Molecular genetics of influenza virus haemagglutinin production: Developing a rational basis for optimising pandemic vaccine yield

The influenza group at NIBSC has been closely involved in influenza vaccine virus development, standardisation and control for decades. More recently, we have adopted a reverse genetics system (Fodor at al., 1999; Nicolson et al., 2005) that allows the rapid generation of vaccine reference viruses. Using this technology, we have generated vaccine reference viruses based on highly pathogenic avian influenza viruses of subtype H5N1 (Table ) which are recommended by WHO and suitable for vaccine manufacture.

In a pandemic, vaccine will be required as quickly as possible and in large amounts. However, current world-wide influenza vaccine manufacturing capacity falls short of the likely demand for a pandemic vaccine. Therefore, antigen sparing strategies, such as the use of adjuvants, are being actively investigated in many laboratories. Regardless of the latter, any vaccine reference virus should, ideally, be high-yielding, i.e. result in high levels of specific antigen after industrial processing.

Unfortunately, experience using one particular H5N1 vaccine reference virus, NIBRG14 (generated at NIBSC and based on the wild-type virus A/Viet Nam/1194/2004) suggests that final yields of haemagglutinin (HA) antigen are lower than expected when compared to most seasonal (epidemic) vaccine reference viruses. This feature is of obvious concern for a vaccine virus that may be used in a pandemic situation. We do not know, however, whether this property is unique to NIBRG14 or is common among potential H5N1 vaccine reference viruses.

In 2006, we obtained funding from the MRC ( MRC grant G0600509 ) for a 3-year research project aimed at understanding the basis of the low yield of HA antigen of NIBRG14 and at developing a strategy to improve yields of NIBRG14. Moreover, it is hoped that we can find generally applicable mechanisms to improve yields of pandemic vaccine strains.

This work involves the generation of genetically altered vaccine reference viruses based on NIBRG14 and evaluation of their HA yield. We are also working on improving the methods used for analysis of HA yield and HA content of virus preparations. Finally, we will evaluate whether or not any alteration found to increase HA yield of NIBRG14 may also improve yields of other low-yielding vaccine strains.

References:

E. Fodor, L. Devenish, O. G. Engelhardt, P. Palese, G. G. Brownlee, A. García-Sastre. Rescue of Influenza A Virus from Recombinant DNA. J. Virol. (1999), 73: 9679–9682.

C. Nicolson, D. Major, J. M. Wood, J. S. Robertson. Generation of influenza vaccine viruses on Vero cells by reverse genetics: an H5N1 candidate vaccine strain produced under a quality system. Vaccine (2005), 23: 2943–2952.