Growth Potential of Human Leukemia Blast Cells in SCID Mice and Association with Prognosis of Human Acute Leukemias.

We have described a severe combined immunodeficiency (SCID) mouse model that permits the subcutaneous growth of primary human acute leukemia blast cells into a measurable subcutaneous nodule which may be followed by the development of disseminated disease. Utilizing the SCID mouse model, we examined the ability of patient-derived leukemic blasts to generate leukemic growth in the animals after subcutaneous inoculation without conditioning treatment. Leukemia blasts derived from 133 patients with acute leukemias, (67 acute lymphoblastic leukemia (ALL) and 66 acute myeloid leukemia (AML)), were inoculated into SCID mice. The leukemias displayed three distinct growth patterns: "aggressive", "indolent", or "no tumor growth". Out of 133 patients, leukemia samples 46 (34.5%) displayed an aggressive growth pattern, 14 (10.5%) indolent growth and 73 (55.0%) did not grow in SCID mice. The growth probability of leukemias from relapsed and/or refractory disease was 3 fold higher than that from patients with newly diagnosed disease. Serial observations found that leukemic blasts from the same individual, which did not initiate tumor growth at initial presentation and/or at early relapse, may engraft and grow in the later stages of disease, suggesting that the ability of leukemia cells for engraftment and proliferation was gradually acquired following the process of leukemia progression. Nine autonomous growing leukemia cell lines were established in vitro. These displayed an aggressive proliferation pattern, suggesting a possible correlation between the capacity of human leukemia cells for autonomous proliferation in vitro and an aggressive growth potential in SCID mice. It was demonstrated that patients whose leukemic blasts displayed an aggressive growth and dissemination pattern in SClD mice had a poor clinical outcome in patients with ALL as well as AML. Patients whose leukemic blasts grew indolently or whose leukemia cells failed to induce growth had a significantly longer DFS and more favorable clinical course.