HIV This Week

Willberg CB, McConnell JJ, Eriksson EM, Bragg LA, York VA, Liegler TJ, Hecht FM, Grant RM, Nixon DF. Immunity to HIV-1 is influenced by continued natural exposure to exogenous virus. PLoS Pathog. 2008;4(10):e1000185.

Unprotected sexual intercourse between individuals who are both infected with HIV-1 can lead to exposure to their partner’s virus, and potentially to super-infection. However, the immunological consequences of continued exposure to HIV-1 by individuals already infected, has to our knowledge never been reported. Willberg and colleagues measured T cell responses in 49 HIV-1 infected individuals who were on antiretroviral therapy with suppressed viral loads. All the individuals were in a long-term sexual partnership with another HIV-1 infected individual, who was either also on HAART and suppressing their viral loads, or viraemic (>9000 copies/ml). T cell responses to HIV-1 epitopes were measured directly ex-vivo by the Interferon-gamma enzyme linked immuno-spot assay and by cytokine flow cytometry. Sexual exposure data was generated from questionnaires given to both individuals within each partnership. Individuals who continued to have regular sexual contact with a HIV-1 infected viraemic partner had significantly higher frequencies of HIV-1-specific T cell responses, compared to individuals with aviraemic partners. Strikingly, the magnitude of the HIV-1-specific T cell response correlated strongly with the level and route of exposure. Responses consisted of both CD4(+) and CD8(+) T cell subsets. Longitudinally, decreases in exposure were mirrored by a lower T cell response. However, no evidence for systemic super-infection was found in any of the individuals. Continued sexual exposure to exogenous HIV-1 was associated with increased HIV-1-specific T cell responses, in the absence of systemic super-infection, and correlated with the level and type of exposure.

Editors’ note: When one already has HIV infection and is on antiretroviral therapy, another person’s HIV can act as a natural immune stimulus with unknown benefits or disadvantages. In this study of 49 seroconcordant couples in which one person was virally suppressed and the other either was either suppressed or viraemic, exposure to the partner’s virus appeared to boost T-cell specific responses to HIV with little effect on general immune activation. The authors speculate that this may represent limited superinfection within rectal tissues.