Leukemia X fibroblast hybrid cells prolong the lives of leukemic mice.

ASL-1 leukemia X LM(TK-) fibroblast hybrid cells prolong the livers of leukemic (A/JXC3H/HeJ)F1 mice. The hybrid cells, like the fibroblast cells used in forming the hybrid, have lost malignant growth properties in immunocompetent recipients and are rejected. Mice receiving hybrid cells along with ASL-1 cells exhibit immunity toward the leukemia cells; approximately 50% of the animals injected with 10(6) or more hybrid cells along with ASL-1 cells survive more than 60 days; animals in the control group injected with leukemia cells alone invariably die in shorter intervals. The immunity generated is persistent for at least 6 months. Some leukemic mice receiving doses of combination chemotherapy which are insufficient to cure them of the disease survive for prolonged and at times indefinite periods if they are injected with hybrid cells. The immunity generated in mice receiving hybrid cells is directed toward a leukemia-associated antigen of leukemia cells expressed by hybrid cells as well. In mixed lymphocyte culture a heightened stimulation of spleen cells from hybrid cell-injected mice toward ASL-1 cells is observed.