For flow cytometry and imaging studies with murine tissues, the following antibodies were purchased from Biolegend: anti-CD45 (30-F11), anti-CD31 (390), anti-PDPN (8.1.1), anti-α-smooth muscle actin (1A4), anti-Thy1 (53–2.1), anti-CD140α (APA5), anti-CD140b (APB5), anti-CD106 (429), anti-CD4 (RM4.5), and anti-CD8 (RM2206). The anti-FAP used for flow cytometry analysis was provided by Ellen Pure and has been validated (anti-mouse FAP 73.3)(8 (link)). For immunofluorescent analysis, the Roche anti-FAP 28H1 clone was used (26 (link)). Functional-grade purified anti-CD3ε (145–2C11) was from BD Biosciences, and anti-CD28 (37.51) was from Biolegend. Antibodies used to stain human samples include viability dye (L10119; Life Technologies), anti-PDPN (clone NZ1.3; eBioscience), anti-Thy1 (clone 5E10; BD Biosciences), anti-CD4 (clone A161A1; Biolegend) and anti-CD8 (clone HIT8α; Biolegend). For PBMC stimulation, anti-human CD3 (clone OKT3; eBioscience) and anti-human CD28 (clone CD28.2; eBioscience) were used. L-NMMA (NG-monomethyl-L-arginine) was purchased from Calbiochem and CFSE (carboxyfluorescein diacetate succinimidyl ester) was from Invitrogen.