Short Lecture : Process development and scale up of a potential cancer vaccine
The trematode Schistosoma mansoni Sm14 antigen was expressed in the yeast Pichia pastoris. Expression of this antigen is part of the larger strategy to use P. pastoris for the production of recombinant proteins for cancer vaccine. The strategy is to treat cancer using cancer-testis antigens which will potential the immune response. Sm14 belongs to a family of fatty-acid binding proteins and appears to play an important role in uptake, transport, and compartmentalization of lipids in S. mansoni. It is currently the focus of various studies for its use as a dual-purpose vaccine against schistosomiasis in humans and fascioliasis in animals, and has been included among the vaccine antigens endorsed by the WHO for phase I/II clinical trials. There is much evidence supporting the association between schistosomiasis and bladder cancer, further increasing the importance of this antigen. The Sm14 gene was codon-optimized for expression in P. pastoris, and placed under regulation of the strong methanol inducible AOX1 promoter. Cells with a Mut+ phenotype were selected and used in fed-batch fermentation with an on-line methanol control system in order to maintain constant methanol levels during induction. Optimal conditions for the expression of Sm14 by P. pastoris were found to be: dissolved oxygen at 40%, temperature of 25oC, pH 5.0, and methanol concentration of 1gL-1. Our results show that a correctly processed Sm14 was secreted into the culture medium at levels of 250 mgL-1. Purification of Sm14 from clarified culture medium was done using a two-step procedure: anion-exchange chromatography followed by hydrophobic interaction chromatography, resulting in >95% purity with a final yield of 40% from the starting cell culture medium. Together, our results demonstrate that soluble Sm14 can be produced and purified in sufficient quantities for use in functionality studies and protective assays against S. mansoni and other helminthes.