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

Abstract

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 PDGFR-Fc (sPDGFR-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 sPDGFR-Fc and sNRP2-Fc.\n\nAccordingly, 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 virions gO and gH content, and for infection inhibition by sPDGFR-Fc and sNrp2-Fc.\n\nFull-length and partial gO GT swapping may strongly alter the virions 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 g/ml sPDGFR-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 g/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 sPDGFR-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.\n\nOur 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 sPDGFR-Fc inhibition.\n\nImportanceHuman cytomegalovirus (HCMV) is known for its broad cell tropism as reflected by the different organs and tissues affected by HCMV infection. Hence, inhibition of HCMV entry into distinct cell types could be considered as a promising therapeutic option to limit cell-free HCMV infection. Soluble forms of cellular entry receptor PDGFR rather than those of entry receptor neuropilin-2 inhibit infection of multiple cell types. sPDGFR specifically interacts with gO of the trimeric gH/gL/gO envelope glycoprotein complex. HCMV strains may differ with respect to the virions amount of trimer and the highly polymorphic gO sequence. In this study, we show that gO polymorphism rather than gO levels may affect the inhibitory capacity of sPDGFR. The finding that gO intragenic recombination may lead to moderate evasion from sPDGFR inhibition is of major value to the development of potential anti-HCMV therapeutic compounds based on sPDGFR.