Background

Vascularized composite allotransplantation (VCA) is a novel and life-enhancing procedure to restore a patient's function and/or appearance. Current immunosuppression in VCA recipients is based on calcineurin inhibitor (CNI) therapy that can lead to severe complications, such that inducing immune tolerance is a major goal of VCA research. In contrast to CNI, rapamycin (RPM) is thought to be beneficial to the development of immune tolerance by suppressing T-effector cells (Teffs) and expanding T-regulatory (Treg) cells. However, we found high dose RPM monotherapy prolonged VCA survival by only a few days, leading us to explore the mechanisms responsible.

Methods

A mouse orthotopic forelimb transplantation model (BALB/c- > C57BL/6) was established using WT mice, as well as C57BL/6 recipients with conditional deletion of T-bet within their Treg cells. Events in untreated VCA recipients or those receiving RPM or FK506 therapy were analyzed by flow-cytometry, histopathology and real-time qPCR. Results. Therapy with RPM (2 mg/kg/d, p < .005) or FK506 (2 mg/kg/d, p < .005) each prolonged VCA survival. In contrast to FK506, RPM increased the ratio of splenic Treg to Teff cells (p < .05) by suppressing Teff and expanding Treg cells. While the proportion of activated splenic CD4 + Foxp3- T cells expressing IFN-γ were similar in control and RPM-treated groups, RPM decreased the proportions ICOS+ and CD8+ IFN-γ + splenic T cells. However, RPM also downregulated CXCR3+ expression by Tregs, and forelimb allografts had reduced infiltration by CXCR3+ Treg cells. In addition, allograft recipients whose Tregs lacked T-bet underwent accelerated rejection compared to WT mice despite RPM therapy.

Conclusions

We demonstrate that while RPM increased the ratio of Treg to Teff cells and suppressed CD8+ T cell allo-activation, it failed to prevent CD4 Teff cell activation and impaired CXCR3-dependent Treg graft homing, thereby limiting the efficacy of RPM in VCA recipients.

中文翻译：

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雷帕霉素单一疗法在血管化复合同种异体移植中的疗效有限。

背景

血管化复合同种异体移植（VCA）是一种新颖且可延长生命的过程，可恢复患者的功能和/或外观。当前VCA受体中的免疫抑制是基于钙调神经磷酸酶（CNI）治疗的，它可能导致严重的并发症，因此诱导免疫耐受是VCA研究的主要目标。与CNI相反，雷帕霉素（RPM）被认为通过抑制T效应细胞（Teffs）和扩展T调节（Treg）细胞而有益于免疫耐受的发展。但是，我们发现高剂量RPM单药疗法仅将VCA生存期延长了几天，从而使我们探索了引起这种作用的机制。

方法

使用WT小鼠以及在其Treg细胞内条件性删除T-bet的C57BL / 6受体，建立了小鼠原位前肢移植模型（BALB / c-> C57BL / 6）。通过流式细胞仪，组织病理学和实时定量PCR分析未经治疗的VCA受体或接受RPM或FK506治疗的患者的事件。结果。RPM（2 mg / kg / d，p  <.005）或FK506（2 mg / kg / d，p <.005）的治疗均延长了VCA生存期。与FK506相比，RPM增加了脾脏Treg与Teff细胞的比例（p <.05）通过抑制Teff并扩增Treg细胞。在对照组和RPM处理组中，表达IFN-γ的活化脾CD4 + Foxp3- T细胞的比例相似，而RPM降低了ICOS +和CD8 +IFN-γ+脾T细胞的比例。然而，RPM也下调了Tregs的CXCR3 +表达，并且前肢同种异体移植物减少了CXCR3 + Treg细胞的浸润。此外，尽管进行了RPM治疗，但与WT小鼠相比，Treg缺乏T-bet的同种异体移植受体经历了加速排斥反应。

结论

我们证明，虽然RPM增加了Treg与Teff细胞的比率并抑制了CD8 + T细胞的同种激活作用，但它未能阻止CD4 Teff细胞激活并损害了CXCR3依赖性Treg移植物归巢，从而限制了RPM在VCA受体中的功效。