Boon, A. C. M.,de Mutsert, G.,van Baarle, D.,Smith, D. J.,Lapedes, A. S.,Fouchier, R. A. M.,Sintnicolass, K.,Ostrhaus, A. D. M. E.,Rimmelzwaan, G. F.

In the present study, the recognition of epitope variants of influenza A viruses by human CTL was investigated. To this end, human CD8(+) CTL clones, specific for natural variants of the HLA-B*3501- restricted epitope in the nucleoprotein (NP418-426), were generated. As determined in Cr-51 release assays and by flow cytometry with HLA-B*3501-peptide tetrameric complexes, CTL clones were found to be specific for epitopes within one subtype or cross-reactive with heterosubtypic variants of the epitope. Using eight natural variants of the epitope, positions in the 9-mer important for T cell recognition and involved in escape from CTL immunity were identified and visualized using multidimensional scaling. It was shown that positions 4 and 5 in the 9-mer epitope were important determinants of T cell specificity. The in vivo existence of CD8(+) cells cross-reactive with homo- and heterosubtypic variants of the epitope was further confirmed using polyclonal T cell populations obtained after stimulation of PBMC with different influenza A viruses. Based on the observed recognition patterns of the clonal and polyclonal T cell populations and serology, it is hypothesized that consecutive infections with influenza viruses containing different variants of the epitope select for cross-reactive T cells in vivo. The Journal of Immunology, 2004, 172: 2453-2460.