Vaccine-induced IgG antibodies to V1V2 regions of multiple HIV-1 subtypes correlate with decreased risk of HIV-1 infection

Abstract

In the RV144 HIV-1 vaccine efficacy trial, IgG antibody (Ab) binding levels to variable regions 1 and 2 (V1V2) of the HIV-1 envelope glycoprotein gp120 were an inverse correlate of risk of HIV-1 infection. To determine if V1V2-specific Abs cross-react with V1V2 from different HIV-1 subtypes, if the nature of the V1V2 antigen used to asses cross-reactivity influenced infection risk, and to identify immune assays for upcoming HIV-1 vaccine efficacy trials, new V1V2-scaffold antigens were designed and tested. Protein scaffold antigens carrying the V1V2 regions from HIV-1 subtypes A, B, C, D or CRF01_AE were assayed in pilot studies, and six were selected to assess cross-reactive Abs in the plasma from the original RV144 case-control cohort (41 infected vaccinees, 205 frequency-matched uninfected vaccinees, and 40 placebo recipients) using ELISA and a binding Ab multiplex assay. IgG levels to these antigens were assessed as correlates of risk in vaccine recipients using weighted logistic regression models. Levels of Abs reactive with subtype A, B, C and CRF01_AE V1V2-scaffold antigens were all significant inverse correlates of risk (p-values of 0.0008-0.05; estimated odds ratios of 0.53-0.68 per 1 standard deviation increase). Thus, levels of vaccine-induced IgG Abs recognizing V1V2 regions from multiple HIV-1 subtypes, and presented on different scaffolds, constitute inverse correlates of risk for HIV-1 infection in the RV144 vaccine trial. The V1V2 antigens provide a link between RV144 and upcoming HIV-1 vaccine trials, and identify reagents and methods for evaluating V1V2 Abs as possible correlates of protection against HIV-1 infection.

Trial registration: ClinicalTrials.gov NCT00223080.

Figure 1. Diagrams of the V1V2-scaffold antigens used to study V1V2 antibodies in RV144 plasma specimens.

(A) tags-V1V2 scaffold antigen ; (B) gp70-V1V2 scaffold antigen ; (C) JO8-V1V2 scaffold antigen. , .

Figure 2. Reactivity in ELISA of the 19 V1V2-scaffold antigens used in the Phase 1 study.

Results are shown as box plots of reactivity with each of the 19 Phase 1 V1V2-scaffold antigens and two negative controls (“No Antigen” and “gp70_WT”) with 40 plasma samples from pilot sample set C. Results shown are the baseline-adjusted (i.e., Week 26 minus Week 0) areas under the dilution curves (AUC).

Figure 3. Heat map and hierarchical clustering tree of Spearman rank correlations of pairs of 19 V1V2-scaffold antigens.

The heat map and clustering tree are based on ELISA results derived from Phase 1 studies with specimens from 32 vaccine recipients from pilot sample set C using the baseline adjusted (i.e., Week 26 minus Week 0) area under the dilution curve read-out.

Figure 4. Reactivity in ELISA of the 13 V1V2-scaffold antigens used in the Phase 2 study.

Results are shown as box plots of reactivity with each of the 13 Phase 2 V1V2-scaffold antigens and the scaffold control antigen (gp70_WT) with 60 plasma samples from set V2L. Results shown are Week 26 read-outs at a 1∶100 dilution with the exception of tags.A(Q23)-V1V2 and tags.C(1086)-V1V2 which were run at a 1∶300, dilution and gp70.AE(92TH023)-V1V2 which was run at 1∶900. AP, LL and GN denote production of comparable reagents by Drs. Pinter, Liao, and Nabel.

Figure 5. Heat map and hierarchical clustering tree of Spearman rank correlations of pairs of 13 V1V2-scaffold antigens.

The heat map and hierarchical clustering tree are derived from ELISA data from all pairs of the 13 Phase 2 V1V2-scaffold antigens, and are based on read-outs from the 40 vaccine recipients from pilot sample set V2L. The solid black line to the left cuts the clustering tree into four clusters. The four boxes, labeled 1–4, highlight the pairwise correlations of each of these clusters. AP, LL and GN denote production of comparable reagents by Drs. Pinter, Liao and Nabel.

Figure 6. Reactivity in ELISA of V1V2-scaffold antigens with plasma from Week 26 case-control specimens.

Results are shown as box plots of reactivity with each of the six V1V2-scaffold antigens with plasma from the 286 case-control specimens. Values are from ELISA-generated data with optical density (OD) read-outs based on a wavelength of 405 nM. Data were generated using plasma diluted 1∶100, except for assay of gp70.AE(92TH023)-V1V2 (1∶900) and tags.C(1086)-V1V2 (1∶300). Box plots show the 25^th percentile (lower edge of the box), 50^th percentile (horizontal line in the box), and 75^th percentile (upper edge of the box). Participants are stratified according to HIV-1 infection status and treatment assignment. Gender and immune response categories are indicated by the color and shape of the points. Low, Medium, and High are defined as tertiles of the Week 26 immune response for the vaccine group, and are divided by the gray shaded horizontal bands. AP and LL denote production of comparable reagents by Drs. Pinter and Liao.

Figure 7. Reactivity in BAMA of V1V2-scaffold antigens with plasma from Week 26 case-control specimens.

Results are shown as box plots of reactivity of each of the six V1V2-scaffold antigens with plasma from the 286 case-control specimens. All data were generated using plasma diluted 1∶100. The y-axis shows the natural log-transformation of the median fluorescence intensity (MFI).

Figure 8. Estimated cumulative incidences of HIV-1 infection in placebo and vaccine recipients.

The probability of acquiring HIV infection in vaccine recipients is shown for vaccine recipients with Low, Medium and High V1V2-scaffold IgG Ab responses as measured (A) by ELISA and (B) by BAMA at Week 26. The x-axis shows months since the Week 26 visit (two weeks post last immunization) and the y-axis shows the estimated probability of acquiring HIV-1 infection.

Figure 9. Estimated vaccine efficacy (VE).

Estimated VE is shown for vaccine recipients with Low, Medium and High V1V2-scaffold IgG Ab responses at Week 26 versus the placebo group as defined by (A) ELISA data, and (B) BAMA data. VE is estimated as one minus the odds of infection in vaccine recipients with Low/Medium/High responses divided by the odds of infection in the entire HIV-1 negative placebo group at week 24. Points show the estimated VE values, and vertical lines delineate 95% confidence intervals. Two-sided p-values are from Wald tests.