DNAM1 and 2B4 Costimulatory Domains Enhance the Cytotoxicity of Anti-GPC3 Chimeric Antigen Receptor-Modified Natural Killer Cells Against Hepatocellular Cancer Cells in vitro

Purpose

Hepatocellular cancer (HCC) is the sixth most prevalent cancer and the third leading cause of cancer-related death worldwide. Cellular immunotherapy against glypican 3 (GPC3) has recently been used in the treatment of HCC, following the success of chimeric antigen receptor (CAR)-T therapy in treatment of B cell malignancy. However, CAR-T cells are not “off-the-shelf” and always cause cytokine release syndrome, which can be eliminated by using natural killer (NK) cells as effector cells. Since a costimulatory signal is necessary for the activation, persistence, or cytotoxicity of CAR-T cells, we speculated that the costimulatory signal is also required for CAR-NK cells in HCC treatment.

Methods

Five anti-GPC3 CAR plasmids containing different costimulatory domains were constructed. They included Z (only the CD3ζ domain, no costimulatory domain), CD28.Z (T-cell costimulatory domain CD28), DNAM1/2B4.Z (NK-cell-associated costimulatory domain DNAM1 or 2B4), and DNAM1.2B4.Z (both NK-cell-associated costimulatory domains). Respective CAR-NK-92 cells were generated. The MTT viability assay was performed to evaluate the effect of the different costimulatory domains on CAR-NK-cell proliferation. The effect on persistence was analyzed using an apoptosis assay and flow cytometry. Special cytotoxicity against normal hepatocellular cells and GPC3⁺ malignant cells was investigated in vitro. The concentration of cytokines (TNF-α and IFN-γ) released by CAR-NK-92 cells was also measured by ELISA.

Results

NK-cell-associated costimulatory signal was necessary for CAR-NK-92 cells. CAR-NK-92 cells with DNAM1 and/or 2B4 expanded more quickly and persisted with a lower apoptotic ratio, compared to the presence of CD28 or no costimulatory signal. All CAR-NK-92 cells showed special cellular cytotoxicity in vitro. CAR-NK-92 cells with NK-cell-associated costimulatory domains exhibited higher cytotoxic ability compared with those without any costimulatory domain or with T-cell costimulatory domain. CAR-NK-92 cells with both DNAM1 and 2B4 displayed the highest cytotoxicity. The cytokine release assay results were consistent with those of the cytotoxicity assay.

Conclusion

We provided the first evidence supporting a strategy using DNAM1 and 2B4 costimulatory domains to generate anti-GPC3 CAR-NK-92 cells, which exhibits enhanced cytotoxicity against hepatocellular cancer cells in vitro.

Characterization of Human NK Cell-Derived Exosomes: Role of DNAM1 Receptor In Exosome-Mediated Cytotoxicity Against Tumor

Despite the pivotal role of natural killer (NK) cells in defenses against tumors, their exploitation in cancer treatment is still limited due to their reduced ability to reaching tumor sites and the inhibitory effects of tumor microenvironment (TME) on their function. In this study, we have characterized the exosomes from IL2- or IL15-cultured human NK cells. Both cytokines induced comparable amounts of exosomes with similar cargo composition. Analysis of molecules contained within or exposed at the exosome surface, allowed the identification of molecules playing important roles in the NK cell function including IFN-γ, Lymphocyte Function-Associated Antigen (LFA-1), DNAX Accessory Molecule-1 (DNAM1) and Programmed Cell Death Protein (PD-1). Importantly, we show that DNAM1 is involved in exosome-mediated cytotoxicity as revealed by experiments using blocking antibodies to DNAM1 or DNAM1 ligands. In addition, antibody-mediated inhibition of exosome cytotoxicity results in a delay in target cell apoptosis. We also provide evidence that NK-exosomes may exert their cytolytic activity after short time interval and even at low concentrations. Regarding their possible use in immunotherapy, NK exosomes, detectable in peripheral blood, can diffuse into tissues and exert their cytolytic effect at tumor sites. This property offers a clue to integrate cancer treatments with NK exosomes.

IL-15 and CD155 expression regulate LAT expression in murine DNAM1+ NK cells, enhancing their effectors functions

NK cells are innate immune cells characterized by their ability to spontaneously lyse tumor and virally infected cells. We have recently demonstrated that IL-15-sufficient DC regulate NK cell effector functions in mice. Here, we established that among ITAM-proximal signaling molecules, the expression levels of the scaffold molecule Linker for Activation of T cells (LAT) and its transcription factor ELF-1 were reduced 4 days after in vivo depletion of DC. Addition of IL-15, a cytokine presented by DC to NK cells, regulates LAT expression in NK cells with a significant effect on the DNAM1⁺ subset compared to DNAM1^- cells. We also found that LAT expression is regulated via interaction of the DNAM1 receptor with its ligand CD155 in both immature and mature NK cells, independently of NK cell education. Finally, we found that LAT expression within DNAM1⁺ NK cells might be responsible for enhanced calcium mobilization following the triggering of activating receptors on NK cells. Altogether, we found that LAT expression is tightly regulated in DNAM1⁺ NK cells, via interaction(s) with DC, which express CD155 and IL-15, resulting in rapid activation of the DNAM1⁺ subset during activating receptor triggering.

Impaired NK cell recognition of vemurafenib-treated melanoma cells is overcome by simultaneous application of histone deacetylase inhibitors

Therapy of metastatic melanoma advanced recently with the clinical implementation of signalling pathway inhibitors, such as vemurafenib, specifically targeting mutant BRAF^V600E. In general, patients experience remarkable clinical responses under BRAF inhibitor (BRAFi) treatment but eventually progress within 6-8 months due to resistance development. Responding metastases show an increased immune cell infiltrate, including also NK cells, that, however, is no longer detectable in BRAFi-resistant lesions, suggesting NK cell activity should be exploited to prevent disease progression. Here, we examined the effects of BRAFi on the expression of ligands targeting activating NK cells receptors immediately after treatment onset, prior to resistance development. We demonstrate that BRAF^V600E mutant melanoma cells cultured in the presence of vemurafenib, strongly decreased surface expression of ligands for NK activating receptors including the NKG2D-ligand, MICA, and the DNAM-1 ligand, CD155, and became significantly less susceptible to NK cell attack. NKG2D-ligand protein downregulation was due to a significant decrease in mRNA levels, already detectable 24 h after drug treatment. Interestingly, vemurafenib-induced MICA downregulation could be counteracted by treatment of melanoma cells with the histone deacetylase (HDAC) inhibitor (HDACi) sodium butyrate, that also upregulated the DNAM1-ligand, Nectin-2. HDACi treatment enhanced surface expression of NKG2D-ligands in the presence of BRAFi, accompanied by recovery of NK cell recognition, but only upon simultaneous drug application. These results suggest that co-administration of BRAFi and HDAC inhibitors as well as having direct effects on melanoma cell survival, could also synergise to improve NK cell recognition and avoid tumour immune evasion.

IL12-mediated sensitizing of T-cell receptor-dependent and -independent tumor cell killing

Interleukin 12 (IL12) is a key inflammatory cytokine critically influencing Th1/Tc1-T-cell responses at the time of initial antigen encounter. Therefore, it may be exploited for cancer immunotherapy. Here, we investigated how IL12, and other inflammatory cytokines, shape effector functions of human T-cells. Using a defined culture system, we followed the gradual differentiation and function of antigen-specific CD8(+) T cells from their initial activation as naïve T cells through their expansion phase as early memory cells to full differentiation as clonally expanded effector T cells. The addition of IL12 8 days after the initial priming event initiated two mechanistically separate events: First, IL12 sensitized the T-cell receptor (TCR) for antigen-specific activation, leading to an approximately 10-fold increase in peptide sensitivity and, in consequence, enhanced tumor cell killing. Secondly, IL12 enabled TCR/HLA-independent activation and cytotoxicity: this "non-specific" effect was mediated by the NK cell receptor DNAM1 (CD226) and dependent on ligand expression of the target cells. This IL12 regulated, DNAM1-mediated killing is dependent on src-kinases as well as on PTPRC (CD45) activity. Thus, besides enhancing TCR-mediated activation, we here identified for the first time a second IL12 mediated mechanism leading to activation of a receptor-dependent killing pathway via DNAM1.

NK cell autoreactivity and autoimmune diseases

Increasing evidences have pointed out the relevance of natural killer (NK) cells in organ-specific and systemic autoimmune diseases. NK cells bear a plethora of activating and inhibiting receptors that can play a role in regulating reactivity with autologous cells. The activating receptors recognize natural ligands up-regulated on virus-infected or stressed or neoplastic cells. Of note, several autoimmune diseases are thought to be linked to viral infections as one of the first event in inducing autoimmunity. Also, it is conceivable that autoimmunity can be triggered when a dysregulation of innate immunity occurs, activating T and B lymphocytes to react with self-components. This would imply that NK cells can play a regulatory role during adaptive immunity; indeed, innate lymphoid cells (ILCs), comprising the classical CD56⁺ NK cells, have a role in maintaining or alternating tissue homeostasis secreting protective and/or pro-inflammatory cytokines. In addition, NK cells display activating receptors involved in natural cytotoxicity and the activating isoforms of receptors for HLA class I that can interact with healthy host cells and induce damage without any evidence of viral infection or neoplastic-induced alteration. In this context, the interrelationship among ILC, extracellular-matrix components, and mesenchymal stromal cells can be considered a key point for the control of homeostasis. Herein, we summarize evidences for a role of NK cells in autoimmune diseases and will give a point of view of the interplay between NK cells and self-cells in triggering autoimmunity.