Specific activation of CMV-primed human T lymphocytes by cytomegalovirus pp65 expressed in fission yeast

Threatening virus infections constantly illustrate the growing need for novel vaccines that specifically induce efficient T cell-mediated immune responses. In this study, we used a human whole blood assay to determine the activation of antigen-specific human T lymphocytes by a viral antigen of human cytomegalovirus (HCMV). The major HCMV tegument protein pp65, recombinantly expressed in fission yeast (Schizosaccharomyces pombe), specifically activated antigen-specific CD4- and CD8-positive memory T cells in blood of HCMV seropositive donors. Moreover, the immune response against recombinant pp65, in particular that of CD8 class I major histocompatibility complex-restricted cytotoxic T cells, was similar to the response against the intact HCMV. Since fission yeast cells per se did not activate a significant number of human T lymphocytes ex vivo, the system described here might represent a novel approach in vaccine development as well as in the identification of vaccine candidates directly from human whole blood.