FIG. 6.

A: In a clinically relevant combination, low-dose rapamycin treatment significantly prolonged islet graft survival and synergized with oATP treatment in promoting long-term islet graft survival in BALB/c islet allografts transplanted into hyperglycemic C57BL/6 mice (***P < 0.0001 vs. untreated: §P < 0.05 vs. oATP-treated and rapamycin), and rapamycin was more effective in prolonging graft survival in P2X7R^−/− than in wild-type recipients (n = 7; #P < 0.05 vs. rapamycin-treated wild-type). Histological analysis of graft islets at day 100 after transplantation in oATP+rapamycin-treated mice revealed preserved islet structure (B) and insulin (F) and glucagon production (G) with mild extraislet T-cell (C) and macrophage infiltration (E) as well as substantial Treg numbers (D). Splenocytes obtained from oATP+rapamycin-treated islet-transplanted mice at day 100 displayed a lower number of cells producing IFN-γ compared with untreated or oATP-treated mice at day 14 when challenged with irradiated donor splenocytes (n = 3, ***P < 0.0001 vs. untreated; §§P < 0.01 vs. oATP-treated) (H). The percentages of CD4⁺ effector T cells at day 14 (n = 3, *P < 0.05 vs. untreated; §P < 0.05 vs. oATP-treated) (I) and CD8⁺ effector T cells at day 14 (n = 3, *P < 0.05, ***P < 0.0001 vs. untreated) (J) were also reduced. No differences in the number of Th17 cells were observed at day 14 (n = 3, *P < 0.05 vs. untreated) (K), whereas a slight reduction was seen in the percentage of Tregs (n = 3, *P < 0.05 vs. untreated) (L) when rapamycin was added to the treatment protocol. A better protection of the islet graft structure was observed in rapamycin-treated P2X7R^−/− (S, W, and X) compared with untreated P2X7R^−/− recipients (M, Q, and R) at day 14 after transplantation. Immune cell infiltration was reduced in rapamycin-treated P2X7R^−/− recipients (T, U, and V) compared with untreated P2X7R^−/− recipients (N, O, and P). H&E, hematoxylin and eosin.