Critical role for Lymphocytes in Producing FLT3LG in Tumors and Driving Checkpoint Therapy-Receptive Immune Microenvironments

Intratumoral stimulatory dendritic cells (SDCs) play an important role in locally restimulating cytotoxic T cells and driving immune responses against cancer. However, the mechanisms that control SDC numbers remain poorly understood. In human melanoma, SDC numbers correlated with intratumoral expression of the gene encoding the cytokine FLT3LG, and we subsequently found in mouse and human tumors that this cytokine was predominantly produced by lymphocytes, notably including natural killer (NK) cells. NK cells stably formed conjugates with SDCs in the mouse tumor microenvironment (TME) and genetic and cellular ablation of NK cells in mice demonstrated their importance in regulation of SDC numbers through production of Flt3L. Although anti-PD-1 “checkpoint” immunotherapy for cancer largely targets T cells, we found that NK cells correlated with protective SDCs in human cancers, with patient responsiveness to anti-PD-1 immunotherapy, and with better overall survival. Our studies reveal that innate immune SDCs and NK cells cluster together as the best prognostic tool for T cell directed immunotherapy and that these innate cells are necessary for enhanced T cell tumor responses, suggesting this axis for novel therapies. Overall design: This dataset is n=11 biologically independent metastatic melanoma samples from patient tumors. There is no control dataset.

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Barry KC, Hsu J, Broz ML, Cueto FJ, Binnewies M, Combes AJ, Nelson AE, Loo K, Kumar R, Rosenblum MD, Alvarado MD, Wolf DM, Bogunovic D, Bhardwaj N, Daud AI, Ha PK, Ryan WR, Pollack JL, Samad B, Asthana S, Chan V, Krummel MF