Renal inflamm-aging provokes intra-graft inflammation following experimental kidney transplantation.

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.

Joining Forces in Basic Science: ITS Meeting 2.0.

The second International Transplant Science (ITS) meeting jointly organized by the European Society for Organ Transplantation (ESOT), the American Society of Transplantation (AST), and The Transplantation Society (TTS) took place in May 2022 in one of Europe's most iconic cities: Berlin, Germany. The ITS meeting 2022 was designed to serve as an international platform for scientific discussions on the latest ground-breaking discoveries in the field, while providing an excellent opportunity to present cutting-edge research to the scientific community. We think this is fundamental for the exchange of new ideas and establishment of collaborative work between advanced transplant experts, young professionals and early-stage researchers and students. Scientific sessions tackled hot topics in transplantation such as mechanisms of tolerance, biomarkers, big data and artificial intelligence. Our educational pre-meeting focused on the breakthrough and challenges in single-cell multimodal omics. The program included panel discussions illuminating various topics concerning conflicts and problems related to gender, such as challenges for female scientists. Attendees returned to their institutes with not only profound knowledge of the latest discoveries, technologies, and concepts in basic and translational science, but also inspired and excited after discussions and networking sessions with fellow scientists which have been duly missed during the pandemic.

SARS-CoV2 mRNA Vaccine-Specific B-, T- and Humoral Responses in Adolescents After Kidney Transplantation.

Protection of adult kidney transplant recipients against SARS-CoV2 was shown to be strongly impaired owing to low reactogenicity of available vaccines. So far, data on vaccination outcomes in adolescents are scarce due to later vaccination approval for this age group. We therefore comprehensively analyzed vaccination-specific humoral-, T- and B-cell responses in kidney transplanted adolescents aged 12-18 years in comparison to healthy controls 6 weeks after standard two-dose BNT162b2 ("Comirnaty"; Pfizer/BioNTech) vaccination. Importantly, 90% (18/20) of transplanted adolescents showed IgG seroconversion with 75% (15/20) developing neutralizing titers. Still, both features were significantly diminished in magnitude compared to controls. Correspondingly, spike-specific B cells were quantitatively reduced and enriched for non-isotype-class-switched IgD+27+ memory cells in patients. Whereas spike specific CD4+ T cell frequencies were similar in both groups, cytokine production and memory differentiation were significantly impaired in transplant recipients. Although our data identify limitations in all arms of vaccine-specific immunity, the majority of our adolescent patients showed robust humoral responses despite antimetabolite-based treatment being associated with poor vaccination outcomes in adults.

B and T Cell Responses after a Third Dose of SARS-CoV-2 Vaccine in Kidney Transplant Recipients.

BACKGROUND: Accumulating evidence sugges ts solid organ transplant recipients, as opposed to the general population, show strongly impaired responsiveness toward standard SARS-CoV-2 mRNA-based vaccination, demanding alternative strategies for protectio n o f this vulnerable group. METHODS: In line with recent recommendations, a third dose of either heterologous ChAdOx1 (AstraZeneca) or homologous BNT162b2 (BioNTech) was administered to 25 kidney transplant recipients (KTR) without humoral response after two doses of BNT162b2, followed by analysis of serological responses and vaccine-specific B- and T-cell immunity. RESULTS: Nine out of 25 (36%) KTR under standard immunosuppressive treatment seroconverted until day 27 after the third vaccination, whereas one patient developed severe COVID-19 infection immediately after vaccination. Cellular analysis 7 days after the third dose showed significantly elevated frequencies of viral spike-protein receptor-binding domain-specific B cells in humor al responders as compared with nonresponders. Likewise, portions of spike-reactive CD4 + T helper cells were significantly elevated in patients who were seroconverting. Furthermore, overall frequencies of IL-2 + , IL-4 + , and polyfunctional CD4 + T cells significantly increased after the third dose, whereas memory/effector differentiation remained unaffected. CONCLUSIONS: Our data suggest a fraction of transplant recipients benefit from triple vaccination, where seroconversion is associated with quantitative and qualitative changes of cellular immunity. At the same time, the study highlights that modified vaccination approaches for immunosuppressed patients remain an urgent medical need. PODCAST: This article contains a podcast at https://www.asn-online.org/media/podcast/JASN/2021_11_23_briggsgriffin112321.mp3.

Signatures and Specificity of Tissue-Resident Lymphocytes Identified in Human Renal Peritumor and Tumor Tissue.

BACKGROUND: Tissue-resident memory T (TRM) cells are known to be important for the first line of defense in mucosa-associated tissues. However, the composition, localization, effector function, and specificity of TRM cells in the human kidney and their relevance for renal pathology have not been investigated. METHODS: Lymphocytes derived from blood, renal peritumor samples, and tumor samples were phenotypically and functionally assessed by applying flow cytometry and highly advanced histology (multi-epitope ligand cartography) methods. RESULTS: CD69+CD103+CD8+ TRM cells in kidneys display an inflammatory profile reflected by enhanced IL-2, IL-17, and TNFα production, and their frequencies correlate with increasing age and kidney function. We further identified mucosa-associated invariant T and CD56dim and CD56bright natural killer cells likewise expressing CD69 and CD103, the latter significantly enriched in renal tumor tissues. CD8+ TRM cell frequencies were not elevated in kidney tumor tissue, but they coexpressed PD-1 and TOX and produced granzyme B. Tumor-derived CD8+ TRM cells from patients with metastases were functionally impaired. Both CD69+CD103-CD4+ and CD69+CD103-CD8+ TRM cells form distinct clusters in tumor tissues in proximity to antigen-presenting cells. Finally, EBV, CMV, BKV, and influenza antigen-specific CD8+ T cells were enriched in the effector memory T cell population in the kidney. CONCLUSIONS: Our data provide an extensive overview of TRM cells' phenotypes and functions in the human kidney for the first time, pointing toward their potential relevance in kidney transplantation and kidney disease.

Mucosal associated invariant T cells are differentially impaired in tolerant and immunosuppressed liver transplant recipients.

Mucosal associated invariant T (MAIT-) cells represent a semi-invariant T cell population responsive to microbial vitamin B metabolite and innate cytokine stimulation, executing border tissue protection and particularly contributing to human liver immunity. The impact of immunosuppressants on MAIT cell biology alone and in context with solid organ transplantation has not been thoroughly examined. Here, we demonstrate that in vitro cytokine activation of peripheral MAIT cells from healthy individuals was impaired by glucocorticoids, whereas antigen-specific stimulation was additionally sensitive to calcineurin inhibitors. In liver transplant (LTx) recipients, significant depletion of peripheral MAIT cells was observed that was largely independent of the type and dosage of immunosuppression, equally applied to tolerant patients, and was reproducible in kidney transplant recipients. However, MAIT cells from tolerant LTx patients exhibited a markedly diminished ex vivo activation signature, associated with individual regain of functional competence toward antigenic and cytokine stimulation. Still, MAIT cells from tolerant and treated liver recipients exhibited high levels of PD1, accompanied by functional impairment particularly toward bacterial stimulation that also affected polyfunctionality. Our data suggest interlinked effects of primary liver pathology and immunosuppressive treatment on overall MAIT cell fitness after transplantation and propose their monitoring in context with tolerance induction protocols.

T- and B-cell therapy in solid organ transplantation: current evidence and future expectations.

Cell therapy has emerged as an attractive therapeutic option in organ transplantation. During the last decade, the therapeutic potency of Treg immunotherapy has been shown in various preclinical animal models and safety was demonstrated in first clinical trials. However, there are still critical open questions regarding specificity, survival, and migration to the target tissue so the best Treg population for infusion into patients is still under debate. Recent advances in CAR technology hold the promise for Treg-functional superiority. Another exciting strategy is the generation of B-cell antibody receptor (BAR) Treg/cytotoxic T cells to specifically regulate or deplete alloreactive memory B cells. Finally, B cells are also capable of immune regulation, making them promising candidates for immunomodulatory therapeutic strategies. This article summarizes available literature on cell-based innovative therapeutic approaches aiming at modulating alloimmune response for transplantation. Crucial areas of investigation that need a joined effort of the transplant community for moving the field toward successful achievement of tolerance are highlighted.

The TL1A-DR3 Axis Selectively Drives Effector Functions in Human MAIT Cells.

Mucosal-associated invariant T (MAIT) cells are semi-invariant T cells specifically recognizing riboflavin derivatives that are synthesized by many bacteria and fungi presented by MHC class I-related MR1 molecules. Accumulating evidence, however, indicates that MAIT cell functions are inducible by cytokine stimuli in the absence of TCR ligation, identifying MAIT cells as innate sentinels in inflammatory environments. In this study, we demonstrate that death receptor 3 (DR3), a member of the TNFR superfamily, is ex vivo expressed and predominantly upregulated on the surface of human MAIT cells by innate cytokine stimulation. In turn, the DR3 ligand TNF-like protein 1A (TL1A) licenses innate TNF-α production in the absence of cognate triggers, being sufficient to promote activation of primary endothelial cells in vitro. TL1A further amplifies synthesis of IFN-γ and granzyme B in the presence of otherwise weak innate stimuli and strongly augments polyfunctionality. Mechanistically, TL1A potentiates T-bet expression, early NF-κB, and late p38 MAP kinase phosphorylation, with the latter being indispensable for TNF-α production by MAIT cells. Of note, endogenous TL1A is also rapidly released from PBMC cultures in response to bacterial triggering, thereby equally augmenting Ag-specific MAIT cell effector functions. In summary, to our knowledge, we identify a new inflammatory mechanism in MAIT cells linking the DR3/TL1A axis with amplification of TCR-dependent and -independent effector functions, particularly inducing excessive innate TNF-α production. Given that both TL1A and TNF-α are abundantly present at sites of chronic inflammation, the contribution of MAIT cells in such scenarios needs to be determined.

Identification of the activating cytotoxicity receptor NKG2D as a senescence marker in zero-hour kidney biopsies is indicative for clinical outcome.

The definition of biological donor organ age rather than chronological age seems obvious for the establishment of a valid pre-transplant risk assessment. Therefore, we studied gene expression for candidate markers in 60 zero-hour kidney biopsies. Compared with 29 younger donors under age 55, 31 elderly donors age 55 and older had significant mRNA expression for immunoproteasome subunits (PSMB8, PSMB9 and PSMB10), HLA-DRB, and transcripts of the activating cytotoxicity receptor NKG2D. Gene expression was validated in an independent donor cohort consisting of 37 kidneys from donors 30 years and under (Group I), 75 kidneys from donors age 31-54 years (Group II) and 75 kidneys from donors age 55 and older (Group III). Significant gene induction was confirmed in kidneys from Group III for PSMB9 and PSMB10. Strikingly, transcripts of NKG2D had the significantly highest gene induction in Group III versus Group II and Group I. Similar results were obtained for CDKN2A, but not for telomere length. Both NKG2D and CDKN2A mRNA expression were significantly correlated with creatinine levels at 24 months after transplantation. Univariate regression analysis showed significant predictive power regarding graft function at 6 and 12 months for NKG2D and CDKN2A. However, only NKG2D remained significantly predictive in the multivariate model at 12 months. Thus, our results reveal novel candidate markers in aged renal allografts, which could be helpful in the assessment of organ quality.

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.

NK cell killer Ig-like receptor repertoire acquisition and maturation are strongly modulated by HLA class I molecules.

The interaction between clonally distributed inhibitory receptors and their activating counterparts on NK cells and HLA class I molecules defines NK cell functions, but the role of HLA class I ligands in the acquisition of their receptors during NK development is still unclear. Although some studies demonstrated that HLA-C affects the expression of killer Ig-like receptors (KIR), other studies showed that NK cells acquire their KIR repertoire in a stochastic manner. Only when infected with human CMV is an expansion of self-specific KIR(+) NKG2C(+) NK cells detected. To gain more insight into this question, we compared the coexpression of different KIR molecules, NKG2A, CD8, and CD57, on NK cells in healthy donors and seven patients with deficient HLA class I expression due to mutations in one of the TAP genes. Our results show a correlation between the presence/absence of HLA class I molecules and the coexpression of their receptors. In an HLA class I low-expression context, an increase in KIR molecules' coexpression is detected on the NKG2A(+) CD8(+) subset. In functional assays, hyporesponsiveness was observed for TAP-deficient NK cells derived from four patients. In contrast, NK cells from patient five were functional, whereas CD107a(+) and IFN-γ(+) CD56(dim) NK cells presented a different pattern of HLA class I receptors compared with healthy donors. Taken together, our results provide strong evidence for the role of HLA class I molecules in NK cell maturation and KIR repertoire acquisition.

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.

Adiponectin modulates NK-cell function.

Adiponectin (APN) has been shown to exert antiinflammatory effects in various disease models but little is known concerning its regulation of NK-cell function. Here, we show that the majority of human CD56(dim) NK cells express surface Adiponectin receptor (AdipoR) 1 and 2 while most CD56(high) NK cells are AdipoR-negative. Toll-like receptor (TLR) ligand-induced IFN-γ production was diminished by APN while it had no influence on NK-cell cytotoxicity. In contrast only a small subpopulation of murine NK cells expresses surface AdipoRs, but about 90% store them intracellularly. APN-deficient knockout (KO) mice had elevated frequencies of NK cells. However, cytotoxic degranulation of NK cells was decreased in APN knockout (APN-KO) animals. Accordingly, frequencies of CD11b(high) CD27(high) and CD94(high) effector NK cells and expression of NKG2D were lower in APN-KO mice. Upon CVB3 infection NK-cell function was restored in APN-KO mice. Our data suggest that in addition to its antiinflammatory effects APN also influences the numerical and differentiation status of NK cells, which may further impact the outcome of immune-mediated diseases in APN-KO mice.

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.

Bilirubin rinse of the graft ameliorates ischemia reperfusion injury in heart transplantation.

Ischemia and reperfusion contribute to substantial organ damage in transplantation. Clinically feasible measures for the prevention thereof are scarce. We tested whether rinsing rodent hearts with the antioxidant bilirubin ameliorates ischemia reperfusion injury (IRI). Left ventricular end-diastolic pressure (LVEDP), left ventricular developed pressure (LVDevP), rate per pressure product (RPP), coronary flow, maximum (+dP/dt) and minimum (-dP/dt) rate of contraction were analyzed in Lewis rat hearts rinsed with bilirubin prior to reperfusion on a Langendorff apparatus after 12 h of cold ischemia. In vivo, isogenic C57Bl/6 mouse hearts rinsed with bilirubin were transplanted after 12 h of cold ischemia. Cardiac function and apoptosis were assessed 24 h after reperfusion. Heart lysates recovered 15 min after reperfusion were probed for the total and the phosphorylated forms of extracellular signal-related protein kinases (ERK), JNK, p38-MAPK, and Akt. In isolated perfused hearts, bilirubin rinse resulted in significantly lower LVEDP and improved LVDevP, RPP, coronary flow, +dP/dt and -dP/dt. In vivo, after reperfusion, all mitogen-activated protein kinases (MAPKs) were suppressed significantly by bilirubin pretreatment. Bilirubin rinse improved cardiac scores (3.4 ± 0.5 vs. 2.0 ± 1.0 in controls, P < 0.05) and significantly suppressed apoptosis. Ex vivo administration of bilirubin to heart grafts prior reperfusion ameliorates IRI and provides a simple and effective tool to ameliorate outcome in heart transplantation.

CD3 downregulation identifies high-avidity, multipotent SARS-CoV-2 vaccine- and recall antigen-specific Th cells with distinct metabolism.

Functional avidity is supposed to critically shape the quality of immune responses, thereby influencing host protection against infectious agents including SARS-CoV-2. Here we show that after human SARS-CoV-2 vaccination, a large portion of high-avidity spike-specific CD4+ T cells lost CD3 expression after in vitro activation. The CD3- subset was enriched for cytokine-positive cells, including elevated per-cell expression levels, and showed increased polyfunctionality. Assessment of key metabolic pathways by flow cytometry revealed that superior functionality was accompanied by a shift toward fatty acid synthesis at the expense of their oxidation, whereas glucose transport and glycolysis were similarly regulated in SARS-CoV-2-specific CD3- and CD3+ subsets. As opposed to their CD3+ counterparts, frequencies of vaccine-specific CD3- T cells positively correlated with both the size of the naive CD4+ T cell pool and vaccine-specific IgG levels. Moreover, their frequencies negatively correlated with advancing age and were impaired in patients under immunosuppressive therapy. Typical recall antigen-reactive T cells showed a comparable segregation into functionally and metabolically distinct CD3+ and CD3- subsets but were quantitatively maintained upon aging, likely due to earlier recruitment in life. In summary, our data identify CD3- T helper cells as correlates of high-quality immune responses that are impaired in at-risk populations.

The genetic predisposition of natural killer cell to BK virus-associated nephropathy in renal transplant patients.

BK virus (BKV) infection represents a serious complication in renal transplant patients resulting in BKV-associated nephropathy and subsequent allograft loss. Natural killer cells are crucial in the antiviral immune response; however, an understanding of the role of natural killer cells in protection against BKV is limited. To elucidate whether killer-cell immunoglobulin-like receptors and their interaction between donor-/recipient-related ligands have a role in BKV infection, we performed genotyping analysis in 48 kidney transplant recipients with a history of severe BKV infection/BKV-associated nephropathy and 110 recipients with stable renal function and no BKV reactivation. Of interest, we found that telomeric gene content motif was significantly associated with severe course of BKV infection/BKV-associated nephropathy and detected significantly higher percentage of patients with BKV-associated nephropathy carrying low numbers of activating receptors compared with the control group. Detailed analysis of each single receptor revealed significantly lower frequencies of the activating receptor KIR3DS1 in patients with BKV infection/nephropathy as compared with the controls. Thus, our study supports protective effects of activating receptors in BKV infection and suggest natural killer-cell-related genetic predisposition to the development of BKV-associated nephropathy.

Targeting the Kv1.3 potassium channel for immunosuppression in vascularized composite allotransplantation - a pilot study.

Kv1.3-channels are critically involved in activation and function of effector memory T cells. Blocking Kv1.3-channels was investigated for its effect on skin rejection in a rat limb-transplantation-model. Animals received the Kv1.3-blocker correolide C systemically or locally as intra-graft-treatment in combination with tacrolimus. Systemic (intraperitoneal) administration of correolide C resulted in slight, but significant prolongation of allograft survival compared with untreated and placebo treated controls. In 4/6 correolide C treated animals, histology showed an intact epidermis and a mild infiltrate by day 10. High correolide C plasma trough levels correlated with prolonged allograft survival. A decrease in CD4+ and CD8+ effector memory T cells was observed in allograft skin, peripheral blood and the spleen on day 5. When applied subcutaneously in combination with systemic tacrolimus (30 days+/-anti-lymphocyte serum) detectable, but insignificant prolongation of graft survival was achieved. 2/5 animals showed an intact epidermis and a mild infiltrate until day 45. Tapering systemic tacrolimus and weaning on day 50 resulted in rejection by day 55, regardless of local correolide C treatment. Subcutaneous injection did not lead to systemic plasma levels. The Kv1.3-channel is a potential drug target worth exploring in more detail for immunosuppression in vascularized composite allotransplantation.

ILC2 require cell-intrinsic ST2 signals to promote type 2 immune responses.

The initiation of type 2 immune responses at mucosal barriers is regulated by rapidly secreted cytokines called alarmins. The alarmins IL-33, IL-25 and TSLP are mainly secreted by stromal and epithelial cells in tissues and were linked to chronic inflammatory diseases, such as allergic lung inflammation, or to resistance against worm infections. Receptors for alarmins are expressed by a variety of immune cells, including group 2 innate lymphoid cells (ILC2s), an early source of the type 2 cytokines, such as IL-5 and IL-13, which have been linked to atopic diseases and anti-worm immunity as well. However, the precise contribution of the IL-33 receptor signals for ILC2 activation still needs to be completed due to limitations in targeting genes in ILC2. Using the newly established Nmur1 iCre-eGFP mouse model, we obtained specific conditional genetic ablation of the IL-33 receptor subunit ST2 in ILC2s. ST2-deficient ILC2s were unresponsive to IL-33 but not to stimulation with the alarmin IL-25. As a result of defective ST2 signals, ILC2s produced limited amounts of IL-5 and IL-13 and failed to support eosinophil homeostasis. Further, ST2-deficient ILC2s were unable to expand and promote the recruitment of eosinophils during allergic lung inflammation provoked by papain administration. During infection with Nippostrongylus brasiliensis, ILC2-intrinsic ST2 signals were required to mount an effective type 2 immune response against the parasite leading to higher susceptibility against worm infection in conditional knockout mice. Therefore, this study argues for a non-redundant role of cell-intrinsic ST2 signals triggering proper activation of ILC2 for initiation of type 2 immunity.