Thymic dependent leukemia in AKR mice: requirement of an intact thymic stroma

Neonatal thymectomy is known to prevent lymphatic leukemia in AKR mice, but intact thymus graft from syngeneic mice completely restores the capacity of these mice to produce the disease. The present experiments were designed to study the leukogenic role of spleen cells and thymocytes. Normal AKR mice developed 90% leukemia (mean 275 days), whereas neonatal thymectomy induced 15% wasting disease and 0% leukemia until 400 days of observation period. However, 2 wk old normal and thymectomized mice injected i.p. with spleen cells (50 x 10⁶) from 2 mth old AKR mice developed (mean 259 days) leukemia: 93% in normal animals and only 17% (mean 387 days) in thymectomized mice. In contrast, thymectomized mice injected with thymus cells (200 x 10⁶) had 0% death at 400 days. In addition, thymectomized AKR mice were able to reject allogenic skin grafts within 13.4 days as compared to 9.4 days for normal mice. This may suggest that thymectomy at birth has not drastically reduced the immunocompetent cells from AKR mice. Preleukemic spleen cells from 5 mth old AKR mice significantly accelerated the disease both in normal (mean 136 days) and thymectomized animals (mean 226 days). The underlying mechanism of the latter results may have been due to the larger concentration of leukemia virus in 5 mth old spleen cells. However, these experiments suggest the need of an intact thymic architecture to permit the thymic dependent cells (young) to transform as neoplastic cells in AKR mice.