Unmasking the roles of viral glycoproteins in oral transmission of KSHV

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PROJECT SUMMARY More than 44,000 new cases of Kaposi sarcoma (KS) are reported globally each year, 84% of which occur in Africa. This and other Kaposi sarcoma-associated herpesvirus (KSHV)-induced malignancies predominate in people with acquired or iatrogenic immunodeficiencies. Although KSHV can be detected in other human body fluids, its frequent detection in saliva in groups both with and without risk of sexually transmitted infections (e.g., children) suggests that the oral cavity is the site of primary acquisition. However, the mechanism of KSHV oral transmission in vivo, particularly the critical viral envelope glycoproteins (gps) required for viral entry, remains unresolved. Several KSHV–host interactions have been identified, but all prior experiments were performed in vitro and have not been validated in vivo due to prior lack of an appropriate animal model. Through collaboration with the Wisconsin National Primate Research Center, our laboratory has access to the common marmoset (Callithrix jacchus, CJ), a recently developed KSHV non-human primate model that is susceptible to KSHV oral infection, and under immunosuppression acquires KS-like skin lesions. The objective of this application is to elucidate the minimum gps required to initiate primary oral infection in vivo, as a prerequisite to selecting key gps for developing an effective prophylactic vaccine candidate. This application builds on Dr. Ogembo’s recently completed NCI K01 CA184388-05 research on KSHV entry mechanisms and vaccine development. Recently, we showed that in vitro, the KSHV glycoprotein gH/gL is essential for viral infection of epithelial, endothelial, and fibroblasts cells, but not B cells. Notably, we and others have also shown that both monoclonal and polyclonal Abs to KSHV glycoproteins gB, gH/gL, and gpK8.1, can neutralize KSHV infection of diverse permissive human cells in vitro. Building on this success, we generated KSHV deletion mutants lacking the four glycoproteins thought to be critical for viral entry (gB, gH/gL, gpK8.1) and various monoclonal antibodies specific to these gps. In this project, we will use human ex vivo samples and the CJ KSHV model to test the hypothesis that gB and gH/gL are critical for KSHV in vivo oral transmission. The premise of our proposal is built on strong evidence that 1) KSHV can infect CJ, which develop KS-like skin lesions, and 2) Abs against the KSHV glycoproteins gB and gH/gL can neutralize KSHV infection in vitro and ex vivo. Furthermore, the permissiveness to KSHV infection of human cells ex vivo and CJ makes these platforms ideal to test the KSHV gp requirements for infection. Successful completion of the proposed study will elucidate the minimum KSHV gps required for primary infection in ex vivo and in vivo models, advancing our long-term goal of defining the initial steps in KSHV infection of humans and the role of antibodies in protecting against the early steps of KSHV transmission. This will ultimately inform design and development of prophylactic vaccines that can prevent KSHV infection and its associated cancers.