FcRIIB engagement drives agonistic activity of Fc-engineered OX40 antibody to stimulate human tumor-infiltrating T cells

Background OX40 (CD134) is a costimulatory molecule of the tumor necrosis factor receptor superfamily that is currently being investigated as a target for cancer immunotherapy. However, despite promising results in murine tumor models, the clinical efficacy of agonistic alpha OX40 antibodies in the treatment of patients with cancer has fallen short of the high expectation in earlier-stage trials. Methods Using lymphocytes from resected tumor, tumor-free (TF) tissue and peripheral blood mononuclear cells (PBMC) of 96 patients with hepatocellular and colorectal cancers, we determined OX40 expression and the in vitro T-cell agonistic activity of OX40-targeting compounds. RNA-Seq was used to evaluate OX40-mediated transcriptional changes in CD4+ and CD8+ human tumor-infiltrating lymphocytes (TILs). Results Here, we show that OX40 was overexpressed on tumor-infiltrating CD4+ T cells compared with blood and TF tissue-derived T cells. In contrast to a clinical candidate alpha OX40 antibody, treatment with an Fc-engineered alpha OX40 antibody (alpha OX40_v12) with selectively enhanced Fc gamma RIIB affinity, stimulated in vitro CD4+ and CD8+ TIL expansion, as well as cytokine and chemokine secretions. The activity of alpha OX40_v12 was dependent on Fc gamma RIIB engagement and intrinsic CD3/CD28 signals. The transcriptional landscape of CD4+ and CD8+ TILs shifted toward a prosurvival, inflammatory and chemotactic profile on treatment with alpha OX40_v12. Conclusions OX40 is overexpressed on CD4+ TILs and thus represents a promising target for immunotherapy. Targeting OX40 with currently used agonistic antibodies may be inefficient due to lack of OX40 multimerization. Thus, Fc engineering is a powerful tool in enhancing the agonistic activity of alpha OX40 antibody and may shape the future design of antibody-mediated alpha OX40 immunotherapy.