Characterization of Adenovirus-specific T Cell Responses in AdHu5-based Vaccine Recipients
Natalie Hutnick*1, D Carnathan1, K Cox2, S Dubey2, D Casimiro2, H Ertl3, and M Betts1
1Univ of Pennsylvania, Philadelphia, US; 2Merck Res Labs, West Point, PA, US; and 3Wistar Inst, Philadelphia, PA, US
Background: Despite the prominent role that adenovirus
(Ad) vectors play in HIV vaccine development, the human T cell response to Ad
has been largely unstudied. In the recent phase II Ad5 HIV vaccine STEP trial,
results showed participants with high Ad5 neutralizing antibody (nAb) titers
were at a higher risk of HIV infection. One hypothesis for this result is that
Ad-specific T cells present in individuals with pre-existing immunity to Ad5
were activated upon vaccination and served as optimal targets for HIV
infection. In light of this finding, we aim to characterize Ad-specific T cell
responses before and after Ad-vaccination.
Methods: Ad-specific T cell responses were studies
in 5 groups of Merck phase I subjects with a range of Ad5 doses and vaccination
schedules with group E following the same protocol as used for the STEP trial.
Vaccinee samples were obtained from weeks 0, 4, 8, 18, 26, 30, 42, 52, and 78.
Longitudinal samples were obtained from placebo-matched controls. T cell
responses to Ad were measured by stimulating peripheral blood mononuclear cells
(PBMC) overnight with whole Ad vector before measuring functionality (interferon-g
[IFN-g], tumor necrosis factor-a [TNF-a], interleukin-2 [IL-2], macrophage
inhibitory protein-1a [MIP-1a], and perforin) and memory phenotype (CD27,
CD45RO, CD57) by 14-color flow cytometry. Statistics were performed using mixed
Results: Ad-specific T cell responses were
identified in approximately 73% of all vaccinees prior to receiving Ad5
vectors, and their magnitude and presence did not correlate with Ad5 nAb
titers. In group E (3 injections of 3x1010 viral particles Ad5
gag/pol/nef) there was a significant increase in the percentage of Ad-specific
CD4+ and CD8+ cells through the course of vaccination
that was not observed consistently within the other vaccine groups. In group E,
an expansion of effector-like MIP-1a/perforin-producing CD4+ cells
was also observed following Ad5 vaccination.
Conclusions: Repeat vaccination with a high dose (3x1010)
viral particles AdHu5-based vaccine results in the expansion of Ad-specific T cells,
especially cells producing IFN-g as has
been shown in mouse models. Expansion of cytokine producing cells was largely
absent in groups given a lower dose of AdHu5. The unique expansion of
effector-like MIP-1a activity by Ad-specific CD4+ T cells may render
these cells resistant to infection by CCR5-tropic HIV.