FUNCTIONALLY AND PHENOTYPICALLY MATURE MOUSE CD8(-CELLS DEVELOP IN PORCINE THYMUS GRAFTS IN MICE() T)

Mouse CD4(+) T cells efficiently develop in fetal pig thymus (FP THY) grafts and repopulate the periphery of T cell and NK cell-depleted, th ymectomized (ATX) mice. However, efficient peripheral repopulation of mouse CD8(+) T cells does not occur in these mice. We have therefore e valuated the maturation and function of mouse CD8 single positive (SP) thymocytes in fetal pig thymus and liver fragment (FP THY LIV) grafts . Phenotypic maturity, as measured by upregulated expression of TCR, c lass I MHC, and Qa-2, and downregulated expression of heat stable anti gen (HSA) on CD8 SP cells in FP THY grafts, was similar to that in hos t thymi of euthymic control mice. Cytolytic T lymphocyte (CTL) activit y of thymocytes from FP THY grafts was similar to that of thymocytes f rom host thymi of euthymic mice, indicating that functional maturation of CD8 SP cells had taken place in the grafts. Furthermore, similarly efficient deletion of V beta 5.1/5.2(+) and V beta 11(+) CD8 SP cells was observed in FP THY grafts as in host thymi of euthymic control mi ce. Similar percentages of V beta 6, V beta 7, and V beta 8.1/8.2 expr essing cells were also detected among CD8 SP cells in FP THY grafts an d host thymi of euthymic controls. Together, our results suggest that normal positive and negative selection occurs, and that mouse CD8(+) c ells can undergo normal functional and phenotypic maturation in FP THY grafts. Thus, other explanations must be sought for the failure of CD 8(+) cells to repopulate the peripheral lymphoid tissues of ATX, T cel l-depleted, pig THY/LIV-grafted mice.