MerTK-dependent efferocytosis by monocytic-MDSCs mediates resolution of post-lung transplant injury.

Rationale: Patients with end stage lung diseases require lung transplantation (LTx) that can be impeded by ischemia-reperfusion injury (IRI) leading to subsequent chronic lung allograft dysfunction (CLAD) and inadequate outcomes. Objectives: We examined the undefined role of MerTK (receptor Mer tyrosine kinase) on monocytic myeloid-derived suppressor cells (M-MDSCs) in efferocytosis (phagocytosis of apoptotic cells) to facilitate resolution of lung IRI. Methods: Single-cell RNA sequencing of lung tissue and BAL from post-LTx patients was analyzed. Murine lung hilar ligation and allogeneic orthotopic LTx models of IRI were used with Balb/c (WT), cebpb -/- (MDSC-deficient), Mertk -/- or MerTK-CR (cleavage resistant) mice. Lung function, IRI (inflammatory cytokine and myeloperoxidase expression, immunohistology for neutrophil infiltration), and flow cytometry of lung tissue for efferocytosis of apoptotic neutrophils were assessed in mice. Measurements and Main Results: A significant downregulation in MerTK-related efferocytosis genes in M-MDSC populations of CLAD patients compared to healthy subjects was observed. In the murine IRI model, significant increase in M-MDSCs, MerTK expression and efferocytosis was observed in WT mice during resolution phase that was absent in cebpb -/- Land Mertk -/- mice. Adoptive transfer of M-MDSCs in cebpb -/- mice significantly attenuated lung dysfunction, and inflammation leading to resolution of IRI. Additionally, in a preclinical murine orthotopic LTx model, increases in M-MDSCs were associated with resolution of lung IRI in the transplant recipients. In vitro studies demonstrated the ability of M-MDSCs to efferocytose apoptotic neutrophils in a MerTK-dependent manner. Conclusions: Our results suggest that MerTK-dependent efferocytosis by M-MDSCs can significantly contribute to the resolution of post-LTx IRI.

The common TMEM173 HAQ, AQ alleles rescue CD4 T cell death, restore T-regs, and prevent SAVI (N153S) inflammatory disease in mice.

STING activation induces lymphocyte cell death that is independent of type I IFNs. The in vivo significance and mechanism of STING-mediated cell death is unclear. Using STING knock-in mice, we found that lymphocytes from the HAQ, AQ, and Q293 mice are resistant to STING-mediated cell death ex vivo, establishing a critical role of STING residue 293 in cell death. CD4 T cellpenia is evident in STING-associated vasculopathy with onset in infancy (SAVI), an autosomal dominant, fatal inflammatory disease caused by gain-of-function human STING mutations. The HAQ/SAVI(N153S) and AQ/SAVI(N153S) mice have similar spleen CD4 T cells as the WT mice reversing the CD4 T cellpenia by the gain-of-function N153S STING. The HAQ/SAVI(N153S), AQ/SAVI(N153S) mice have more (~10-fold, ~20-fold, respectively) T-regs than WT/SAVI(N153S) mice. Remarkably, while have comparable TBK1, IRF3, NFκB activation as the WT/SAVI, the AQ/SAVI mice have no tissue inflammation, regular body weight, and normal lifespan. The type I IFNs-independent function of STING in health and diseases has been increasingly recognized. We propose that STING activation promotes tissue inflammation by depleting T-regs cells in vivo. Billions of modern humans have the dominant HAQ, AQ alleles. STING research and STING targeting immunotherapy should consider TMEM173 heterogeneity in humans.

Management of nontuberculous mycobacteria in lung transplant cases: an international Delphi study.

Rationale: Nontuberculous mycobacterial (NTM) diseases are difficult-to-treat infections, especially in lung transplant (LTx) candidates. Currently, there is a paucity of recommendations on the management of NTM infections in LTx, focusing on Mycobacterium avium complex (MAC), M. abscessus and M. kansasii. Methods: Pulmonologists, infectious disease specialists, LTx surgeons and Delphi experts with expertise in NTM were recruited. A patient representative was also invited. Three questionnaires comprising questions with multiple response statements were distributed to panellists. Delphi methodology with a Likert scale of 11 points (5 to -5) was applied to define the agreement between experts. Responses from the first two questionnaires were collated to develop a final questionnaire. The consensus was described as a median rating >4 or <-4 indicating for or against the given statement. After the last round of questionnaires, a cumulative report was generated. Results: Panellists recommend performing sputum cultures and a chest computed tomography scan for NTM screening in LTx candidates. Panellists recommend against absolute contraindication to LTx even with multiple positive sputum cultures for MAC, M. abscessus or M. kansasii. Panellists recommend MAC patients on antimicrobial treatment and culture negative can be listed for LTx without further delay. Panellists recommend 6 months of culture-negative for M. kansasii, but 12 months of further treatment from the time of culture-negative for M. abscessus before listing for LTx. Conclusion: This NTM LTx study consensus statement provides essential recommendations for NTM management in LTx and can be utilised as an expert opinion while awaiting evidence-based contributions.

Resolution of post-lung transplant ischemia-reperfusion injury is modulated via Resolvin D1-FPR2 and Maresin 1-LGR6 signaling.

BACKGROUND: Dysregulation of inflammation-resolution pathways leads to postlung transplant (LTx) ischemia-reperfusion (IR) injury and allograft dysfunction. Our hypothesis is that combined treatment with specialized pro-resolving lipid mediators, that is, Resolvin D1 (RvD1) and Maresin-1 (MaR1), enhances inflammation-resolution of lung IR injury. METHODS: Expression of RvD1 and MaR1 was analyzed in bronchoalveolar lavage (BAL) fluid of patients on days 0, 1, and 7 post-LTx. Lung IR injury was evaluated in C57BL/6 (WT), FPR2-/-, and LGR6 siRNA treated mice using a hilar-ligation model with or without administration with RvD1 and/or MaR1. A donation after circulatory death and murine orthotopic lung transplantation model was used to evaluate the protection by RvD1 and MaR1 against lung IR injury. In vitro studies analyzed alveolar macrophages and type II epithelial cell activation after treatment with RvD1 or MaR1. RESULTS: RvD1 and MaR1 expressions in BAL from post-LTx patients was significantly increased on day 7 compared to days 0 and 1. Concomitant RvD1 and MaR1 treatment significantly mitigated early pulmonary inflammation and lung IR injury in WT mice, which was regulated via FPR2 and LGR6 receptors. In the murine orthotopic donation after cardiac death LTx model, RvD1 and MaR1 treatments significantly attenuated lung IR injury and increased PaO2 levels compared to saline-treated controls. Mechanistically, RvD1/FPR2 signaling on alveolar macrophages attenuated HMGB1 and TNF-α secretion and upregulated uptake of macrophage-dependent apoptotic neutrophils (efferocytosis), whereas MaR1/LGR6 signaling mitigated CXCL1 secretion by epithelial cells. CONCLUSIONS: Bioactive proresolving lipid mediator-dependent signaling that is, RvD1/FPR2 and MaR1/LGR6- offers a novel therapeutic strategy in post-LTx injury.

Hyperammonemia After Lung Transplantation: Systematic Review and a Mini Case Series.

Background: Hyperammonemia after lung transplantation (HALT) is a rare but serious complication with high mortality. This systematic review delineates possible etiologies of HALT and highlights successful strategies used to manage this fatal complication. Methods: Seven biomedical databases and grey literature sources were searched using keywords relevant to hyperammonemia and lung transplantation for publications between 1995 and 2020. Additionally, we retrospectively analyzed HALT cases managed at our institution between January 2016 and August 2018. Results: The systematic review resulted in 18 studies with 40 individual cases. The mean peak ammonia level was 769 µmol/L at a mean of 14.1 days post-transplant. The mortality due to HALT was 57.5%. In our cohort of 120 lung transplants performed, four cases of HALT were identified. The mean peak ammonia level was 180.5 µmol/L at a mean of 11 days after transplantation. HALT in all four patients was successfully treated using a multimodal approach with an overall mortality of 25%. Conclusion: The incidence of HALT (3.3%) in our institution is comparable to prior reports. Nonetheless, ammonia levels in our cohort were not as high as previously reported and peaked earlier. We attributed these significant differences to early recognition and prompt institution of multimodal treatment approach.

Set Up for Failure: Pre-Existing Autoantibodies in Lung Transplant.

Lung transplant patients have the lowest long-term survival rates compared to other solid organ transplants. The complications after lung transplantation such as primary graft dysfunction (PGD) and ultimately chronic lung allograft dysfunction (CLAD) are the main reasons for this limited survival. In recent years, lung-specific autoantibodies that recognize non-HLA antigens have been hypothesized to contribute to graft injury and have been correlated with PGD, CLAD, and survival. Mounting evidence suggests that autoantibodies can develop during pulmonary disease progression before lung transplant, termed pre-existing autoantibodies, and may participate in allograft injury after transplantation. In this review, we summarize what is known about pulmonary disease autoantibodies, the relationship between pre-existing autoantibodies and lung transplantation, and potential mechanisms through which pre-existing autoantibodies contribute to graft injury and rejection.

Macrophage activating syndrome causing decompensated right heart failure.

BACKGROUND: Macrophage activating syndrome (MAS) is a form of hemophagocytic lymphohistiocytosis (HLH), a rare complication of autoimmune disease that is characterized by cytokine storm and multiorgan failure. CASE SUMMARY: A 32-year-old male presented with acutely decompensated pulmonary arterial hypertension and right heart failure secondary to MAS. The patient was immediately started on inhaled and intravenous epoprostenol, vasopressors and dexamethasone and anakinra were administered. Despite the therapies given, the patient's condition continued to decline, and he was placed on veno-arterial extracorporeal membrane oxygenation (VA-ECMO) support. Over a few days, his clinical condition improved, and he was decannulated from VA-ECMO and later transitioned oral treprositinil and was discharged home. Due to its non-specific clinical manifestations, the diagnosis of MAS depends on high clinical suspicion and initial laboratory work up such as thrombocytopenia, transaminitis, hyperferritinemia, hypertriglyceridemia, hypofibrinogenemia, etc. In our patient, MAS led to decompensated Pulmonary Arterial Hypertension (PAH) leading to right heart failure that was refractory to inhaled and intravenous epoprostenol and vasopressors and required VA-ECMO as a bridge to recovery while his MAS was managed by anakinra and dexamethasone. CONCLUSION: MAS can result in acute decompensation of PAH and right heart failure. Besides RV failure management, immunosuppressants such as anakinra, etoposide, etc. should be utilized early in the management of MAS. In refractory right heart failure, VA-ECMO can be considered as a bridge to recovery. There is a paucity of literature supporting the utilization of VA-ECMO in the management of refractory right heart failure caused by MAS in adults and much of the data stems from pediatric studies. This case serves as a fine example of successful use of VA-ECMO in adult population.

In vivo reprogramming of pathogenic lung TNFR2+ cDC2s by IFNß inhibits HDM-induced asthma.

Asthma is a common inflammatory lung disease with no known cure. Previously, we uncovered a lung TNFR2+ conventional DC2 subset (cDC2s) that induces regulatory T cells (Tregs) maintaining lung tolerance at steady state but promotes TH2 response during house dust mite (HDM)-induced asthma. Lung IFNß is essential for TNFR2+ cDC2s-mediated lung tolerance. Here, we showed that exogenous IFNß reprogrammed TH2-promoting pathogenic TNFR2+ cDC2s back to tolerogenic DCs, alleviating eosinophilic asthma and preventing asthma exacerbation. Mechanistically, inhaled IFNß, not IFNα, activated ERK2 signaling in pathogenic lung TNFR2+ cDC2s, leading to enhanced fatty acid oxidation (FAO) and lung Treg induction. Last, human IFNß reprogrammed pathogenic human lung TNFR2+ cDC2s from patients with emphysema ex vivo. Thus, we identified an IFNß-specific ERK2-FAO pathway that might be harnessed for DC therapy.

A novel injury site-natural antibody targeted complement inhibitor protects against lung transplant injury.

Complement is known to play a role in ischemia and reperfusion injury (IRI). A general paradigm is that complement is activated by self-reactive natural IgM antibodies (nAbs), after they engage postischemic neoepitopes. However, a role for nAbs in lung transplantation (LTx) has not been explored. Using mouse models of LTx, we investigated the role of two postischemic neoepitopes, modified annexin IV (B4) and a subset of phospholipids (C2), in LTx. Antibody deficient Rag1-/- recipient mice were protected from LTx IRI. Reconstitution with either B4 or C2nAb restored IRI, with C2 significantly more effective than B4 nAb. Based on these information, we developed/characterized a novel complement inhibitor composed of single-chain antibody (scFv) derived from the C2 nAb linked to Crry (C2scFv-Crry), a murine inhibitor of C3 activation. Using an allogeneic LTx, in which recipients contain a full nAb repertoire, C2scFv-Crry targeted to the LTx, inhibited IRI, and delayed acute rejection. Finally, we demonstrate the expression of the C2 neoepitope in human donor lungs, highlighting the translational potential of this approach.

Successful Preoperative Optimization for Lung Transplantation With Transcatheter Mitral Valve Repair.

Surgically treatable valvular heart disease is common in patients with end-stage lung disease. Nevertheless, advanced lung disease is often seen as a contraindication to cardiac surgery, and severe valvular disease is seen as a contraindication to lung transplantation. This report describes the case of a patient presenting with very severe chronic obstructive pulmonary disease and severe mitral regurgitation who was managed with transcatheter mitral valve repair and who subsequently underwent successful lung transplantation. Critical valvular heart disease in patients with chronic respiratory failure may be amenable to transcatheter therapy, which may favorably affect lung transplantation candidacy.

MicroRNA-206 antagomiR‒enriched extracellular vesicles attenuate lung ischemia‒reperfusion injury through CXCL1 regulation in alveolar epithelial cells.

BACKGROUND: Our hypothesis is that the immunomodulatory capacities of mesenchymal stem cell‒derived extracellular vesicles (EVs) can be enhanced by specific microRNAs (miRNAs) to effectively attenuate post-transplant lung ischemia‒reperfusion (IR) injury. METHODS: The expression of miR-206 was analyzed in bronchoalveolar lavage (BAL) fluid of patients on Days 0 and 1 after lung transplantation. Lung IR injury was evaluated in C57BL/6 mice using a left lung hilar-ligation model with or without treatment with EVs or antagomiR-206‒enriched EVs. Murine lung tissue was used for miRNA microarray hybridization analysis, and cytokine expression, lung injury, and edema were evaluated. A donation after circulatory death and murine orthotopic lung transplantation model was used to evaluate the protection by enriched EVs against lung IR injury. In vitro studies analyzed type II epithelial cell activation after coculturing with EVs. RESULTS: A significant upregulation of miR-206 was observed in the BAL fluid of patients on Day 1 after lung transplantation compared with Day 0 and in murine lungs after IR injury compared with sham. Treatment with antagomiR-206‒enriched EVs attenuated lung dysfunction, injury, and edema compared with treatment with EVs alone after murine lung IR injury. Enriched EVs reduced lung injury and neutrophil infiltration as well as improved allograft oxygenation after murine orthotopic lung transplantation. Enriched EVs significantly decreased proinflammatory cytokines, especially epithelial cell‒dependent CXCL1 expression, in the in vivo and in vitro IR injury models. CONCLUSIONS: EVs can be used as biomimetic nanovehicles for protective immunomodulation by enriching them with antagomiR-206 to mitigate epithelial cell activation and neutrophil infiltration in the lungs after IR injury.

International Society for Heart and Lung Transplantation consensus statement for the standardization of bronchoalveolar lavage in lung transplantation.

Bronchoalveolar lavage (BAL) is a key clinical and research tool in lung transplantation (LTx). However, BAL collection and processing are not standardized across LTx centers. This International Society for Heart and Lung Transplantation-supported consensus document on BAL standardization aims to clarify definitions and propose common approaches to improve clinical and research practice standards. The following 9 areas are covered: (1) bronchoscopy procedure and BAL collection, (2) sample handling, (3) sample processing for microbiology, (4) cytology, (5) research, (6) microbiome, (7) sample inventory/tracking, (8) donor bronchoscopy, and (9) pediatric considerations. This consensus document aims to harmonize clinical and research practices for BAL collection and processing in LTx. The overarching goal is to enhance standardization and multicenter collaboration within the international LTx community and enable improvement and development of new BAL-based diagnostics.

Successful bridge to lung transplantation with transcatheter aortic valve replacement.

End-stage lung disease and advanced cardiac conditions are frequently seen together and represent a clinical dilemma. Even though both issues may be amenable to surgical management, combining lung transplant with surgical valve repair is rarely done and theoretically associated with increased morbidity and mortality risks, especially in elderly patients. Here, we describe 2 patients presenting with end-stage lung disease and significant aortic stenosis who were successfully bridged to lung transplant via transcatheter aortic valve replacement. Patient 1 was a 66-year-old man who underwent a double lung transplant 56 days after transcatheter aortic valve replacement. Patient 2 was a 70-year-old man who underwent a single right lung transplant 103 days after transcatheter aortic valve replacement. Both patients had uneventful postoperative courses and are alive at the 1-year time point with excellent performance status. This report suggests that transcatheter aortic valve replacement may favorably impact lung transplant candidacy for patients with end-stage lung disease in the setting of severe aortic stenosis, likely representing a better alternative to concomitant aortic valve replacement and lung transplant in elderly patients.

Lung IFNAR1hi TNFR2+ cDC2 promotes lung regulatory T cells induction and maintains lung mucosal tolerance at steady state.

The lung is a naturally tolerogenic organ. Lung regulatory T cells (T-regs) control lung mucosal tolerance. Here, we identified a lung IFNAR1hiTNFR2+ conventional DC2 (iR2D2) population that induces T-regs in the lung at steady state. Using conditional knockout mice, adoptive cell transfer, receptor blocking antibodies, and TNFR2 agonist, we showed that iR2D2 is a lung microenvironment-adapted dendritic cell population whose residence depends on the constitutive TNFR2 signaling. IFNß-IFNAR1 signaling in iR2D2 is necessary and sufficient for T-regs induction in the lung. The Epcam+CD45- epithelial cells are the sole lung IFNß producer at the steady state. Surprisingly, iR2D2 is plastic. In a house dust mite model of asthma, iR2D2 generates lung TH2 responses. Last, healthy human lungs have a phenotypically similar tolerogenic iR2D2 population, which became pathogenic in lung disease patients. Our findings elucidate lung epithelial cells IFNß-iR2D2-T-regs axis in controlling lung mucosal tolerance and provide new strategies for therapeutic interventions.

Alpha-1 Antitrypsin Attenuates Acute Lung Allograft Injury in a Rat Lung Transplant Model.

Ischemia-reperfusion injury (IRI) after lung transplantation triggers a cascade of inflammatory changes that can contribute to acute allograft injury. This influences both the short- and long-term survival of the lung allograft. Alpha-1 antitrypsin (AAT) is a protease inhibitor with known anti-inflammatory and immune-regulatory properties that mitigate tissue damage. This study explores the protective effects of AAT in the setting of IRI utilizing a rat lung transplant model. METHODS: Orthotopic left single lung transplantation was performed from Lewis to Sprague-Dawley rats; recipients did not receive systemic immunosuppression. Before transplantation, the donor lungs were primed with either albumin (control) or AAT. Starting the day of transplantation, recipient rats also received either albumin (control) or AAT with subsequent doses administered over the next 7 days. On the eighth postoperative day, lung allografts were recovered and analyzed. RESULTS: Degree of inflammatory infiltrate, as quantified by the allograft weight (g)/body weight (kg) ratio, was significantly reduced in the AAT-treated group compared with controls (3.5 vs 7.7, respectively, P < 0.05). Treatment with AAT also significantly decreased allograft necrosis in treated animals, as measured by a semiquantitative score that ranged from 0 to 4 (1.25 vs 4, P < 0.05). In addition, lymphocytes isolated from recipients treatment group showed significant proliferative inhibition via a mixed lymphocyte response assay in response to donor antigens. CONCLUSIONS: AAT attenuates acute allograft injury and necrosis in a rat model of lung transplantation, suggesting that AAT may play a role in reducing IRI-induced inflammation.

Initial skin cancer screening for solid organ transplant recipients in the United States: Delphi method development of expert consensus guidelines.

Skin cancer is the most common malignancy affecting solid organ transplant recipients (SOTR), and SOTR experience increased skin cancer-associated morbidity and mortality. There are no formal multidisciplinary guidelines for skin cancer screening after transplant, and current practices are widely variable. We conducted three rounds of Delphi method surveys with a panel of 84 U.S. dermatologists and transplant physicians to establish skin cancer screening recommendations for SOTR. The transplant team should risk stratify SOTR for screening, and dermatologists should perform skin cancer screening by full-body skin examination. SOTR with a history of skin cancer should continue regular follow-up with dermatology for skin cancer surveillance. High-risk transplant patients include thoracic organ recipients, SOTR age 50 and above, and male SOTR. High-risk Caucasian patients should be screened within 2 years after transplant, all Caucasian, Asian, Hispanic, and high-risk African American patients should be screened within 5 years after transplant. No consensus was reached regarding screening for low-risk African American SOTR. We propose a standardized approach to skin cancer screening in SOTR based on multidisciplinary expert consensus. These guidelines prioritize and emphasize the need for screening for SOTR at greatest risk for skin cancer.

Collagen type-V is a danger signal associated with primary graft dysfunction in lung transplantation.

BACKGROUND: Primary graft dysfunction (PGD) is the leading cause of early mortality after lung transplantation. Anti-collagen type-V (col(V)) immunity has been observed in animal models of ischemia-reperfusion injury (IRI) and in PGD. We hypothesized that collagen type-V is an innate danger signal contributing to PGD pathogenesis. METHODS: Anti-col(V) antibody production was detected by flow cytometric assay following cultures of murine CD19+ splenic cells with col.(V). Responding murine B cells were phenotyped using surface markers. RNA-Seq analysis was performed on murine CD19+ cells. Levels of anti-col(V) antibodies were measured in 188 recipients from the Lung Transplant Outcomes Group (LTOG) after transplantation. RESULTS: Col(V) induced rapid production of anti-col(V) antibodies from murine CD19+ B cells. Subtype analysis demonstrated innate B-1 B cells bound col.(V). Col(V) induced a specific transcriptional signature in CD19+ B cells with similarities to, yet distinct from, B cell receptor (BCR) stimulation. Rapid de novo production of anti-col(V) Abs was associated with an increased incidence of clinical PGD after lung transplant. CONCLUSIONS: This study demonstrated that col.(V) is an rapidly recognized by B cells and has specific transcriptional signature. In lung transplants recipients the rapid seroconversion to anti-col(V) Ab is linked to increased risk of grade 3 PGD.

The Impact of Donor and Recipient Age: Older Lung Transplant Recipients Do Not Require Younger Lungs.

BACKGROUND: Lung transplantation for patients with end-stage lung disease continues to grow worldwide. Increasing demand for this therapy generates significant waitlist mortality, indicating that alternative sources of donor lungs, such as older donors, are needed. The effect of the donor-recipient age relationship on outcomes remains unclear. METHODS: A retrospective review of the United Network for Organ Sharing Standard Transplant Analysis and Research database was performed for adult lung recipients from 2005 to 2015. Variables examined included donor age, recipient age, listing diagnosis, episodes of acute cellular rejection in the first year, and survival. Both donors and recipients were stratified according to age ranges. Survival was compared with the log-rank test. Propensity score matching was done stratifying donors younger than 60 years versus older than 60 years for the recipient population of 60 to 69 years. RESULTS: From May 2005 to February 2015, 15,844 patients underwent lung transplantation. Unadjusted comparisons of donor-to-recipient age showed that older donor age appeared to be more relevant for recipients 60 to 69 years old (p = 0.002). Nevertheless, when propensity matching was done based on relevant covariates for recipients in this age range by donors younger or older than 60 years, there were no differences in survival. CONCLUSIONS: Our results suggest that even though donor and recipient age may be important in lung transplantation, the interplay between donor and recipient age alone is not an independent determinant of survival. Careful selection of lungs from donors older than 60 years old should be exercised, taking into consideration the totality of donor demographics and risk factors rather than dismissing lungs based on advanced age alone.

Correction: Type V Collagen Induced Tolerance Suppresses Collagen Deposition, TGF-ß and Associated Transcripts in Pulmonary Fibrosis.

[This corrects the article DOI: 10.1371/journal.pone.0076451.].