RT-PCR of sorted CD14⁺ and CD3⁺ CB cells. Five hundred sorted cells from each subset were processed for RT-PCR as described in Materials and Methods. The cDNA from each subset was aliquoted and amplified by PCR in separate reactions using primers for FLT3 (lanes 3 and 4) and β2-microglobulin (lanes 6 and 7), respectively. Lane 1, molecular-weight marker. Lane 2, FLT3 RT-PCR product from NALM-1 cells (positive control). Lane 3, cDNA corresponding to CD14⁺ monocytes. Lane 4, CD3⁺ T cells. Lane 5, FLT3 RT-PCR of K562 cells (negative control). Lanes 6 and 7, RT-PCR of CD14⁺ and CD3⁺ cells, respectively, using primers recognizing two different exons of the β2-microglobulin gene.