According to the cancer stem cell (CSC) theory, therapies that do not target the CSC compartment have limited, if any, chances to eradicate established tumors. While cytotoxic T lymphocytes (CTLs) have the potential to recognize and kill single neoplastic cells within a tissue, whether CSCs can be targeted by the immune system during spontaneous or vaccination-elicited responses is poorly defined. Here, we provide experimental evidence showing that CSC lines established from the prostate of transgenic adenocarcinoma of the mouse prostate (TRAMP) mice expressed prostate cancer-associated antigens, MHC Class I and II molecules as well as ligands for natural killer (NK) cell receptors. Indeed, CSC were targets for both NK cell- and CTL-mediated cytotoxicity, both in vitro and in vivo. The administration of dendritic cells pulsed with irradiated CSCs induced a tumor-specific immune response that was more robust than that induced by dendritic cells pulsed with differentiated tumor cells, delayed tumor growth in mice challenged with prostate CSCs and caused tumor regression in TRAMP mice. Thus, CSC are targeted by both innate and adaptive immune responses and might be exploited for the design of novel immunotherapeutic approaches against cancer.
Keywords: cancer stem cells; dendritic cell; prostate cancer; tumor immunity; vaccination.