70 KDA HEAT-SHOCK COGNATE PROTEIN IS A TRANSFORMATION-ASSOCIATED ANTIGEN AND A POSSIBLE TARGET FOR THE HOSTS ANTITUMOR IMMUNITY

We previously investigated a novel heat-inducible transformation-assoc iated cell surface Ag that is expressed on the activated H-ras oncogen e-transformed rat fibrosarcoma W31, but not its parental nontransforme d fibroblast WFB. This Ag was detected by mAb 067. Herein, we characte rized the molecular nature of the Ag by using anti-heat shock protein (HSP) mAb. The accumulated data indicated that the cell surface expres sion of Ag was clearly enhanced by several stressors, such as TNF, L-a zetidine-2-carboxylic acid, and sodium arsenite. The immunoprecipitate made with mAb 067 and W31 cell lysates reacted with anti-rat 70 kDa h eat shock cognate (HSC) mAb, TG5E, indicating that 067-defined Ag may be a rat 70 kDa HSC. Because this Ag seemed to be one of the transform ation-associated Ag of WFB, we further studied whether it could play a n important role in the host's anti-tumor immunity. Peripheral T cells of rats primed with live BCG showed cytotoxicity to W31 but not to WF B. Because the possibility existed that HSP may interact with certain populations of T cells, we focused on the reactivity of CD4- CD8- doub le negative T (DNT) cells against 067-defined molecule. DNT cells from spleen and PBL of live BCG-primed rats showed the cytotoxicity agains t W31 cells. This cytotoxicity was completely blocked by mAb 067 and a nti-CD3 mAb. However, it was not blocked by mAb R48B1 and 109, which d etect the MHC class I nonpolymorphic determinant and a target molecule of the cytolysis by poly I:C-induced NK cells, respectively. Furtherm ore, brefeldin A was able to block the cytotoxicity against W31 target s by DNT cells, but not by NK cells. These data suggest that 70 kDa HS C may be a tumor Ag and may act as a presenting molecule perhaps compl exed with cellular peptides to certain DNT cells.