title: Sequential emergence and clinical implications of viral mutants with K70E and K65R mutation in reverse transcriptase during prolonged tenofovir monotherapy in rhesus macaques with chronic RT-SHIV infection.
abstract: BACKGROUND
  We reported previously on the emergence and clinical implications of simian immunodeficiency virus (SIVmac251) mutants with a K65R mutation in reverse transcriptase (RT), and the role of CD8+ cell-mediated immune responses in suppressing viremia during tenofovir therapy. Because of significant sequence differences between SIV and HIV-1 RT that affect drug susceptibilities and mutational patterns, it is unclear to what extent findings with SIV can be extrapolated to HIV-1 RT. Accordingly, to model HIV-1 RT responses, 12 macaques were inoculated with RT-SHIV, a chimeric SIV containing HIV-1 RT, and started on prolonged tenofovir therapy 5 months later.
  
  
  RESULTS
  The early virologic response to tenofovir correlated with baseline viral RNA levels and expression of the MHC class I allele Mamu-A*01. For all animals, sensitive real-time PCR assays detected the transient emergence of K70E RT mutants within 4 weeks of therapy, which were then replaced by K65R mutants within 12 weeks of therapy. For most animals, the occurrence of these mutations preceded a partial rebound of plasma viremia to levels that remained on average 10-fold below baseline values. One animal eventually suppressed K65R viremia to undetectable levels for more than 4 years; sequential experiments using CD8+ cell depletion and tenofovir interruption demonstrated that both CD8+ cells and continued tenofovir therapy were required for sustained suppression of viremia.
  
  
  CONCLUSIONS
  This is the first evidence that tenofovir therapy can select directly for K70E viral mutants in vivo. The observations on the clinical implications of the K65R RT-SHIV mutants were consistent with those of SIVmac251, and suggest that for persons infected with K65R HIV-1 both immune-mediated and drug-dependent antiviral activities play a role in controlling viremia. These findings suggest also that even in the presence of K65R virus, continuation of tenofovir treatment as part of HAART may be beneficial, particularly when assisted by antiviral immune responses.
authors.affiliation: California National Primate Research Center, University of California, Davis, USA. kkvanrompay@ucdavis.edu
authors.forename: Koen K A
authors.initials: KK
authors.lastname: Van Rompay
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Johnson
authors.forename: Emily J
authors.initials: EJ
authors.lastname: Blackwood
authors.forename: Raman P
authors.initials: RP
authors.lastname: Singh
authors.forename: Jonathan
authors.initials: J
authors.lastname: Lipscomb
authors.forename: Timothy B
authors.initials: TB
authors.lastname: Matthews
authors.forename: Marta L
authors.initials: ML
authors.lastname: Marthas
authors.forename: Niels C
authors.initials: NC
authors.lastname: Pedersen
authors.forename: Norbert
authors.initials: N
authors.lastname: Bischofberger
authors.forename: Walid
authors.initials: W
authors.lastname: Heneine
authors.forename: Thomas W
authors.initials: TW
authors.lastname: North
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D019943:Amino Acid Substitution; D000818:Animals; D019380:Anti-HIV Agents / Q000494:pharmacology / Q000627:therapeutic use; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D004195:Disease Models, Animal; D024882:Drug Resistance, Viral / Q000235:genetics*; D054303:HIV Reverse Transcriptase / Q000235:genetics*; D015497:HIV-1 / Q000235:genetics*; D008212:Lymphocyte Depletion; D008251:Macaca; D020125:Mutation, Missense; D063065:Organophosphonates / Q000494:pharmacology* / Q000627:therapeutic use; D012367:RNA, Viral / Q000097:blood; D012641:Selection, Genetic; D016097:Simian Acquired Immunodeficiency Syndrome / Q000188:drug therapy / Q000276:immunology / Q000821:virology*; D015302:Simian Immunodeficiency Virus / Q000235:genetics*; D000068698:Tenofovir; D019562:Viral Load; D014766:Viremia
chemical_list: D019380:Anti-HIV Agents; D063065:Organophosphonates; D012367:RNA, Viral; D000068698:Tenofovir; D054303:HIV Reverse Transcriptase; D000225:Adenine