Mosaic HIV-1 vaccines expand the breadth and depth of cellular immune responses in rhesus monkeys

Abstract

The worldwide diversity of HIV-1 presents an unprecedented challenge for vaccine development. Antigens derived from natural HIV-1 sequences have elicited only a limited breadth of cellular immune responses in nonhuman primate studies and clinical trials to date. Polyvalent 'mosaic' antigens, in contrast, are designed to optimize cellular immunologic coverage of global HIV-1 sequence diversity. Here we show that mosaic HIV-1 Gag, Pol and Env antigens expressed by recombinant, replication-incompetent adenovirus serotype 26 vectors markedly augmented both the breadth and depth without compromising the magnitude of antigen-specific T lymphocyte responses as compared with consensus or natural sequence HIV-1 antigens in rhesus monkeys. Polyvalent mosaic antigens therefore represent a promising strategy to expand cellular immunologic vaccine coverage for genetically diverse pathogens such as HIV-1.

Figure 1

Breadth and magnitude of epitope-specific T lymphocyte responses to PTE peptides. (a) Numbers of epitope-specific CD4⁺ (top) and CD8⁺ (bottom) T lymphocyte responses to individual PTE peptides are shown following a single immunization of rAd26 vectors expressing mosaic (blue), M consensus (green), clade B + clade C (purple), or optimal natural clade C (red) HIV-1 Gag, Pol, and Env antigens. Individual monkeys are depicted on the x-axis. The different shades of each color reflect responses to the different antigens (Gag, Pol, Env) as indicated. (b) Numbers of CD4⁺ (top) and CD8⁺ (bottom) T lymphocyte response regions. (c) Magnitude of all Gag-, Pol-, and Env-specific CD8⁺ (left and middle panels) and CD4⁺ (right panel) T lymphocyte responses arranged from lowest to highest. Spot-forming cells (SFCs) per 10⁶ PBMCs are shown for each epitope-specific response.

Figure 2

Depth of epitope-specific T lymphocyte responses to PTE peptides. (a) Example of mapped T lymphocyte responses in monkey 366 that received the optimal natural clade C antigens. (b) Example of mapped T lymphocyte responses in monkey 361 that received the 2-valent mosaic antigens. In (a) and (b), vaccine sequences are shown on the top (OptC, Mos1, Mos2), and reactive PTE peptides are shown beneath the vaccine sequences denoted by the antigen (G, Gag; P, Pol; E, Env) and the PTE peptide number. The minimal overlap region is shown in bold. Sequence polymorphisms between the two mosaic antigens are shown in blue. Differences between the vaccine sequences and the reactive PTE peptides are shown in red. Complete alignments of all positive peptides organized by response regions are shown in Supplementary Fig. 3. (c) Depth of CD4⁺ (top) and CD8⁺ (bottom) T lymphocyte responses following immunization with rAd26 vectors expressing mosaic, M consensus, clade B + clade C, or optimal natural clade C antigens. Individual monkeys are depicted on the x-axis. One response variant (light shade) or >1 response variants (dark shade) are shown for each epitopic region.

Figure 3

Breadth of epitope-specific T lymphocyte responses to five HIV-1 Gag sequences from clades A, B, and C. Breadth of cellular immune responses was assessed utilizing subpools of overlapping peptides spanning the following strains of HIV-1 Gag: clade C DU422, clade C ZM651, consensus C, consensus A, and consensus B. Numbers of positive subpools are shown following a single immunization of rAd26 vectors expressing mosaic (blue), M consensus (green), clade B + clade C (purple), or optimal natural clade C (red) HIV-1 Gag, Pol, and Env antigens. Individual monkeys are depicted on the x-axis.

Figure 4

Cellular and humoral immune responses following the boost immunization. (a) Magnitude and (b) breadth of T lymphocyte subpool responses at week 4 post-prime (left side of each panel) and at week 44 post-boost (right side of each panel) for each monkey. Monkeys were primed at week 0 with rAd26 vectors and boosted at week 40 with rAd5HVR48 vectors expressing mosaic, M consensus, or optimal natural clade C HIV-1 Gag, Pol, and Env antigens. Individual monkeys are depicted on the x-axis. In (a), red denotes epitope-specific CD8⁺ T lymphocyte responses, blue denotes epitope-specific CD4⁺ T lymphocyte responses, lines depict responses observed at both timepoints, and dots depict responses observed at only one timepoint. In (b), the different shades of each color reflect responses to the different antigens (Gag, Pol, Env) as indicated. (c) Env-specific ELISA endpoint titers are shown at weeks 0, 4, and 44. (d) Neutralizing antibody (NAb) titers to the tier 1 clade A (DJ263.8), clade B (SF162.LS), and clade C (MW965.26) viruses are shown at week 44. NAb titers to murine leukemia virus as a negative control were <20 for all samples (data not shown).