Dissecting the mechanistic basis of response to combined decitabine and ipilimumab following hematopoietic stem cell transplantation for relapsed acute myelogenous leukemia

同种异体造血干细胞移植（HCT）主要基于强大的移植物抗白血病效应（GvL），为高风险急性髓性白血病（AML）提供了潜在的根治性治疗。HCT后AML的复发仍然是死亡率的主要来源，因此提高GvL的努力是高度优先的。与此同时，尽管HCT的临床记录由来已久，但GvL的机制基础仍未完全阐明。最近临床可用的免疫调节剂，如检查点阻断剂，以及现有的主动治疗方法，如低甲基化药物，为增强GvL打开了新的大门。单独使用这些药物的临床试验表明，这些药物在治疗hct后AML复发方面具有良好的临床活性，表明这些治疗方式的组合可以提供更大的效果。这就是DFCI正在进行的NCI ETCTN/CTEP I期研究（#10026）的基本原理，该研究旨在探索伊匹单抗和地西他滨联合治疗hct后AML复发。早期数据表明，这种方法在临床上是活跃的。我们假设对地西他滨和伊匹单抗联合的应答者将具有不同的疾病和免疫微环境特性，并表现出针对肿瘤抗原的激活T细胞反应。本研究中专门的纵向生物标本收集提供了丰富的机会来剖析这种新型治疗组合后反应的基础。今天，强大的研究工具可以在前所未有的深度上研究癌症免疫学。大规模平行测序、高通量单细胞技术和计算引导抗原发现方法为研究对象的样品综合评估提供了令人兴奋的基础。通过应用先进的免疫基因组学工具，并基于我在肿瘤反应性T细胞的单T细胞受体（TCR）分析方面的经验，我的目标是阐明GvL效应的免疫机制。因此，目标1将对肿瘤样本进行基因组评估，以将反应与肿瘤抗原负荷和对免疫信号通路至关重要的基因表达等疾病特异性特性联系起来。目的2将利用流式细胞术、单细胞RNA测序和细胞质量仪跟踪免疫微环境的定量和定性变化。目的3将利用单个TCR测序和方法来发现肿瘤反应性TCR的同源抗原，以了解肿瘤抗原- t细胞相互作用驱动反应。这些目标的完成有望揭示HCT后免疫反应的重要原理，并将阐明检查点阻断和低甲基化药物如何增强GvL。这将具有直接的临床意义，因为结果可以帮助确定从这种治疗组合中受益的患者，并可能为开发新的治疗方法（如疫苗接种或过继T细胞转移策略）铺平道路。

Allogeneic hematopoietic stem cell transplantation (HCT) provides potentially curative therapy for high-risk acute myelogenous leukemia (AML), mainly based on potent graft-versus-leukemia effects (GvL). Relapse of AML after HCT remains the key source of mortality, and hence efforts to enhance GvL are of high priority. At the same time, despite the long-established clinical track record of HCT, the mechanistic basis of GvL remains not fully elucidated.The recent clinical availability of immunomodulatory agents such as checkpoint blockade along with existing active therapeutics, for example hypomethylating agents, opens new doors for enhancing GvL. Clinical trials with single use of these agents have demonstrated promising clinical activity in addressing post-HCT AML relapse, suggesting combination of these treatment modalities could provide even greater effectiveness. This was the rationale for an ongoing NCI ETCTN/CTEP phase I study (#10026) at DFCI which seeks to probe the combination of ipilimumab and decitabine in AML relapse post-HCT. Early data indicate that this approach is clinically active.We hypothesize that responders to combined decitabine and ipilimumab will have distinct disease and immune microenvironment properties and show activated T cell responses against tumor antigens. The dedicated longitudinal biospecimen collection from this study provides a rich opportunity to dissect the basis of response following this novel therapeutic combination. Today powerful research tools are available to study cancer immunology at unprecedented depth. Massively parallel sequencing, high throughput single cell technologies and computationally guided antigen discovery approaches provide exciting foundations for comprehensive evaluation of samples from study subjects. Through application of advanced immunogenomic tools and building on my experience in single T cell receptor (TCR) analysis of tumor-reactive T cells, my objective is to elucidate the immune mechanisms underlying GvL effects.Aim 1 will thus undertake genomic evaluation of tumor samples to link response to disease-specific properties such as tumor antigen load and expression of genes critical to immune signaling pathways. Aim 2 will track quantitative and qualitative changes in the immune microenvironment using flow cytometry, single-cell RNA sequencing and mass cytometry. Aim 3 will exploit single TCR sequencing and methods to uncover cognate antigens of tumor-reactive TCRs to understand tumor antigen-T cell interactions driving responses.Completion of these aims is expected to reveal important principles of immune responses after HCT and will shed light on how checkpoint blockade and hypomethylating agents enhance GvL. This will have direct clinical implications as the results could aid in identifying patients that benefit from this therapeutic combination and might pave the way for developing novel therapeutic approaches like vaccination or adoptive T cell transfer strategies.