Deletion of the activating NK cell receptor NKG2D accelerates rejection of cardiac allografts.

It has already been shown that neutralization of the activating NK cell receptor NKG2D in combination with co-stimulation blockade prolongs graft survival of vascularized transplants. In order to clarify the underlying cellular mechanisms, we transplanted complete MHC-disparate BALB/c-derived cardiac grafts into C57BL/6 wildtypes or mice deficient for NKG2D (Klrk1-/- ). Although median survival was 8 days for both recipient groups, we detected already at day 5 posttransplantation significantly greater intragraft frequencies of NKp46+ NK cells in Klrk1-/- recipients than in wildtypes. This was followed by a significantly greater infiltration of CD4+ , but a lesser infiltration of CD8+ T cell frequencies. Contrary to published observations, co-stimulation blockade with CTLA4-Ig resulted in a significant acceleration of cardiac rejection by Klrk1-/- recipients, and this result was confirmed by applying a neutralizing antibody against NKG2D to wildtypes. In both experimental setups, grafts derived from Klrk1-/- recipients were characterized by significantly higher levels of interferon-γ mRNA, and both CD4+ and CD8+ T cells displayed a greater capacity for degranulation and interferon-γ production. In summary, our results clearly illustrate that NKG2D expression in the recipient is important for cardiac allograft survival, thus supporting the hypothesis that impairment of NK cells prevents the establishment of graft acceptance.

Donor brain death leads to differential immune activation in solid organs but does not accelerate ischaemia-reperfusion injury.

A comparative analysis of inflammation between solid organs following donor brain death (BD) is still lacking and the detailed influence of BD accelerating ischaemia-reperfusion injury (IRI) post-transplantation remains to be addressed. Applying a murine model of BD, we demonstrated that 4 h after BD organs were characterized by distinct inflammatory expression patterns. For instance, lipocalin 2 (LCN2), a marker of acute kidney injury, was selectively induced in BD livers but not in kidneys. BD further resulted in significantly reduced frequencies of CD3(+) CD4(+) , CD3(+) CD8(+) T cells and NKp46(+) NK cells in the liver, whereas BD kidneys and hearts were characterized by significantly lower frequencies of conventional dendritic cells (cDCs). Syngeneic models of kidney (KTx) and heart transplantation (HTx) illustrated stronger gene expression in engrafted BD hearts only, but 20 h post-transplantation both organs displayed comparable intragraft lymphocyte frequencies, except for NK cells and graft function. Moreover, the complement factor C3d deposit detected in small vessels and capillaries in cardiac syngrafts did not significantly differ between BD and sham-transplanted groups. Finally, no further influence of donor BD on graft survival was detected in an allogeneic heart transplantation setting (C57BL/6 grafts into BALB/c recipients). We show for the first time that BD organs are characterized by a varying inflammatory profile; however, BD does not accelerate IRI in syngeneic KTx and HTx.

The activating receptor NKG2D of natural killer cells promotes resistance against enterovirus-mediated inflammatory cardiomyopathy.

In enterovirus-induced cardiomyopathy, information regarding the detailed impact of natural killer (NK) cells on the outcome of the disease is limited. We therefore hypothesized that NK cells and certain NK cell receptors determine the different outcome of coxsackievirus B3 (CVB3) myocarditis. Here, we demonstrate in murine models that resistance to chronic CVB3 myocarditis in immunocompetent C57BL/6 mice is characterized by significantly more mature CD11b(high) NK cells, the presence of NKG2D on NK cells, and enhanced NKG2D-dependent cytotoxicity compared to CVB3-susceptible A.BY/SnJ mice. The highly protective role of NKG2D in myocarditis was further proven by in vivo neutralization of NKG2D as well as in NKG2D-deficient mice but was shown to be independent of CD8(+) T-cell-dependent immunity. Moreover, the adoptive transfer of immunocompetent C57BL/6 NK cells pre- (day -1) as well as post-infectionem (day +2) displayed the potential to prevent permissive A.BY/SnJ mice from a progressive outcome of CVB3 myocarditis reflected by significantly improved cardiopathology and heart function. Altogether, our results provide firm evidence for a protective role of NKG2D-activated NK cells in CVB3 myocarditis leading to an effective virus clearance, thus offering novel therapeutic options in the treatment of virus-induced myocarditis.

Report of the joint ESOT and TTS basic science meeting 2013: current concepts and discoveries in translational transplantation.

A joint meeting organized by the European (ESOT) and The Transplantation (TTS) Societies for basic science research was organized in Paris, France, on November 7-9, 2013. Focused on new ideas and concepts in translational transplantation, the meeting served as a venue for state-of-the-art developments in basic transplantation immunology, such as the potential for tolerance induction through regulation of T-cell signaling. This meeting report summarizes important insights which were presented in Paris. It not only offers an overview of established aspects, such as the role of Tregs in transplantation, presented by Nobel laureate Rolf Zinkernagel, but also highlights novel facets in the field of transplantation, that is cell-therapy-based immunosuppression or composite tissue transplantation as presented by the emotional story given by Vasyly Rohovyy, who received two hand transplants. The ESOT/TTS joint meeting was an overall productive and enjoyable platform for basic science research in translational transplantation and fulfilled all expectations by giving a promising outlook for the future of research in the field of immunological transplantation research.

High incidence of hepatocellular carcinoma and postoperative complications in patients with nonalcoholic steatohepatitis as a primary indication for deceased liver transplantation.

BACKGROUND AND AIMS: Nonalcoholic steatohepatitis (NASH) is an increasingly prevalent indication for liver transplantation (LT) across the world. The relative outcomes following transplantation are poorly described in this cohort. We aimed to analyze the incidence and outcome of LT for NASH as compared with other indications. PATIENTS AND METHODS: This is a retrospective analysis of 513 patients who underwent deceased-donor, adult LT between 2002 and 2012 as recorded at the Medical University of Innsbruck, Austria. RESULTS: The prevalence of NASH cirrhosis as indication for liver transplantation was 12.7% (65/513). Patient survival in patients with NASH was comparable to other indications, including alcohol-induced liver steatosis (ALD) and hepatitis C virus (HCV) (P=0.208). Patients with NASH were older, had a higher model of end-stage liver disease score and a higher BMI, but patient survival and graft survival were equivalent to other indications. Patients with hepatocellular carcinoma (HCC) as primary indication for liver transplantation showed significantly inferior overall survival as compared with the other indications (P=0.003). Patients with NASH had coexisting HCC in 53.7% of cases, whereas HCC in ALD, HCV and other indications was prevalent in 31.2, 47.7, and 34.5%, respectively (P<0.0001). Patients with NASH had a higher incidence of advanced HCCs (outside the Milan criteria) than patients with ALD, HCV, and other indications (P=0.034). Postoperative complications were significantly higher in the NASH cohort (P=0.048). CONCLUSION: In this single-center LT database analysis, patients with NASH have a higher incidence and a more rapid progression of HCC as well as an increased incidence of postoperative complications. Our findings warrant confirmation by others.

Disturbances in iron homeostasis result in accelerated rejection after experimental heart transplantation.

BACKGROUND: Clinical data suggest that iron disturbances deleteriously affect graft survival after heart transplantation (HTx), but immunological mechanisms underlying this phenomenon have not yet been elucidated. METHODS: To identify the mechanistic influence of iron in a murine model of HTx, fully allogeneic BALB/c donor organs were transplanted into iron-overloaded or iron-deficient C57BL/6 mice, and recipients were analyzed for functional and immunological parameters. RESULTS: After HTx, iron overload accelerated acute rejection as observed by shortened graft survival (HTx vs HTx + iron; p = 0.01), elevated rejection score (p < 0.01), and induction of troponin T (p < 0.01). Compared with controls, allografts and recipient spleens derived from iron-overloaded recipients were characterized by a pronounced graft infiltration of CD4+ T cells (p < 0.01), CD3-NKp46+ natural killer cells (p < 0.05), and reduced frequencies of regulatory T cells (p < 0.01). This was accompanied by lower mRNA expression levels of anti-inflammatory cytokines, including interleukin-10, transforming graft factor-ß, and Foxp3. Cardiac allograft survival was further tested under co-stimulation blockade (CTLA4-Ig) showing that naïve grafts transplanted into iron-overloaded recipients illustrated restricted graft outcome compared with wild types (p = 0.0051), which was rescued after treatment with the iron chelator deferoxamine. Iron deficiency (ID) also resulted in enhanced intragraft infiltration of inflammatory cells and accelerated rejection in the acute setting (HTx vs HTx + ID; p = 0.02) and after co-stimulation blockade (p = 0.0059). CONCLUSIONS: We provide novel insights into the understanding of disturbances in iron homeostasis and their consequences after HTX, allowing novel insights regarding improvements in personalized immunosuppression to prolong allograft survival.

The Role of Natural Killer Cells in Humoral Rejection.

Antibody-mediated rejection (AMR) has been identified among the most important factors limiting long-term outcome in cardiac and renal transplantation. Therapeutic management remains challenging and the development of effective treatment modalities is hampered by insufficient understanding of the underlying pathophysiology. However, recent findings indicate that in addition to AMR-triggered activation of the classical complement pathway, antibody-dependent cellular cytotoxicity by innate immune cell subsets also promotes vascular graft injury. This review summarizes the accumulating evidence for the contribution of natural killer cells, the key mediators of antibody-dependent cellular cytotoxicity, to human AMR in allotransplantation and xenotransplantation and illustrates the current mechanistic conceptions drawn from animal models.