ENHANCEMENT OF ANTITUMOR IMMUNITY IN SYNGENEIC MICE AFTER MHC CLASS-II GENE TRANSFECTION

The relationship between tumorigenicity and expression of MHC class II molecules in a class II-negative murine leukaemia cell line (LBC) was studied. Analysis of structural DNA sequences encoding MHC class II p roteins was performed by Southern blot with DNA isolated from both the original LB tumour and LBC cell line, digested with EcoRI, BamHI and HindllI and hybridised with specific probes for I-A alpha(d) and I-A b eta(d) chains. Similar patterns were obtained For LB, LBC and normal B ALB/c lymphocytes. In vitro treatment with IFN-gamma (20-1000 IU ml(-1 )) failed to induce the expression of MHC class II antigens in LBC cel l line. LBC cells were tri-transfected by a liposome-mediated protocol with I-A alpha(d), I-A beta(d) genes and pSV2neo. Cells were selected for growth in medium containing Geneticin (G418). Surviving transfect ants were cloned and three I-A(+) clones were obtained after 20 days ( LBCT cells). Syngeneic mice inoculated with 1.0 x 10(3) LBCT (I-A(+)) cells failed to develop a tumour, whereas the DT50 of mice injected wi th 1.0 x 10(6) LBCT cells was three limes the value for mice injected with LBC cells (I-A(-)). Furthermore, specific CTL response against tu mour cells was significantly enhanced upon priming with irradiated LBC -transfected cells (27 +/- 2%) compared with irradiated LBC cells (15 +/- 1.5%) in a 4 h Cr-51-release assay. It is suggested that neoexpres sion of MHC class II molecules enhances anti-tumour response by transf orming tumour cells into professional antigen-presenting cells (APCs), which may be used to Improve tumour-specific immunity in the autologo us host.