Large numbers of CD4+ T lymphocytes are infected and killed during acute SIV and SHIV infections. We previously reported that by day 7 PI, 30 to 70% of memory CD4+ T cells systemically are infected with SIV and by day 10 PI, 30 to 90% of circulating CD4+ T cells (both nave and memory subsets) are infected by pathogenic SHIVs. In situ hybridization/immunohistochemical studies and FACS analyses have revealed that the majority of virus infected cells during the acute infection do not express activation markers. During the first fifteen years of the AIDS epidemic, the prevailing dogma was that HIV and SIV were unable to replicate in quiescent CD4+ T lymphocytes. This failure to infect non-activated T cells in culture was attributed to multiple mechanisms including inefficient reverse transcription, impaired nuclear import of reverse transcripts, and low intracellular dNTP pools. It was also believed that HIV was unable to integrate into the genome of resting CD4+ T cells. Since unintegrated DNA has been reported to be inefficiently transcribed, impaired integration could also contribute to the failure of lymphocytes in the G0/1a stage of the cell cycle to support productive infections. These results have been extended to answer whether virus production by resting CD4+ T cells continue ex vivo, following their isolation from acutely infected monkeys. Negatively selected resting CD4+ T lymphocytes were purified from SIV (day 7 PI) and SHIV (day 10 PI) infected rhesus macaques and cultivated in the presence of autologous serum and in the absence of IL-2 for 4 days. Infectious virus was, in fact, detected in the supernatant medium from each ex vivo culture. In a separate series of experiments, the integration status of viral DNA in resting nave and memory CD4+ T cells, recovered from SIV and SHIV infected macaques on days 7 and 10 PI, respectively, was determined by limiting dilution Alu-LTR PCR. High frequencies of integrated SIV DNA were detected in memory but not nave CD4+ T cells, in agreement with the differential expression of the CCR5 coreceptor in these two lymphocyte subsets. In animals inoculated with X4-tropic SHIV, 13 to 51% of the circulating nave CD4+ T cells contained integrated DNA, assuming each cell carries a single integrated provirus. These results indicate that during acute infection in vivo, integration of viral DNA occurs in a prototypical resting cell. We have also investigated whether a 28-day course of potent ART, initiated at a time (48h p.i.) following SIV inoculation when acquisition of a viral infection was virtually assured, would sufficiently sensitize the immune system and result in controlled virus replication when treatment was stopped. Administration of Tenofovir 48h post SIV inoculation to six Mamu-A*01 negative rhesus macaques did, in fact, potently suppress virus replication in all of the treated rhesus macaques but plasma viral RNA rapidly became detectable in all six animals following its cessation. Unexpectedly, the viral set-points in the treated monkeys became established at two distinct levels. Three controller macaques had chronic phase virus loads in the 1 x 10e3 RNA copies/ml range whereas three non-controller animals had set-points of 2 to 8 x 10e5 RNA copies/ml. All of the non-controller monkeys have died with symptoms of immunodeficiency by week 60 post-infection, whereas two of the three controller animals are alive at week 80. Interestingly, the three controller macaques each carried MHC class I alleles previously reported to confer protection against SIV and two of these animals generated CTL escape viral variants during the course of their infections.
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