HIV-1 Genetic Diversity Among Incident Infections in Mbeya, Tanzania.

In preparation for vaccine trials, HIV-1 genetic diversity was surveyed between 2002 and 2006 through the Cohort Development study in the form of a retrospective and prospective observational study in and around the town of Mbeya in Tanzania's Southwest Highlands. This study describes the molecular epidemiology of HIV-1 strains obtained from 97 out of 106 incident HIV-1 infections identified in three subpopulations of participants (one rural, two urban) from the Mbeya area. Near full-genome or half-genome sequencing showed a subtype distribution of 40% C, 17% A1, 1% D, and 42% inter-subtype recombinants. Compared to viral subtyping results previously obtained from the retrospective phase of this study, the overall proportion of incident viral strains did not change greatly during the study course, suggesting maturity of the epidemic. A comparison to a current Phase I-II vaccine being tested in Africa shows ∼17% amino acid sequence difference between the gp120 of the vaccine and subtype C incident strains. Phylogenetic and recombinant breakpoint analysis of the incident strains revealed the emergence of CRF41_CD and many unique recombinants, as well as the presence of six local transmission networks most of which were confined to the rural subpopulation. In the context of vaccine cohort selection, these results suggest distinct infection transmission dynamics within these three geographically close subpopulations. The diversity and genetic sequences of the HIV-1 strains obtained during this study will greatly contribute to the planning, immunogen selection, and analysis of vaccine-induced immune responses observed during HIV-1 vaccine trials in Tanzania and neighboring countries.

Genetic impact of vaccination on breakthrough HIV-1 sequences from the STEP trial.

We analyzed HIV-1 genome sequences from 68 newly infected volunteers in the STEP HIV-1 vaccine trial. To determine whether the vaccine exerted selective T cell pressure on breakthrough viruses, we identified potential T cell epitopes in the founder sequences and compared them to epitopes in the vaccine. We found greater distances to the vaccine sequence for sequences from vaccine recipients than from placebo recipients. The most significant signature site distinguishing vaccine from placebo recipients was Gag amino acid 84, a site encompassed by several epitopes contained in the vaccine and restricted by human leukocyte antigen (HLA) alleles common in the study cohort. Moreover, the extended divergence was confined to the vaccine components of the virus (HIV-1 Gag, Pol and Nef) and not found in other HIV-1 proteins. These results represent what is to our knowledge the first evidence of selective pressure from vaccine-induced T cell responses on HIV-1 infection in humans.

Evaluation of HIV type 1 strains in men having sex with men and in female sex workers in Mombasa, Kenya.

We compared HIV-1 strains in incident and prevalent infections in a cohort of men having sex with men (MSM) and female sex workers (FSW) near Mombasa, Kenya and conducted a cross-sectional study of viral isolates from a sample of HIV-1-infected MSM and FSW in Kilifi, Coast Province, Kenya. RNA extracted from plasma of 13 MSM, 9 FSW, and one heterosexual male was amplified by nested RT-PCR and the products were directly sequenced. HIV-1 strains from 21 individuals were characterized with one or more complete genome sequences, and two were sequenced in the Nef gene. The envelope quasispecies was also studied in one individual. Among MSM, eight strains were subtype A and five were recombinant. There were two epidemiologically linked pairs of sequences; one pair was subtype A and the other pair was a complex AA2CD recombinant of identical structure. Another MSM was dually infected with DG recombinant strains of related, but nonidentical, structure. MSM also harbored AC and AD recombinant strains. The FSW harbored seven subtype A strains, an AD recombinant, and an AA2D strain related to CRF16_A2D. The one heterosexual male studied had a subtype A infection. This MSM epidemic in Kenya appears to be of local origin, harboring many strains typical of the broader Kenyan epidemic. Characteristics of a close social network were identified, with extended chains of transmission, novel recombinant strains possibly generated within the network, and a relatively high proportion of recombinant and dual infections.