In a murine xenograft model of irradiation, a PD-1 blockade combination with an induced colony-stimulating factor 1 (CSF-1) inhibitor significantly reduced external beam radiation-associated repopulation of the tumor microenvironment with macrophages and led to potent synergy due to the lack of immunosuppressive signaling from macrophages [93]. Here, PDCD1 is linked to neoplasm.