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IL-10 is required for the prevention of islet xenograft rejection by ex vivo-expanded human regulatory T cells in a humanized mouse model

Shounan Yi, Ming Ji, Jingjing Wu, Xiaoqian Ma, Peta Phillips, Wayne Hawthorne, Philip O’Connell

Westmead Hospital, Centre for Transplant & Renal Research, Westmead Millennium Institute, Westmead Hospital, Sydney, NSW, Australia

Islet xenograft rejection is initiated predominately by a T-cell mediated immune response. Our previous study has shown that ex vivo-expanded human regulatory T cells (Tregs) can suppress xenogeniec CD4+ T cell-mediated immune response in vitro via IL-10-involved mechanisms. This study aimed to investigate the ability of human Tregs to regulate the human anti-pig xenogeneic response in vivo and the mechanism(s) involved. Neonatal porcine islet cell clusters (NICC) recipient NOD-SCID IL2rgamma-/- mice were transferred with 2 x 10 ⁶ ex vivo-expanded CD4+CD25+CD127lo human Tregs 7 days prior to rechallenge with or without 1 x 10⁷ CD25+ cell-depleted autologous peripheral blood mononuclear cells (PBMCs), and treatment with or without anti-human IL-10 monoclonal antibody or IgG isotype antibody at days 0, 3, 7, 10 of human PBMC rechallenge. In a separate experiment, NICC recipient mice were reconstituted with 1 x 10⁷ CD25+ cell-depleted human PBMCs and treated with or without recombinant human IL-10 (rhIL-10). Graft survival was monitored by immunohistochemical examination after human PBMC transfer. Mice receiving human PBMCs alone rejected their NICC xenogafts within 28 days post PBMC transfer, whereas those also receiving autologous Tregs beforehand displayed long-term graft survival along with reduced graft infiltration by human CD4+CD25- cells and their production of IFN-gamma and detection of intragraft human Tregs expressing Foxp3 and IL-10. Neutralization of human IL-10 in mice receiving both human Tregs and PBMCs resulted in markedly shortened xenograft survival associated with impaired Treg-mediated suppression of the human anti-pig xenogeneic response. However, when treated with rhIL-10 mice receiving human PBMCs alone demonstrated prolonged graft survival compared with their untreated counterparts. We show for the first time that human Tregs can prevent islet xenograft rejection by inhibiting effector function and graft infiltration through IL-10-mediated suppression, highlighting a potential strategy to induce tolerance in islet xenotransplantation.