Glycoproteins gM and gN are indispensable factors for rhesus macaque rhadinovirus replication and spread but can be reconstituted by KSHV chimeras

Rhesus macaque rhadinovirus (RRV) is a primate gamma-2 herpesvirus (rhadinovirus) closely related to Kaposi sarcoma-associated herpesvirus (KSHV), the human oncovirus that causes Kaposi sarcoma. Like Other herpesviruses, KSHV and RRV encode numerous envelope glycoproteins involved in cell attachment, entry, as well as assembly and release of progeny virions from infected cells. Two glycoproteins postulated to form a complex and reported to be virus-neutralizing targets are glycoproteins M (gM) and N (gN). To investigate gM and gN in rhadinovirus Infection, we utilized infectious and pathogenic Bacterial artificial chromosomes (BAC). RRV BACmids with nonsense mutations introduced into gM or gN did not yield an infectious virus. However, when gM or gN of RRV were exchanged for gM or gN from KSHV, each of the KSHV-chimeric RRV BACmids restored virus replication and infectious spread. Interestingly, we also discovered that the substitution of KSHVgM into the RRV BACmid was associated with attenuation in viral spread, an effect that was not countered by a double-chimeric virus. In contrast, the substitution of RRV gN into a KSHV BACmid negatively affected the assembly of KSHV, independent of gM/gN complex formation. Therefore, here, we revealed that in KSHV and RRV, gM and gN are interchangeable, contribute to crucial functions for viral assembly and spread, and have evolved in a virus-specific manner. Although more research is needed to define the roles of gM and gN, our work establishes the first glycoprotein-chimeric viruses for KSHV and RRV, which can now be used to corroborate gM/gN as targets for a Cancer vaccine.IMPORTANCEKaposi sarcoma (KS) is a human Cancer caused by KSHV and is one of the most frequently occurring cancers in HIV/AIDS patients, as well as in regions where KSHV is endemic. In this report, we have constructed and authenticated the first KSHV glycoprotein-encoding chimeric viruses for evaluations in the RRV/rhesus macaque model and have also uncovered fundamental roles for the glycoproteins gM and gN. Our work is significant by successfully bridging the human-specific, species barrier that has previously restricted preclinical evaluations of the KSHV glycoproteins as vaccine targets in vivo. Although there is no KSHV-specific animal model that is widely used, these KSHV-chimeric viruses may be useful as tools to guide future vaccine design and strategy as vaccine candidates progress toward clinical trials.

Kaposi's sarcoma-associated herpesvirus; animal models; chimeras; gM; gN; glycoproteins; nonsense mutations; primate rhadinovirus; rhesus macaque rhadinovirus; vaccine development.