TAP1-deficient mice select a CD8(+) T cell repertoire that displays both diversity and peptide specificity

Mice deficient in the gene encoding the transporter associated with antigen processing 1 (TAP1) are defective in providing major histocompatibility complex (MHC) class I molecules with cytosolic peptides. Consequently, these mice express reduced levels of MHC class I glycoproteins on the cell surface, and have reduced numbers of CD8(+) T cells in the periphery. In the present study, we have addressed the diversity and specificity of the peripheral CD8(+) T cell population in TAP1 -/- mice. CD8(+) T cells were polyclonal with regard to T cell receptor (TCR) V beta expression. Overall, V beta usage in TAP1 -/- mice appeared to be very similar to that in wild-type mice, with significantly reduced levels of V beta 5.1/5.2-expressing CD8(+) T cells as the only clear exception. This polyclonal population of CD8(+) T cells readily mounted epitope-specific CTL responses against four out of five well-defined MHC class I-restricted peptides. In contrast to allospecific CTL, peptide-specific CTL from TAP1 -/- mice did not crossreact on cells expressing normal levels of H-2(h) class I. The present results demonstrate that a polyclonal CD8(+) T cell repertoire. displaying both diversity and peptide specificity, is positively selected in mice devoid of a functional peptide transporter. These observations imply that TAP-dependent peptides are not absolutely required for positive selection of a functionally diverse repertoire of CD8(+) T cells.