Inhibition of alloreactive cytotoxic T lymphocytes by peptides from the α2domain of HLA–A2

Class I major histocompatibility complex (MHC) molecules function in the recognition of antigens by cytotoxic T lymphocytes (CTL)1,2. Although this biological role is firmly established and much has been learnt about their structure and polymorphic variation3–6, little is known of the regions of class I molecules that are involved in functional interactions with components of the T-cell surface. Here we show that peptides derived from residues 98–113 of the α2 domain of HLA–A2 specifically inhibit the recognition of target cells by many HLA–A2-specific CTL. In addition to identifying a region that is probably involved in binding the T-cell receptor these results raise the possibility that alloreactive CTL may recognize degraded fragments of class I histocompatibility antigens.