Chimeric simian–human immunodeficiency viruses (SHIVs) that contain the HIV-1 tat, rev, vpu, and env genes inserted into the proviral genome of the pathogenic SIVmac239 clone have been constructed to test the functions of HIV-1 gene products and constitute a valuable model system in the assessment of candidate vaccines directed against the HIV-1 envelope glycoproteins in macaque models (4, 6, 10). However, SHIV constructs require in vivo adaptation and serial in vivo passage to acquire the ability of depleting CD4+ T cells and inducing simian AIDS. Balfe(2004) found that the animals which later received passage virus had more diverse quasispecies, which supported the model of quasispecies diversity as a predictor of pathogenesis (1).
SHIV-CN97001 was constructed by replacing the gp120 and partial gp41 region of SHIV-KB9 which was used as backbone with corresponding region of HIV-1 B'/C recombinant virus strain HIV-CN97001, the predominant prevalent strain in China. SHIVCN97001 was rapidly and serially passaged five times in Chinese origin rhesus macaques. It was found that the virus replication ability reached the peak in the third passage, then declined. At the same time, no obvious CD4+ lymphocytes decline was detected in all infected animals, indicating that there was no pathogenic virus strain during passage. In this study, we tried to explore the molecular basis why the biological phenotype such as virulence did not change during passage.
Sequence Variation in the Gp120 region of SHIV-CN97001 during in vivo Passage
- Received Date: 23 July 2007
- Accepted Date: 10 November 2007
Abstract: SHIV-CN97001 played an important role in assessing the immune effect and strategy of the AIDS vaccine which included genes of the predominant prevalent HIV-1 strain in China. In this study, SHIV-CN97001 was in vivo passaged serially to construct pathogenic SHIV-CN97001/rhesus macaques model. To identify variation in the gp120 region of SHIV-CN97001 during passage, the fragments of gp120 gene were amplified by RT-PCR from the plasma of SHIV-CN97001 infected animals at the peak viral load time point and the gene distances (divergence, diversity) were calculated using DISTANCE. The analysis revealed that the genetic distances of SHIV-CN97001 in the third passage animals were the highest during in vivo passage. It had a relationship between viral divergence from the founder strain and viral replication ability. The nucleic acid sequence of the V3 region was highly conservative. All of the SHIV-CN97001 strains had V3 loop central motif (GPGQ) and were predicted to be using CCR5 co-receptor on the basis of the critical amino acids within V3 loop. These results show that there was no significant increase in the genetic distance during serial passage, and SHIV-CN97001 gp120 gene evolved toward ancestral states upon transmission to a new host. This could partly explain why there was no pathogenic viral strain obtained during in vivo passage