Comparative neutralizing potencies of antibodies suggest conservation as well as mechanistic differences in human cytomegalovirus entry into epithelial and endothelial cells

Daniel C Freed,Ying Qi,Li He,Xiaohong Cui,Michael A Mcvoy,Tong-Ming Fu,Qiang Ruan,Laura Hertel,Lawrence M Kauvar

doi:10.1186/s12985-020-01320-2

Abstract

Antibody neutralization of cytomegalovirus (CMV) entry into diverse cell types is a key consideration for development of vaccines and immunotherapeutics. CMV entry into fibroblasts differs significantly from entry into epithelial or endothelial cells: fibroblast entry is mediated by gB and gH/gL/gO, whereas both epithelial and endothelial cell entry require an additional pentameric complex (PC) comprised of gH/gL/UL128/UL130/UL131A. Because PC-specific antibodies in CMV-seropositive human sera do not affect fibroblast entry but potently block entry into epithelial or endothelial cells, substantially higher neutralizing potencies for CMV-positive sera are observed when assayed using epithelial cells as targets than when using fibroblasts. That certain sera exhibit similar discordances between neutralizing potencies measured using epithelial vs. endothelial cells (Gerna G. et al.J Gen Virol, 89:853–865, 2008) suggested that additional mechanistic differences may also exist between epithelial and endothelial cell entry. To further explore this issue, neutralizing potencies using epithelial and endothelial cells were simultaneously determined for eight CMV-positive human sera, CMV-hyperimmune globulin, and a panel of monoclonal or anti-peptide antibodies targeting specific epitopes in gB, gH, gH/gL, or the PC. No significant differences were observed between epithelial and endothelial neutralizing potencies of epitope-specific antibodies, CMV-hyperimmune globulin, or seven of the eight human sera. However, one human serum exhibited a six-fold higher potency for neutralizing entry into epithelial cells vs. endothelial cells. These results suggest that epitopes exist that are important for epithelial entry but are less critical, or perhaps dispensable, for endothelial cell entry. Their existence should be considered when developing monoclonal antibody therapies or subunit vaccines representing limited epitopes.

Highlights

In order to determine if qualitative or quantitative discordances exist in the ability of human CMV-positive sera to neutralize CMV entry into epithelial vs. endothelial cells, quantitative green fluorescent protein (GFP)based neutralizing assays were performed as described previously with minor modifications [9, 10]
Fusion occurs at the plasma membrane and is mediated by an interplay between the fusogenic glycoprotein B and a trimeric complex comprised of glycoproteins H, L, and O
Entry into epithelial, endothelial, and certain myeloid lineage cells involves endocytosis followed by endosomal acidification and, in addition to glycoprotein B (gB) and Glycoprotein H (gH)/Glycoprotein L (gL)/Glycoprotein O (gO), requires a pentameric complex (PC) comprised of gH/gL plus UL128, UL130, and UL131A [2,3,4,5]

Summary

Introduction

In order to determine if qualitative or quantitative discordances exist in the ability of human CMV-positive sera to neutralize CMV entry into epithelial vs. endothelial cells, quantitative green fluorescent protein (GFP)based neutralizing assays were performed as described previously with minor modifications [9, 10]. For reasons that remain unclear, PC-specific antibodies often neutralize epithelial or endothelial cell entry with potencies two to three logs higher than those targeting the other complexes [6, 7].

Results

Conclusion