IL3 and neoplasm: Since IL-3-transfected cells do not readily form tumor in vivo[20], [22], twice the number of IL-3 expressing cells (TRAMP-C1/mIL3 and TRAMP-C1/mIL3-sr39tk) were used compared to non-IL-3 expressing cells (TRAMP-C1 and TRAMP-C1/sr39tk) for all following in vivo experiments.