Strain Agnostic Influenza Virus Propagation in a Serum-Free, Suspension-Adapted MDCK Cell Line

The continuing circulation and evolution of seasonal influenza viruses remains a public health and socioeconomic threat on a global scale. Viral surveillance and vaccination of the public have been relied upon to confer and boost immunity in the population. Traditionally, influenza strains are propagated in embryonated chicken eggs, but this process remains imperfect and subject to genetic drift of the virus and a reliable source of eggs. Cell culture-based propagation of influenza virus has recently been commercialized, but this method has been difficult to adapt to lab settings.

Madin-Darby canine kidney (MDCK) cells were adapted to thrive in serum-free growth in suspension. The suspension MDCK (sMDCK) line was characterized by measuring replication and viability during routine passage and infection. Fifteen different influenza strains were propagated using this model and were assayed to determine hemagglutination and plaque forming units and compared to influenza strains grown in adherent cell culture. Microneutralization tests were also conducted to ensure each strain maintained the proper antigenicity.

The cell line was successfully adapted to serum-free growth in suspension. For each virus strain, the sMDCK platform successfully produced a virus stock in 1-3 days. Additionally, sMDCK progeny virus maintained its antigenicity based on neutralization assays.

This simple, scalable method was used to reliably propagate 15 influenza strains with the elimination of costly reagents and animal serum. The results are comparable to traditional methods, and the protocol presented in this work could be adapted to nearly any laboratory setting.