The Biology of the HIV-1 Latent Reservoir and Implications for Cure Strategies

For decades, the standard model of HIV-1 persistence during antiretroviral therapy (ART) assumed that the virus survived solely within a small, stable population of long-lived, resting memory CD4+ T cells. This review challenges that view, highlighting that the reservoir is far more dynamic. While ART effectively suppresses viral replication, it does not eliminate the integrated proviral genome. The authors synthesize recent evidence showing that the reservoir is maintained through the sustained clonal expansion of infected cells, meaning that the virus persists not just because the cells live a long time, but because they actively divide.

Three primary, non-mutually exclusive mechanisms drive the clonal expansion of these infected cells. First, HIV-1 integration can occur near host genes involved in cell growth, potentially providing a survival or proliferative advantage. Second, homeostatic proliferation—the process by which T cells divide in response to cytokines like IL-7 to maintain immune balance—allows infected cells to replicate without necessarily triggering viral reactivation. Finally, chronic exposure to antigens, such as those from co-infections like CMV or EBV, drives the expansion of antigen-specific T cells that happen to harbor the virus. This antigen-driven process creates a cycle of expansion and contraction, ensuring the reservoir persists even while the virus remains largely invisible to the immune system.

Understanding that the reservoir is maintained by cell proliferation shifts the focus of potential cure strategies. Traditional 'shock-and-kill' approaches, which aim to reverse latency to make infected cells visible to the immune system, have faced challenges due to limited efficacy and the difficulty of clearing antigen-expressing cells. The authors suggest that future strategies must address the proliferative nature of the reservoir. This could involve 'block-and-lock' approaches to permanently silence the virus, or immunotherapies that specifically target the expanded clones. Additionally, the authors emphasize that because the reservoir is established early and varies by factors like sex, age, and timing of treatment, a 'one-size-fits-all' cure is unlikely. Future progress will require better mapping of the whole-body viral burden and a deeper understanding of how the immune system can be trained to control the virus in the absence of lifelong medication.