Maturation and function of mouse T-cells with a transgenic TCR positively selected by highly disparate xenogeneic porcine MHC

Remarkably normal cellular immune function, along with specific T-cell tole rance to highly disparate xenogeneic donors, can be achieved by grafting fe tal pig thymus (FP THY) tissue to T and NK cell-depleted, thymectomized (AT X) mice. Porcine MHC can mediate positive selection of mouse CD4(+) T-cells with a mouse MHC-restricted TCR in FP THY-grafted, T- and NK cell-depleted , ATX TCR-transgenic "AND" mice. However, functional studies were not perfo rmed on transgenic mouse T-cells selected in a FP THY graft. We have now pe rformed further studies to confirm the ability of porcine MHC to mediate th e positive selection of mouse T-cells with a mouse MHC-restricted TCR, and to exclude the possibility that the maturation of mouse T-cells with a mous e MHC-restricted TCR in FP THY grafts in ATX "AND" mice is a special case. For this purpose, TCR-transgenic mice with an unrelated transgenic TCR ["3A 9", specific for hen egg lysozyme (HEL) peptide 46-61 presented by I-A(k)] were employed. Similar to FP THY-grafted ATX "AND" mice, large numbers of m ouse CD4 single positive thymocytes expressing the transgenic TCR (V beta8. 2) and expressing a mature phenotype (Qa-2(high) and heat stable antigen, H SA(low)) were detected in FP THY grafts. Porcine thymus grafting led to a h igh level of peripheral repopulation with mouse naive-type (CD44(low) CD45R B(high) CD62L(high)) CD4(+) cells expressing the transgenic TCR in T and NK cell-depleted ATX "3A9" mice, regardless of whether the recipients had a p ositive selecting or a non-selecting, class II deficient MHC background. Th e mouse CD4(+) T-cells expressing the "3A9" TCR showed efficient primary pr oliferative responses to the protein antigen (HEL) when it was presented by mouse class II+ antigen presenting cells (APC) in vitro. These results, co llectively, support the general conclusion that discordant xenogeneic porci ne MHC can mediate positive selection of mouse T-cells with mouse MHC-restr icted TCR. This study has implications for the potential clinical use of xe nogeneic thymus transplantation to reconstitute cellular immunity in the se tting of thymic insufficiency or thymectomy, and hence for its applicabilit y to the induction of xenograft tolerance and in the treatment of immunodef iciency diseases.