Quantification of leukaemic cells based on heteroduplex formation of tal-1 gene sequences after PCR coamplification.

Based on the high sensitivity of the polymerase chain reaction (PCR) several assays have already been described which can be applied to monitor minimal residual disease in patients with leukaemia. However, most of these approaches are only qualitative or semiquantitative at best. Moreover, the semiquantitative assays require rather large-scale procedures such as oligonucleotide hybridization or sampling of aliquots during the exponential phase of PCR amplification, which is time consuming and may be error prone. Using the deletion in the tal-1 gene as a clonal marker of malignant cells, which can be found in about 10-25% of T-cell acute lymphoblastic leukaemia, we have developed a rapid and simple PCR assay for the quantification of residual leukaemic cells. The assay is based on heteroduplex formation between standard and template DNA sequences after coamplification of both DNA sequences in the same PCR reaction. The sensitivity of this PCR approach allows the detection of neoplastic cells at frequency of at least 10(-4). Application of such an assay needs not to be restricted to patients harbouring a tal-1 gene deletion. It may easily be adapted to other clonal DNA markers of blast cells and therefore facilitate monitoring of minimal residual disease in many different kinds of leukaemia.