Incidence of Leukemia and Other Tumors in Thymectomized Irradiated Mice Bearing Thymic Transplants2

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Abstract
The effect of transplants of thymic tissue from newborn mice on the incidence of radiation-induced leukemia was investigated in strain C57BL mice. Thymectomized irradiated mice either were given an intrasplenic or a subcutaneous transplant of neonatal thymic tissue or were subjected to a sham intrasplenic transplantation. Mice bearing an intrasplenic transplant of thymic tissue and those given a sham intrasplenic transplant had essentially the same incidence of leukemia (10.5 and 8.7%, respectively). Mice bearing subcutaneous transplants of thymic tissue had a higher incidence of leukemia (31.6%) though not as high as the irradiated, nonthymectomized control animals (63.6%). The thymic implants were identified in the spleens of 34 percent of the animals examined during the 14-month observation period after transplantation. Histologic study of early and late implants showed normal growth and development of the thymic tissue in the spleens of irradiated mice. An apparent increase in the incidence of epithelial tumors in thymectomized X-irradiated mice is discussed briefly.