TRANSCRIPTION OF TAL-1, A PUTATIVE ONCOGENE PLAYING AN IMPORTANT ROLEIN CHILDHOOD T-ALL, CAN BE SHOWN IN NORMAL PERIPHERAL-BLOOD CELLS BY A HIGHLY SENSITIVE RT-PCR ASSAY

Rearrangement of the tal-1 gene is the most frequent clonal marker in childhood T cell acute leukemia. Previously, tal-1 mRNA expression has been observed only in cells of the erythroid, most cell, and megakary ocytic lineages and in blastic lymphoid cells of normal bone marrow, n ot in normal lymphocytes or monocytes of the peripheral blood (PB). In this study we addressed the question of tal-1 expression during norma l hematopoietic development by performing reverse transcription-polyme rase chain reaction (RT-PCR) on RNA from PB cells of 12 healthy donors . Ten of 10 unsorted samples were RT-PCR positive for tal-1 expression . Sorted T cells and monocytes from three donors showed tal-1 RT-PCR p roducts. This is the first direct experimental evidence of tal-1 trans cripts in these two normal PB cell types.