Assessing proviral competence: current approaches to evaluate HIV-1 persistence

PURPOSE OF REVIEW: Despite decades of suppressive antiretroviral therapy (ART), HIV-1 reservoirs persist and fuel viral rebound if therapy is interrupted. The persistence of viral reservoirs in infected individuals is the main obstacle to achieving HIV-1 eradication or a long-term remission. Accurate assessment of the viral reservoir size is necessary for monitoring the effectiveness of the curative interventions. Here, we review the recent progress in the development of assays to measure HIV-1 persistence, highlighting their key advantages and limitations. RECENT FINDINGS: To estimate the viral reservoir size, a number of assays have been developed that assess different aspects of HIV-1 persistence in ART-treated individuals. These include viral outgrowth assays to measure proviral replication competence, sequencing-based assays to measure genetic intactness of HIV-1 proviruses, and diverse techniques that measure the ability of proviruses to produce viral RNA and/or proteins (transcription and translation competence), with or without ex vivo stimulation. Recent years have seen the development of next-generation reservoir assays that, in addition to measuring viral persistence markers, assess the proviral integration sites and characterize the HIV-1 reservoir cells on the single-cell level. SUMMARY: Although no assay yet can measure the HIV-1 reservoir with 100% accuracy, recent technical advances allow reliable estimation of its size and composition.