Insights into leukemia-initiating cell frequency and self-renewal from a novel canine model of leukemia

Leukemia-initiating cells (LICs) have been the subject of considerable investigation because of their ability to self-renew and maintain leukemia. Thus, selective targeting and killing of LICs would provide highly efficient and novel therapeutic strategies. Here we explored whether we could use a canine leukemia cell line (G374) derived from a dog that received HOXB4-transduced repopulating cells to study leukemia in the murine xenograft model and the dog.

G374 cells were infused in dogs intravenously and in nonobese diabetic/severe combined immunodeficient and nonobese diabetic/severe combined immunodeficient/IL2Rγ(null) mice either intravenously or directly into the bone cavity. Animals were bled to track engraftment and proliferation of G374 cells, and were sacrificed when they appeared ill.

We found that canine LICs are capable of sustained in vitro self-renewal while maintaining their ability to induce acute myeloid leukemia, which resembles human disease in both dogs and mice. Furthermore, we developed a novel strategy for the quantification of LIC frequency in large animals and showed that this frequency was highly comparable to that determined by limited dilution in mouse xenotransplants. We also demonstrated, using single-cell analysis, that LICs are heterogeneous in their self-renewal capacity and regenerate a leukemic cell population consistent with a hierarchical leukemia model.

The availability of this novel framework should accelerate the characterization of LICs and the translation of animal studies into clinical trials.