Antiretroviral Therapy Rhesus Macaques during Combined Simian Immunodeficiency Virus-Infected No Viral Evolution in the Lymph Nodes of

ombination antiretroviral therapy (cART) has transformedhuman immunodeficiency virus (HIV) infection from an in-curablediseasetoamanageableone.Itsuppressestheviralburdeninpatientstoundetectablelevels(1–3),lowersthechanceofviraltransmission (4), increases the number of CD4 T lymphocytes(1, 2), reconstitutes immunity (5–7), and extends the life expec-tancy of patients (8). However, cART does not cure patients be-causeofitsinabilitytoeradicatethevirusfrominfectedindividu-als (9), suggesting the existence of a viral reservoir that isrefractorytocART.ItsidentificationanderadicationarethereforerequisitesforafunctionalcureforAIDS.ToestablishastrategyforeradicationoftheHIVreservoir,themechanismofpersistenceofthevirusmustbeelucidated.Twomechanismsofviralpersistencehavebeenproposed:oneisongoingcyclesofviralreplicationde-spite the presence of antivirals (10), and the other is provirus in-tegrationintolong-livedcells(11).Whereaspreviousstudiescon-cerning this issue have been extensively conducted with clinicalspecimens from HIV-1-infected patients, including plasma,peripheral blood mononuclear cells, and gut-associated lym-phatictissues(12–14),lymphnodes,whichareepicentersofvirusreplication in infected individuals not undergoing therapy (15–17),haveonlyrarelybeensubjectedtoscrutiny.InanimalmodelsofcART,inparticular,thesimianimmunodeficiencyvirus(SIV)-macaquemodel,whichallowssystemicexamination,thelocationoftheviralreservoirandthemechanismofviralholdinghavenotbeen studied in detail.To elucidate how the virus is maintained during cART in ananimal model of anti-HIV chemotherapy, we administered acombination of nucleotide/nucleoside reverse transcriptase in-hibitors (azidothymidine, lamivudine, and tenofovir disoproxilfumarate) and protease inhibitors (lopinavir with ritonavir) tofour SIV239-infected rhesus macaques for 1 year (18). Althoughthe plasma viral RNA loads of the animals were suppressed tolevelsbelowtheassaydetectionlimitduringtheperiodofchemo-therapy, a systemic analysis conducted at the completion of ther-apy revealed viral RNA present in lymphatic tissues, especially inmesentericandspleniclymphnodes(MLNandSLN,respectively)athightiters.Reasoningthatanypossiblemode(s)ofviralpersis-tence should be in operation in tissues with high levels of viralRNA expression, we investigated viral genes in these tissues.It is expected that viral genes accumulate nucleotide substitu-tions in proportion to the time postinfection in individuals notundergoing therapy because of continuous virus replication me-diated by the error-prone viral reverse transcriptase. Such muta-tionrateshaveindeedbeenobservedintheV3loopof