The effect of daily low dose gamma irradiation on growth and differentiation of human myeloid leukaemic bone marrow in diffusion chambers.

Bone marrow from each of 8 untreated patients with myeloproliferative disorders was grown in diffusion chambers in 760 rad total body irradiated rats. Rats were then exposed to 11.5, 57.5, or 108.5 rad daily for 14-2l d and cell growth compared to that detected in unirradiated chambers. Cells from acute myelogenous leukaemia patients exposed to 11.5 rad per d grew for 11-21 d and there was no consistent stimulation of differentiation of immature granulocytic cells to mature granulocytes that was attributable to irradiation. Cells from a chronic myeloid leukaemia patient in chronic phase or blast crisis, and a polycythaemia vera patient with myeloid metaplasia showed significant morphologic differentiation from immature to mature granulocytes in control chambers with no additional effect of daily irradiation. Marrow specimens from 2 AML patients exposed to each of 3 daily dose fractions over 14 d revealed a dose-dependent decrease in immature granulocytes with no persistent increase in mature granulocytes. In both irradiated and control chambers, macrophages increased over 21 d. Thus, cells from patients with myeloproliferative disorders may not necessarily differentiate to mature granulocytes following in vivo exposure to ionizing irradiation.