Absence of thymus crosstalk in the fetus does not preclude hematopoietic induction of a functional thymus in the adult.

Cortical and medullary thymic epithelial cells provide essential signals for a normal programme of T-cell development. Current models of thymus development suggest that thymocyte-derived signals play an important role in establishing thymic microenvironments, a process termed thymus crosstalk. Studies on CD3epsilontg26 mice lacking intrathymic T-cell progenitors provided evidence that normal development of the thymic cortex depends upon thymocyte-derived signals.