Hansenula polymorpha expressed heat shock protein gp96 exerts potent T cell activation activity as an adjuvant

Previous studies together with ours showed that heat shock protein gp96 as an adjuvant induces antigen specific T cell responses against cancer and infectious diseases. However, at present there is no efficient method to obtain high amount of full-length gp96 by in vitro expression. Here, we used the yeast Hansenula polymorpha as an efficient host for gp96 recombinant protein production. The transformant clones with highly expressed recombinant proteins were screened and selected by measuring the halo size which indicates enzymatic hydrolysis of starch in the medium. High-level production of gp96 (around 150mg/mL) was achieved by using high-cell density fed-batch cultivations. We showed that peptide binding of the recombinant protein has similar specificity and intrinsic binding parameters as that of the native gp96. We next examined the self-assembly properties and high-order structures of the recombinant protein. Moreover, the H. polymorpha expressed recombinant gp96 can effectively induce HBV-specific CTL response in immunized mice while Escherichia coli-expressed gp96 cannot. Our results therefore may provide bases for structure and functional studies of gp96 and thereby potentially expedite the development of gp96-based vaccines for immunotherapy of cancer or infectious diseases.