Latent HIV reservoirs are groups of infected cells that contain HIV genetic material but do not actively produce new viruses. These reservoirs allow HIV to persist in the body even when antiretroviral therapy successfully suppresses viral replication. Understanding how these reservoirs develop, where they exist, and how they reactivate is important for HIV research. Scientists continue to study viral latency.
Latent HIV reservoirs are populations of long-lived cells that contain HIV DNA integrated into their genetic material. In these cells, the virus remains inactive or produces very little viral material. Because infected cells do not actively release large amounts of virus, they can remain undetected by the immune system and are not effectively eliminated by standard antiretroviral medications.
HIV reservoir formation commonly begins during the early stages of infection. After entering a CD4 T cell, HIV converts its RNA into DNA using an enzyme called reverse transcriptase. The viral DNA then integrates into the host cell's DNA with the help of another enzyme called integrase. Once integrated, the viral genetic material may remain inactive.
Several biological processes contribute to the development and maintenance of latent reservoirs.
Cellular integration: HIV inserts its genetic material into the DNA of infected immune cells.
Immune cell longevity: Some infected memory CD4 T cells can survive for many years.
Cellular inactivity: When infected cells remain inactive, they produce little or no new virus.
Clonal expansion: Infected cells can multiply through normal cell division, creating additional cells containing the same HIV genetic material.
Immune system limitations: The immune system may not recognize infected cells that are not actively producing viral proteins.
Latent reservoirs are not limited to one location. They have been identified in different tissues, including lymph nodes, the gastrointestinal tract, and other immune system compartments. These locations provide biological environments where infected cells can persist.
HIV viral replication is the biological process through which the virus produces new copies of itself inside infected cells. During active infection, HIV uses the host cell's machinery to reproduce and spread to additional immune cells. However, latent HIV behaves differently because the integrated viral genetic material remains transcriptionally inactive or minimally active.
When a latently infected cell receives particular biological signals, the virus may become active again. This process is known as HIV reactivation. Once activated, the infected cell can begin producing viral RNA and proteins, eventually allowing the formation of new virus particles.
The major stages of HIV replication include:
Attachment: HIV attaches to the CD4 receptor and a coreceptor, usually CCR5 or CXCR4, on a target immune cell.
Fusion: The viral envelope fuses with the cell membrane, allowing viral contents to enter.
Reverse transcription: Reverse transcriptase converts viral RNA into DNA.
Integration: Viral DNA becomes integrated into the host cell's genetic material.
Transcription and translation: The infected cell produces viral RNA and proteins.
Assembly: Newly produced viral components gather to form immature virus particles.
Budding and maturation: New particles leave the cell and undergo maturation to become infectious.
Antiretroviral therapy targets different stages of this replication process. When taken consistently, ART can prevent new rounds of viral replication and maintain viral suppression. However, existing latent reservoirs can remain unaffected because standard HIV medications do not remove integrated viral DNA from inactive cells.
Researchers are investigating several approaches to address this challenge, including latency-reversing agents, immune-based therapies, broadly neutralizing antibodies, and strategies designed to eliminate or permanently silence HIV-infected cells. These approaches remain areas of scientific investigation, and a widely available cure has not yet been established.