Genotypic tropism testing (GTT) for co-receptor usage is a recommended tool for clinical practice before administration of the CCR5-antagonist maraviroc. For some isolates, phenotypic tropism testing (PTT) revealed discordant results with GTT. In this study, we performed a comparative study between GTT and PTT in HIV-1C from East Africa (HIV-1CEA) and compared the data with HIV-1B and 01_AE and described the maraviroc susceptibility in the CCR5-tropic strains. Patient-derived HIV-1 envgp120 region was cloned into a modified pNL4-3 plasmid expressing the luciferase gene. rPhenotyping dissected single clones from 31 HIV-1CEA infected patients and four strains with known phenotype. Additionally, 68 clones from 18 patients (HIV-1B: 5, 01_AE: 7, HIV-1CEA: 6) were used to determine the PTT in GHOST cell line. The respective V3-sequences were used for GTT. R5-tropic strains from HIV-1CEA (n = 20) and non-C (n = 12) were tested for maraviroc sensitivity in TZMbl cell line. The GTT falsely called a higher proportion of X4-tropic strains in HIV-1CET compared to PTT by both rPhenotyping and the GHOST-cell assay. When multiple clones were tested in a subset of patients’ samples, both dual-tropic and R5-tropic strains were identified for HIV-1C. Relatively higher EC50 values were observed in HIV-1C strains than the non-C strains (p = 0.002).

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Geno2Pheno (coreceptor), a genotypic tropism test, demonstrates excellent agreement with the phenotypic tropism test for subtype B and some other subtypes. However, potential X4-overcalling for CRF01_AE might occur with the present version. To confirm X4 overcalling for AE and to optimize the algorithm for use with AE, we compared the tropism of 22 AE samples by both genotypic and phenotypic methods. The env V3 region was analyzed by bulk sequencing, and tropism was evaluated using the Geno2Pheno algorithm. PhenXR, a phenotypic tropism test, was performed in parallel to determine chemokine receptor preferences. A high X4-overcalling for select samples and a low rate of R5-concordant samples (9.1%) were observed for AE with the current version of Geno2Pheno (coreceptor). On the other hand, the new version, namely, Geno2Pheno (Sanger), showed a high concordance rate of 81.8%, with PhenXR. Because majority of the samples were selected based on discrepancies in the genotypic tropism calls between the present version Geno2Pheno (coreceptor) (FPR<10%) and the new version Geno2Pheno (Sanger) (X4-risk<36), it remains to be determined whether the new version provides improved R5-calls for the AE sequences in general or only in this setting. Further clinical validation studies are warranted.