Development of obliterative bronchiolitis in a murine model of orthotopic lung transplantation

Lobar lung transplantation in the mouse

Background

As an important supplementary approach to clinical in orthotopic lung transplantation (LTx), lobar LTx currently lacks a stable animal model and in the orthotopic left LTx model, the right lung of the donor mouse is completely removed and discarded. We introduce a novel mouse lobar LTx model that potentially provides a mouse model for clinical lobar LTx and increase the utilization rate of the experimental donor.

Methods

Lobar and orthotopic left LTx were performed in syngeneic strain combinations. We performed micro-computed tomography and tested arterial blood gases to assess the graft function 28 days after transplantation. Hematoxylin-eosin and Masson's trichrome staining were used to evaluate pathological changes.

Results

We performed ten lobar LTx with an operation success rate of 90%, accompanied by ten orthotopic left LTx from the same donors with an operation success rate of 100%. The graft preparation for lobar LTx was longer than that of the orthotopic left LTx (42.11±3.79 vs. 30.10±3.14 minutes, P<0.001). The recipient procedure for lobar LTx was nearly equivalent to the orthotopic left LTx. The graft function and histopathological changes for lobar LTx were comparable to those of orthotopic left LTx 28 days after transplantation.

Conclusions

We describe a lobar LTx model in the mouse, which potentially provides a model for clinical lobar LTx and effectively addresses the issue of resource wastage in the orthotopic left LTx model.

The nature of chronic rejection after lung transplantation: a murine orthotopic lung transplant study

Introduction

Chronic rejection is a major complication post-transplantation. Within lung transplantation, chronic rejection was considered as airway centred. Chronic Lung Allograft Dysfunction (CLAD), defined to cover all late chronic complications, makes it more difficult to understand chronic rejection from an immunological perspective. This study investigated the true nature, timing and location of chronic rejection as a whole, within mouse lung transplantation.

Methods

40 mice underwent an orthotopic left lung transplantation, were sacrificed at day 70 and evaluated by histology and in vivo µCT. For timing and location of rejection, extra grafts were sacrificed at day 7, 35, 56 and investigated by ex vivo µCT or single cell RNA (scRNA) profiling.

Results

Chronic rejection originated as innate inflammation around small arteries evolving toward adaptive organization with subsequent end-arterial fibrosis and obliterans. Subsequently, venous and pleural infiltration appeared, followed by airway related bronchiolar folding and rarely bronchiolitis obliterans was observed. Ex vivo µCT and scRNA profiling validated the time, location and sequence of events with endothelial destruction and activation as primary onset.

Conclusion

Against the current belief, chronic rejection in lung transplantation may start as an arterial response, followed by responses in venules, pleura, and, only in the late stage, bronchioles, as may be seen in some but not all patients with CLAD.

Targeting PD-1/PD-L1 inhibits rejection in a heterotopic tracheal allograft model of lung transplantation

Immune checkpoint molecules such as programmed death-1 (PD-1) and programmed death ligand-1 (PD-L1) have revolutionized the field of lung cancer treatment. As part of our study, we examined the role of these proteins in acute rejection in a mouse model of heterotopic tracheal transplantation. Recipient mice were untreated (Allo group) or treated with anti-PD-L1 (aPDL1 group) or PD-L1 Fc recombinant protein (PD-L1 Fc group). A further group of C57BL/6 mice received isografts (Iso group). The occlusion rate was significantly higher in the Allo group than in the Iso group (p = 0.0075), and also higher in the aPD-L1 group (p = 0.0066) and lower in the PD-L1 Fc group (p = 0.030) than in the Allo group. PD-L1 Fc recombinant protein treatment significantly decreased interleukin-6 and interferon-γ levels and reduced the CD4+/CD8+ T cell ratio, without increasing PD-1 and T-cell immunoglobulin mucin 3 expression in CD4+ T cells. These data suggest that PD-L1 Fc recombinant protein decreases the levels of inflammatory cytokines and the proportion of CD4+ T cells without exhaustion. The PD-L1-mediated immune checkpoint mechanism was associated with rejection in the murine tracheal transplant model, suggesting a potential novel target for immunotherapy in lung transplantation.

Differential gene analysis during the development of obliterative bronchiolitis in a murine orthotopic lung transplantation model: A comprehensive transcriptome-based analysis

BACKGROUND

Obliterative bronchiolitis (OB) is a known issue during minor histocompatibility antigen (mHA) disparity during lung transplantation. This study evaluated gene expression in a murine orthotropic lung transplantation model using microarray analysis.

METHODS

Left lungs from C57BL/10(H-2b) donor mice were transplanted into mHA-mismatched C57BL/6(H-2b) recipient mice. Three groups (OB, non-OB, and sham controls) were confirmed pathologically and analyzed. Gene expression changes in the lung grafts were determined by microarray and immunohistochemical staining, and genes were verified by quantitative PCR in the lungs and mediastinal lymph nodes (LNs).

RESULTS

A total of 1343 genes were upregulated in the OB lungs compared to the sham group. Significant upregulation was observed for genes related to innate, e.g. Tlr2 and CCL3 and adaptive immunity, e.g. H2-ab1 and Il-21. Positive labeling for MHC class II antigen was observed in the bronchial epithelium of OB accompanied with B cells. We found increased Tlr2, Ccl3, H2-ab1, Il-21, Ighg3, Ifng, and Pdcd1 mRNA expression in the OB lung, and increased Il-21, Ighg3, and Pdcd1 expression in the OB LNs.

CONCLUSIONS

Adaptive and innate immune reactions were involved in OB after lung transplantation, and genetic examination of related genes could be used for detection of OB.

Rat lung transplantation model: modifications of the cuff technique

Background

Although the cuff technique in rat lung transplantation (LTx) has a long history, it remains technically challenging. We have developed key tricks and modifications in the devices and the cuff technique that optimize the rat LTx model to achieve successful operations during a short learning period.

Methods

Altogether, 180 consecutive rats underwent orthotopic left LTx performed by a single surgeon using our modified devices and procedures. Allogeneic and syngeneic transplantation were performed using Lewis rats as recipients and Brown Norway and Lewis rats as donors. Allogeneic recipients were treated with cyclosporine during the first week. Recipients were sacrificed at various time points after ≥2 weeks.

Results

A special cuff-preparation plate was created using a petri dish and two foam blocks. This modified plate stabilizes the preparation and prevents donor lung compression. A "┴"-shaped incision was carved into the front wall of the pulmonary artery (PA) using micro-scissors. "V"-shaped incisions were made from the inferior-to-superior branches of the pulmonary vein (PV) and bronchus. A "pendulum model" was applied at implantation to make the hilar anastomosis tension-free and technically easier to perform. There were no intraoperative complications. Ten rats (5.6%) experienced partial or full pulmonary atelectasis. Five deaths (2.8%) due to pleural effusion occurred during the follow-up period. The operative times for heart-lung block retrieval, cuff preparation, cold ischemia, warm ischemia, and total procedure time were 8.4±0.8, 11.6±1.5, 25.1±2.2, 8.1±1.2, and 46.7±2.8 min, respectively.

Conclusions

The key tricks and improvements we made in the cuff technique for rat LTx provided the advantages of expeditiousness, a low complication rate, and a high success rate.

Vendor-specific microbiome controls both acute and chronic murine lung allograft rejection by altering CD4+ Foxp3+ regulatory T cell levels

Despite standardized postoperative care, some lung transplant patients suffer multiple episodes of acute and chronic rejection while others avoid graft problems for reasons that are poorly understood. Using an established model of C57BL/10 to C57BL/6 minor antigen mismatched single lung transplantation, we now demonstrate that the recipient microbiota contributes to variability in the alloimmune response. Specifically, mice from the Envigo facility in Frederick, Maryland contain nearly double the number of CD4⁺ Foxp3⁺ regulatory T cells (T_regs ) than mice from the Jackson facility in Bar Harbor, Maine or the Envigo facility in Indianapolis, Indiana (18 vs 9 vs 7%). Lung graft recipients from the Maryland facility thus do not develop acute or chronic rejection. Treatment with broad-spectrum antibiotics decreases T_regs and increases both acute and chronic graft rejection in otherwise tolerant strains of mice. Constitutive depletion of regulatory T cells, using Foxp3-driven expression of diphtheria toxin receptor, leads to the development of chronic rejection and supports the role of T_regs in both acute and chronic alloimmunity. Taken together, our data demonstrate that the microbiota of certain individuals may contribute to tolerance through T_reg -dependent mechanisms and challenges the practice of indiscriminate broad-spectrum antibiotic use in the perioperative period.

Inhibition of B cell-dependent lymphoid follicle formation prevents lymphocytic bronchiolitis after lung transplantation

Lung transplantation (LTx) is the only therapeutic option for many patients with chronic lung disease. However, long-term survival after LTx is severely compromised by chronic rejection (chronic lung allograft dysfunction [CLAD]), which affects 50% of recipients after 5 years. The underlying mechanisms for CLAD are poorly understood, largely due to a lack of clinically relevant animal models, but lymphocytic bronchiolitis is an early sign of CLAD. Here, we report that lymphocytic bronchiolitis occurs early in a long-term murine orthotopic LTx model, based on a single mismatch (grafts from HLA-A2:B6-knockin donors transplanted into B6 recipients). Lymphocytic bronchiolitis is followed by formation of B cell-dependent lymphoid follicles that induce adjacent bronchial epithelial cell dysfunction in a spatiotemporal fashion. B cell deficiency using recipient μMT-/- mice prevented intrapulmonary lymphoid follicle formation and lymphocytic bronchiolitis. Importantly, selective inhibition of the follicle-organizing receptor EBI2, using genetic deletion or pharmacologic inhibition, prevented functional and histological deterioration of mismatched lung grafts. In sum, we provided what we believe to be a mouse model of chronic rejection and lymphocytic bronchiolitis after LTx and identified intrapulmonary lymphoid follicle formation as a target for pharmacological intervention of long-term allograft dysfunction after LTx.

Models of Lung Transplant Research: a consensus statement from the National Heart, Lung, and Blood Institute workshop

Lung transplantation, a cure for a number of end-stage lung diseases, continues to have the worst long-term outcomes when compared with other solid organ transplants. Preclinical modeling of the most common and serious lung transplantation complications are essential to better understand and mitigate the pathophysiological processes that lead to these complications. Various animal and in vitro models of lung transplant complications now exist and each of these models has unique strengths. However, significant issues, such as the required technical expertise as well as the robustness and clinical usefulness of these models, remain to be overcome or clarified. The National Heart, Lung, and Blood Institute (NHLBI) convened a workshop in March 2016 to review the state of preclinical science addressing the three most important complications of lung transplantation: primary graft dysfunction (PGD), acute rejection (AR), and chronic lung allograft dysfunction (CLAD). In addition, the participants of the workshop were tasked to make consensus recommendations on the best use of these complimentary models to close our knowledge gaps in PGD, AR, and CLAD. Their reviews and recommendations are summarized in this report. Furthermore, the participants outlined opportunities to collaborate and directions to accelerate research using these preclinical models.

Heterotopic Cervical Heart Transplantation in Mice

The heterotopic cervical heart transplantation in mice is a valuable tool in transplant and cardiovascular research. The cuff technique greatly simplifies this model by avoiding challenging suture anastomoses of small vessels thereby reducing warm ischemia time. In comparison to abdominal graft implantation the cervical model is less invasive and the implanted graft is easily accessible for further follow-up examinations. Anastomoses are performed by pulling the ascending aorta of the graft over the cuff with the recipient's common carotid artery and by pulling the main pulmonary artery over the cuff with the external jugular vein. Selection of appropriate cuff size and complete mobilization of the vessels are important for successful revascularization. Ischemia-reperfusion (I/R) injury can be minimized by perfusing the graft with a cardioplegic solution and by hypothermia. In this article, we provide technical details for a simplified and improved cuff technique, which should allow surgeons with basic microsurgical skills to perform the procedure with a high success rate.

Local origin of mesenchymal cells in a murine orthotopic lung transplantation model of bronchiolitis obliterans

Bronchiolitis obliterans is the leading cause of chronic graft failure and long-term mortality in lung transplant recipients. Here, we used a novel murine model to characterize allograft fibrogenesis within a whole-lung microenvironment. Unilateral left lung transplantation was performed in mice across varying degrees of major histocompatibility complex mismatch combinations. B6D2F1/J (a cross between C57BL/6J and DBA/2J) (Haplotype H2b/d) lungs transplanted into DBA/2J (H2d) recipients were identified to show histopathology for bronchiolitis obliterans in all allogeneic grafts. Time course analysis showed an evolution from immune cell infiltration of the bronchioles and vessels at day 14, consistent with acute rejection and lymphocytic bronchitis, to subepithelial and intraluminal fibrotic lesions of bronchiolitis obliterans by day 28. Allografts at day 28 showed a significantly higher hydroxyproline content than the isografts (33.21 ± 1.89 versus 22.36 ± 2.33 μg/mL). At day 40 the hydroxyproline content had increased further (48.91 ± 7.09 μg/mL). Flow cytometric analysis was used to investigate the origin of mesenchymal cells in fibrotic allografts. Collagen I-positive cells (89.43% ± 6.53%) in day 28 allografts were H2Db positive, showing their donor origin. This novel murine model shows consistent and reproducible allograft fibrogenesis in the context of single-lung transplantation and represents a major step forward in investigating mechanisms of chronic graft failure.