Objective: grp170 is a major ER-resident molecular chaperone that assists protein folding, transport, and trafficking. grp170 is induced by stress conditions such as hypoxia. Like several other chaperones grp170 can induce both innate and adaptive immune responses against the tumor from which it was purified. Although grp170 is an ER resident chaperone it can be modified into a secretable form by deletion of the C-terminal ER-retention signal that is normally recognized by ERD2 receptor in post-ER compartment and serves to retrieve grp170 back to ER. In the studies presented here we use a grp170 secreting cell system and address two points: 1) Can tumor cells engineered to secrete grp170 generate an anti-tumor specific immune response? 2) Does the secreted grp170 bind to and co-transport, out of tumor cells full-length proteins that may play a role in the anti-tumor immune response?

Methods and Results: We demonstrated here that targeting grp170 to the extracellular environment has immunological consequences resulting in tumor rejection that is CD8+ dependent. We also showed, using gel electrophoresis, western blot and mass spectrometry techniques, that secreted grp170 chaperones several full-length proteins into the extracellular environment including the envelope protein gp70 of the Murine leukemia virus (MuLV), other chaperones such as gp96 and hsp70, MHC class I molecules and a subunit of the proteasome suggesting the presence of a multiprotein complex on the intrinsic antigen processing and quality control pathways.

Conclusions: Together, these results indicate that immunization of animals with grp170-secreting tumor cells results in rejection of the tumor by induction of antigen-specific, CD8-dependent immune responses. Furthermore, the secreted grp170 is able to deliver full-length tumor antigens to the tumor microenvironment, thus making them available for uptake by antigen presenting cells (APCs) to initiate a tumor-specific immune response. This approach has the potential of being exploited as a tumor-specific vaccine in tumors of various histological origins.