Sensitive NOD-scid-IL2γ^null (NOG-scid) Assay for Human Precursor B Acute Lymphoblastic Leukemias (ALL).

Results of treatment for childhood ALL have improved considerably over the past few decades, yet still ∼20% of pediatric patients relapse. New in vivo models of human ALL might increase understanding of ALL biology and speed preclinical development of novel treatment regimens. Multiple strains of immunodeficient mice support growth of human ALL cells (Bachmann, Current Drugs Target 2007, review). The recently described highly immunodeficient NOD-scid-IL2γ^null (NOG-scid) mouse strain offers a number of advantages over the widely-used NOD-scid strain: NOG-scid mice have a normal lifespan, do not develop spontaneous lymphomas, and require ∼10-fold fewer normal human hematopoietic stem-progenitor cells to generate human hematopoiesis (Hiramatsu, Blood 2003; Ishikawa, Blood 2005). In addition, NOG-scid mice support generation of human leukemia from transplanted human acute myeloid leukemia (AML) (Ninomiya, Leukemia 2007). Herein we report a sensitive in vivo model using transplant of human childhood precursor B ALL cells into sublethally irradiated NOG-scid mice. Transplanted mice developed fatal leukemia 4–5 weeks after intravenous injection of 5x10⁴ REH or KOPN8 cells (established precursor B ALL cell lines derived from pediatric ALL patients). At necropsy, the mice had massive splenomegaly and hyperplastic bone marrow. Blood, spleen, and marrow contained abundant human cells with immunophenotype matching the transplanted ALL cell line. We went on to similarly transplant primary leukemic blast cells from pediatric ALL patients. In 3 of 5 tested primary ALL cases, fatal human leukemias developed in the NOG-scid mice. In titrations of 10³-2.5x10⁶ transplanted ALL cells, time to clinical leukemia was dose-dependent, and 1000 primary human cells was sufficient to initiate leukemia development. In addition, we detected human leukemic blast cells by flow cytometric immunophenotyping in the blood of transplanted NOG-scid mice as early as 10 days post-transplant, enabling objective leukemia diagnosis ∼4 weeks prior to clinical signs.

CONCLUSIONS: NOG-scid mice supported the generation of human precursor B ALL from cell lines and primary ALL cases, objectively detectable as early as 10 days post-transplant. Our dose titration results suggest that this model detects a high frequency of ALL-initiating cells. This in vivo model may provide a powerful assay both for fundamental questions regarding the biology of leukemia stem cells and for preclinical studies of novel anti-neoplastic agents and regimens.