HEAT-SHOCK-PROTEIN-72 (HSP72), A HYPERTHERMIA-INDUCIBLE IMMUNOGENIC DETERMINANT ON LEUKEMIC K562 AND EWINGS-SARCOMA CELLS

Following non-lethal heat stress (41.8 degrees C) and a recovery perio d at 37 degrees C, the inducible 72kDa HSP (HSP72) is detectable selec tively on the cell surface of human Ewing's Sarcoma (ES) and of leukem ic K562 cells but not on EBV transformed B cells (B-LCL) which were ge nerated from PBL of healthy human volunteers. The HSP72 expression was measured by flowcytometric analysis using a monoclonal antibody (moAb ) that specifically recognizes HSP72, the inducible form of the HSP70 group. The major histocompatibility complex (MHC) class I expression, detected with the moAb W6/32 was not affected by non-lethal heat expos ure and a recovery period at 37 degrees C for 12h: ES cells express MH C class I molecules on about 80% of the cells; K562 cells exhibited no MHC class I expression neither before nor after heat shock. Inhibitio n of RNA- (actinomycin D) or protein-synthesis (cycloheximide) prior t o heat treatment completely inhibits the expression of HSP72 on the ce ll surface of both tumour cells, thus indicating that de novo protein synthesis is required for HSP72 cell surface expression. Since, apart from HSP72, protein synthesis in general is down-modulated by heat sho ck we speculate that HSP72 molecules that are expressed on the cell su rface of tumour cells might be recruited from newly synthesized protei ns. The heat-inducible HSP72 cell surface expression on tumour cells c ould be correlated with an increased sensitivity of leukemic and sarco ma cells to lysis mediated by NX effector cells. The results of cold t arget inhibition assays revealed that histologically different tumour cells (sarcoma and leukemic cells) that were exposed to non-lethal tem peratures have to share a similar if not identical HSP72 immunogenic d eterminant.