PROJECT SUMMARY This project is proposed to respond to Provocative Question 6 in RFA-CA-19-032. Objective: Paracrine transformation is a theoretical concept that was proposed years ago to explain the unconventional ?non-autonomous? oncogenesis observed during development of Kaposi?s sarcoma (KS), one of the most common AIDS-associated malignancies. This proposal is designed to prove its existence, to dissect its mechanism, identify the players therein, and to define its roles in KS tumorigenesis using our novel animal models and an engineered microphysiological platform. Rationale: Kaposi?s sarcoma herpes virus (KSHV) causes an endothelial cell tumor, KS, in the skin and internal organs. A paradox in KS oncogenesis is that while most KS tumor cells are latently infected with minimal viral gene expression, only lytic-stage cells express vGPCR, the only known viral oncogene that is necessary and sufficient for KS development. Provocative Question: How vGPCR, a lytic viral gene expressed in cells destined to die, can cause cancer? Challenges: This question remained unanswered due to the lack of proper animal models, engineered in vitro or ex vivo systems to study pathogenesis, persistence, and tumor development that recapitulate this HIV/AIDS- associated malignancies. Innovation & Strategy: We have developed a series of novel animal models and Vascularized Skin Chip platform. Using these technical advancements, we will prove the existence of paracrine transformation, identify its cellular (immune cells, HIV) and molecular (vGPCR-loaded exosome) players, and characterize its mechanism as the main oncogenic driver for KS tumorigenesis. Impact: Our study will address the decades-long conundrum on KS tumor development by defining the existence and mechanism of paracrine transformation. This provocative concept of paracrine transformation will not only force us to move our focus beyond the lytic-infected cells as the oncogenic drivers, but also expand the way we understand the initiation, progression, and metastasis of cancer. In addition, this study will open a new door to novel anti-KS therapeutics, and provide a solid justification to investigate the presence of equivalent non-autonomous transformation in other non-viral oncogenesis, such as breast and colon cancers.