Fig. 2. IAC induces transient upregulation of CD25 and expansion of host Tregs following MHC-matched HCT.

(A) B6 (H-2^b) mice were non-ablatively conditioned (5.5Gy TBI) and 24 hours later transplanted with 4 × 10⁶ 129P3/J B6 (H-2^b) T-cell depleted bone marrow (Day 0). Three and 5 days post-HCT, recipient mice were administered IAC ip. At one week post-HCT, circulating PBL were analyzed for CD25 expression on CD4⁺ cells, represented by MFI (results represent MFI values ± SEM; n = 3 mice/group, 3 independent experiments). (B) In an independent experiment, B6 mice were conditioned and transplanted with 129P3/J as described in Fig. 1A. IAC or PBS was infused at days +3 and +5. At the indicated intervals post-HCT, PBL were analyzed for CD25 MFI on CD4⁺ cells (*p < 0.05; n = 3 mice/group). Data presented as MFI ± SEM. Data points without error bars indicate SEM values within symbols. IAC induced rapid and transient activation of host Treg cells. (C) B6 mice conditioned with 5.5 Gy TBI and transplanted with 4 × 10⁶ BALB. B TCD-BM were infused with IAC or PBS at days +3 and +5. Recipient mice or normal B6 PBL were then analyzed for circulating CD4⁺ CD25⁺ FoxP3⁺ cells (gated on mononuclear cells) at 1 week post-HCT. Results represent mean cell counts/100μl ± SEM (n = 3 pools of 2 mice/group; normal B6 control mice: n = 4 mice/group, individual data points analyzed). IAC infusion resulted in marked expansion of circulating host Treg populations post-HCT.