Amplification of the murine leukemia virus Mr 70,000 glycoprotein gene product by human xenografts in athymic mice.

Passage of human tumors in athymic mice is accompanied by an increase in serum levels of the Mr 70,000 murine leukemia virus envelope protein, gp70. Elevated levels of gp70 can be detected in tissues of the hematopoietic systems of mice bearing human xenografts, but there is no evidence of synthesis of gp70 in these tissues. By far, the highest concentration of gp70 is in the human xenografts themselves.