Novel antigen expression on syngeneic somatic cell hybrids of murine spontaneous mammary tumor cells.

Spontaneous mammary carcinoma cells of C3H/He mice were fused with syngeneic L-cells, and two types of hybrid cell clones were obtained. In group A, hybrid cells showed contact inhibition, and parental H-2k and L-antigens were well expressed. Metacentric chromosomes of L-cell origin and estrogen dependency were also well preserved in this group. However, in group B, hybrid cells proliferated to pile up, and the expression of parental antigens, H-2 and L-cell antigens, was strongly suppressed. But, mouse mammary tumor antigens (MM-antigens), which were expressed on ascites mammary tumor cells with hypotetraploidy of C3H/He origin and which were not expressed on both parent cells, were newly expressed. The number of metacentric chromosomes was decreased, and estrogen dependency was lost in this group. The relationship between the expression of MM-antigens and that of H-2 antigens was reciprocal, and tumorigenicity was independent of cellular behavior in vitro and of MM-antigen expression. MM-antigen-positive hybrid cell clones were frequently obtained when tumor cells were fused with metaphase-rich L-cells.