Process development and cGMP manufacturing of a recombinant ricin vaccine: An effective and stable recombinant ricin a-chain vaccine-RVEc Delta TM

Ricin is a potent toxin and a potential bioterrorism weapon with no specific countermeasures or vaccines available. The holotoxin is composed of two polypeptide chains linked by a single disulfide bond: the A-chain (RTA), which is an N-glycosidase enzyme, and the B-chain (RTB), a lectin polypeptide that binds galactosyl moieties on the surface of the mammalian target cells. Previously (McHugh et al.), a recombinant truncated form of RTA (rRTA1-33/44-198 protein, herein denoted RVEa Delta TM) expressed in Escherichia coli using a codon-optimized gene was shown to be non-toxic, stable, and protective against a ricin challenge in mice. Here, we describe the process development and scale-up at the 12 L fermentation scale, and the current Good Manufacturing Practice (cGMP)-compliant production of RVEc Delta TM at the 40 L scale. The average yield of the final purified bulk RVEc Delta TM is approximately 16 g/kg of wet cell weight or 1.2 g/L of fermentation broth. The RVEc Delta TM was >99% pure by three HPLC methods and SDS-PAGE. The intact mass and peptide mapping analysis of RVEc Delta TM confirmed the identity of the product and is consistent with the absence of posttranslational modifications. Potency assays demonstrated that RVEc Delta TM was immunoprotective against lethal ricin challenge and elicited neutralizing anti-ricin antibodies in 95-100% of the vaccinated mice. Published 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011.