Evaluation of the replication efficiency of human noroviruses in salivary gland cells

Neda Nasheri, Health Canada (HC)

Jennifer Harlow, Simon Briggs, Katherine Pham, Neda Nasheri Bureau Microbial Hazards, Health Canada Microbiology and Immunology Department, University of Ottawa

Entry and Replication

Human noroviruses are notoriously difficult to culture, which has hindered vaccine and antiviral development. Current protocols, such as employment of human intestinal enteroids and the B-cell culture system, have limitations in efficiency, reproducibility, and scalability. It has been recently shown that noroviruses can infect salivary glands, and transformed salivary gland cell lines, NS-SV-TT-DC (ductal) and NS-SV-TT-AC (acinar), allow for replication and passaging of norovirus GII.4 Sydney. Herein, we examined whether we can independently observe viral replication in salivary gland cells and if other strains of human norovirus can replicate in these cells. For this reason, we first evaluated the replication of 25 norovirus strains from 7 genotypes in NS-SV-TT-DC cells by either infecting them with vesicle-cloaked viruses or total viruses in filtrates. Success in replication was measured by an increase in the viral titers at 96 hours post infection (hpi) compared to 6 hpi. Low levels of viral replication were observed for 11 samples and vesicle isolation did not improve viral replication. Next, we screened 50 norovirus samples from 9 genotypes, and 13 isolates demonstrated over a two-fold higher viral titers at 96hpi compared to 6 hpi. Viral replication reached to 10 fold (1 log) in two of the isolates. We observed that the initial viral load in the samples positively affects replication efficiency, and successful replication was achieved for multiple genotypes. Then, we examined whether serial passaging of the isolates would improve viral replication. Since working with NS-SV-TT-DC is relatively easy and could be performed routinely, they have the potential to be employed to study various aspects of viral replication and allow for high-throughput drug screening and to support vaccine development.