CD8 T Cell–Evasive Functions of Human Cytomegalovirus Display Pervasive MHC Allele Specificity, Complementarity, and Cooperativity

Immunoevasive proteins ("evasins") of human CMV (HCMV) modulate stability and localization of MHC class I (MHC I) molecules, and their supply of antigenic peptides. However, it is largely unknown to what extent these evasins interfere with recognition by virus-specific CD8 T cells. We analyzed the recognition of HCMV-infected cells by a panel of CD8 T cells restricted through one of nine different MHC I allotypes. We employed a set of HCMV mutants deleted for three or all four of the MHC I modulatory genes US2, US3, US6, and US11. We found that different HCMV evasins exhibited different allotype-specific patterns of interference with CD8 T cell recognition of infected cells. In contrast, recognition of different epitopes presented by the same given MHC I allotype was uniformly reduced. For some allotypes, single evasins largely abolished T cell recognition; for others, a concerted action of evasins was required to abrogate recognition. In infected cells whose Ag presentation efficiency had been enhanced by IFN-γ pretreatment, HCMV evasins cooperatively impared T cell recognition for several different MHC I allotypes. T cell recognition and MHC I surface expression under influence of evasins were only partially congruent, underscoring the necessity to probe HCMV immunomodulation using specific T cells. We conclude that the CD8 T cell evasins of HCMV display MHC I allotype specificity, complementarity, and cooperativity.