Transmission of Myeloid Leukemia in Mice. ∗

Myeloid leukemia, the most common type of leukemia in man, is rare in animals. A survey of this disease leaves doubt whether myeloid leukemia has ever been observed in domesticated animals (Jármai 1 ). It has been described in mice by Simonds, 2 although neither the bone marrow nor blood smears were available to him.

Myeloid leukemia was rarely found among our mice until a large number of them had been exposed to a single dose of approximately 400 r-units of X-rays or to smaller doses repeated at approximately monthly intervals. Table I contains a preliminary survey of this experiment and shows the frequent occurrence of myeloid leukemia and mediastinal lymphosarcoma among the irradiated mice as compared to the unirradiated, closely related control mice.

Increase of spontaneous lymphomatosis in mice by exposure to X-rays was observed by Krebs, Rask-Nielsen and Wagner. 3 Aubertin 4 called attention to the frequent occurrence of myeloid leukemia in X-ray workers.

The mouse from which the first strain of myeloid leukemia of mice took its origin was an unirradiated male mouse (No. Ar117). At the age of 16 months, the spleen of this mouse was greatly enlarged while the lymph nodes were of normal size or only slightly enlarged. The leukocyte count was 105,000. The most significant feature of the differential count was the presence of 9.5% of immature myeloid cells with coarse basophile granules in the blood. Neutrophile polynuclear leukocytes were 31%, neutrophile myelocytes and metamyelocytes 20%, eosinophile granulocytes 0.5%, cells like monocytes 17%, cells like monocytes with basophile cytoplasm 11.5%, lymphocytes 10.5%. At post mortem examination the liver, bone marrow, and spleen showed extensive infiltrations by myeloid cells with basophile granules and the same cells filled the sinuses of many lymph nodes. Many of these myeloid cells were in the process of mitotic division.