Two long terminal repeat circles and persistent HIV-1 replication.

Building on the success of combination antiretroviral drug therapy will require a better understanding of the underlying basis for viral persistence. Characterization of the therapeutic, viral, and immunological factors that influence the size and stability of viral reservoirs will foster the development of strategies to control or eliminate HIV-1 from infected individuals. Here we review recent work aimed at delineating the complex interplay between viral replication, the immune system, and viral reservoirs. Finally, we address the implications and clinical significance of the residual replication that persists in infected individuals on potent antiretroviral therapy to evaluate both the possible risks and benefits of ongoing HIV-1 replication.

Persistence of episomal HIV-1 infection intermediates in patients on highly active anti-retroviral therapy.

Treatment of HIV-1-infected individuals with a combination of anti-retroviral agents results in sustained suppression of HIV-1 replication, as evidenced by a reduction in plasma viral RNA to levels below the limit of detection of available assays. However, even in patients whose plasma viral RNA levels have been suppressed to below detectable levels for up to 30 months, replication-competent virus can routinely be recovered from patient peripheral blood mononuclear cells and from semen. A reservoir of latently infected cells established early in infection may be involved in the maintenance of viral persistence despite highly active anti-retroviral therapy. However, whether virus replication persists in such patients is unknown. HIV-1 cDNA episomes are labile products of virus infection and indicative of recent infection events. Using episome-specific PCR, we demonstrate here ongoing virus replication in a large percentage of infected individuals on highly active anti-retroviral therapy, despite sustained undetectable levels of plasma viral RNA. The presence of a reservoir of 'covert' virus replication in patients on highly active anti-retroviral therapy has important implications for the clinical management of HIV-1-infected individuals and for the development of virus eradication strategies.

Vpx is required for dissemination and pathogenesis of SIV(SM) PBj: evidence of macrophage-dependent viral amplification.

The viral accessory protein Vpx is required for productive in vitro infection of macrophages by simian immunodeficiency virus from sooty mangabey monkeys (SIV(SM)). To evaluate the roles of Vpx and macrophage infection in vivo, we inoculated pigtailed macaques intravenously or intrarectally with the molecularly cloned, macrophage tropic, acutely pathogenic virus SIV(SM) PBj 6.6, or accessory gene deletion mutants (deltaVpr or deltaVpx) of this virus. Both wild-type and SIV(SM) PBj deltaVpx viruses were readily transmitted across the rectal mucosa. A subsequent 'stepwise' process of local amplification of infection and dissemination was observed for wild-type virus, but not for SIV(SM) PBj deltaVpx, which also showed considerable impairment of the overall kinetics and extent of its replication. In animals co-inoculated with equivalent amounts of wild-type and SIV(SM) Pbj deltaVpx intravenously or intrarectally, the deltaVpx mutant was at a strong competitive disadvantage. Vpx-dependent viral amplification at local sites of initial infection, perhaps through a macrophage-dependent mechanism, may be a prerequisite for efficient dissemination of infection and pathogenic consequences after exposure through either mucosal or intravenous routes.

Matrix metalloproteinase expression during mouse peri-implantation development.

PROBLEM: The purpose of this study was to define the temporal expression and to quantitate the mRNA levels of collagenase, 72 kDa, 92 kDa, and membrane-type matrix metalloproteinase during the peri-implantation period of pregnancy in the mouse uterus. Embryonic expression of 72 kDa and 92 kDa matrix metalloproteinases, as well as interleukin 1 alpha, was also investigated. METHODS: Uterine matrix metalloproteinases were detected using gelatin substrate gel electrophoresis (zymography) and reverse-transcription polymerase chain reaction methodology was used to detect and quantitate different mRNA species in the mouse uterus and blastocyst. RESULTS: Collagenase, 72 kDa, and 92 kDa matrix metalloproteinases are developmentally regulated during the peri-implantation period of pregnancy, but membrane-type matrix metalloproteinase appears to be expressed constitutively. Matrix metalloproteinase mRNA levels have been quantitated and confirm the observed developmental expression patterns. Prominent expression of bot 92 kDa matrix metalloproteinase and interleukin 1 alpha was observed in blastocysts during outgrowth while weak expression of the 72 kDa matrix metalloproteinase was detected. CONCLUSIONS: The date provide evidence of matrix metalloproteinase expression in vivo and substantiate their potential role in tissue remodeling prior to and during blastocyst implantation. Expression of interleukin 1 alpha, 92 kDa, and 72 kDa matrix metalloproteinases suggests that these proteins are important for trophoblast invasion associated with implantation of the early embryo.