Abstract 3322: Protective antitumor immunity induced by ALDEFLUOR+ enriched cancer stem cells
Authors: Ning Ning , Teitz-Tennenbaum Seagal , Yet Ji , Moyer Jeffrey S. , Ginestier Christophe , Wicha Max S. , Xu Yingxin , Chang Alfred E. , Li Qiao 
Published: February 2011

Abstract
The isolation of human cancer stem cells represents a new paradigm for the development of cancer treatments. In theory, therapies that expressly target cancer stem cells are more likely to be successful. So far, the majority of the stem cell studies have been confined to human tumors inoculated into severely immunosuppressed hosts (e.g. SCID mice), which are not suitable for immunologic evaluation. The lack of immunocompetent syngeneic animal tumor models where stem cells can be isolated has been the primary obstacle to evaluating the immunogenicity of tumor stem cells. In this study, we used ALDEFLUOR/ALDH1 as a marker and identified cancer stem cell (CSC)-enriched populations in two of our murine models (melanoma B16-D5 and pancreas cancer PAN-02). We found that: 1). a very small percentage (0.5-2.5%) of ALDEFLUOR+ cells exist in these murine tumors; 2). only sorted, and as few as 500 ALDEFLUOR+ cells could form tumors in syngeneic hosts; 3).the stem cell nature of the ALDELFUOR+ cells was confirmed by their ability to form spheres in culture and to self-renew in vivo. We hypothesize that CSCs may induce immunity specifically targeting CSCs. We proceeded to evaluate the protective antitumor responses induced by vaccination with dendritic cells (DC) pulsed with the lysate of ALDEFLUOR+ D5 cells (CSC-TPDC) in the syngeneic immunocompetent host. Normal mice were vaccinated with CSC-TPDC or DC pulsed with lysate from unsorted heterogeneous D5 cells (H-TPDC), followed by challenge with D5 tumor cells intravenously. Lungs were harvested 20 days later to enumerate metastases. Compared with non-vaccinated, PBS-injected controls, H-TPDC induced modest protective immunity against tumor challenge, which is consistent with our previous observations. More importantly, mice that received CSC-TPDC had significantly fewer lung metastases than both the control group and the H-TPDC treated group (p&lt; 0.02). In a different setting utilizing CSC as antigen, CSC-TPDC vaccination induced a potent immune response that resulted in significant inhibition of s.c tumor growth. Like the pulmonary metastasis model, there was enhanced protection against tumor growth mediated by CSC-TPDC vs. H-TPDC. Splenocytes isolated from CSC-TPDC vaccinated hosts produced significantly higher levels of IgG and cytotoxic IgG2b. Together, these results suggest that enriched CSCs are immunogenic and are significantly more effective as an antigen source compared with unselected tumor cells in inducing protective antitumor immunity. CSC-conferred protection is associated with the induction of humoral immune responses. Establishing the superior immunogenicity of CSCs compared to unselected tumor cells in the immunocompetent host is novel because it has not been previously described. The findings from these studies provide a basis for developing novel immunological approaches for cancer treatment by specifically targeting cancer stem cells.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3322.