TARGETED APPROACH TO LUNG REPAIR AND REGENERATION IN ALVEOLAR TYPE II CELL DISEASE

Topic Area: Acute Lung Injury and Lung InjuryRationale: Over 14 percent of Veterans that have been deployed develop lung disease – a prevalence higher than that of the general population.[1] This suggests that deployment exposures (e.g., dust, sand, burn pit emissions, aeroallergens from desert areas, and chemical and metal particles) may be linked to lung injury and its progression to chronic lung disease. Medical treatments are unable to reverse lung disease or restore normal function. The new cellular therapy we propose could promote lung repair and regeneration, potentially treating lung disease at its source. Specifically, we address injury of alveolar type II (ATII) cells, which appear central to the pathogenesis of multiple acute and chronic lung diseases, such as acute respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD), and idiopathic pulmonary fibrosis.Innovative Aspects of the Research: Our team has developed a first-of-its-kind approach to specifically target and remove only ATII cells in lung disease secondary to injury of those cells. This leaves the lung scaffold intact to facilitate healthy exogenous ATII cells to engraft, as a potential method to repair and regenerate lung. (i) We have designed a novel fusion protein that links Surfactant Protein A (SPA), known to be produced and taken up by ATII cells, to a shortened version of Diphtheria Toxin (DT388). The resulting compound, DT388-SPA, is an inhalable treatment approach that seeks to ablate ATII cells selectively and leaves the rest of the lung epithelium and structure intact. In our preliminary data, we have shown that rat and mouse ATII cells can recognize and uptake DT388-SPA. (ii) This innovative approach will allow us for the first time to treat ATII cell-dependent lung diseases with a specific molecule targeting dysfunctional cell types, potentially soon after lung injury or early in lung disease progression. (iii) In lung disease research, we are the first to aim to remove only the dysfunctional cells and replace them with therapeutic cells, re-establishing alveolar homeostasis. (iv) Our novel fusion protein technology, if proved successful, could be used to design similar treatment molecules for other cell-type-specific lung diseases – providing a new paradigm for lung repair and regeneration.Hypothesis: ATII cells will take up DT388-SPA and undergo selective apoptosis, leaving a void that can then be repopulated by healthy exogenous ATII cells.Study Design: The specific aims that will test this hypothesis are as follows: Aim 1: To determine the effect and specificity of DT388-SPA in vitro. We will define the functionality, specificity, and half maximum effective concentration (EC50) of DT388-SPA in healthy and defective mouse ATII cells in vitro. For our defective ATII cells, we chose Surfactant Protein C-deficient (SPC-/-) mice, which are normal at birth but then develop severe, progressive pulmonary disease due to inherited ATII cell defect. Aim 2: To define the parameters to deliver DT388-SPA via inhalation in an ex vivo lung bioreactor. Different modalities of nebulization will be tested to deliver high concentrations of DT388-SPA to ATII cells in the alveolar region of mice lungs. Aim 3: To establish the therapeutic potential in vivo of a two-step approach consisting of DT388-SPA administration followed by the introduction of healthy exogenous ATII cells. We will evaluate the targeted removal of defective ATII cells through DT388-SPA in SPC (-/-) mouse lungs directly in vivo. The void left by deceased ATII cells will be repopulated by intratracheal injection of healthy wild-type ATII cells to promote lung repair and regeneration.Expected Results: We anticipate that we will: (i) define the efficacy and specificity of DT388-SPA to target and induce apoptosis of ATII cells while preserving the surrounding lung environment in vivo and (ii) gain insights into repair mechanisms using therapeutic cells that could be applied to other lung diseases.Foundation for Future Research: The results obtained will: (i) lay essential groundwork for future studies to characterize the long-term therapeutic effects of healthy exogenous ATII cells, in which we could assess their ability to revert or stop the progression of pulmonary fibrosis in SPC (-/-) mice at 6-9 months after implantation and (ii) open new avenues of investigation for all lung diseases in which a specific cell membrane target is identified, with the potential to adapt our innovative fusion molecule technology to make cellular therapies a viable alternative to lung transplant. This represents an innovative therapeutic strategy that could improve the lives of millions of military personnel, Veterans, and civilians with lung disease.[1] Study: Iraq, Afghanistan Veterans at increased risk of respiratory illness. U.S. Department of Veterans Affairs, August 2014 (https://www.research.va.gov/currents/summer2014/summer2014-24.cfm).