Heat shock/chaperone protein (HSCP)-peptide complexes can access the cross-priming pathways of antigen presenting cells (APCs), and the gp96-associated peptides can be re-presented on APC MHC class I molecules to elicit CD8 + T cell activation. This immunological circuit is thought to provide the functional basis for HSCP function in tumor immunity. Recent findings identifying a 'natural adjuvant' function for HSCPs suggest complementary, or perhaps alternative, mechanisms of HSCP-mediated tumor rejection.