(A) X-inactivation patterns with the HUMARA assay and BCR/ABL mRNA expression in MNC, CD34⁺HLA-DR⁺, CD34⁺HLA-DR⁻, and DR⁻ derived LTC-IC in steady-state marrow in ECP CML. HUMARA PCR and BCR/ABL and β-actin RT-PCR reactions were performed as described in Materials and Methods. Results are shown for one experiment in marrow from UPN 1. HUMARA PCRs are shown without (−) and with (+) prior exposure toHpaII and Cfo I restriction endonucleases. Shadow bands are due to slippage of Taq polymerase. BCR/ABL yielded positive signals in the MNC and DR⁺ fraction and in one LTC-IC–derived colony, after hybridization with a B3A2 probe. No positive signal was detected in the other samples. The housekeeping gene β-actin was used as an internal control for the presence of mRNA. (B) HUMARA analysis and BCR/ABL mRNA expression in mobilized PB in ECP CML. Results are shown for day 3 harvest from UPN 1. HUMARA PCR and BCR/ABL and β-actin RT-PCR reactions were performed as described in Materials and Methods. HUMARA was performed without (−) and with (+) predigestion with the methylation-sensitive endonucleases HpaII andCfo I. MNC displayed monoclonal patterns and BCR/ABL mRNA positivity, whereas CD34⁺HLA-DR⁺ and CD34⁺HLA-DR⁻ progenitors were polyclonal and BCR/ABL mRNA⁻. The erythroleukemic cell line K562 served as a positive control for BCR/ABL (B3A2) expression. The housekeeping gene β-actin was used as a control for the presence of mRNA.