Phenotypic and Functional Analysis of Immune CD8+ T Cell Responses Induced by a Single Injection of a HIV DNA Vaccine in Mice

Abstract

HIV DNA vaccines are potent inducers of cell-mediated immune (CMI) response in mice but elicit poor HIV-specific IFN-γ-producing T cells in monkeys and humans. In this study, we performed kinetic analyses on splenocytes of BALB/c mice that were immunized by a single injection with a unique DNA vaccine. Using IFN-γ-ELISPOT and multiparametric FACS analysis, we characterized the induced CMI response. We found that the response was detectable for at least 63 wk. ELISPOT detection of IFN-γ-producing T cells showed a profile with two waves separated by a long period of minimal response. Multiparametric FACS analysis showed two populations of CD3+CD8+ T cells that were specific for all HIV Ags. These cells had similar robust proliferation abilities and contained granzyme B. However, only a few produced IFN-γ. Both IFN-γ-producing and non-IFN-γ-producing HIV-specific CD8+ T cells were detected in the early stage (week (W)1 and W2 postimmunization (PI)), in the prolonged intermediate period of minimal response (W4-W26 PI), and in the final late phase of increased response (W30-W63 PI). Our longitudinal characterization showed that both subsets of cells underwent expansion, contraction, and memory generation/maintenance phases throughout the lifespan of the animal. Altogether, these findings bring insight to the heterogeneity of the immune T cell response induced by a single immunization with this DNA and strengthen the concept that used of the IFN-γ-ELISPOT assay alone may be insufficient to detect critical T cell responses to candidate HIV vaccines.