P822: EPIGENETIC REGULATION OF CD155 ON MULTIPLE MYELOMA CELLS INFLUENCES ANTI-TUMOR NOVEL IMMUNOTHERAPEUTIC APPROACHES

Topic: 13. Myeloma and other monoclonal gammopathies - Biology & Translational Research Background: Cytotoxicity is a key mechanism against tumor development. Cytotoxic cells (i.e.T cells and NK cells) are tightly regulated by immune checkpoint events, which dictate presenting cell destiny. In recent studies, the interaction between CD155 and TIGIT appeared to play an important role in cytotoxicity inhibition. Epigenetics is an important player in the regulation of gene expression, including immune checkpoint regulators. Novel immunotherapeutic strategies, such as Bispecific T-cell engagers (BiTE) and Chimeric antigen receptor (CAR) therapies, are being evaluated for MM treatment, with promising results. Aims: To validate the relevance of CD155 on cytotoxic cells (CD8+ T cells and NK cells) and its role in novel immunotherapies against malignant plasma cells, as well as to determine if patient stratification based on CD155 expression is associated with outcome. Methods: Methylation data was obtained from the Infinium Methylation450k BeadChip Kit (Illumina) for different hematological cell lines and the status of the promoter region of CD155 was studied in the context of MM. Bisulfite sequencing, quantitative PCR and azacytidine treatment were used to validate the in-silico data. We created CD155 depletion models in RPMI-8226 and JJN-3 cells using short hairpin RNA and developed an in vitro coculture system. Cytotoxic cells (either T-cells from healthy donors, anti-BCMA CAR-T, or anti-BCMA CAR-NK cells) faced MM cells. Surviving tumor cells were measured by flow cytometry. Moreover, T-cells were also incubated with anti-BCMA/CD3 BiTE. Subsequently, we used an anti-TIGIT neutralizing monoclonal antibody to determine whether the CD155-TIGIT interaction mediates the mechanism of action of CD155 in tumor escape. Finally, we analyzed the correlation between CD155 expression and survival in newly diagnosed MM samples from the CoMMpass project public data (N= 793). Results: After validating the methylation regulation of CD155, we studied CD155 participation in T-cell cytotoxicity and observed how CD155 reduced T-cell activation. RPMI-8226 and JJN-3 controls showed higher resistance to cytotoxicity (p=0.02 and p<0.001, respectively). The cytotoxic effect increased in the presence of 100pg/mL of anti-BCMA/CD3 BiTE, but the depleted models were more sensitive to it (p<0.001). When we incorporated anti-TIGIT into the system, we again observed expressing models with higher survival than depleted models on IgG controls and increased cytotoxicity in the presence of anti-TIGIT (RPMI-8226, p=0.005; JJN-3, p=0.004). When the models were treated with CAR-modified cells, the effects were always in the same direction; CD155-depleted models were more sensitive to cytotoxic effects either by 1:4 anti-BCMA CAR-T cells or by 1:8 anti-BCMA CAR-NK and 10ug/mL of anti-TIGIT. Supporting these results, the data obtained from the CoMMpass project showed that newly diagnosed MM patients with higher expression of CD155 had shorter overall survival (median overall survival of CD155 high: 56 months; CD155 low: not reached; p<0.001). Summary/Conclusion: In the context of MM, expression of CD155 effectively reduces the cytotoxic cell response, which is mediated by the interaction of CD155 on MM cells and TIGIT on cytotoxic cells. This interaction seems to impact patients treated with current therapies since patients’ outcomes correlate with CD155 expression. Furthermore, novel therapies focused on enhancing immune cytotoxicity benefit from CD155 depletion. These results warrant further investigation of CD155 as a biomarker and target for novel immunotherapies. Keywords: Tumor immunology, Epigenetic, Multiple myeloma, Immunotherapy