Tumorigenic potential of lung tissue cells from MMT mice. (a) Single-cell suspensions were isolated from lungs of mice double transgenic for PyMT and MUC1 antigen (MMT) at the indicated ages, counted and then injected into the left and right mammary fat pads of syngeneic wild-type (WT) mice at various doses. Eight weeks after inoculation, the recipient mice were sacrificed and the mammary glands were harvested, processed for whole mount and photographed. WT mice injected with sorted CD44+ mammary tumor cells or single-cell suspension obtained from the lungs of MUC1.Tg mice were used as positive or negative controls, respectively. The solid masses indicated by circles are the tumors. (b) Tumor incidence and tumor size in the whole mount were summarized and compared using one-way analysis of variance. (c and d) The mammary glands as shown in (a) were processed for histology and (c) stained with H&E or anti-CD44 and Sca1 monoclonal antibodies by (d)immunohistochemical (IHC) staining.