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Background: Lenacapavir is a highly potent first-in-class inhibitor of HIV-1 capsid approved for the treatment of heavily treatment-experienced (HTE) people with HIV-1 (PWH) harboring multidrug resistant (MDR) virus, in combination with an optimized background regimen (OBR). Resistance analyses conducted after 2 years of lenacapavir treatment in the phase 2/3 CAPELLA study are described., Methods: CAPELLA enrolled viremic HTE PWH with resistance to 2 or more drugs per class in at least 3 of the 4 main drug classes. Post-baseline resistance was evaluated in participants experiencing virologic failure using resistance assays (HIV-1 capsid, protease, reverse transcriptase, and integrase genotypic/phenotypic tests). Adherence to OBR was assessed by plasma drug measurement using tandem liquid chromatography/mass spectrometry., Results: After 2 years, lenacapavir plus OBR treatment led to HIV-1 RNA suppression in 82% of participants (missing=excluded). Treatment-emergent capsid resistance occurred in 19% (14/72) of participants, including capsid mutations M66I, Q67H/K/N, K70H/N/R/S, and/or N74D/H/K, which were all associated with functional lenacapavir monotherapy. Seven participants with lenacapavir resistance reattained HIV-1 RNA <50 copies/mL upon OBR resumption or change, while remaining on lenacapavir., Conclusions: Emergence of lenacapavir resistance after 2 years in CAPELLA was a consequence of functional lenacapavir monotherapy. In half of participants with lenacapavir resistance, continued treatment with lenacapavir + active OBR led to HIV-1 RNA resuppression., (© The Author(s) 2025. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Background: Lenacapavir is a long-acting HIV-1 capsid inhibitor for treatment of HIV-1 infection. We evaluated the efficacy and safety of lenacapavir in combination with an investigator-selected optimized background regimen (OBR) after 104 weeks in adults with multidrug-resistant HIV-1., Methods: This ongoing, international, Phase 2/3 trial at 42 sites included 72 adults living with multidrug-resistant HIV-1. Following a 2-week oral lenacapavir loading phase, participants received subcutaneous lenacapavir every 26 weeks with an OBR. HIV-1 RNA, CD4 cell counts, and adverse events were assessed over 104 weeks. One participant did not enter the extension phase., Results: At Week 104, 44 of 71 participants (62%, 95% CI 50; 73) had HIV-1 RNA <50 copies/mL via US Food & Drug Administration (FDA) snapshot algorithm. When missing data (including discontinuations) were excluded, 44 of 54 participants (82%) had HIV-1 RNA <50 copies/mL at Week 104, mean CD4 cell count increased by 122 cells/µL (95% CI 80; 165), and the proportion of participants with CD4 cell count <200 cells/µL decreased from 64% (46 of 72) at Baseline to 29% (16 of 55). Fourteen participants had treatment-emergent lenacapavir resistance; seven resuppressed (HIV-1 RNA <50 copies/mL) while maintaining lenacapavir use. There were no Grade 4 or serious treatment-related adverse events. One participant discontinued study drug due to an injection site reaction., Conclusions: Treatment with subcutaneous lenacapavir in combination with an OBR was well tolerated and resulted in a high rate of virological suppression over 104 weeks. Lenacapavir represents an important treatment option in people with multidrug-resistant HIV-1., (© The Author(s) 2024. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Background: Lenacapavir (LEN) is a first-in-class inhibitor of human immunodeficiency virus type 1 (HIV-1) capsid function in clinical development for the treatment of heavily treatment-experienced (HTE) people with HIV (PWH) harboring multidrug resistance (MDR) in combination with an optimized background regimen (OBR). Here we describe resistance analyses conducted in the pivotal phase 2/3 CAPELLA study., Methods: CAPELLA enrolled viremic HTE PWH with resistance to ≥3 of 4 of the main antiretroviral (ARV) classes and resistance to ≥2 ARV drugs per class. Baseline resistance analyses used commercial assays (HIV-1 protease, reverse transcriptase, integrase genotypic/phenotypic tests). Postbaseline resistance was evaluated in participants experiencing virologic failure., Results: At baseline, 46% of participants had resistance to the 4 main ARV drug classes, with one-third of participants having exhausted all drugs from ≥3 of the 4 main ARV classes. Treatment with LEN + OBR for 26 weeks led to viral suppression in 81% of participants. Postbaseline resistance mutations to lenacapavir occurred in 8 participants (6 with M66I, 1 with K70H, 1 with Q67H + K70R) who were receiving unintended functional LEN monotherapy at the time of resistance selection., Conclusions: LEN added to OBR led to high efficacy in this HTE patient population with MDR but could select for resistance when used unintentionally as functional monotherapy., Competing Interests: Potential conflicts of interest. All authors are employees and stockholders of Gilead Sciences, Inc. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2022. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Unlabelled: We assessed the efficacy and safety of ledipasvir/sofosbuvir plus ribavirin for 24 weeks in 9 human immunodeficiency virus/hepatitis C virus-coinfected patients who relapsed after receiving 12 weeks of treatment with ledipasvir/sofosbuvir. Eight of 9 (89%) achieved sustained virologic response 12 weeks after the end of treatment. One patient relapsed at posttreatment week 4. These results suggest an effective salvage therapy for patients for whom direct-acting antiviral treatment has failed., Clinical Trials Registration: NCT02073656., (© The Author 2016. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail journals.permissions@oup.com.)

Background: Sofosbuvir (SOF) exhibits a high barrier to resistance, with no S282T NS5B substitution or phenotypic resistance detected in phase 3 registration studies., Methods: Here, emergence of the NS5B variants L159F and V321A and possible association with resistance was evaluated in 8 studies of SOF (NEUTRINO, FISSION, POSITRON, FUSION, VALENCE, PHOTON-1, PHOTON-2, and P7977-2025) and 5 studies of combination ledipasvir (LDV) and SOF (LDV/SOF; LONESTAR, ELECTRON [LDV/SOF arms], ION1, ION2, and ION3), using deep sequencing., Results: Deep sequencing detected L159F in 15% (53 of 353) and V321A in 5% (17 of 353) of patients with virologic failure in the SOF studies. Intensification of SOF treatment with LDV reduced the emergence of L159F or V321A to 2% (1 of 50 each) at virologic failure. L159F and V321A did not influence the outcome of retreatment with SOF, ribavirin, and pegylated interferon. At baseline, L159F was detected only in genotype 1-infected patients (1%) and was only associated with increased virologic failure in patients treated for short durations with SOF and ribavirin., Conclusions: Deep-sequencing analysis confirmed that NS5B variants L159F and V321A emerged in a subset of patients treated with SOF at virologic failure. These variants had no impact on retreatment outcome with SOF, ribavirin, and pegylated interferon. Baseline L159F in genotype 1 did not affect the treatment outcome with LDV/SOF., (© The Author 2015. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail journals.permissions@oup.com.)

Background: Sofosbuvir is a chain-terminating nucleotide analogue inhibitor of the hepatitis C virus (HCV) NS5B RNA polymerase that is efficacious in subjects with HCV genotype 1-6 infection. Sofosbuvir resistance is primarily conferred by the S282T substitution in NS5B., Methods: NS5B sequencing and susceptibility testing of HCV from subjects infected with genotypes 1-6 who participated in phase 2 and 3 sofosbuvir clinical trials was performed., Results: No NS5B variants present at baseline among 1645 sofosbuvir-treated subjects were associated with treatment failure; sofosbuvir susceptibility was within 2-fold of reference. Among 282 subjects who did not achieve sustained virologic response, no novel sofosbuvir resistance-associated variants were identified, and the NS5B changes observed did not confer significant reductions in sofosbuvir susceptibility. In 1 subject with S282T observed at relapse 4 weeks after sofosbuvir monotherapy, the resistant variant (13.5-fold reduced sofosbuvir susceptibility, replication capacity <2% of control) became undetectable by deep sequencing 12 weeks after treatment. L159F and V321A were identified as treatment-emergent variants but did not confer resistance to sofosbuvir in the replicon system., Conclusions: These data demonstrate a uniform susceptibility of subject-derived HCV to sofosbuvir, and also show that selection of sofosbuvir-resistant HCV is exceedingly rare and is associated with a significant reduction in viral fitness., (© The Author 2014. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)