Date of Award
Doctor of Philosophy (PhD)
Human immunodeficiency virus type 1 (HIV-1), the virus that causes acquired immune deficiency syndrome (AIDS), is one of the world’s most serious health and development challenges. Worldwide there are approximately 36.7 million people living with HIV, and tens of millions have died of AIDS-related causes since the beginning of the epidemic. Treatment of HIV-1 infection with combinations of antiretroviral drugs has significantly reduced the death rate and improved the quality of life of HIV-1 infected individuals. Despite over thirty years of HIV-1 research, however, both a cure and a vaccine remain elusive. Complete eradication of HIV-1 by antiretroviral drugs is prevented by the persistence of rare, long-lived, latently infected cells. These cells, called the latent reservoir, are thought to resist immune clearance and viral cytopathic effects by harboring a transcriptionally quiescent integrated HIV-1 provirus. As a result, interruption of suppressive therapy almost inevitably results in rapid viral rebound, which originates from these latently infected cells and prevents HIV-1 cure. It is thought that establishing the reservoir requires intact retroviral integration into the host cell genome and subsequent transcriptional silencing of the integrated provirus. These are rare events and these cells have no known distinguishing surface markers, which has made it difficult to define the precise cellular and molecular nature of the reservoir. The long half-life of the latent reservoir has been attributed to a stable pool of long-lived latently infected CD4+ T cells. An alternative explanation, consistent with the frequent occurrence of monotypic viral sequences, is that infected latent cells are maintained in part by cell proliferation. T cell division and productive HIV-1 transcription are mediated by shared metabolic and transcriptional pathways, and productive HIV-1 infection typically leads to CD4+ T cell death. Thus, how infected cells survive while dividing is unknown. I focused my thesis on characterizing this latent reservoir in virally suppressed, HIV-1 infected individuals and examining the mechanisms of HIV-1 latency. In the first part of this thesis, using a novel single-cell, high throughput integration site sequencing method, I demonstrate that HIV-1 infected cells are capable of cell division, but that the great majority of the largest expanded clones contain defective proviruses which cannot contribute to the replication competent rebound virus. In the second part of this thesis, using an assay to qualitatively and quantitatively characterize the latent reservoir, I suggest that the replication competent latent reservoir may, in fact, be maintained in part by rare cell division events. And finally, I developed a novel isolation strategy which allowed single cell characterization of recently reactivated latent cells. I was able to obtain reactivated latent T cells that produced intact, replication competent HIV-1. By sequencing the T cell receptors, I prove that these isolated latent cells are expanded T cell clones. Single cell gene expression analysis revealed that latent cells share a specific gene profile that prominently includes genes implicated in silencing the virus, T cell exhaustion markers, and genes that may aid in identification of specific CD4+ T cell subsets prone to latent infection. Together, the data supports a model for latency whereby infected T cells turn on a gene expression program that suppresses viral replication during cell division thereby preventing activation of the cell death pathways that are normally triggered by HIV-1 infection.
Cohn, Lillian Brumer, "Single Cell Analysis of the HIV-1 Latent Reservoir" (2018). Student Theses and Dissertations. 484.