In a human artery-engrafted Severe Combined Immunodeficiency (SCID) mouse model, injection of peripheral blood mononuclear cells (PBMCs) from GCA patients followed by administration of an anti-PD-1 antibody resulted in marked T-cell infiltration into the vessel wall, accompanied by excessive production of proinflammatory cytokines such as IFN-γ, IL-17, and IL-21. Here, IL17A is linked to temporal arteritis.