GENETIC AND BIOLOGIC CHARACTERIZATION OF HIV-1 SUBTYPE C ISOLATES FROM BRAZIL
The high level of genetic diversity of human immunodeficiency virus type 1 (HIV-1) is responsible for the emergence of viral strains with different biological properties. Such feature has been a major obstacle in the development of a globally useful vaccine for AIDS and treatment strategies. Among the genetic forms of HIV-1, the subtype C is the most prevalent, accounting for 56% of infections worldwide. This figure suggests that this subtype may present particular features in its spreading ability. The subtype C is responsible for nearly 40% of new infections in the South of Brazil, however, the characterization of non-B subtypes in the country is very limited. Thus, we aimed to investigate the genetic and biological diversity of HIV-1 subtype C strains circulating in Brazil. On this purpose, 22 blood samples from HIV-1-infected individuals from Porto Alegre were processed. Viral isolates were obtained using the co-culture method, as recommended by World Health Organization. The subtype was determined by sequencing gag and env genes. The sequences were compared with others subtypes B, C and F strains from different countries using phylogenetic methods. Phenotypic characteristics of five subtype C isolates and two C/B recombinants were investigated. To evaluate the virus ability to infect macrophages and to form syncytium in CD4+ T cell lines, these cells were exposed to HIV-1 positive supernatants. To investigate the coreceptor usage, U87 cells were exposed to infectious supernatants. Out of 22 samples, we observed six subtype C (27.3%), eight subtype B (36.4%), one subtype F (4.5%), six C/B recombinant (27.3%) and one B/F recombinant (4.5%) samples. Subtype C sequences from Brazil formed a unique phylogenetic group and presented 6 and 18 specific amino acid signatures in gag and env, respectively. Three distinct patterns of C/B recombinants were observed. All tested isolates were able to replicate in macrophages. Among 5 subtype C isolates, 4 used only CCR5 as coreceptor and were non-syncytium-inducing viruses, while the other subtype C isolate was also able to use the CXCR4 receptor and to induce syncytium. The C/B recombinants used both coreceptors and were syncytium-inducing viruses. The V3 region of subtype C sequences was 3 times more conserved than the V3 region of subtype B sequences. These findings suggest that subtype C viruses circulating in Brazil are the result of a unique and recent introduction into the country. Recombination events between subtypes B and C are occurring in elevated rates for more than 10 years in the South region of Brazil. Biological characterization confirms the hypothesis that subtype C is distinct from the others in the evolution of coreceptor utilization.
Advisor:Dumith Chequer Bou-Habib
School:Faculdades Oswaldo Cruz
Source Type:Master's Thesis
Keywords:HIV-1 subtype C genetic and biologic characterization
Date of Publication:03/30/2006