Studies 1844 and 1878 demonstrated non-inferior efficacy of switching suppressed HIV-1-infected adults to bictegravir/emtricitabine/tenofovir alafenamide (B/F/TAF) versus continuing dolutegravir- (DTG) or boosted protease inhibitor (PI)-based regimens. At week 48, 93% in the B/F/TAF groups versus 95% in the DTG group and 89% in the PI group had HIV-1 RNA <50 copies/mL by snapshot algorithm, after which B/F/TAF treatment continued open-label. Here, we present resistance analyses and virologic outcomes after 2 years of B/F/TAF treatment.
Archived preexisting HIV-1 drug resistance was assessed by historical genotypes (documented resistance to study drugs was exclusionary) and retrospective baseline proviral DNA genotyping (Archive assay, Monogram Biosciences). Participants with resistance to study drugs detected post-randomization were allowed to continue on study. Virologic outcomes were based on last available on-treatment HIV-1 RNA.
Altogether, 572 participants switched to B/F/TAF and were treated for a median of 108 weeks (IQR 106-118 weeks). Pre-switch reverse transcriptase (RT) genotypic data were available for 78% (447/572) of B/F/TAF-treated participants; integrase data were available for 55% (314/572). Preexisting primary NRTI resistance (-R), NNRTI-R, and INSTI-R substitutions were observed in 16% (71/447), 21% (93/447), and 1.9% (6/314), respectively. High frequencies of NRTI-R substitutions M184V or M184I (9.8%, 44/447) and thymidine analog mutations (TAMs; 8.5%, 38/447) were detected by DNA genotyping. Substitutions associated with resistance to the NNRTI rilpivirine (RPV) were observed in 9.6% (43/447). At the time of analysis, 99% (564/572) of B/F/TAF-treated participants were suppressed (HIV-1 RNA <50 copies/mL), including 95% (42/44) with archived M184V/I, 95% (36/38) with TAMs, 98% (42/43) with RPV-R, and 100% (6/6) with INSTI-R. There was no resistance development in B/F/TAF-treated participants through week 48, and no participants met criteria for resistance testing after week 48.
Preexisting RT resistance was common among suppressed participants switching to B/F/TAF, notably RPV-R and previously unidentified M184V/I and TAMs. High rates of virologic suppression were observed in the overall and drug resistant populations through 108 weeks of B/F/TAF treatment with no resistance development, indicating that B/F/TAF is a durable switch option for suppressed patients, including those with evidence of this archived NNRTI and NRTI resistance.