Increased frequency of Tregs in lymphoid and nonlymphoid tissues of IRX4204-treated recipients. (A-B) BALB/c recipients were lethally irradiated and infused with 10⁷ B6 NTCD BM cells and 5 × 10⁶ B6 splenocytes. Recipients were treated IP with either vehicle or IRX4204 daily. The frequency of donor Tregs and representative flow cytometry plots show Foxp3 expression in donor CD4⁺ cells on days 7 (spleen [SPL], mesenteric lymph nodes [MLN]) (A) and 14 (B) after transplantation. Data from an experiment with n = 5 per group per day. (C) Naive CD4⁺ T cells (CD4⁺ CD44^loCD62L^hi) were activated with soluble anti-CD3, TGF-β, and irradiated T-cell–depleted syngeneic splenocytes, with or without 100 nM IRX4204. The percentage of Foxp3⁺ cells was determined on day 4 by flow cytometry. Data are representative of 2 experiments. *P < .05; **P < .01; ***P < .001; ****P < .0001.