Background: Recently, a small population of cancer stem cells in adult and pediatric brain tumors has been identified. Some evidence has suggested that CD133 is a marker for a subset of leukemia and glioblastoma cancer stem cells. Especially, CD133 positive cells isolated from human glioblastoma may initiate tumors and represent novel targets for therapeutics. The gene expression and the drug resistance property of CD133 positive cancer stem cells, however, are still unknown.

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Glioblastoma multiforme is the most aggressive primary brain tumor, with current treatment remaining palliative. Immunotherapies harness the body’s own immune system to target cancers and could overcome the limitations of conventional treatments. One active immunotherapy strategy uses dendritic cell (DC)-based vaccination to initiate T cell-mediated anti-tumor immunity. It has been proposed that cancer stem-like cells (CSCs) may play a key role in cancer initiation, progression and resistance to current treatments. However, whether using human CSC antigens may improve the anti-tumor effect of DC vaccination against human cancer is unclear. In this study, we explored the suitability of CSCs as sources of antigens for DC vaccination again human GBM, with the aim of achieving CSC-targeting and enhanced anti-tumor immunity. We found that CSCs express high levels of tumor associated antigens (TAAs) as well as major histocompatibility complex (MHC) molecules. Furthermore, DC vaccination using CSC antigens elicited antigen-specific T cell responses against CSCs. DC vaccination induced interferon (IFN) -γ production is positively correlated with the number of antigen-specific T cells generated. Finally, using a 9L CSC brain tumor model, we demonstrate that vaccination with DCs loaded with 9L CSCs, but not daughter cells or conventionally cultured 9L cells, induced CTLs against CSCs, and prolonged survival in animals bearing 9L CSC tumors. Understanding how immunization with CSCs generates superior anti-tumor immunity may accelerate development of CSC-specific immunotherapies and cancer vaccines.

BACKGROUND: Cancerous stem-like cells (CSCs) have been implicated as cancer-initiating cells in a range of malignant tumours. Diverse genetic programs regulate CSC behaviours, and CSCs from glioblastoma patients are qualitatively distinct from each other. The intrinsic connection between the presence of CSCs and malignancy is unclear. We set out to test whether tumour stem-like cells can be identified from benign tumours. METHODS: Tumour sphere cultures were derived from hormone-positive and -negative pituitary adenomas. Characterisation of tumour stem-like cells in vitro was performed using self-renewal assays, stem cell-associated marker expression analysis, differentiation, and stimulated hormone production assays. The tumour-initiating capability of these tumour stem-like cells was tested in serial brain tumour transplantation experiments using SCID mice. RESULTS: In this study, we isolated sphere-forming, self-renewable, and multipotent stem-like cells from pituitary adenomas, which are benign tumours. We found that pituitary adenoma stem-like cells (PASCs), compared with their differentiated daughter cells, expressed increased levels of stem cell-associated gene products, antiapoptotic proteins, and pituitary progenitor cell markers. Similar to CSCs isolated from glioblastomas, PASCs are more resistant to chemotherapeutics than their differentiated daughter cells.

The rat 9L gliosarcoma is a widely used syngeneic rat brain tumor model that closely simulates glioblastoma multiforme when implanted in vivo. In this study, we sought to isolate and characterize a subgroup of cancer stem-like cells (CSLCs) from the 9L gliosarcoma cell line, which may represent the tumor-initiating subpopulation of cells. We demonstrate that these CSLCs form clonalderived spheres in media devoid of serum supplemented with the mitogens epidermal growth factor and basic fibroblast growth factor, express the NSC markers Nestin and Sox2, self-renew, and differentiate into neuron-like and glial cells in vitro. More importantly, these cells can propagate and recapitulate tumors when implanted into the brain of syngeneic Fisher rats, and they display a more aggressive course compared with 9L gliosarcoma cells grown in monolayer cultures devoid of mitogens. Furthermore, we compare the chemosensitivity and proliferation rate of 9L gliosarcoma cells grown as a monolayer to those of cells grown as floating spheres and show that the sphere-generated cells have a lower proliferation rate, are more chemoresistant, and express several antiapoptosis and drug-related genes, which may prove to have important clinical implications.