Isolation of processed, H-2Kb-binding ovalbumin-derived peptides associated with the stress proteins HSP70 and gp96

Stress-induced proteins or heat shock proteins (HSP) of 96 kDa mass (gp96) and 70 kDa mass (HSP70) have been shown previously to elicit specific immunity to tumors from which they are isolated. This immunity is dependent on CD8+ cytotoxic T cells which are readily primed in vivo by immunization with HSP. The immunization capacity of HSP relies on their ability to bind antigenic peptides. Here we show that HSP70 and gp96 preparations purified from the ovalbumin (OVA)-transfected cell line E.G7 are associated with processed H-2Kb-binding peptides which contain the major H-2Kb-associated epitope SIINFEKL (OVA257-264). Our data show for the first time in the well-defined OVA antigen system that not only endoplasmic reticulum-resident HSP, like gp96, are associated with processed antigenic peptides but that also the cytosolic HSP70 protein forms complexes with major finally processed MHC-binding epitopes.