Human immunodeficiency virus type 1 specific cytotoxic T lymphocyte responses in Chinese infected with HIV-1 B'/C Recombinant (CRF07_BC)

Abstract

Background: The characterization of HIV-1-specific T cell responses in people infected with locally circulating HIV-1 strain will facilitate the development of HIV-1 vaccine. Sixty intravenous drug users infected with HIV-1 circulating recombinant form 07_BC (CRF07_BC), which has been spreading rapidly in western China from north to south, were recruited from Xinjiang, China to assess the HIV-1-specific T cell responses at single peptide level with overlapping peptides (OLP) covering the whole concensus clades B and C proteome.

Results: The median of the total magnitude and total number of OLPs recognized by CTL responses were 10925 SFC/million PBMC and 25 OLPs, respectively, when tested by clade C peptides, which was significantly higher than when tested by clade B peptides. The immunodominant regions, which cover 14% (58/413) of the HIV-1 proteome, are widely distributed throughout the HIV-1 proteome except in Tat, Vpu and Pol-PR, with Gag, Pol-RT, Pol-Int and Nef being most frequently targeted. The subdominant epitopes are mostly located in p24, Nef, integrase, Vpr and Vif. Of the responses directed to clade C OLPs, 61.75% (972/1574) can be observed when tested with corresponding clade B OLPs. However, Pol-PR and Vpu tend to be targeted in the clade B sequence rather than the clade C sequence, which is in line with the recombinant pattern of CRF07_BC. Stronger and broader CTL responses in subjects with CD4 cell counts ranging from 200 to 400/mm3 were observed when compared to those with less than 200/mm3 or more than 400/mm3, though there have been no significant correlations identified between the accumulative CTL responses or overall breadth and CD4 cell count or plasma viral load.

Conclusion: This is the first study conducted to comprehensively address T cell responses in Chinese subjects infected with HIV-1 CRF07_BC in which subtle differences in cross-reactivity were observed, though similar patterns of overall immune responses were demonstrated with clade B infected populations. The immunodominant regions identified in this population can facilitate future HIV-1 vaccine development in China.

Figure 1

The overall CTL responses in the study population. (A) 3-D figures depicting individual CTL responses showing similar clustering patterns targeting clade B and Clade C peptide sets. The CD4 counts of each subject are dotted in the left of the figures. (B) The average magnitudes induced by individual peptides covering the clades B and C proteome. (C) The recognition frequency of individual peptides by the study population. Inserted clade B fragments in the CRF07_BC genome are indicated as red bars adjacent to the X-axis. Significant differences were observed when comparing the average magnitude (B) and percent of responders (C) for different peptide sets.

Figure 2

The immunodominance and cross-reactivity analysis. The location of immunodominant and subdominant epitopes in the HIV-1 proteome. Five classes of recognition frequency are represented in the figure, (i) recognition frequency more than 15%, (ii) more than 10% but less than 15%, (iii) more than 5% but less than 10%, (iv) more than 0% but less than 5% and (v) not recognized in the study population. Inserted clade B fragments in the CRF07_BC genome are indicated as red bars adjacent to X-axis.

Figure 3

Area-proportional Venn diagram of cross recognition. The expressed whole genome of HIV-1 clade B or clade C were digested as 413 overlapping peptides and the two sets of peptides were tested in ELISPOT assay for each subject enrolled in this study. Cross-recognition of CTL responses to clade B and Clade C peptides were assessed by the classification of (i) both B and C peptides not recognized, (ii) both B and C peptides recognized by at least one subject, (iii) only C peptides recognized by at least one subject and (iv) only B peptides recognized by at least one subject.

Figure 4

Subjects grouped with different CD4 cell counts mounted a different magnitude and breadth of CTL responses targeting Gag. For each portion of the HIV-1 proteins (Gag, p17, p24 or p15), the total magnitude or breadth of each individual is dotted and the median values are shown as a dash. Black dots are responses targeting consensus clade B peptides and blue dots for responses targeting clade C peptides. The filled dots designate the values from the group of CD4 cell counts less than 200/μl, the circles for individuals with CD4 cell counts ranging from 200–400/μl and the triangles for CD4 cell counts more than 400/μl. The p values were obtained using One Way Analysis of Variance (ANOVA) for multiple group comparison and Dunn's method or Holm-Sidak method for pair wise multiple comparison, when appropriate for data distribution.