Mesenchymal thymic niche cells enable regeneration of the adult thymus and T cell immunity.

A perivascular Postn+ mesenchymal subset of thymic stroma, identified by single-cell analysis of human and mouse tissue, proved to be a critical niche for T lymphopoiesis. Depleting these cells, which likely produce the chemokine Ccl19, blocks recruitment of T cell progenitors, and the subset declines with age and after hematopoietic stem cell transplant conditioning. Adoptively transferred Postn+ cells durably engraft the atrophic thymus, recruit early T progenitors, increase T cell neogenesis and improve T cell responses to vaccination; Ccl19-expressing mesenchymal populations give similar effects.