Development of T-cell leukemia in the recipients of SPA-1^−/− HPCs expressing C3G-F. (A) HPCs from SPA-1^−/− mice were infected with empty (Vect) or C3G-F–containing retrovirus and transplanted into lethally irradiated B6 mice. Nine to 12 weeks later, the proportions and numbers of GFP⁺ cells in various tissues as well as the leukocyte and red blood cell counts in blood were determined. Six of 12 recipients of C3G-F/SPA-1^−/− HPCs (○) became moribund in 9 to 12 weeks, when they were killed. Bars indicate the mean values; statistical analysis was done by Student t test. (B) Representative thymus and spleen of each group. In C3G-F/SPA-1^−/− HPC recipients, lymphoadenopathy was frequently detected, and a swollen abdominal lymph node is also shown. (C) Hematoxylin-eosin–stained photographs of the indicated organs of Vect/SPA-1^−/− and C3G-F/SPA-1^−/− HPC recipients. Magnifications are indicated. C indicates cortex; M, medulla.