Isolation of mouse mammary tumor cells showing spontaneous regression

The tumor cells, TMT-3, was isolated from TMT-2 tumor cells by way of repeated selections of large colonies in soft agar. The cells can grow either in mice or in suspension culture. TD50 of the ascites tumor cells was 1.5 +/- 1.0. Plating efficiencies in soft agar were 40-70% for cells of ascites tumors and 25-30% for cells of solid tumors. The cells showed 4 marker chromosomes common to the parent cells and 6 new marker chromosomes. They also shared MM-antigen, but its quantity was about half of the parent cells. The growth curves of the solid tumors were characterized by temporary decrease in tumor volume followed by regrowth or regression.