Chemotherapy-induced elimination of MLL-AF4 positive cells in bone marrow specimens from ALL patients. (A) INF1 is an infant t(4;11) ALL case diagnosed in March 1995. (B). PEDS5 is a normal diploid ALL case diagnosed in December 1993. Sequential bone marrow specimens were analyzed for the presence of MLL-AF4 fusion transcripts using nested RT-PCR, as described. Amplified mRNA from the RS4;11 cell line was used as a positive control (POS CON). Negative controls (NEG CON) were PCR products from RNA-free and DNA-polymerase-free reaction mixtures.1-2