Waking Up Is Hard To Do: New Model To Study Latent HIV Infection in Quiescent Cells
How can human immunodeficiency virus (HIV) patients be successfully treated, when the virus becomes integrated into the human genome? This difficult question has been at the center of HIV research since the early days of the AIDS epidemic, and researchers continue to search for better therapies with which to treat this challenging infection. One school of thought suggests driving infected cells into deep latency so they can no longer produce viruses, while another school of thought proposes reactivating latently infected cells, which are easier to target with antiretroviral drugs.
Viral reactivation compounds can be used on latently infected cells to reveal HIV-infected cells that can then be destroyed. Unfortunately, no compound reactivates all latent HIV infections, and any infected cells that may remain can serve as a reservoir to reactivate and spread the infection again. For this shock-and-kill strategy to work, scientists must understand how to activate all latently infected cells. A new Journal of Virology study describes a new culture model that can help in developing a strategy to better understand, and hopefully activate, latent HIV in quiescently-infected cells as well as proliferating cells.
HIV is hard to eliminate from infected individuals because it incorporates into the nuclear DNA of host immune cells, primarily CD4+ T cells, as well as macrophage and hematopoietic stem and progenitor cells (HSPCs). Infected cells can contain the viral DNA without producing progeny virons in a state known as latency; this happens frequently in quiescent memory T cells, which aren’t actively dividing and are less metabolically active than proliferating cells. Because these quiescent cells avoid elimination with antiviral treatment and can become a new source of virus when treatment stops, authors Mark Painter, Thomas Zaikos, and Kathleen Collins wanted a better method to study latent HIV infection—and reactivation—in these quiescent cells.
The researchers discovered that culturing primary HSPCs at 30°C instead of 37°C reduced proliferation and differentiation of the cells. The hypothermia-induced quiescent cells had a lower frequency of active infection, and were less likely to revert to active viral replication than cells maintained at 37°C. This simple hypothermic culture model allowed the research team to investigate the mechanisms required to establish and revert latency. The researchers were able to pinpoint a difference in hypothermia-induced latency due to different HSP90 expression levels, and found that by inhibiting HSP90 in 37°C cultures, they were able to recapitulate cell quiescence and viral latency.
Several compounds are used to stimulate latent virus reactivation in proliferating cells, including TNFα, histone deacetylase inhibitors, and HMBA. When the researchers tested these on hypothermia-induced and HSP90-suppressed quiescent cells, the observed that viral latency was reversed by some stimulants, like TNFα, but not others. The different effects of these reactivation stimulants on proliferating versus quiescent cells suggest that the latent genomes differ between the two cell states. These experiments demonstrate the importance of studying both cell states in the search for effective reactivation stimulants—and provide a culture system for future experiments.