CD69 prevents PLZF hi innate precursors from prematurely exiting the thymus and aborting NKT2 cell differentiation

While CD69 may regulate thymocyte egress by inhibiting S1P expression, CD69 expression is not thought to be required for normal thymocyte development. Here we show that CD69 is in fact specifically required for the differentiation of mature NKT2 cells, which do not themselves express CD69. Mechanistically, CD69 expression is required on CD24 PLZF innate precursors for their retention in the thymus and completion of their differentiation into mature NKT2 cells. By contrast, CD69-deficient CD24 PLZF innate precursors express S1P and prematurely exit the thymus, while S1P inhibitor treatment of CD69-deficient mice retains CD24 PLZF innate precursors in the thymus and restores NKT2 cell differentiation. Thus, CD69 prevents S1P expression on CD24 PLZF innate precursor cells from aborting NKT2 differentiation in the thymus. This study reveals the importance of CD69 to prolong the thymic residency time of developing immature precursors for proper differentiation of a T cell subset.