When hematopoietic stem and progenitor cells (HSPC) are harvested for transplantation, either from the bone marrow or from mobilized blood, the graft contains a significant number of T cells. It is these T cells that are the major drivers of graft-vs-host disease (GvHD). The risk for GvHD can simply be reduced by the removal of these T cells from the graft. However, this is not always desirable, as this procedure also decreases the engraftment of the transplanted HSPCs and, if applicable, a graft-vs-tumor effect. This poses an important conundrum in the field: T cells act as a double-edged sword upon allogeneic HSPC transplantation, as they support engraftment of HSPCs and provide anti-tumor activity, but can also cause GvHD. It has recently been suggested that T cells also enhance the engraftment of autologous HSPCs, thus supporting the notion that T cells and HSPCs have an important functional interaction that is highly beneficial, in particular during transplantation. The underlying reason on why and how T cells contribute to HSPC engraftment is still poorly understood. Therefore, we evaluate in this review the studies that have examined the role of T cells during HSPC transplantation and the possible mechanisms involved in their supporting function. Understanding the underlying cellular and molecular mechanisms can provide new insight into improving HSPC engraftment and thus lower the number of HSPCs required during transplantation. Moreover, it could provide new avenues to limit the development of severe GvHD, thus making HSPC transplantations more efficient and ultimately safer.

中文翻译：

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T细胞对造血干细胞和祖细胞功能的影响：好人还是坏人？

当从骨髓或动员的血液中收获造血干细胞和祖细胞（HSPC）进行移植时，移植物中会包含大量的T细胞。这是是移植物的主要驱动这些T细胞VS -host病（GVHD）。通过从移植物中去除这些T细胞，可以简单地降低GvHD的风险。然而，这并不总是理想的，因为该过程也降低了移植的HSPC的植入和，如果适用，接枝VS肿瘤效应。这在该领域构成了一个重要难题：T细胞在异体HSPC移植后起了双刃剑的作用，因为它们支持HSPC的植入并提供抗肿瘤活性，但也会引起GvHD。最近已经提出，T细胞还增强了自体HSPC的移植，因此支持了这样的观念，即T细胞和HSPC具有重要的功能相互作用，这是非常有益的，特别是在移植过程中。关于T细胞为何以及如何促成HSPC植入的根本原因仍知之甚少。因此，我们在这篇综述中评估了研究T细胞在HSPC移植过程中的作用及其参与其支持功能的可能机制的研究。了解潜在的细胞和分子机制可以为改善HSPC植入提供新的见识，从而减少移植期间所需的HSPC数量。而且，它可以提供新的途径来限制严重GvHD的发展，从而使HSPC移植更有效，最终更安全。