DOT1L, reconstitution of plasmacytoid dendritic cells and alloimmunity

少年派：张毅 移植物抗宿主病(GVHD)是异基因造血细胞移植后癌症患者发生危及生命的并发症的原因之一，它会导致供者浆细胞样树突状细胞(PDCs)重建失败，因为pDCs对免疫保护和耐受至关重要。然而，对GVHD相关的PDC分子缺陷以及供体PDCs在癌症中对GVHD的确切影响知之甚少。我们使用小鼠和人类系统来揭示GVHD导致供体PDC缺陷的机制。GVHD耗尽了维持pDC的供体多能祖细胞，导致pDC生成受损。MPP缺失与产生MPP的造血干细胞(HSCs)数量减少和氧化应激导致剩余增殖的MPP死亡有关；这与移植物抗宿主病(GVHD)中常见的低血细胞计数的临床观察相关。在我们的模型中，同种异体反应性T细胞产生GM-CSF来抑制TCF4的MPP表达，TCF4是PDC发育所必需的转录因子，颠覆PDC的MPP产生。GM-CSF不影响PDC前体细胞的成熟。值得注意的是，异基因造血干细胞移植(allo-HSCT)后早期过继移植时供体pDC的恢复增强抑制了GVHD，并恢复了受体小鼠供体pDC的从头生成。PDCs通过I型干扰素信号依赖机制抑制活化的T细胞的增殖和扩增。它们还产生PD-L1和LILRB4来抑制T细胞产生干扰素-。因此，MPP是支持PDC重建以预防GVHD的有效目标。尽管有这些有希望的初步发现，但在癌症患者和因其他疾病接受allo-HSCT的患者中，MPP产生PDCs和GVHD损害MPP的机制仍不清楚。 我们的持续研究表明，催化H3K79甲基化的DOT1L对PDC的发育至关重要。DOT1L对HSC和MPP向pDC，尤其是表达PD-L1和LILRB4的pDC(称为P/L+pDC)的分化起关键作用。GVHD降低MPPS的DOT1L功能。因此，DOT1L活性受损可能是移植物抗宿主病中PDC缺陷的主要原因。成功地利用pDC预防GVHD将取决于对DOT1L如何调节MPP的产生、维持和pDC形成的理解。我们假设DOT1L促进了MPP的产生和维持，并调节了MPPS的PDC规范。同种异体反应性T细胞反应可以抑制这种DOT1L效应，导致PDC缺陷和前馈GVHD加重。AIM-1将确定DOT1L在PDC重建中的作用以及GVHD对HSPC中DOT1L作用的影响。AIM-2将确定PDCs抑制同种异体反应性T细胞反应的分子机制。目的-3重点研究人pDC对同种异体反应性T细胞反应的影响，并评价同种异体移植物中供者P/L+pDCs是否可用于预测癌症患者的GVHD。我们的建议探索了DOT1L在控制PDC的生产和功能中迄今未被认识到的作用。如果成功，我们的工作将为更好地了解PDC的病理生理学开辟新的途径，并将基于PDC的治疗方法转化为临床，以帮助接受allo-HSCT的恶性血液病和其他血液疾病患者。

PI: Yi Zhang Graft-versus-host disease (GVHD), a cause of life-threatening complication in cancer patients following allogeneic hematopoietic cell transplantation, causes reconstitution of donor plasmacytoid dendritic cells (pDCs) to fail, as pDCs are critical for immune protection and tolerance. However, little is known about GVHD-associated pDC molecular defects and the precise effect of donor pDCs on GVHD in cancer. We used both murine and human systems to uncover the mechanisms by which GVHD induces donor pDC defects. GVHD depleted donor multipotent progenitors (MPPs) that sustain pDCs, leading to impaired pDC generation. MPP loss was associated with decreased numbers of MPP-producing hematopoietic stem cells (HSCs) and oxidative stress-induced death of remaining proliferating MPPs; this correlates with the common clinical observation of low blood counts in the setting of GVHD. In our models, alloreactive T cells produce GM-CSF to inhibit MPP expression of Tcf4, the transcription factor essential for pDC development, subverting MPP production of pDCs. GM-CSF did not affect the maturation of pDC precursors. Notably, enhanced recovery of donor pDCs upon adoptive transfer early after allogeneic HSC transplantation (allo-HSCT) repressed GVHD and restored de novo generation of donor pDCs in recipient mice. pDCs suppress the proliferation and expansion of activated T cells via a type-I IFN signaling-dependent mechanism. They also produce PD-L1 and LILRB4 to inhibit T cell production of IFN-. Thus, MPPs represent an effective target to bolster pDC reconstitution for GVHD prevention. In spite of these promising preliminary findings, the mechanisms by which MPPs produce pDCs and GVHD impairs MPPs after allo-HSCT in cancer patients as well as patients undergoing allo-HSCT for other diseases remain unknown. Our continuing studies suggested that Dot1l, which catalyzes H3K79 methylation, is crucial for pDC development. Dot1l appears to be critical for HSC and MPP differentiation into pDCs, PD-L1- and LILRB4-expressing pDCs (termed P/L+ pDCs) in particular. GVHD decreases Dot1l function in MPPs. Thus, impaired Dot1l activity may be the major contributor to pDC defects during GVHD. Successful harnessing of pDCs for GVHD prevention will rely on an understanding of how Dot1l regulates MPP generation, maintenance and pDC formation. We hypothesize that Dot1l promotes the generation and maintenance of MPPs and regulates pDC specification of MPPs. Alloreactive T cell responses can inhibit this Dot1l effect, inducing pDC defects and causing feed-forward GVHD exacerbation. Aim-1 will define the role of Dot1l in pDC reconstitution and the impact of GVHD on Dot1l action in HSPCs. Aim-2 will determine the molecular mechanisms through which pDCs repress alloreactive T cell responses. Aim-3 focuses on the impact of human pDCs on alloreactive T cell responses and assesses whether donor P/L+ pDCs in the allografts can be utilized to predict GVHD in cancer patients. Our proposal explores a heretofore unrecognized role of Dot1l in controlling pDC production and function. If successful, our work will open up new avenues to better understand pDC pathophysiology and translate pDC-based therapies to the clinic to help patients with hematologic malignancies and other blood diseases undergoing allo-HSCT.