Expression and purification of the cancer antigen SSX2: A potential cancer vaccine

SSX2 is a cancer testis antigen expressed in a wide variety of cancers, including synovial sarcoma and melanoma. It holds promise as a potential antigen for cancer immunotherapy. A process for the production of recombinant SSX2 was developed by overexpressing a His-tagged fusion protein of SSX2 in Escherichia coli C41 (DE3). A T-7 promoter system was employed and a plasmid was introduced into the strain to compensate for rare codons in the SSX2 sequence. The production of SSX2 was scaled up to a 2-L fermentation that was operated under fed-batch conditions to improve productivity. After 32 h cultivation, the wet cell mass reached 260 mg/ml, with SSX2 produced mainly as inclusion bodies at a concentration of 1.1 g/L. Urea-solubilized SSX2 was purified by nickel affinity, ion exchange and hydrophobic interaction chromatography. The recovery of SSX2 was 20%, and over 87% purity was obtained with an endotoxin level of 0.11 EU/μg. The purified recombinant SSX2 was characterized by ELISA and was shown to be recognized by human sera that have been reported to carry anti-SSX2 antibodies.