ABSTRACT: 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_ receptor (Fc_R) engagement (e.g., atezolizumab). It is unknown whether variation in the ability of the IgG1 Fc region to engage Fc_Rs renders mAbs with superior therapeutic activity. In this study, we used humanized Fc_R mice to study the contribution of Fc_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_RIIB-blocking antibody, which was co-administered to overcome the suppressor function of Fc_RIIB in the tumor microenvironment (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_RIIIA. Treatment with the Fc-afucosylated version of avelumab 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 associated 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_R pathways and suggest two strategies to enhance Fc_R engagement to optimize anti-PD-L1 immunotherapy.