Identification of novel antagonistic anti-PD-1 antibodies that are non-blocking of the PD-1 / PD-L1 interaction.

3072 Background: Monoclonal antibodies (mAbs) that act through PD-1 blockade have had significant clinical success as cancer immunotherapeutic agents particularly in melanoma and non-small cell lung cancers with considerably lower toxicities compared to similar therapies. Current anti-PD-1 Abs have relied on the blockade of the PD-1/PD-L1 interaction. Methods: A screening strategy was established to identify a panel of mAbs that bind with high affinity to diverse epitopes on PD-1. In vitro functional activity of the mAbs was evaluated by the capacity to restore proliferation to exhausted CD8 T cells from viremic HIV infected donors and using a mixed lymphocyte reaction assay (MLR). Results: Our studies show that antagonistic mAbs targeting PD-1 can be blocking or non-blocking of the PD-1/PD-L1 interaction. Compared to benchmark blocking mAbs (pembrolizumab and nivolumab), an epitope specific set of non-blocking anti-PD-1 mAbs have equivalent antagonistic activity in: 1) restoring proliferation to exhausted HIV specific CD8 T cells and 2) promoting proliferation and up-regulating IFNγ production of CD4 T cells in a MLR assay. Importantly, combinations of blocking and non-blocking anti-PD-1 mAbs synergize in significantly improving functional activity as to that achieved with either therapeutic agent alone. Conclusions: A panel of non-blocking mAbs targeting PD-1 with strong antagonistic activity have been generated and extensively characterized in their ability to recover exhausted antigen-specific CD4 and CD8 T cells and to improve a variety of functions. Importantly, combination of non-blocking with blocking anti-PD-1 mAbs resulted in significantly improved functional activity. These results provide the scientific rationale to investigate whether combination therapy may enhance therapeutic benefit in cancer immunotherapy or whether non-blocking anti-PD-1 Abs may be effective in low PD-L1 positive tumors. Humanized non-blocker anti-PD-1 mAbs have been generated and are being advanced into clinical development.