Administration of tetrahydrobiopterin (BH4) has been shown to attenuate acute allograft rejection in a murine heart transplantation model in a manner similar to that of cyclosporine A. However, its mechanism of action on immune cells remains largely unknown. A fully MHC-mismatched (C3H/He to C57BL/6) mouse heart transplant model was used in this study. The recipients were treated with BH4 or cyclosporine A six days. The degree of acute rejection was assessed by histopathological analysis, splenocytes were analyzed by flow cytometry, and cytokine production was estimated based on the level of protein and RNA in sera and grafts and in vitro in T cell cultures. Proliferation of regulatory T cells and mast cells, suppressor capacity of Tregs, and MLR of T cells were conducted in vitro. Survival curves confirmed the significant improvement observed in the BH4-treated animals. BH4-treatment resulted in a substantial increase in Tregs and mast cells in the secondary lymphoid organs. In vitro assays showed increased proliferation of BH4-treated Tregs and mast cells. Cytokine production in vivo and in vitro in BH4-treated animals revealed an increase in the expression of IL-10, IL-5 and IL-4. BH4-dependent mast cell-derived tryptophan hydroxylase-1 could be excluded as a treatment target in recipient knockout mice. These data suggest that BH4 modulates the innate and adaptive immune systems, resulting in increased proliferation of regulatory T and mast cells accompanied by a modulation of anti-inflammatory cytokines.

The emergence of resistance to mutant BRAF‐specific inhibitors (BRAFi) requires novel strategies for melanoma treatment. The progression of these tumors involves metabolic adaptations, which also affect the cellular redox status. Previous studies have linked RAF kinase signaling, a key component of the MAPK/ERK pathway involved in cell division and survival, to the suppression of mitochondrial reactive oxygen species (ROS) production, resulting in protection against cell death. In BRAF‐transformed cells, we have identified impaired JNK1/2‐dependent activation of the mitochondrial prooxidant protein p66Shc as a potential cause. In the present study, we dissected signaling and mitochondrial alterations that characterize the transition from BRAFi responsiveness to resistance in A375 melanoma cells. Insensitivity to BRAFi dabrafenib exposure was associated with reactivation of ERK1/2 phosphorylation, increased JNK1/2 kinase activity, p66ShcS36 phosphorylation, and elevated ROS production. Utilizing high‐resolution respirometry (HRR) and transmission electron microscopy (TEM), we show that dabrafenib‐resistant cells displayed mitochondrial damage, compensated by increased respiration, leading to high ROS levels. Moreover, dabrafenib‐resistant cells (A375D) have more efficient antioxidant systems, which may explain why despite ongoing cell death, net cell growth was observed. Treatment of both parental and resistant cells with phenethyl isothiocyanate (PEITC) increased ROS production but caused substantial cell death only in A375D melanoma cells. This PEITC effect could be demonstrated in two further dabrafenib‐resistant cell lines, WM164D and 451LuP. These results suggest that the altered redox status is linked to compromised mitochondria and is associated with the development of BRAFi resistance, rendering cells exquisitely sensitive to the actions of selective ROS‐inducing therapeutics.

Administration of tetrahydrobiopterin (BH4) has been shown to attenuate acute allograft rejection in a murine heart transplantation model in a manner similar to that of cyclosporine A. However, its mechanism of action on immune cells remains largely unknown. A fully MHC-mismatched (C3H/He to C57BL/6) mouse heart transplant model was used in this study. The recipients were treated with BH4 or Cyclosporine A six days. The degree of acute rejection was assessed by histopathological analysis, splenocytes were analyzed by flow cytometry, and cytokine production was estimated based on the level of protein and RNA in sera and grafts and in vitro in T cell cultures. Proliferation of regulatory T cells and mast cells, suppressor capacity of Tregs, and MLR of T cells were conducted in vitro. Survival curves confirmed the significant improvement observed in the BH4-treated animals. BH4-treatment resulted in a substantial increase in Tregs and mast cells in the secondary lymphoid organs. In vitro assays showed increased proliferation of BH4-treated Tregs and mast cells. Cytokine production in vivo and in vitro in BH4-treated animals revealed an increase in the expression of IL-10, IL-5 and IL-4. BH4-dependent mast cell-derived tryptophan hydroxylase-1 could be excluded as a treatment target in recipient knockout mice. These data suggest that BH4 modulates the innate and adaptive immune systems, resulting in increased proliferation of regulatory T and mast cells accompanied by a modulation of anti-inflammatory cytokines.

Long-term results following solid organ transplantation do not mirror the excellent short-term results achieved in recent decades. It is therefore clear that current immunosuppressive maintenance protocols primarily addressing the adaptive immune system no longer meet the required clinical need. Identification of novel targets addressing this shortcoming is urgently needed. There is a growing interest in better understanding the role of the innate immune system in this context. In this review, we focus on macrophages, which are known to prominently infiltrate allografts and, during allograft rejection, to be involved in the surge of the adaptive immune response by expression of pro-inflammatory cytokines and direct cytotoxicity. However, this active participation is janus-faced and unspecific targeting of macrophages may not consider the different subtypes involved. Under this premise, we give an overview on macrophages, including their origins, plasticity, and important markers. We then briefly describe their role in acute allograft rejection, which ranges from sustaining injury to promoting tolerance, as well as the impact of maintenance immunosuppressants on macrophages. Finally, we discuss the observed immunosuppressive role of the vitamin-like compound tetrahydrobiopterin and the recent findings that suggest the innate immune system, particularly macrophages, as its target.

Donor age is a major risk factor for allograft outcome in kidney transplantation. The underlying cellular mechanisms and the recipient's immune response within an aged allograft have yet not been analyzed. A comprehensive immunophenotyping of naïve and transplanted young versus aged kidneys revealed that naïve aged murine kidneys harbor significantly higher frequencies of effector/memory T cells, whereas regulatory T cells were reduced. Aged kidney-derived CD8+ T cells produced more IFNγ than their young counterparts. Senescent renal CD8+ T and NK cells upregulated the cytotoxicity receptor NKG2D and the enrichment of memory-like CD49a+ CXCR6+ NK cells was documented in aged naïve kidneys. In the C57BL/6 to BALB/c kidney transplantation model, recipient-derived T cells infiltrating an aged graft produced significantly more IFNγ, granzyme B and perforin on day 7 post-transplantation, indicating an enhanced inflammatory, cytotoxic response towards the graft. Pre-treatment of aged kidney donors with the senolytic drug ABT-263 changed the recipient-derived effector molecule profile to significantly reduced levels of IFNγ and IL-10 compared to controls. Graft function after ABT-263 pre-treatment was significantly improved 28 days post kidney transplantation. In conclusion, renal senescence also occurs at the immunological level (inflamm-aging) and aged organs provoke an altered recipient-dominated immune response in the graft.

The liver has been proposed as an important “immune organ” of the body, as it is critically involved in a variety of specific and unique immune tasks. It contains a huge resident immune cell repertoire, which determines the balance between tolerance and inflammation in the hepatic microenvironment. Liver-resident immune cells, populating the sinusoids and the space of Disse, include professional antigen-presenting cells, myeloid cells, as well as innate and adaptive lymphoid cell populations. Machine perfusion (MP) has emerged as an innovative technology to preserve organsex vivowhile testing for organ quality and function prior to transplantation. As for the liver, hypothermic and normothermic MP techniques have successfully been implemented in clinically routine, especially for the use of marginal donor livers. Although there is evidence that ischemia reperfusion injury-associated inflammation is reduced in machine-perfused livers, little is known whether MP impacts the quantity, activation state and function of the hepatic immune-cell repertoire, and how this affects the inflammatory milieu during MP. At this point, it remains even speculative if liver-resident immune cells primarily exert a pro-inflammatory and hence destructive effect on machine-perfused organs, or in part may be essential to induce liver regeneration and counteract liver damage. This review discusses the role of hepatic immune cell subtypes during inflammatory conditions and ischemia reperfusion injury in the context of liver transplantation. We further highlight the possible impact of MP on the modification of the immune cell repertoire and its potential for future applications and immune modulation of the liver.

(1) Background: Prior studies suggested a significant impact of previous live births on peripheral natural killer cells (pNK) in patients with recurrent pregnancy loss (RPL). Patients with primary RPL (pRPL, no live birth) showed higher numbers of pNK than secondary RPL patients (sRPL, ≥ 1 live birth). (2) Methods: To further determine immunological differences between RPL patients and controls, we analysed pNK subpopulations and activation markers in pRPL (n = 47), sRPL (n = 24) and controls with previous live birth (sCtrl, n = 25) and nullipara (pCtrl, n = 60) within a prospective study. Percentages and numbers of CD56dimCD16bright cells, subpopulations and activation markers (CD57+, CD62L+, NKG2D+, NKp46+) were measured in non-pregnant RPL patients and n = 85 controls (n = 60 pCtrl, n = 25 sCtrl) in the mid-luteal phase by flow cytometry. (3) Results: Compared to sRPL patients, sCtrls showed higher CD56+ and CD56dimCD16bright numbers. Further, sRPL patients showed lower numbers of CD56dimCD16brightNKG2D+ and CD56dimCD16brightNKp46+ than sCtrls. (4) Conclusion: We suggest a chronic immune stimulation leading to a lower NK-cell count in sRPL patients with a lower NK cytotoxicity. This underlines the necessity to investigate pNK subpopulations as well as pRPL and sRPL separately to delineate the immune alterations in RPL.

Due to the lack of suitable organs transplant surgeons have to accept unfavorable extended criteria donor (ECD) organs. Recently, we demonstrated that the perfusion of kidney organs with anti-human T-lymphocyte globulin (ATLG) prior to transplantation ameliorates ischemia-reperfusion injury (IRI). Here, we report on the results of perioperative ATLG perfusion in a randomized, single-blinded, placebo-controlled, feasibility trial (RCT) involving 30 liver recipients (LTx). Organs were randomly assigned for perfusion with ATLG/Grafalon® (AP) (n = 16) or saline only (control perfusion = CP) (n = 14) prior to implantation. The primary endpoint was defined as graft function reflected by aspartate transaminase (AST) values at day 7 post-transplantation (post-tx). With respect to the primary endpoint, no significant differences in AST levels were shown in the intervention group at day 7 (AP: 53.0 ± 21.3 mg/dL, CP: 59.7 ± 59.2 mg/dL, p = 0.686). Similarly, exploratory analysis of secondary clinical outcomes (e.g., patient survival) and treatment-specific adverse events revealed no differences between the study groups. Among liver transplant recipients, pre-operative organ perfusion with ATLG did not improve short-term outcomes, compared to those who received placebo perfusion. However, ATLG perfusion of liver grafts was proven to be a safe procedure without the occurrence of relevant adverse events.

Abstract Study question Within this prospective study, we aim to differentiate immune cell subpopulations in recurrent implantation failure (RIF) patients and fertile controls. Summary answer A misbalanced immune profile of NK cell subpopulations is present in RIF patients and might be a potential risk factor that requires further detailed analysis. What is known already So far, there is no conclusive opinion on the prognostic value of testing immune cell populations in women with RIF. Increased numbers of cytotoxic (CD56dimCD16bright) peripheral natural killer (pNK)-cells and CD56brightCD16dim mainly in the uterus occurring NK cells (uNK) seemed to be more prevalent in RIF patients. NK cell cytotoxicity is regulated by a complex interaction of activating and inhibiting receptors, such as the NKGD2 and natural cytotoxicity receptors including NKp46, NKp30 and NKp44. Dysregulated pNK cells could affect the adhesion and implantation of the embryo thereby contributing to RIF. Study design, size, duration Within this prospective study between March 2018 and August 2020 immune diagnostics of pNK cells and subpopulations as well as regulatory T-cells in RIF patients (defined as ≥ 3 failed fresh or frozen embryo transfers of good quality embryos (Istanbul criteria) and non-pregnant controls (nulli- and multipara) were performed using flow cytometry analysis. Participants/materials, setting, methods In total, n = 42 RIF and n = 85 controls were included. Absolute numbers and percentages of total lymphocytes of CD56dimCD16bright, CD56brightCD16dim NK cells, CD45+CD25+FoxP3+-regulatory T-cells and activation markers (CD57+, CD62L+, NKGD2+, NKp46+) were measured in patients and controls (n = 60 nulligravida, n = 25 para) in the mid-luteal phase. Statistical analysis was performed using SPSS Version 26 considering p < 0.05 statistically significant. Main results and the role of chance RIF patients showed significantly lower numbers and percentages of CD56dimCD16bright pNK cells (mean±SD per µl: 187,5±113,3 vs. 281,9±163,4 p = 0.001;%: 87,4±8,8 vs. 90,6±6,0 p = 0.017) and higher levels of CD56brightCD16dim pNK cells (mean±SD per%: 10,5±8,3 vs. 7,6±5,5 p = 0.021) compared to controls. Further, lower percentages of CD56dimCD16brightCD62L + (mean±SD per%: 23,5±11,1 vs. 32,0±14,0 p = 0.001), CD56dimCD16brightNKGD2 + (mean±SD per%: 94,0±6,8 vs. 96,4±4,2 p = 0.014) and CD56dimCD16brightNKp46 + (mean±SD per%: 65,8±19,5 vs. 76,1±14,0 p = 0.001) were observed in RIF patients (p < 0.05). A different activation of pNK cells represented by high levels of CD62L+, NKGD2+, NKp46+ surface markers in controls and higher levels of CD56brightCD16dim pNK cells in RIF patients could contribute to RIF. No difference was present in levels of CD45+CD25+FoxP3+-regulatory T-cells within the study population. Limitations, reasons for caution As controls composed out of not only nulli- but also multipara, higher levels of pNK cells in controls, could be induced by fetal microchimerism in multiparas, however, results remained significant after removing multipara from statistical analysis. Wider implications of the findings: These findings condense into the assumption of a non-linear association between NK cytotoxicity and successful pregnancy. A lower NK cytotoxicity in RIF patients could potentially lead to an altered immune environment impeding a successful implantation process. Trial registration number Drks00020803

In search for novel biomarkers to assess graft quality, we investigated whether defined candidate genes are predictive for outcome after liver transplantation (LT). Zero-hour liver biopsies were obtained from 88 livers. Gene expression of selected candidate markers was analyzed and correlated with clinical parameters as well as short and long-term outcomes post LT. Whereas both, the calculated Eurotransplant Donor-Risk-Index and the donor body mass index, had either a poor or no predictive value concerning serum levels indicative for liver function (ALT, AST, GGT, bilirubin) after 6 months, chronological donor age was weakly predictive for serum bilirubin (AUC=0.67). In contrast, the major histcompatibility complex class I related chain A (MICA) mRNA expression demonstrated a high predictive value for serum liver function parameters revealing an inverse correlation (e.g. for ALT: 3 months p=0.0332; 6 months p=0.007, 12 months 0.0256, 24 months p=0.0098, 36 months, p=0.0153) and proved significant also in a multivariate regression model. Importantly, high expression of MICA mRNA revealed to be associated with prolonged graft survival (p=0.024; log rank test) after 10 years of observation, whereas low expression was associated with the occurrence of death in patients with transplant related mortality (p=0.031). Given the observed correlation with short and long-term graft function, we suggest MICA as a biomarker for pre-transplant graft evaluation.

Background and Objectives: We examined retrospectively whether the combination of standard dacarbazine (DTIC) and/or fotemustine chemotherapy and autologous peptide-loaded dendritic cell (DC) vaccination may improve survival of stage IV melanoma patients. Furthermore, a small cohort of long-term survivors was studied in more detail. Patients and methods: Between 1998 and 2008, 41 patients were vaccinated at least three times with DCs while receiving chemotherapy and compared to all other 168 patients in our database who only received chemotherapy (1993-2008). Results: Median life expectancy of patients receiving additional DC-vaccination was 18 months, compared to eleven months for patients under standard chemotherapy alone. In contrast to patients with other haplotypes, the HLA-A1/A1 subset of DC-treated patients showed significantly lower median survival (12 vs. 25 months). Autoantibodies were frequently detected in serum of both vaccinated and non-vaccinated patients, and there was no correlation between titers, loss or appearance of autoantibodies and survival. Additionally, phenotyping of DCs and PBMCs also did not reveal any conspicuous correlation with survival. Conclusions: Combining standard chemotherapy and DC vaccination appears superior to chemotherapy alone. The impact of HLA haplotypes on survival emphasizes the importance of a careful selection of patients with specific, well-defined HLA haplotypes for future vaccination trials using peptide-pulsed DCs, possibly combined with checkpoint inhibitors.

Zielsetzung Als immunologische Ursachen für rezidivierende Spontanaborte (RSA) und rezidivierendes Implantationsversagen (RIF) werden erhöhte periphere (pNK) und uterine natürliche Killerzellen (uNK). Während uNK meist CD56brightCD16dim Oberflächenmarker aufweisen und zytoregulatorische Eigenschaften haben, zeigen CD56dimCD16bright Zellen eine hohe Zytotoxizität und dominieren im peripheren Blut. Ziel dieser Studie ist die Analyse der pNK- und uNK-Zellsubpopulationen bei RSA- und RIF-Patientinnen im Vergleich zu gesunden Kontrollen.

OBJECTIVES Ischaemia and subsequent reperfusion during heart transplantation inevitably result in donor organ injury. Toll-like receptor (TLR)-3 is a pattern recognition receptor activated by viral and endogenous RNA released by injured cells. We hypothesized that ischaemia/reperfusion injury (IRI) leads to RNA release with subsequent TLR3 activation in transplanted hearts. METHODS Human endothelial cells were subjected to IRI and treated with TLR3 agonist polyinosinic-polycytidylic acid or a TLR3/double-stranded RNA complex inhibitor. TLR3 activation was analysed using reporter cells. Gene expression profiles were evaluated via next-generation sequencing. Neutrophil adhesion was assessed in vitro. Syngeneic heart transplantation of wild-type or Tlr3-/- mice was performed following 9 h of cold ischaemia. Hearts were analysed for inflammatory gene expression, cardiac damage, apoptosis and infiltrating leucocytes. RESULTS IRI resulted in RNA release with subsequent activation of TLR3. Treatment with a TLR3 inhibitor abrogated the inflammatory response upon IRI. In parallel, TLR3 stimulation caused activation of the inflammasome. Endothelial IRI resulted in TLR3-dependent adhesion of neutrophils. Tlr3-/- animals showed reduced intragraft and splenic messenger ribonucleic acid (mRNA) expression of proinflammatory cytokines, resulting in decreased myocardial damage, apoptosis and infiltrating cells. Tlr3 deficiency protected from cardiac damage, apoptosis and leucocyte infiltration after cardiac transplantation. CONCLUSIONS We uncover the release of RNA by injured cells with subsequent activation of TLR3 as a crucial pathomechanism of IRI. Our data indicate that TLR3 represents a novel target in the prevention of IRI in solid organ transplantation.

Background: Tetrahydrobiopterin is a naturally occurring antioxidant and vitamin-like compound which exerts immunomodulatory activities in ischemia-reperfusion injury as well as in acute and chronic graft rejection models. While nitric oxide synthases have been shown to be involved in the attenuation of ischemia-reperfusion injury and allograft vasculopathy, the immunosuppressive mechanisms in acute rejection models are still unknown. Herein, we wanted to further dissect its immunosuppressive property. Methods/Materials: A fully MHC mismatched (C3H/He to C57BL/6) mouse heterotopic heart transplantation model was used. Recipient mice were either treated with tetrahydrobiopterin (50mg/kg b.w.) three times a day or with Cyclosporine A (15mg/kg b.w.) every 24h. Syngeneic and untreated allograft recipients served as controls. We analysed graft survival as well as graft function by daily palpation and inspection. At day six days post-transplantation the organ was retrieved. The severity of acute rejection was assessed by histopathological analysis according to the International Society for Heart and Lung Transplantation score. Splenocytes were analyzed by flow cytometry. Results: At day six the median graft functioning score was significantly higher in tetrahydrobiopterin treated compared to untreated animals (p < 0.05). It was comparable with Cyclosporine A treated animals (p = ns) as well as with syngeneic controls (p = ns). This result was reflected also by prolonged allograft survival in tetrahydrobiopterin and CsA treated recipients (p < 0.05). Histopathological analyses showed severe rejection in untreated allografts and absent to mild rejection in syngeneic controls. Cyclosporine A treated grafts displayed mild rejection (p < 0.05 compared to untreated grafts). Tetrahydrobiopterin treatment resulted in heterogeneous lymphocytic infiltrates varying between mild and severe (p = ns). Flow cytometry revealed in Cyclosporine A and tetrahydrobiopterin treated animals, comparable amounts of dendritic cells and NK cells. Tetrahydrobiopterin treated animals showed a substantial increase in cytotoxic T cells (p < 0.05), however, displaying lower CD28 expression (p < 0.05). Of note, mast cells and regulatory T cells were significantly increased in tetrahydrobiopterin treated animals compared to control and Cyclosporine A treated animals (p < 0.05). Conclusion: Prolonged allograft survival by tetrahydrobiopterin is associated in this murine heart transplantation model with increased mobilization of mast cells and regulatory T-cells. These two cells are known to create a functional tolerogenic unit and might account for the immunosuppressive property of tetrahydrobiopterin in this acute rejection model.

Mitochondria sense changes resulting from the ischemia and subsequent reperfusion of an organ and mitochondrial reactive oxygen species (ROS) production initiates a series of events, which over time result in the development of full-fledged ischemia-reperfusion injury (IRI), severely affecting graft function and survival after transplantation. ROS activate the innate immune system, regulate cell death, impair mitochondrial and cellular performance and hence organ function. Arresting the development of IRI before the onset of ROS production is currently not feasible and clinicians are faced with limiting the consequences. Ex vivo machine perfusion has opened the possibility to ameliorate or antagonize the development of IRI and may be particularly beneficial for extended criteria donor organs. The molecular events occurring during machine perfusion remain incompletely understood. Accumulation of succinate and depletion of adenosine triphosphate (ATP) have been considered key mechanisms in the initiation; however, a plethora of molecular events contribute to the final tissue damage. Here we discuss how understanding mitochondrial dysfunction linked to IRI may help to develop novel strategies for the prevention of ROS-initiated damage in the evolving era of machine perfusion.

Resistance to chemotherapy is one of the primary obstacles in acute myeloid leukemia (AML) therapy. Micro-RNA-23a (miR-23a) is frequently deregulated in AML and has been linked to chemoresistance in solid cancers. We, therefore, studied its role in chemoresistance to cytarabine (AraC), which forms the backbone of all cytostatic AML treatments. Initially, we assessed AraC sensitivity in three AML cell lines following miR-23a overexpression/knockdown using MTT-cell viability and soft-agar colony-formation assays. Overexpression of miR-23a decreased the sensitivity to AraC, whereas its knockdown had the opposite effect. Analysis of clinical data revealed that high miR-23a expression correlated with relapsed/refractory (R/R) AML disease stages, the leukemic stem cell compartment, as well as with inferior overall survival (OS) and event-free survival (EFS) in AraC-treated patients. Mechanistically, we demonstrate that miR-23a targets and downregulates topoisomerase-2-beta (TOP2B), and that TOP2B knockdown mediates AraC chemoresistance as well. Likewise, low TOP2B expression also correlated with R/R-AML disease stages and inferior EFS/OS. In conclusion, we show that increased expression of miR-23a mediates chemoresistance to AraC in AML and that it correlates with an inferior outcome in AraC-treated AML patients. We further demonstrate that miR-23a causes the downregulation of TOP2B, which is likely to mediate its effects on AraC sensitivity.