Lymphatic Dysfunction and Development of Post-Transplant Obliterative Bronchiolitis

PROJECT SUMMARY The etiology of bronchiolitis obliterans syndrome (BOS), a serious complication that affects the terminal airways of the transplanted lung and is the main cause of long-term graft dysfunction and failure after lung Tx, is unknown. We hypothesize that loss of lymphatic function after lung Tx is critical to the development and progression of BOS and, post-reconstitution is affected by disruption of interactions between lymphatic endothelial cells (LECs) and Foxp3+ T-regulatory (Treg) cells. This hypothesis is based on our preliminary data. First, using orthotopic murine models of lung Tx, we have shown that deletion of lymphatics (loss of function, LOF) within the transplanted lung leads to acute inflammation and promotes BOS, as does conditional deletion of lymphotoxin-beta receptor (LTbR) within LECs. Second, we found stimulation of lymphangiogenesis in a gain of function (GOF) model involving conditional deletion of the lipid phosphatase, Pten, can protect against BOS. Third, adoptive transfer of LTb+ but not LTb- Treg cells can protect against lung injury and the development of BOS post-Tx. Specific Aim 1. Determine the mechanisms of lymphatic vascular function after lung Tx. Hypothesis: Lymphatic function post-Tx is mediated by immunomodulatory adaption of donor LECs and signaling via the LTbR/LTa1b2 axis. Using lymphatic reporter mice, i) we will determine the contribution of donor versus host-derived LECs to the lymphatic vasculature post-Tx. ii) We will also map LEC heterogeneity and subtypes that define the lymphatic vascular adaptation in lung Tx. Finally, iii) we will use mice deficient in LTbR, LTa or LTb to determine the mechanistic role of these pathways in lymphatic function post-lung Tx. Specific Aim 2. Strategies to promote lymphangiogenesis in the lung Tx. Hypothesis: GOF strategies to promote lymphangiogenesis within the transplanted lung will protect against the development of BOS. This will involve 3 independent lines of investigation, i) administration of an agonistic mAb directed against LTbR expressed by LEC; ii) delivery of recombinant VEGF-C by AAV; and iii) blockade of epsins to reduce VEGFR3 endocytosis and degradation and thereby increase VEGFR3 protein expression and promote lymphangiogenesis. Specific Aim 3. Strategies to promote CLAD-free Treg-dependent lung allograft survival. Hypothesis: Therapeutic strategies that enhance endogenous Treg numbers and/or function will promote CLAD-free Tx survival. Accordingly, we will test the ability of therapy with i) IL-2 muteins alone or ii) in conjunction with Cdk8/19 inhibitors (Cdk8/19i) to expand the recipient Foxp3+ Treg cell population and promote beneficial outcomes in lung Tx models; and iii) assess whether Foxp3 mRNA delivery can likewise expand the host Treg population and promote lung allograft survival. Our proposed research will unravel the complex interactions between lymphatics, host immune responses, and the development of key complications of lung Tx, with the ultimate goal of improving patient outcomes and long-term lung Tx survival.