BACKGROUND:This study explored the role of a tumor suppressor gene, liver kinase B1 (LKB1), a key metabolic regulator in inflammatory and cellular processes associated with lung transplantation. Acute cellular rejection (ACR) after lung transplantation poses a significant threat, escalating the risk for chronic lung allograft dysfunction. We identified LKB1 as a pivotal regulator in lung transplant pathology, particularly in ACR. METHODS:Using NanoSight, ExoView, and Western blot analysis, we characterized plasma-derived small extracellular vesicles (sEVs). Griess reactions were used to measure plasma nitrite/nitrate levels. To determine the role of LKB1 on inflammation, we genetically altered LKB1 in human alveolar basal epithelial cell line and human bronchial epithelial cell line (BEAS-2B) cells, and in vivo analysis, we treated C57BL/6 mice with lipopolysaccharide (LPS). RESULTS:LKB1 levels in sEVs were significantly downregulated in lung transplant recipients, correlating with increased inducible nitric oxide synthase (iNOS). Furthermore, sEVs-LKB1 levels recovered only in 50% of lung transplant recipients after anti-rejection therapy; LKB1 downregulation in ACR was linked to elevated nitrite/nitrate. LKB1 overexpression inhibited LPS-induced iNOS, whereas LKB1 knockdown amplified it. Furthermore, LKB1 deficiency exacerbated transforming growth factor-beta-induced iNOS and tumor necrosis factor-alpha, confirming its protective role against pro-fibrotic signaling. Finally, we demonstrated wild-type LKB1 containing sEVs (W-LKB1-sEVs) activate AMP-activated protein kinase in BEAS-2B cells, and reduced LPS-induced iNOS and tumor necrosis factor-alpha in BEAS-2B cells. This protective effect is largely blocked by the AMP-activated protein kinase inhibitor Compound C. CONCLUSIONS:The study demonstrates that LKB1 is a key suppressor of inflammation, and its downregulation in sEVs during ACR can serve not only as a biomarker but also offers new therapeutic targets.

The coronavirus disease 2019 (COVID-19) global pandemic is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, our understanding of SARS-CoV-2-induced inflammation in alveolar epithelial cells remains very limited. The contributions of intracellular insulin-like growth factor binding protein-2 (IGFBP2) to SARS-CoV-2 pathogenesis are also unclear. In this study, we have uncovered a critical role for IGFBP2, specifically in alveolar epithelial type 2 cells (AEC2), in the immunopathogenesis of COVID-19. Using bulk RNA sequencing, we show that IGFBP2 mRNA expression is significantly downregulated in primary AEC2 cells isolated from fibrotic lung regions from patients with COVID-19-acute respiratory distress syndrome (ARDS) compared to those with idiopathic pulmonary fibrosis (IPF) alone or IPF with a history of COVID-19. Using multicolor immunohistochemistry, we demonstrated that IGFBP2 and its selective ligands IGF1 and IGF2 were significantly reduced in AEC2 cells from patients with COVID-ARDS, IPF alone, or IPF with COVID history than in those from age-matched donor controls. Further, we demonstrated that lentiviral expression of Igfbp2 significantly reduced mRNA expression of proinflammatory cytokines—Tnf-α, Il1β, Il6, Stat3, Stat6 and chemokine receptors—Ccr2 and Ccr5—in mouse lung epithelial cells challenged with SARS-CoV-2 spike protein injury (S2; 500 ng/mL). Finally, we demonstrated higher levels of cytokines—TNF-α; IL-6 and chemokine receptor—CCR5 in AEC2 cells from COVID-ARDS patients compared to the IPF alone and the IPF with COVID history patients. Altogether, these data suggest that anti-inflammatory properties of IGFBP2 in AEC2 cells and its localized delivery may serve as potential therapeutic strategy for patients with COVID-19. Graphical Abstract

Background Primary Graft Dysfunction (PGD) is an early post-lung transplant (LTx) inflammatory condition primarily driven by lung ischemia-reperfusion injury (LIRI). Neutrophils are key mediators of LIRI, but their phenotypic diversity and maturation state remain poorly characterized. In other inflammatory settings, early expansion of immature neutrophils has been linked to increased tissue injury and worse clinical outcomes. Whether immature neutrophils increase following LTx and contribute to PGD severity remains unclear. Methods Circulating neutrophil heterogeneity was analyzed by flow cytometry in 20 LTx candidates with advanced lung disease and 30 LTx recipients. Matched plasma samples were used for cytokine profiling. The role of immature neutrophils in LIRI was studied using a murine left pulmonary hilar clamp model with or without anti-G-CSF treatment. The differentiation and effector functions of immature neutrophils derived from murine hematopoietic progenitors were studied in vitro. Results LTx recipients exhibited an early rise in circulating immature neutrophils, correlated with higher G-CSF levels and PGD severity. In mice, LIRI was linked to increased G-CSF levels, significant mobilization, and lung infiltration of immature neutrophils with an activated, ROS-producing phenotype. These cells showed prolonged survival, strong ROS activity, but impaired phagocytosis. Preoperative anti-G-CSF treatment decreased lung injury while reducing immature neutrophil mobilization and recruitment to the lung. Conclusions Our findings underscore the clinical significance of neutrophil heterogeneity in the early perioperative setting following LTx. Targeting the G-CSF-immature neutrophil axis may offer a novel strategy to improve early lung allograft outcomes.

BACKGROUND:Severe primary graft dysfunction (PGD) after lung transplantation (LTx) is a significant risk factor for the development of bronchiolitis obliterans syndrome (BOS). Recent data from our group demonstrated that small extracellular vesicles (sEVs) isolated from the plasma of LTx recipients with BOS have reduced levels of tumor suppressor gene liver kinase B1 ( LKB1 ) and promote epithelial-to-mesenchymal transition (EMT) and fibrosis. Here, we hypothesized that early inflammatory responses associated with severe PGD (PGD2/3) can downregulate LKB1 levels in sEVs, predisposing to the development of chronic lung allograft dysfunction (CLAD). METHODS:sEVs were isolated from the plasma of human participants by Exosome Isolation Kit followed by 0.20-µm filtration and characterized by NanoSight and immunoblotting analysis. Lung self-antigens (K alpha 1 tubulin, Collagen V), LKB1 , nuclear factor kappa B, and EMT markers in sEVs were compared by densitometry analysis between PGD2/3 and no-PGD participants. Neutrophil-derived factors and hypoxia/reperfusion effects on LKB1 levels and EMT were analyzed in vitro using quantitative real-time polymerase chain reaction and Western blotting. RESULTS:LKB1 was significantly downregulated in PGD2/3 sEVs compared with no-PGD sEVs. Within PGD2/3 participants, lower post-LTx LKB1 was associated with CLAD development. Hypoxia/reperfusion downregulates LKB1 and is associated with markers of EMT in vitro. Finally, lower LKB1 levels in PGD2/3 are associated with increased markers of EMT. CONCLUSIONS:Our results suggest that in post-LTx recipients with PGD2/3, downregulation of LKB1 protein levels in sEVs is associated with increased EMT markers and may result in the development of CLAD. Our results also suggest that ischemia/reperfusion injury during LTx may promote CLAD through the early downregulation of LKB1 .

The role of gastroesophageal reflux in progressive lung damage is increasingly recognized. We have proposed, based on our work with lung transplant recipients, a novel immune mechanism of pulmonary injury after aspiration of gastric contents, during which higher levels of normally sequestered lung self-antigens (SAgs) collagen V (Col-V) and K-alpha-1 tubulin (Kα1T) in circulating small extracellular vesicles (EVs) induce the production of self-antibodies (SAbs) anti-Col-V and anti-Kα1T. Thus, we aimed to determine whether levels of SAbs or SAgs increased in an animal model of aspiration-induced lung damage in a nontransplant setting. We created a murine model of repetitive lung aspiration using C57BL/6J mice. Mice were aspirated weekly with 1 mL/kg of hydrochloric acid (n = 9), human gastric contents (n = 9), or combined (1:1) fluid (n = 9) once, three, or six times (n = 3 in each subgroup; control group, n = 9). Blood samples were periodically obtained, and all animals were sacrificed at day 90 for pathological assessment. SAbs were measured using an enzyme-linked immunosorbent assay; SAgs and NF-κB contained in small EVs were assessed by western blot. Aspirated mice weighed significantly less than controls throughout the study and had histological evidence of pulmonary injury at day 90. Overall, aspirated mice developed higher concentrations of anti-Col-V at day 28 (53.9 ± 28.7 vs. 29.9 ± 4.5 ng/mL, p < 0.01), day 35 (42.6 ± 19.8 vs. 28.6 ± 7.2 ng/mL, p = 0.038), and day 90 (59.7 ± 27.7 vs. 34.1 ± 3.2 ng/mL, p = 0.014) than the control group. Circulating small EVs isolated from aspirated mice on day 90 contained higher levels of Col-V (0.7 ± 0.56 vs. 0.18 ± 0.6 m.o.d., p = 0.009) and NF-κB (0.42 ± 0.27 vs. 0.27 ± 0.09 m.o.d., p = 0.095) than those from controls. This experimental study supports the theory that gastroesophageal reflux leads to the development of lung damage and an increase of humoral markers that may serve as noninvasive biomarkers to detect asymptomatic lung injury among patients with gastroesophageal reflux disease.

The long-term function of transplanted organs, even under immunosuppression, is hindered by rejection, especially chronic rejection. Chronic rejection occurs more frequently after lung transplantation, termed chronic lung allograft dysfunction (CLAD), than after transplantation of other solid organs. Pulmonary infection is a known risk factor for CLAD, as transplanted lungs are constantly exposed to the external environment; however, the mechanisms by which respiratory infections lead to CLAD are poorly understood. The role of extracellular vesicles (EVs) in transplantation remains largely unknown. Current evidence suggests that EVs released from transplanted organs can serve as friend and foe. EVs carry not only major histocompatibility complex antigens but also tissue-restricted self-antigens and various transcription factors, costimulatory molecules, and microRNAs capable of regulating alloimmune responses. EVs play an important role in antigen presentation by direct, indirect, and semidirect pathways in which CD8 and CD4 cells can be activated. During viral infections, exosomes (small EVs <200 nm in diameter) can express viral antigens and regulate immune responses. Circulating exosomes may also be a viable biomarker for other diseases and rejection after organ transplantation. Bioengineering the surface of exosomes has been proposed as a tool for targeted delivery of drugs and personalized medicine. This review focuses on recent studies demonstrating the role of EVs with a focus on exosomes and their dual role (immune activation or tolerance induction) after organ transplantation, more specifically, lung transplantation.

Restrictive allograft syndrome (RAS) is an aggressive variant of CLAD characterized by progressive restrictive ventilatory decline and persistent pleuro-parenchymal changes that can be seen on chest CT. We identified four lung transplant recipients with a progressive restrictive ventilatory defect due to lymphocyte-predominant exudative pleural effusions, but no pleuro-parenchymal abnormalities typical of RAS. Using molecular analysis, we also found increased levels of previously described immune markers of RAS, including NFkB, 20S proteasome, lipocalin, TNFα, and TGFβ, within the circulating small extracellular vesicles of the remaining living lung transplant recipient. Despite the absence of lung parenchymal changes, these patients had a poor prognosis with rapid deterioration in allograft function and no response to pleural-based interventions such as thoracentesis, decortication, and pleurodesis. We hypothesize that these cases represent a distinct CLAD phenotype characterized by progressive restriction due to pleural inflammation, lymphocyte-predominant pleural effusion, resultant compressive atelectasis, and eventual respiratory failure in the absence of lung parenchymal involvement.

The aim of this study (CTOTC-09) was to assess the impact of “preformed” (at transplant) donor-specific anti-HLA antibody (DSA) and first year newly detected DSA (ndDSA) on allograft function at 3 years after pediatric heart transplantation (PHTx). We enrolled children listed at 9 North American centers. The primary end point was pulmonary capillary wedge pressure (PCWP) at 3 years posttransplant. Of 407 enrolled subjects, 370 achieved PHTx (mean age, 7.7 years; 57% male). Pre-PHTx sensitization status was nonsensitized (n = 163, 44%), sensitized/no DSA (n = 115, 31%), sensitized/DSA (n = 87, 24%), and insufficient DSA data (n = 5, 1%); 131 (35%) subjects developed ndDSA. Subjects with any DSA had comparable PCWP at 3 years to those with no DSA. There were also no significant differences overall between the 2 groups for other invasive hemodynamic measurements, systolic graft function by echocardiography, and serum brain natriuretic peptide concentration. However, in the multivariable analysis, persistent first-year DSA was a risk factor for 3-year abnormal graft function. Graft and patient survival did not differ between groups. In summary, overall, DSA status was not associated with worse allograft function or inferior patient and graft survival at 3 years, but persistent first-year DSA was a risk factor for late graft dysfunction.

Accumulation of senescent cells contributes to age-related diseases including idiopathic pulmonary fibrosis (IPF). Insulin-like growth factor binding proteins (IGFBPs) regulate many biological processes; however, the functional contributions of IGFBP2 in lung fibrosis remain largely unclear. Here, we report that intranasal delivery of recombinant IGFBP2 protects aged mice from weight loss and demonstrated antifibrotic effects after bleomycin lung injury. Notably, aged human-Igfbp2 transgenic mice reveal reduced senescence and senescent-associated secretory phenotype factors in alveolar epithelial type 2 (AEC2) cells and they ameliorated bleomycin-induced lung fibrosis. Finally, we demonstrate that IGFBP2 expression is significantly suppressed in AEC2 cells isolated from fibrotic lung regions of patients with IPF and/or pulmonary hypertension compared with patients with hypersensitivity pneumonitis and/or chronic obstructive pulmonary disease. Altogether, our study provides insights into how IGFBP2 regulates AEC2-cell-specific senescence and that restoring IGFBP2 levels in fibrotic lungs can prove effective for patients with IPF.

Humoral and cellular immune responses to SARS-CoV-2 and other coronaviruses in lung transplant recipients are unknown. We measured antibodies and T cell responses against the SARS-CoV-2 spike S2 and nucleocapsid antigens and spike antigens from common respiratory coronaviruses (229E, NL63, OC43, and HKU1) after vaccination or infection of LTxRs. 148 LTxRs from single center were included in this study: 98 after vaccination and 50 following SARS-CoV-2 infection. Antibodies were quantified by enzyme-linked immunosorbent assay. The frequency of T cells secreting IL2, IL4, IL10, IL17, TNFα, and IFNγ were enumerated by enzyme-linked immunospot assay. Our results have shown the development of antibodies to SARS-CoV-2 spike protein in infected LTxRs (39/50) and vaccinated LTxRs (52/98). Vaccinated LTxRs had higher number of T cells producing TNFα but less cells producing IFNγ than infected LTxRs in response to the nucleocapsid antigen and other coronavirus spike antigens. We didn't find correlation between the development of antibodies and cellular immune responses against the SARS-CoV-2 spike protein after vaccination. Instead, LTxRs have pre-existing cellular immunity to common respiratory coronaviruses, leading to cross-reactive immunity against SARS-CoV-2 which likely will provide protection against SARS-Cov-2 infection.

Objective: Aspiration of duodenogastric refluxate may damage the respiratory epithelium of lung allografts in transplant recipients. We sought to define a mech-anism by which aspiration of duodenogastric fluid augments the risk of bronchiolitis obliterans syndrome after lung transplant in a murine model.Methods: We analyzed the immunological effects of acute aspiration of duodeno-gastric fluid (0.5 mL/kg) on transplant naive (strain DBA/2J) and transplanted mice (strain B6D2F1/J to strain DBA/2J). Serum antibodies to the lung self-antigens (SAgs) K-alpha1 tubulin and collagen-V were determined by enzyme-linked immuno-sorbent assay. Exosomes were isolated from serum, and immunoblot membranes were probed for antibodies to lung SAgs. Lung sections were assessed for fibrotic burden and obliterative bronchiolitis lesions by histologic and immunohistochem-ical analyses, including trichrome staining.Results: Transplanted mice that received duodenogastric fluid developed higher levels of antibodies to the lung SAgs K-alpha1 tubulin and collagen-V and exosomes with lung SAgs on posttransplant days 14 and 28 than transplanted mice with sham aspiration or transplant naive mice (with and without aspiration). All lung allografts demonstrated severe grade A4 rejection on posttransplant day 14, with the highest mean fibrotic burden and mean number of obliterative bronchiolitis-like lesions per microscopic field on day 28 in recipients with aspiration. Conclusions: This study links aspiration of duodenogastric fluid after lung trans-plant to higher autoimmune responses to lung SAgs and the release of circu-lating exosomes with lung SAgs, which together promote sustained immune responses leading to extensive lung parenchymal damage and, ultimately, severe obliterative bronchiolitis-the histologic hallmark of bronchiolitis obliterans syndrome. (J Thorac Cardiovasc Surg 2023;1 65:e23-37)