A possible maturation pathway of calicivirus particles

The assembly process of feline calicivirus, a representative member of the Caliciviridae, from subunit components in infected cells was monitored by labelling the virus-specific proteins with 3H-leucine for different periods and harvesting cellular extracts at various phases of infection. A series of protein subunit components was detected and the virus assembly process appeared to have occurred in at least two stages. The first stage involved the very rapid aggregation of precursor polypeptides into 5S subunits which possible through several 'unstable' intermediates formed the stable 15S subunit component. The second stage was the association of 15S subunits with the synthesized viral genomes to form the mature infectious FCV particles which sedimented at 170S. Within 30 min of the initiation of protein synthesis, the process of assembly was complete and mature FCV particles appeared in infected cells.     

Validation of the safety of MDCK cells as a substrate for the production of a cell-derived influenza vaccine

Cell culture-based production methods may assist in meeting increasing demand for seasonal influenza vaccines and developing production flexibility required for addressing influenza pandemics. MDCK-33016PF cells are used in propagation of a cell-based seasonal influenza vaccine (Optaflu^®); but, like most continuous cell lines, can grow in immunocompromised mice to produce tumors. It is, therefore, essential that no residual cells remain within the vaccine, that cell lysates or DNA are not oncogenic, and that the cell substrate does not contain oncogenic viruses or oncogenic DNA. Multiple, redundant processes ensure the safety of influenza vaccines produced in MDCK-33016PF cells. The probability of a residual cell being present in a dose of vaccine is approximately 1 in 10³⁴. Residual MDCK-DNA is ≤10 ng per dose and the ß-propiolactone used to inactivate influenza virus results in reduction of detectable DNA to less than 200 base pairs (bp). Degenerate PCR and specific PCR confirm exclusion of oncogenic viruses. The manufacturing process has been validated for its capacity to remove and inactivate viruses. We conclude that the theoretical risks arising from manufacturing seasonal influenza vaccine using MDCK-33016PF cells are reduced to levels that are effectively zero by the multiple, orthogonal processes used during production.