Allograft Rejection After Lung Transplantation

Apoptosis and the airway epithelium

The airway epithelium functions as a barrier and front line of host defense in the lung. Apoptosis or programmed cell death can be elicited in the epithelium as a response to viral infection, exposure to allergen or to environmental toxins, or to drugs. While apoptosis can be induced via activation of death receptors on the cell surface or by disruption of mitochondrial polarity, epithelial cells compared to inflammatory cells are more resistant to apoptotic stimuli. This paper focuses on the response of airway epithelium to apoptosis in the normal state, apoptosis as a potential regulator of the number and types of epithelial cells in the airway, and the contribution of epithelial cell apoptosis in important airways diseases.

Mechanisms behind local immunosuppression using inhaled tacrolimus in preclinical models of lung transplantation

Inhaled immunosuppression with tacrolimus (TAC) is a novel strategy after lung transplantation. Here we investigate the feasibility of tacrolimus delivery via aerosol, assess its immunosuppressive efficacy, reveal possible mechanisms of action, and evaluate its airway toxicity. Rats received 4 mg/kg TAC via oral or inhaled (AER) administration. Pharmacokinetic properties were compared, and in vivo airway toxicity was assessed. Full-thickness human airway epithelium (AE) was grown in vitro at an air-liquid interface. Equal TAC doses (10-1,000 ng) were either added to the bottom chamber (MED) or aerosolized for gas-phase exposure (AER). Airway epithelium TAC absorption, cell toxicity, and interactions of TAC with NFκB activation were studied. Single-photon emission computed tomography demonstrated a linear tracer accumulation within the lungs during TAC inhalation. The AER TAC generated higher lung-tissue concentrations, but blood concentrations that were 11 times lower. Airway histology and gene expression did not reveal drug toxicity after 3 weeks of treatment. In vitro AE exposed to TAC at 10-1,000 ng, orally or AER, maintained its pseudostratified morphology, did not show cell toxicity, and maintained its epithelial integrity, with tight junction formation. The TAC AER-treated AE absorbed the drug from the apical surface and generated lower-chamber TAC concentrations sufficient to suppress activated lymphocytes. Tacrolimus AER was superior to TAC MED at preventing AE IFN-γ, IL-10, IL-13, monocyte chemoattractant protein-1 chemokine (C-C motif) ligand 5 (RANTES) and TNF-α up-regulation. Tacrolimus inhibited airway epithelial cell NFκB activation. In conclusion, TAC can be delivered easily and effectively into the lungs without causing airway toxicity, decreases inflammatory AE cytokine production, and inhibits NFκB activation.

Lung resident mesenchymal stem cells isolated from human lung allografts inhibit T cell proliferation via a soluble mediator

Development of allograft rejection continues to be the major determinant of morbidity and mortality postlung transplantation. We have recently demonstrated that a population of donor-derived mesenchymal stem cells is present in human lung allografts and can be isolated and expanded ex vivo. In this study, we investigated the impact of lung resident mesenchymal stem cells (LR-MSCs), derived from allografts of human lung transplant recipients, on T cell activation in vitro. Similar to bone marrow-derived MSCs, LR-MSCs did not express MHC II or the costimulatory molecules CD80 or CD86. In vitro, LR-MSCs profoundly suppressed the proliferative capacity of T cells in response to a mitogenic or an allogeneic stimulus. The immunosuppressive function of LR-MSCs was also noted in the absence of direct cell contact, indicating that LR-MSCs mediated their effect predominantly via a soluble mediator. LR-MSCs isolated from lung transplant recipients demonstrated PGE(2) secretion at baseline (385 +/- 375 pg/ml), which increased in response to IL-1beta (1149 +/- 1081 pg/ml). The addition of PG synthesis inhibitors (indomethacin and NS-398) substantially abrogated LR-MSC-mediated immunosuppression, indicating that PGE(2) may be one of the major soluble mediators impacting T cell activity. This is the first report to demonstrate that human tissue-derived MSCs isolated from an allogeneic environment have the potential to mediate immunological responses in vitro.

Non-acidic supraesophageal reflux associated with diffuse alveolar damage and allograft dysfunction after lung transplantation: a case report

Advances in lung transplantation have improved 1-year survival rates, but allograft dysfunction continues to be a significant cause of post-transplant death. Diffuse alveolar damage is an early indication of allograft dysfunction and has been linked to gastroesophageal reflux. We report a case of diffuse alveolar damage-associated allograft dysfunction in a patient found to have significant non-acid gastroesophageal reflux.

Surgical therapies for pulmonary arterial hypertension

Surgical therapies for the treatment of pulmonary arterial hypertension typically are reserved for patients who are deemed to be refractory to medical therapy and have evidence of progressive right-sided heart failure. Atrial septostomy, a primarily palliative procedure, may stave off hemodynamic collapse from right-sided heart failure long enough to permit a more definitive surgical treatment such as lung or combined heart-lung transplantation. This article discusses indications for and results of atrial septostomy and lung and heart-lung transplantation in patients who have pulmonary arterial hypertension.

Metalloproteinase Inhibition Has Differential Effects on Alloimmunity, Autoimmunity, and Histopathology in the Transplanted Lung

BACKGROUND

Upregulation of matrix metalloproteinases (MMPs) has been associated with chronic lung allograft rejection known as bronchiolitis obliterans syndrome. It has been suggested that MMP inhibition could prevent the rejection response. However, the effect of MMP inhibition on lung allograft rejection has not been reported.

METHODS

Utilizing a rat model of lung transplantation, tissue inhibitors of metalloproteinases (TIMP-1 and TIMP-2) were overexpressed by gene therapy in F344 rat lung allografts prior to transplantation into WKY recipient rats. Separately, WKY rats that received F344 lung allografts were treated systemically with COL-3, a global MMP inhibitor.

RESULTS

TIMP-1 and TIMP-2 had differential effects on delayed type hypersensitivity (DTH) responses to donor antigens and type V collagen, an autoantigen involved in the rejection response. Neither TIMP-1 or TIMP-2 affected the onset of rejection pathology. COL-3 suppressed DTH responses to donor antigens and type V collagen, abrogated local production of tumor necrosis factor-alpha, and interleukin-1beta. Although it did not prevent rejection pathology, COL-3 (30 mg/kg) induced intragraft B cell hyperplasia suggestive of posttransplant proliferative disorder (PTLD).

CONCLUSIONS

These data identify a complex role for MMPs and TIMPs in the immunopathogenesis of lung allograft rejection, and indicate their effects are not limited to matrix remodeling.