Survival of rat skin xenografts on mice treated with a donor specific transfusion and anti-CD154 mAb is IL-4 dependent

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Abstract 504
Introduction Clinical organ transplantation is compromised by the paucity of available organs and the requirement for lifelong immunosuppression. In order to address these issues, we designed an animal model of xenotransplantation tolerance and demonstrated that donor specific transfusion (DST) and blockade of the CD40-CD154 costimulation pathway prolonged the survival of rat skin and islet grafts in mice. We hypothesized that this effect is due to interference with the activation of host xenoreactive T-lymphocytes. In order to investigate possible underlying mechanisms, we tested the hypothesis that xenograft survival in mice treated with our tolerance induction protocol requires the presence of specific cytokines. Because IFNγ but not IL-4 or IL-10 are known to be required for the induction of allograft tolerance, we assessed xenograft survival in mice devoid of these cytokines, which are known to influence the development of helper, regulatory, and cytotoxic T-lymphocytes.
Materials and methods We measured rat skin xenograft survival on cytokine knockout mice treated with DST (10 × 106 LEW rat spleen cells intravenously on day −7 relative to grafting) and anti-CD154 mAb (0.25 mg intraperitoneally on days −7, −4, 0, +4). Recipients were C57BL/6+/+, C57BL/6-IFNγnull, C57BL/6-IL-10null, and C57BL/6-IL-4null mice.
Results Genetic deletion of IFNγ or IL-10 did not abrogate xenotolerance induction (Table). In contrast, treatment of IL-4 KO mice with DST plus anti-CD154 mAb did not prolong rat xenograft survival. Rat skin xenografts on IL-4 KO mice were rejected at a rate comparable to that observed in the untreated C57BL/6 group (Table).
Conclusions These data demonstrate that the cytokines IFNγ and IL-10 are not required to prolong rat skin xenografts in mice treated with DST plus anti-CD154 mAb. The data also suggest that IL-4 is a significant factor required for successful skin xenograft transplantation tolerance induction. We conclude that the mechanism of skin xenograft survival in mice treated with DST and anti-CD154 mAb is very different from that of skin allograft survival in similarly treated mice in that it requires IL-4 but not IFNγ.
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