HIV-1-specific immunity in persistently seronegative individuals at high risk for HIV infection

A growing number of reports indicates that certain groups of individuals who almost certainly have been exposed to human immunodeficiency virus (HIV), yet continue to exhibit no signs or symptoms of infection, often have subtle evidence of specific immunity. We studied such a high-risk (HR) cohort of persistently seronegative individuals with histories of long-term sexual exposure to an HIV-infected partner to look for evidence of both humoral and cellular immunity that might have been induced by exposure to the virus. Twenty-three heterosexual and four homosexual monogamous couples with discordant HIV status were included in the study. Twelve of the HR partners were studied for in vitro stimulation of peripheral blood mononuclear cells (PBMC) by HIV envelope-derived peptides. All 12 responded overwhelmingly to a peptide containing the fifth conserved region of gp120. By generating and cloning T cell lines specific for this peptide, we concluded that in these individuals the T cell response to the envelope is mainly focused on the carboxy-terminus region of gp120 and is characterized by an oligoclonal expansion of CD4(+) T cells expressing the same TCR. Eighteen HR partners and 37 HIV-I seropositive subjects were tested for the presence of anti-CD4 antibodies (anti-CD4 Abs) using a recombinant CD4-based enzyme-linked immunosorbent assay (ELISA). Anti-CD4 Abs were detected in eight of the HR partners (six confirmed by Western blot) and in nine of the HIV-I seropositive subjects (eight confirmed by Western blot). Results from binding competition assays with a panel of monoclonal anti-CD4 Abs suggested that the anti-CD4 Abs detected in the HR partners are directed toward epitopes that are induced by gp120 binding. Twenty-seven of the HR partners were tested for the presence of antibodies that cross-react with HLA class I and gp120 (anti-HLA Abs). Anti-HLA Abs were detected in 16 of the HR partner sera and in 4/94 sera from a control population of normal healthy blood donors. Taken together, the results suggest that in some individuals with. history of long-term exposure to HIV, specific immunity may develop in the absence of overt infection. The common trigger for these responses is gp120.