Influence of human cytomegalovirus glycoprotein O polymorphism on the inhibitory effect of soluble forms of trimer- and pentamer-specific entry receptors

Human cytomegalovirus (HCMV) envelope glycoprotein complexes, gH/gL/gO-trimer and gH/gL/UL128L-pentamer, are important for cell-free HCMV entry. While soluble Nrp2-Fc (sNrp2-Fc) interferes with epithelial/endothelial cell entry through UL128, soluble PDGFRα-Fc (sPDGFRα-Fc) interacts with gO thereby inhibiting infection of all cell types. Since gO is the most variable subunit we investigated the influence of gO polymorphism on the inhibitory capacities of sPDGFRα-Fc and sNRP2-Fc. Accordingly, gO genotype 1c (GT1c) sequence was fully or partially replaced by gO GT2b, GT3, GT5 sequences in TB40-BAC4-luc background. All mutants were tested for fibroblast and epithelial cell infectivity, for virions9 gO and gH content, and for infection inhibition by sPDGFRα-Fc and sNrp2-Fc. Full-length and partial gO GT swapping may strongly alter the virions9 gO and gH levels associated with enhanced epithelial cell infectivity. All gO GT mutants except recombinant gO GT1c/3 displayed a near-complete inhibition at 1.25 µg/ml sPDGFRα-Fc on epithelial cells (98% versus 91%) and all on fibroblasts (≥ 99%). While gO GT replacement did not influence sNrp2-Fc inhibition at 1.25 µg/ml on epithelial cells (96%-98%), it rendered mutants with low gO levels moderately accessible to fibroblasts inhibition (20%-40%). In contrast to the steep sPDGFRα-Fc inhibition curves (slope >1.0), sNrp2-Fc dose-response curves on epithelial cells displayed slopes of ~1.0 suggesting functional differences between these entry inhibitors. Our findings suggest that targeting of gO-trimer rather than UL128-pentamer might be a promising target to inhibit infectivity independent of the cell type, gO polymorphism, and gO/gH content. However, intragenic gO recombination may lead to moderate resistence to sPDGFRα-Fc inhibition.