Quantification of residual disease in chronic myelogenous leukemia patients on interferon-α therapy by competitive polymerase chain reaction

Abstract

Interferon-α (IFN-α) induces cytogenetic responses of variable degree in patients with chronic myelogenous leukemia (CML). We sought to establish the relationship between BCR-ABL transcript numbers measured by competitive 2- step reverse transcription polymerase chain reaction (RT-PCR) and cytogenetic status in CML patients treated with IFN-α. A total of 250 peripheral blood and 55 bone marrow samples from 127 Philadelphia chromosome positive (Ph+) and 6 Ph-/BCR-ABL+ CML patients were investigated. Twenty-one patients were Studied at diagnosis and 112 on treatment. Of the 106 Ph+ patients treated with IFN-α, 24 had a complete cytogenetic response, 21 a partial response, 12 a minor response, 26 no response, and 23 were unknown. Using nested RT- PCR, all 305 samples were positive for BCR-ABL transcripts. To standardize results for variability in RNA and cDNA quantity and quality, we quantified total ABL transcripts in each sample as internal control. The validity of ABL as internal control was shown by comparison with glucose-6-phosphate dehydrogenase transcript levels in 145 samples. The median BCR-ABL transcript numbers (and BCR-ABL/ABL ratios expressed as percentages) were 400/μg RNA (0.04%) in complete responders, 20,500/μg RNA (7.1%) in partial responders, 170,000/μg RNA (21.0%) in minor responders, and 430,000/μg RNA (58.7%) in nonresponders (P < .001). The cytogenetic results correlated with the BCR- ABL transcript numbers (r = .82; P < .0001). We conclude that quantitative PCR with internal controls is a sensitive and reliable method for monitoring patients on IFN- α and reduces the need for repeated marrow investigations.