Induction of innate immunity signaling pathways in MDCK cells and their relevance in a bioprocess for influenza vaccine production

Cell culture based processes are increasingly used for influenza vaccine production. Besides a high demand of seasonal vaccines, pandemic outbreaks challenge existing production capacities. A recurring problem in vaccine manufacturing is the difficulty to grow different seasonal influenza A virus strains to equally high titers. Hence, the cellular production system has to be more thoroughly investigated for further process optimization. Striking differences were found in the replication behavior of two influenza A virus strain variants (A/PR/8/34), supplied by either the National Institute for Biological Standards and Control (NIBSC) or the Robert Koch Institute (RKI). Differences between these two variants regarding proteome alterations, apoptosis induction and survival of infected cells were observed. To elucidate possible causes of these differences the induction of cellular signaling pathways involved in antiviral defense and apoptosis, such as type I interferon (IFN) signaling, was analyzed. Interestingly, all monitored signaling cascades were induced significantly stronger by the PR8-NIBSC variant shown to replicate poorly [1]. However, the inhibition of the IFN system by over-expression of viral antagonistic proteins had no significant impact on final virus titers. On the other hand, stimulation of innate cellular immunity by IFN-containing medium slowed down initial virus replication, but failed to reduce final virus yields. This can partially be ascribed to a lacking antiviral activity of the IFN-induced Mx proteins of the production cell line (Madin-Darby canine kidney) used [2]. Overall, innate immunity seems to be of only minor importance for virus yields of the bioprocess investigated. Nevertheless, observations regarding the induction of cellular signaling pathways allow interpreting alterations in cellular proteome and apoptosis induction previously found. [1] Heynisch B, Frensing T, Heinze K, Seitz C, Genzel Y, Reichl U. Differential activation of host cell signalling pathways through infection with two variants of influenza A/PR/8/34 (H1N1) in MDCK cells. Vaccine (submitted) [2] Seitz C, Frensing T, Hoper D, Kochs G, Reichl U. High yields of influenza A virus in Madin-Darby canine kidney cells are promoted by an insufficient interferon-induced antiviral state. J Gen Virol Jul;91(Pt 7):1754-63