Measurement of SIL-TAL1 fusion gene transcripts associated with human T-cell lymphocytic leukemia by real-time reverse transcriptase-PCR.

TAL1 disruption at 1p32 [del(1p)] is a common rearrangement in the development of T-cell acute lymphocytic leukemia (T-ALL). The del(1p) are usually interstitial 90kb deletions placing TAL1 under control of the SCL interrupting locus (SIL) gene forming the SIL-TAL1 fusion product. A reverse transcriptase real-time PCR assay to quantify SIL-TAL1 fusion genes is described. A SIL-TAL1 fusion gene RNA transcript was built that permitted absolute standard curves to be generated. Sensitivity of the RT-PCR assay was determined to be 10 cells (CEM cell line) in 10(6) human lymphocytes. Peripheral blood lymphocytes from 10 healthy adults and 10 neonates were assayed. None of the samples showed any SIL-TAL1 expression. However, when lymphocytes from three adults were cultured in vitro the SIL-TAL1 transcript was detectable in the RNA isolates. No RAG2 expression was detected in these expanded samples, suggesting that the clones bearing the SIL-TAL1 fusion gene may have existed at low levels prior to the ex vivo expansion.