Abstract 6559: Investigating the transcriptomic signature of B7-H7-mediated activation of NK cell activity

Abstract Determining how antibodies that target immune checkpoints alter lymphocyte functions can improve our understanding of immune checkpoint inhibitors responses in patients. HERV-H LTR-associating 2 (HHLA2, B7-H7) is an immune checkpoint expressed by many tumors. Our group previously found that B7-H7 has an inhibitory receptor, KIR3DL3, in addition to having an activating receptor, TMIGD2. Both B7-H7 receptors are expressed by subsets of T cells and NK cells. However, little is known about how different subsets of lymphocytes are affected by B7-H7 engagement of these receptors, and multiple B7-H7:KIR3DL3 blocking antibodies are currently enrolling cancer patients in Phase I clinical trials (NCT05824663, NCT06240728).In this study, we explored the effect of tumors expressing B7-H7 on NK cells in vitro by single cell RNA sequencing (scRNAseq). NK cells were isolated from peripheral blood and co-cultured with K562 cells or K562 cells overexpressing B7-H7 for 2hr. Co-cultures were performed in the presence of different B7-H7 blocking antibodies or isotype controls. 133,017 cells passed quality control, with 9 distinct NK cell populations being identified. Primary NK cells not co-cultured with tumor cells were mainly composed of two TXNIP+ CD96 hi NK cell clusters that had low expression of cytotoxic and inflammatory genes. Additionally, these two clusters had the highest expression of TMIGD2, suggesting that these populations represent resting NK cells. Co-culture with K562 or K562-B7-H7 cells increased the proportion of highly cytotoxic and inflammatory NK cell clusters. However, XCL2, CSF2, IFNγ and IL3 were higher in NK cells co-cultured with K562-B7-H7 than with K562, suggesting B7-H7 on K562 cells is proinflammatory in this early activation model. Notably, only a small subset of peripheral blood NK cells expressed the inhibitory receptor KIR3DL3, as expected in early NK activation. Furthermore, all antibody treatments regardless of the Fc isotype were associated with increased proportions of CRTAM+ IL2RA+ TNFRSF9+ NK cell clusters, compared to NK cells cultured without antibody. Differential gene expression analysis between B7-H7 antibody clones 6F10 and 2C4 by respective Fc (IgG1 or IgG4) suggested blocking TMIGD2 with the dual receptor blocking B7-H7 antibody (6F10) reduces the extent of activation of the NK cells compared to the B7-H7 antibody (2C4) that blocks KIR3DL3 but not TMIGD2.Our work suggests the importance of selecting B7-H7 therapeutics that spare the interaction of B7-H7:TMIDG2 to maintain any NK-dependent antitumor benefit of B7-H7 expression. Citation Format: Michael Gomez, Deepthi Chowbene, Nahuel Perrot, Nikolaos Kalavros, Shuoshuo Wang, Antonella Arruda de amaral, David F. McDermott, Gordon J. Freeman, Ioannis S. Vlachos, Kathleen M. Mahoney. Investigating the transcriptomic signature of B7-H7-mediated activation of NK cell activity abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 6559.