Cytotoxic T cells from human immunodeficiency virus type 2-infected patients frequently cross-react with different human immunodeficiency virus type 1 clades

Abstract

Knowledge of immune mechanisms responsible for the cross-protection between highly divergent viruses such as human immunodeficiency virus type 1 (HIV-1) and HIV-2 may contribute to an understanding of whether virus variability may be overcome in the design of vaccine candidates which are broadly protective across the HIV subtypes. We demonstrate that despite the significant difference in virus amino acid sequence, the majority of HIV-2-infected individuals with different HLA molecules possess a dominant cytotoxic T-cell response which is able to recognize HIV-1 Gag protein. Furthermore, HLA-B5801-positive subjects show broad cross-recognition of HIV-1 subtypes since they mounted a T-cell response that tolerated extensive amino acid substitutions within HLA-B5801-restricted HIV-1 and HIV-2 epitopes. These results suggests that HLA-B5801-positive HIV-2-infected individuals have an enhanced ability to react with HIV-1 that could play a role in cross-protection.

FIG. 1

Recognition of HIV-2 Gag protein by CTL lines of patient 6 (A) Effector cells were tested against autologous target cells at an E/T ratio of 20:1. Before ⁵¹Cr labeling, targets were infected with rVV (VW, wild-type vaccinia virus; Vgag HIV-2, rVV carrying the HIV-2 gag open reading frame; V pol HIV-2, rVV carrying the HIV-2 pol open reading frame. (B) HIV-2 Gag-specific CTL lines were tested against autologous or allogenic target cells infected with wild-type and HIV-2 Gag vaccinia virus. Specific lysis was calculated by subtracting lysis of target cells infected with wild-type vaccinia virus from lysis of those infected with HIV-2 Gag vaccinia virus. Shared HLA alleles are indicated. The complete HLA class I profile of patient 6 is A0201 A3 B5801 B35 C4 C0302. The E/T ratio was 40:1.

FIG. 2

Cross-recognition of HIV-2 and HIV-1 Gag protein by HIV-2 Gag-specific CTL lines. Effector cells were tested against autologous target cells infected with rVV expressing the Gag proteins of HIV-2 and HIV-1 clades A1, A2, B, and C (see the legend to Fig. 1). (A) Patients with broad cross-reactivity; (B and C) patients with limited (B) and no (C) cross-reactivity. HLA class I profiles of the different subjects are shown at the top of each panel. The E/T ratio varied according to the number of cells that grew from each culture but was usually between 20:1 and 50:1. Recognition of different HIV-1 clades was regarded as positive if lysis of different HIV-1 Gag rVV was more than 10% above the level of control vaccinia virus.

FIG. 3

CTL lines show a stable pattern of HIV-1 Gag cross-recognition. CTL lines were produced from PBMC isolated on the date indicated. Effector CTL were tested against autologous target cells infected with the indicated rVV. The E/T ratio is indicated and varied according to the number of cells that grew from each culture.

FIG. 4

Sequences of the 18-mer synthetic peptides covering the whole HIV-2_ROD Gag protein. The mixtures of peptides used for sensitization of target cells in the fine specificity assays are indicated.

FIG. 5

Fine specificity of the Gag-specific CTL response. CTL lines of P1 (a and b), P2 (c and d), and P11 (e and f) were tested against autologous target cells pulsed with peptide mixtures (a, c, and e) or individual peptides selected from the responding mixtures (b, d, and f). The concentration of the peptides used for sensitized target cells was always 1 μM; the E/T ratio was 10:1.

FIG. 6

Different patterns of cross-reactivity expressed by CTL lines recognizing HIV-2 Gag sequences 181–192 and 241–252 and comparison of amino acid sequences of HIV-2_ROD and HIV-1 clade A1, A2, B, and C Gag expressed by different rVV in these two regions. Amino acids which differ from the HIV-2 index sequence are indicated within the boxes. The amino acid sequence of the HIV-1 B57-B58-restricted Gag epitope 240–249 is also shown.

FIG. 7

HLA-restricted recognition of HIV-2 Gag peptide 235–252. HIV-2 Gag peptide 235–252-specific CTL lines of P1 and P2 were tested against autologous target cells, target cells matched only at HLA-B5801, or unmatched target cells pulsed or unpulsed with the peptide at a concentration of 1 μM. The E/T ratio was 10:1. Lysis of the different targets is indicated.

FIG. 8

Recognition of B57-B58-restricted HIV-1 Gag epitope 240–249 by CTL lines specific for HIV-2 Gag peptide 235–252. Lysis of target cells incubated with the HIV-1 and HIV-2 peptides (1 μM) is indicated. The E/T ratio was 10:1.

FIG. 9

HIV-1-specific CTL induction by HIV-1 peptide 240–249. PBMC of patient 2 (HLA-B5801 positive) were stimulated either with HIV-1 Gag peptide 240–249 or HIV-2 Gag peptide 235–252 for 7 days and then tested against HLA-B5801-positive target cells infected with rVV expressing unrelated, HIV-2, and HIV-1 A2 Gag proteins as described in Materials and Methods.