A Transplantable Myelomonocytic Leukemia in BALB/c Mice: Cytology, Karyotype, and Muramidase Content23

Abstract

Myelomonocytic leukemia was detected in a BALB/c mouse which had undergone mineral oil (paraffin) injections intended to induce plasma cell tumor development. The tumor was composed of a mixed population of monocytic and granulocytic cells. On transplantation of the tumor, four distinct sublines developed, two of which retained the original chloroma appearance and were distinguishable by karyotype (one diploid and one tetraploid). The other two nonchloroma sublines were also distinguishable karyologically, because one had a hypodiploid 39 stemline. Chromosome marker studies in vivo and DNA-content studies of cells from mice carrying the tetraploid subline confirmed that in this leukemia both the monocytic and granulocytic cells are neoplastic, indicating the existence of a neoplastic stem cell capable of differentiation into both cell series. Serum and urine samples from mice carrying this tumor contained high levels (frequently over 200 μg/ml) of muramidase, and cell suspensions of the solid tumor also contained this enzyme. This tumor therefore fulfills all the criteria applied to human myelomonocytic leukemia and is a useful laboratory model for this type of leukemia.