“A transient heritable memory regulates HIV reactivation from latency”

Reactivation of human immunodeficiency virus 1 (HIV-1) from latently infected T cells is a critical barrier to successfully eradicate HIV-1 from patients. Latency models in Jurkat T-cells reveal that individual cells reactivate in an all-or-none fashion when exposed to latency reversal agents (LRAs). Remarkably, this heterogeneity arises within a clonal cell population of genetically identical cells containing a single copy of the provirus integrated at the same genomic site. To characterize these single-cell responses, we leverage the classical Luria-Delbrück fluctuation test where single cells are isolated from a clonal population, and exposed to LRAs after a period of colony expansion. If cellular responses are purely random, then the fraction of reactivating cells should have minimal colony-to-colony fluctuations given the large number of cells present after weeks of colony growth. In contrast, data shows considerable colony-to-colony fluctuations with the fraction of reactivating cells following a skewed distribution. Systematic measurements of fluctuations over time in combination with mathematical modeling uncovers the existence of a heritable memory that regulates HIV-1 reactivation, where single cells are in a LRA-responsive state for a few weeks before switching back to an irresponsive state. These results have enormous implications for designing therapies to purge the latent reservoir and illustrate the utility of fluctuation-based assays to uncover hidden transient cellular states underlying phenotypic heterogeneity.