DENDRITIC CELLS, RAPAMYCIN AND TRANSPLANT TOLERANCE

Dendritic cells (DC) are uniquely well-equipped, professional antigen-presenting cells (APC), with the ability to initiate and regulate immune responses. In transplantation, DC of both donor and host origin contribute to graft rejection by inducing T cell activation and proliferation, via the direct and indirect pathways of allorecognition, respectively. Evidence has also accumulated, however, that DC, particularly in an immature state, can promote tolerance induction and prolong organ allograft survival. Rapamycin is a potent immunosuppressant pro-drug that is well-recognized for its inhibitory effects on T cell proliferation. Despite extensive research on rapamycin's impact on lymphocytes, little is known to date regarding its effects on DC. The central hypothesis in these studies was that, rapamycin interferes with the DC maturation and enhances their tolerogenic potential. We first analyzed the influence of rapamycin, in pharmacologically-relevant concentrations, on the maturation, functional activation and T cell stimulatory potential of murine myeloid DC. Herein we show that rapamycin targets DC antigen (Ag)-uptake and IL-4-mediated maturation both in vitro (in bone marrow-derived DC), and in vivo (in freshly-isolated DC, following in vivo administration of rapamycin). Exposure to rapamycin impairs inflammatory cytokine production and effective T cell stimulation by DC. Furthermore, rapamycin-treated DC induce Ag-specific T cell anergy. Next, we determined that presentation of alloAgs to T cells by rapamycin-pretreated DC of host origin, under in vivo (pre-transplant) steady-state conditions, could induce hyporesponsiveness to subsequent challenge and prolong organ (heart) graft survival. A single infusion of these cells, seven days prior to transplant, led to a significant improvement in transplant outcome in an Ag-specific manner. Furthermore, repeated infusion resulted in marked prolongation of graft survival. These studies demonstrate, for the first time, that the immunosuppressive action of rapamycin can be ascribed, in part, to its inhibitory effects on DC and that rapamycin can potentiate the tolerogenic properties of DC. They also reveal the potential of rapamycin-treated DC as therapeutic vectors of transplant tolerance

Banff 2022 liver group meeting report: monitoring long term allograft health.

The Banff Working Group on Liver Allograft Pathology met in September 2022. Participantsincluded hepatologists, surgeons, pathologists, immunologists and histocompatibility specialists.Presentations and discussions focused on the evaluation of long-term allograft health, including noninvasive and tissue monitoring, immunosuppression optimisation and long-term structural changes.Potential revision of the rejection classification scheme to better accommodate and communicate lateT cell-mediated rejection patterns and related structural changes, such as nodular regenerativehyperplasia, were discussed. Improved stratification of long-term maintenance immunosuppression tomatch the heterogeneity of patient settings will be central to improving long-term patient survival.Such personalised therapeutics are in turn contingent on better understanding and monitoring ofallograft status within a rational decision-making approach, likely to be facilitated in implementationwith emerging decision support tools. Proposed revisions to rejection classification emerging fromthe meeting include incorporation of interface hepatitis and fibrosis staging. These will be opened toonline testing, modified accordingly and subject to consensus discussion leading up to the next Banffconference

New approaches to the diagnosis of rejection and prediction of tolerance in liver transplantation

Immunosuppression after liver transplantation is essential for preventing allograft rejection. However, long-term drug toxicity and associated complications necessitate investigation of immunosuppression minimization and withdrawal protocols. Development of such protocols is hindered by reliance on current paradigms for monitoring allograft function and rejection status. The current standard of care for diagnosis of rejection is histopathologic assessment and grading of liver biopsies in accordance with the Banff Rejection Activity Index. However, this method is limited by cost, sampling variability, and interobserver variation. Moreover, the invasive nature of biopsy increases the risk of patient complications. Incorporating noninvasive techniques may supplement existing methods through improved understanding of rejection causes, hepatic spatial architecture, and the role of idiopathic fibroinflammatory regions. These techniques may also aid in quantification and help integrate emerging -omics analyses with current assessments. Alternatively, emerging noninvasive methods show potential to detect and distinguish between different types of rejection while minimizing risk of adverse advents. Although biomarkers have yet to replace biopsy, preliminary studies suggest that several classes of analytes may be used to detect rejection with greater sensitivity and in earlier stages than traditional methods, possibly when coupled with artificial intelligence. Here, we provide an overview of the latest efforts in optimizing the diagnosis of rejection in liver transplantation

Image_3_Liver mesenchymal stem cells are superior inhibitors of NK cell functions through differences in their secretome compared to other mesenchymal stem cells.tiff

Liver-resident mesenchymal stem cells (L-MSCs) are superior inhibitors of alloreactive T cell responses compared to their counterparts from bone marrow (BM-MSCs) or adipose tissue (A-MSCs), suggesting a role in liver’s overall tolerogenic microenvironment. Whether L-MSCs also impact NK cell functions differently than other MSCs is not known. We generated and characterized L-MSCs, A-MSCs and BM-MSCs from human tissues. The mass spectrometry analysis demonstrated that L-MSC secretome is uniquely different than that of A-MSC/BM-MSC, with enriched protein sets involved in IFNγ responses and signaling. When co-cultured with primary human NK cells, L-MSCs but not other MSCs, decreased surface expression of activating receptors NKp44 and NKG2D. L-MSCs also decreased IFNγ secretion by IL-2-stimulated NK cells more effectively than other MSCs. Cytolytic function of NK cells were reduced significantly when co-cultured with L-MSCs, whereas A-MSCs or BM-MSCs did not have a major impact. Mechanistic studies showed that the L-MSC-mediated reduction in NK cell cytotoxicity is not through changes in secretion of the cytotoxic proteins Perforin, Granzyme A or B, but through increased production of HLA-C1 found in L-MSC secretome that inhibits NK cells by stimulating their inhibitory receptor KIRDL2/3. L-MSCs are more potent inhibitors of NK cell functions than A-MSC or BM-MSC. Combined with their T cell inhibitory features, these results suggest L-MSCs contribute to the tolerogenic liver microenvironment and liver-induced systemic tolerance often observed after liver transplantation.</p

Image_2_Liver mesenchymal stem cells are superior inhibitors of NK cell functions through differences in their secretome compared to other mesenchymal stem cells.tiff

Liver-resident mesenchymal stem cells (L-MSCs) are superior inhibitors of alloreactive T cell responses compared to their counterparts from bone marrow (BM-MSCs) or adipose tissue (A-MSCs), suggesting a role in liver’s overall tolerogenic microenvironment. Whether L-MSCs also impact NK cell functions differently than other MSCs is not known. We generated and characterized L-MSCs, A-MSCs and BM-MSCs from human tissues. The mass spectrometry analysis demonstrated that L-MSC secretome is uniquely different than that of A-MSC/BM-MSC, with enriched protein sets involved in IFNγ responses and signaling. When co-cultured with primary human NK cells, L-MSCs but not other MSCs, decreased surface expression of activating receptors NKp44 and NKG2D. L-MSCs also decreased IFNγ secretion by IL-2-stimulated NK cells more effectively than other MSCs. Cytolytic function of NK cells were reduced significantly when co-cultured with L-MSCs, whereas A-MSCs or BM-MSCs did not have a major impact. Mechanistic studies showed that the L-MSC-mediated reduction in NK cell cytotoxicity is not through changes in secretion of the cytotoxic proteins Perforin, Granzyme A or B, but through increased production of HLA-C1 found in L-MSC secretome that inhibits NK cells by stimulating their inhibitory receptor KIRDL2/3. L-MSCs are more potent inhibitors of NK cell functions than A-MSC or BM-MSC. Combined with their T cell inhibitory features, these results suggest L-MSCs contribute to the tolerogenic liver microenvironment and liver-induced systemic tolerance often observed after liver transplantation.</p