IN-VIVO GROWTH-STIMULATION OF COLLAGEN GEL EMBEDDED NORMAL HUMAN AND MOUSE PRIMARY MAMMARY EPITHELIAL-CELLS

A new system for studying growth of normal human mammary epithelial ce lls in an in vivo environment using athymic nude mice is described. Hu man mammary epithelial cells dissociated from reduction mammoplasty sp ecimens were embedded within collagen gels and subsequently transplant ed subcutaneously into nude mice. Histological sections of recovered c ollagen gels showed epithelial cells arranged as short tubules with so me branching. Proliferation of mammary epithelial cells was quantitate d in vivo by 3 days' continuous infusion with 5 bromo-2'-deoxy-uridine followed by immunostaining of sections from recovered gels. Ovarian s teroids administered to the host animals, resulting in blood serum lev els normally found in the human female, had little or no effect on the proliferation of human mammary epithelial cells. Collagen gel embedde d mouse mammary epithelial cells, mouse mammary explants, and host mam mary glands all responded similarly to ovarian steroids, suggesting th at the unresponsiveness of the human mammary epithelial cells under th ese conditions was not due to dissociation per se. However, an increas ed dose of 17 beta-estradiol or a growth factor combination containing epidermal growth factor, cholera toxin, and cortisol significantly st imulated the proliferation of human outgrowths. The growth factor resp onse was dependent on the location of the cells, with the greatest res ponse seen in the part of the gel proximal to the osmotic pump deliver ing the growth factors and the effect gradually waning in area more di stal to the pump. The effect was especially striking since the mitotic figures could be easily identified and the labeling index was as high as 75%. The host mouse mammary gland also responded to growth factors , resulting in ductal hyperplasia. The proliferative and morphogenetic effects of various agents on normal human mammary epithelial cells em bedded in collagen gel can be studied in vivo in nude mice. (C) 1995 W iley-Liss, Inc.