The composition of the carbon source and the time of cell harvest are critical determinants of the final yield of human papillomavirus type 16 L1 protein produced in Saccharomyces cerevisiae.

Abstract

The L1 protein is a major component of prophylactic human papillomavirus (HPV) vaccines. Little effort has been made to improve the productivity of L1 protein by optimizing cell culture conditions although the high price of the vaccines is considered one of the factors limiting its widespread use. In biopharmaceutical manufacturing, strategies for optimizing culture conditions tend to focus on improvements in upstream processing rather than final yield because of the complexities of purification procedures. In this study, we investigated L1 protein productivity as a function of the composition of the carbon source and the point of cell harvesting in the Saccharomyces cerevisiae expression system. We performed 44 series of purifications and achieved the highest productivity when the cells were cultured in a medium composed of 7% glucose and 1% galactose for 144 h. The final yield of L1 protein was markedly affected by the glucose: galactose ratio and the point at which cells were harvested: there was a 15-fold difference between the lowest and highest yields. We believe that optimization of the composition of the carbon source and the time of cell harvest have considerable potential for reducing the cost of production of HPV L1 protein.