Stimulation of mammary tumor virus production in a mouse mammary tumor cell line.

Abstract

Summary A mouse mammary tumor cell line (MMT), which has shown since its isolation in 1962 a limited, but continuous, budding of B particles, was stimulated to high production by alternate passages of the cells through mice or rats and tissue culture. Newborn C57BL, Af, and A mice and Amsterdam/IMR rats have been used as transient hosts. Detection and semiquantitative estimations of virus production in the cultures were made by thin-section electron microscopy, whole-cell-mount electron microscopy, membrane immunofluorescence, and immunodiffusion. Passage of the MMT cells into mice and back to tissue culture stimulated a 4-fold increase of B particle production but remained subject to variations in successive subcultures. Passage of the MMT cells into rats stimulated a 25- to 30-fold increase; budding of the virions remained constant and the tumor-inducing capabilities were high through multiple subcultures. The greater stability in pH and even rate of growth of the rat-passaged cells opens the possibility of producing in tissue culture a mammary tumor virus of greater reliability and purity than that obtained from milk or tumor extracts.