CD8(-) T cell transfectants that express a high affinity T cell receptor exhibit enhanced peptide-dependent activation

T cells are activated by binding of the T cell receptor (TCR) to a peptide- major histocompatibility complex (MHC) complex (pMHC) expressed on the surf ace of antigen presenting cells. Various models have predicted that activat ion is limited to a narrow window of affinities (or dissociation rates) for the TCP-pMHC interaction and that above or below this window, T cells will fail to undergo activation. However, to date there have not been TCRs with sufficiently high affinities in order to test this hypothesis. In this rep ort we examined the activity of a CD8-negative T cell line transfected with a high affinity mutant TCR (K-D = 10 nM) derived from cytotoxic T lymphocy te clone 2C by in vitro engineering. The results show that despite a 300-fo ld higher affinity and a 45-fold longer off-rate compared with the wild-typ e TCR, T cells that expressed the mutant TCRs were activated by peptide. In fact, activation could be detected at significantly lower peptide concentr ations than with T cells that expressed the wildtype TCR. Furthermore, bind ing and functional analyses of a panel of peptide variants suggested that p MHC stability could account for apparent discrepancies between TCR affinity and T cell activity observed in several prior studies.