Beware of contaminating mouse cells in human xenografts from nude mice

Human tumor xenografts in nude mice are widely utilized model system for th e transplantation of human surgical specimens and human established cell li nes. Gene expression studies are often carried out in these model systems. With an increasing use of PCR based analyses, the extreme sensitivity of th is technique poses a serious challenge with regards to the extent of contam inating host mouse cells in the human tumor xenografts. These xenografts ar e never fr ee of host cell contamination. We detected mouse estrogen recept or expression in several human tumor xenografts using RT-PCR demonstrating that precaution is necessary when utilizing PCR based analyses in human tum or xenografts. A cytologically based methodology which distinguishes human versus mouse cells will be more suitable for ER expression studies using hu man xenograft models Both (1) in situ hybridization using human probe and ( 2) immunocytochemistry using a monoclonal antibody directed against human c ytokeratin have been used successfully to distinguish human cells versus ho st mouse cells in human xenografts in nude mice. Immunostaining of ER can t hen be utilized to determine the expression pattern of ER in the transplant ed human cells.