Mechanism of Interferon Gamma Primed Mesenchymal Stromal Cell Efferocytosis of Activated T Cells

摘要 移植物抗宿主病(GVHD)是造血细胞移植后发病率和死亡率的主要原因。 移植(HCT)影响高达70%的患者，直接占与方案相关的死亡的三分之一。 30多年来，标准的预防措施没有改变，特别是缺乏有前途的新药物。 间充质基质细胞(MSCs)具有免疫抑制的特性，已被吹捧为治疗 GVHD，但临床试验在不同的研究中产生了相互矛盾的结果，引发了对其有效性的怀疑。在我们的 Galleu等人最近的研究认为，骨髓间充质干细胞临床成功开发的根本障碍。 尽管如此，我们对MSC介导的免疫机制还没有一个统一的模型 体内抑制。我们最近发现，干扰素γ激活的骨髓间充质干细胞(γMSCs)，其流量为次要的 淋巴器官(SLO)后的HCT，是吞噬细胞吞噬同种异体反应性T细胞。这一过程 在小鼠模型中对抑制T细胞增殖和预防致死性移植物抗宿主病至关重要。这个 抑制效应取决于(I)转运至次级淋巴器官，(Ii)γ间充质干细胞剂量和(Iii) 有可能吞噬T细胞。因此，我们认为，要提高γ骨髓间充质干细胞预防移植物抗宿主病的效力，必须 增强γ间充质干细胞的吞噬功能。这项提案的首要目标是确定可行的 γ间充质干细胞吞噬分子机制中的靶点可以被用来增加 γ间充质干细胞被吞噬，从而抑制移植物抗宿主病。在目标1中，我们将确定趋化因子和 相应的受体控制γ间充质干细胞向SLO的转运。然后，我们将强制执行相关的 以确定这是否会增加运输的效率，从而导致γ的本地化， 更大的T细胞抑制，更有效的GVHD预防。在目标2中，我们将确定 AX1/Gas6介导活化T细胞的结合和吞噬。此外，我们将确定是否 AXL的强制表达增强了γ间充质干细胞的结合和吞噬，从而抑制了 GVHD。在目标3中，我们将确定γMSCs参与Lc3相关吞噬作用(LAP)的程度 吞噬活化的T细胞。LAP是一种非正规性自噬，可被西罗莫司刺激 (雷帕霉素)。如果LAP是T细胞吞噬的主要机制，那么西罗莫司联合治疗可能 增强γ对移植物抗宿主病的抑制作用。这份为期5年的计划书中产生的数据可能会对 所有接受HCT的患者，并可能通过降低与方案相关的风险来扩大HCT的资格 发病率和死亡率。

Abstract Graft versus host disease (GVHD) is the primary cause of morbidity and mortality after hematopoietic cell transplantation (HCT) affecting up to 70% of patients and directly accounting for a third of regimen-related death. Standard prophylaxis has not changed in over 30 years and especially promising new agents are lacking. Mesenchymal stromal cells (MSCs), with immune suppressive properties, have been touted as therapy for GVHD, but clinical trials have generated conflicting results across studies raising doubt of their utility. In our view, the fundamental barrier to the successful clinical development of MSCs, the recent study of Galleu et al. notwithstanding, is that we do not have a unified model of the mechanisms of MSC-mediated immune suppression in vivo. We have recently shown that interferon γ primed MSCs (γMSCs), which traffic to secondary lymphoid organs (SLO) after HCT, are phagocytes that engulf alloreactive T cells by efferocytosis. This process is essential for suppression of T cell proliferation and prevention of lethal GVHD in a murine model. The suppressive effect is dependent on (i) trafficking to secondary lymphoid organs (SLO), (ii) γMSC dose and (iii) potential to engulf T cells. Thus, we posit to enhance the potency of γMSC prophylaxis of GVHD, we must enhance the potency of γMSC efferocytosis. The overarching objective of this proposal is to identify actionable targets in the molecular mechanism of γMSC efferocytosis that can be leveraged to increase the potency of γMSC engulfment, and thereby, suppression of GVHD. In aim 1, we will identify the chemokines and corresponding receptors that govern γMSC trafficking to SLO. Then, we will enforce expression of the relevant receptors in γMSCs to determine if that will increase the efficiency of trafficking resulting in great SLO localization, greater T cell suppression, and more effective GVHD prophylaxis. In Aim 2, we will determine the extent to which Axl/Gas6 mediates the binding and engulfment of activated T cells. Additionally, we will determine if enforced Axl expression enhances binding and engulfment and thereby the potency of γMSC suppression of GVHD. In Aim 3, we will determine the extent to which γMSCs engage LC3-associated phagocytosis (LAP) to engulf activated T cells. LAP is a form of noncanonical autophagy that can be stimulated by sirolimus (rapamycin). If LAP is the primary mechanism of T cell engulfment, then concomitant therapy with sirolimus could potentiate γMSC suppression of GVHD. The data generated in this 5-year proposal has the potential to impact all patients undergoing HCT and possibly expand the eligibility for HCT by decreasing the risk of regimen-related morbidity and mortality.