{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,21]],"date-time":"2026-09-21T10:00:33Z","timestamp":1789984833092,"version":"4.0.1"},"reference-count":40,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,9,20]],"date-time":"2026-09-20T00:00:00Z","timestamp":1789862400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001323","name":"Poliomyelitis Research Foundation","doi-asserted-by":"publisher","award":["21\/66"],"award-info":[{"award-number":["21\/66"]}],"id":[{"id":"10.13039\/501100001323","id-type":"DOI","asserted-by":"publisher"}]},{"award":["21\/66"],"award-info":[{"award-number":["21\/66"]}],"id":[{"id":"https:\/\/ror.org\/02d540t02","id-type":"ROR","asserted-by":"publisher"}]},{"name":"Department of Molecular Medicine and Haematology"},{"id":[{"id":"https:\/\/ror.org\/03rp50x72","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Viruses"],"abstract":"<jats:p>Islatravir is a novel nucleoside reverse transcriptase translocation inhibitor recently approved for the treatment of HIV-1 infection in virologically suppressed PLWH. While we previously documented high-level phenotypic resistance to islatravir (ISL) in HIV-1 subtype C variants harboring combinations of type 2 thymidine analogue mutations (TAM2) along with the M184V resistance-associated mutation, the primary contributor to the observed phenotype remains unclear. This report dissects the relative contribution of M184V to ISL resistance in the context of TAM2-containing variants through systematic reversion analysis. We show that reverting mutant 184V to wildtype M184 resulted in substantial sensitization to ISL, with fold-change reductions ranging from 8.1 to 13.4-fold across three TAM2 genetic backgrounds. Contrary to the well-documented antagonism between M184V and TAMs in zidovudine resistance, these two resistance pathways exhibit cooperative rather than antagonistic interactions in the context of ISL resistance. These findings provide critical evidence for refinement of genotypic resistance interpretation algorithms for ISL and have direct implications for the future clinical management of ISL-based antiretroviral therapy in people living with HIV. Importantly, elucidating the mechanistic basis of M184V-TAM2 cooperation would establish a more predictive framework for understanding how complex resistance mutation patterns impact ISL susceptibility and guide treatment decisions in virologically experienced individuals. Considering the diminished use of TAM2-seletive antiretroviral drugs in contemporary ART regimens, islatravir is likely to be an effective treatment option.<\/jats:p>","DOI":"10.3390\/v18091046","type":"journal-article","created":{"date-parts":[[2026,9,21]],"date-time":"2026-09-21T08:03:47Z","timestamp":1789977827000},"page":"1046","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["M184V: The Major Determinant of Cooperative ISL Resistance When in Combination with Multiple TAM2 Mutations in HIV-1 Subtype C"],"prefix":"10.3390","volume":"18","author":[{"given":"Kyla","family":"Nel","sequence":"first","affiliation":[{"name":"HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Parktown, Johannesburg 2193, South Africa"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9504-0950","authenticated-orcid":false,"given":"Maria Antonia","family":"Papathanasopoulos","sequence":"additional","affiliation":[{"name":"HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Parktown, Johannesburg 2193, South Africa"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7541-8132","authenticated-orcid":false,"given":"Adriaan Erasmus","family":"Basson","sequence":"additional","affiliation":[{"name":"HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Parktown, Johannesburg 2193, South Africa"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"73","DOI":"10.1016\/S0753-3322(99)80063-8","article-title":"Highly Active Antiretroviral Therapy (HAART) for the Treatment of Infection with Human Immunodeficiency Virus Type 1","volume":"53","author":"Shafer","year":"1999","journal-title":"Biomed. Pharmacother."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"734","DOI":"10.1056\/NEJM199709113371102","article-title":"Treatment with Indinavir, Zidovudine, and Lamivudine in Adults with Human Immunodeficiency Virus Infection and Prior Antiretroviral Therapy","volume":"337","author":"Gulick","year":"1997","journal-title":"N. Engl. J. Med."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"HIV-CAUSAL Collaboration, Ray, M., Logan, R., Sterne, J.A.C., Hern\u00e1ndez-D\u00edaz, S., Robins, J.M., Sabin, C., Bansi, L., van Sighem, A., and de Wolf, F. (2010). The Effect of Combined Antiretroviral Therapy on the Overall Mortality of HIV-Infected Individuals. AIDS, 24, 123\u2013137.","DOI":"10.1097\/QAD.0b013e3283324283"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"219","DOI":"10.1016\/S1368-7646(02)00118-8","article-title":"HIV Mutagenesis and the Evolution of Antiretroviral Drug Resistance","volume":"5","author":"Mansky","year":"2002","journal-title":"Drug Resist. Updat."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"e1","DOI":"10.2165\/11633630-000000000-00000","article-title":"HIV-1 Antiretroviral Resistance: Scientific Principles and Clinical Applications","volume":"72","author":"Tang","year":"2012","journal-title":"Drugs"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"582","DOI":"10.1016\/j.coviro.2011.10.020","article-title":"Drug Resistance in HIV-1","volume":"1","author":"Kuritzkes","year":"2011","journal-title":"Curr. Opin. Virol."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Charpentier, C., Le Hingrat, Q., Ferr\u00e9, V.M., Damond, F., and Descamps, D. (2023). Future of Antiretroviral Drugs and Evolution of HIV-1 Drug Resistance. Viruses, 15.","DOI":"10.3390\/v15020540"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"35681","DOI":"10.1074\/jbc.M109.036616","article-title":"Mechanism of Inhibition of HIV-1 Reverse Transcriptase by 4\u2019-Ethynyl-2-Fluoro-2\u2019-Deoxyadenosine Triphosphate, a Translocation-Defective Reverse Transcriptase Inhibitor","volume":"284","author":"Michailidis","year":"2009","journal-title":"J. Biol. Chem."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"e0045824","DOI":"10.1128\/aac.00458-24","article-title":"Intracellular Islatravir-Triphosphate Half-Life Supports Extended Dosing Intervals","volume":"68","author":"Zang","year":"2024","journal-title":"Antimicrob. Agents Chemother."},{"key":"ref_10","unstructured":"(2026, August 07). Merck Announces Clinical Holds on Studies Evaluating Islatravir for the Treatment and Prevention of HIV-1 Infection. Available online: https:\/\/www.merck.com\/news\/merck-announces-clinical-holds-on-studies-evaluating-islatravir-for-the-treatment-and-prevention-of-hiv-1-infection\/."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"68","DOI":"10.1097\/QAI.0000000000002879","article-title":"Brief Report: Efficacy and Safety of Oral Islatravir Once Daily in Combination with Doravirine Through 96 Weeks for Treatment-Naive Adults with HIV-1 Infection Receiving Initial Treatment with Islatravir, Doravirine, and Lamivudine","volume":"91","author":"Molina","year":"2022","journal-title":"J. Acquir. Immune Defic. Syndr."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"e440","DOI":"10.1016\/S2352-3018(26)00033-0","article-title":"Fixed-Dose Daily Doravirine (100 Mg) with Islatravir (0\u00b725 Mg) versus Bictegravir, Emtricitabine, and Tenofovir Alafenamide for Initial HIV-1 Therapy: 48-Week Results of a Phase 3, Randomised, Controlled, Double-Blind, Non-Inferiority Trial","volume":"13","author":"Rockstroh","year":"2026","journal-title":"Lancet HIV"},{"key":"ref_13","unstructured":"(2026, September 12). FDA Approves Merck\u2019s Once-Daily IDVYNSO\u2122 (Doravirine\/Islatravir). Available online: https:\/\/www.merck.com\/news\/fda-approves-mercks-once-daily-idvynso-doravirine-islatravir\/."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"168","DOI":"10.7326\/ANNALS-25-01939","article-title":"Once-Weekly Oral Islatravir Plus Lenacapavir Versus Daily Oral Bictegravir, Emtricitabine, and Tenofovir Alafenamide in Persons with HIV-1: A Phase 2 Randomized Study","volume":"179","author":"Colson","year":"2026","journal-title":"Ann. Intern. Med."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"e0013322","DOI":"10.1128\/aac.00133-22","article-title":"Islatravir Has a High Barrier to Resistance and Exhibits a Differentiated Resistance Profile from Approved Nucleoside Reverse Transcriptase Inhibitors (NRTIs)","volume":"66","author":"Diamond","year":"2022","journal-title":"Antimicrob. Agents Chemother."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"527","DOI":"10.68040\/2026343.527532","article-title":"Current Evidence on Islatravir Drug Resistance and Implications for Future HIV Treatment","volume":"34","author":"Wensing","year":"2026","journal-title":"Top. Antivir. Med."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"O14","DOI":"10.1186\/1742-4690-8-S2-O14","article-title":"Interactions of Different Drug Resistance Mutations in HIV Reverse Transcriptase in Defining Patterns of Drug Resistance","volume":"8","author":"Wainberg","year":"2011","journal-title":"Retrovirology"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"791","DOI":"10.1177\/135965350501000705","article-title":"Thymidine Analogue Mutation Profiles: Factors Associated with Acquiring Specific Profiles and Their Impact on the Virological Response to Therapy","volume":"10","author":"Ruiz","year":"2005","journal-title":"Antivir. Ther."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"298","DOI":"10.1093\/nar\/gkg100","article-title":"Human Immunodeficiency Virus Reverse Transcriptase and Protease Sequence Database","volume":"31","author":"Rhee","year":"2003","journal-title":"Nucleic Acids Res."},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Byun, H., Papathanasopoulos, M.A., Steegen, K., and Basson, A.E. (2024). Thymidine Analogue Mutations with M184V Significantly Decrease Phenotypic Susceptibility of HIV-1 Subtype C Reverse Transcriptase to Islatravir. Viruses, 16.","DOI":"10.20944\/preprints202410.1632.v1"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"169100","DOI":"10.1016\/j.jmb.2025.169100","article-title":"Kinetic Investigation of Resistance to Islatravir Conferred by Mutations in HIV-1 Reverse Transcriptase","volume":"437","author":"Zalenski","year":"2025","journal-title":"J. Mol. Biol."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"239","DOI":"10.2144\/btn-2022-0085","article-title":"A Simple and Economical Site-Directed Mutagenesis Method for Large Plasmids by Direct Transformation of Two Overlapping PCR Fragments","volume":"73","author":"Yang","year":"2022","journal-title":"Biotechniques"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1608","DOI":"10.1086\/503914","article-title":"Web Resources for HIV Type 1 Genotypic-Resistance Test Interpretation","volume":"42","author":"Liu","year":"2006","journal-title":"Clin. Infect. Dis."},{"key":"ref_24","unstructured":"Posit Team (RStudio: Integrated Development Environment for R, 2026). RStudio: Integrated Development Environment for R, Version 2026.07.1, Build 147."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"1686","DOI":"10.21105\/joss.01686","article-title":"Welcome to the Tidyverse","volume":"4","author":"Wickham","year":"2019","journal-title":"J. Open Source Softw."},{"key":"ref_26","unstructured":"Kassambara, A. (Rstatix: Pipe-Friendly Framework for Basic Statistical Tests, 2026). Rstatix: Pipe-Friendly Framework for Basic Statistical Tests, Version 0.7.3."},{"key":"ref_27","unstructured":"Pohlert, T. (PMCMRplus: Calculate Pairwise Multiple Comparisons of Mean Rank Sums Extended, 2024). PMCMRplus: Calculate Pairwise Multiple Comparisons of Mean Rank Sums Extended, Version 1.9.12."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"vlaf072","DOI":"10.1093\/immhor\/vlaf072","article-title":"Making Multiple Comparisons Easy: A Decision Tree and Visual Statistics Guide for Data with More than Two Groups","volume":"10","author":"Gurski","year":"2026","journal-title":"Immunohorizons"},{"key":"ref_29","unstructured":"Hadley, W. (2016). Ggplot2: Elegant Graphics for Data Analysis, Springer."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"693","DOI":"10.1016\/j.jmb.2008.10.071","article-title":"Structure and Function of HIV-1 Reverse Transcriptase: Molecular Mechanisms of Polymerization and Inhibition","volume":"385","author":"Sarafianos","year":"2009","journal-title":"J. Mol. Biol."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"48725","DOI":"10.1074\/jbc.M108352200","article-title":"The Emergence of Different Resistance Mechanisms toward Nucleoside Inhibitors Is Explained by the Properties of the Wild Type HIV-1 Reverse Transcriptase","volume":"276","author":"Isel","year":"2001","journal-title":"J. Biol. Chem."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"4971","DOI":"10.1128\/JVI.80.10.4971-4977.2006","article-title":"The K65R Mutation in Human Immunodeficiency Virus Type 1 Reverse Transcriptase Exhibits Bidirectional Phenotypic Antagonism with Thymidine Analog Mutations","volume":"80","author":"Parikh","year":"2006","journal-title":"J. Virol."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"489","DOI":"10.1177\/135965350300800605","article-title":"Nucleoside and Nucleotide Analogue Reverse Transcriptase Inhibitors: A Clinical Review of Antiretroviral Resistance","volume":"8","author":"Gallant","year":"2003","journal-title":"Antivir. Ther."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"696","DOI":"10.1126\/science.7542804","article-title":"Potential Mechanism for Sustained Antiretroviral Efficacy of AZT-3TC Combination Therapy","volume":"269","author":"Larder","year":"1995","journal-title":"Science"},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"24533","DOI":"10.1074\/jbc.M114.562694","article-title":"4\u2019-Ethynyl-2-Fluoro-2\u2019-Deoxyadenosine (EFdA) Inhibits HIV-1 Reverse Transcriptase with Multiple Mechanisms","volume":"289","author":"Michailidis","year":"2014","journal-title":"J. Biol. Chem."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"403","DOI":"10.1006\/jmbi.2000.3823","article-title":"The Role of Steric Hindrance in 3TC Resistance of Human Immunodeficiency Virus Type-1 Reverse Transcriptase1","volume":"300","author":"Gao","year":"2000","journal-title":"J. Mol. Biol."},{"key":"ref_37","unstructured":"National Department of Health South Africa (2010). Guidlines for the Management of HIV in Children, South Africa National Department of Health."},{"key":"ref_38","unstructured":"South Africa National Department of Health (2026). National Consolidate Guidlines for the Prevention and Management of HIV in Adults, Adolescents, Children, Infants and Pregnant & Breastfeeding Women, South Africa National Department of Health."},{"key":"ref_39","first-page":"12","article-title":"Longer-Term Virologic Outcomes on Tenofovir-Lamivudine-Dolutegravir in Second-Line ART","volume":"26","author":"Zhao","year":"2025","journal-title":"South. Afr. J. HIV Med."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"e381","DOI":"10.1016\/S2352-3018(22)00092-3","article-title":"Efficacy and Safety of Dolutegravir or Darunavir in Combination with Lamivudine plus Either Zidovudine or Tenofovir for Second-Line Treatment of HIV Infection (NADIA): Week 96 Results from a Prospective, Multicentre, Open-Label, Factorial, Randomised, Non-Inferiority Trial","volume":"9","author":"Paton","year":"2022","journal-title":"Lancet. HIV"}],"container-title":["Viruses"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1999-4915\/18\/9\/1046\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,21]],"date-time":"2026-09-21T09:03:36Z","timestamp":1789981416000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1999-4915\/18\/9\/1046"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,20]]},"references-count":40,"journal-issue":{"issue":"9","published-online":{"date-parts":[[2026,9]]}},"alternative-id":["v18091046"],"URL":"https:\/\/doi.org\/10.3390\/v18091046","relation":{},"ISSN":["1999-4915"],"issn-type":[{"value":"1999-4915","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,9,20]]}}}