Objective: To design the appropriate primers of gag gene for HIV-1 subtyping in molecular epidemiology survey based on the genetic characteristics derived from the main HIV-1 strains prevailing in China.
Methods: The gag genes of HIV-1 CRF07_BC, CRF08_BC, and subtype C, together with subtyping reference sequences, were obtained from HIV sequence database. Referring to the alignments and genetic characteristics of HIV-1 full gag sequences, new primers of gag gene for amplification and subtyping were designed. The target fragment was used to construct neighbor-joining phylogenetic tree and evaluate its reliability. The newly designed primers (GUX/GDX) were used to amplify the plasma samples to evaluate their efficiency.
Results: The phylogenetic tree of 306/c-gag fragments (positions 836-1507 of HIV-1 strain HXB2) showed that CRF07_BC and subtype C strains formed clusters with low bootstrap values (59% for CRF07_BC and 70% for subtype C), and the phylogenetic tree could not distinguish the sequences of CRF07_BC, CRF08_BC, and subtype C very well. Whereas the sequences of CRF07_BC, CRF08_BC, and subtype C from GUX/GDX (positions 781-1861) were clustered separately with higher bootstrap values (99%, 99%, and 77% respectively). In practice, a very good amplification and sequencing efficiency with over 90% positive results on average were obtained with GUX/GDX. Five clusters of subtype B, C, CRF01_AE, CRF07_BC, and CRF08_BC were formed with higher confidence (Bootstrap values all above 80%). The reliable phylogenetic tree could be constructed based on the fragments sequenced only with antisense primer (GDX).
Conclusion: Fragments obtained with GUX/GDX primers of gag gene can be used to reconstruct phylogenetic tree with high reliability to distinguish the HIV-1 strains circulating in China, especially for the major BC recombinant and subtype C strains, which provides a useful tool in HIV molecular epidemiologic research.