Quantitative and qualitative differences in the T cell response to HIV in uninfected Ugandans exposed or unexposed to HIV-infected partners.

HIV-exposed and yet persistently uninfected individuals have been an intriguing, repeated observation in multiple studies, but uncertainty persists on the significance and implications of this in devising protective strategies against HIV. We carried out a cross-sectional analysis of exposed uninfected partners in a Ugandan cohort of heterosexual serodiscordant couples (37.5% antiretroviral therapy naive) comparing their T cell responses to HIV peptides with those of unexposed uninfected individuals. We used an objective definition of exposure and inclusion criteria, blinded ex vivo and cultured gamma interferon (IFN-γ) enzyme-linked immunospot assays, and multiparameter flow cytometry and intracellular cytokine staining to investigate the features of the HIV-specific response in exposed versus unexposed uninfected individuals. A response rate to HIV was detectable in unexposed uninfected (5.7%, 95% confidence interval [CI] = 3.3 to 8.1%) and, at a significantly higher level (12.5%, 95% CI = 9.7 to 15.4%, P = 0.0004), in exposed uninfected individuals. The response rate to Gag was significantly higher in exposed uninfected (10/50 [20.%]) compared to unexposed uninfected (1/35 [2.9%]) individuals (P = 0.0004). The magnitude of responses was also greater in exposed uninfected individuals but not statistically significant. The average number of peptide pools recognized was significantly higher in exposed uninfected subjects than in unexposed uninfected subjects (1.21 versus 0.47; P = 0.0106). The proportion of multifunctional responses was different in the two groups, with a higher proportion of single cytokine responses, mostly IFN-γ, in unexposed uninfected individuals compared to exposed uninfected individuals. Our findings demonstrate both quantitative and qualitative differences in T cell reactivity to HIV between HESN (HIV exposed seronegative) and HUSN (HIV unexposed seronegative) subject groups but do not discriminate as to whether they represent markers of exposure or of protection against HIV infection.

Tat mutations in an African cohort that do not prevent transactivation but change its immunogenic properties.

Humoral responses against extra-cellular HIV-1 Tat may be beneficial as Tat has been implicated in the viral pathogenesis associated with HIV-1 disease progression. We determined the levels of anti-Tat IgG in sera of HIV-1 seropositive individuals from the Rural Clinical Cohort in Uganda using nine different Tat proteins representative of the major subtypes presently accounting for 97% of infections worldwide. We observed the presence of anti-Tat IgG able to react against the various subtypes tested, although none cross-reacted against all nine variants. We show that 46.25% of seropositive patients were able to recognise at least one Tat variant with 1:1000 sera dilution. We also show that the C terminus of Tat is the most variable region and an important epitope that might explain the limitation of cross-recognition of Tat antibodies regarding Tat variants. This study shows in seropositive patients that Tat can tolerate mutations without modification of its primary function but with changes in its immunogenic properties. These findings should be considered when designing Tat-based HIV-1 vaccines.

Recent HIV-1 infection in a high-risk Ugandan cohort: implications for Phase IIB test-of-concept HIV vaccine trials.

Assessment of vaccine efficacy on end points used in Phase IIB test-of-concept trials will require taking into consideration the effect of variables correlated with the end points and distribution of the variables within subgroups of the trial population. Here we report that evaluation of sexual activity in vaccinees and longitudinal collection of plasma viral load data from putative transmitters prior to transmission will contribute to the plausible assessment of efficacy against acquisition of infection. Data also suggest that efficacy on post-infection end points may depend on whether transmission pairs are matched or mismatched for HLA class I alleles.

The relationship between HIV type 1 disease progression and V3 serotype in a rural Ugandan cohort.

Antigenic properties of the V3 region are reflected by HIV-1 serotypes. These may represent biological properties of the virus. We serotyped HIV-1 in 142 serum samples from participants in a rural Uganda cohort who seroconverted between August 1991 and December 2001. Clinical progression was assessed using Cox proportional hazards and Kaplan-Meier methods. Of 112 (79%) samples successfully serotyped, 36% were serotype A, 17% serotype B, 18% serotype C, and 29% serotype D. Median follow-up time, age at enrollment, and first CD4 count were similar in each serotype group. Clinical progression was faster for serotype D than other serotypes to AIDS or death, death, and CD4 count <200 cells/mm(3) (all p < 0.05). HIV-1 V3 serotypes are associated with variations in the pathogenicity of HIV-1 and should be taken into account when studying the biological relevance of HIV-1 diversity.