Long-term allograft survival in IL-2–JES6-1–treated mice. (A) Streptozotocin-induced diabetic C57BL/6 (H2^b) mice were treated with PBS (n = 10), 1 µg IL-2 (n = 4), or 1 µg/5 µg IL-2–JES6-1 (n = 34) on three consecutive days (days −3, −2, and −1). On day 0, mice were transplanted with BALB/c (H2^d) islets, and BGLs were monitored as a measure of graft function and survival. Grafts were considered rejected after two consecutive BGLs >16 mmol/liter after a period of normoglycemia. Cumulative data from nine independent experiments are shown. (B) Representative hematoxylin-eosin–stained islet graft under the kidney capsule (>100 POD; left), islet graft stained for insulin (middle), and graft with minor peri-islet mononuclear accumulation (arrow; right; n = 5). (C) Mixed lymphocyte reaction using T cells from long-term engrafted mice or control naive mice as responders, and syngeneic C57BL/6, donor BALB/c, or third party CBA/Ca-irradiated splenocytes as stimulators. The proliferation of responders was measured by incorporation of [³H]thymidine. Data are means ±SEM. (D) Survival of BALB/c islet grafts in B6.RAG^−/− hosts after adoptive transfer of 2 ×10⁷ splenocytes i.v. from long-term engrafted mice (n = 9) or control naive C57BL/6 mice (n = 3). (E) Survival of BALB/c islet grafts in C57BL/6 hosts after challenge with BALB/c T-depleted splenocytes at either <100 d (n = 6) or >100 d (n = 5) after grafting. Data are shown as a Kaplan-Meier graft survival (left) or blood glucose measurement (the horizontal gray line indicates a BGL of 16 mmol/liter, the threshold for rejection; right). (F) Representative immunohistochemical staining for Foxp3⁺ cells in peri-islet mononuclear accumulation (inset; n = 5). Foxp3⁺ cells are denoted by horseradish peroxidase staining (arrowheads). I, islet graft. Data are representative of three independent experiments unless otherwise specified. Bars: (B) 100 µm; (F, left) 750 µm; (F, right) 20 µm.