CD146 is a novel marker for highly tumorigenic cells and a potential therapeutic target in malignant rhabdoid tumor.

Malignant rhabdoid tumor (MRT) is a rare, highly aggressive pediatric malignancy that primarily develops during infancy and early childhood. Despite the existing standard of intensive multimodal therapy, the prognosis of patients with MRT is dismal; therefore, a greater understanding of the biology of this disease is required to establish novel therapies. In this study, we identified a highly tumorigenic sub-population in MRT, based on the expression of CD146 (also known as melanoma cell adhesion molecule), a cell adhesion molecule expressed by neural crest cells and various derivatives. CD146+ cells isolated from four MRT cell lines by cell sorting exhibited enhanced self-renewal and invasive potential in vitro. In a xenograft model using immunodeficient NOD/Shi-scid IL-2Rγ-null mice, purified CD146+ cells obtained from MRT cell lines or a primary tumor exhibited the exclusive ability to form tumors in vivo. Blocking of CD146-related mechanisms, either by short hairpin RNA knockdown or treatment with a polyclonal antibody against CD146, effectively suppressed tumor growth of MRT cells both in vitro and in vivo via induction of apoptosis by inactivating Akt. Furthermore, CD146 positivity in immunohistological analysis of 11 MRT patient samples was associated with poor patient outcomes. These results suggest that CD146 defines a distinct sub-population in MRT with high tumorigenic capacity and that this marker represents a promising therapeutic target.

In vitro expansion of CD34(+)CD38(-) cells under stimulation with hematopoietic growth factors on AGM-S3 cells in juvenile myelomonocytic leukemia.

Using serum-containing culture, we examined whether AGM-S3 stromal cells, alone or in combination with hematopoietic growth factor(s), stimulated the proliferation of CD34(+) cells from patients with juvenile myelomonocytic leukemia (JMML). AGM-S3 cells in concert with stem cell factor plus thrombopoietin increased the numbers of peripheral blood CD34(+) cells to approximately 20-fold of the input value after 2 weeks in nine JMML patients with either PTPN11 mutations or RAS mutations, who received allogeneic hematopoietic transplantation. Granulocyte-macrophage colony-stimulating factor (GM-CSF) also augmented the proliferation of JMML CD34(+) cells on AGM-S3 cells. The expansion potential of CD34(+) cells was markedly low in four patients who achieved spontaneous hematological improvement. A large proportion of day-14-cultured CD34(+) cells were negative for CD38 and cryopreservable. Cultured JMML CD34(+)CD38(-) cells expressed CD117, CD116, c-mpl, CD123, CD90, but not CXCR4, and formed GM and erythroid colonies. Day-7-cultured CD34(+) cells from two of three JMML patients injected intrafemorally into immunodeficient mice stimulated with human GM-CSF after transplantation displayed significant hematopoietic reconstitution. The abilities of OP9 cells and MS-5 cells were one-third and one-tenth, respectively, of the value obtained with AGM-S3 cells. Our culture system may provide a useful tool for elucidating leukemogenesis and for therapeutic approaches in JMML.