MECHANISMS OF GVHD PREVENTION WITH POST-TRANSPLANT CYCLOPHOSPHAMIDE

描述(申请人提供)：在人类白细胞抗原配型相合的环境中，新出现的临床数据表明，移植后给予大剂量环磷酰胺(Cy)作为单一药物，在预防异基因造血干细胞移植(AllHSCT)后的急性和慢性移植物抗宿主病(GVHD)方面都有效。使用这种策略进行移植的患者感染发生率较低，尽管疾病晚期，但他们的存活率很好，这表明这种方法保留了移植物抗白血病的效果。大剂量Cy作为移植后免疫抑制剂的疗效背后的确切机制尚不完全清楚，在我们正在进行的多机构临床试验的背景下对T细胞免疫恢复的相关性进行系统研究将对完全理解这些机制至关重要。我们假设，大剂量Cy通过减少效应T细胞的频率，同时保留关键调节性T细胞(Treg)池来预防急性GVHD。此外，我们预测，调节性T细胞稳态的快速建立对于耐受性的发展和慢性移植物抗宿主病的存在至关重要。最后，我们假设，在大剂量Cy预防后需要常规免疫抑制治疗的2-4级急性GVHD将与Treg间隔中多样化T细胞受体(TCR)谱系的恢复显著延迟有关。为了检验我们假设的有效性，我们将首先测试在接受移植后环磷酰胺治疗的患者中，效应器和调节性T细胞亚群的细胞和分子变化与2-4级急性移植物抗宿主病发生之间的关联。其次，我们将确定Treg曲谱重建和胸腺恢复是否影响慢性GVHD的缺失和耐受性的发展。第三，通过使用高通量DNA测序技术测量幼稚、记忆和调节性T细胞亚群中TCR2链CDR3区序列的多样性，我们将分析在大剂量Cy预防后发生的任何显著的GVHD是否与不同Treg谱系的延迟重建有关。这项拟议的工作有望提供基本的机制见解，支持使用短程GVHD预防，促进耐受诱导，并在没有正在进行的药物免疫抑制的环境中提供免疫系统重建。它还将提供T细胞亚群免疫光谱的高分辨率图像，并照亮一条更好地控制同种异体反应性的途径。公共卫生相关性：移植后使用环磷酰胺作为短程GVHD预防，促进耐受诱导，有望减少与慢性免疫抑制相关的毒性，并改善GVHD的预防，GVHD是异基因造血干细胞移植(AllHSCT)后发病率和死亡率的主要原因。我们预计，一旦了解了环磷酰胺预防GVHD和诱导耐受的有效性背后的操作机制，并获得了其对移植后免疫恢复影响的高分辨率图像，该策略可能会为提高肿瘤特异性免疫和防止疾病复发的免疫治疗干预提供一个最佳平台。此外，这种方法可能会将异基因造血干细胞移植的适用范围扩大到非恶性血液病和自身免疫性疾病的患者。

DESCRIPTION (provided by applicant): Emerging clinical data in the HLA-matched setting suggest that high-dose post-transplant cyclophosphamide (Cy) given as a single agent is effective in preventing both acute and chronic graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (alloHSCT). Patients who undergo transplants using this strategy have a low incidence of infections, and despite advanced disease stage, their survival rate is favorable, suggesting that this approach retains the graft-versus-leukemia effect. The exact mechanisms behind the efficacy of high-dose Cy as a post-transplant immunosuppressant are not fully understood, and systematic study of the correlates of T-cell immune recovery in the context of our ongoing multiinstitutional clinical trial will be crucial for complete understandingof the mechanisms. We hypothesize that high-dose Cy prevents acute GVHD by reducing the frequency of effector T cells while sparing the critical regulatory T-cell (Treg) pool. In addition we predict that the rapid establishment of regulatory T-cell homeostasis is critical for the development of tolerance and the absence of chronic GVHD. Finally, we hypothesize that grade 2-4 acute GVHD that requires treatment with conventional immune suppression after high-dose Cy prophylaxis will be associated with a significant delay in the recovery of a diverse T-cell receptor (TCR) repertoire in the Treg compartment. To test the validity of our hypotheses, we will first test for associations between the cellular and molecular changes in the effector and regulatory T-cell subsets and the development of grade 2-4 acute GVHD in patients treated with post-transplantation Cy. Second, we will determine whether the absence of chronic GVHD and the development of tolerance are influenced by Treg repertoire reconstitution and thymic recovery. Third, by measuring the TCR 2 chain CDR3 region sequence diversity in the naive, memory and regulatory T- cell compartments using high-throughput DNA sequencing technology, we will analyze whether any significant GVHD that occurs after the high-dose Cy prophylaxis is associated with the delayed reconstitution of a diverse Treg repertoire. The work proposed is expected to provide essential mechanistic insights supporting the use of a short course of GVHD prophylaxis that promotes tolerance induction and provides immune system reconstitution in an environment free of ongoing pharmacologic immunosuppression. It will also provide a high- resolution picture of the immune spectra in T-cell subsets and illuminate a path toward better control of alloreactivity. PUBLIC HEALTH RELEVANCE: The use of post-transplantation cyclophosphamide as short-course GVHD prophylaxis that promotes tolerance induction carries the promise of decreasing the toxicities associated with chronic immunosuppression and of improving the prevention of GVHD, which is the major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplant (alloHSCT). We expect that once the operational mechanisms behind the efficacy of cyclophosphamide in GVHD prevention and tolerance induction are understood and a high- resolution picture of its effect on post-transplant immune recovery is gained, this strategy may potentially provide an optimal platform for immunotherapeutic interventions that boost tumor-specific immunity and prevent disease relapse. In addition, this approach may extend the applicability of alloHSCT to patients with non-malignant hematological and autoimmune disorders.