Effect of splenic irradiation on circulating colony-forming cells in chronic granulocytic leukaemia.

Patients with chronic granulocytic leukaemia (CGL) have increased numbers of granulocyte colony-forming cells (CFC) in the peripheral blood. I When the disease is controlled by chemotherapy, leucapheresis, or irradiation circulating CFC fall to low levels.2 Since irradiation in vitro impairs granulocyte colony growth3 the therapeutic effect of splenic irradiation is presumably related to CFC damage, but many factors may operate in vivo to potentiate or diminish the effect. We undertook this study to define the in-vivo action of splenic irradiation on circulating CFC, and to relate changes in CFC numbers to other haematological variables. The patient presented in 1972 at the age of 68 with CGL. A Philadelphia chromosome was present. His condition was successfully controlled with busulphan for two years. In 1975 he developed increasing splenomegaly and his leucocyte count rose to 200-0 x 109/l (200 000/mm3) despite treatment. A course of splenic irradiation was given to a 13 x 10 cm anterior field with 60Co (Mobaltron) in 13 fractions of 75 rad over a period of 28 days to a total of 975 rad, during which time his spleen size decreased and his leucocyte count later fell to 8 0 x 109/1. His condition remained controlled for two months without further treatment before his leucocyte count rose to 30 0 x 109/1. The nature of the study was explained to the patient and his consent was obtained. Five ml blood was taken immediately before and immediately after splenic irradiation for routine blood counts and colony studies. Two hundred cell-differential leucocyte counts were made on a Wright's stained film. Myeloblasts were defined as undifferentiated mononuclear cells with one or more nucleoli. Colony cultures followed the technique described by Pike and Robinson.4 Triplicate cultures of 2 x 105 washed buffy-coat cells were plated on normal peripheral blood leucocyte feeder layers. To ensure maximum reproducibility feeder layers were prepared each week from the buffy-coat of one of four subjects who consistently showed good colony stimulation; the same batch of human AB serum was used throughout. Absolute numbers of CFC and cluster-forming cells fell progressively during treatment and remained at low levels for 18 weeks. The decline in CFC occurred several weeks before the fall in the total leucocyte count. Immediately after irradiation the absolute number of CFC and cluster-forming cells fell on nine out of 11 occasions (fig), the mean ratio of the post:pre value being 0 6. In the first …