Induction of peptide-specific CD8⁺ CTL clones in β₂-microglobulin- deficient mice

We have examined the ability of β₂-m^- mice to produce CD4^-8⁺ T cells by generating CD8⁺ CTLs to a defined ligand. We report here the first demonstration of peptide-specific, self-class I MHC-restricted CTLs from β₂-m-deficient mice. We have used the KOD mouse, an H-2(d) β₂-m^- strain, to generate CTLs that recognize the class I MHC molecule L(d) in association with one of two L(d)-binding immunogenic peptides. Testing of these CTLs on a panel of L(d)-binding peptides reveals a high degree of peptide specificity. Peptide-specific CTL bulk cultures from KOD mice differ from those generated in β₂-m⁺ mice in that they possess altered affinities for their peptide ligands. In addition, we show that CTLs generated from β₂-m^- mice in the presence of β₂-m⁺ stimulator cells and exogenous peptide are specific either for the exogenous peptide or for endogenous peptides that are present in association with L(d) on the surface of β₂-m⁺ cells, but are not present at detectable levels on β₂-m^- cells. These results demonstrate that positive selection of CD8⁺ CTLs can occur in vivo on the very low levels of class I MHC found in the KOD mouse. Furthermore, CTLs from the KOD mouse maintain a high degree of peptide specificity despite reduced levels of class I MHC.