DOWN-REGULATION OF QA GENE-EXPRESSION ON DRUG-MODIFIED TUMOR-CELLS

Background: Mouse leukemia, L1210, strongly enhances its immunogenicit y following in vivo treatment with 5-(3-3'-dimethyl-1-triazeno) imidaz ole-4-carboxamide (DTIC). Previous experiments have shown that transfo rmed cells elicit a cell-mediated response accountable for rejection a nd resistance to a subsequent injection of parental tumor into a synge neic host. L1210 expresses classical H-2 class I molecules, and since it has been shown that DTIC treatment does not modify the expression o f these molecules, this is a suitable model to study nonclassical clas s I antigens, such as Qa2 glycoproteins, and their potential role in t umoregenicity. Methods: Cloned cells from L1210 were treated with DTIC and then H-2D, and Ca antigen expression was studied on four clones, before and after xenogenization with DTIC. Results and conclusions: a strong decrease of Qa2 molecule expression was demonstrated by radioim munoassay and immunofluorescent staining and was confirmed by FACS and 2D-gel analysis. The presence or the absence of Ca antigens on tumor cells could thus be involved in tolerance or rejection of tumor cells in syngeneic animals.