The Leukocytopenic Effect of Focal Splenic X-Irradiation in Leukemic Patients

The mechanism whereby focal irradiation of the spleen reduces the circulating leukocytes in leukemia is not known (1–4). Possibly the effect is mediated by a humoral factor liberated by the spleen in response to radiation. To test this hypothesis, plasma drawn before and after irradiation directed to the spleen was reinfused into leukemic patients. This report describes the effect of such infusions on the circulating leukocytes in 7 cases of chronic leukemia. Materials and Method Subjects: The subjects were 5 men and 2 women, ranging in age from twenty-two to seventy years. Four of these patients had chronic granulocytic leukemia and 3 had chronic lymphocytic leukemia. The diagnosis in each instance had been established clinically and confirmed by aspiration biopsy of sternal bone marrow. The patients were hospitalized during the experimental periods and were seen on an outpatient basis between studies. Leukocyte counts on blood obtained from the ear lobe were made daily during the entire period of observation. The counts in all cases were done by the same technician. Standard Experimental Procedure: Following admission of the patient to the hospital, 500 ml. of blood was drawn on each of two consecutive days (control plasma). (In the case of anemic patients, blood was not collected until one week after the hemoglobin level had been brought within the normal range by multiple blood transfusions.) After the second withdrawal, the patient was given 1,000 ml. of whole blood. Irradiation directed to the spleen, in a dose range of 25 to 100 r daily five times a week, was then begun. When the daily counts showed that the leukocyte level was dropping rapidly, 500 ml. of blood was again drawn on each of two consecutive days (experimental plasma), being replaced by 1,000 ml. of blood after the second withdrawal. The plasma was separated by centrifugation, and 50,000 units of water-soluble penicillin and 0.5 gm. of streptomycin were added as preservatives to each unit. The plasma was then stored in the frozen state until used. Radiation therapy was discontinued when the leukocyte count reached 25,000 cells per cubic millimeter. The patient was then discharged from the hospital and was seen daily as an outpatient. When the daily leukocyte count indicated that hematologic relapse had occurred, he was readmitted. After the counts had been stable for three days or more, an infusion of 600 ml. of control plasma was given and its effect on the leukocytes was followed by serial blood counts. As soon as the leukocyte count had again remained stable for at least three days, 600 ml. of experimental plasma was administered and its effect was similarly studied. The standard experimental procedure as carried out in a representative study on one patient is shown in Figure 1. Leukocyte, differential, reticulocyte, and platelet counts, and hemoglobin determinations were performed daily six days a week.