HSCs and Tregs cooperate to preserve extramedullary hematopoiesis under chronic inflammation
Hematopoietic stem cells (HSCs) are localized within specialized niches of the bone marrow (BM). However, during hematological disorders or infections, the functionality of HSCs in the BM is compromised, leading to extramedullary hematopoiesis (EMH). Chronic inflammation drives EMH, yet its impact on HSCs outside the BM is poorly understood. Using a mouse model of chronic autoinflammatory disease, we demonstrated the presence of extramedullary HSCs in blood, spleen, and inflamed tails and paws. Single-cell transcriptomics revealed a unique expression profile in extramedullary HSCs, with significant upregulation of Cd53, MHCII-associated, and immunosuppressive genes. We further demonstrated that extramedullary CD53+ HSCs act as antigen-presenting cells, promoting the development of regulatory T cells (Tregs) to control chronic inflammation at extramedullary sites. Conversely, Tregs exert a protective role on extramedullary HSCs. Altogether, our findings revealed a mutually supportive relationship between a unique subset of HSCs and T cells in inflamed tissues during chronic inflammation.