The onset of aGVHD is not correlated with an increase in circulating Th17 cells. PBMCs from transplanted patients were collected at the onset of GVHD before commencing steroid therapy (GVHD⁺; n = 20) and one week before onset of GVHD (n = 10). Healthy donors (HDs; n = 20) and transplanted patients without GVHD (n = 14) served as controls (GVHD⁻). PBMCs were stimulated with phorbol myristate acetate and ionomycin, and gated CD3⁺ T cells were analyzed for production of (A) IL-17 (GVHD⁺, 0.33% ± 0.05%; GVHD⁻, 0.52% ± 0.11%; healthy donors, 0.18% ± 0.04%) and (B) IL-22 (GVHD⁺, 0.88% ± 0.11%; GVHD⁻, 1.33% ± 0.31%; healthy donors, 0.75% ± 0.17%.). Supernatants from PBMCs activated via αCD3/CD28 were analyzed for production of (C) IL-17 (GVHD⁺, 4.83 ± 2.28 pg/mL, n = 7; GVHD⁻, 64.3 ± 8.76 pg/mL, n = 10; healthy donors, 84.55 ± 28.05 pg/mL, n = 8) and (D) IL-22 (GVHD⁺, 433 ± 254 pg/mL, n = 7; GVHD⁻ patients, 2146 ± 451 pg/mL, n = 10; and healthy donors 1361.0 ± 209.7 pg/mL, n = 8). Amounts of (E) IL-17 and (F) IL-22 secreted by phorbol myristate acetate and ionomycin stimulated PBMCs isolated one week before the onset of GHVD was compared with production at onset (P = not significant). Each spot represents an individual donor/patient. Error bars represent SEM. *P < .05.