Lost in transcription: molecular mechanisms that control HIV latency

Feline immunodeficiency virus latency

Despite highly effective anti-retroviral therapy, HIV is thought to persist in patients within long-lived cellular reservoirs in the form of a transcriptionally inactive (latent) integrated provirus. Lentiviral latency has therefore come to the forefront of the discussion on the possibility of a cure for HIV infection in humans. Animal models of lentiviral latency provide an essential tool to study mechanisms of latency and therapeutic manipulation. Of the three animal models that have been described, the feline immunodeficiency virus (FIV)-infected cat is the most recent and least characterized. However, several aspects of this model make it attractive for latency research, and it may be complementary to other model systems. This article reviews what is known about FIV latency and chronic FIV infection and how it compares with that of other lentiviruses. It thereby offers a framework for the usefulness of this model in future research aimed at lentiviral eradication.

Selective recognition of viral promoters by host cell transcription complexes: challenges and opportunities to control latency

The rate of transcription driven by the HIV promoter defines both the entry into and reactivation from viral latency. The HIV core promoter plays a pivotal role in HIV latency by recruiting host cell RNA polymerase II pre-initiation complexes essential for viral transcription. Pioneering studies on the HIV core promoter revealed that the architecture of the HIV core promoter is specifically required for the amplification of transcription in response to the viral trans-activator Tat, and provided the proof-of-concept that the HIV core promoter represents a tractable drug target. The recent discovery of host cell transcription complexes that selectively recognize the HIV core promoter provides new impetus to investigate their components as novel targets to therapeutically extinguish or eradicate latent HIV.

Therapeutics for HIV-1 reactivation from latency

Intensive combined antiretroviral therapy successfully suppresses HIV-1 replication and AIDS disease progression making infection manageable, but it is unable to eradicate the virus that persists in long-lived, drug-insensitive and immune system-insensitive reservoirs thus asking for life-long treatments with problems of compliance, resistance, toxicity and cost. These limitations and recent insights into latency mechanisms have fueled a renewed effort in finding a cure for HIV-1 infection. Proposed eradication strategies involve reactivation of the latent reservoir upon induction of viral transcription followed by the elimination of reactivated virus-producing cells by viral cytopathic effect or host immune response. Several molecules identified by mechanism-directed approaches or in large-scale screenings have been proposed as latency reversing agents. Some of them have already entered clinical testing in humans but with mixed or unsatisfactory results.