Down regulation of Qa gene expression on drug-modified tumor cells.

BACKGROUND: Mouse leukemia, L1210, strongly enhances its immunogenicity following in vivo treatment with 5-(3-3'-dimethyl-1-triazeno) imidazole-4-carboxamide (DTIC). Previous experiments have shown that transformed cells elicit a cell-mediated response accountable for rejection and resistance to a subsequent injection of parental tumor into a syngeneic host. L1210 expresses classical H-2 class I molecules, and since it has been shown that DTIC treatment does not modify the expression of these molecules, this is a suitable model to study nonclassical class I antigens, such as Qa2 glycoproteins, and their potential role in tumorigenicity. METHODS: Cloned cells from L1210 were treated with DTIC and then H-2D, and Qa 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 radioimmunoassay and immunofluorescent staining and was confirmed by FACS and 2D-gel analysis. The presence or the absence of Qa antigens on tumor cells could thus be involved in tolerance or rejection of tumor cells in syngeneic animals.

Functional studies of H-2k-like epitopes on DTIC treated and untreated L1210 (H-2d) clones.

Following 'in vivo' treatment with 5-(3-3'-dimethyl-1-triazeno)imidazole-4-carboxamide (DTIC), murine leukemic cells acquire new antigenic specificities not detectable on parental cells and responsible for the rejection of the tumour by syngeneic hosts. 'In vivo' and 'in vitro' experiments pointed out an immunological cross reactivity between DTIC treated and untreated lines. Furthermore, specific CTLs raised against DTIC treated L1210 tumour cells (H-2d) were cytotoxic for H-2k target cells. The aim of this study is to investigate whether the H-2k cross reactivity displayed by L1210/DTIC is related to the drug treatment rather than due to an antigen already present in the parental line and maintained after treatment. Cloned cells from L1210, obtained by limiting dilution 'in vitro', were recloned 'in vivo' and then treated with DTIC. Syngeneic and allogeneic CTLs raised 'in vitro' against parental and treated clones showed lytic activity against H-2k target cells. Treated and untreated clones were then checked for the presence of H-2k-like determinants using monoclonal antibodies. One of these, HB-53 (IgG2bKkDk) was highly positive with all the clones tested in binding assay using iodinated Fab anti-mouse Ig, fluorescence and FACS analysis. Others displayed a low reactivity against both treated and untreated clones without significant differences. After neuraminidase treatment of two clones (D and D/DTIC), the H-100.5 (anti H-2Kk)-reactive epitope was dramatically exposed on the DTIC tumour cells but not on the parental clones. These data suggest that the H-2k cross reactivity is related to the presence of a TAA that is maintained after treatment.(ABSTRACT TRUNCATED AT 250 WORDS)