Fc gamma RIIB is a T cell checkpoint in antitumor immunity

thought to be exclusively expressed on B cells and innate immune cells, is upregulated on tumor-infiltrating effector CD8 + T cells in an experimental melanoma model and expressed on CD8 + T cells in patients with melanoma. Genetic deficiency of Fcgr2b resulted in enhanced tumor-infiltrating CD8 + T cell responses and significantly reduced tumor burden. Adoptive transfer experiments of Fcgr2b –/– tumor antigen-specific T cells into Fc γ RIIB-sufficient hosts resulted in an increased frequency of tumor-infiltrating CD8 + T cells with greater effector function. Finally, Fc γ RIIB was expressed on CD8 + memory T cells isolated from patients with melanoma. These data illuminate a cell-intrinsic role for the Fc γ RIIB checkpoint in suppressing tumor-infiltrating CD8 + T cells. role of Fc γ RIIB-expressing CD8 + T cells in modulating antigen-specific CD8 + T cell accumulation and effector function within tumors is unknown. Here, we demonstrate that Fc γ RIIB is upregulated on a subset of activated, tumor-infiltrating CD8 + T cells and plays a cell-autonomous role in the suppression of tumor-infiltrating CD8 + T cells in a mouse model of melanoma. Our findings illuminate the role of a potentially novel checkpoint inhibitor in potently regulating CD8 + antitumor immunity in the setting of melanoma. within tumors and regulating CD8 + T cell effector function in the context of melanoma. Moreover, this study provides evidence that CD8 + T cells in patients with melanoma express Fc γ RIIB, supporting the notion that this T cell inhibitory pathway could be at play in regulating antitumor responses in humans. This work is consistent with a previous report demonstrating surface expression of Fc γ RIIB on CD8 + T cells in models of bacterial and viral infection (23). Moreover, 2 recent studies examining the gene expression profile of virus-specific CD8 + T cells identified Fcgr2b as being a differentially expressed gene (21, 22), showing that the Fcgr2b transcript is produced by CD8 + T cells (and not solely obtained by trogocytosis of Fc γ RIIB protein from other cell types). However, whether there was a cell-autonomous functional role of Fc γ RIIB on tumor-infiltrating CD8 + T cells had not been demonstrated. In light of previous data that demonstrated ectopic expression of Fc γ RIIB on human melanoma cells but found no signaling function of the receptor, it is not a forgone conclusion that Fc γ RIIB does influence tumor infiltration through CD8 + T cell–autonomous inhibitory signaling (27). This study by Sautes-Fridman et al. examined 259 primary and 187 metastatic lesions from 12 different cancer types and noted the selective expression of Fc γ RIIB by metastatic melanoma cells. They hypothesized that melanoma metastases acquire expression of the inhibitory Fc γ RIIB as a decoy receptor to serve as a sink for IgG, as a means to escape Fc γ R-mediated lysis by antitumor IgG antibodies. However, our work demonstrates that on CD8 + T cells within the tumor, Fc γ RIIB had a functional, inhibitory role in suppressing CD8 + antitumor immunity. This work contradicts a long-held dogma that T cells do not express Fc receptors. for 4 hours at 37°C in the of 30 mL PMA, 400 ng/mL Ionomycin, and 10 μ g/mL GolgiPlug (BD Biosciences). In some experiments, were activated with 30 nM OVA SIINFEKL peptide (GenScript) and 10 μ g/mL GolgiPlug (BD Biosciences). 4 hours, were processed using the BD Cytofix/Cytoperm Kit (BD Biosciences) according to manufacturer’s instructions and with PE/Cy7 anti-human TNF- α Antibody and Alexa Fluor 700 anti-human IFN- γ Antibody (BioLegend). were determined by CountBright Absolute Counting Beads according to the manufacturer’s instructions (Thermo Flow cytometric analysis was performed on an LSRII flow cytometer (BD Biosciences). were analyzed 9.9. 4