Quantification of melanoma cell-specific MART-I mRNA in peripheral blood by a calibrated competitive reverse transcription-PCR

Background: Reverse transcription-PCR (RT-PCR) amplification of melanoma ce ll-specific mRNA can detect melanoma cells in the peripheral blood of patie nts with malignant melanoma. We present a method to quantify mRNA coding fo r the melanoma-specific melanoma antigen recognized by T cells #1 (MART-1) in RNA isolated from peripheral blood. Methods: To establish a calibration curve, we measured the concentration of MART-1 mRNA in SK-MEL-28 melanoma cells grown in vitro by competitive RT-P CR. Serial dilutions of these cells were used as calibrators in the assay. The assay was conducted by adding a fixed amount of a RNA internal standard to RNA isolated from either peripheral blood or the calibrators before RT- PCR amplification with MART-1 primers in a nested PCR design. The amount of MART-1 mRNA in blood samples was calculated from the calibration curve. Results: Addition of melanoma cells grown in vitro to blood from healthy do nors demonstrated that the method can detect a single SK-MEL-28 melanoma ce ll in 1 mL of blood (1.5 x 10(-21) mol MART-1 mRNA/mL). MART-1 mRNA was obs erved in 4 of 12 blood samples from patients with malignant melanoma, at co ncentrations of 3-18 x 10(-21) mol MART-1 mRNA/mL of blood. No MART-1 mRNA was detected in blood samples from 25 controls without malignant melanoma. Intra- and interassay CVs were 15% (n = 12; mean = 44 x 10(-21) mol MART-1 mRNA/mL) and 33% (15 samples analyzed in two different analytical runs; mea n = 30 x 10(-21) mol MART-1 mRNA/mL), respectively. Conclusions: Our method is the first competitive RT-PCR assay for quantific ation of melanoma cells in blood samples that compensates for the variation of both the reverse transcription and PCR reactions. The method allows the inclusion of control samples for continuous quality assessment. (C) 2000 A merican Association for Clinical Chemistry.