Kinetics and repertoire selection of T cells derived from the early waves of fetal thymus colonization after thymus grafting in allogeneic nude recipients.

The survival of T cells derived from the early waves of thymus colonization by haemopoietic cell precursors was investigated by grafting thymus from B6.Thy1.1 day 14 embryos (E14) (first wave) or E17 or newborn thymus (subsequent waves) into allogeneic athymic BALB/c (Thy1.2) nude recipients. The survival of donor-derived Thy1.1 cells was longer when they were derived from early thymocytes. Donor B6.Thy1.1 V beta 5 and V beta 11 T cells, although maturing in BALB/c host presenting Mls2a superantigens, were not deleted, in contrast to host Thy1.2 T cells differentiating from endogenous stem cells. These results show that the population of T cells derived from early precursors undergoes particular selection characteristics, which favour the inclusion of potentially autoreactive cells with prolonged survival, even in H-2 allogeneic conditions which normally do not allow the survival of peripheral T cells.