mAbs were prepared as previously described [10 (link), 11 (link)]. Briefly, female Balb/c mice (6–8 weeks old) were injected i. p. with 100 μg of KLH conjugated with peptide PF corresponding to the PAX3-FOXO1 translocation region aa 100-117 (TIGNGLSPQNSIRHNLSL) in Freund’s adjuvant (Sigma) followed by additional i.p. injections of 100 μg of purified KLH peptide in Freund’s adjuvant at two weeks intervals. Two weeks after the third injection, one mouse received i.p. and i.v. boosts of purified KLH peptide in PBS for 3 consecutive days. A day after the final boost, the spleen of the mouse was removed and fused with the myeloma cell line P3x63Ag8.653 as previously described using 50% PEG with 5% DMSO. Fused cells were resuspended in HY media supplemented with 20% FBS, HAT, and 1× Nutridoma-CS (Roche) and seeded into 96-well plates. Hybridoma colonies were screened by ELISA for secretion of mAbs that bound to ovalbumin coupled peptide. Hybridomas secreting mAbs of interest were subcloned twice by limiting dilution and final hybridoma clones were isotyped using a murine antibody isotyping kit (Roche).