Wild-type mammary stem cells are unable to efficiently repopulate macrophage-deficient fat pads. (a) Wild-type CD29hiCD24+ cells transplanted into Csf1op/opfat pads resulted in only a single small outgrowth whereas those transplanted into wild-type recipients resulted in extensive filling of the fat pad, all harvested at eight weeks post-transplantation. (b) Histogram showing percent outgrowth and the extent of fat pad filling following transplantation of normal CD29hiCD24+ cells into wild-type or Csf1op/opfat pads. Error bars represent standard error of the mean for three independent experiments. (c) Clodronate liposomes inhibit mammary stem cell function. CD29hiCD24+ cells (200) from Rosa26 mice were co-transplanted with liposomes containing either saline or clodronate into the cleared mammary fat pads of syngeneic wild-type female mice. The cells co-transplanted with clodronate liposomes resulted in no outgrowths or rudimentary structures, an example of which is shown. Scale bars = 1 mm. Csf1 = colony stimulating factor 1.