CD56(+)CD146(+) Cells in Normal Human Bone Marrow-Stroma Proliferated to Form Tumors in severe Combined Immunodeficiency Mice

We reported that acute myelogenous leukemia blasts and chronic myelogenous leukemia cells converted to stromal myofibroblasts to create an environment for the proliferation of leukemic cells in vitro and in vivo. Recently, we also reported that myelogenous leukemia-derived myofibroblasts formed blastomas in non-obese diabetes severe combined immunodeficiency (NOD/SCID) mice, in which the CD56-positive cell-fraction was selectively proliferated (16^th EHA). To ascertain whether normal human bone marrow-stroma-derived cells also behave like leukemia-derived cells, stromal cells were injected to NOD/SCID mice, and tumor-formation was observed.

Bone marrow cells were collected from informed normal individuals, whose adherent cells were separated and were cultured for one month to eliminate monocyte/macrophage, vascular cell, and pericyte to prepare stromal myofibroblast-rich fraction. Cells were injected to NOD/SCID mice intra-venously, peritoneally, and subcutaneously (3 × 10⁶/mice). When the tumor formation was observed or mice were dead, they were sacrificed and the engrafted cells were analyzed.

Between at day 70 and 90 after injection mice were dead. Autopsy findings revealed tumor formation at subcutaneous injection sites, and cells were also infiltrated to the liver and ascitic fluid. These cells expressed CD56, CD146, and Nestin strongly, but not other lineage-specific markers including CD133; however, the ratio of CD56(+)CD146(+) fraction in the injected stromal cells was below 0.1%. When the tumor cells were cultured in vitro, they exhibited spindle-shaped appearance, and doubling time was 12 to 16 hours. They expressed c-Myc, Klf4, Nanog, Sox2, and other molecules that are expressed in an immature somatic stem cell. These observations indicate that CD56(+)CD146(+) cell-fraction in bone marrow-stroma is very immature and highly proliferative. We are now analyzing biological characteristics of this specific cell-fraction, and determining the contribution to normal hematopoiesis.

No relevant conflicts of interest to declare.