Figure 1. CSC/CIC targeting immunotherapy. (A) Characters of CSC/CIC. CSC/CIC has three distinct characteristics: (1) high tumor-initiating ability, (2) self-renewal ability and (3) differentiation ability. (B) Three groups of tumor-associated antigens. Tumor-associated antigens can be classified into 3 groups according to the expression in CSC/CIC and non-CSC/CIC: (1) CSC/CIC antigens, which are expressed in CSCs/CICs but not in non-CSCs/CICs (e.g., MAGE-A3 and MAGE-A4); (2) shared antigens, which are expressed in both CSCs/CICs and non-CSCs/CICs (e.g., CEP55, SURVIVIN); and (3) non-CSC/CIC antigens, which are expressed in only non-CSCs/CICs but not in CSCs/CICs (e.g., AMACR, HIFPH3). (C) CSC/CIC-targeting immunotherapy. CSC/CIC antigen specific CTLs recognize only higher tumorigenic CSCs/CICs, whereas shared antigen specific CTLs, NK cells and γδT cells recognize both CSCs/CICs and non-CSCs/CICs. CSCs/CICs might be eliminated most efficiently by CSC/CIC antigen-specific CTLs.