FIGURE 3.

K19⁺ Multipotent Medullary Thymic Epithelial Progenitors Give Rise to Functionally Distinct mTEC Subsets in Embryonic Thymus. mTEC development involves a series of precursor‐product relationships that gives rise to the generation of multiple functionally distinct mTEC subtypes. In a recent study,^{[ 84 ]} we identified a multipotent mTEC progenitor (mmTECp) within the mTEClo compartment defined by expression of K19. K19⁺ mmTECp are mTEC‐restricted and capable of the long‐term production of multiple mTEC types, including Aire⁺ mTEC, thymic tuft cells, and CCL21⁺ mTEC^lo. The ability of mmTECp to give rise to other mTEC subtypes, including additional thymic mimetic populations, requires further study.