We have established 3 CD8+ cytotoxic T lymphocyte (CTL) clones from the peripheral blood mononuclear cells of two HIV-1-seropositive asymptomatic donors. The epitopes recognized by these CTL clones were defined using synthetic peptides. The epitopes were located on HIV-1gag protein between amino acid (a.a.) 145 and 155 (QAISPRTLNAW), a.a.193 and 201 (GHQAAMQML), and a.a.260 and 267 (EIYKRWII), and were presented by HLA-A25, HLA-B38 and HLA-B8, respectively. The former 2 epitopes have not been previously defined. The HLA-A25-restricted epitope overlapped with HLA-B57-restricted and HLA-Cw3-restricted epitopes previously reported. In addition, this epitope overlapped with an HLA-DQ-restricted epitope recognized by CD4+ CTL. The HLA-B38-restricted epitope overlapped with HLA-A2-restricted and HLA-Bw52-restricted epitopes that were previously reported. The HLA-B38-restricted epitope between a.a.193 and 201 was highly conserved among HIV-1 strains. The results demonstrate that two new epitopes were defined in a region of gag protein that includes multiple epitopes presented by multiple HLA.

We analyzed the CD4+ T-lymphocyte response of a donor who had received an experimental live-attenuated dengue 4 virus (D4V) vaccine. Bulk culture proliferative responses of peripheral blood mononuclear cells (PBMC) to noninfectious dengue virus (DV) antigens showed the highest proliferation to D4V antigen, with lesser, cross-reactive proliferation to D2V antigen. We established CD4+ cytotoxic T-lymphocyte clones (CTL) by stimulation with D4 antigen. Using recombinant baculovirus antigens, we identified seven CTL clones that recognized D4V capsid protein. Six of these CTL clones were cross-reactive between D2 and D4, and one clone was specific for D4. Using synthetic peptides, we found that the D4V-specific CTL clone recognized an epitope between amino acids (aa) 47 and 55 of the capsid protein, while the cross-reactive CTL clones each recognized epitopes in a separate location, between aa 83 and 92, which is conserved between D2V and D4V. This region of the capsid protein induced a variety of CD4+ T-cell responses, as indicated by the fact that six clones which recognized a peptide spanning this region showed heterogeneity in their recognition of truncations of this same peptide. The bulk culture response of the donor's PBMC to the epitope peptide spanning aa 84 to 92 was also examined. Peptides containing this epitope induced proliferation of the donor's PBMC in bulk culture, but peptides not containing the entire epitope did not induce proliferation. Also, PBMC stimulated in bulk culture with noninfectious D4V antigen lysed autologous target cells pulsed with peptides containing aa 84 to 92. These results indicate that this donor exhibits memory CD4+ T-cell responses directed against the DV capsid protein and suggest that the response to the capsid protein is dominant not only in vitro at the clonal level but in bulk culture responses as well. Since previous studies have indicated that the CTL responses to DV infection seem to be directed mainly against the envelope (E) and NS3 proteins, these results are the first to indicate that the DV capsid protein is also a target of the antiviral T-cell response.