A Homolog Pentameric Complex Dictates Viral Epithelial Tropism, Pathogenicity and Congenital Infection Rate in Guinea Pig Cytomegalovirus

In human cytomegalovirus (HCMV), tropism to epithelial and endothelial cells is dependent upon a pentameric complex (PC). Given the structure of the placenta, the PC is potentially an important neutralizing antibody target antigen against congenital infection. The guinea pig is the only small animal model for congenital CMV. Guinea pig cytomegalovirus (GPCMV) potentially encodes a UL128-131 HCMV PC homolog locus (GP128-GP133). In transient expression studies, GPCMV gH and gL glycoproteins interacted with UL128, UL130 and UL131 homolog proteins (designated GP129 and GP131 and GP133 respectively) to form PC or subcomplexes which were determined by immunoprecipitation reactions directed to gH or gL. A natural GP129 C-terminal deletion mutant (aa 107–179) and a chimeric HCMV UL128 C-terminal domain swap GP129 mutant failed to form PC with other components. GPCMV infection of a newly established guinea pig epithelial cell line required a complete PC and a GP129 mutant virus lacked epithelial tropism and was attenuated in the guinea pig for pathogenicity and had a low congenital transmission rate. Individual knockout of GP131 or 133 genes resulted in loss of viral epithelial tropism. A GP128 mutant virus retained epithelial tropism and GP128 was determined not to be a PC component. A series of GPCMV mutants demonstrated that gO was not strictly essential for epithelial infection whereas gB and the PC were essential. Ectopic expression of a GP129 cDNA in a GP129 mutant virus restored epithelial tropism, pathogenicity and congenital infection. Overall, GPCMV forms a PC similar to HCMV which enables evaluation of PC based vaccine strategies in the guinea pig model.
Author Summary Congenital CMV is a leading cause of mental retardation and deafness in newborns. An effective vaccine against congenital CMV remains an elusive goal. HCMV encodes a pentameric glycoprotein complex (PC) necessary for tropism to epithelial, endothelial and myeloid cells. Given the structure of the placenta, the viral PC is considered important for congenital infection and potentially an important neutralizing antibody vaccine target antigen. The guinea pig, with a placenta structure similar to humans, is the only small animal model for congenital CMV. In this paper, GPCMV is shown to encode a homolog PC which enables epithelial tropism on a newly established cell line. It is likely that the GPCMV PC improves virus tropism to various cell types as PC positive virus has improved virus pathogenicity and congenital infection in vivo. This study lays important foundations for development of a PC based intervention strategy against congenital CMV in this model.