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

Abstract

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.

Clinical trials registration: NCT01095224.

Keywords: HIV-1; adenovirus; clinical trial; epitope mapping; immunogenicity; prime-boost; vaccines.

© The Author 2015. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail journals.permissions@oup.com.

Figures

Figure 1.

Vaccination with heterologous human immunodeficiency virus type 1 (HIV-1) env sequences and heterologous adenovirus vectors elicited T-cell responses in human volunteers. Cellular immune responses were quantified with an interferon γ enzyme-linked immunospot assay, using autologous peptide pools derived from the EnvA insert (A) and the EnvB insert (B). Positive responders are shown in red and negative responders in blue, with background responses (to medium alone) subtracted. Box plots show the distribution of responses among the positive responders only. The box indicates the median and interquartile range (IQR); the whiskers extend to 1.5 times the IQR from the upper or lower quartile. The response rates are indicated along the x-axis. Abbreviations: PBMC, peripheral blood mononuclear cell; SFC, spot-forming cell.

Figure 2.

Map of CD8+ T-cell epitopes elicited by vaccination. Two sets of overlapping peptides (EnvA and EnvB) were used to map the enzyme-linked immunospot assay responses of each participant to a single 15mer peptide. The frequency of responses to each peptide were computed for each treatment group and plotted according to their start position in the human immunodeficiency virus type 1 envelope protein.

Figure 3.

Epitope conservation analyses. For each participant, the epitopes underlying the observed responses were determined using 2 sets of criteria, one based on the entire overlapping region of 15mer responses and the second based on predicted HLA binding. A, An example of the 2 criteria shows the mean number of observed responses or underlying epitopes for participants in the Ad35-EnvA/Ad5-EnvB group (± standard error of the mean [SEM]). Responses were to either an EnvA (blue) or EnvB (red) 15mer peptide, whereas epitopes could additionally be attributed to overlapping EnvA and EnvB peptides (“shared”). The number of amino acid mismatches (MM) between the overlapping peptides is indicated by the color of the stacked bars. B, Comparison of epitopes determined using the HLA criteria for participants in each treatment group (± SEM). Regimens using both clades induced a greater proportion of epitopes that are shared between the 2 clades.

Figure 4.

Comparison of the number of epitopes recognized by heterologous versus homologous vector regimens and by heterologous versus homologous insert regimens. A, Heterologous vector regimens induced significantly higher numbers of total, EnvA, and EnvB epitopes than homologous vector regimens. B, Heterologous insert regimens induced significantly higher numbers of EnvB and shared epitopes than homologous insert regimens.

Figure 5.

Sequential boosting with heterologous inserts improves targeting of conserved regions of human immunodeficiency virus type 1 envelope protein. A, Entropy and coverage of vaccine-elicited epitopes. Repertoire entropy was defined to be the single most-conserved epitope for each responder, where entropy of each epitope was computed as the mean site-wise entropies, given the amino acid distributions in the Los Alamos National Laboratory (LANL)–derived set of 1569 sequences uploaded in 2012. B, Repertoire coverage for each responder is defined as the fraction of sequences in the LANL-derived set that match exactly at least 1 of their epitopes. C, Relaxed definition of repertoire coverage tolerates 1 amino acid mismatch between an epitope and a sequence for it to be considered covered. For each regimen, the box indicates the interquartile range (IQR) and the median, with whiskers extending to the lowest and highest observation within 1.5 × IQR.

Figure 6.

Prime-boost using heterologous env sequences does not augment antibody responses. Binding antibody responses were measured by an human immunodeficiency virus type 1 (HIV-1) envelope binding antibody multiplex assay using a consensus clade A envelope (A), a consensus clade B envelope (B), and the V1V2 variable region (C). Antibodies specific for the CD4 binding site were assessed by differential binding to the clade B isolate YU2 gp120 old core and the D368R mutant (D). Positive responders are shown in red and negative responders in blue (A, B, and C), with background responses (to medium alone) subtracted. Boxplots show the distribution of responses among the positive responders only. The box indicates the median and interquartile range (IQR); the whiskers extend to 1.5 times the IQR from the upper or lower quartile. The response rates are indicated along the x-axis. Abbreviation: MFI, mean fluorescence intensity.