Development of a transient mammalian expression process for the production of the cancer testis antigen NY-ESO-1

The cancer-testis antigen NY-ESO-1 is expressed in a wide range of tumor types while normal tissue expression is restricted to germ cells. It is highly immunogenic, frequently eliciting spontaneous humoral and cellular immune responses in patients with advanced tumors expressing the protein. A series of different NY-ESO-1 vaccines are currently being explored in early clinical trials worldwide. We have developed a reproducible process for the transient expression of full-length NY-ESO-1 in mammalian cells. Either Chinese hamster ovary (CHO) DG44 or HEK 293 cells were transfected with NY-ESO-1 DNA using polyethylenimine. NY-ESO-1 was expressed intracellularly as a histidine-tagged protein in agitated suspension cultures at volumes to 400 rut at levels up to 30 mg/L as estimated in crude cell lysates by Western blot. The protein was purified by immobilized metal affinity chromatography (IMAC) after detergent lysis and was shown to be reactive with sera from patients with tumors expressing NY-ESO-1.