A new experimental model for in vivo studies on differentiation and proliferation of leukemic cells using a mouse myeloid leukemia aneuploid line.

We developed an experimental model to investigate in vivo differentiation and proliferation of leukemia cells using mouse myeloid leukemia aneuploid cells (LL-2) and syngeneic SL mice. The LL-2 cells were near-tetraploid cells isolated from mouse myeloid leukemia cell line M1 (clone D501). In suspension culture, the LL-2 cells were myeloblastic and grew well like parent D501 cells, but were distinct from the parental cells due to the large size of their nucleus, double chromosome number and DNA content. The LL-2 cells as well as D501 cells could be induced to differentiate in vitro into mature macrophage-like cells by a protein inducer of differentiation. After transplantation of 4 X 10(6) LL-2 cells into the intraperitoneal cavity of syngeneic SL mice, most of them died of leukemia within 10 weeks. On microscopic examination of the peritoneal cells of the mice, the transplanted LL-2 cells were clearly distinguishable from normal host cells by the size of their nucleus. We determined the increase in the LL-2 cells in the peritoneal cavity by morphological examination of the large-sized LL-2 cells. Survival times of the mice inoculated with the LL-2 cells were prolonged by administrations of an inducer of differentiation, poly(I).poly(C). We found morphological changes in the peritoneal blastic LL-2 cells to mature macrophage-like cells after the serial administrations of poly(I).poly(C) to the recipient mice. Thus the aneuploid LL-2 cells that grow in syngeneic mice may be useful to study in vivo differentiation and proliferation of leukemia cells, and to develop a therapeutic strategy of leukemia using various treatments including differentiation inducers.