RECOGNITION OF THE ALL-SPECIFIC BCR-ABL JUNCTION IN P190(BCR-ABL) BY MONOCLONAL-ANTIBODY ER-FP1

The Ph chromosome, resulting from the t(9;22) translocation, is the mo st frequently observed cytogenetic aberration in acute lymphoblastic l eukemia (ALL). Two genes, bcr and abl, are involved in this translocat ion. As a consequence, parts of the bcr and abl genes are fused, resul ting in chimeric bcr-abl genes encoding chimeric BCR-ABL proteins. Thr ee bcr-abl genes and proteins have been identified: e1-a2 P190(bcr-abl ), b2-a2 P210(bcr-abl), and b3-a2 P210(bcr-abl). Since these chimeric proteins only occur in Ph-chromosome-positive leukemic cells, they are by definition tumor-specific markers. Ph-chromosome-positive ALL is c orrelated with a bad prognosis, therefore the detection of chimeric BC R-ABL proteins is of prime importance in ALL diagnosis. In the present study, we report on the generation of a monoclonal antibody termed ER -FP1, raised against the tumor-specific e1-a2 BCR-ABL junction in P190 (bcr-abl). We show that ER-FP1 reacts highly specifically with e1-a2 p 190(bcr-abl) in different assays. The reactivity of ER-FP1 with e1-a2 P190(bcr-abl) in soluble form was analyzed in an immunoprecipitation a ssay; specificity was confirmed by peptide inhibition studies. Binding of ER-FP1 to e1-a2 P190(bcr-abl) at the single cell level was detecte d by using immunofluorescence techniques. Immunological double-stainin g experiments using ER-FP1 and a monoclonal antibody recognizing all B CR-ABL proteins confirmed the specificity of ER-FP1 for the e1-a2 fusi on point.