Detection of MLL-AF4 fusion transcripts in pediatric ALL BM specimens by standard and nested RT-PCR. RNA samples from primary leukemic cells of 32 (A, 14 patients; B, 18 patients) newly diagnosed pediatric ALL patients were examined forMLL-AF4 fusion transcript expression by standard RT-PCR (A1 and B1) and nested RT-PCR (A2 and B2). PEDS 76 shown in A.2 was a normal diploid case (see Tables 3 and 6). PEDS 87 shown in B.1. and B.2 was a hyperdiploid t(4;11) ALL case and PEDS 58 shown in B.2. was a hyperdiploid non-t(4;11) case with del(11)(q23) (see Tables 3 and 6). Amplified mRNA from the RS4;11 cell line was used as a positive control (POS CON). Negative controls were PCR products from RNA-free reaction mixture 1 plus reaction mixture 2 (NEG CON 1) and reaction mixture 1 plus DNA polymerase-free reaction mixture 2 (NEG CON 2).