Growth and immunogenicity of foot‐and‐mouth disease virus in baby hamster kidney cells adapted to and continuously grown in a serum‐free chemically defined media

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Abstract
The production of foot‐and‐mouth disease (FMD) virus in baby hamster kidney (BHK) suspension cells grown in serum‐free media for subsequent use in vaccines was attempted because of the limited availability of serum in quantities sufficient for propagation of large amounts of cells, as well as the possible presence of mycoplasma, viral contaminants, and interfering antibodies in sera. Suspension cultures (50 to 600 ml) of BHK‐21 cells adapted to and continually passed in a glutamine‐free autoclavable, chemically defined medium (BHK‐S system) were infected with all seven types of FMD virus. Cells were infected at multiplicities of infection (MOI) ranging from 10−1 to 10−7 plaque‐forming units per cell (PFU/cell). The time course of infectious virus release and the amount of complement‐fixing (CF) antigen produced were then followed. Peak harvest infectivities of approximately 108.5 PFU/ml were obtained from 12 to 24 hr after inoculation, depending on input MOI, and were apparently independent of cell concentration over the range 1.5 to 4.0 million cells/ml; the CF endpoint dilutions increased from 1:12 at the lower cell concentrations to 1:48 at the highest cell concentration. Monovalent and trivalent vaccines have been produced using viruses from the BHK‐S system, inactivated with acetylethyleneimine and emulsified in oil, and the results of tests in steers and guinea pigs are presented.