Physiological factors of growth and susceptibility to virus regulating Vero cells for optimum yield of vaccinia and cloned gene product (β-hCG)

Abstract

Replication of vaccinia virus carrying β-hCG gene at the 'tk' locus was studied in microcarrier culture of Vero cell. The yields of recombinant vaccinia virus and its expressed product (β-hCG) were influenced by the physiological state of the host cell, at which it was infected. Cells infected with the virus between the 3rd and 6th day gave maximum amount of virus and β-hCG in a parallel manner, the yields of which were 2.3×10⁹ pfu per 10⁶ cells and 450 ng per 10⁶ cells, respectively. The yields were reduced by 33-36% in the virus-infected stationary culture of the 8th day. The physiological state of the host cell has been quantified by the cellular activity parameter 'P' (μ(t)/μ_max) in the scale of 1 to 0. The value of 'P' was highest in the exponentially growing culture, which reduced with decline in growth rate. The cellular energy generation has been related with the parameter 'P'. ATP generation was reduced to 55% in the stationary culture on the 8th day (P=0). Also, the adsorption of virus was reduced by nearly 55% in extremely slow growing or stationary culture. Host cells at moderate growth rate (P≥0.15) were found to be optimum for maximizing the yield of viral products.