Antigen-specific T cell responses induced by Towne cytomegalovirus (CMV) vaccine in CMV-seronegative vaccine recipients

Abstract Background Towne cytomegalovirus (CMV) vaccine is safe and immunogenic, though its protective efficacy has yet to be optimized. Objective Describe antigen-specific T cell responses to Towne vaccination. Study design 3000 pfu Towne CMV vaccine were given to 12 CMV-seronegative volunteers. CMV-specific CD4+ and CD8+ T cell proliferation and IFNγ expression were measured by flow cytometry after stimulation with CMV lysate or peptides. Results All vaccinees developed CD4+ and CD8+ T cell proliferation and CD4+ T cell IFNγ responses to multiple CMV antigens, but their CD8+ T cells had low or undetectable IFNγ responses to pp65 peptide pool. The seven HLA-A2+ subjects had higher CD8+ T cell proliferation and IFNγ responses to IE than pp65, and two never developed CD8+ T cell IFNγ responses to pp65. Peak CD4+ T cell IFNγ responses to CMV lysate were lower than values observed in natural CMV seropositives. Initial CD4+ and CD8+ T cell responses to lysate and pp65 waned after 12 months to levels that were lower than those in healthy CMV seropositives, while vaccinees’ CD8+ T cell responses to IE were robust and prolonged. Conclusion Correlating CMV antigen-specific T cell responses with clinical protective efficacy may facilitate future CMV vaccine development.