Comparative Analysis of the Magnitude, Quality, Phenotype, and Protective Capacity of Simian Immunodeficiency Virus Gag-Specific CD8+ T Cells following Human-, Simian-, and Chimpanzee-Derived Recombinant Adenoviral Vector Immunization

Abstract

Recombinant adenoviral vectors (rAds) are the most potent recombinant vaccines for eliciting CD8+ T cell-mediated immunity in humans; however, prior exposure from natural adenoviral infection can decrease such responses. Here we show low seroreactivity in humans against simian- (sAd11, sAd16), or chimpanzee-derived (chAd3, chAd63) compared to human-derived (rAd5, rAd28, rAd35) vectors across multiple geographic regions. We then compared the magnitude, quality, phenotype and protective capacity of CD8+ T cell responses in mice vaccinated with rAds encoding SIV Gag. Using a dose range (1 × 107 to 109 PU), we defined a hierarchy among rAd vectors based on the magnitude and protective capacity of CD8+ T cell responses, from most to least as: rAd5 and chAd3, rAd28 and sAd11, chAd63, sAd16, and rAd35. Selection of rAd vector or dose could modulate the proportion and/or frequency of IFNγ+TNFα+IL-2+ and KLRG1+CD127- CD8+ T cells, but strikingly ~30–80% of memory CD8+ T cells co-expressed CD127 and KLRG1. To further optimise CD8+ T cell responses, we assessed rAds as part of prime-boost regimens. Mice primed with rAds and boosted with NYVAC generated Gag-specific responses that approached ~60% of total CD8+ T cells at peak. Alternatively, priming with DNA or rAd28 and boosting with rAd5 or chAd3 induced robust and equivalent CD8+ T cell responses compared to prime or boost alone. Collectively, these data provide the immunologic basis for using specific rAd vectors alone or as part of prime-boost regimens to induce CD8+ T cells for rapid effector function or robust long-term memory, respectively.

Epitope Specificity Delimits the Functional Capabilities of Vaccine-Induced CD8 T Cell Populations

“…Vaccinations were conducted using one-time, split-site inoculations of Ad5.Gag.Pol in a total volume of 100 ml. Low-dose vaccination comprised 10 8 PU total in 100 ml, and highdose vaccination comprised 10 10 PU total in 100 ml (33)(34)(35)(36)(37). In all cases, equal 50-ml aliquots of the vaccine were administered s.c. in each footpad.…”

Antigen expression determines adenoviral vaccine potency independent of IFN and STING signaling

“…In this study, we assessed the mechanisms that underlie the hierarchy of protective CD8 T cell immune responses induced by human-, chimpanzee-, and simian-derived rAds (9). We performed correlative analyses of Ag expression, innate immunity, CD8 T cell immunity and protection after rAd vaccination.…”

“…In a previous study, the magnitude, quality, and phenotype of CD8 T cell responses induced by rAds in C57BL/6 mice were characterized at several different doses (9). Based on these data, a dose of 1 × 10 8 particle units (PU) given subcutaneously was chosen to provide a hierarchy of potency when memory CD8 T cell responses were established, 70 days after vaccination and hereafter referred to as "at memory."…”

“…rAd serotype 5 (rAd5) is the most potent vector in preclinical and clinical studies but has high seroprevalence in human populations due to natural infection (8,9), which may limit optimal CD8 immunity. This led to the development of alternative rAds based on serotypes with low seroprevalence (2,3,7), but these vary substantially in their potency and protective capacity (7)(8)(9)(10). Of note, a chimpanzee-derived rAd, chAd3, has recently entered accelerated phase I clinical trials for Ebola virus infection, after inducing a high level of protection in a preclinical nonhuman primate model (11).…”

“…Gag-specific CD8 T cell responses were characterized in the spleen, blood, and lung using peptide-MHC I tetramer staining. Mice were then challenged with recombinant Listeria monocytogenes expressing Gag, as a CD8 T cell-dependent model of protection (9,22). rAd5 induced the most potent and protective CD8 T cell responses, followed by rAd28 and rAd35 ( Figure 2, A and B).…”