Administration of oIL-2 expands oIL-2Rβ Tregs early after allo-HSCT. Expansion of donor oIL-2Rβ Treg^luc+ cells in BALB/c recipients. After 8.8 Gy TBI, BALB/c mice received TCD BM + CD45.1⁺ Foxp3^GFP+luc+ Tregs (1 × 10⁶ or 0.2 × 10⁶) that were transduced with oIL-2Rβ. To induce aGVHD, the mice were infused with 1 × 10⁶ of C57BL/6 T cells on day 2. (A-B) Whole-body photons derived from Treg^luc+ cells expanding in BALB/c recipients at days 7 and 14 after allo-HSCT. (A) The animals that received oIL-2 protein (n = 10) (top) and those that received PBS (n = 10) (bottom) are shown. (B) Quantification of whole-body photons using the 1:1 (top) and 5:1 (bottom) Tcon:Treg ratio. (C-D) Ex vivo BLI pictures of donor oIL-2Rβ Treg^luc+ in the spleen, pLNs, mLNs, and GIT imaging. (C) The animals that received oIL-2 protein (top) and those injected with PBS at different time points after allo-HSCT (bottom) are shown. (D) Mean ± SD of total flux (photons per second [p/s]) obtained from each region of interest. Photons derived from Treg^luc+ cells in the spleen (left) and mLNs (right) at days 2, 3, 5, and 7 after allo-HSCT. (E) PB, spleen, pLNs, and mLNs were recovered and analyzed by flow cytometry on day 7 after allo-HSCT. Pooled data from 3 independent experiments including 4 to 5 mice per group per each experiment. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001. Color bar represents signal intensity code over body surface area.