RT-PCR products from CD34⁺Lin⁻ cells, unilineage erythroid differentiating cells and single sorted cells using primers recognizing lineage-specific markers linked to differentiation. Autoradiographs are shown. At days 0, 6, and 12, the mRNA from 100 cells was isolated and processed as described in Materials and Methods. The cDNA derived from 100 cells was divided into 7 aliquots and each aliquot was processed for RT-PCR using primers recognizing CD7 (pre-T/T cells), CD13 (myelomonocytic cells), CD14 (monocytic cells), CD16 (NK cells), CD19 (pre-B/B cells), GPA (erythroid cells), or β2-microglobulin (β2m). Day 0: freshly purified CD34⁺Lin⁻ cells isolated by positive/negative selection (MiniMACS). Day 6: CD34⁺Lin⁻ cells from unilineage erythroid cultures as described in Materials and Methods. Day 12: CD34⁺Lin⁻ cells induced to unilineage erythroid differentiation. Control: RT-PCR sensitivity testing. Each hybridization signal represents RT-PCR products from mRNA corresponding to 0.5 cell equivalents of flow cytometry sorted cells that expressed CD7, CD13, CD14, CD16, CD19, or GPA. The outermost right band represents the β2-microglobulin RT-PCR product of a single sorted CD34⁺CD38⁻ cell. Note the absence of nonerythroid CD7, CD13, CD14, CD16, and CD19 transcripts in erythroid differentiating cells at days 6 and 12 of unilineage erythroid culture.