(A) CD8⁺CD39⁺CD26^– Tregs sorted from the peripheral blood of GCA patients and controls were mixed with CD4⁺ T cells and activated CD4⁺ pZAP70⁺ T cells were measured by flow cytometry after 15 minutes. Representative contour plots and results from 7 controls and 7 GCA patients. (B) CD8⁺ Tregs induced ex vivo from GCA patients and controls were mixed with CD4⁺ T cells, and pZAP70 was quantified as above. Representative contour plots and results from 6 controls and 6 GCA patients. (C and D) Freshly sorted and ex vivo–induced CD8⁺ Tregs were mixed with CFSE-labeled CD4⁺ T cells. Proliferation was measured 5 days later. Representative histograms from 6 controls and 6 GCA patients. (E and F) CD8⁺ Tregs were induced ex vivo, CFSE labeled, and mixed with heathy PBMCs before adoptive transfer into NSG mice. One control group received no CD8⁺ Tregs. (E) Absolute numbers of CD8⁺ Treg cells in the blood and spleen measured by flow cytometry. Results from 12 mice. (F) Absolute numbers of human CD4⁺ T cells in the spleen measured by flow cytometry. Results from 6 mice each. (G–I) Vasculitis was induced in human arteries engrafted into NSG mice. Ex vivo–induced CD8⁺ Tregs from patients and controls (HC) were coinjected. (G) Vessel wall–infiltrating T cells visualized by immunostaining for CD3 (green). Nuclei marked with DAPI. Representative images from the 3 study cohorts (n = 6 each). Scale bar: 20 μm. (H) Frequencies of vessel wall–infiltrating CD3⁺ T cells. Each dot represents 1 inflamed artery. (I) Tissue transcriptome of explanted arteries analyzed by RT-PCR; β-actin served as control. Each dot represents 1 artery specimen. Data are mean ± SEM. *P < 0.05; **P < 0.01; ***P < 0.001 by 1-way ANOVA and post-ANOVA pairwise 2-group comparisons conducted with Tukey’s method (E, F, H, and I) or unpaired Mann-Whitney-Wilcoxon rank test (A and B).