Holistic process development to mitigate proteolysis of a subunit rotavirus vaccine candidate produced in Pichia pastoris by means of an acid pH pulse during fed-batch fermentation.

To meet the challenges of global health, vaccine design and development must be reconsidered to achieve cost of goods as low as 15¢ per dose. A new recombinant protein-based rotavirus vaccine candidate derived from non-replicative viral subunits fused to a P2 tetanus toxoid CD4(+) T cell epitope is currently under clinical development. We have sought to simplify the existing manufacturing process to meet these aims. To this end, we have taken a holistic process development approach to reduce process complexity and costs while producing a product with the required characteristics. We have changed expression system from Escherichia coli to Pichia pastoris, to produce a secreted product, thereby reducing the number of purification steps. However, the presence of proteases poses challenges to product quality. To understand the effect of fermentation parameters on product quality small-scale fermentations were carried out. Media pH and fermentation duration had the greatest impact on the proportion of full-length product. A novel acidic pH pulse strategy was used to minimize proteolysis, and this combined with an early harvest time significantly increased the proportion of full-length material (60-75%). An improved downstream process using a combination of CIEX and AIEX to further reduce proteases, resulted in maintaining product quality (95% yield).

Oral immunization with rotavirus VP7 expressed in transgenic potatoes induced high titers of mucosal neutralizing IgA.

Rotaviruses (RV) are a common cause of severe diarrhea in young children, resulting in nearly one million deaths worldwide annually. Rotavirus VP7 was the rotavirus neutralizing protein. Previous study reported that VP7 DNA vaccine can induce high levels of IgG in mice but cannot protect mice against challenge (Choi, A.H., Basu, M., Rae, M.N., McNeal, M.M., Ward, R.L., 1998. Virology 250, 230-240). We found that rotavirus VP7 could maintain its neutralizing immunity when it was transformed into the potato genome. Mice immunized with the transformed tubers successfully elicited serum IgG and mucosal IgA specific for VP7. The mucosal IgA titer was as high as 1000, while serum IgG titer was only 600. Neutralizing assays indicated that IgA could neutralize rotavirus. These results indicate the potential usefulness of plants for production and delivery of edible rotavirus vaccines.