MHA research has been focusing on the characterization of the natural immune responses in patients with cancer with a special focus on immune regulation. The understanding of regulatory cells is based on the discovery of suppressor cells, which are indispensable to assure peripheral cells and immune homeostasis. Especially, the importance of regulatory T cells (Tregs) for the regulation of immunity, e.g., modulating host responses to tumors or inhibiting the development of autoimmunity, has received much attention.