ESTABLISHMENT OF A RETRODIFFERENTIATED CELL-LINE FROM A SINGLE DIFFERENTIATED RAT MYELOMONOCYTIC LEUKEMIA-CELL - POSSIBLE ROLES OF RETRODIFFERENTIATION IN RELAPSES OF LEUKEMIA AFTER DIFFERENTIATION-INDUCING THERAPY

In order to demonstrate possible roles of retrodifferentiation in rela pses after differentiation therapies, we have established a retrodiffe rentiated cell line (RD-1) from a single rat myelomonocytic leukemia c ell which differentiated into a macrophage-like cell by treatment with lipopolysaccharide (LPS). The established RD-1 cells showed microscop ic features slightly maturer than their parent cells. The RD-1 cells h ad the ability to differentiate into macrophagelike cells by treatment with fewer doses of LPS than those for parent cells. All rats inocula ted with the parent cells (more than 10(2)/rat) died within 50 days. R ats inoculated with 10(4) RD-1 cells survived for more than 120 days, whereas two out of four rats inoculated with 10(5) cells and all the r ats inoculated with 5 x 10(5) cells died of leukemia. These results su ggest that RD-1 cells are retrodifferentiated cells from a single rat myelomonocytic leukemia cell which differentiated into a macrophage-li ke cell; they have similar phenotypes and lower tumorigenicity than th e parent cells and they also suggest that the appearance of retrodiffe rentiated leukemia cells may be responsible for relapse after differen tiation therapy for leukemia in some cases.