Butyrophilin-like 9 cooperates with JAM-A to drive anti-tumor immunity 2261194

Introduction Butyrophilin-like 9 (BTNL9), is downregulated across multiple cancer types, including ovarian cancer (OV), its decreased expression directly correlates with poorer patient outcomes, and it is known to bind T cells, suggesting a role in anti-tumor immunity. Methods To investigate this, in vitro, NY-ESO-1+ OV cells were transduced with BTNL9 ORF or empty plasmid and incubated overnight with antigen-specific T cells, and IFNy (ELISA) and cytotoxicity were measured. In vivo, BL/6 mice were implanted intraperitoneally with BTNL9-proficient or BTNL9-knockout OV tumors and were administered aCD8 antibodies or control IgG every three days while survival was recorded (n = 5 per condition). Additionally, we performed immunoprecipitation of BTNL9 from OV cells followed by LC-MS2 and identified BTNL9 binding partners. Results T cells incubated with cells overexpressing BTNL9 displayed significantly more IFNy and cytotoxicity (∼2 fold increase) while mice bearing BTNL9-proficient tumors survived significantly longer than those with BTNL9-deficient tumors; this advantage disappeared with CD8 T cell depletion. LC-MS2 identified the junctional adhesion molecule JAM-A as a binding partner of BTNL9. Blockade of JAM-A’s receptor, LFA-1, abrogates the stimulatory phenotype of BTNL9 in our in vitro assays. Conclusion This work serves to characterize a novel mechanism in OV by which BTNL9 enhances T cell stimulation via the JAM-A:LFA-1 interaction and provides new opportunities to potentially improve cancer immunotherapies.