Inhibition of parental tumor colony formation by cells from a semi allogeneic mixed spleen cell reaction.

Cells capable of inhibiting colony formation by the DBA/2 fibrosarcoma SaD2-AG and mammary adenocarcinoma CaD2 are generated in vitro during semiallogeneic histoincompatibility reactions between DBA/2 and (C3H/He X DBA/2)F1 hybrid spleen cells. These colony-inhibiting cells adhere strongly to plastic, develop from nonadherent precursors, and retain colony-inhibiting ability even after receiving 5,000 rads of ionizing radiation.