Objectives: We previously reported vicriviroc (VCV) resistance in an HIV-infected subject and used deep sequencing and clonal analyses to track the evolution of V3 sequence forms over 28 weeks of therapy. Here, we test the contribution of gp120 mutations to CCR5 antagonist resistance and investigate why certain minority V3 variants emerged as the dominant species under drug pressure.
Methods: Nineteen site-directed HIV-1 mutants were generated that contained gp120 VCV resistance mutations. Viral sensitivities to VCV, maraviroc, TAK-779, and HGS004 were determined.
Results: Three patterns of susceptibilities were observed as follows: sigmoid inhibition curves with 50% inhibitory concentration similar to pretreatment virus [07J-week 0 (W0)], single mutants with decreased 50% inhibitory concentrations compared with 07J-W0, and mutants that contained ≥5 of 7 VCV resistance mutations with flattened inhibition curves and decreased or negative percent maximal inhibition. Substitutions such as S306P, which sensitized virus to CCR5 antagonists when present as single mutations, were not detected in the baseline virus population but were necessary for maximal resistance when incorporated into V3 backbones that included preexisting VCV resistance mutations.
Conclusions: CCR5 antagonist resistance was reproduced only when a majority of V3 mutations were present. Minority V3 loop variants may serve as a scaffold upon which additional mutations lead to complete VCV resistance.