Dana Luu

Introduction. Human cytomegalovirus (HCMV) establishes a life-long infection in more than 70% of the population. HCMV has multiple strains and has the ability to infect different types of cells, meaning it can be found in a variety of tissues. HCMV is latent, and its reactivation causes severe morbidity and mortality, especially in immunosuppressed individuals, and may contribute to retinitis, gastroenteritis, and encephalitis.^1,2,3 In addition, it is the most frequent cause of congenital infection and of non-hereditary hearing loss and neurodevelopmental disabilities in the developing world.⁴ While few cell receptors have been identified, many remain elusive. Discovery of new receptors, such as OR14I1, is significant for understanding the mechanisms of viral entry and developing antivirals and vaccines.^3,5 Methods. Two parallel genome-wide CRISPR screens using either epithelial-tropic TB40E infection of ARPE-19 retinal epithelial cells through the pentamer complex (PC) or fibroblast-tropic AD169 infection of human embryonic lung (HEL) fibroblasts through the trimer complex (PC) were used to identify host factors for HCMV infection. Cells expressing Cas9 and theGeCKO v.2 sgRNA library were exposed repeatedly to HCMV for 3 months. Cells with sgRNA-induced resistance to HCMV underwent next-generation sequencing (NSG) to select high-confidence candidates that scored with ≥3 unique sgRNAs, each with ≥20 NGS reads. A review of candidates found solely in the epithelial cell screen revealed OR14I1. ARPE-19 and HEL cells +OR14I1/ -OR14I1 were then subjected to the lab-adapted virions and assessed for HCMV tropism by qPCR.³ Results. There was a reduction of TB40E virus binding to OR14I1-deficient epithelial cells, but not complete blockage, indicating OR14I1 is required for optimal binding. However, loss of the viral PC did not affect HCMV infection of fibroblasts, suggesting OR14I1 receptor is not required for the AD169 strain to infect fibroblasts. Manipulating the most N-terminal peptide of OR14I1 receptor also prevented the virus from binding and infecting the cells and limited its long term replication. Conclusion. HCMV entry in epithelial and endothelial cells is vital for virus proliferation, disease progression, and persistence.⁶ The PC was identified as being required for epithelial cell infection and tropism, and the majority of neutralizing antibody responses are directed against this.³ Identification of a peptide in OR14I1 blocking HCMV provides insight for potential avenues of treatment, however, more research is needed to understand the exact mechanism of HCMV transmission and replication among different cell and tissue types.^3,6,7

1. Kschonsak M, Rougé L, Arthur CP, et al. Structures of HCMV Trimer reveal the basis for receptor recognition and cell entry. Cell. 2021;184(5):1232-1244.e16. doi:10.1016/j.cell.2021.01.036
2. Gardner TJ, Tortorella D. Virion Glycoprotein-Mediated Immune Evasion by Human Cytomegalovirus: a Sticky Virus Makes a Slick Getaway. Microbiology and Molecular Biology Reviews. 2016;80(3):663-677. doi:10.1128/mmbr.00018-16
3. E X, Meraner P, Lu P, et al. OR14I1 is a receptor for the human cytomegalovirus pentameric complex and defines viral epithelial cell tropism. Proceedings of the National Academy of Sciences. 2019;116(14):7043-7052. doi:10.1073/pnas.1814850116
4. Fowler KB, Ross SA, Shimamura M, et al. Racial and Ethnic Differences in the Prevalence of Congenital Cytomegalovirus Infection. The Journal of Pediatrics. 2018;200:196-201.e1. doi:10.1016/j.jpeds.2018.04.043
5. Kschonsak M, Rougé L, Arthur CP, et al. Structures of HCMV Trimer reveal the basis for receptor recognition and cell entry. Cell. 2021;184(5):1232-1244.e16. doi:10.1016/j.cell.2021.01.036
6. Martinez-Martin N, Marcandalli J, Huang CS, et al. An Unbiased Screen for Human Cytomegalovirus Identifies Neuropilin-2 as a Central Viral Receptor. Cell. 2018;174(5):1158-1171.e19. doi:10.1016/j.cell.2018.06.028
7. Plotkin SA, Boppana SB. Vaccination against the human cytomegalovirus. Vaccine. 2019;37(50):7437-7442. doi:10.1016/j.vaccine.2018.02.089