ABSTRACT
INTRODUCTION Cytotoxic T cells are unique in their capability to eliminate cancer cells whether these are proliferating or temporarily non-dividing, and whether they are cancer stem cells or their progeny. Moreover, T cells are found and can act in almost all compartments of the body with limited activity only in immunoprivileged sites such as the brain or testes. In mouse models, numerous approaches have shown that T cells can-as a monotherapy-eradicate large established tumors ( 1 – 4 ). The capacity of T cells to completely eradicate target cells is also evident from their key role in fi ghting viral diseases by eliminating virus-infected cells. It is therefore highly attractive to fi nd a means of mounting T-cell responses against malignant cells for cancer therapy. However, given the enormous cytotoxic potential of T cells, the specifi city of target recognition and a tight control of their activity are important for the therapeutic use of T cells in cancer treatment. The induction of various kinds of autoimmune reactions by anti-cytotoxic T lymphocyte-associated antigen 4 antibody ipilimumab concurrent with its anti-tumor activity ( 5 ) demonstrates the diffi culty of mounting T-cell responses that are specifi c for tumor cells.
