Antigenicity and immunogenicity of transmitted/founder, consensus, and chronic envelope glycoproteins of human immunodeficiency virus type 1

Abstract

Human immunodeficiency virus type 1 (HIV-1) vaccine development requires selection of appropriate envelope (Env) immunogens. Twenty HIV-1 Env glycoproteins were examined for their ability to bind human anti-HIV-1 monoclonal antibodies (MAbs) and then used as immunogens in guinea pigs to identify promising immunogens. These included five Envs derived from chronically infected individuals, each representing one of five common clades and eight consensus Envs based on these five clades, as well as the consensus of the entire HIV-1 M group, and seven transmitted/founder (T/F) Envs from clades B and C. Sera from immunized guinea pigs were tested for neutralizing activity using 36 HIV-1 Env-pseudotyped viruses. All Envs bound to CD4 binding site, membrane-proximal, and V1/V2 MAbs with similar apparent affinities, although the T/F Envs bound with higher affinity to the MAb 17b, a CCR5 coreceptor binding site antibody. However, the various Envs differed in their ability to induce neutralizing antibodies. Consensus Envs elicited the most potent responses, but neutralized only a subset of viruses, including mostly easy-to-neutralize tier 1 and some more-difficult-to-neutralize tier 2 viruses. T/F Envs elicited fewer potent neutralizing antibodies but exhibited greater breadth than chronic or consensus Envs. Finally, chronic Envs elicited the lowest level and most limited breadth of neutralizing antibodies overall. Thus, each group of Env immunogens elicited a different antibody response profile. The complementary benefits of consensus and T/F Env immunogens raise the possibility that vaccines utilizing a combination of consensus and T/F Envs may be able to induce neutralizing responses with greater breadth and potency than single Env immunogens.

Fig 1

HIV-1 Env designs used in the study. (A) Schematic representation of HIV-1 gp160, as well as recombinant HIV-1 gp140C with a deletion of the cleavage site (C) in the junction of gp120 and gp41 by the mutation of two Arg residues to Glu residues as indicated; gp140CF with deletion of the cleavage site and the fusion domain (CF); and gp140 CFI with deletions of the cleavage site, fusion domain, and immunodominant domain (CFI). (B) Blue native PAGE analysis of HIV-1 gp140 Envs. Names of individual Env proteins are shown on the top of the lane. Arrowheads indicate the monomeric, dimeric, trimeric, and tetrameric forms of gp140.

Fig 2

Neutralization activity of guinea pig groups immunized with HIV-1 Envs. Geometric means of IC₅₀ neutralization titers (y axis) for groups of guinea pig that received the indicated HIV-1 Envs (grouped into consensus, T/F, and chronic families) were determined against a panel of subtype A, B, C, and E pseudoviruses using the traditional approach (A) or the inclusive approach (B). The same color codes were used for each subtype for both Env immunogens, as shown in the lower right portions of panels A and B. Pseudoviruses are ordered the same way in each panel, according to the key at the bottom, to facilitate comparisons between vaccine responses.

Fig 3

Heat maps reflecting HIV-1 neutralization activity of each individual guinea pigs immunized with HIV-1 gp140 Envs. The neutralizing activity of individual guinea pigs immunized with a particular HIV-1 Env is presented as a heat map, with stronger neutralizing activity indicated by color, as shown in the key at the upper left. Serum samples from individual guinea pigs are identified by a string beginning with the name of the HIV-1 Env used to immunize the animal, followed by a unique guinea pig ID number. The panel of 36 HIV-1 pseudoviruses is listed at the bottom of the heat map, arranged in order of decreasing susceptibility to neutralization. The neutralizing activity of individual guinea pig sera was analyzed using both the traditional approach (A) and the inclusive approach (B).

Fig 3

Heat maps reflecting HIV-1 neutralization activity of each individual guinea pigs immunized with HIV-1 gp140 Envs. The neutralizing activity of individual guinea pigs immunized with a particular HIV-1 Env is presented as a heat map, with stronger neutralizing activity indicated by color, as shown in the key at the upper left. Serum samples from individual guinea pigs are identified by a string beginning with the name of the HIV-1 Env used to immunize the animal, followed by a unique guinea pig ID number. The panel of 36 HIV-1 pseudoviruses is listed at the bottom of the heat map, arranged in order of decreasing susceptibility to neutralization. The neutralizing activity of individual guinea pig sera was analyzed using both the traditional approach (A) and the inclusive approach (B).

Fig 4

Comparison of breadth of antibody responses induced by HIV-1 T/F, consensus, and chronic Env immunogens. The breadth (the vertical axis shows the percentage of the panel of 36 pseudoviruses neutralized, averaged across all immunized animals) for each of the individual HIV-1 Env immunogens (x axis) using the inclusive approach (A) and the traditional approach (B). The immunogens were classed as T/F, consensus, or chronic Envs, and the P values are for comparisons between these classes.

Fig 5

Heat map reflecting breadth of antibody responses induced by HIV-1 consensus, chronic, and T/F Env immunogens. Heat map showing the fitted probability that a guinea pig in each of the individual immunization groups (rows) would have shown neutralizing activity against the panel of 36 HIV-1 pseudoviruses (columns). A higher probability of a positive response (traditional criterion) is indicated by a darker color, as detailed in the key at the upper left.

Fig 6

Heat map showing the fitted strength (predicted log₁₀ titer) of positive responses induced by HIV-1 immunogens. As in Fig. 5, rows correspond to immunogens, whereas columns are labeled by the pseudovirus strain. The key at the upper left shows both the color scale (with the strongest predicted responses corresponding to titers of 10,000, as seen for some tier 1 Envs) and the distribution of fitted values: many lie near log₁₀(20) ≈ 1.3, indicating that some responses near the threshold of the assay may be weak but positive.

Fig 7

Levels and specificities of serum antibodies of immunized guinea pigs to HIV-1 Envs. Serum samples of immunized guinea pigs grouped by immunogens of consensus (red), chronic (blue), and T/F (green) were tested in ELISA for binding to the autologous Env in serial 1:3 dilutions (1:30 to 1:5,314,410) to compare the levels of antibody responses for the different classes of immunogens. Prebleed serum was used as a negative control and had negligible binding to HIV-1 Env. Serum binding antibody titers were expressed as the EC₅₀ (reciprocal serum dilutions) on the y axis (A). The open circles in each column represent the EC₅₀ for each member of a group of animals immunized with the same immunogen; the filled circles represent the geometric mean of the group. This geometric mean score was used to represent each of the immunogens and to statistically compare the classes of vaccines. The median value of the geometric means is indicated by the horizontal bar. Vaccine classes (consensus, chronic, and T/F) were compared by using a Kruskal-Wallis omnibus test; if it was significant (P = 0.003), pairwise comparisons were then made between the vaccine classes, and consensus and chronic vaccines were shown to show higher-magnitude autologous responses than T/F vaccines. The immune sera were also tested for blocking the binding of sCD4 to HIV-1 Env JRFL gp140 (B), MAbs 1b12 to HIV-1 Env JRFL (C), PG9 to HIV-1 Env A244 (D), and 2G12 to HIV-1 Env JRFL (E) at a 1:50 serum dilution. The percentage of inhibition of the binding by guinea pig sera of each group was plotted and statistically compared in a in a manner analogous to the strategy described in panel A, except that for panels B to E, the filled circles represent the mean value for each vaccine group and not the geometric mean. Among the inhibition assays (B-E), only the inhibition of PG9 binding was statistically significant (D), and the T/F vaccines had lower levels of PG9 inhibition than either consensus or chronic.