CTLA4 and neoplasm: In addition, therapy using anti-CTLA4, which depletes T regulatory cells in the tumor as a necessary mechanism of action [36, 37], synergizes with hypofractionated radiation therapy in mouse models [38, 39] and a number of clinical anecdotes have been reported where anti-CTLA4 plus hypofractionated palliative radiation have resulted in systemic tumor cure [7].