In vivo detection of pulmonary mucociliary clearance: present challenges and future directions.

Pulmonary mucociliary clearance (MCC) is an important defence mechanism of the respiratory system and clears pathogens and foreign particles from the airways. Understanding the effect of disease states, drugs, toxins and airway manipulations on MCC could be beneficial in preventing early pulmonary disease and developing new pulmonary therapeutics. This review summarises the current methods and future efforts to detect pulmonary MCC in vivo.

ACPSEM position paper: recommendations for a digital general X-ray quality assurance program.

This guideline has been prepared by the ACPSEM to provide a standardised quality assurance program to be used within General X-ray imaging environments. The guideline includes the responsibilities of various multidisciplinary team members within medical imaging facilities. It must be noted that the listed tests and testing frequencies are not intended to replace or become regulatory requirements. Implementing a quality assurance program as outlined in this position paper is there to ensure best practice for imaging facilities by providing a framework to establish and monitor correct equipment performance. The current document has been produced through an extensive review of current international practices and local experience within the Australasian healthcare environment. Due to the constant evolution of digital radiographic equipment, there is no current consensus in international quality assurance guidelines as they continue to be adapted and updated. This document describes the current state of the use of digital General X-ray equipment in the Australasian environment and provides recommendations of test procedures that may be best suited for the current medical imaging climate in Australasia. Due to the everchanging developments in the medical imaging environment and the ability of new technologies to perform more complex tasks it is believed that in the future this document will be further reviewed in the hopes of producing a more globally agreed upon standard quality assurance program. Any such adjustments that are deemed to be necessary to Version 1.0 of this document will be provided in electronic format on the ACPSEM website with a notification to all parties involved in the use of digital General X-ray equipment. This guideline does not provide detailed methodologies for all the quality control tests recommended as it is it is expected that the professionals implementing aspects of this quality assurance program have the working knowledge and access to appropriate resources to develop testing methodologies appropriate for their local imaging environment.

Stem cells, cell therapies, and bioengineering in lung biology and diseases 2023.

Repair and regeneration of a diseased lung using stem cells or bioengineered tissues is an exciting therapeutic approach for a variety of lung diseases and critical illnesses. Over the past decade, increasing evidence from preclinical models suggests that mesenchymal stromal cells, which are not normally resident in the lung, can be used to modulate immune responses after injury, but there have been challenges in translating these promising findings to the clinic. In parallel, there has been a surge in bioengineering studies investigating the use of artificial and acellular lung matrices as scaffolds for three-dimensional lung or airway regeneration, with some recent attempts of transplantation in large animal models. The combination of these studies with those involving stem cells, induced pluripotent stem cell derivatives, and/or cell therapies is a promising and rapidly developing research area. These studies have been further paralleled by significant increases in our understanding of the molecular and cellular events by which endogenous lung stem and/or progenitor cells arise during lung development and participate in normal and pathological remodeling after lung injury. For the 2023 Stem Cells, Cell Therapies, and Bioengineering in Lung Biology and Diseases Conference, scientific symposia were chosen to reflect the most cutting-edge advances in these fields. Sessions focused on the integration of "omics" technologies with function, the influence of immune cells on regeneration, and the role of the extracellular matrix in regeneration. The necessity for basic science studies to enhance fundamental understanding of lung regeneration and to design innovative translational studies was reinforced throughout the conference.

Airway disease decreases the therapeutic potential of epithelial stem cells.

BACKGORUND: Tissue-engineered tracheal grafts (TETG) can be recellularized by the host or pre-seeded with host-derived cells. However, the impact of airway disease on the recellularization process is unknown. METHODS: In this study, we determined if airway disease alters the regenerative potential of the human tracheobronchial epithelium (hTBE) obtained by brushing the tracheal mucosa during clinically-indicated bronchoscopy from 48 pediatric and six adult patients. RESULTS: Our findings revealed that basal cell recovery and frequency did not vary by age or region. At passage 1, all samples produced enough cells to cellularize a 3.5 by 0.5 cm2 graft scaffold at low cell density (~ 7000 cells/cm2), and 43.75% could cellularize a scaffold at high cell density (~ 100,000 cells/cm2). At passage 2, all samples produced the number of cells required for both recellularization models. Further evaluation revealed that six pediatric samples (11%) and three (50%) adult samples contained basal cells with a squamous basal phenotype. These cells did not form a polarized epithelium or produce differentiated secretory or ciliated cells. In the pediatric population, the squamous basal cell phenotype was associated with degree of prematurity (< 28 weeks, 64% vs. 13%, p = 0.02), significant pulmonary history (83% vs. 34%, p = 0.02), specifically with bronchopulmonary dysplasia (67% vs. 19%, p = 0.01), and patients who underwent previous tracheostomy (67% vs. 23%, p = 0.03). CONCLUSIONS: In summary, screening high-risk pediatric or adult population based on clinical risk factors and laboratory findings could define appropriate candidates for airway reconstruction with tracheal scaffolds. LEVEL OF EVIDENCE: Level III Cohort study.

Partial decellularization eliminates immunogenicity in tracheal allografts.

There is currently no suitable autologous tissue to bridge large tracheal defects. As a result, no standard of care exists for long-segment tracheal reconstruction. Tissue engineering has the potential to create a scaffold from allografts or xenografts that can support neotissue regeneration identical to the native trachea. Recent advances in tissue engineering have led to the idea of partial decellularization that allows for the creation of tracheal scaffolds that supports tracheal epithelial formation while preserving mechanical properties. However, the ability of partial decellularization to eliminate graft immunogenicity remains unknown, and understanding the immunogenic properties of partially decellularized tracheal grafts (PDTG) is a critical step toward clinical translation. Here, we determined that tracheal allograft immunogenicity results in epithelial cell sloughing and replacement with dysplastic columnar epithelium and that partial decellularization creates grafts that are able to support an epithelium without histologic signs of rejection. Moreover, allograft implantation elicits CD8+ T-cell infiltration, a mediator of rejection, while PDTG did not. Hence, we establish that partial decellularization eliminates allograft immunogenicity while creating a scaffold for implantation that can support spatially appropriate airway regeneration.

Regeneration of tracheal neotissue in partially decellularized scaffolds.

Extensive tracheal injury or disease can be life-threatening but there is currently no standard of care. Regenerative medicine offers a potential solution to long-segment tracheal defects through the creation of scaffolds that support the generation of healthy neotissue. We developed decellularized tracheal grafts (PDTG) by removing the cells of the epithelium and lamina propria while preserving donor cartilage. We previously demonstrated that PDTG support regeneration of host-derived neotissue. Here, we use a combination of microsurgical, immunofluorescent, and transcriptomic approaches to compare PDTG neotissue with the native airway and surgical controls. We report that PDTG neotissue is composed of native tracheal cell types and that the neoepithelium and microvasculature persisted for at least 6 months. Vascular perfusion of PDTG was established within 2 weeks and the graft recruited multipotential airway stem cells that exhibit normal proliferation and differentiation. Hence, PDTG neotissue recapitulates the structure and function of the host trachea and has the potential to regenerate.

Biobanked tracheal basal cells retain the capacity to differentiate.

Objective: While airway epithelial biorepositories have established roles in the study of bronchial progenitor stem (basal) cells, the utility of a bank of tracheal basal cells from pediatric patients, who have or are suspected of having an airway disease, has not been established. In vitro study of these cells can enhance options for tracheal restoration, graft design, and disease modeling. Development of a functional epithelium in these settings is a key measure. The aim of this study was the creation a tracheal basal cell biorepository and assessment of recovered cells. Methods: Pediatric patients undergoing bronchoscopy were identified and endotracheal brush (N = 29) biopsies were collected. Cells were cultured using the modified conditional reprogramming culture (mCRC) method. Samples producing colonies by day 14 were passaged and cryopreserved. To explore differentiation potential, cells were thawed and differentiated using the air-liquid interface (ALI) method. Results: No adverse events were associated with biopsy collection. Of 29 brush biopsies, 16 (55%) were successfully cultured to passage 1/cryopreserved. Samples with higher initial cell yields were more likely to achieve this benchmark. Ten unique donors were then thawed for analysis of differentiation. The average age was 2.2 ± 2.2 years with five donors (50%) having laryngotracheal pathology. Nine donors (90%) demonstrated differentiation capacity at 21 days of culture, as indicated by detection of ciliated cells (ACT+) and mucous cells (MUC5B+). Conclusion: Pediatric tracheal basal cells can be successfully collected and cryopreserved. Recovered cells retain the ability to differentiate into epithelial cell types in vitro. Level of Evidence: Level 3.

Tissue-engineered composite tracheal grafts create mechanically stable and biocompatible airway replacements.

We tested composite tracheal grafts (CTG) composed of a partially decellularized tracheal graft (PDTG) combined with a 3-dimensional (3D)-printed airway splint for use in long-segment airway reconstruction. CTG is designed to recapitulate the 3D extracellular matrix of the trachea with stable mechanical properties imparted from the extraluminal airway splint. We performed segmental orthotopic tracheal replacement in a mouse microsurgical model. MicroCT was used to measure graft patency. Tracheal neotissue formation was quantified histologically. Airflow dynamic properties were analyzed using computational fluid dynamics. We found that CTG are easily implanted and did not result in vascular erosion, tracheal injury, or inflammation. Graft epithelialization and endothelialization were comparable with CTG to control. Tracheal collapse was absent with CTG. Composite tracheal scaffolds combine biocompatible synthetic support with PDTG, supporting the regeneration of host epithelium while maintaining graft structure.

Assemblies of JAG1 and JAG2 determine tracheobronchial cell fate in mucosecretory lung disease.

Mucosecretory lung disease compromises airway epithelial function and is characterized by goblet cell hyperplasia and ciliated cell hypoplasia. Goblet and ciliated cell types are derived from tracheobronchial stem/progenitor cells via a Notch-dependent mechanism. Although specific arrays of Notch receptors regulate cell fate determination, the function of the ligands Jagged1 (JAG1) and JAG2 is unclear. This study examined JAG1 and JAG2 function using human air-liquid-interface cultures that were treated with γ-secretase complex (GSC) inhibitors, neutralizing peptides/antibodies, or WNT/ß-catenin pathway antagonists/agonists. These experiments revealed that JAG1 and JAG2 regulated cell fate determination in the tracheobronchial epithelium; however, their roles did not adhere to simple necessity and sufficiency rules. Biochemical studies indicated that JAG1 and JAG2 underwent posttranslational modifications that resulted in generation of a JAG1 C-terminal peptide and regulated the abundance of full-length JAG2 on the cell surface. GSC and glycogen synthase kinase 3 were implicated in these posttranslational events, but WNT agonist/antagonist studies and RNA-Seq indicated a WNT-independent mechanism. Collectively, these data suggest that posttranslational modifications create distinct assemblies of JAG1 and JAG2, which regulate Notch signal strength and determine the fate of tracheobronchial stem/progenitor cells.

Assessment of Beta-2 Microglobulin Gene Edited Airway Epithelial Stem Cells as a treatment for Sulfur Mustard Inhalation.

Respiratory system damage is the primary cause of mortality in individuals who are exposed to vesicating agents including sulfur mustard (SM). Despite these devastating health complications, there are no fielded therapeutics that are specific for such injuries. Previous studies reported that SM inhalation depleted the tracheobronchial airway epithelial stem cell (TSC) pool and supported the hypothesis, TSC replacement will restore airway epithelial integrity and improve health outcomes for SM-exposed individuals. TSC express Major Histocompatibility Complex (MHC-I) transplantation antigens which increases the chance that allogeneic TSC will be rejected by the patient's immune system. However, previous studies reported that Beta-2 microglobulin (B2M) knockout cells lacked cell surface MHC-I and suggested that B2M knockout TSC would be tolerated as an allogeneic graft. This study used a Cas9 ribonucleoprotein (RNP) to generate B2M-knockout TSC, which are termed Universal Donor Stem Cells (UDSC). Whole genome sequencing identified few off-target modifications and demonstrated the specificity of the RNP approach. Functional assays demonstrated that UDSC retained their ability to self-renew and undergo multilineage differentiation. A preclinical model of SM inhalation was used to test UDSC efficacy and identify any treatment-associated adverse events. Adult male Sprague-Dawley rats were administered an inhaled dose of 0.8 mg/kg SM vapor which is the inhaled LD50 on day 28 post-challenge. On recovery day 2, vehicle or allogeneic Fisher rat UDSC were delivered intravenously (n = 30/group). Clinical parameters were recorded daily, and planned euthanasia occurred on post-challenge days 7, 14, and 28. The vehicle and UDSC treatment groups exhibited similar outcomes including survival and a lack of adverse events. These studies establish a baseline which can be used to further develop UDSC as a treatment for SM-induced airway disease.

Tracheal Macrophages During Regeneration and Repair of Long-Segment Airway Defects.

OBJECTIVES/HYPOTHESIS: Tissue-engineered tracheal grafts (TETGs) offer a potential solution for repair of long-segment airway defects. However, preclinical and clinical TETGs have been associated with chronic inflammation and macrophage infiltration. Macrophages express great phenotypic heterogeneity (generally characterized as classically activated [M1] vs. alternatively activated [M2]) and can influence tracheal repair and regeneration. We quantified and characterized infiltrating host macrophages using mouse microsurgical tracheal replacement models. STUDY DESIGN: Translational research, animal model. METHODS: We assessed macrophage infiltration and phenotype in animals implanted with syngeneic tracheal grafts, synthetic TETGs, or partially decellularized tracheal scaffolds (DTSs). RESULTS: Macrophage infiltration was observed following tracheal replacement with syngeneic trachea. Both M1 and M2 macrophages were present in native trachea and increased during early tracheal repair (P = .014), with an M1/M2 ratio of 0.48 ± 0.15. In contrast, orthotopic implantation of synthetic TETGs resulted in a shift to M1 predominant macrophage phenotype with an increased M1/M2 ratio of 1.35 ± 0.41 by 6 weeks following implant (P = .035). Modulation of the synthetic scaffold with the addition of polyglycolic acid (PGA) resulted in a reduction of M1/M2 ratio due to an increase in M2 macrophages (P = .006). Using systemic macrophage depletion, the M1/M2 ratio reverted to native values in synthetic TETG recipients and was associated with an increase in graft epithelialization. Macrophage ratios seen in DTSs were similar to native values. CONCLUSIONS: M1 and M2 macrophages are present during tracheal repair. Poor epithelialization with synthetic TETG is associated with an elevation of the M1/M2 ratio. Macrophage phenotype can be altered with scaffold composition and host-directed systemic therapies. DTSs exhibit M1/M2 ratios similar to those seen in native trachea and syngeneic tracheal replacement. LEVEL OF EVIDENCE: NA Laryngoscope, 132:737-746, 2022.

Repeated injury promotes tracheobronchial tissue stem cell attrition.

Chronic lung disease has been attributed to stem cell aging and/or exhaustion. We investigated these mechanisms using mouse and human tracheobronchial tissue-specific stem cells (TSC). In mouse, chromatin labeling and flow cytometry demonstrated that naphthalene (NA) injury activated a subset of TSC. These activated TSC continued to proliferate after the epithelium was repaired and a clone study demonstrated that ~96% of activated TSC underwent terminal differentiation. Despite TSC attrition, epithelial repair after a second NA injury was normal. The second injury accelerated proliferation of previously activated TSC and a nucleotide-label retention study indicated that the second injury recruited TSC that were quiescent during the first injury. These mouse studies indicate that (a) injury causes selective activation of the TSC pool; (b) activated TSC are predisposed to further proliferation; and (c) the activated state leads to terminal differentiation. In human TSC, repeated proliferation also led to terminal differentiation and depleted the TSC pool. A clone study identified long- and short-lived TSC and showed that short-lived TSC clones had significantly shorter telomeres than their long-lived counterparts. The TSC pool was significantly depleted in dyskeratosis congenita donors, who harbor mutations in telomere biology genes. The remaining TSC had short telomeres and short lifespans. Collectively, the mouse and human studies support a model in which epithelial injury increases the biological age of the responding TSC. When applied to chronic lung disease, this model suggests that repeated injury accelerates the biological aging process resulting in abnormal repair and disease initiation.

Modulation of Synthetic Tracheal Grafts with Extracellular Matrix Coatings.

Synthetic scaffolds for the repair of long-segment tracheal defects are hindered by insufficient biocompatibility and poor graft epithelialization. In this study, we determined if extracellular matrix (ECM) coatings improved the biocompatibility and epithelialization of synthetic tracheal grafts (syn-TG). Porcine and human ECM substrates (pECM and hECM) were created through the decellularization and lyophilization of lung tissue. Four concentrations of pECM and hECM coatings on syn-TG were characterized for their effects on scaffold morphologies and on in vitro cell viability and growth. Uncoated and ECM-coated syn-TG were subsequently evaluated in vivo through the orthotopic implantation of segmental grafts or patches. These studies demonstrated that ECM coatings were not cytotoxic and, enhanced the in vitro cell viability and growth on syn-TG in a dose-dependent manner. Mass spectrometry demonstrated that fibrillin, collagen, laminin, and nephronectin were the predominant ECM components transferred onto scaffolds. The in vivo results exhibited similar robust epithelialization of uncoated and coated syn-TG patches; however, the epithelialization remained poor with either uncoated or coated scaffolds in the segmental replacement models. Overall, these findings demonstrated that ECM coatings improve the seeded cell biocompatibility of synthetic scaffolds in vitro; however, they do not improve graft epithelialization in vivo.

Regeneration of partially decellularized tracheal scaffolds in a mouse model of orthotopic tracheal replacement.

Decellularized tracheal scaffolds offer a potential solution for the repair of long-segment tracheal defects. However, complete decellularization of trachea is complicated by tracheal collapse. We created a partially decellularized tracheal scaffold (DTS) and characterized regeneration in a mouse model of tracheal transplantation. All cell populations except chondrocytes were eliminated from DTS. DTS maintained graft integrity as well as its predominant extracellular matrix (ECM) proteins. We then assessed the performance of DTS in vivo. Grafts formed a functional epithelium by study endpoint (28 days). While initial chondrocyte viability was low, this was found to improve in vivo. We then used atomic force microscopy to quantify micromechanical properties of DTS, demonstrating that orthotopic implantation and graft regeneration lead to the restoration of native tracheal rigidity. We conclude that DTS preserves the cartilage ECM, supports neo-epithelialization, endothelialization and chondrocyte viability, and can serve as a potential solution for long-segment tracheal defects.

Spatial and Temporal Analysis of Host Cells in Tracheal Graft Implantation.

OBJECTIVES/HYPOTHESIS: The ideal trachea replacement would be a living graft that is genetically identical to the host, avoiding the need for immunosuppression. We have developed a mouse model of syngeneic tracheal transplant that results in long-term survival without graft stenosis or delayed healing. To understand how host cells contribute to tracheal transplant integration, we quantified the populations of host cells in the graft and native trachea following implant. STUDY DESIGN: Tracheal transplant, tracheal replacement, regenerative medicine, animal model. METHODS: Tracheal grafts were obtained from female C57BL/6 mice and orthotopically transplanted into syngeneic male recipients. Cohorts were euthanized on day 14, day 45, and day 90 post-transplantation. Host and graft tracheas were explanted and analyzed by histology. Male host cells were quantified using fluorescence in situ hybridization, and macrophages were quantified with immunofluorescence. RESULTS: Evidence of host-derived cells was found in the midgraft at the earliest time point (14 days). Host-derived cells transiently increased in the graft on day 45 and were predominantly found in the submucosa. By day 90, the population of host-derived cells population declined to a similar level on day 14. Macrophage infiltration of host and graft tissue was observed at all time points and was greatest on day 90. CONCLUSIONS: Tracheal graft integration occurs by way of subacute transient host-cell infiltration and is primarily inflammatory in nature. Host-cell contribution to the graft epithelium is limited. These data indicate that creation of living, nonimmunogenic tracheal graft could serve as a viable solution for long-segment tracheal defects. LEVEL OF EVIDENCE: 3 Laryngoscope, 131:E340-E345, 2021.

Airway epithelial stem cell chimerism in cystic fibrosis lung transplant recipients.

BACKGROUND: The conducting airway epithelium is repaired by tissue specific stem cells (TSC). In response to mild/moderate injury, each TSC repairs a discrete area of the epithelium. In contrast, severe epithelial injury stimulates TSC migration and expands the stem cell's reparative domain. Lung transplantation (LTx) can cause a moderate/severe airway injury and the remodeled airway contains a chimeric mixture of donor and recipient cells. These studies supported the hypothesis, LTx stimulates TSC migration resulting in epithelial chimerism. We tested this hypothesis in cystic fibrosis (CF) LTx patients. METHODS: Airway mucosal injury was quantified using bronchoscopic imaging and a novel grading system. Bronchial brushing was used to recover TSC from 10 sites in the recipient and allograft airways. TSC chimerism was quantified by short tandem repeat analysis. TSC self-renewal and differentiation potential were assayed using the clone forming cell frequency and air-liquid-interface methods. Electrophysiology was used to determine if TSC chimerism altered epithelial ion channel activity. RESULTS: LTx caused a mild to moderate airway mucosal injury. Donor and recipient TSC were identified in 91% of anastomotic sites and 93% of bronchial airways. TSC chimerism did not alter stem cell self-renewal or differentiation potential. The frequency of recipient TSC was proportional to CF Transmembrane Conductance Regulator (CFTR)-dependent ion channel activity and 33% of allograft regions were at risk for abnormal CFTR activity. CONCLUSIONS: LTx in CF patients stimulates bidirectional TSC migration across the anastomoses. TSC chimerism may alter ion homeostasis and compromise the host defense capability of the allograft airway epithelium.

Best practices for the development, analytical validation and clinical implementation of flow cytometric methods for chimeric antigen receptor T cell analyses.

Chimeric Antigen Receptor (CAR) T cells are recognized as efficacious therapies with demonstrated ability to produce durable responses in blood cancer patients. Regulatory approvals and acceptance of these unique therapies by patients and reimbursement agencies have led to a significant increase in the number of next generation CAR T clinical trials. Flow cytometry is a powerful tool for comprehensive profiling of individual CAR T cells at multiple stages of clinical development, from product characterization during manufacturing to longitudinal evaluation of the infused product in patients. There are unique challenges with regard to the development and validation of flow cytometric methods for CAR T cells; moreover, the assay requirements for manufacturing and clinical monitoring differ. Based on the collective experience of the authors, this recommendation paper aims to review these challenges and present approaches to address them. The discussion focuses on describing key considerations for the design, optimization, validation and implementation of flow cytometric methods during the clinical development of CAR T cell therapies.

Correction of Airway Stem Cells: Genome Editing Approaches for the Treatment of Cystic Fibrosis.

Cystic fibrosis (CF) is an autosomal recessive disease caused by variations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Although CF affects multiple organs, the primary cause of mortality is respiratory failure resulting from poor clearance of hyperviscous secretions and subsequent airway infection. Recently developed CFTR modulators provide significant therapeutic benefit to the majority of CF individuals. However, treatments directed at the underlying cause are needed for the ∼7% of CF patients who are not expected to be responsive to these modulators. Genome editing can restore the native CFTR genetic sequence and function to mutant cells, representing an approach to establish durable physiologic CFTR correction. Although editing the CFTR gene in various airway cell types may transiently restore CFTR activity, effort is focused on editing airway basal stem/progenitor cells, since their correction would allow appropriate and durable expression of CFTR in stem cell-derived epithelial cell types. Substantial progress has been made to directly correct airway basal cells in vitro, theoretically enabling transplantation of autologous corrected cells to regenerate an airway with CFTR functional cells. Another approach to create autologous, gene-edited airway basal cells is derivation of CF donor-specific induced pluripotent stem cells, correction of the CFTR gene, and subsequent directed differentiation to airway basal cells. Further work is needed to translate these advances by developing effective transplantation methods. Alternatively, gene editing in vivo may enable CFTR correction. However, this approach will require robust delivery methods ensuring that basal cells are efficiently targeted and corrected. Recent advances in gene editing-based therapies provide hope that the genetic underpinning of CF can be durably corrected in airway epithelial stem cells, thereby preventing or treating lung disease in all people with CF.

Deconstructing tissue engineered trachea: Assessing the role of synthetic scaffolds, segmental replacement and cell seeding on graft performance.

The ideal construct for tracheal replacement remains elusive in the management of long segment airway defects. Tissue engineered tracheal grafts (TETG) have been limited by the development of graft stenosis or collapse, infection, or lack of an epithelial lining. We applied a mouse model of orthotopic airway surgery to assess the impact of three critical barriers encountered in clinical applications: the scaffold, the extent of intervention, and the impact of cell seeding and characterized their impact on graft performance. First, synthetic tracheal scaffolds electrospun from polyethylene terephthalate / polyurethane (PET/PU) were orthotopically implanted in anterior tracheal defects of C57BL/6 mice. Scaffolds demonstrated complete coverage with ciliated respiratory epithelium by 2 weeks. Epithelial migration was accompanied by macrophage infiltration which persisted at long term (>6 weeks) time points. We then assessed the impact of segmental tracheal implantation using syngeneic trachea as a surrogate for the ideal tracheal replacement. Graft recovery involved local upregulation of epithelial progenitor populations and there was no evidence of graft stenosis or necrosis. Implantation of electrospun synthetic tracheal scaffold for segmental replacement resulted in respiratory distress and required euthanasia at an early time point. There was limited epithelial coverage of the scaffold with and without seeded bone marrow-derived mononuclear cells (BM-MNCs). We conclude that synthetic scaffolds support re-epithelialization in orthotopic patch implantation, syngeneic graft integration occurs with focal repair mechanisms, however epithelialization in segmental synthetic scaffolds is limited and is not influenced by cell seeding. STATEMENT OF SIGNIFICANCE: The life-threatening nature of long-segment tracheal defects has led to clinical use of tissue engineered tracheal grafts in the last decade for cases of compassionate use. However, the ideal tracheal reconstruction using tissue-engineered tracheal grafts (TETG) has not been clarified. We addressed the core challenges in tissue engineered tracheal replacement (re-epithelialization and graft patency) by defining the role of cell seeding with autologous bone marrow-derived mononuclear cells, the mechanism of respiratory epithelialization and proliferation, and the role of the inflammatory immune response in regeneration. This research will facilitate comprehensive understanding of cellular regeneration and neotissue formation on TETG, which will permit targeted therapies for accelerating re-epithelialization and attenuating stenosis in tissue engineered airway replacement.

A Review of Forensic Fellowship Training: Similar Challenges, Diverse Approaches.

OBJECTIVE: As the specialty of forensic psychiatry and the numbers of justice involved individuals with mental illness continue to grow, forensic education is receiving more attention. To add to this discussion, the authors reviewed current training practices in forensic psychiatry fellowship programs. METHODS: As part of a project funded by the state legislature looking at psychiatry and psychology training, with special focus on state hospital partnerships, the authors interviewed and surveyed forensic psychiatry fellowship program directors and conducted site visits to select programs. Given the mandate, special attention was given to programs with state hospital and psychology training affiliations. RESULTS: The literature and fellowship directors identified several key features and challenges for forensic training programs. Forensic fellowships focused primarily on evaluations and consultations but differed in their offerings related to training in treatment, scholarship, and particular types of evaluations. Common concerns included maintaining adequate funding, variety of training experiences, adequate faculty time, and adequate institutional support. Directors described cultivating institutional support by demonstrating mutual benefit as particularly important for securing resources. CONCLUSION: Forensic fellowships operational during the 2016-2017 academic year offered a range of forensic training activities, but experienced common challenges such as inadequate funding and faculty supervision. Empirical studies are needed to evaluate the relationship between programmatic offerings, the noted challenges, and acquired competencies.