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 β8 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. 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.