B7-H3 and B7x are members of the B7 family of immune regulatory ligands that are thought to attenuate peripheral immune responses through co-inhibition. Previous studies have correlated their overexpression with poor prognosis and decreased tumor-infiltrating lymphocytes in various carcinomas including uterine endometrioid carcinomas, and mounting evidence supports an immuno-inhibitory role in ovarian cancer prognosis. We sought to examine the expression of B7-H3 and B7x in 103 ovarian borderline tumors and carcinomas and study associations with clinical outcome. Using immunohistochemical tissue microarray analysis on tumor specimens, we found that 93 and 100% of these ovarian tumors express B7-H3 and B7x, respectively, with expression found predominantly on cell membranes and in cytoplasm. In contrast, only scattered B7-H3-and B7x-positive cells were detected in non-neoplastic ovarian tissues. B7-H3 was also expressed in the endothelium of tumor-associated vasculature in 44% of patients, including 78% of patients with high-stage tumors (FIGO stages III and IV), nearly all of which were high-grade serous carcinomas, and 26% of patients with low-stage tumors (FIGO stages I and II; Po0.001), including borderline tumors. Analysis of cumulative survival time and recurrence incidence revealed that carcinomas with B7-H3-positive tumor vasculature were associated with a significantly shorter survival time (P ¼ 0.02) and a higher incidence of recurrence (P ¼ 0.03). The association between B7-H3-positive tumor vasculature and poor clinical outcome remained significant even when the analysis was limited to the high-stage subgroup. These results show that ovarian borderline tumors and carcinomas aberrantly express B7-H3 and B7x, and that B7-H3-positive tumor vasculature is associated with high-grade serous histological subtype, increased recurrence and reduced survival. B7-H3 expression in tumor vasculature may be a reflection of tumor aggressiveness and has diagnostic and immunotherapeutic implications in ovarian carcinomas.

Most patients with cancer do not develop durable antitumor responses after programmed cell death protein 1 (PD-1) or programmed cell death ligand 1(PD-L1) checkpoint inhibition monotherapy because of an ephemeral reversal of T cell dysfunction and failure to promote long-lasting immunological T cell memory. Activating costimulatory pathways to induce stronger T cell activation may improve the efficacy of checkpoint inhibition and lead to durable antitumor responses. We performed single-cell RNA sequencing of more than 2000 tumor-infiltrating CD8 + T cells in mice receiving both PD-1 and GITR (glucocorticoid-induced tumor necrosis factor receptor-related protein) antibodies and found that this combination synergistically enhanced the effector function of expanded CD8 + T cells by restoring the balance of key homeostatic regulators CD226 and T cell immunoreceptor with Ig and ITIM domains (TIGIT), leading to a robust survival benefit. Combination therapy decreased CD8 + T cell dysfunction and induced a highly proliferative precursor effector memory T cell phenotype in a CD226-dependent manner.PD-1 inhibition rescued CD226 activity by preventing PD-1-Src homology region 2 (SHP2) dephosphophorylation of the CD226 intracellular domain, whereas GITR agonism decreased TIGIT expression. Unmasking the molecular pathways driving durable antitumor responses will be essential to the development of rational approaches to optimizing cancer immunotherapy.

Tissue-specific expression of B7x protects against autoimmunity.