiency in the Apcmin/+ mouse model of intestinal tumorigenesis led to reduced intratumoral IFNγ production, reduced tumorigenesis and enhanced survival, suggesting that the high levels of IFNγ observed in the tumors of CRC patients may be a consequence of NKG2D engagement. The mechanisms governing the contribution of NKG2D to CRC progression highlighted in this study will fuel discussions about (i) the benefit of targeting NKG2D in CRC patients and (ii) the need to define the predictive value of NKG2D and NKG2D ligand expression across tumor types.

T cells engineered with full-length NKG2D linked to signaling domains of 4-1BB and CD3ζ show enhanced antitumor activity

Since NKG2D ligands (NKG2DLs) are primarily overexpressed on multiple types of solid tumors but absent on most normal tissues, NKG2DLs could be optimal antigens for CAR-T cells. To date, there have been two types of NKG2DL CARs: (i) the extracellular domain of NKG2D fused to the CD8a transmembrane domain, signaling domains of 4-1BB and CD3ζ (NKBz) and (ii) full-length NKG2D fused to the CD3ζ signaling domain (chNKz). Although NKBz- and chNKz-engineered T cells both showed antitumor activities, a comparison of their functions has not been reported. In addition, use of the 4-1BB signaling domain into the CAR construct could prolong the persistence and resistance to antitumor activities of CAR-T cells, we designed a new NKG2DL CAR, full-length NKG2D fused to the signaling domains of 4-1BB and CD3ζ (chNKBz). Among the two types of NKG2DL CAR-T cells reported in previous studies, we found that chNKz T cells had stronger antitumor ability than NKBz T cells in vitro, but their antitumor activity in vivo is similar. The chNKBz T cells showed antitumor activity superior to that of chNKz T cells and NKBz T cells in vitro and in vivo, providing a new option for the immunotherapy of NKG2DL-positive tumor patients.

Coordinated Loss and Acquisition of NK Cell Surface Markers Accompanied by Generalized Cytokine Dysregulation in COVID-19

Coronavirus disease 2019 (COVID-19), caused by the SARS-CoV-2 virus, is accompanied by a dysregulated immune response. In particular, NK cells, involved in the antiviral response, are affected by the infection. This study aimed to investigate circulating NK cells with a focus on their activation, depletion, changes in the surface expression of key receptors, and functional activity during COVID-19, among intensive care unit (ICU) patients, moderately ill patients, and convalescents (CCP). Our data confirmed that NK cell activation in patients with COVID-19 is accompanied by changes in circulating cytokines. The progression of COVID-19 was associated with a coordinated decrease in the proportion of NKG2D⁺ and CD16⁺ NK cells, and an increase in PD-1, which indicated their exhaustion. A higher content of NKG2D⁺ NK cells distinguished surviving patients from non-survivors in the ICU group. NK cell exhaustion in ICU patients was additionally confirmed by a strong negative correlation of PD-1 and natural cytotoxicity levels. In moderately ill patients and convalescents, correlations were found between the levels of CD57, NKG2C, and NKp30, which may indicate the formation of adaptive NK cells. A reduced NKp30 level was observed in patients with a lethal outcome. Altogether, the phenotypic changes in circulating NK cells of COVID-19 patients suggest that the intense activation of NK cells during SARS-CoV-2 infection, most likely induced by cytokines, is accompanied by NK cell exhaustion, the extent of which may be critical for the disease outcome.

Immune index: A gene and cell prognostic signature for immunotherapy response prediction in hepatocellular carcinoma

The heterogeneity of tumor immune microenvironment (TIME) plays important roles in the development and immunotherapy response of hepatocellular carcinoma (HCC). Using machine learning algorithms, we introduced the immune index (IMI), a prognostic model based on the HCC immune landscape. We found that IMI low HCCs were enriched in stem cell and proliferating signatures, and yielded more TP53 mutation and 17p loss compared with IMI high HCCs. More importantly, patients with high IMI exhibited better immune-checkpoint blockade (ICB) response. To facilitate clinical application, we employed machine learning algorithms to develop a gene model of the IMI (IMI_G), which contained 10 genes. According to our HCC cohort examination and single-cell level analysis, we found that IMI_G high HCCs exhibited favorable survival outcomes and high levels of NK and CD8⁺ T cells infiltration. Finally, after coculture with autologous tumor infiltrating lymphocytes, IMI_G high tumor cells exhibited a better response to nivolumab treatment. Collectively, the IMI and IMI_G may serve as powerful tools for the prognosis, classification and ICB treatment response prediction of HCC.

Recruiting T cells and sensitizing tumors to NKG2D immune surveillance for robust antitumor immune response

Although recruiting T cells to convert cold tumors into hot can prevent some tumors from evading immune surveillance, tumors have evolved more mechanisms to achieve immune evasion, such as downregulating major histocompatibility complex I (MHC I) molecules expression to prevent T cells from recognizing tumor-antigens, or secreting immune suppression cytokines that disable T cells. Tumor immune evasion not only promotes tumor growth, but also weakens the efficacy of existing tumor immunotherapies. Therefore, recruiting T cells while reshaping innate immunity plays an important role in preventing tumor immune escape. In this study, we constructed a long-acting in situ forming implant (ISFI) based on the Atrigel technology, co-encapsulated with G3-C12 and sulfisoxazole (SFX) as a drug depot in the tumor site (SFX + G3-C12-ISFI). First, G3-C12 could recruit T cells, and transform cold into hot tumors. Furthermore, SFX could inhibit tumor-derived exosomes secretion, reduce the shedding of NKG2D ligand (NKG2DL), repair NKG2D/NKG2DL pathway, reinvigorate natural killer (NK) cells, and evade the effects of MHC I molecules missing. In the humanized cold tumor model, our strategy showed an excellent anti-tumor effect, providing a smart strategy for solving tumor evasion immune surveillance.

NKp44-based chimeric antigen receptor effectively redirects primary T cells against synovial sarcoma

BACKGROUND

T-cell receptor-engineered T-cell therapies have achieved promising response rates against synovial sarcoma in clinical trials, but their applicability is limited owing to the HLA matching requirement. Chimeric antigen receptor (CAR) can redirect primary T cells to tumor-associated antigens without requiring HLA matching. However, various obstacles, including the paucity of targetable antigens, must be addressed for synovial sarcoma. Ligands for natural killer (NK) cell-activating receptors are highly expressed by tumor cells.

METHODS

The surface expression of ligands for NK cell-activating receptors in synovial sarcoma cell lines was analyzed. We analyzed RNA sequencing data deposited in a public database to evaluate NKp44-ligand expression. Primary T cells retrovirally transduced with CAR targeting NKp44 ligands were evaluated for their functions in synovial sarcoma cells. Alterations induced by various stimuli, including a histone deacetylase inhibitor, a hypomethylating agent, inflammatory cytokines, and ionizing radiation, in the expression levels of NKp44 ligands were investigated.

RESULTS

Ligands for NKp44 and NKp30 were expressed in all cell lines. NKG2D ligands were barely expressed in a single cell line. None of the cell lines expressed NKp46 ligand. Primary synovial sarcoma cells expressed the mRNA of the truncated isoform of MLL5, a known cellular ligand for NKp44. NKp44-based CAR T cells specifically recognize synovial sarcoma cells, secrete interferon-γ, and exert suppressive effects on tumor cell growth. No stimulus altered the expression of NKp44 ligands.

CONCLUSION

NKp44-based CAR T cells can redirect primary human T cells to synovial sarcoma cells. CAR-based cell therapies may be an option for treating synovial sarcomas.

Reforming the Chimeric Antigen Receptor by Peptide Towards Optimized CAR T Cells With Enhanced Anti-Cancer Potency and Safety

The emerging chimeric antigen receptor (CAR) T cell revolutionized the clinic treatment of hematological cancers, but meet its Waterloo in solid tumor therapy. Although there exist many reasons for this limitation, one of the largest challenges is the scarcity of recognition for tumor cells, resulting in the undesirable side effects and the subsequent ineffectiveness. To overcome it, a lung-cancer-cell-targeting peptide termed A1 was used in this work to reform the scFv domain of CAR by genetic manipulation. As a result, this modified ^A1CAR T exhibited the optimized cancer-cell targeting and cytotoxicity in vitro and in vivo. More importantly, by tuning the sensitivity of CAR to antigen, peptide-based ^A1CAR T cells could distinguish tumors from normal tissue, thereby eliminating the off-tumor toxicity in healthy organs. Collectively, we herein constructed a genetic peptide-engineered CAR T cells by inserting A1 peptide into the scFv domain. Profitted from the optimized recognition pattern and sensitivity, ^A1CAR T cells showed the ascendancy in solid tumor treatment. Our findings demonstrate that peptide-based CAR T holds great potential in solid tumor therapy due to an excellent targeting ability towards tumor cells.

Mechanisms of Senescence-Related NKG2D Ligands Release and Immune Escape Induced by Chemotherapy in Neuroblastoma Cells

Chemotherapy-induced senescence promotes immunocyte aggregation in the tumor microenvironment by upregulating the surface expression of activating ligands in cancer cells. However, these senescent tumor cells cannot be completely cleared and can induce tumor recurrence. Previous studiesshowed that soluble natural killer (NK) group 2D (NKG2D) ligands impair the recognition of multiple immune cells. In this study, we established an in vitro senescence model using neuroblastoma cells subjected to low-dose Chemotherapeutic drug doxorubicin or the Aurora A inhibitor MLN8237. The results showed that different neuroblastoma cell lines showed increased secretion of the NKG2D ligand MHC class I polypeptide-related sequence A/B (MICA/B) following proteolysis after treatment, with MICA/B subsequently recruited to exosomes to downregulate NKG2D expression in NK cells. Interestingly, disintegrin and metalloproteinase domain-containing 10 (ADAM10) was upregulated in senescent tumor cells, and combined treatment with the ADAM10 inhibitor GI254023X and chemotherapeutic drugs inhibited MICA/B secretion and enhanced recognition and killing by NK cells. Additionally, we found that expression of the long noncoding RNA MALAT1 was significantly increased in senescent neuroblastoma cells, and that MALAT1 served as a sponge for microRNA (miR)-92a-3p to counteract miR-92a-3p-mediated repression of ADAM10 levels. Furthermore, administration of a MALAT1 inhibitor or an miR-92a-3p mimic reduced the MICA/B shedding and enhanced recognition and killing by NK cells. These results confirmed that low-dose chemotherapy induces senescence in neuroblastoma cells, and that senescent tumor cells promote the shedding of the NKG2D ligand MICA/B through the MALAT1/miR-92a/ADAM10 axis, thereby contributing to the formation of a suppressive immune microenvironment and promoting immune escape.

Phosphoantigen-stimulated γδ T cells suppress natural killer cell-responses to missing-self

γδ T cells stimulated by phosphoantigens (pAg) are potent effectors that secrete Th1 cytokines and kill tumor cells. Consequently, they are considered candidates for use in cancer immunotherapy. However, they have proven only moderately effective in several clinical trials. We studied the consequences of pAg-stimulated γδ T-cell interactions with Natural Killer (NK) cells and CD8+ T cells, major innate and adaptive effectors, respectively. We found that pAg-stimulated γδ T cells suppressed NK-cell responses to "missing-self" but had no effect on antigen-specific CD8+ T-cell responses. Extensive analysis of the secreted cytokines showed that pAg-stimulated γδ T cells had a pro-inflammatory profile. CMV-pp65-specific CD8+ T cells primed with pAg-stimulated γδ T cells showed little effect on responses to pp65-loaded target cells. By contrast, NK cells primed similarly with γδ T cells had impaired capacity to degranulate and produce IFNγ in response to HLA class I-deficient targets. This effect depended on BTN3A1 and required direct contact between NK cells and γδ T cells. γδ T cell-priming of NK cells also led to a downregulation of NKG2D and NKp44 on NK cells. Every NK-cell subset was affected by γδ T cell-mediated immunosuppression, but the strongest effect was on KIR+NKG2A- NK cells. We therefore report a previously unknown function for γδ T cells, as brakes of NK-cell responses to "missing-self". This provides a new perspective for optimizing the use of γδ T cells in cancer immunotherapy and for assessing their role in immune responses to pAg-producing pathogens.

Transmissible cancer influences immune gene expression in an endangered marsupial, the Tasmanian devil (Sarcophilus harrisii)

Understanding the effects of wildlife diseases on populations requires insight into local environmental conditions, host defence mechanisms, host life‐history trade‐offs, pathogen population dynamics, and their interactions. The survival of Tasmanian devils (Sarcophilus harrisii) is challenged by a novel, fitness limiting pathogen, Tasmanian devil facial tumour disease (DFTD), a clonally transmissible, contagious cancer. In order to understand the devils’ capacity to respond to DFTD, it is crucial to gain information on factors influencing the devils’ immune system. By using RT‐qPCR, we investigated how DFTD infection in association with intrinsic (sex and age) and environmental (season) factors influences the expression of 10 immune genes in Tasmanian devil blood. Our study showed that the expression of immune genes (both innate and adaptive) differed across seasons, a pattern that was altered when infected with DFTD. The expression of immunogbulins IgE and IgM:IgG showed downregulation in colder months in DFTD infected animals. We also observed strong positive association between the expression of an innate immune gene, CD16, and DFTD infection. Our results demonstrate that sampling across seasons, age groups and environmental conditions are beneficial when deciphering the complex ecoevolutionary interactions of not only conventional host‐parasite systems, but also of host and diseases with high mortality rates, such as transmissible cancers.

piggyBac system to co-express NKG2D CAR and IL-15 to augment the in vivo persistence and anti-AML activity of human peripheral blood NK cells

Promising progress has been made in adoptive transfer of allogeneic natural killer (NK) cells to treat relapsed or refractory acute myeloid leukemia (AML). In this regard, chimeric antigen receptor (CAR)-modification of NK cells is considered as a compelling approach to augment the specificity and cytotoxicity of NK cells against AML. Using a non-viral piggyBac transposon technology and human peripheral blood-derived primary NK cells, we generated CAR-NK cells to target NKG2D ligands and demonstrated their in vitro activity in lysing cancer cells expressing the ligands and in vivo efficacy in inhibiting tumor growth in a xenograft KG-1 AML model. We further generated CAR-NK cells co-expressing transgenes for the NKG2D CAR and interleukin-15 (IL-15). The ectopic expression of IL-15 improved the in vitro and in vivo persistence of NKG2D CAR-NK cells, leading to enhanced in vivo tumor control and significant prolongation of mouse survival in the KG-1 AML model. Collectively, our findings demonstrate the ectopic expression of IL-15 as an important means to improve the antileukemic activity of NKG2D CAR-NK cells. Our study further illustrates the feasibility of using the piggyBac non-viral platform as an efficient and cost-effective way for CAR-NK cell manufacturing.

NK Cells Can Preferentially Target Prostate Cancer Stem-like Cells via the TRAIL/DR5 Signaling Pathway

BACKGROUND

The occurrence of androgen-dependent prostate cancer mainly depends on prostate cancer stem cells. To reduce the risk of androgen-dependent prostate cancer, the direct elimination of prostate cancer stem cells is important, but an elimination strategy has not yet been established. A previous study showed that natural killer (NK) cells can preferentially target cancer stem cells in several solid tumors except prostate cancer. In this context, this study was undertaken to investigate if NK cells can selectively attack androgen-dependent prostate cancer stem cells.

METHODS

Prostate cancer stem-like cells were separated from an androgen-dependent prostate cancer cell line (LNCaP) using a three-dimensional culture system. LNCaP stem-like cells or LNCaP cells were co-cultured with human NK cells (KHYG-1) for 24-72 h, and cell viability was determined using the WST-8 method. The expression of each protein in the cell membrane was evaluated through FACS analysis, and mRNA levels were determined using real-time PCR.

RESULTS

KHYG-1 cells had more potent cytotoxicity against LNCaP stem-like cells than LNCaP cells, and the potency of the cytotoxicity was strongly related to the TRAIL/DR5 cell death pathway.

CONCLUSION

NK cells can preferentially target prostate cancer stem-like cells via the TRAIL/DR5 pathway.

The Role of the Innate Immune System in Cancer Dormancy and Relapse

Metastatic spread and recurrence are intimately linked to therapy failure, which remains an overarching clinical challenge for patients with cancer. Cancer cells often disseminate early in the disease process and can remain dormant for years or decades before re-emerging as metastatic disease, often after successful treatment. The interactions of dormant cancer cells and their metastatic niche, comprised of various stromal and immune cells, can determine the length of time that cancer cells remain dormant, as well as when they reactivate. New studies are defining how innate immune cells in the primary tumor may be corrupted to help facilitate many aspects of dissemination and re-emergence from a dormant state. Although the scientific literature has partially shed light on the drivers of immune escape in cancer, the specific mechanisms regulating metastasis and dormancy in the context of anti-tumor immunity are still mostly unknown. This review follows the journey of metastatic cells from dissemination to dormancy and the onset of metastatic outgrowth and recurrent tumor development, with emphasis on the role of the innate immune system. To this end, further research identifying how immune cells interact with cancer cells at each step of cancer progression will pave the way for new therapies that target the reactivation of dormant cancer cells into recurrent, metastatic cancers.

Chimeric Antigen Receptor T-Cell Therapy: The Light of Day for Osteosarcoma

Simple Summary

As a novel immunotherapy, chimeric antigen receptor (CAR) T-cell therapy has achieved encouraging results in leukemia and lymphoma. Furthermore, CAR-T cells have been explored in the treatment of osteosarcoma (OS). However, there is no strong comprehensive evidence to support their efficacy. Therefore, we reviewed the current evidence on CAR-T cells for OS to demonstrate their feasibility and provide new options for the treatment of OS.

Abstract

Osteosarcoma (OS) is the most common malignant bone tumor, arising mainly in children and adolescents. With the introduction of multiagent chemotherapy, the treatments of OS have remarkably improved, but the prognosis for patients with metastases is still poor, with a five-year survival rate of 20%. In addition, adverse effects brought by traditional treatments, including radical surgery and systemic chemotherapy, may seriously affect the survival quality of patients. Therefore, new treatments for OS await exploitation. As a novel immunotherapy, chimeric antigen receptor (CAR) T-cell therapy has achieved encouraging results in treating cancer in recent years, especially in leukemia and lymphoma. Furthermore, researchers have recently focused on CAR-T therapy in solid tumors, including OS. In this review, we summarize the safety, specificity, and clinical transformation of the targets in treating OS and point out the direction for further research.

Nanoliposomes co-encapsulating Ce6 and SB3CT against the proliferation and metastasis of melanoma with the integration of photodynamic therapy and NKG2D-related immunotherapy on A375 cells

Purpose. To overcome the insufficiency of conventional photodynamic therapy (PDT) for treating metastatic melanoma, the combination of smart nanoparticles and PDT with immunotherapy was used to achieve a higher efficiency by accumulating more photosensitizers in tumor areas and triggering stronger immune responses against tumors after PDT.Methods. In this study, we designed a nanoliposome co-encapsulation of chlorin E6 (Ce6) and SB-3CT to realize significant antitumoral proliferation and metastasis efficacy after laser irradiation in A375 cells. The morphology, size distribution, and loading efficiency of Ce6-SB3CT@Liposome (Lip-SC) were characterized. The reactive oxygen species (ROS) generation and cytotoxicity were evaluated in A375 cells, and the mechanisms of natural killer (NK) cell-mediated killing were assessed.Results. Lip-SC showed good stability and was well-dispersed with a diameter of approximately 140 nm in phosphate-buffered saline. The nanoliposomes could accumulate in tumor areas and induce apoptosis in cancer cells upon 660 nm light irradiation, which could trigger an immune response and induce the expression of NK group 2 member D (NKG2D) ligands. The subsequently released SB-3CT could further activate NK cells effectively and strengthen the immune system by inhibiting the shedding of soluble NKG2D ligands.Discussion. Taken together, the synergistic effects of SB-3CT on nanoliposomes for Ce6-mediated PDT were analyzed in detail to provide a new platform for future anti-melanoma treatment.

Altered NK-cell compartment and dysfunctional NKG2D/NKG2D-ligand axis in patients with ataxia-telangiectasia

Ataxia-telangiectasia (A-T) is a multisystem disorder caused by biallelic pathogenic variants in the gene encoding A-T mutated (ATM) kinase, a master regulator of the DNA damage response (DDR) pathway. Most A-T patients show cellular and/or humoral immunodeficiency that has been associated with cancer risk and reduced survival, but NK cells have not been thoroughly studied. Here we investigated NK cells of A-T patients with a special focus on the NKG2D receptor that triggers cytotoxicity upon engagement by its ligands (NKG2DLs) commonly induced via the DDR pathway on infected, transformed, and variously stressed cells. Using flow cytometry, we examined the phenotype and function of NK cells in 6 A-T patients as compared with healthy individuals. NKG2D expression was evaluated also by western blotting and RT-qPCR; plasma soluble NKG2DLs (sMICA, sMICB, sULBP1, ULBP2) were measured by ELISA. Results showed that A-T NK cells were skewed towards the CD56^neg anergic phenotype and displayed decreased expression of NKG2D and perforin. NKG2D was reduced at the protein but not at the mRNA level and resulted in impaired NKG2D-mediated cytotoxicity in 4/6 A-T patients. Moreover, in A-T plasma we found 24-fold and 2-fold increase of sMICA and sULBP1, respectively, both inversely correlated with NKG2D expression. Overall, NK cells are disturbed in A-T patients showing reduced NKG2D expression, possibly caused by persistent engagement of its ligands, that may contribute to susceptibility to cancer and infections and represent novel targets for therapeutic interventions.

The diterpenoid adenanthin upregulates the expression of natural killer group 2D receptor ligands in hepatocellular carcinoma cells

OBJECTIVE

The natural killer (NK) group 2D (NKG2D) receptor plays a crucial role in NK cell-mediated anti-tumor immunity. NKG2D anti-proliferative effect is mediated by direct interactions of the receptor with its ligands that may be considered as a potential target for NK-based immunotherapeutic strategy in cancer cells.

METHODS

Here we report that a natural product adenanthin significantly promotes NKG2D ligands expression in hepatoma cells. The effect was determined using flow cytometry analysis. The activity of NK cell was evaluated by measuring its degranulation activity and cytotoxicity.

RESULTS

Our data indicates that the induction of NKG2D ligand binding to liver cancer cell surface receptors greatly improves the killing activity of NK cells against the cancer cells.

CONCLUSIONS

This is the first report of a new mechanism anti-cancer effects of adenanthin mediated by an indirect activation of NK cells. Our data suggests that adenanthin may be used to sensitize NK cells in tumor immunotherapy.

Methionine enkephalin (MENK) suppresses lung cancer by regulating the Bcl-2/Bax/caspase-3 signaling pathway and enhancing natural killer cell-driven tumor immunity

The aim of this study was to investigate how methionine enkephalin (MENK) regulates the biological behavior of lung cancer cells and to further explore its anti-lung cancer mechanisms in vitro and in vivo. The results showed that MENK enhanced the expression of opioid receptor (OGFr) and induced apoptosis of lung cancer cells by activating the Bcl-1/Bax/caspase-3 signaling pathway in vitro and in vivo. However, the regulatory effects of MENK disappeared after blockade of the OGFr. This confirmed that a prerequisite for the anti-tumor action of MENK is binding to OGFr. Additionally, we observed that MENK treatment enhanced the immunogenicity of lung cancer by enhancing the exposure of calreticulin and high mobility group box 1, and increasing the expression of NKG2D ligands. Further studies showed that MENK treatment increased the expression of natural killer (NK) cell-related cytokines such as granzyme B and interferon-γ and NK cell activation. Thus, we concluded that MENK might inhibit the proliferation of lung cancer cells by activating the Bcl-2/Bax/caspase-3 signaling pathway and enhancing immunogenicity and NK cell-driven tumor immunity.

Harnessing Natural Killer Cells in Cancer Immunotherapy: A Review of Mechanisms and Novel Therapies

Natural killer (NK) cells are lymphocytes that are integral to the body's innate immunity, resulting in a rapid immune response to stressed or infected cells in an antigen-independent manner. The innate immune system plays an important role in the recognition of tumor-derived stress-related factors and is critical to subsequent adaptive immune responses against tumor antigens. The aim of this review is to discuss mechanisms by which tumor cells evade NK cells and to outline strategies that harness NK cells for cancer immunotherapy. We discuss strategies to relieve the exhausted state of NK cells, recent therapies focused on targeting NK-cell-specific activating and inhibitory receptors, the use of cytokines IL-2 and IL-15 to stimulate autologous or allogeneic NK cells, and ongoing trials exploring the use of genetically modified NK cells and chimeric antigen-receptor-modified NK (CAR-NK) cells.

Epigenetic modulation of immune synaptic-cytoskeletal networks potentiates γδ T cell-mediated cytotoxicity in lung cancer

γδ T cells are a distinct subgroup of T cells that bridge the innate and adaptive immune system and can attack cancer cells in an MHC-unrestricted manner. Trials of adoptive γδ T cell transfer in solid tumors have had limited success. Here, we show that DNA methyltransferase inhibitors (DNMTis) upregulate surface molecules on cancer cells related to γδ T cell activation using quantitative surface proteomics. DNMTi treatment of human lung cancer potentiates tumor lysis by ex vivo-expanded Vδ1-enriched γδ T cells. Mechanistically, DNMTi enhances immune synapse formation and mediates cytoskeletal reorganization via coordinated alterations of DNA methylation and chromatin accessibility. Genetic depletion of adhesion molecules or pharmacological inhibition of actin polymerization abolishes the potentiating effect of DNMTi. Clinically, the DNMTi-associated cytoskeleton signature stratifies lung cancer patients prognostically. These results support a combinatorial strategy of DNMTis and γδ T cell-based immunotherapy in lung cancer management.

Clinical Impact of Natural Killer Group 2D Receptor Expression and That of Its Ligand in Ovarian Carcinomas: A Retrospective Study

PURPOSE

Natural killer (NK) cells are innate immune cells with antitumor activity. NKG2D is the most important activating receptor expressed on the NK cell surface; this receptor binds to the ligands MICA/B and ULBPs to activate NK cells. The current study aimed to evaluate the expression of NKG2D by NK cells, and to the evaluate expression of its ligands in ovarian carcinomas; it also examined the clinical relevance of NK receptor/ligand expression by analyzing the relationship between expression, clinicopathological parameters, and prognosis.

MATERIALS AND METHODS

Formalin-fixed paraffin-embedded archival ovarian high-grade serous carcinoma (HGSC, n=79) tissue samples were used for tissue microarray analysis. The expressions of NK cell markers (CD56 and NKG2D) and NKG2D ligands (MICA/B, ULBP1, ULBP3, and ULBP2/5/6) in carcinoma tissues were evaluated by immunohistochemical staining, and the association between these results and clinical prognostic parameters was analyzed statistically.

RESULTS

ULBP1 was highly expressed in 51 cases (64.6%), and ULBP2/5/6 was highly expressed in 56 cases (70.9%) of HGSC. High expression of ULBP1 and ULBP2/5/6 was significantly associated with lower recurrence of HGSC, whereas high expression of ULBP3 was significantly associated with higher recurrence. Multivariate Cox regression analysis revealed that high expression of ULBP1 was associated with increased overall survival and a decreased hazard ratio (0.150, p=0.044), suggesting that it is an independent predictor of better survival.

CONCLUSION

High expression of ULBP1 predicts a better prognosis for HGSC, suggesting that ULBP1 expression could be a novel prognostic indicator in this subset of carcinomas.

Immunogenicity of CAR T cells in cancer therapy

Patient-derived T cells genetically reprogrammed to express CD19-specific chimeric antigen receptors (CARs) have shown remarkable clinical responses and are commercially available for the treatment of patients with certain advanced-stage B cell malignancies. Nonetheless, several trials have revealed pre-existing and/or treatment-induced immune responses to the mouse-derived single-chain variable fragments included in these constructs. These responses might have contributed to both treatment failure and the limited success of redosing strategies observed in some patients. Data from early phase clinical trials suggest that CAR T cells are also associated with immunogenicity-related events in patients with solid tumours. Generally, the clinical implications of anti-CAR immune responses are poorly understood and highly variable between different CAR constructs and malignancies. These observations highlight an urgent need to uncover the mechanisms of immunogenicity in patients receiving CAR T cells and develop validated assays to enable clinical detection. In this Review, we describe the current clinical evidence of anti-CAR immune responses and discuss how new CAR T cell technologies might impact the risk of immunogenicity. We then suggest ways to reduce the risks of anti-CAR immune responses to CAR T cell products that are advancing towards the clinic. Finally, we summarize measures that investigators could consider in order to systematically monitor and better comprehend the possible effects of immunogenicity during trials involving CAR T cells as well as in routine clinical practice.

Targeting the NKG2D/NKG2D-L axis in acute myeloid leukemia

Natural killer group 2, member D (NKG2D) receptor is a crucial activating receptor in the immune recognition and eradication of abnormal cells by natural killer (NK) cells, and T lymphocytes. NKG2D can transmit activation signals and activate the immune system by recognizing the NKG2D ligands (NKG2D-L) on acute myeloid leukemia (AML) cells. Downregulation of NKG2D-L in AML can circumvent resistance to chemotherapy and immune recognition. Considering this effect, the exploration of targeting the NKG2D/NKG2D-L axis is considered to have tremendous potential for the discovery of novel biomacromolecule antibodies and pharmacological modulators in AML. This review was to outline the impact of NKG2D/NKG2D-L axis on intrinsic immunosurveillance and the development of AML. Furthermore, the NKG2D/NKG2D-L axis related modulators and progress in preclinical and clinical trials was also to be reviewed.

Immune checkpoint molecules in natural killer cells as potential targets for cancer immunotherapy

Recent studies have demonstrated the potential of natural killer (NK) cells in immunotherapy to treat multiple types of cancer. NK cells are innate lymphoid cells that play essential roles in tumor surveillance and control that efficiently kill the tumor and do not require the major histocompatibility complex. The discovery of the NK's potential as a promising therapeutic target for cancer is a relief to oncologists as they face the challenge of increased chemo-resistant cancers. NK cells show great potential against solid and hematologic tumors and have progressively shown promise as a therapeutic target for cancer immunotherapy. The effector role of these cells is reliant on the balance of inhibitory and activating signals. Understanding the role of various immune checkpoint molecules in the exhaustion and impairment of NK cells when their inhibitory receptors are excessively expressed is particularly important in cancer immunotherapy studies and clinical implementation. Emerging immune checkpoint receptors and molecules have been found to mediate NK cell dysfunction in the tumor microenvironment; this has brought up the need to explore further additional NK cell-related immune checkpoints that may be exploited to enhance the immune response to refractory cancers. Accordingly, this review will focus on the recent findings concerning the roles of immune checkpoint molecules and receptors in the regulation of NK cell function, as well as their potential application in tumor immunotherapy.

Modulating NK cell metabolism for cancer immunotherapy

Natural killer (NK) cells are lymphocytes with potent antitumor functions and, therefore, multiple NK cell-based cancer immunotherapies have been developed and are currently being tested. However, there is a necessity to find new means to improve these therapies, and immunometabolism represents an attractive target. NK cell effector functions are intricately linked to their metabolism, and modulating the latter could be the key to release their full potential. In this review, we have summarized how NK cell metabolism is regulated during some processes, such as maturation, viral infection, and cytokine stimulation. Additionally, we provide an overview of how NK cell metabolism is affected by current therapeutic approaches aimed to promote NK cell expansion and/or to increase their effector functions. We have also recapitulated several strategies that could help alleviating the metabolic impairment that characterizes tumor-infiltrating NK cells, and thus increase or restore their effector functions. Furthermore, we have reviewed several therapeutic approaches targeting cancer metabolism that could synergize with NK cell-based cancer immunotherapies, and thus enhance their efficacy.

T Cells Expressing NKG2D CAR with a DAP12 Signaling Domain Stimulate Lower Cytokine Production While Effective in Tumor Eradication

Cytokine-related toxicity associated with the use of highly active chimeric antigen receptor T cells (CAR-T cells) is a significant clinical problem. By fusing the natural killer group 2D (NKG2D) ectodomain to 4-1BB and the DAP12 cytoplasmic domain containing only one immunoreceptor tyrosine-based activation motif, we have developed a 2nd-generation (2nd-Gen) NKG2D CAR for stable expression in human T cells. When compared to T cells modified with NKG2D CAR containing the commonly used CD3ζ activation domain, T cells expressing the NKG2D-DAP12 CAR stimulated lower level release of interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), and interleukin (IL)-2 during tumor cell lysis and their proliferative activity was lower upon repeated antigen stimulation, although no difference between the two CARs was observed in mediating in vitro tumor cell lysis. In tumor-bearing NSG mice, both types of CAR-T cells displayed similar anti-tumor activity, being able to completely eradicate established solid tumor xenografts. However, treatment with the NKG2D-CD3ζ CAR-T cells led to the death of most mice from xenogeneic graft versus host disease starting 30 days post-CAR-T cell injection, which was associated with a higher level of cytokine release, whereas all the mice treated with the NKG2D-DAP12 CAR-T cells survived well. Thus, the incorporation of the DAP12 activation domain in a CAR design may possibly provide a potential clinical advantage in mitigating the risk of cytokine release syndrome (CRS).

Arming cytotoxic lymphocytes for cancer immunotherapy by means of the NKG2D/NKG2D-ligand system

INTRODUCTION

The activating NKG2D receptor plays a central role in the immune recognition and elimination of abnormal self-cells by cytotoxic lymphocytes. NKG2D binding to cell stress-inducible ligands (NKG2DL) up-regulated on cancer cells facilitates their immunorecognition. Yet tumor cells utilize various escape mechanisms to avert NKG2D-based immunosurveillance. Hence, therapeutic strategies targeting the potent NKG2D/NKG2DL axis and such immune escape mechanisms become increasingly attractive in cancer therapy.

AREAS COVERED

This perspective provides a brief introduction into the NKG2D/NKG2DL axis and its relevance for cancer immune surveillance. Subsequently, the most advanced therapeutic approaches targeting the NKG2D system are presented focusing on NKG2D-CAR engineered immune cells and antibody-mediated strategies to inhibit NKG2DL shedding by tumors.

EXPERT OPINION

Thus far, NKG2D-CAR engineered lymphocytes represent the most advanced therapeutic approach utilizing the NKG2D system. Similarly to other tumor-targeting CAR approaches, NKG2D-CAR cells demonstrate powerful on-target activity, but may also cause off-tumor toxicities or lose efficacy, if NKG2DL expression by tumors is reduced. However, NKG2D-CAR cells also act on the tumor microenvironment curtailing its immunosuppressive properties, thus providing an independent therapeutic benefit. The potency of tumoricidal NKG2D-expressing lymphocytes can be further boosted by enhancing NKG2DL expression through small molecules and therapeutic antibodies inhibiting tumor-associated shedding of NKG2DL.

Engineering of chimeric natural killer cell receptors to develop precision adoptive immunotherapies for cancer

Natural killer (NK) cells are innate immune effectors which play a crucial role in recognizing and eliminating virally infected and cancerous cells. They effectively distinguish between healthy and distressed self through the integration of signals delivered by germline‐encoded activating and inhibitory cell surface receptors. The frequent up‐regulation of stress markers on genetically unstable cancer cells has prompted the development of novel immunotherapies that exploit such innate receptors. One prominent example entails the development of chimeric antigen receptors (CAR) that detect cell surface ligands bound by NK receptors, coupling this engagement to the delivery of tailored immune activating signals. Here, we review strategies to engineer CARs in which specificity is conferred by natural killer group 2D (NKG2D) or other NK receptor types. Multiple preclinical studies have demonstrated the remarkable ability of chimeric NK receptor‐targeted T cells and NK cells to effectively and specifically eliminate cancer cells and to reject established tumour burdens. Importantly, such systems act not only acutely but, in some cases, they also incite immunological memory. Moreover, CARs targeted with the NKG2D ligand binding domain have also been shown to disrupt the tumour microenvironment, through the targeting of suppressive T regulatory cells, myeloid‐derived suppressor cells and tumour vasculature. Collectively, these findings have led to the initiation of early‐phase clinical trials evaluating both autologous and allogeneic NKG2D‐targeted CAR T cells in the haematological and solid tumour settings.

Co-Expression of IL-7 Improves NKG2D-Based CAR T Cell Therapy on Prostate Cancer by Enhancing the Expansion and Inhibiting the Apoptosis and Exhaustion

Chimeric antigen receptor (CAR) T-cell therapy is a promising approach in treating solid tumors but the therapeutic effect is limited. Prostate cancer is a typical solid malignancy with invasive property and a highly immunosuppressive microenvironment. Ligands for the NKG2D receptor are primarily expressed on many cancer cells, including prostate cancer. In this study, we utilized NKG2D-based CAR to treat prostate cancer, and improved the therapeutic effect by co-expression of IL-7. The results showed that NKG2D-CAR T cells performed significantly increased cytotoxicity against prostate cancer compared to non-transduced T cells in vitro and in vivo. Moreover, the introduction of the IL-7 gene into the NKG2D-CAR backbone enhanced the production of IL-7 in an antigen-dependent manner. NKG2DIL7-CAR T cells exhibited better antitumor efficacy at 16 h and 72 h in vitro, and inhibited tumor growth in xenograft models more effectively. In mechanism, enhanced proliferation and Bcl-2 expression in CD8⁺ T cells, decreased apoptosis and exhaustion, and increased less-differentiated cell phenotype may be the reasons for the improved persistence and survival of NKG2DIL7-CAR T cells. In conclusion, these findings demonstrated that NKG2D is a promising option for CAR T-cell therapy on prostate cancer, and IL-7 has enhanced effect on NKG2D-based CAR T-cell immunotherapy, providing a novel adoptive cell therapy for prostate cancer either alone or in combination with IL-7.