Frequent Detection of HIV-1 Variants With Mixed Coreceptor Usage Among People Who Inject Drugs Infected With CRF01_AE: Possible Association With Coreceptor Switch.

Background: Our previous study suggested that mixed infection with R5 and X4/dual human immunodeficiency virus type 1 (HIV-1) may contribute to coreceptor switch from R5 to X4 HIV-1. To confirm this hypothesis, we investigated mixed HIV-1 infections in people who inject drugs (PWID) infected with the CRF01_AE subtype. Methods: Viral plasma RNA from PWID were extracted, the V3 region of the HIV-1 gp120 gene was amplified, and deep sequencing was performed. Coreceptor usage was determined using phenotypic assay by cloning each V3 region. Coreceptor usage of minor HIV-1 variants detected by deep sequencing was predicted based on the amino acid sequences of the V3 region. Results: Deep sequencing of plasma from 36 PWID revealed that mixed HIV-1 infection involving different coreceptor usage occurred in 13 cases (36.1%). Phylogenetic analysis revealed that R5 variants were dominant, whereas X4/dual variants were detected as minor populations in most cases. In 1 case, however, R5 variants emerged as a distinct minor population mixed with X4/dual variants as the major population. Notably, plasma viral RNA load (pVL) was higher in cases of mixed infection with R5 and X4/dual HIV-1 than in those infected solely with R5 HIV-1. Conclusions: Our observations suggest a possible association between mixed HIV-1 coreceptor usage and coreceptor switch in CRF01_AE-infected PWID, and that mixed infection may be associated with pVL.