异基因造血干细胞移植（HSCT）是多种血液疾病唯一可能的根治方法。然而，异基因HSCT的疗效依赖于充分有效的免疫恢复、最小化的移植物抗宿主病（GVHD）和持久的病情控制。在过去几十年中，要实现这种平衡一直是一个具有挑战性的问题。HSCT的两步法于2005年在托马斯·杰斐逊大学提出并首次实施，并成为我们机构进行异基因移植的主要平台。在移植准备方案给药后，病人在第-6天接受固定剂量的供体CD3+细胞（HSCT第一步-DLI）作为移植物的淋巴部分，旨在优化和控制T细胞的剂量。环磷酰胺（CY）在DLI后（-3天和-2天）给予以诱导供受者间的双向耐受性。第0天，CD34选定的造血干细胞移植物作为移植物的髓系部分（第二步）给予。在这种两步法中，干细胞移植物在耐受性环磷酰胺处理后输入，避免了干细胞暴露于烷化剂，使计数迅速恢复。本文描述了这种两步法及过去二十年研究中的关键结果。最后，该综述详细阐明了已经学到的教训和目前优化异基因移植抗肿瘤效应并减少移植相关毒性的策略。版权所有 © 2023 Ibikunle、Grosso和Gergis。

Allogeneic hematopoietic stem cell transplantation (HSCT) provides the only potentially curative option for multiple hematological conditions. However, allogeneic HSCT outcomes rely on an optimal balance of effective immune recovery, minimal graft-versus-host disease (GVHD), and lasting control of disease. The quest to attain this balance has proven challenging over the past few decades. The two-step approach to HSCT was conceptualized and pioneered at Thomas Jefferson University in 2005 and remains the main platform for allografting at our institution. Following administration of the transplant conditioning regimen, patients receive a fixed dose of donor CD3+ cells (HSCT step one-DLI) as the lymphoid portion of the graft on day -6 with the aim of optimizing and controlling T cell dosing. Cyclophosphamide (CY) is administered after the DLI (days -3 and -2) to induce donor-recipient bidirectional tolerance. On day 0, a CD34-selected stem cell graft is given as the myeloid portion of the graft (step two). In this two-step approach, the stem cell graft is infused after CY tolerization, which avoids exposure of the stem cells to an alkylating agent, allowing rapid count recovery. Here, the two-step platform is described with a focus on key results from studies over the past two decades. Finally, this review details lessons learned and current strategies to optimize the graft-versus-tumor effect and limit transplant-related toxicities.Copyright © 2023 Ibikunle, Grosso and Gergis.