Genotypic Tropism Testing in HIV-1 Proviral DNA Can Provide Useful Information at Low-Level Viremia

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Abstract
The possibility of performing genotypic tropism testing (GTT) with proviral DNA (pvDNA) even during suppressed viremia would facilitate the use of CCR5 inhibitors as part of switching, simplification, or intensification strategies. Thus, we aimed to evaluate the tropism concordance between plasma RNA and pvDNA samples and to assess which factors could affect possible discrepancies between the two compartments. GTT was performed using both plasma RNA and pvDNA from 55 sample pairs from drug-experienced patients. Potential differences between the two compartments were evaluated by analyzing coreceptor usage and genetic variability. Paired samples were also stratified in three levels of viremia (500 copies/ml). Overall, Geno2Pheno comparisons of false-positive rates in the two compartments showed good correlation ( r = 0.72). A high level of concordance in tropism predictions for the two compartments was found (46/55 sample pairs [83.6%]). Among the 9 sample pairs with discordant tropisms, a larger proportion of pvDNA samples harboring CXCR4/dual-mixed-tropic viruses was found, in comparison with plasma RNA samples (88.9% versus 11.1%; P = 0.0034). Discordant samples were characterized by greater genetic variability than were concordant samples. With stratification of the paired samples according to viremia levels, the prevalence of discordant samples decreased with increasing viremia (500 copies/ml, 6.7%; P = 0.2). Our findings confirm that prediction of viral tropism using pvDNA is feasible even in low-level viremia and provides useful information for therapy optimization for patients with low or suppressed viremia.

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