Kinetics of Human Immunodeficiency Virus Type 1 Decay following Entry into Resting CD4 ⁺ T Cells

Abstract

In untreated human immunodeficiency virus type 1 (HIV-1) infection, most viral genomes in resting CD4؉ T cells are not integrated into host chromosomes. This unintegrated virus provides an inducible latent reservoir because cellular activation permits integration, virus gene expression, and virus production. It remains controversial whether HIV-1 is stable in this preintegration state. Here, we monitored the fate of HIV-1 in resting CD4؉ cells by using a green fluorescent protein (GFP) reporter virus carrying an X4 envelope. After virus entry into resting CD4؉ T cells, both rescuable virus gene expression, visualized with GFP, and rescuable virion production, assessed by p24 release, decayed with a half-life of 2 days. In these cells, reverse transcription goes to completion over 2 to 3 days, and 50% of the viruses that have entered undergo functional decay before reverse transcription is complete. We distinguished two distinct but closely related factors contributing to loss of rescuable virus. First, some host cells undergo virus-induced apoptosis upon viral entry, thereby reducing the amount of rescuable virus. Second, decay processes directly affecting the virus both before and after the completion of reverse transcription contribute to the loss of rescuable virus. The functional half-life of full-length, integration-competent reverse transcripts is only 1 day. We propose that rapid intracellular decay processes compete with early steps in viral replication in infected CD4 ؉ T cells. Decay processes dominate in resting CD4؉ T cells as a result of the slow kinetics of reverse transcription and blocks at subsequent steps. Therefore, the reservoir of unintegrated HIV-1 in recently infected resting CD4 ؉ T cells is highly labile.

Low-level viremia persists for at least 7 years in patients on suppressive antiretroviral therapy

“…The half-life of third-phase viremia (39-63 weeks or 9-15 months) is comparable to that previously described for latently infected CD4 ϩ T cells (6-44 months) (23)(24)(25), implicating this cell type, which may also contribute to the fourth phase of viremia. The stability of fourth-phase viremia also raises the possibility that a very small fraction of infected cells is capable of surviving indefinitely while continuing to produce virus, perhaps by division at a rate equal to its death rate.…”

HIV DNA Subspecies Persist in both Activated and Resting Memory CD4 + T Cells during Antiretroviral Therapy

“…2). These ex vivo results differ markedly from the results of in vitro experiments that generally delineate the inability of HIV RNA to complete reverse transcription in resting CD4 ϩ T cells (3,23,24), although these studies did not differentiate memory from naive cell populations but considered bulk resting CD4 ϩ T cell populations. On the other hand, downstream events such as the likelihood of HIV DNA proceeding to integration rather than spontaneously circularizing to an episomal form were certainly less likely in resting cells (Table 1).…”

Primitive hematopoietic cells resist HIV-1 infection via p21Waf1/Cip1/Sdi1

“…This late-occurring change in BrdU incorporation may well be derived from the virus interaction with host cells, either by synthesis of viral DNA in cells or virus-induced further downregulation of p21. Studies have shown that HIV-1 DNA integration occurs before cell cycling, such as in HIV-1 infection of quiescent T lymphocytes and nondividing cells (22)(23)(24)(25)(26). We found that HIV-1 infection ultimately downregulated p21 expression in infected cells that were without RNA interference (RNAi) treatment (Supplemental Figure 5).…”