Abstract
Pre-existing immunity to adenovirus (Ad) reduces the efficacy of Ad-based vaccines. The goal of this study was to define the prevalence, magnitude, functionality and phenotype of Ad-specific human T cells directly ex vivo. To study the magnitude of T-cell responses to Ad, we developed a highly reproducible whole Ad vector stimulation assay for use with polychromatic flow cytometry. Ad-specific CD4(+) and CD8(+) T-cells were detected in all 17 human subjects tested and were capable of proliferating upon restimulation. Ad5-specific CD4(+) T cells were primarily monofunctional CD4(+) T cells that produced IL-2, IFN-gamma or TNFalpha and expressed the memory markers CD27 and CD45RO. In contrast, Ad5-specific CD8(+) T cells were more polyfunctional, expressing effector-like combinations of IFN-gamma, MIP1alpha and perforin, and generally lacked CD27 and CD45RO expression. Ad-specific CD4(+) and CD8(+) T-cell responses against chimpanzee-derived AdC6 and AdC7 were found in all subjects, indicating the commonality of cross-serotype reactivity of Ad-specific T cells. This cross-reactivity is due in part to extensive CD4(+) and CD8(+) T-cell recognition of hexon regions conserved between multiple Ad serotypes. The prevalence, cross-reactivity and effector-like functions of Ad-specific T cells in humans may affect the efficacy of Ad vector-based vaccines by eliminating vector infected cells even when rare serotype Ad vectors are employed.