Return of Human Leukemic Myeloblasts From Blood to Bone Marrow

A patient with acute myeloblastic leukemia received a single intravenous injection of Methotrexate, followed 16 hours later by vincristine. The total blast count remained stable for 16 hours after Methotrexate, then declined moderately, and from 24 to 48 hours after Methotrexate fell exponentially with a half‐time of approximately 4 hours to 1/50 of the original value. This is not easily explained from leukemic cell kill alone, and it is suggested that such a rapid and massive reduction in blood blast count may in part be due to an anatomical redistribution of blast cells. That blast cells do return from the blood to the marrow was shown by studies of the fate of labeled cells: immediately prior to Methotrexate, blast cells from the blood were labeled with 3H‐cytidine and then rapidly reinfused. Serial blood and marrow smears were obtained and autoradiographed. The number of labeled blasts in the blood closely paralleled the total number of blasts in the blood throughout the 6‐day study period. Nine bone marrows were obtained between 6 and 96 hours after autotransfusion; in all samples significant numbers of labeled blasts were found in the marrow which could not be accounted for by blood contamination. An attempt to demonstrate that labeled cells, which return to the marrow, will resume cell division was unsuccessful.