Establishment and characterization of a transplantable rat myelomonocytic leukemia

A transplantable myelomonocytic leukemia was established from a leukemia of a WKA/Hok rat which had been inoculated with Rauscher virus at birth. The tumor grew in ascites form in normal syngeneic rats and, after the middle stage of i.p. transplantation, leukemia cells consisting of a mixed population of monocytic and granulocytic cells were observed in the peripheral blood. A complement-dependent cytotoxicity test failed to demonstrate Rauscher virus-related antigen on the tumor cell surface. Membrane marker analysis revealed that most of the tumor cells possessed receptors for both complement and neuraminidase-treated sheep RBC. More than 90% of ascitic tumor cells displayed phagocytic activity and a positive nonspecific esterase reaction. Serum from rats bearing this tumor contained high levels of muramidase. Ultrastructurally, the tumor cells resembled both immature and mature cells of the monocyte-macrophage series. On serial transplantation into the peritoneal cavity, the tumor displayed consistent differentiation from undifferentiated blast cells to monocytes and cells indistinguishable from granulocytes. The karyotype analysis revealed that the modal number of chromosomes of the tumor cells was 81, and no structural abnormalities of chromosomes were observed after quinacrine mustard staining. This transplantable leukemia will provide a useful experimental model for the study of granulocyte-monocyte differentiation and for human myelomonocytic leukemia.