Chaperon and adjuvant activity of hsp70: different natural killer requirement for cross-priming of chaperoned and bystander antigens.

Heat shock proteins (HSP) convey both chaperoned propeptide and danger signal to dendritic cells (DC). However, few studies have compared the two activities. Using a murine inducible hsp70 secreted by cells distinct from those providing the tumor antigens, we showed that hsp70 exerts efficacious adjuvant effects toward DC cross-priming. Hsp70 induces DC maturation and phagocytosis of cellular debris both in vitro and in vivo, which are conducive to CTL response to chaperoned and nonchaperoned antigens. Whereas the ability of hsp70 to induce cross-presentation of chaperoned peptides is natural killer (NK) independent, the adjuvant activity requires NK cells at the site of DC-hsp70 interaction to induce CTL response and therapeutic effect against lung metastases. However, although bystander activity provides equal CTL induction, the best therapeutic efficacy rests on cell vaccine secreting hsp70 that combines chaperoned antigen and danger signal within the same cell.