| Abstract
| - Adult T-cell leukemia (ATL) is known to be frequently accompanied by hypercalcemia, but the mechanisms responsible for hypercalcemia in this disorder are not fully understood. We have recently experienced two male patients (25 and 36 yr old) with ATL diagnosed from typical leukemic cells with grooved and folded nucleus, surface marker, anti-ATLA antibody etc. Serum calcium levels of these patients were 16.4 and 21.4 mg/dl, respectively, with no radiological evidence of bone destruction. Peripheral blood leukemic lymphocytes from these patients were purified by the Ficoll-Hypaque method and cultured at a concentration of 1.5 × 106 cells/ml for 3 days on F-10 medium supplemented with 10% fetal calf serum. The supernatant fluids from the cell cultures were bioassayed for bone resorption-stimulating activity (BRSA) by an assay based on the release of 45Ca from prelabeled fetal mouse forearm bones in organ culture according to Raisz's method. The supernatant fluid of cultures from both patients which showed marked BRSA was nondialyzable through a dialysis membrane with a molecular weight cutoff of 3500. Parathyroid hormone and prostaglandins were not detectable in the supernatant fluids of the leukemic cell cultures. In one patient, BRSA was measured twice and found to be decreased to a normal level when the patient was in hematological remission with a normal calcium level (8.3 mg/dl). These results suggest that the hypercalcemia observed in patients with ATL is due, in part, to a bone resorptionstimulating factor which is produced by leukemic T-cell lymphocytes.
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