Seed Virus Testing
As with a cell bank, a virus seed is banked under GMP. A Vaccine virus bank is referred to as the Master Viral Seed (MVS) and Working Viral Seed (WVS). The virus seed is frequently derived from a pure pre-viral seed since the original viral phenotype is likely to have been attenuated by multiple passage or be genetically manipulated by reassortment or recombination since its original isolation. It is prudent to have a viral seed beyond the level used in production to allow for the generation of genotype and phenotypic stability data. The guidance on vaccine virus seeds stresses the importance of extensive characterization of the MVS including: its sequence, and analysis of viral subpopulations and its genetic and phenotypic stability.
The history of the derivation and growth is particularly pertinent to biosafety testing, particularly the adventitious agent testing since it is important to consider the original host, any biological materials used in its derivation including plasmids, parental viruses, the history of any cells including species, that the virus has been passaged through since isolation and the source of any raw materials used such as trypsin or serum. The viral seed has to be tested for agents from all the species that it may have been exposed to.
There are a number of viruses, often difficult to detect, that are considered to be high risk of being present in vaccine seeds and PCR for these “Small Viruses” is recommended. The viruses include Torque teno virus, Bovine parvovirus 2 and Bovine parvovirus 3, Adeno-associated virus 2 and Bovine kobu virus (Aichivirus B), Human bocavirus (Aichivirus A) and Aichivirus C (Porcine kobu virus).
Adeno-associated virus is considered a special case because of the association of AAV with adenovirus and testing for AAV is currently recommended in the Master Cell Bank, the Master Virus Seed Stock, and the final product in adenovirus productions.
Summary of Virus Seed and Harvest Testing
|Assay||Virus Seed||Virus Harvest|
|In Vitro Assay*||+||+|
|In Vivo Assay**||+||-|
*Seed lots prepared using Insect cells should be testing with an in vitro assay which includes an insect cell line other than the production cell line.
**Seeds lots prepared on avian tissues should be tested with an additional in vivo assay using embryonated chickens eggs.