Vaccination with Heterologous HIV-1 Envelope Sequences and Heterologous Adenovirus Vectors Increases T-Cell Responses to Conserved Regions: HVTN 083

Background. Increasing the breadth of human immunodeficiency virus type 1 (HIV-1) vaccine-elicited immune responses or targeting conserved regions may improve coverage of circulating strains. HIV Vaccine Trials Network 083 tested whether cellular immune responses with these features are induced by prime-boost strategies, using heterologous vectors, heterologous inserts, or a combination of both. Methods. A total of 180 participants were randomly assigned to receive combinations of adenovirus vectors (Ad5 or Ad35) and HIV-1 envelope (Env) gene inserts (clade A or B) in a prime-boost regimen. Results. T-cell responses to heterologous and homologous insert regimens targeted a similar number of epitopes (ratio of means, 1.0; 95% confidence interval [CI],. 6-1.6; P =. 91), but heterologous insert regimens induced significantly more epitopes that were shared between EnvA and EnvB than homologous insert regimens (ratio of means, 2.7; 95% CI, 1.2-5.7; P =. 01). Participants in the heterologous versus homologous insert groups had T-cell responses that targeted epitopes with greater evolutionary conservation (mean entropy [±SD], 0.32 ± 0.1 bits; P =. 003), and epitopes recognized by responders provided higher coverage (49%; P =. 035). Heterologous vector regimens had higher numbers of total, EnvA, and EnvB epitopes than homologous vector regimens (P =. 02,. 044, and. 045, respectively). Conclusions. These data demonstrate that vaccination with heterologous insert prime boosting increased T-cell responses to shared epitopes, while heterologous vector prime boosting increased the number of T-cell epitopes recognized.