Natural killer (NK) cells are innate lymphocytes that recognize and clear infected and transformed cells. The importance of NK cells in tumor surveillance underlies the development of NK cell therapy as cancer treatment. The NK-92 cell line has been successfully modified to express high-affinity CD16 receptor for antibody-dependent cellular cytotoxicity and/or chimeric antigen receptors (CARs) that can recognize antigens expressed on tumor cells and mediate NK cell activation. Since there is no need for human leukocyte antigen matching or prior exposure to the tumor antigens, NK-92 provides an opportunity for the development of next-generation off-the-shelf cell therapy platforms. CAR-engineered NK-92 cells have demonstrated robust antitumor activity in in vitro and in vivo preclinical studies, propelling the clinical development of CAR NK-92 cells. Preliminary phase 1 data indicate that CAR NK-92 can be safely administered in the clinic. In this review, we provide an overview of recent advances in the research and clinical application of this novel cell immunotherapy.

Background: Different types of tumors have varying susceptibility to immunotherapy and hence require different treatment strategies; these cover a spectrum ranging from ‘hot’ tumors or those with high mutational burden and immune infiltrates that are more amenable to targeting to ‘cold’ tumors that are more difficult to treat due to the fewer targetable mutations and checkpoint markers. We hypothesized that an effective anti-tumor response requires multiple agents that would (1) engage the immune response and generate tumor-specific effector cells; (2) expand the number and breadth of the immune effector cells; (3) enable the anti-tumor activity of these immune cells in the tumor microenvironment; and (4) evolve the tumor response to widen immune effector repertoire. Methods: A hexatherapy combination was designed and administered to MC38-CEA (warm) and 4T1 (cool) murine tumor models. The hexatherapy regimen was composed of adenovirus-based vaccine and IL-15 (interleukin-15) superagonist (N-803) to engage the immune response; anti-OX40 and anti-4-1BB to expand effector cells; anti-PD-L1 (anti-programmed death-ligand 1) to enable anti-tumor activity; and docetaxel to promote antigen spread. Primary and metastatic tumor growth inhibition were measured. The generation of anti-tumor immune effector cells was analyzed using flow cytometry, ELISpot (enzyme-linked immunospot), and RNA analysis. Results: The MC38-CEA and 4T1 tumor models have differential sensitivities to the combination treatments. In the ‘warm’ MC38-CEA, combinations with two to five agents resulted in moderate therapeutic benefit while the hexatherapy regimen outperformed all these combinations. On the other hand, the hexatherapy regimen was required in order to decrease the primary and metastatic tumor burden in the ‘cool’ 4T1 model. In both models, the hexatherapy regimen promoted CD4⁺ and CD8⁺ T cell proliferation and activity. Furthermore, the hexatherapy regimen induced vaccine-specific T cells and stimulated antigen cascade. The hexatherapy regimen also limited the immunosuppressive T cell and myeloid derived suppressor cell populations, and also decreased the expression of exhaustion markers in T cells in the 4T1 model. Conclusion: The hexatherapy regimen is a strategic combination of immuno-oncology agents that can engage, expand, enable, and evolve the immune response and can provide therapeutic benefits in both MC38-CEA (warm) and 4T1 (cool) tumor models.

The discovery of immune checkpoints and the development of immune checkpoint inhibitors (ICI) have achieved a durable response in advanced-stage cancer patients. However, there is still a high proportion of patients who do not benefit from ICI therapy due to a lack of response when first treated (primary resistance) or detection of disease progression months after objective response is observed (acquired resistance). Here, we review the current FDA-approved ICI for the treatment of certain solid malignancies, evaluate the contrasting responses to checkpoint blockade in different cancer types, explore the known mechanisms associated with checkpoint blockade resistance (CBR), and assess current strategies in the field that seek to overcome these mechanisms. In order to improve current therapies and develop new ones, the immunotherapy field still has an unmet need in identifying other molecules that act as immune checkpoints, and uncovering other mechanisms that promote CBR.

Innovative strategies to re-establish the immune-mediated destruction of malignant cells is paramount to the success of anti-cancer therapy. Accumulating evidence suggests that radiotherapy and select chemotherapeutic drugs and small molecule inhibitors induce immunogenic cell stress on tumors that results in improved immune recognition and targeting of the malignant cells. Through immunogenic cell death, which entails the release of antigens and danger signals, and immunogenic modulation, wherein the phenotype of stressed cells is altered to become more susceptible to immune attack, radiotherapies, chemotherapies, and small-molecule inhibitors exert immune-mediated anti-tumor responses. In this review, we discuss the mechanisms of immunogenic cell death and immunogenic modulation and their relevance in the anti-tumor activity of radiotherapies, chemotherapies, and small-molecule inhibitors. Our aim is to feature the immunological aspects of conventional and targeted cancer therapies and highlight how these therapies may be compatible with emerging immunotherapy approaches.

Chordoma is a rare tumor derived from notochord remnants that has a propensity to recur and metastasize despite conventional multimodal treatment. Cancer stem cells (CSC) are implicated in chordoma's resistant and recurrent behavior; thus, strategies that target CSCs are of particular interest. Using in vitro cytotoxicity models, we demonstrated that anti-programmed death ligand 1 (anti–PD-L1; N-601) and anti-EGFR (cetuximab) antibodies enhanced lysis of chordoma cells by healthy donor and chordoma patient NK cells through antibody-dependent cellular cytotoxicity (ADCC). Treatment of NK cells with an IL15 superagonist complex (N-803) increased their cytotoxicity against chordoma cells, which was further enhanced by treatment with N-601 and/or cetuximab. PD-L1–targeted chimeric antigen receptor NK cells (PD-L1 t-haNKs) were also effective against chordoma cells. CSCs were preferentially vulnerable to NK-cell killing in the presence of N-601 and N-803. Flow cytometric analysis of a chordoma CSC population showed that CSCs expressed significantly more NK-activating ligand B7-H6 and PD-L1 than non-CSCs, thus explaining a potential mechanism of selective targeting. These data suggest that chordoma may be effectively targeted by combinatorial NK cell–mediated immunotherapeutic approaches and that the efficacy of these approaches in chordoma and other CSC-driven tumor types should be investigated further in clinical studies. Significance: Combinatory immunotherapy using NK-mediated approaches demonstrates robust antitumor activity in preclinical models of chordoma and selectively targets chordoma CSCs.

Background: First-line treatment with pembrolizumab plus chemotherapy in recurrent and metastatic head and neck squamous cell carcinomas (HNSCC) has improved survival. However, the overall response rate with this standard of care regimen (SOC) remains limited. Interleukin (IL)-12 is a potent cytokine that facilitates the crosstalk between innate and adaptive immunity, making it crucial in the antitumor response. Alum-anchored murine IL-12 (mANK-101) has been demonstrated to elicit robust antitumor responses in diverse syngeneic models, which were correlated with increased immune effector functions and prolonged local retention of IL-12. This study investigates the therapeutic benefit of combining mANK-101 with SOC in the MOC1 and MOC2 murine HNSCC tumor models. Methods: MOC1 and MOC2 tumor-bearing C57BL/6 mice were administered with a single intratumoral injection of mANK-101 and weekly intraperitoneal injections of cisplatin and α-programmed death 1 (PD-1) for 3 weeks. For MOC1, flow cytometry and cytokine array were performed to assess the immune effector functions associated with the combinational treatment. Multiplex immunofluorescence was employed to characterize the influence of the treatment on the immune architecture in the tumors. RNA analysis was implemented for in-depth examination of the macrophage and effector populations. Results: In the MOC1 and MOC2 models, combination therapy with mANK-101, cisplatin, and α-PD-1 resulted in superior tumor growth inhibition and resulted in the highest rate of tumor-free survival when compared with treatment cohorts that received mANK-101 monotherapy or SOC treatment with α-PD-1 plus cisplatin. Furthermore, the combination therapy protected against tumor re-growth on rechallenge and controlled the growth of distal tumors. The improved therapeutic effect was associated with increased CD8⁺ T-cell recruitment, increased CD8⁺ and CD4⁺ activity, and repolarization of the macrophage population from M2 to M1 at the tumor site. Elevated and prolonged interferon-γ expression is central to the antitumor activity mediated by the combination therapy. In addition, the combination therapy with mANK-101+cisplatin+α-PD-1 induced the formation of tertiary lymphoid structure-like immune aggregates in the peritumoral space. Conclusion: The current findings provide a rationale for the combination of alum-tethered IL-12 with cisplatin and α-PD-1 for HNSCC.