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 cellpenia, restore T-regs, and prevent SAVI (N153S) inflammatory disease in mice.

The significance of STING (encoded by the TMEM173 gene), in tissue inflammation and cancer immunotherapy has been increasingly recognized. Intriguingly, common human STING alleles R71H-G230A-R293Q (HAQ) and G230A-R293Q (AQ) are carried by ~60% of East Asians and ~40% of Africans, respectively. Here, we examine the modulatory effects of HAQ, AQ alleles on STING-associated vasculopathy with onset in infancy (SAVI), an autosomal dominant, fatal inflammatory disease caused by gain-of-function human STING mutations. CD4 T cellpenia is evident in SAVI patients and mouse models. Using STING knock-in mice expressing common human STING alleles HAQ, AQ, and Q293, we found that HAQ, AQ, and Q293 splenocytes resist STING-mediated cell death ex vivo, establishing a critical role of STING residue 293 in cell death. The HAQ/SAVI(N153S) and AQ/SAVI(N153S) mice did not have CD4 T cellpenia. The HAQ/SAVI(N153S), AQ/SAVI(N153S) mice have more (~10-fold, ~20-fold, respectively) T-regs than WT/SAVI(N153S) mice. Remarkably, while they have comparable TBK1, IRF3, and NFκB activation as the WT/SAVI, the AQ/SAVI mice have no tissue inflammation, regular body weight, and normal lifespan. 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.

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.

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.

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.

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.

A 42-Year-Old Woman With Anemia, Shock, and Ischemic Stroke After Lung Transplantation.

CASE PRESENTAION: A 42-year-old woman with mixed connective tissue disease-associated interstitial lung disease underwent bilateral lung transplantation. She had an uneventful surgery and was extubated 3 h later. Induction immunosuppression therapy included methylprednisolone 500 mg intraoperatively, basiliximab (anti-IL-2 monoclonal antibody) on days 0 and 4 after transplantation, and methylprednisolone 125 mg intravenously bid for 2 days following surgery. Maintenance immunosuppression therapy consisted of prednisone 20 mg daily, mycophenolate mofetil 750 mg bid, and enteral tacrolimus 0.5 mg bid. Both the donor and the recipient were seropositive for cytomegalovirus. Infectious disease prophylaxis consisted of valganciclovir, trimethoprim-sulfamethoxazole, and voriconazole.

A 48-Year-Old Man With Leukopenia, Jaundice, and Skin Rash After Lung Transplantation.

A 48-year-old African-American male subject presented with progressive fatigue, jaundice, and new-onset leukopenia 12 weeks after undergoing bilateral lung transplantation for advanced pulmonary sarcoidosis. His transplant surgery and immediate posttransplantation course were uneventful. Induction immunosuppression included methylprednisolone 500 mg intraoperatively and basiliximab (anti-IL-2 monoclonal antibody) on days 0 and 4 after transplantation. His maintenance immunosuppression posttransplantation was prednisone 20 mg daily, tacrolimus with target tacrolimus levels 10 to 15 ng/mL, and mycophenolate mofetil 750 mg twice daily. Both the donor and recipient were seropositive for cytomegalovirus and Epstein-Barr virus. Infectious disease prophylaxis consisted of valganciclovir, trimethoprim/sulfamethoxazole, and voriconazole. Results of the surveillance bronchoscopy conducted after the lung transplant were negative for acute cellular rejection or infection at 4 and 12 weeks' posttransplantation. Findings on spirometry had continuously improved since transplantation.

Humoral immunity and the development of obliterative bronchiolitis after lung transplantation: is there a link?

Lung transplantation is considered the definitive treatment for many end-stage lung diseases. However, the lung is rejected more commonly than other solid organ allografts. Obliterative bronchiolitis (OB) is the leading cause of chronic allograft dysfunction, and the key reason why the 5-year survival of lung transplant recipients is only 50%. The pathophysiology of OB is incompletely understood. Although a clear role for the immune response to donor antigens has been observed (also known as anti-human leukocyte antigens), evidence is emerging about the role of autoimmunity to self-antigens. This review highlights the current understanding of humoral immunity in the development of OB after lung transplantation.

Cross-reactivity in the Platelia™ Aspergillus enzyme immunoassay caused by blastomycosis.

It is well known that cross reactions with other fungal pathogens including Histoplasma capsulatum can occur with the use of the Platelia™ Aspergillus galactomannan assay. We report two patients with confirmed blastomycosis whose bronchoalveolar lavage (BAL) fluid tested positive for Aspergillus galactomannan despite no evidence of aspergillosis.