In vivo treatment with xanthosine expands the mammary stem cell population

Mammary stem cells provide for growth and maintenance of the mammary gland and are therefore likely targets for means to improve the productivity and efficiency of dairy animals. Xanthosine treatment has been shown to promote expansion of hepatic stem cells in vitro. The objective of this study was to determine if in vivo treatment with xanthosine can increase the mammary stem cell population. Xanthosine was infused into the right mammary glands of four Holstein calves (3 mo old) for 5 consecutive days. The right rear quarter received a supplemental injection of xanthosine directly into the mammary parenchyma. Immediately after each xanthosine treatment, calves were injected intravenously with 5-bromo-2-deoxyuridine (BrdU). Forty days after the final treatment, mammary tissue was obtained at slaughter. BrdU-label retaining epithelial cells (LREC) were detected immunohistochemically and quantified. We and others have employed the retention of BrdU as a method for labeling putative bovine mammary stem cells. Infusion of xanthosine into the bovine mammary gland significantly increased the number of LREC in treated quarters compared to contralateral control quarters (P = 0.06). LREC averaged 0.4% of epithelial cells in control and 0.84% in xanthosine-treated quarters. Data indicate that in vivo treatment with xanthosine can be used to increase the number of mammary stem cells. This is the first demonstration of an in vivo treatment to increase the endogenous population of adult mammary stem cells in any species. Utility of this treatment for biomedical research and for dairy management is of considerable interest.