Kaposi Sarcoma herpesvirus reactivation and replication are dispensable for cell-lineage specific tumorigenesis in whole genome transgenic mice

Herpesvirus reactivation and replication depend on an ordered cascade of gene expression. The viral immediate-early replication and transcription activator protein (Rta) is necessary and sufficient to initiate this process. For Kaposi sarcoma herpesvirus (KSHV), Rta-interacting and Rta-regulated proteins are thought to contribute to cellular transformation. Using a novel, whole-genome transgenic mouse model, we show that KSHV tumorigenesis is independent of Rta in vivo. Rta-deleted, KSHV bacmid transgenic (tgKSHV{Delta}Rta) mice developed latency-associated nuclear antigen (LANA)-positive vascular sarcomas with the same endothelial cell-lineage composition and transcriptional profile as human Kaposi sarcoma (KS). The viral miRNAs were expressed in the tumors, as were all canonical latency and the K1 and K15 oncogenes. Importantly, this system is the first to model both KS and lymphoma, reflecting the development of both malignancies observed in KSHV-infected individuals. These results separate virus replication from KS tumorigenesis, which can proceed independently so long as the virus genome is maintained in a susceptible cell. SignificanceKaposi sarcoma (KS) is the most common cancer in people living with HIV worldwide. Like all herpesviruses, KS-associated herpesvirus (KSHV) has a latent and lytic phase. Hitherto, viral lytic genes are thought to play a role in KS. The KSHV replication and transcription activator (Rta) is both necessary and sufficient for reactivation and lytic viral replication, but Rta was not required for vascular tumor development in a whole virus genome mouse model. This new tgKSHV{Delta}RTA mouse model separates virus replication from viral tumorigenesis and defines a minimal set of viral oncogenes. This model enables mechanistic studies in vivo, and treatment modalities to be evaluated within a complete immune and stromal microenvironment.