HexaBody-OX40 promotes antitumor immunity through FcγR crosslinking-independent OX40 agonist activity and enhances effects of PD-1 blocking antibodies

Purpose: Engagement of the co-stimulatory receptor OX40on activated T cells enhances T-cell activation, survival, and proliferation. First-generation agonistic OX40 antibodies have shown limited clinical efficacy so far. The investigational HexaBody®-OX40 (GEN1055/BNT315) was designed to promote FcγR-independent higher-order OX40 clustering on the cell surface, thereby leveraging receptor biology to achieve optimal stimulation. We assessed the in vitro and in vivo functional activity of HexaBody-OX40, and evaluated the potential of concomitantly blocking PD-1/PD-L1 inhibitory signals to amplify T-cell activity. Experimental Design: Reporter assays and primary human T-cell assays using healthy donor and cancer patient cells were used to study the effects of HexaBody-OX40, alone and in combination with PD-(L)1 blocking antibodies, on T-cell activation and proliferation in vitro. Antitumor activity and pharmacodynamic effects were evaluated in human OX40 knock-in mice and human OX40/PD-1 double knock-in mice bearing MC38 tumors. Results: HexaBody-OX40 exhibited FcγR-independent OX40 agonistic activity in vitro, enhancing T-cell activation, proliferation, and cytokine secretion, and promoted tumor-infiltrating lymphocyte expansion in primary tumor samples ex vivo. In vivo, HexaBody-OX40 demonstrated antitumor activity accompanied by peripheral and intratumoral T-cell immunomodulation. PD-(L)1 blockade further potentiated HexaBody-OX40-induced T-cell proliferation, activation, and cytokine secretion in assays using PBMCs from either healthy donors or cancer patients previously treated with PD-(L)1 blocking antibody. Combined with pembrolizumab, HexaBody-OX40 enhanced antitumor activity and T-cell immunomodulation beyond either monotherapy in vivo. Conclusions: HexaBody-OX40 agonistically enhanced T-cell mediated antitumor immunity through FcγR-independent OX40 agonism. The combination of HexaBody-OX40 with PD-(L)1 blocking antibodies enhanced the effect of both single agent treatments.