Improved detection of melanoma antigen-specific T cells expressing low or high levels of CD8 by HLA-A2 tetramers presenting a Melan-A/MART-1 peptide analogue

MHC class I tetramers containing peptide epitopes are sensitive tools for d etecting antigen-specific CD8(+) T-cell responses. We demonstrate here that binding of HLA-A2 tetramers to CD8(+) T cells specific for the melanoma-as sociated antigen Melan-A/MART-I can be fine-tuned by altering either the bo und peptide epitope or residues in the alpha3 domain of HLA-A2, which is im portant for CD8 binding. Antigen-specific T cells expressing high levels of CD8 could be detected using HLA-A2 tetramers containing the peptide AAGIGI LTV, an epitope which is naturally processed and presented from Melan-A/MAR T-I. In contrast, low CD8-expressing, antigen-specific T cells could be det ected efficiently only by using a mutated HLA-A2 tetramer with an altered C D8 binding site or, less efficiently, using the wild-type HLA-A2 tetramer l oaded with the peptide analogue ELAGIGILTV, which is superior in stimulatin g antigen-specific T-cell responses. Our results suggest ways to optimize t he identification and expansion of antigen-specific T cells with different requirements for the costimulatory CD8 molecule in facilitating T-cell rece ptor binding to peptide variants. (C) 2002 Wiley-Liss, Inc.