Recognition of a defined region within p24 gag by CD8+ T cells during primary human immunodeficiency virus type 1 infection in individuals expressing protective HLA class I alleles

Abstract

Human immunodeficiency virus type 1 (HIV-1)-specific immune responses during primary HIV-1 infection appear to play a critical role in determining the ultimate speed of disease progression, but little is known about the specificity of the initial HIV-1-specific CD8(+) T-cell responses in individuals expressing protective HLA class I alleles. Here we compared HIV-1-specific T-cell responses between subjects expressing the protective allele HLA-B27 or -B57 and subjects expressing nonprotective HLA alleles using a cohort of over 290 subjects identified during primary HIV-1 infection. CD8(+) T cells of individuals expressing HLA-B27 or -B57 targeted a defined region within HIV-1 p24 Gag (amino acids 240 to 272) early in infection, and responses against this region contributed over 35% to the total HIV-1-specific T-cell responses in these individuals. In contrast, this region was rarely recognized in individuals expressing HLA-B35, an HLA allele associated with rapid disease progression, or in subjects expressing neither HLA-B57/B27 nor HLA-B35 (P < 0.0001). The identification of this highly conserved region in p24 Gag targeted in primary infection specifically in individuals expressing HLA class I alleles associated with slower HIV-1 disease progression provides a rationale for vaccine design aimed at inducing responses to this region restricted by other, more common HLA class I alleles.

FIG. 1.

(A) Protein specificity of HIV-1-specific T-cell responses during primary HIV-1 infection. Forty-three subjects with primary HIV-1 infection were screened by IFN-γ ELISPOT assay using 410 overlapping peptides spanning the entire clade B consensus sequence. The percentage contributions of HIV-1-specific T cells to the total number of IFN-γ responses are shown for the different HIV-1 proteins (Gag, Nef, Pol, Env, Vpr, Vif, Rev, Tat, and Vpu). All three large structural HIV-1 proteins Gag, Env, and Pol, as well as the smaller accessory Nef protein, were targeted evenly. The contributions to the total number of immune responses against the four most targeted epitopes (Gag, Pol, Nef, and Env) did not differ significantly (P > 0.05). (B) Comparison of protein specificity of T-cell responses between subjects expressing HLA-B27/B57 or HLA-B35 and subjects expressing neither HLA-B27/B57 nor HLA-B35. The contribution to the total HIV-1-specific T-cell response is shown for the different HIV-1 proteins (Gag, Nef, Pol, Env, Vpr, Vif, Rev, Tat, and Vpu) stratified according to the three HLA groups. Significant differences (P < 0.05) are indicated with asterisks (*). (C) Comparison of protein specificity within the Gag protein of T-cell responses between subjects expressing HLA-B27/B57 or HLA-B35 and subjects expressing neither HLA-B27/B57 nor HLA-B35. The contribution to the total HIV-1-specific response is shown for the different proteins encoded within Gag: p17, p24, and p15 (p2-p7-p1-p6) and stratified according to the three HLA groups. In subjects expressing HLA-B35, no responses against p15 were detected (indicated with X). Significant differences (P < 0.05) are indicated with asterisks.

FIG. 2.

Assessment of the fine specificity of Gag-specific responses in subjects expressing HLA-B27/B57. Values show the magnitude of a response in SFCs/10⁶ cells. Each graph represents one subject. The percentages of Gag contribution to the total number of responses for every subject are as follows: AC-138, 30%; AC-154, 51%; AC-34, 19%; AC-153, 42%; AC-160, 62%; AC-162, 56%; AC-207, 41%; AC-183, 22%. Bars on the left represent the immune responses detected with overlapping peptides spanning the entire Gag clade B consensus sequence, while bars on the right represent the respective response to the optimal epitope encoded within the overlapping peptide when tested individually.

FIG. 3.

(A) Frequency of recognition of optimal HIV-1-specific CD8⁺ T-cell epitopes described for the respective HLA class I allele of subjects expressing HLA-B57. Twenty-one subjects expressing HLA-B57 were screened by optimal HLA-matched epitopes 8 weeks (±10 days) postdiagnosis. The epitope TSTLQEQIGW (TW10 [p24 Gag]) was recognized in 86% of the subjects, followed by IVLPEKDSW (IW9 [RT]) in 61.9% and KAFSPEVIPMF (KF11 [p24 Gag]) in 52.4%. (B) Frequency of recognition of optimal HIV-1-specific CD8⁺ T-cell epitopes described for the respective HLA class I allele of subjects expressing HLA-B27. Thirteen subjects expressing HLA-B27 were screened by optimal HLA-matched epitopes 8 weeks (±10 days) postdiagnosis. The epitope KRWIILGLNK (KK10 [p24 Gag]) was recognized in 92% of the subjects, while the other HLA-B27-restricted epitopes were less frequently recognized. (C) Contribution of epitope-specific HLA-B57 responses to the total HIV-1-specific CD8⁺ T-cell response. Twenty-one subjects expressing HLA-B57 were screened for responses against the optimal HIV-1-specific CD8⁺ T-cell epitopes described for their respective HLA class I alleles. The epitope TW10 (p24 Gag) contributed 31% (±33.3%) to the total HIV-1-specific CD8⁺ T-cell response, while other HLA-B57-restricted responses had a significantly lower contribution to the total HIV-1 specific CD8⁺ T-cell response calculated by using a one-way ANOVA (P < 0.001). (D) Contribution of epitope-specific HLA-B27 responses to the total HIV-1-specific CD8 T-cell response. Thirteen subjects expressing HLA-B27 were screened for responses against the optimal HIV-1-specific CD8⁺ T-cell epitopes described for their respective HLA class I alleles. The epitope KK10 (p24 Gag) contributed 39.7% (±20.5%) to the total HIV-1-specific CD8⁺ T-cell response, while other HLA-B27-restricted responses had a significantly lower contribution to the total HIV-1-specific CD8⁺ T-cell response, calculated by using a one-way ANOVA (P < 0.001).