Targeting Treg cells in cancer immunotherapy

Foxp3-expressing regulatory T (Treg) cells, which are indispensable for preventing autoimmunity, also suppress effective tumor immunity. Treg cells abundantly infiltrate into tumor tissues, which is often associated with poor prognosis in cancer patients. Removal of Treg cells enhances anti-tumor immune responses but may also elicit autoimmunity. A key issue in devising Treg-targeting cancer immunotherapy is, therefore, how to specifically deplete Treg cells infiltrating into tumor tissues without affecting tumor-reactive effector T cells, while suppressing autoimmunity. This can be achieved by differentially controlling Treg and effector T cells by various ways. In this review, we discuss how tumor-infiltrating Foxp3⁺ Treg cells hamper effective anti-tumor immune responses especially in tumor tissues and how they can be specifically targeted for augmenting tumor immunity but not autoimmunity.