Abstract: KS was one of the first AIDS defining illnesses and world-wide continues to be the most common tumor of AIDS patients. The main tumor cell of KS is the spindle cell, a cell that expresses markers of lymphatic endothelium. All spindle cells in late stage tumors maintain Kaposi's Sarcoma-herpesvirus infection. Kaposi's Sarcoma-herpesvirus (KSHV) is a gamma- herpesvirus and is the etiologic agent of Kaposi's Sarcoma (KS). Over 95% of spindle cells in the KS tumor express only latent genes while only a very low percentage express additional lytic proteins. Current treatments for KS involve general chemotherapy for the tumor but do not directly target the virus. All direct treatment for herpesviruses target elements of lytic replication. There are no treatments for latent herpesvirus infection. Due to the limited gene expression during latency it is difficult to identify viral therapeutic targets for eliminating latent infection. However, KSHV dramatically alters the host cell during latent infection. Therefore, it might be possible to target pathological changes to the host cell during latent infection to eliminate latently infected cells. We have performed a whole genome Crispr/Cas9 screen in tert-immortalized endothelial cells to identify genes cellular genes and signaling pathways that are required for the proliferation or survival of latently infected endothelial cells but not their uninfected counterparts. Our initial studies have identified a large number of cellular genes required for latently infected cells to proliferate and survive that appear to have little effect on uninfected endothelial cells. We propose to further validate these studies in primary endothelial cells. We will also examine specific pathways that were identified in the screen including the Rho family Guanine exchange factors (GEFs) and GTPase activating proteins (GAPs) and their signaling pathways. The goals of the proposal are to identify novel cellular targets that could be used to eliminate cells latently infected with KSHV.