Cyclosporine A prevents the generation of single positive mature T cells in newborn mice.

The effect of Cyclosporin A (CsA) during T cell development was investigated in newborn mice. CsA treatment completely blocked the generation of peripheral single positive (SP) mature T cells: the lymphatic tissues were hypoplastic. However, double negative (DN) T3 expressing lymphocytes were still detectable. Thymuses from CsA-treated mice lacked the SP L3T4(CD4)+ subset, DN and double positive (DP) thymocytes were still present. We further defined a SP Lyt2(CD8)+ thymic subpopulation which lacked CD3 expression and displayed no functional activity in vitro. Thus, CsA critically interferes with the maturation of SP T lymphocytes; we found no evidence for 'leaky' autoreactive peripheral SP T cells in CsA-treated newborn mice.