A subset of CD45+/CD19 - cells in bone marrow may be associated with clinical outcomes of patients with mantle cell lymphoma

Tumorigenic role of Musashi-2 in aggressive mantle cell lymphoma

SOX11 overexpression has been associated with aggressive behavior of mantle cell lymphomas (MCL). SOX11 is overexpressed in embryonic and cancer stem cells (CSC) of some tumors. Although CSC have been isolated from primary MCL, their relationship to SOX11 expression and contribution to MCL pathogenesis and clinical evolution remain unknown. Here, we observed enrichment in leukemic and hematopoietic stem cells gene signatures in SOX11+ compared to SOX11- MCL primary cases. Musashi-2 (MSI2) emerged as one of the most significant upregulated stem cell-related genes in SOX11+ MCLs. SOX11 is directly bound to the MSI2 promoter upregulating its expression in vitro. MSI2 intronic enhancers were strongly activated in SOX11+ MCL cell lines and primary cases. MSI2 upregulation was significantly associated with poor overall survival independently of other high-risk features of MCL. MSI2 knockdown decreased the expression of genes related to apoptosis and stem cell features and significantly reduced clonogenic growth, tumor cell survival and chemoresistance in MCL cells. MSI2-knockdown cells had reduced tumorigenic engraftment into mice bone marrow and spleen compared to control cells in xenotransplanted mouse models. Our results suggest that MSI2 might play a key role in sustaining stemness and tumor cell survival, representing a possible novel target for therapeutic interventions in MCL.

Cancer Stem Cells of Diffuse Large B Cell Lymphoma Are Not Enriched in the CD45+CD19- cells but in the ALDHhigh Cells

Although the existence of cancer stem cells (CSCs) has been suggested in diffuse large B cell lymphoma (DLBCL), there is still no definitive marker. CD45⁺CD19^- has been regarded as a potential marker of CSCs in mantle cell lymphoma (MCL). So, we explored the role of CD45⁺CD19^- in DLBCL. However, both CD45⁺CD19^- cells and CD45⁺CD19⁺ cells did not generate tumors until more than 100,000 cells were inoculated in NOD/SCID mice, even CD45⁺CD19⁺ cells generated more and larger tumors, as well as the soft agar colony formation in vitro; The aldehyde dehydrogenase (ALDH) activity was also identified in this study. Only 1,500 ALDH^high cells were enough to generate tumors in mice while the same number of ALDH^- cells were not. Moreover, both groups formed tumors when more cells were inoculated, but ALDH^high cells formed more and larger tumors. The similar result was obtained in vitro clonogenicity experiments. OCT4, SOX2, Nanog, and ABCG2 genes did not show any difference in CD45⁺CD19⁺, CD45⁺CD19^-, ALDH^high and ALDH^- cells. Taken together, CSCs are not enriched in the CD45⁺CD19^- cells but in the ALDH^high cells in DLBCL cell lines.

FOXO4 expression is related to stem cell-like properties and resistance to treatment in diffuse large B-cell lymphoma

Cancer stem cells are proposed to be responsible for resistance to chemotherapeutic agents, including doxorubicin. As phenylbutyrate enhances cancer stem cell properties, we analyzed surviving lymphoma cells after treatment with doxorubicin and phenylbutyrate. Human B-cell lymphoma cell lines, including Toledo, BJAB, Daudi, and Raji were incubated with IC₉₀ concentrations of doxorubicin (300 nM) or phenylbutyrate (8 mM). After 48 h, live cells were sorted and analyzed for their resistance to treatment by examining gene expression profiles using cDNA microarray and biological characteristics. A small fraction of lymphoma cells that survived after drug application showed higher expression of stem cell markers (NANOG, andSOX2) and superior ability of self-renewal and sphere formation, compared to untreated control cells (P < 0.05). Gene expression analysis disclosed elevated expression of 41 genes, including FOXO4, in the four lymphoma cell lines that survived drug treatment. Overexpression of FOXO4 was evident in lymphoma cells surviving after phenylbutyrate treatment and refractory patient-derived lymphoma cells. Induction of FOXO4 expression promoted self-renewal whereas its knockdown led to diminished expression of stem cell markers and colony-forming ability of lymphoma cells. Immunohistochemical staining for FOXO4 in tumor tissue of diffuse large B-cell lymphoma revealed nuclear localization and significant association with poor prognosis. In conclusion, lymphoma cells resistant to treatment exhibit stem cell-like properties and enhanced FOXO4 expression. The presence of FOXO4-expressing cells in tumor tissue and their association with poor survival supports a role of FOXO4 in promoting stem cell properties resulting in poor outcomes.