Erythropoietin receptor on cDC1s dictates immune tolerance
Type 1 conventional dendritic cells (cDC1s) are unique in their efferocytosis and cross-presenting abilities, resulting in T cell-mediated immunity or tolerance. However, the factors that dictate whether cDC1s induce a tolerogenic or immunogenic response remain largely unknown. Here, we show that the erythropoietin receptor (EpoR) acts as a critical switch that determines the tolerogenic function of cDC1s and the threshold of Ag-specific T cell responses. In total lymphoid irradiation and anti-thymocyte serum (TLI/ATS)-induced allograft tolerance, cDC1s upregulate EpoR expression, and conditional knockout of EpoR in cDC1s diminishes antigen (Ag)-specific FOXP3+ Treg induction and expansion, resulting in allograft rejection. Mechanistically, EpoR promotes efferocytosis-induced tolerogenic maturation of splenic cDC1s towards late-stage CCR7? cDC1s characterized by elevated integrin ß8 gene (Itgb8) expression, and conditional knockout of Itgb8 in cDC1s impairs TLI/ATS-induced tolerance. Migratory cDC1s in peripheral lymph nodes preferentially express EpoR, and their capacity to induce FOXP3? Tregs is enhanced by EPO. Reciprocally, EpoR deficiency enables immunogenic maturation of both pLN migratory and splenic CCR7? cDC1s by upregulating genes essential for MHC class II-mediated Ag presentation, cross-presentation and costimulation. Loss of cDC1 EpoR reduces tumor growth by enhancing anti tumor CD8??T cell immunity, particularly by promoting tumor Ag specific CD8??T cell priming in tumor draining lymph nodes to generate more precursor exhausted T cells?(Tpex) and by sustaining intratumoral Tpexs while decreasing Tregs. Targeting EpoR on cDC1s to either induce or inhibit immune tolerance could pave the way for novel treatments of a variety of diseases. Overall design: To investigate the tolerogenic mechanisms employed by cDC1s, on the day after the last dose of TLI/ATS, we performed RNA-seq of XCR1+CD8a+ cDC1s that had been purified by fluorescence activated cell sorting (FACS).  To comprehensively define the tolerogenic properties of EpoR+ cDC1s, we further performed RNA-seq on EpoR+ and EpoR- cDC1s following TLI/ATS. Comparison of the transcriptome of spleen CCR7+XCR1+SIRPa- cDC1s and peripheral lymph node migratory XCR1+SIRPa- cDC1s, Eporflox/flox vs. Epor-Xcr1-Cre cKO mice.