Fc glycoengineering of a PD-L1 antibody harnesses Fc? receptors for increased antitumor efficacy

FDA-approved anti-PD-L1 monoclonal antibodies (mAbs) bear the IgG1 isotype, whose scaffolds are either wild -type (e.g., avelumab) or Fc-mutated and lacking Fc gamma receptor (Fc gamma R) engagement (e.g., atezolizumab). It is unknown whether variation in the ability of the IgG1 Fc region to engage Fc gamma Rs renders mAbs with superior therapeutic activity. In this study, we used humanized Fc gamma R mice to study the contribution of Fc gamma R signaling to the antitumor activity of human anti-PD-L1 mAbs and to identify an optimal human IgG scaffold for PD -L1 mAbs. We observed similar antitumor efficacy and comparable tumor immune responses in mice treated with anti-PD-L1 mAbs with wild-type and Fc-mutated IgG scaffolds. However, in vivo antitumor activity of the wild-type anti-PD-L1 mAb avelumab was enhanced by combination treatment with an Fc gamma RIIB-blocking an-tibody, which was co-administered to overcome the suppressor function of Fc gamma RIIB in the tumor microenviron-ment (TME). We performed Fc glycoengineering to remove the fucose subunit from the Fc-attached glycan of avelumab to enhance its binding to the activating Fc gamma RIIIA. Treatment with the Fc-afucosylated version of ave-lumab also enhanced antitumor activity and induced stronger antitumor immune responses compared with the parental IgG. The enhanced effect by afucosylated PD-L1 antibody was dependent on neutrophils and associ-ated with decreased frequencies of PD-L1+ myeloid cells and increased infiltration of T cells in the TME. Our data reveal that the current design of FDA-approved anti-PD-L1 mAbs does not optimally harness Fc gamma R pathways and suggest two strategies to enhance Fc gamma R engagement to optimize anti-PD-L1 immunotherapy.