Triggering receptor expressed on myeloid cells 1 (TREM-1) has been shown to amplify inflammatory signals, such as Toll-like receptor signaling, after infection and sterile injury. While previous studies have demonstrated that TREM-1 activation in circulating immune cells promotes injury, the role of TREM-1 signaling in tissue-resident cells in the context of sterile inflammation remains poorly understood. Here, we used a cardiac transplantation model to dissect how Trem1/3 expression on heart-resident cells regulates sterile inflammation. TREM-1 is expressed in heart-resident C-C chemokine receptor 2 (CCR2)+ macrophages in mice and humans. TREM-1/3 signaling in tissue-resident CCR2+ macrophages promotes C-C motif chemokine ligand 3 (CCL3) production and is critical for recruiting neutrophils and CCR2+ monocytes after heart transplantation. We demonstrate prolonged allograft survival after transplantation of Trem1/3-deficient compared with wild-type hearts. We identify TREM-1/3 signaling in donor grafts as a potential future therapeutic target to blunt inflammation after myocardial ischemia-reperfusion injury.

The presence of bronchus-associated lymphoid tissue (BALT) in donor lungs has been suggested to accelerate graft rejection after lung transplantation. Although chronic smoke exposure can induce BALT formation, the impact of donor cigarette use on alloimmune responses after lung transplantation is not well understood. Here, we show that smoking-induced BALT in mouse donor lungs contains Foxp3+ T cells and undergoes dynamic restructuring after transplantation, including recruitment of recipient-derived leukocytes to areas of pre-existing lymphoid follicles and replacement of graft-resident donor cells. Our findings from mouse and human lung transplant data support the notion that a donor's smoking history does not predispose to acute cellular rejection or prevent the establishment of allograft acceptance with comparable outcomes to nonsmoking donors. Thus, our work indicates that BALT in donor lungs is plastic in nature and may have important implications for modulating proinflammatory or tolerogenic immune responses following transplantation.

The term "chronic lung allograft dysfunction" has emerged to describe the clinical syndrome of progressive, largely irreversible dysfunction of pulmonary allografts. This umbrella term comprises 2 major clinical phenotypes: bronchiolitis obliterans syndrome and restrictive allograft syndrome. Here, we discuss the clinical manifestations, diagnostic challenges, and potential therapeutic avenues to address this major barrier to improved long-term outcomes. In addition, we review the immunologic mechanisms thought to propagate each phenotype of chronic lung allograft dysfunction, discuss the various models used to study this process, describe potential therapeutic targets, and identify key unknowns that must be evaluated by future research strategies.

The human leukocyte antigen (HLA) complex has been implicated in key immune responses such as recognition of self versus nonself, susceptibility to autoimmune disease, drug hypersensitivity, and tolerance to organ transplantation. The peptide-HLA complex serves as the ligand for the antigen-specific T cell receptor (TCR) on T cells. The principal function of HLA molecules is to facilitate immune surveillance of the intracellular (class I) and extracellular (class II) environments by presenting antigens to T cells. Donor-specific antibodies (DSA) are antibodies against donor HLA molecules that are present in the recipient at any time before or after transplantation. The presence of preexisting DSA prior to lung transplantation, also known as allosensitization , is a major contributing factor to waitlist mortality. Anti-HLA antibodies play an important role in cardiac allograft injury.

Neutrophils are the primary cell type involved in lung ischemia-reperfusion injury (IRI), which remains a frequent and morbid complication after organ transplantation. Endogenous lipid mediators that become activated during acute inflammation-resolution have gained increasing recognition for their protective role(s) in promoting the restoration of homeostasis, but their influence on early immune responses following transplantation remains to be uncovered. Resolvin D1, 7S,8R,17S-trihydroxy-4Z,9E,11E,13Z,15E,19Z-docosahexaenoic acid (RvD1), is a potent stereoselective mediator that exhibits proresolving and anti-inflammatory actions in the setting of tissue injury. Here, using metabololipidomics, we demonstrate that endogenous proresolving mediators including RvD1 are increased in human and murine lung grafts immediately following transplantation. In mouse grafts, we observe lipid mediator class switching early after reperfusion. We use intravital two-photon microscopy to reveal that RvD1 treatment significantly limits early neutrophil infiltration and swarming, thereby ameliorating early graft dysfunction in transplanted syngeneic lungs subjected to severe IRI. Through integrated analysis of single-cell RNA sequencing data of donor and recipient immune cells from lung grafts, we identify transcriptomic changes induced by RvD1. These results support a role for RvD1 as a potent modality for preventing early neutrophil-mediated tissue damage after lung IRI that may be therapeutic in the clinics.

Tertiary lymphoid organs (TLOs) are collections of immune cells resembling secondary lymphoid organs (SLOs) that form in peripheral, non-lymphoid tissues in response to local chronic inflammation. While their formation mimics embryologic lymphoid organogenesis, TLOs form after birth at ectopic sites in response to local inflammation resulting in their ability to mount diverse immune responses. The structure of TLOs can vary from clusters of B and T lymphocytes to highly organized structures with B and T lymphocyte compartments, germinal centers, and lymphatic vessels (LVs) and high endothelial venules (HEVs), allowing them to generate robust immune responses at sites of tissue injury. Although our understanding of the formation and function of these structures has improved greatly over the last 30 years, their role as mediators of protective or pathologic immune responses in certain chronic inflammatory diseases remains enigmatic and may differ based on the local tissue microenvironment in which they form. In this review, we highlight the role of TLOs in the regulation of immune responses in chronic infection, chronic inflammatory and autoimmune diseases, cancer, and solid organ transplantation.

Pulmonary transplantation is generally avoided in the context of ABO incompatibility because of fear of preformed recipient antibodies binding foreign donor blood antigens, resulting in hyperacute or acute antibody-mediated rejection. Most documented cases of ABO-incompatible lung transplantation have thus far occurred in the setting of clerical errors with variable clinical outcomes. One widely publicized case of unintentional ABO-incompatible lung transplantation resulted in rapid development of severe rejection with graft dysfunction and ultimately death.1 Other unintentional cases have resulted in longer graft survival but required close monitoring of anti-ABO blood group antibody titers and utilization of aggressive postoperative immunosuppressive interventions including plasmapheresis, intravenous immunoglobulin, immunoadsorption, anti-CD20 antibody, and cyclophosphamide therapy.2-4 These recipient-centric desensitization strategies have since been utilized in 2 cases of intentional ABO-incompatible lung transplantation with acceptable short-term outcomes.5,6 Altogether, the rigorous immunosuppression required and the perilous clinical outcomes associated with intentional ABO-incompatible lung transplantation continue to limit its utility. In addition to rising rates of waitlist mortality due to shortage of available donor organs, ABO incompatibilities limited access to donor organs. This disparity has persisted despite numerous changes to organ allocation policies over the last 2 decades, resulting in a significantly higher risk of waitlist mortality for patients with blood type O.7 Because of the paucity of available donors in the current climate of drastic need and the unfortunate risks associated with ABO-incompatible lung transplantation, the development of donor-centric strategies to safely expand the pool of universal donor organs and eliminate blood type disparities in organ availability is paramount. In a recent issue of Science Translational Medicine, Wang et al8 reported remarkable findings demonstrating successful conversion of blood type A human donor lungs into universal donor type lungs by cleaving the A-antigen from graft endothelium using enzymatic ex vivo perfusion. The authors utilized 2 enzymes derived from the bacterium Flavonifractor plautii to cleave the N-acetyl-galactosamine residue (referred to as Azymes: FpGalNAc deacetylase and FpGalNase) from blood type A-antigen and convert it to H-antigen, effectively rendering treated tissues as blood type O. The authors first demonstrated that A-antigen could be effectively cleared from lung perfusate and excised human aortic tissue using even small doses of Azymes. Subsequently, blood type A1 human donor lungs deemed unsuitable for clinical transplantation were randomized to normothermic ex vivo lung perfusion (EVLP) using blood type O human plasma perfusate with or without the addition of Azymes. Remarkably, the authors found that within 1 h of Azyme treatment, A-antigen within the graft had been almost entirely depleted from the vascular endothelium and nearly 50% of the A-antigen had been cleaved from alveolar epithelium. Additionally, Azyme-treated lungs had significantly lower anti-A-antibody binding capacities and preserved lung physiology compared with untreated controls. This innovative approach holds substantial promise for re-engineering and personalizing donor organs for transplantation and may provide an elegant solution for mitigating the increased waitlist mortality for blood type O lung transplant candidates. Additionally, this approach proposes an exciting new niche for the utilization of EVLP technology in lung transplantation. Several open questions remain before it will be possible to translate these findings to clinical transplantation: Will similar findings be observed with ex vivo perfusion when whole blood is used instead of cell-free plasma? Will antibody-mediated rejection be triggered in vivo because of the presence of other molecular and cellular physiologic cues not reproducible in an ex vivo perfusion model? How long can the donor blood type remain camouflaged? As astutely pointed out by the authors, endogenous glycosyltransferases installing ABO blood antigens will remain present within the donor tissues and would likely regenerate the cleaved donor antigens within a matter of hours. Once the reemergence of these donor blood antigens occurs, could the recipient immune responses be altered to promote accommodation of the donor graft and induce a state of ABO tolerance? Even if hyperacute and antibody-mediated rejection are effectively prevented, how will this strategy affect longer-term outcomes such as graft function and development of chronic lung allograft dysfunction? Additionally, it remains unclear whether the incomplete depletion of donor blood antigens elsewhere in the donor graft, such as alveolar epithelium, may result in adverse outcomes. To this end, alternative routes of enzyme administration (such as nebulization) may be necessary to achieve complete donor blood antigen depletion. Incorporation of additional variables such as cellular perfusion and in vivo physiology remain pivotal to answering these questions and to further delineating the clinical relevance of this novel strategy. Indeed, evaluating antibody binding, lung physiology, and graft function after longer periods of perfusion with ABO-incompatible plasma and whole blood will be necessary. Additionally, utilization of transgenic mice that express human ABO blood antigens in transplant models may provide crucial insights regarding the re-expression kinetics of blood antigens following enzyme treatment and its associated long-term effects and posttransplant outcomes.9 Importantly, the development of donor-centric strategies to modify and personalize organs before transplantation could help provide other solutions to the worldwide donor organ shortage. For example, this technology could plausibly be expanded to allow cleavage of human leukocyte antigens, which remain a major barrier to transplantation for sensitized lung transplant candidates. One could also envision adding this approach to recent breakthroughs in transgenic modification of porcine organs to further advance the field of xenotransplantation.10 Undoubtedly, the possibility of using EVLP to clean the antigenic slate of excised donor lungs opens many exciting windows for expanding the pool of universal donor organs and beyond.

Ischemia reperfusion injury represents a common pathological condition that is triggered by the release of endogenous ligands. While neutrophils are known to play a critical role in its pathogenesis, the tissue-specific spatiotemporal regulation of ischemia-reperfusion injury is not understood. Here, using oxidative lipidomics and intravital imaging of transplanted mouse lungs that are subjected to severe ischemia reperfusion injury, we discovered that necroptosis, a nonapoptotic form of cell death, triggers the recruitment of neutrophils. During the initial stages of inflammation, neutrophils traffic predominantly to subpleural vessels, where their aggregation is directed by chemoattractants produced by nonclassical monocytes that are spatially restricted in this vascular compartment. Subsequent neutrophilic disruption of capillaries resulting in vascular leakage is associated with impaired graft function. We found that TLR4 signaling in vascular endothelial cells and downstream NADPH oxidase 4 expression mediate the arrest of neutrophils, a step upstream of their extravasation. Neutrophil extracellular traps formed in injured lungs and their disruption with DNase prevented vascular leakage and ameliorated primary graft dysfunction. Thus, we have uncovered mechanisms that regulate the initial recruitment of neutrophils to injured lungs, which result in selective damage to subpleural pulmonary vessels and primary graft dysfunction. Our findings could lead to the development of new therapeutics that protect lungs from ischemia reperfusion injury.

An increased focus on improving efficiency and decreasing costs has resulted in alternative models of donor management and organ recovery. The specialized donor care facility model provides highly efficient and cost-effective donor care at a free-standing facility, resulting in improved organ yield, shorter ischemic times, decreased travel, and fewer nighttime operations. Ex vivo lung perfusion (EVLP) improves utilization of extended criteria donor lungs, and centralized EVLP facilities have the potential to increase transplant volumes for smaller transplant programs in specified geographic regions. These alternative models are increasingly being used in the United States to improve waitlist mortality and combat the ongoing donor organ shortage.

BACKGROUND Donor hearts and lungs are more susceptible to the inflammatory physiologic changes that occur after brain death. Prior investigations have shown that protocolized management of potential organ donors can rehabilitate donor organs that are initially deemed unacceptable. In this review we discuss advances in donor management models with particular attention to the specialized donor care facility model. In addition we review specific strategies to optimize donor thoracic organs and improve organ yield in thoracic transplantation. METHODS We performed a literature review by searching the PubMed database for medical subject heading terms associated with organ donor management models. We also communicated with our local organ procurement organization to gather published and unpublished information first-hand. RESULTS The specialized donor care facility model has been shown to improve the efficiency of organ donor management and procurement while reducing costs and minimizing travel and its associated risks. Lung protective ventilation, recruitment of atelectatic lung, and hormone therapy (eg, glucocorticoids and triiodothyronine/thyroxine) are associated with improved lung utilization rates. Stroke volume-based resuscitation is associated with improved heart utilization rates, whereas studies evaluating hormone therapy (eg, glucocorticoids and triiodothyronine/thyroxine) have shown variable results. CONCLUSIONS Lack of high-quality prospective evidence results in conflicting practices across organ procurement organizations, and best practices remain controversial. Future studies should focus on prospective, randomized investigations to evaluate donor management strategies. The specialized donor care facility model fosters a collaborative environment that encourages academic inquiry and is an ideal setting for these investigations. (C) 2022 by The Society of Thoracic Surgeons

Drug overdoses have tripled in the United States over the last two decades. With the increasing demand for donor organs, one potential consequence of the opioid epidemic may be an increase in suitable donor organs. Unfortunately, organs from donors dying of drug overdose have poorer utilization rates than other groups of brain-dead donors, largely due to physician and recipient concerns about viral disease transmission. During the study period of 2011 to 2016, drug overdose donors (DODs) account for an increasingly greater proportion of the national donor pool. We show that a novel model of donor care, known as specialized donor care facility (SDCF), is associated with an increase in organ utilization from DODs compared to the conventional model of hospital-based donor care. This is likely related to the close relationship of the SDCF with the transplant centers, leading to improved communication and highly efficient donor care.

Purpose of review The aim of this study was to provide a critical appraisal of the literature on the effects of the COVID-19 pandemic on organ transplantation, with a specific focus on lung transplantation given the predominant pulmonary involvement of the virus. Recent findings There was a significant decrease in lung transplant volumes during the first wave of the COVID-19 pandemic due to a combination of reduced availability of donors and an imbalance between waitlist additions and inactivations. SARS-CoV-2 infection was subsequently associated with an exuberant immune response that can lead to the development of postinfectious fibrotic lung disease. Few lung transplants have been performed in previously infected recipients and long-term outcomes remain unknown. Although the lung transplant volume rebounded during the second wave, it is unclear what the long-term effects of healthcare resource limitation and public health measures will have on transplant volumes in the future. Outcomes after SARS-CoV-2 infection in previous lung transplant recipients appear to be worse than the general public, and, although an immunosuppressed state likely contributes to these outcomes, whether immunosuppression should be altered in those exposed to or infected with SARS-CoV-2 remains unanswered in the absence of unequivocal data. Summary The COVID-19 pandemic has presented a number of challenges for lung transplant programs across the globe. Multiple research questions remain to be answered in order to optimally manage lung transplant recipients in the context of this pandemic.

Tertiary lymphoid organs are aggregates of immune and stromal cells including high endothelial venules and lymphatic vessels that resemble secondary lymphoid organs and can be induced at nonlymphoid sites during inflammation. The function of lymphatic vessels within tertiary lymphoid organs remains poorly understood. During lung transplant tolerance, Foxp3+ cells accumulate in tertiary lymphoid organs that are induced within the pulmonary grafts and are critical for the local downregulation of alloimmune responses. Here, we showed that tolerant lung allografts could induce and maintain tolerance of heterotopic donor-matched hearts through pathways that were dependent on the continued presence of the transplanted lung. Using lung retransplantation, we showed that Foxp3+ cells egressed from tolerant lung allografts via lymphatics and were recruited into donor-matched heart allografts. Indeed, survival of the heart allografts was dependent on lymphatic drainage from the tolerant lung allograft to the periphery. Thus, our work indicates that cellular trafficking from tertiary lymphoid organs regulates immune responses in the periphery. We propose that these findings have important implications for a variety of disease processes that are associated with the induction of tertiary lymphoid organs.

The life-saving benefits of organ transplantation can be thwarted by allograft dysfunction due to both infectious and sterile inflammation post-surgery. Sterile inflammation can occur after necrotic cell death due to the release of endogenous ligands [such as damage-associated molecular patterns (DAMPs) and alarmins], which perpetuate inflammation and ongoing cellular injury via various signaling cascades. Ischemia-reperfusion injury (IRI) is a significant contributor to sterile inflammation after organ transplantation and is associated with detrimental short- and long-term outcomes. While the vicious cycle of sterile inflammation and cellular injury is remarkably consistent amongst different organs and even species, we have begun understanding its mechanistic basis only over the last few decades. This understanding has resulted in the developments of novel, yet non-specific therapies for mitigating IRI-induced graft damage, albeit with moderate results. Thus, further understanding of the mechanisms underlying sterile inflammation after transplantation is critical for identifying personalized therapies to prevent or interrupt this vicious cycle and mitigating allograft dysfunction. In this review, we identify common and distinct pathways of post-transplant sterile inflammation across both heart and lung transplantation that can potentially be targeted.

Purpose This study aimed to classify and grade airway complications after lung transplant and to evaluate the risk of airway complications associated with antifibrotic use at a single lung transplant center. Methods All cases of lung transplantation at Barnes-Jewish Hospital between 1/1/2015 and 5/31/2018 were reviewed. Airway complications were graded using the 2018 ISHLT Consensus Statement on Adult Anastomotic Airway Complications. Antifibrotic use within 2 weeks of transplant was evaluated for association with airway complications by logistic regression. Results Based on the ISHLT Consensus definition, 159/261 patients (60.9%) had an airway complication; among these, only 20 (7.6%) were considered severe. There was no association between diagnosis for transplant and the development of an airway complication. AF use was associated with severe ischemic airway complication; among 58 who were on an AF agent pre-transplant, 8 (13.8%) developed an airway complication after transplant (odds ratio [OR] 2.547; 95% confidence interval [CI], 0.988 to 6.567; p = 0.053). This association was significant for nintedanib (OR 3.767; 95% CI, 1.119 to 12.681; p = 0.032) but not pirfenidone (OR 1.471; 95% CI, 0.465 to 4.660; p = 0.511). AF use was also associated with development of anastomotic stenosis; 14/58 (24.1%) developed anastomotic stenosis (OR 2.074; 95% CI, 1.004 to 4.283; p = 0.049). This association was not significant for nintedanib (OR 2.044; 95% CI, 0.693 to 6.022; p = 0.195) or pirfenidone (OR 1.781; 95% CI, 0.774 to 4.100; p = 0.175). AF use was not associated with anastomotic dehiscence; 8/58 (13.8%) developed a dehiscence (OR 1.139; 95% CI, 0.484 to 2.681; p = 0.765). Conclusion The grading system proposed by the 2018 ISHLT Consensus Statement led to identification of airway complication in >60% of lung transplants in this cohort, but most were considered mild and did not require intervention. Antifibrotic use was associated with increased risk of severe ischemic airway complications and anastomotic stenosis. This study aimed to classify and grade airway complications after lung transplant and to evaluate the risk of airway complications associated with antifibrotic use at a single lung transplant center. All cases of lung transplantation at Barnes-Jewish Hospital between 1/1/2015 and 5/31/2018 were reviewed. Airway complications were graded using the 2018 ISHLT Consensus Statement on Adult Anastomotic Airway Complications. Antifibrotic use within 2 weeks of transplant was evaluated for association with airway complications by logistic regression. Based on the ISHLT Consensus definition, 159/261 patients (60.9%) had an airway complication; among these, only 20 (7.6%) were considered severe. There was no association between diagnosis for transplant and the development of an airway complication. AF use was associated with severe ischemic airway complication; among 58 who were on an AF agent pre-transplant, 8 (13.8%) developed an airway complication after transplant (odds ratio [OR] 2.547; 95% confidence interval [CI], 0.988 to 6.567; p = 0.053). This association was significant for nintedanib (OR 3.767; 95% CI, 1.119 to 12.681; p = 0.032) but not pirfenidone (OR 1.471; 95% CI, 0.465 to 4.660; p = 0.511). AF use was also associated with development of anastomotic stenosis; 14/58 (24.1%) developed anastomotic stenosis (OR 2.074; 95% CI, 1.004 to 4.283; p = 0.049). This association was not significant for nintedanib (OR 2.044; 95% CI, 0.693 to 6.022; p = 0.195) or pirfenidone (OR 1.781; 95% CI, 0.774 to 4.100; p = 0.175). AF use was not associated with anastomotic dehiscence; 8/58 (13.8%) developed a dehiscence (OR 1.139; 95% CI, 0.484 to 2.681; p = 0.765). The grading system proposed by the 2018 ISHLT Consensus Statement led to identification of airway complication in >60% of lung transplants in this cohort, but most were considered mild and did not require intervention. Antifibrotic use was associated with increased risk of severe ischemic airway complications and anastomotic stenosis.

Background: Little evidence exists for de-escalation of nosocomial pneumonia therapy without positive cultures. Objective: The purpose of this study was to identify potential predictors of treatment failure following de-escalation to a fluoroquinolone in culture-negative nosocomial pneumonia. Methods: The study involved a single-center, retrospective cohort of patients admitted with diagnosis of nosocomial pneumonia and positive chest radiography who received at least 24 hours of fluoroquinolone monotherapy following at least 24 hours of appropriate empirical antibiotics. Treatment failure was defined using a composite of all-cause death within 30 days of discharge, treatment re-escalation, or readmission for pneumonia within 30 days of discharge. The Cox proportional hazards model was used to analyze predictors of treatment failure. Duration of empirical antibiotics and significant univariable exploratory predictors were included in multivariable analysis. Results: Of 164 patients, 23 (14%) failed de-escalation. Duration of empirical antibiotics (68.5 ± 32.1 vs 65.8 ± 35 hours) was not associated with treatment failure in univariable (Hazard Ratio [HR] = 1.002 [95% CI = 0.991-1.013]) or multivariable analyses (HR = 1.003 [95% CI = 0.991-1.015]). Significant exploratory predictors on univariable analysis included active cancer, intensive care unit (ICU) admission at empirical initiation, APACHE II score, and steroid use ≥20-mg prednisone equivalent. ICU admission at empirical initiation (HR = 2.439 [95% CI = 1.048-5.676]) and steroid use ≥20-mg prednisone equivalent (HR = 2.946 [95% CI = 1.281-6.772]) were associated with treatment failure on multivariable analysis. Conclusion and Relevance: Duration of empirical antibiotics does not appear to influence failure of de-escalation to fluoroquinolone monotherapy in culture-negative nosocomial pneumonia.

BACKGROUND:A well-known complication of peripheral nerve block is peripheral nerve injury, whether from the needle or toxicity of the medication used. In this study, we sought to determine the extent of damage that results from intrafascicular injection of various commonly used local anesthetics (LAs). METHODS:Sixteen Lewis rats received an intrafascicular injection of saline (control) or 1 of 3 LAs (bupivacaine, lidocaine, or ropivacaine) into the sciatic nerve (n = 4). At a 2-week end point, the sciatic nerves were harvested for histomorphometric and electron microscopic analysis. RESULTS:Animals that received intrafascicular LA injections showed increased severity of injury as compared with control. In particular, there was a significant loss of large-diameter fibers as indicated by decreased counts (P < 0.01 for all LAs) and area (P < 0.01 for all LAs) of remaining fibers in severely injured versus noninjured areas of the nerve. There was a layering of severity of injury with most severely injured areas closest to and noninjured areas furthest from the injection site. Bupivacaine caused more damage to large fibers than the other 2 LAs. In all groups, fascicular transection injury from the needle was observed. Electron microscopy confirmed nerve injury. CONCLUSIONS:Frequently used LAs at traditional concentrations are toxic to and can injure the peripheral nerve. Any combination of motor and/or sensory sequelae may result due to the varying fascicular topography of a nerve.