NK cells for PD-1/PD-L1 blockade immunotherapy: pinning down the NK cell

Local, Sustained, and Targeted Co-Delivery of MEK Inhibitor and Doxorubicin Inhibits Tumor Progression in E-Cadherin-Positive Breast Cancer

Effectively utilizing MEK inhibitors in the clinic remains challenging due to off-target toxicity and lack of predictive biomarkers. Recent findings propose E-cadherin, a breast cancer diagnostic indicator, as a predictor of MEK inhibitor success. To address MEK inhibitor toxicity, traditional methodologies have systemically delivered nanoparticles, which require frequent, high-dose injections. Here, we present a different approach, employing a thermosensitive, biodegradable hydrogel with functionalized liposomes for local, sustained release of MEK inhibitor PD0325901 and doxorubicin. The poly(δ-valerolactone-co-lactide)-b-poly(ethylene-glycol)-b-poly(δ-valerolactone-co-lactide) triblock co-polymer gels at physiological temperature and has an optimal degradation time in vivo. Liposomes were functionalized with PR_b, a biomimetic peptide targeting the α5β1 integrin receptor, which is overexpressed in E-cadherin-positive triple negative breast cancer (TNBC). In various TNBC models, the hydrogel-liposome system delivered via local injection reduced tumor progression and improved animal survival without toxic side effects. Our work presents the first demonstration of local, sustained delivery of MEK inhibitors to E-cadherin-positive tumors alongside traditional chemotherapeutics, offering a safe and promising therapeutic strategy.

Chimeric Antigen Receptor-Natural Killer Cells: A New Breakthrough in the Treatment of Solid Tumours

Natural killer (NK) cells can quickly and directly eradicate tumour cells without recognising tumour-specific antigens. NK cells also participate in immune surveillance, which arouses great interest in the development of novel cancer therapies. The chimeric antigen receptor (CAR) family is composed of receptor proteins that give immune cells extra capabilities to target specific antigen proteins or enhance their killing effects. CAR-T cell therapy has achieved initial success in haematological tumours, but is prone to adverse reactions, especially with cytokine release syndrome in clinical applications. Currently, CAR-NK cell therapy has been shown to successfully kill haematological tumour cells with allogeneic NK cells in clinical trials without adverse reactions, proving its potential to become an off-the-shelf product with broad clinical application prospects. Meanwhile, clinical trials of CAR-NK cells for solid tumours are currently underway. Here we will focus on the latest advances in CAR-NK cells, including preclinical and clinical trials in solid tumours, the advantages and challenges of CAR-NK cell therapy and new strategies to improve the safety and efficacy of CAR-NK cell therapy.

Next Generation Immuno-Oncology Strategies: Unleashing NK Cells Activity

In recent years, immunotherapy has become a powerful therapeutic option against multiple malignancies. The unique capacity of natural killer (NK) cells to attack cancer cells without antigen specificity makes them an optimal immunotherapeutic tool for targeting tumors. Several approaches are currently being pursued to maximize the anti-tumor properties of NK cells in the clinic, including the development of NK cell expansion protocols for adoptive transfer, the establishment of a favorable microenvironment for NK cell activity, the redirection of NK cell activity against tumor cells, and the blockage of inhibitory mechanisms that constrain NK cell function. We here summarize the recent strategies in NK cell-based immunotherapies and discuss the requirement to further optimize these approaches for enhancement of the clinical outcome of NK cell-based immunotherapy targeting tumors.

Radiosensitization effect by HDAC inhibition improves NKG2D-dependent natural killer cytotoxicity in hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death worldwide. Radiotherapy (RT) controls HCC unsatisfactorily and temporarily. Histone deacetylase inhibitor (HDACi) is a heterogeneous group of epigenetic therapeutics with promising anticancer effects and synergism in combination with RT. HDACi modulates natural killer (NK) cell ligand expression on tumor cells, and leads to immune evasion of cancer cells. Expressions of NK group 2D (NKG2D) ligands on cancer cells determine the cytotoxic effect by interacting with NKG2D receptor on NK cells. However, the role of NKG2D signaling in HCC upon combined RT and HDACi remains unclear.

Method

In vitro co-culture system with NK cells was tested for human and murine HCC cell lines. Pan-HDACi (panobinostat) and specific HDAC4 knockdown (HDAC4-KD) were used for HDAC inhibition. Clonogenic assay and flow cytometry examined HCC cell survival and NKG2D ligand expression, respectively. Syngeneic mouse model was used to validate the radiosensitizing effect in vivo.

Results

Combined RT and HDACi/HDAC4-KD significantly enhanced NK cell-related cytotoxicity and increased NKG2D ligands, MICA/MICB expressions in human and RAE-1/H60 expressions in murine HCC cells. Delayed tumor growth in vivo by the combinational treatment of RT and HDACi/HDAC4-KD was shown with the associated NKG2D ligand expressions. However, NKG2D receptor did not significantly change among tumors.

Conclusion

Radiosensitizing effect with combined RT and HDAC inhibition increased the expression of NKG2D ligands in HCC cells and enhanced their susceptibility to NK cell-mediated cytotoxicity. These findings imply the potential use of combined RT/HDACi and NK cell-directed immunotherapy.

Differential Engraftment of Parental A20 PD-L1 WT and PD-L1 KO Leukemia Cells in Semiallogeneic Recipients in the Context of PD-L1/PD-1 Interaction and NK Cell-Mediated Hybrid Resistance

The contribution of natural killer (NK) cells to tumor rejection in the context of programmed death-ligand 1/programmed death 1 (PD-L1/PD-1) blockade is a matter of intense debate. To elucidate the role of PD-L1 expression on tumor cells and the functional consequences of engaging PD-1 receptor on cytotoxic cells, PD-L1 expression was genetically inactivated and WT or PD-L1-deficient parental tumor cells were adoptively transferred intravenously into F1 recipients. The engraftment of PD-L1-deficient A20 tumor cells in the spleen and liver of F1 recipients was impaired compared with A20 PD-L1 WT tumor counterparts. To elucidate the mechanism responsible for this differential tumor engraftment and determine the relevance of the role of the PD-L1/PD-1 pathway in the interplay of tumor cells/NK cells, a short-term competitive tumor implantation assay in the peritoneal cavity of semiallogeneic F1 recipients was designed. The results presented herein showed that NK cells killed target tumor cells with similar efficiency regardless of PD-L1 expression, whereas PD-L1 expression on A20 tumor cells conferred significant tumor protection against rejection by CD8 T cells confirming the role of the co-inhibitory receptor PD-1 in the modulation of their cytotoxic activity. In summary, PD-L1 expression on A20 leukemia tumor cells modulates CD8 T-cell-mediated responses to tumor-specific antigens but does not contribute to inhibit NK cell-mediated hybrid resistance, which correlates with the inability to detect PD-1 expression on NK cells neither under steady-state conditions nor under inflammatory conditions.

Killers on the loose: Immunotherapeutic strategies to improve NK cell-based therapy for cancer treatment

Natural killer (NK) cells are innate lymphocytes that control tumor progression by not only directly killing cancer cells, but also by regulating other immune cells, helping to orchestrate a coordinated anti-tumor response. However, despite the tremendous potential that this cell type has, the clinical results obtained from diverse NK cell-based immunotherapeutic strategies have been, until recent years, rather modest. The intrinsic regulatory mechanisms that are involved in the control of their activation as well as the multiple mechanisms that tumor cells have developed to escape NK cell-mediated cytotoxicity likely account for the unsatisfactory clinical outcomes. The current approaches to improve long-term NK cell function are centered on modulating different molecules involved in both the activation and inhibition of NK cells, and the latest data seems to advocate for combining strategies that target multiple aspects of NK cell regulation. In this review, we summarize the different strategies (such as engineered NK cells, CAR-NK, NK cell immune engagers) that are currently being used to take advantage of this potent and complex immune cell.

The PD-1 Interactome

T cell activation is a fine-tuned process that involves T cell receptor and costimulation signals. To prevent undue activation of T cells, inhibitory molecules including PD-1 (programmed death 1) are induced and function as brakes for T cell signaling. In a steady state, the interaction of PD-1 with its ligands PD-L1 (B7-H1, CD274) and PD-L2 (B7-DC, CD273) maintains peripheral immune tolerance. However, the expression of PD-L1 on tumor cells and interaction with PD-1 on T cells dampen anti-tumor immunity. Therapeutic inhibitors of the PD-1 pathway have revolutionized tumor immunotherapy. Unfortunately, the majority of patients do not develop sustained anti-tumor responses. However, the knowledge about unique PD-1 interactions and their role in mediating PD-1 inhibitory signals is currently limited. Advances in the mechanistic understanding of the molecular and signaling integration of the PD-1 pathway could unleash the great potential in tumor immunotherapy by allowing the development of combinatorial approaches that target not only PD-1 and its ligands but also its unique downstream signal mediators. In this review, the current advances in understanding the mechanisms of extracellular and intracellular PD-1 interactions and their significance in potential future therapeutic approaches are discussed.

Non-canonical PD-1 signaling in cancer and its potential implications in clinic

Programmed cell death 1 (PD-1)-based immunotherapy has revolutionized the treatment of various cancers. However, only a certain group of patients benefit from PD-1 blockade therapy and many patients succumb to hyperprogressive disease. Although, CD8 T cells and conventional T cells are generally considered to be the primary source of PD-1 in cancer, accumulating evidence suggests that other distinct cell types, including B cells, regulatory T cells, natural killer cells, dendritic cells, tumor-associated macrophages and cancer cells, also express PD-1. Hence, the response of patients with cancer to PD-1 blockade therapy is a cumulative effect of anti-PD-1 antibodies acting on a myriad of cell types. Although, the contribution of CD8 T cells to PD-1 blockade therapy has been well-established, recent studies also suggest the involvement of non-canonical PD-1 signaling in blockade therapy. This review discusses the role of non-canonical PD-1 signaling in distinct cell types and explores how the available knowledge can improve PD-1 blockade immunotherapy, particularly in identifying novel biomarkers and combination treatment strategies.

Chimeric antigen receptor-natural killer cells: Novel insight into immunotherapy for solid tumors (Review)

The chimeric antigen receptor (CAR) is an artificially modified fusion protein consisting of an extracellular antigen-binding domain, transmembrane domain and intracellular signalling domain. CAR-T therapy has demonstrated remarkable clinical efficacy in hematological malignancies. However, cytokine release syndrome and other side effects have hindered its application in solid tumors. CAR-natural killer (NK) cells have attracted broad attention due to their safety in clinical applications, their mechanism in recognising cancer cells and the abundance of its clinical specimens. Preclinical and clinical trials of human primary NK cells and NK-92 cell lines demonstrated that CAR-NK cells are able to fight haematological malignancies and solid tumors. However, the implication of CAR-NK cell therapy also has certain challenges, including the expansion and activation of primary NK cells in vitro, selection of CAR targets, survival time of CAR-NK cells in vivo, storage and transportation of NK cells, and efficiency of NK cell transduction. This review focuses on the latest progress of CAR-NK cells in the treatment of solid tumors.

Natural Killer Cells as a Potential Biomarker for Predicting Immunotherapy Efficacy in Patients with Non-Small Cell Lung Cancer

BACKGROUND

Immunotherapy with immune checkpoint inhibitors for non-small cell lung cancer (NSCLC) has emerged as an important treatment option. Although immunotherapy may significantly improve survival and quality of life, response rates are as low as 20% in NSCLC patients.

OBJECTIVE

The identification of reliable biomarkers predicting response to immunotherapy is required urgently to determine patient selection guidelines.

PATIENTS AND METHODS

Peripheral blood mononuclear cells (PBMCs) from nine NSCLC patients were collected pre- and post-treatment with immunotherapy. The immune cell composition of PBMCs was analyzed using CyTOF with an optimized 32-marker panel. The natural killer (NK) cell activity was assessed with the measurement of interferon (INF)-γ using an NK Vue™ kit.

RESULTS

We found that the percentages of NK cell populations in the immune cells of PBMCs were prominently elevated in the immunotherapy responder group when compared with non-responders. While no meaningful differences were observed in other populations of immune cells, consistent with these results, the overall activity of NK cells in responders was highly elevated compared with that of non-responders. From the analysis of NK subsets, although differences in the population of early NK cells were not observed, the functionally differentiated late NK cells were prominently high in responders.

CONCLUSIONS

The overall activity or number of NK cells may be a useful biomarker to predict immunotherapy response in patients with NSCLC.

Hemagglutinating virus of Japan-envelope containing programmed cell death-ligand 1 siRNA inhibits immunosuppressive activities and elicits antitumor immune responses in glioma

The programmed cell death‐1/programmed cell death‐ligand 1 (PD‐1/PD‐L1) pathway is involved in preventing immune system‐mediated destruction of malignant tumors including glioblastoma. However, the therapeutic influence of PD‐1/PD‐L1 inhibition alone in glioblastoma is limited. To develop effective combination therapy involving PD‐1/PD‐L1 inhibition, we used a non‐replicating virus‐derived vector, hemagglutinating virus of Japan‐envelope (HVJ‐E), to inhibit tumor cell PD‐L1 expression by delivering siRNA targeting PD‐L1. HVJ‐E is a promising vector for efficient delivery of enclosed substances to the target cells. Moreover, HVJ‐E provokes robust antitumoral immunity by activating natural killer (NK) cells and cytotoxic T lymphocytes (CTLs), and by suppressing regulatory T lymphocytes (Treg). We hypothesized that we could efficiently deliver PD‐L1‐inhibiting siRNAs to tumor cells using HVJ‐E, and that synergistic activation of antitumoral immunity would occur due to the immunostimulating effects of HVJ‐E and PD‐1/PD‐L1 inhibition. We used artificially induced murine glioma stem‐like cells, TS, to create mouse (C57BL/6N) glioblastoma models. Intratumoral injection of HVJ‐E containing siRNA targeting PD‐L1 (siPDL1/HVJ‐E) suppressed the expression of tumor cell PD‐L1 and significantly suppressed tumor growth in subcutaneous models and prolonged overall survival in brain tumor models. Flow cytometric analyses of brain tumor models showed that the proportions of brain‐infiltrating CTL and NK cells were significantly increased after giving siPDL1/HVJ‐E; in contrast, the rate of Treg/CD4⁺ cells was significantly decreased in HVJ‐E‐treated tumors. CD8 depletion abrogated the therapeutic effect of siPDL1/HVJ‐E, indicating that CD8⁺ T lymphocytes mainly mediated this therapeutic effect. We believe that this non‐replicating immunovirotherapy may be a novel therapeutic alternative to treat patients with glioblastoma.

Indirect Impact of PD-1/PD-L1 Blockade on a Murine Model of NK Cell Exhaustion

The induction of exhaustion on effector immune cells is an important limiting factor for cancer immunotherapy efficacy as these cells undergo a hierarchical loss of proliferation and cytolytic activity due to chronic stimulation. Targeting PD-1 has shown unprecedented clinical benefits for many cancers, which have been attributed to the prevention of immune suppression and exhaustion with enhanced anti-tumor responses. In this study, we sought to evaluate the role of the PD-1/PD-L1 pathway in murine natural killer (NK) cell activation, function, and exhaustion. In an in vivo IL-2-dependent exhaustion mouse model, neutralization of the PD-1/PD-L1 pathway improved NK cell activation after chronic stimulation when compared to control-treated mice. These cells displayed higher proliferative capabilities and enhanced granzyme B production. However, the blockade of these molecules during long-term in vitro IL-2 stimulation did not alter the progression of NK cell exhaustion (NCE), suggesting an indirect involvement of PD-1/PD-L1 on NCE. Given the expansion of CD8 T cells and regulatory T cells (Tregs) observed upon acute and chronic stimulation with IL-2, either of these two populations could influence NK cell homeostasis after PD-L1/PD-1 therapy. Importantly, CD8 T cell activation and functional phenotype were indeed enhanced by PD-1/PD-L1 therapy, particularly with anti-PD-1 treatment that resulted in the highest upregulation of CD25 during chronic stimulation and granted an advantage for IL-2 over NK cells. These results indicate a competition for resources between NK and CD8 T cells that arguably delays the onset of NCE rather than improving its activation during chronic stimulation. Supporting this notion, the depletion of CD8 T cells reversed the benefits of PD-1 therapy on chronically stimulated NK cells. These data suggest a bystander effect of anti-PD1 on NK cells, resulting from the global competition that exists between NK and CD8 T cells for IL-2 as a key regulator of these cells' activation. Thus, achieving an equilibrium between these immune cells might be important to accomplish long-term efficacy during anti-PD-1/IL-2 therapy.

PD-1-positive Natural Killer Cells have a weaker antitumor function than that of PD-1-negative Natural Killer Cells in Lung Cancer

Antibodies targeting the immune checkpoint inhibitor, programmed cell death 1 (PD-1), have provided a breakthrough in the treatment of lung cancer. However, the function of PD-1 in natural killer (NK) cells of cancer patients remains unclear. Herein, we analyzed the expression of PD-1 on the NK cells in the peripheral blood of patients with lung cancer and found that the level of PD-1⁺ NK cells in patients was significantly higher than that in healthy individuals. Moreover, these PD-1⁺ NK cells demonstrated a weaker ability to secrete interferon-gamma (INF-γ), granzyme B, and perforin, and exhibited lower CD107a expression. Importantly, in patients with lung cancer, the percentage of PD-1⁺ NK cells was significantly positively correlated with the concentration of IL-2 in the plasma, which was also higher than that in healthy individuals. In addition, IL-2 could increase the expression of PD-1 on NK cells in vitro, indicating that high IL-2 level in the plasma is largely responsible for the abundance of PD-1⁺ NK cells in patients with lung cancer. These findings demonstrate intriguing mechanisms for understanding the expression of PD-1 on NK cells and the function of PD-1⁺ NK cells in lung cancer. This study confirms and extends previous studies demonstrating that PD-1 can negatively regulate the antitumor function of NK cells.

Listeria-based hepatocellular carcinoma vaccine facilitates anti-PD-1 therapy by regulating macrophage polarization

Recently, patients with advanced cancers have been benefited greatly from immune checkpoint blockade immunotherapy. However, immune checkpoint blockade is still suboptimal in HCC treatment and more immune modifications are needed to achieve an efficient therapeutic goal. Here, we investigated the combined administration of a Listeria-based HCC vaccine, Lmdd-MPFG, and the anti-PD-1 immune checkpoint blockade antibody. We found that Lmdd-MPFG promoted the expression of PD-L1 in HCC cells but resensitized the tumor local T cell to respond to the anti-PD-1 immunotherapy. Mechanistically, the Lmdd-MPFG vaccine activates the NF-κB pathway in the tumor-associated macrophages (TAMs) through the TLR2 and MyD88 pathway, and recruits p62 to activate the autophagy pathway. The overall effect is skewing the TAMs from M2-polarized TAMs into the M1-polarized TAMs. Most importantly, it skewed the cytokine profiles into antitumor one in the tumor microenvironment (TME). This change restores the T-cell reactivity to the anti-PD-1 blockade. Our results suggested that Lmdd-MPFG combined with PD-1 blockade exerted synergistic antitumor effects through modifying TAMs in the TME and removing T-cell inhibitory signals, thereby providing a new potential strategy for HCC treatment.

Characterization and Potential Applications of Dog Natural Killer Cells in Cancer Immunotherapy

Natural killer (NK) cells of the innate immune system are a key focus of research within the field of immuno-oncology based on their ability to recognize and eliminate malignant cells without prior sensitization or priming. However, barriers have arisen in the effective translation of NK cells to the clinic, in part because of critical species differences between mice and humans. Companion animals, especially dogs, are valuable species for overcoming many of these barriers, as dogs develop spontaneous tumors in the setting of an intact immune system, and the genetic and epigenetic factors that underlie oncogenesis appear to be similar between dogs and humans. Here, we summarize the current state of knowledge for dog NK cells, including cell surface marker phenotype, key NK genes and genetic regulation, similarities and differences of dog NK cells to other mammals, especially human and mouse, expression of canonical inhibitory and activating receptors, ex vivo expansion techniques, and current and future clinical applications. While dog NK cells are not as well described as those in humans and mice, the knowledge of the field is increasing and clinical applications in dogs can potentially advance the field of human NK biology and therapy. Better characterization is needed to truly understand the similarities and differences of dog NK cells with mouse and human. This will allow for the canine model to speed clinical translation of NK immunotherapy studies and overcome key barriers in the optimization of NK cancer immunotherapy, including trafficking, longevity, and maximal in vivo support.