Comprehensive analysis of west nile virus-specific T cell responses in humans

Background. Cellular responses have been shown to play a role in immune control and clearance of West Nile virus (WNV) in murine models. However, little is known about the immunogenic regions of the virus or the phenotype of responding T cells in human infection. Methods. Frozen peripheral blood mononuclear cells (PBMCs) from 35 WNV-infected blood donors were screened for virus-specific T cell responses by an interferon-gamma(IFN-gamma) enzyme-linked immunosorbent spot assay that used 452 overlapping peptides spanning all WNV proteins. More-detailed phenotypic studies were performed on subjects with high-magnitude T cell responses. Results. In individuals with identified responses, the total number of recognized WNV peptides ranged from 1 to 9 (median, 2 peptides), and the overall magnitude of responses ranged from 50 to 4210 spot-forming cells (SFCs) per 106 PBMCs (median, 130 SFCs/106 PBMCs). A subset of 8 frequently recognized peptides from the regions of the genome encoding membrane, envelope, and nonstructural 3 and 4b proteins was identified. Phenotypic study of the highest magnitude WNV-specific T cell responses revealed that most were mediated by CD8(+) cells that expressed perforin and/or granzyme B. Conclusions. These findings are the first to define the breadth and characteristics of the human T cell response to WNV and have implications for candidate vaccine design and evaluation.