Flow-cytometric evaluation of T cell responses elicited by an alphavirus replicon particle vaccine for cytomegalovirus (CMV) in healthy adults (132.14)

Abstract

Abstract We recently completed a Phase I evaluation of a bivalent, virus-like replicon particle (VRP) vaccine (AVX601) expressing three CMV proteins in CMV seronegative adults. One VRP component expressed the pp65 and IE1 genes as a polyprotein and the second expressed gB. AVX601 was well-tolerated, with no significant safety issues identified. Analysis of the immune responses by IFN-γ ELISPOT and CMV neutralization showed the vaccine to be highly immunogenic. In this study, multiparameter flow cytometry was used to further characterize the AVX601-induced T cell responses. Overall, the CD8 T cell responses to all 3 antigens were of higher magnitude than the CD4 T cell responses. The highest levels of CD8 and CD4 antigen-specific responses detected were 0.97% and 0.17% for pp65, 0.12% and 0.10% for IE1, and 0.18% and 0.08% for gB. Antigen-specific T cells were analyzed for their ability to produce IFNγ, TNFα and/or IL-2 after CMV peptide stimulation. Polyfunctional subsets of both CD4 and CD8 lineages specific for all 3 antigens were detected at all time points tested. The maximum % of CD8 T cells positive for 2 or 3 cytokines at any time point studied was 0.58% for pp65, 0.03% for IE1 and 0.07% for gB, and for CD4 T cells was 0.12% for pp65, 0.06% for IE1 and 0.05% for gB. These data demonstrate that this novel alphavirus replicon particle vaccine for CMV elicited polyfunctional CD4 and CD8 T cells to all 3 CMV immunogens.