The intragraft microenvironment as a central determinant of chronic rejection or local immunoregulation/tolerance

Immunomodulation by allograft endothelial cells

It is increasingly appreciated that the expression of immunoregulatory molecules within tumors have potential to shape a microenvironment that promotes local immunoevasion and immunoregulation. However, little is known about tissue-intrinsic immunomodulatory mechanisms following transplantation. We propose that differences in the phenotype of microvascular endothelial cells impact the alloantigenicity of the graft and its potential to promote immunoregulation following transplantation. We focus this review on the concept that graft-dependent immunoregulation may evolve post-transplantation, and that it is dependent on the phenotype of select subsets of intragraft endothelial cells. We also discuss evidence that long-term graft survival is critically dependent on adaptive interactions among immune cells and endothelial cells within the transplanted tissue microenvironment.

The Transplant Bellwether: Endothelial Cells in Antibody-Mediated Rejection

Ab-mediated rejection of organ transplants remains a stubborn, frequent problem affecting patient quality of life, graft function, and grant survival, and for which few efficacious therapies currently exist. Although the field has gained considerable knowledge over the last two decades on how anti-HLA Abs cause acute tissue injury and promote inflammation, there has been a gap in linking these effects with the chronic inflammation, vascular remodeling, and persistent alloimmunity that leads to deterioration of graft function over the long term. This review will discuss new data emerging over the last 5 y that provide clues into how ongoing Ab-endothelial cell interactions may shape vascular fate and propagate alloimmunity in organ transplants.

Metabolic reprogramming of myeloid-derived suppressor cells in the context of organ transplantation

Myeloid-derived suppressor cells (MDSCs) are naturally occurring leukocytes that develop from immature myeloid cells under inflammatory conditions that were discovered initially in the context of tumor immunity. Because of their robust immune inhibitory activities, there has been growing interest in MDSC-based cellular therapies for transplant tolerance induction. Indeed, various pre-clinical studies have introduced in vivo expansion or adoptive transfer of MDSC as a promising therapeutic strategy leading to a profound extension of allograft survival due to suppression of alloreactive T cells. However, several limitations of cellular therapies using MDSCs remain to be addressed, including their heterogeneous nature and limited expansion capacity. Metabolic reprogramming plays a crucial role for differentiation, proliferation and effector function of immune cells. Notably, recent reports have focused on a distinct metabolic phenotype underlying the differentiation of MDSCs in an inflammatory microenvironment representing a regulatory target. A better understanding of the metabolic reprogramming of MDSCs may thus provide novel insights for MDSC-based treatment approaches in transplantation. In this review, we will summarize recent, interdisciplinary findings on MDSCs metabolic reprogramming, dissect the underlying molecular mechanisms and discuss the relevance for potential treatment approaches in solid-organ transplantation.

Allografts: expanding the surgeon's armamentarium

In Germany, bone allografts are widely used and their application in clinics has increased over the years. Successful use of allografts depends on many factors such as the procurement, processing, sterilization and the surgeon's surgical experience. Tissue banks have provided safe and sterile allografts for decades ranging from hard to soft tissue. Allografts are obtained from various tissues such as bone, tendon, amniotic membrane, meniscus and skin. An advantage of allografts is their wide applicability that has never been limited by indication restrictions thus providing a huge benefit for surgeon's. The use of the correct allograft in different indications is extremely important. Thereby surgeons have access to various allograft forms such as mineralized, demineralized, freeze-dried, paste, powder, chips strips and putty. The vast options of allografts allow surgeon's to use allografts in indications they deem fit. Currently, the application of allografts is at the discretion of the expert surgeon. However, regulations are often changed locally or internationally and may impact/limit allograft use to certain indications. Here, we report the different indications where our peracetic acid (PAA) sterilised bone allografts were used as well as general literature on bone allograft use in other indications.

Inhibition of mevalonate metabolism by statins augments the immunoregulatory phenotype of vascular endothelial cells and inhibits the costimulation of CD4+ T cells

The statin family of therapeutics is widely used clinically as cholesterol lowering agents, and their effects to target intracellular mevalonate production is a key mechanism of action. In this study, we performed full transcriptomic RNA sequencing and qPCR to evaluate the effects of mevalonate on the immunoregulatory phenotype of endothelial cells (EC). We find that mevalonate-dependent gene regulation includes a reduction in the expression of multiple pro-inflammatory genes including TNFSF4 (OX40-L) and TNFSF18 (GITR-L) and a co-incident induction of immunoregulatory genes including LGALS3 (Galectin-3) and LGALS9 (Galectin-9). In functional assays, pretreatment of EC with simvastatin to inhibit mevalonate metabolism resulted in a dose-dependent reduction in the costimulation of CD45RO⁺ CD4⁺ T cell proliferation as well as IL-2, IFNγ and IL-6 production versus vehicle-treated EC. In contrast, pre-treatment of EC with L-mevalonate in combination with simvastatin reversed phenotypic and functional responses. Collectively, these results indicate that relative mevalonate metabolism by EC is critical to sustain EC-dependent mechanisms of immunity. Our findings have broad relevance for the repurposing of statins as therapeutics to augment immunoregulation and/or to inhibit local tissue pro-inflammatory cytokine production following transplantation.

Function of Deptor and its roles in hematological malignancies

Deptor is a protein that interacts with mTOR and that belongs to the mTORC1 and mTORC2 complexes. Deptor is capable of inhibiting the kinase activity of mTOR. It is well known that the mTOR pathway is involved in various signaling pathways that are involved with various biological processes such as cell growth, apoptosis, autophagy, and the ER stress response. Therefore, Deptor, being a natural inhibitor of mTOR, has become very important in its study. Because of this, it is important to research its role regarding the development and progression of human malignancies, especially in hematologic malignancies. Due to its variation in expression in cancer, it has been suggested that Deptor can act as an oncogene or tumor suppressor depending on the cellular or tissue context. This review discusses recent advances in its transcriptional and post-transcriptional regulation of Deptor. As well as the advances regarding the activities of Deptor in hematological malignancies, its possible role as a biomarker, and its possible clinical relevance in these malignancies.