MECHANISMS OF ESCAPE FROM CD8(-CELL CLONES SPECIFIC FOR THE HER-2() T)NEU PROTOONCOGENE EXPRESSED IN OVARIAN CARCINOMAS - RELATED AND UNRELATED TO DECREASED MHC CLASS-1 EXPRESSION/

We have developed an in vitro model to study mechanisms by which ovari an tumor cells that over-express the HER-2/neu proto-oncogene escape r ecognition by T-CD8(+). Nine tumor-specific, HLA AZ-restricted T-CD8() clones were isolated from 2 ovarian tumor-specific T-CD8(+) lines de rived from tumorinfiltrating or -associated lymphocytes. Of these, 2 c lones recognized the previously defined HER-2/neu epitope E75 (a.a, 36 9-377) and one recognized the C85 epitope (a.a. 971-979), whereas the specificity of the remaining 6 clones was unknown, Three different tum or escape variants (EVC8, EVC22 and EVC36) were produced by co-culturi ng an ovarian tumor line over-expressing HER-2/neu with these autologo us T-CD8(+) clones. Cell surface expression of HLA A2 was markedly dec reased on all 3 escape variants, relative to the parental tumor line, while no significant decrease in their expression of the HER-2/neu, IC AM-1 or LFA-3 molecules was found. There was a correlation between the level of tumor-specific recognition and HLA A2 expression among the t umor clones isolated from 2 of the escape variants (EVC8 and EVC36). I n contrast, high HLA A2-expressing tumor clones isolated from the EVC2 2 variant, or EVC22 which had regained high HLA A2 expression through IFN-gamma treatment, were not recognized by the HER-2/neu-specific T-C D8(+) clone C-22, No mutations were found in the cDNA or the genomic D NA derived from the PCR product corresponding to a 496 bp fragment inc luding the region coding for the E75 epitope of the HER2/neu gene in t he EVC22 variant. Collectively, this in vitro model underlines the imp ortance of decreased expression of the HLA restriction element for esc ape from tumor-specific T-CD8(+) but also demonstrates that additional mechanisms exist. (C) 1997 Wiley-Liss, Inc.