Human breast epithelium transplanted into nude mice. Proliferation and milk protein production in response to pregnancy.

Epithelial components of the normal human breast and their response to hormonal manipulation have been studied in the nude mouse. Six to eight week-old female athymic nude mice were used as the recipients of enzymatically prepared breast organoids, composed of ductal and lobuloalveolar structures. After 12 weeks in situ in the mouse mammary fat pad the human breast tissue retains its normal morphology as demonstrated by the presence of myosin positive myoepithelial cells and keratin positive luminal cells. Monoclonal antibodies M8 and M18 raised to components of the human milk fat globule membrane give a similar staining pattern in the xenografted organoids to that seen in the donor tissue. On mating the recipient female nude mice, the human breast tissue responds with both an increased 3H-thymidine labelling index and alpha-lactalbumin production. This model in conjunction with in vitro studies is, therefore, suitable for the study of extrinsic and intrinsic factors controlling differentiation and morphogenesis in the human breast.