Antigen-driven C-C chemokine-mediated HIV-1 suppression by CD4(+) T cells from exposed uninfected individuals expressing the wild-type CCR-5 allele

Abstract

Despite repeated exposure to HIV-1, certain individuals remain persistently uninfected. Such exposed uninfected (EU) people show evidence of HIV-1-specific T cell immunity and, in rare cases, selective resistance to infection by macrophage-tropic strains of HIV-1. The latter has been associated with a 32-base pair deletion in the C-C chemokine receptor gene CCR-5, the major coreceptor of macrophage-tropic strains of HIV-1. We have undertaken an analysis of the HIV-specific T cell responses in 12 EU individuals who were either homozygous for the wild-type CCR-5 allele or heterozygous for the deletion allele (CCR-5Delta32). We have found evidence of an oligoclonal T cell response mediated by helper T cells specific for a conserved region of the HIV-1 envelope. These cells produce very high levels of C-C chemokines when stimulated by the specific antigen and suppress selectively the replication of macrophage-tropic, but not T cell-tropic, strains of HIV-1. These chemokine-producing helper cells may be part of a protective immune response that could be potentially exploited for vaccine development.

Figure 1

(a) Reactivity of EU T cells to different HIV-1 gp120 peptides. PBMC from exposed uninfected (EU) partners (closed symbols) and control unexposed uninfected (UU) individuals (open symbols) were cultured in RPMI medium supplemented with 5% human serum in the presence of 30 μg/ml of peptide. On day 7, cells were washed and then incubated for a further 5 d in fresh medium containing rIL-2 (20 U/ml). On day 12, 3 × 10⁴ T cells were cultivated together with 10⁵ autologous irradiated PBMC in the presence of the specific peptide and the proliferative responses measured after 3 d by [³H]thymidine incorporation. The data are expressed as stimulation index (S.I.). An individual was considered positive when the S.I. was >2. The peptides used were derived from the following HIV-1IIIb sequence: peptide C1, HEDIISLWDQSLKPCVKLT; peptide V3, RIHIGPGRAFYTTKN; peptide C4, KQFINMWQEWGKAMYA; peptide C5, SELYKYKVVKIEPLGVAPTKAKRR. The sequence of the control peptide was TPSLLEQEVKPSTELEYLGPDEND. (b) Frequency of gp120–C5 specific T cells in EU partners. (Left) A representative experiment with PBMC from one EU and one control UU individual. (Right) Individual frequencies of C5-specific T cells from EU and UU PBMC.

Figure 2

(a) Antigen driven release of C–C chemokines by EU clones. Peptide C5-specific clones from exposed uninfected (EU) partners (10⁶ cells/ml) were cultivated with autologous B-LCL cells (5 × 10⁵/ml) in the presence of 30 μg/ml of the C5 peptide (closed bars), PHA (dashed bars), or an unrelated control peptide (open bars). Supernatants were collected after 48 h and tested for the presence of RANTES, MIP-1α, and MIP-1β using commercially available ELISA (R&D Systems). Clones from unexposed uninfected individuals (UU) were stimulated under the same conditions in the presence of PHA or control peptide only. (b) EU clones suppress HIV-1 NSI primary isolates. Supernatants of EU clones collected after 48-h stimulation with PHA in the presence of autologous B-LCL cells were added to cultures of PBMC from UU subjects that had been inoculated with two HIV-1 NSI primary isolates, HIV-1₄₀ (open bars), HIV-1₄₃ (closed bars). Results are expressed as percent suppression of p24 Ag production. (c) Anti-C–C chemokine antibodies abrogate the suppressive activity of EU clones. Growth of a NSI primary isolate (HIV-1₄₃) on control PBMCs in the presence of supernatant from clone EU23.9, which was pretreated with a mixture of α-RANTES, α-MIP-1α, and α-MIP-1β antibodies or control goat IgG.