Endothelial Cells Promote Endogenous Thymic Regeneration after Injury Via BMP4 Signaling

Thymopoiesis is a complex process involving crosstalk between developing thymocytes and the non-hematopoietic stromal microenvironment, which includes thymic epithelial cells (TECs), fibroblasts and endothelial cells (ECs). Despite its importance, the thymus is exquisitely sensitive to cellular insults, including cytoreductive chemo- and radiation therapy required for successful hematopoietic stem cell transplantation; therefore identification of thymic repair mechanisms will offer promising therapeutic targets for immune regeneration. Recent studies in tissues such as liver, lung and bone marrow have revealed that ECs not only passively deliver oxygen and nutrients to tissues, but also actively produce distinct paracrine factors that can orchestrate their repair. The role of thymic ECs in thymopoiesis beyond their contribution of local circulation and the importation of lymphoid progenitors has not been comprehensively studied.