Perspectives for Improvement of the Thymic Microenvironment through Manipulation of Thymic Epithelial Cells: A Mini-Review

Thymic involution during aging is a major reason for the decreased production of naive T cells and reduced immunity. Alterations within the thymic microenvironment, characterized by the loss of function of thymic epithelial cells (TECs) and fibro-adipogenetic transformation, seem to underlie this process, mainly through declining communication between thymic stromal cells and developing thymocytes. Specifically, the signaling mediated by cytokines and hormones secreted by TECs declines during aging. Many therapies based on the manipulation of growth factors and hormones have succeeded in partially recovering the lymphoid compartment and promoting thymic function. However, considering that aging-induced thymic involution is multifactorial, the thymic reestablishment achieved with treatments that target isolated pathways is incomplete and transitory. Here, we discuss the development of three novel approaches for potentially sustained thymic recovery: the induction of sustained forkhead box N1 expression, the activation of endogenous thymic epithelial progenitor cells (TEPCs), and the generation of TEPCs from pluripotent stem cells. Combined approaches targeting both TECs and lymphoid cells will provide a potentially more effective strategy for sustained rejuvenation of the thymus.