A recombinant adenovirus serotype 5 (rAd5) vector-based vaccine for HIV-1 has recently failed in a phase 2b efficacy study in humans1, 2. Consistent with these results, preclinical studies have demonstrated that rAd5 vectors expressing SIV Gag failed to reduce peak or setpoint viral loads following SIV challenge of rhesus monkeys that lacked the protective MHC class I allele Mamu-A*013. Here we show that an improved T cell-based vaccine regimen utilizing two serologically distinct adenovirus vectors afforded substantially improved protective efficacy in this stringent challenge model. In particular, a heterologous rAd26 prime, rAd5 boost vaccine regimen expressing SIV Gag elicited cellular immune responses with augmented magnitude, breadth, and polyfunctionality as compared with the homologous rAd5 regimen. Following SIVmac251 challenge, monkeys vaccinated with the heterologous rAd26/rAd5 regimen exhibited a 1.4 log reduction of peak and a 2.4 log reduction of setpoint viral loads as well as decreased AIDS-related mortality as compared with control animals. These data demonstrate that durable partial immune control of a pathogenic SIV challenge for over 500 days can be achieved by a T cell-based vaccine in Mamu-A*01-negative rhesus monkeys in the absence of a homologous Env antigen. These findings have important implications for the development of next generation T cell-based vaccine candidates for HIV-1.
Defining the earliest virologic events following human immunodeficiency virus type 1 (HIV-1) transmission may be critical for the design of vaccine strategies aimed at blocking acquisition of HIV-1 infection. In particular, the length of the eclipse phase and the number of transmitted virus variants may define the window in which a prophylactic vaccine must act. Here we show that the dose of the virus inoculum affects these key virologic parameters following intrarectal simian immunodeficiency virus (SIV) infection of rhesus monkeys. Low-dose SIV infection resulted in a lengthened eclipse phase, fewer transmitted virus variants, and decreased innate immune activation compared with these parameters in high-dose SIV infection. These data suggest a mechanism by which it may be considerably easier for a vaccine to protect against low-risk HIV-1 transmission than against high-risk HIV-1 transmission. These findings have implications for the design and interpretation of HIV-1 vaccine efficacy studies.
The discovery of complex vascular lesions in SHIV-nef- but not SIV-infected animals, and the presence of Nef in the vascular cells of patients with HRPH, suggest that Nef plays a key role in the development of severe pulmonary arterial disease.
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