MECHANISMS OF GVHD PREVENTION WITH POST-TRANSPLANT CYCLOPHOSPHAMIDE

描述（由申请方提供）：HLA匹配背景下的新临床数据表明，移植后高剂量环磷酰胺（Cy）单药给药可有效预防异基因造血干细胞移植（alloHSCT）后的急性和慢性移植物抗宿主病（GVHD）。使用这种策略进行移植的患者感染发生率低，尽管疾病处于晚期，但其存活率是有利的，这表明这种方法保留了移植物抗白血病效应。高剂量Cy作为移植后免疫抑制剂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细胞免疫恢复相关性的系统研究对于完全理解机制至关重要。我们推测，高剂量的Cy通过降低效应T细胞的频率，同时保留关键的调节性T细胞（Treg）库来预防急性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GVHD的缺乏是至关重要的。最后，我们假设在高剂量Cy预防后需要用常规免疫抑制治疗的2-4级急性GVHD将与Treg隔室中的多种T细胞受体（TCR）库的恢复的显著延迟相关。为了检验我们的假设的有效性，我们将首先检验效应和调节性T细胞亚群的细胞和分子变化与移植后Cy治疗的患者中2-4级急性GVHD的发展之间的关联。其次，我们将确定慢性GVHD的缺乏和耐受性的发展是否受到Treg库重建和胸腺恢复的影响。第三，通过使用高通量DNA测序技术测量初始、记忆和调节性T细胞区室中的TCR 2链CDR 3区序列多样性，我们将分析在高剂量Cy预防后发生的任何显著GVHD是否与多种Treg库的延迟重建相关。这项工作预计将提供必要的机制的见解，支持使用一个短期的GVHD预防，促进耐受诱导，并提供免疫系统重建的环境中没有正在进行的药理学免疫抑制。它还将提供T细胞亚群中免疫谱的高分辨率图像，并阐明更好地控制同种异体反应性的途径。

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.