Examination of CD25 was chosen because of potent combined effects of SBRT and IL-2 in the clinic [27]; CTLA-4 and PD-1 because of potent (combined) efficacy of α-CTLA4 and α-PD-1 mAbs in late-stage melanoma patients [32] and CD137 because of potent combined effects of α-CD137/α-PD-1 mAbs and SBRT in mouse breast cancer models [14, 22]. Here, CTLA4 is linked to breast cancer.