Preclinical studies on detection of circulating melanoma cells in patients: Telomerase as a recognition marker of malignancy

Preclinical studies based on a "simulation design", were performed with cultured melanoma cells prelabeled with Cr-51, added to normal blood and subjected to separation and recognition steps. Mononuclear cells (MNC) were isolated on ficoll-hypaque gradient, and melanoma cells were separated from lymphocytes using anti-CD45 immunomagnetic beads. Malignant cells were then recognized by measuring telomerase activity (TRAP and TRAP-EUSA assays). It was found that: (a) recovery of prelabeled cells present in MNC did not exceed 75%; (b) further recovery of prelabeled cells after separation from lymphocytes did not exceed 68%. Therefore, the overall recovery of prelabeled cells did not exceed 48%; (c) the entire procedure was able to reliably detect as few as 30 malignant cells added to normal blood, providing a telomerase signal significantly higher than that found in absence of melanoma cells. These results furnish the technical bases.for developing a tumor detection assay in the blood of melanoma patients.