Transmission of cell-associated human cytomegalovirus isolates between various cell types using polymorphonuclear leukocytes as a vehicle

Berenike Braun,Christian Sinzger

doi:10.1007/s00430-021-00713-6

Abstract

Polymorphonuclear leukocytes (PMNs) are regarded as vehicles for the hematogenous dissemination of human cytomegalovirus (HCMV). In cell culture, this concept has been validated with cell-free laboratory strains but not yet with clinical HCMV isolates that grow strictly cell-associated. We, therefore, aimed to evaluate whether PMNs can also transmit such isolates from initially infected fibroblasts to other cell types, which might further clarify the role of PMNs in HCMV dissemination and provide a model to search for potential inhibitors. PMNs, which have been isolated from HCMV-seronegative individuals, were added for 3 h to fibroblasts infected with recent cell-associated HCMV isolates, then removed and transferred to various recipient cell cultures. The transfer efficiency in the recipient cultures was evaluated by immunofluorescence staining of viral immediate early antigens. Soluble derivatives of the cellular HCMV entry receptor PDGFRα were analyzed for their potential to interfere with this transfer. All of five tested HCMV isolates could be transferred to fibroblasts, endothelial and epithelial cells with transfer rates ranging from 2 to 9%, and the transferred viruses could spread focally in these recipient cells within 1 week. The PDGFRα-derived peptides IK40 and GT40 reduced transfer by 40 and 70% when added during the uptake step. However, when added during the transfer step, only IK40 was effective, inhibiting transmission by 20% on endothelial cells and 50–60% on epithelial cells and fibroblasts. These findings further corroborate the assumption of cell-associated HCMV dissemination by PMNs and demonstrate that it is possible to inhibit this transmission mode.

Highlights

The human cytomegalovirus (HCMV) belongs to the family of herpesviruses and is widespread in the population
While the HCMV-antigenemia phenomenon has already been simulated in cell culture, demonstrating uptake of pp65 Ag by Polymorphonuclear leukocytes (PMNs) from monolayer cultures infected with HCMV laboratory strains [18, 19, 21, 41], it has not yet been formally demonstrated whether PMNs can take up strictly cell-associated HCMV isolates from infected cultures and transfer them to uninfected cell layers
The data obtained in this study provide formal evidence that PMNs can transfer cell-associated HCMV isolates from infected fibroblast cultures to various uninfected cultures

Summary

Introduction

The human cytomegalovirus (HCMV) belongs to the family of herpesviruses and is widespread in the population. Low-passage isolates were included in these analyses, formal proof was missing that they were still growing in a cell-associated manner It is still unclear whether PMNs can take up HCMV from infected cells that do not release infectious progeny. While attachment and penetration of cell-free virus into target cells can be inhibited by soluble derivatives of the cellular HCMV receptor platelet-derived growth factor receptor alpha (PDGFRα) [29,30,31], it is unclear whether any of these derivatives can inhibit isolates that spread strictly cell-associated Their mode of action resembles inhibition by neutralizing antibodies (nAbs), which can bind to epitopes on the surface of virions, prevent their entry into the target cell, and thereby completely inhibit infection with cell-free HCMV [32]. Smaller 40-mer fragments of the extracellular domain of PDGFRα were identified as entry inhibitors [29], and it is tempting to assume that they might have an impact on cell-associated transmission

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Conclusion