CD244 loss on monocytes promotes differentiation into M1 macrophages and potentiates PD-L1 blockade in melanoma

Abstract Accumulating data have highlighted the role of monocytes/macrophages in immune escape by generating immunologically “cold” tumors that do not respond to immunotherapy. CD244 (SLAMF4, 2B4), a member of the signaling lymphocyte activation molecule family, is expressed on myeloid cells, but its precise role has not been elucidated. Using monocyte lineage-specific CD244-deficient micechallenged with B16F10 melanoma, we report for the first time that CD244 negatively regulates tumor immunity by inhibiting the differentiation and functional maturation of monocytes into macrophageswithin the tumor microenvironment. CD244-deficient macrophages more effectively activated antigen-specific T cell responsescompared to WT macrophages, thus delaying tumor growth in the B16F10 melanoma model. Moreover, combinatorial intervention of anti-PD-L1 antibodies with CD244-KO BMDM markedly improved tumor rejectioncompared to the anti-PD-L1 antibody alone or in combination with WT BMDM. Consistent with the murine data, transcriptome analysis of human melanoma tissue single-cell RNA-sequencing dataset, revealed DEGs of CD244 −monocytes and macrophages were associated with phagocytosis, antigen presentation, and autophagy. Additionally, cell type deconvolution analysis within melanoma patients bulk RNA-seq datasets from TCGA database, revealed presence of CD244-monocytes/macrophages significantly increased patient survival in primary and metastatic tumors. Hence, we proposed that CD244 serve as a critical immunoregulatory receptor on macrophages, and CD244-deficient macrophages may represent a novel therapeutic modality, which can function synergistically with checkpoint blockade therapies. Supported by grants from National Research Foundation of Korea (NRF-2020R1A2C2103061, NRF-2018M3A9D3079288, NRF-2016M3A9B6948342)