PLET1 and thymus atrophy: As the potential of adult Plet1+ cells in regeneration of mTEC and cTEC is still controversial (28, 29, 95), the fate-mapping of adult Bpifa1+ Plet1+ cell differentiation may help to reveal the mechanisms of maintenance of thymic architecture in adult and regeneration of thymic tissue after injury or drug-induced thymic atrophy.