Division of Hematology, Oncology, Stem Cell Transplantation and Regenerative Medicine, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, 94305, USA.
Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, CA, 94305, USA.
Stem Cell Res Ther. 2024 Oct 29;15(1):387. doi: 10.1186/s13287-024-03981-0.
Hematopoietic stem cell transplantation (HSCT) is a curative treatment for many diverse blood and immune diseases. However, HSCT regimens currently commonly utilize genotoxic chemotherapy and/or total body irradiation (TBI) conditioning which causes significant morbidity and mortality through inducing broad tissue damage triggering infections, graft vs. host disease, infertility, and secondary cancers. We previously demonstrated that targeted monoclonal antibody (mAb)-based HSC depletion with anti(α)-CD117 mAbs could be an effective alternative conditioning approach for HSCT without toxicity in severe combined immunodeficiency (SCID) mouse models, which has prompted parallel clinical αCD117 mAbs to be developed and tested as conditioning agents in clinical trials starting with treatment of patients with SCID. Subsequent efforts have built upon this work to develop various combination approaches, though none are optimal and how any of these mAbs fully function is unknown.
To improve efficacy of mAb-based conditioning as a stand-alone conditioning approach for all HSCT settings, it is critical to understand the mechanistic action of αCD117 mAbs on HSCs. Here, we compare the antagonistic properties of αCD117 mAb clones including ACK2, 2B8, and 3C11 as well as ACK2 fragments in vitro and in vivo in both SCID and wildtype (WT) mouse models. Further, to augment efficacy, combination regimens were also explored.
We confirm that only ACK2 inhibits SCF binding fully and prevents HSC proliferation in vitro. Further, we verify that this corresponds to HSC depletion in vivo and donor engraftment post HSCT in SCID mice. We also show that SCF-blocking αCD117 mAb fragment derivatives retain similar HSC depletion capacity with enhanced engraftment post HSCT in SCID settings, but only full αCD117 mAb ACK2 in combination with αCD47 mAb enables enhanced donor HSC engraftment in WT settings, highlighting that the Fc region is not required for single-agent efficacy in SCID settings but is required in immunocompetent settings. This combination was the only non-genotoxic conditioning approach that enabled robust donor engraftment post HSCT in WT mice.
These findings shed new insights into the mechanism of αCD117 mAb-mediated HSC depletion. Further, they highlight multiple approaches for efficacy in SCID settings and optimal combinations for WT settings. This work is likely to aid in the development of clinical non-genotoxic HSCT conditioning approaches that could benefit millions of people world-wide.
造血干细胞移植（HSCT）是许多不同血液和免疫疾病的治愈性治疗方法。然而，HSCT 方案目前通常使用遗传毒性化疗和/或全身照射（TBI）来调节，这会通过广泛的组织损伤引发感染、移植物抗宿主病、不育和继发性癌症而导致显著的发病率和死亡率。我们之前证明，用抗（α）-CD117 mAb 靶向单克隆抗体（mAb）清除 HSC 可以作为 HSCT 的一种有效替代调节方法，在严重联合免疫缺陷（SCID）小鼠模型中没有毒性，这促使开发并测试平行的临床 αCD117 mAbs 作为临床试验中的调节剂，从治疗 SCID 患者开始。随后的努力在此基础上发展了各种组合方法，尽管没有一种是最佳的，也不知道这些 mAb 是如何完全发挥作用的。
为了提高 mAb 为基础的调节作为所有 HSCT 环境的独立调节方法的功效，了解 αCD117 mAb 对 HSC 的作用机制至关重要。在这里，我们比较了 ACK2、2B8 和 3C11 以及 ACK2 片段等 αCD117 mAb 克隆在 SCID 和野生型（WT）小鼠模型中的体外和体内拮抗特性。此外，为了增强功效，还探索了联合方案。
我们证实只有 ACK2 完全抑制 SCF 结合并阻止 HSC 在体外增殖。此外，我们验证了这对应于体内 HSC 耗竭以及 SCID 小鼠 HSCT 后供体植入。我们还表明，SCF 阻断的 αCD117 mAb 片段衍生物在 SCID 环境中保留了类似的 HSC 耗竭能力，并且在 SCID 环境中在 HSCT 后增强供体 HSC 植入，但只有完整的 αCD117 mAb ACK2 与 αCD47 mAb 联合使用才能增强 WT 环境中的供体 HSC 植入，这表明 Fc 区在 SCID 环境中不需要单药治疗功效，但在免疫功能正常的环境中是需要的。这种组合是唯一一种非遗传毒性调节方法，能够在 WT 小鼠中实现强大的供体植入。
这些发现为 αCD117 mAb 介导的 HSC 耗竭的机制提供了新的见解。此外，它们突出了 SCID 环境中的多种功效方法和 WT 环境中的最佳组合。这项工作可能有助于开发临床非遗传毒性 HSCT 调节方法，使全世界数百万人受益。
