Erythropoietin receptor on cDC1s dictates immune tolerance

Type 1 conventional dendritic cells (cDC1s) are unique in their efferocytosis¹ and cross-presenting abilities², resulting in antigen-specific T cell immunity³ or tolerance^4-8. However, the mechanisms that underlie cDC1 tolerogenic function 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 antigen-specific T cell responses. In total lymphoid irradiation-induced allograft tolerance^9,10, cDC1s upregulate EPOR expression, and conditional knockout of EPOR in cDC1s diminishes antigen-specific induction and expansion of FOXP3⁺ regulatory T (T_reg) cells, resulting in allograft rejection. Mechanistically, EPOR promotes efferocytosis-induced tolerogenic maturation^7,11 of splenic cDC1s towards late-stage CCR7⁺ cDC1s characterized by increased expression of the integrin β8 gene¹² (Itgb8), and conditional knockout of Itgb8 in cDC1s impairs tolerance induced by total lymphoid irradiation plus anti-thymocyte serum. Migratory cDC1s in peripheral lymph nodes preferentially express EPOR, and their FOXP3⁺ T_reg cell-inducing capacity is enhanced by erythropoietin. Reciprocally, loss of EPOR enables immunogenic maturation of peripheral lymph node migratory and splenic CCR7⁺ cDC1s by upregulating genes involved in MHC class II- and class I-mediated antigen presentation, cross-presentation and costimulation. EPOR deficiency in cDC1s reduces tumour growth by enhancing anti-tumour T cell immunity, particularly increasing the generation of precursor exhausted tumour antigen-specific CD8⁺ T cells¹³ in tumour-draining lymph nodes and supporting their maintenance within tumours, while concurrently reducing intratumoural T_reg cells. Targeting EPOR on cDC1s to induce or inhibit T cell immune tolerance could have potential for treating a variety of diseases.