HLA-associated immune escape pathways in HIV-1 subtype B Gag, Pol and Nef proteins

Abstract

Background: Despite the extensive genetic diversity of HIV-1, viral evolution in response to immune selective pressures follows broadly predictable mutational patterns. Sites and pathways of Human Leukocyte-Antigen (HLA)-associated polymorphisms in HIV-1 have been identified through the analysis of population-level data, but the full extent of immune escape pathways remains incompletely characterized. Here, in the largest analysis of HIV-1 subtype B sequences undertaken to date, we identify HLA-associated polymorphisms in the three HIV-1 proteins most commonly considered in cellular-based vaccine strategies. Results are organized into protein-wide escape maps illustrating the sites and pathways of HLA-driven viral evolution.

Methodology/principal findings: HLA-associated polymorphisms were identified in HIV-1 Gag, Pol and Nef in a multicenter cohort of >1500 chronically subtype-B infected, treatment-naïve individuals from established cohorts in Canada, the USA and Western Australia. At q< or =0.05, 282 codons commonly mutating under HLA-associated immune pressures were identified in these three proteins. The greatest density of associations was observed in Nef (where close to 40% of codons exhibited a significant HLA association), followed by Gag then Pol (where approximately 15-20% of codons exhibited HLA associations), confirming the extensive impact of immune selection on HIV evolution and diversity. Analysis of HIV codon covariation patterns identified over 2000 codon-codon interactions at q< or =0.05, illustrating the dense and complex networks of linked escape and secondary/compensatory mutations.

Conclusions/significance: The immune escape maps and associated data are intended to serve as a user-friendly guide to the locations of common escape mutations and covarying codons in HIV-1 subtype B, and as a resource facilitating the systematic identification and classification of immune escape mutations. These resources should facilitate research in HIV epitope discovery and host-pathogen co-evolution, and are relevant to the continued search for an effective CTL-based AIDS vaccine.

Figure 1. Gag Immune Escape Map.

Escape maps indicate the locations, specific residues and HLA restrictions of HLA-associated polymorphisms. The HIV-1 consensus B amino acid sequence is used as a reference. Alternating black and brown letters in the consensus amino acid sequence distinguish the different proteins in HIV-1 Gag (p17, p24, p2, p7, p1, p6). One hundred amino acids are displayed per line. Shaded vertical bars separate blocks of 10 amino acids. “Adapted” amino acids (those enriched in the presence of the HLA allele) are red. “Non-adapted” amino acids (those depleted in the presence of the HLA allele) are blue. UPPERCASE letters distinguish polymorphisms that survive correction for HIV codon covariation (“direct” associations), while lowercase letters distinguish polymorphisms that do not survive correction for codon covariation (“indirect” associations). Polymorphisms associated with the same HLA allele that occur in proximity to one another are grouped together in yellow boxes. Optimally-defined CTL epitopes containing HLA-associated polymorphisms are indicated above the consensus sequence. Note that the escape map does not list the locations of all published CTL epitopes. This is available at http://www.hiv.lanl.gov/content/immunology. The escape maps show all HLA-associated polymorphisms with q≤0.05. A complete listing of all HLA-associated polymorphisms with q≤0.2 is provided in Table S1.

Figure 2. Protease Immune Escape Map.

Figure 3. Reverse Transcriptase Immune Escape Map.

Figure 4. Integrase Immune Escape Map.

Figure 5. Nef Immune Escape Map.

Figure 6. HLA-B*57-associated escape and covariation pathways in HIV-1 Gag.

The 500 amino acids of consensus B Gag are drawn counterclockwise, with the N-terminus of Gag at the 3 o'clock position. All direct (covariation-corrected) and indirect (covariation uncorrected) B*57-associated polymorphisms at q≤0.2 are identified at their respective positions along the circle's circumference, while covarying amino acids (also q≤0.2) are joined together by arcs within the circle. Note that this figure is limited to “one-hop” covarying amino acids only, meaning that only the codons directly associated with variation at a B*57-associated sites are shown. (Our analyses also identify, for example, codons associated with variation at the “one-hop” sites, and so on and so forth, but for simplicity we have limited the figure to the “one-hop” sites only. The strength of the association between two covarying codons (expressed in terms of q-value) is indicated by the color of the arc. The program used to construct these figures is available at http://research.microsoft.com/en-us/um/redmond/projects/MSCompBio/PhyloDViewer/ .

Figure 7. HLA-B*27-associated escape and covariation pathways in HIV-1 Gag.