IDENTIFICATION OF HUMAN JUVENILE CHRONIC MYELOGENOUS LEUKEMIA STEM-CELLS CAPABLE OF INITIATING THE DISEASE IN PRIMARY AND SECONDARY SCID MICE

Most juvenile chronic myelogenous leukemia (JCML) cells have limited l ong-term proliferative capacity, and only a minority of immature cells give rise to colonies in semisolid cultures. Clonogenic JCML progenit ors cannot be maintained in culture because they differentiate, and wi thin a few weeks the leukemic clone is lost, This makes it difficult t o identify the cell that initiates and maintains the disease in patien ts. To determine the proliferative capacity of JCML cells in vivo, bon e marrow (BM), peripheral blood, or spleen cells from eight patients w ith JCML either at diagnosis or during treatment were transplanted int o sublethally irradiated severe combined immune deficient (SCID) mice. JCML cells from all patients homed to the murine BM and proliferated extensively in response to exogenous stimulation with granulocyte-macr ophage colony-stimulating factor, Within a few weeks, highly engrafted mice became ill and cachectic due to infiltration of leukemic cells a nd secretion of tumor necrosis factor-alpha. Murine BM, spleen, and li ver were infiltrated with leukemic blasts, and typical JCML colony-for ming progenitors could be recovered. Kinetic experiments demonstrated that only a small minority of transplanted cells homed to the murine B M, and that these cells initiated and maintained the disease in vivo b y extensive proliferation and differentiation. To characterize the cel l-surface phenotype of the JCML initiating cell (JCML-IC), JCML blood or spleen cells were fractionated on the basis of CD34/CD38 marker exp ression and transplanted into SCID mice. Only immature CD34(+) cells c ould initiate the disease, while mature CD34(-) cells did not engraft. Within the CD34(+) compartment, there was enrichment for JCML-ICs by immature cells with a CD34(+)/CD38(-) stem-cell-like phenotype. Mice t ransplanted with more mature CD34(+)/CD38(+) populations that also con tained clonogenic JCML progenitors were poorly engrafted. These result s indicate that the JCML-IC is an earlier stage of development than cl onogenic JCML progenitors. Additional evidence that the JCML-IC has st em-cell properties comes from secondary transplant experiments that te st the self-renewal capacity. The JCML-IC from all three patients test ed could successfully reinitiate the disease in secondary murine recip ients. Thus, we have developed a functional in vivo model that replica tes many aspects of human JCML, and have used this model to identify a nd characterize JCML-ICs and their stem-cell properties. (C) 1996 by T he American Society of Hematology.