Primary resistance of CCR5-tropic HIV-1 to maraviroc cannot be predicted by the V3 sequence

Objectives: Resistance of HIV-1 to CCR5 antagonists can occur without coreceptor switching by mutations in envelope glycoproteins that enable virus entry using the inhibitor-bound form of CCR5. We investigated whether mutations in the V3 region of HIV-1 from subjects naive to maraviroc could be associated with primary resistance to this drug, Methods: The frequency of CCR5-tropic HIV-1 subtype B isolates harbouring putative V3 maraviroc resistance mutations was assessed among the HIV tropism database of Toulouse University Hospital, France. Phenotypic assessment of maraviroc susceptibility was performed for 14 isolates representative of the main mutation patterns and 14 controls. V3 mutations were reversed or introduced by site-directed mutagenesis. Results: Ninety-three of 951 (9.8%) isolates harboured V3 mutations assumed to be associated with maraviroc resistance. Maraviroc completely blocked virus entry for all but 1 of the 14 isolates harbouring V3 mutations [IC50 8.6 nM; 95% CI (6.6-47.4)], as in the 14 control isolates [IC50 13.4 nM, 95% CI (7.7-50.3)] (P=0.24). Primary resistance to maraviroc, with a plateau in entry inhibition, was found in one isolate (harbouring a 20F/21I genotype). Site-directed mutagenesis showed that V3 mutations are necessary but not sufficient to induce maraviroc resistance. Conclusions: The impact of V3 mutations depended on the env context in which they occurred. Simple assessment of the V3 genotype thus cannot accurately predict maraviroc resistance. Rather, phenotypic assessment of virus particles expressing the envelope glycoprotein as a whole is required. This approach revealed that primary resistance of CCR5-tropic HIV-1 subtype B isolates to maraviroc seems uncommon.