Strain-dependent Lethal Toxicity in NKG2D Ligand-targeted CAR T-cell Therapy

Advances in natural killer cell therapies for breast cancer

Breast cancer (BC) is the most common cause of cancer death in women. According to the American Cancer Society's yearly cancer statistics, BC constituted almost 15% of all the newly diagnosed cancer cases in 2022 for both sexes. Metastatic disease occurs in 30% of patients with BC. The currently available treatments fail to cure metastatic BC, and the average survival time for patients with metastatic BC is approximately 2 years. Developing a treatment method that terminates cancer stem cells without harming healthy cells is the primary objective of novel therapeutics. Adoptive cell therapy is a branch of cancer immunotherapy that utilizes the immune cells to attack cancer cells. Natural killer (NK) cells are an essential component of innate immunity and are critical in destroying tumor cells without prior stimulation with antigens. With the advent of chimeric antigen receptors (CARs), the autologous or allogeneic use of NK/CAR-NK cell therapy has raised new hopes for treating patients with cancer. Here, we describe recent developments in NK and CAR-NK cell immunotherapy, including the biology and function of NK cells, clinical trials, different sources of NK cells and their future perspectives on BC.

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.

Role of PARP Inhibitors in Cancer Immunotherapy: Potential Friends to Immune Activating Molecules and Foes to Immune Checkpoints

Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) induce cytotoxic effects as single agents in tumors characterized by defective repair of DNA double-strand breaks deriving from BRCA1/2 mutations or other abnormalities in genes associated with homologous recombination. Preclinical studies have shown that PARPi-induced DNA damage may affect the tumor immune microenvironment and immune-mediated anti-tumor response through several mechanisms. In particular, increased DNA damage has been shown to induce the activation of type I interferon pathway and up-regulation of PD-L1 expression in cancer cells, which can both enhance sensitivity to Immune Checkpoint Inhibitors (ICIs). Despite the recent approval of ICIs for a number of advanced cancer types based on their ability to reinvigorate T-cell-mediated antitumor immune responses, a consistent percentage of treated patients fail to respond, strongly encouraging the identification of combination therapies to overcome resistance. In the present review, we analyzed both established and unexplored mechanisms that may be elicited by PARPi, supporting immune reactivation and their potential synergism with currently used ICIs. This analysis may indicate novel and possibly patient-specific immune features that might represent new pharmacological targets of PARPi, potentially leading to the identification of predictive biomarkers of response to their combination with ICIs.

NKG2D-CAR-transduced natural killer cells efficiently target multiple myeloma

CAR-T-cell therapy against MM currently shows promising results, but usually with serious toxicities. CAR-NK cells may exert less toxicity when redirected against resistant myeloma cells. CARs can be designed through the use of receptors, such as NKG2D, which recognizes a wide range of ligands to provide broad target specificity. Here, we test this approach by analyzing the antitumor activity of activated and expanded NK cells (NKAE) and CD45RA- T cells from MM patients that were engineered to express an NKG2D-based CAR. NKAE cells were cultured with irradiated Clone9.mbIL21 cells. Then, cells were transduced with an NKG2D-4-1BB-CD3z-CAR. CAR-NKAE cells exhibited no evidence of genetic abnormalities. Although memory T cells were more stably transduced, CAR-NKAE cells exhibited greater in vitro cytotoxicity against MM cells, while showing minimal activity against healthy cells. In vivo, CAR-NKAE cells mediated highly efficient abrogation of MM growth, and 25% of the treated mice remained disease free. Overall, these results demonstrate that it is feasible to modify autologous NKAE cells from MM patients to safely express a NKG2D-CAR. Additionally, autologous CAR-NKAE cells display enhanced antimyeloma activity demonstrating that they could be an effective strategy against MM supporting the development of NKG2D-CAR-NK-cell therapy for MM.

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.

Experimental treatment of colorectal cancer in mice with human T cells electroporated with NKG2D RNA CAR

Aim: Peritoneal metastasis is often present in end-stage neoplastic diseases, including recurrent colorectal cancer and is associated with decreased overall survival. Novel methods are needed. Materials & methods: We constructed first-, second- and third-generation chimeric antigen receptors (CARs) specific for NKG2D ligands and modified human T cells with mRNA electroporation. Results: NKG2D CAR expression was detectable for at least 6 days postelectroporation and mediated efficient cytotoxicity against NKG2DL+ tumor cells, but not NKG2DL-cells. Multiple infusions of the first-generation CAR-T cells into immunodeficient mice bearing established peritoneal colorectal xenografts led to significantly reduced tumor burden. Conclusion: mRNA CAR is an economical way to test new CARs and potentiates controlling on-target/off-tumor toxicity and cytokine storms. The use of NKG2D RNA CARs to treat colorectal peritoneal metastasis warrants further investigation.

Electroporation of NKG2D RNA CAR Improves Vγ9Vδ2 T Cell Responses against Human Solid Tumor Xenografts

Vγ9Vδ2 T cell-based anticancer immunotherapy has shown some promise in early-phase clinical trials but there is still large room for improvement. Using the extracellular domain of the human NKG2D, a stimulatory receptor expressed by Vγ9Vδ2 T cells, we constructed NKG2D ligand-specific chimeric antigen receptors (CARs). We adopted a non-viral CAR approach via mRNA electroporation to modify Vγ9Vδ2 T cells and demonstrated that, upon interaction with the NKG2D ligand-positive cancer cells, the CARs substantially enhanced the cytotoxic activity of the modified cells toward multiple cultured solid tumor cell lines, including those resistant to Zometa treatment. Repeated doses of the CAR-expressing cells resulted in tumor regression in mice with established tumors, extending median survival time by up to 132% as compared to the PBS control group. The findings suggest clinical potential for RNA CAR-modified Vγ9Vδ2 T cells to treat a wide variety of NKG2D ligand-expressing cancers.

Adoptive Transfer of NKG2D CAR mRNA-Engineered Natural Killer Cells in Colorectal Cancer Patients

By fusing the extracellular domain of the natural killer (NK) cell receptor NKG2D to DAP12, we constructed a chimeric antigen receptor (CAR) to improve NK cell tumor responses. An RNA electroporation approach that provides transient expression of the CAR was adopted as a risk mitigation strategy. Expression of the NKG2D RNA CAR significantly augmented the cytolytic activity of NK cells against several solid tumor cell lines in vitro and provided a clear therapeutic benefit to mice with established solid tumors. Three patients with metastatic colorectal cancer were then treated with local infusion of the CAR-NK cells. Reduction of ascites generation and a marked decrease in number of tumor cells in ascites samples were observed in the first two patients treated with intraperitoneal infusion of low doses of the CAR-NK cells. The third patient with metastatic tumor sites in the liver was treated with ultrasound-guided percutaneous injection, followed by intraperitoneal infusion of the CAR-NK cells. Rapid tumor regression in the liver region was observed with Doppler ultrasound imaging and complete metabolic response in the treated liver lesions was confirmed by positron emission tomography (PET)- computed tomographic (CT) scanning. Our results highlight a promising therapeutic potential of using RNA CAR-modified NK cells to treat metastatic colorectal cancer.

Control of triple-negative breast cancer using ex vivo self-enriched, costimulated NKG2D CAR T cells

Background

Triple-negative breast cancer (TNBC) is an aggressive disease that currently lacks effective targeted therapy. NKG2D ligands (NKG2DLs) are expressed on various tumor types and immunosuppressive cells within tumor microenvironments, providing suitable targets for cancer therapy.

Methods

We applied a chimeric antigen receptor (CAR) approach for the targeting of NKG2DLs expressed on human TNBCs. Lentiviral vectors were used to express the extracellular domain of human NKG2D that binds various NKG2DLs, fused to signaling domains derived from T cell receptor CD3 zeta alone or with CD27 or 4-1BB (CD137) costimulatory domain.

Results

Interleukin-2 (IL-2) promoted the expansion and self-enrichment of NKG2D-redirected CAR T cells in vitro. High CD25 expression on first-generation NKG2D CAR T cells was essential for the self-enrichment effect in the presence of IL-2, but not for CARs containing CD27 or 4-1BB domains. Importantly, self-enriched NKG2D CAR T cells effectively recognized and eliminated TNBC cell lines in vitro, and adoptive transfer of T cells expressing NKG2D CARs with CD27 or 4-1BB specifically enhanced NKG2D CAR surface expression, T cell persistence, and the regression of established MDA-MB-231 TNBC in vivo. NKG2D-z CAR T cells lacking costimulatory domains were less effective, highlighting the need for costimulatory signals.

Conclusions

These results demonstrate that CD27 or 4-1BB costimulated, self-enriched NKG2D CAR-redirected T cells mediate anti-tumor activity against TNBC tumor, which represent a promising immunotherapeutic approach to TNBC treatment.

Electronic supplementary material

The online version of this article (10.1186/s13045-018-0635-z) contains supplementary material, which is available to authorized users.

Functions of NKG2D in CD8+ T cells: an opportunity for immunotherapy

Natural killer group 2 member D (NKG2D) is a type II transmembrane receptor. NKG2D is present on NK cells in both mice and humans, whereas it is constitutively expressed on CD8⁺ T cells in humans but only expressed upon T-cell activation in mice. NKG2D is a promiscuous receptor that recognizes stress-induced surface ligands. In NK cells, NKG2D signaling is sufficient to unleash the killing response; in CD8⁺ T cells, this requires concurrent activation of the T-cell receptor (TCR). In this case, the function of NKG2D is to authenticate the recognition of a stressed target and enhance TCR signaling. CD28 has been established as an archetype provider of costimulation during T-cell priming. It has become apparent, however, that signals from other costimulatory receptors, such as NKG2D, are required for optimal T-cell function outside the priming phase. This review will focus on the similarities and differences between NKG2D and CD28; less well-described characteristics of NKG2D, such as the potential role of NKG2D in CD8⁺ T-cell memory formation, cancer immunity and autoimmunity; and the opportunities for targeting NKG2D in immunotherapy.

Tumor Regression and Delayed Onset Toxicity Following B7-H4 CAR T Cell Therapy

B7-H4 protein is frequently overexpressed in ovarian cancer. Here, we engineered T cells with novel B7-H4-specific chimeric antigen receptors (CARs) that recognized both human and murine B7-H4 to test the hypothesis that B7-H4 CAR T cell therapy can be applied safely in preclinical models. B7-H4 CAR T cells specifically secreted IFN-γ and lysed B7-H4(+) targets. In vivo, B7-H4 CAR T cells displayed antitumor reactivity against B7-H4(+) human ovarian tumor xenografts. Unexpectedly, B7-H4 CAR T cell treatment reproducibly showed delayed, lethal toxicity 6-8 weeks after therapy. Comprehensive assessment of murine B7-H4 protein distribution uncovered expression in ductal and mucosal epithelial cells in normal tissues. Postmortem analysis revealed the presence of widespread histologic lesions that correlated with B7-H4(+) expression, and were inconsistent with graft versus host disease. Lastly, expression patterns of B7-H4 protein in normal human tissue were comparable to distribution in mice, advancing our understanding of B7-H4. We conclude that B7-H4 CAR therapy mediates control of cancer outgrowth. However, long-term engraftment of B7-H4 CAR T cells mediates lethal, off-tumor toxicity that is likely due to wide expression of B7-H4 in healthy mouse organs. This model system provides a unique opportunity for preclinical evaluation of safety approaches that limit CAR-mediated toxicity after tumor destruction in vivo.