Clinical, histological and tissue proteomic features of decline after idiopathic acute lung allograft dysfunction

Introduction: Idiopathic acute lung allograft dysfunction (iALAD) occurs in a subset of lung transplant (LTx) recipients with ALAD, where no identifiable cause is found. Prognostication after iALAD is poorly characterised. This study aimed to 1. Describe the incidence, clinical and histological features of iALAD, and 2. Identify novel tissue proteins associated with prognosis.
Methods: A single centre retrospective analysis of all transbronchial lung biopsies (TBBx) collected between Jan 2017 – Dec 2024, including surveillance and ALAD episodes. ALAD was defined as >10% decline in FEV1 from recent baseline. iALAD was defined as absence of ISHLT acute cellular rejection grade A0B0, positive bronchoalveolar lavage microbiology, donor-specific HLA antibodies, chronic lung allograft dysfunction (CLAD) or another identifiable cause. All iALAD TBBx underwent lung allograft standardized histological analysis (LASHA) assessment. Clinical features at iALAD were recorded. Recovery after iALAD was defined as ≥2 subsequent FEV1 measurements within 90% of baseline FEV1. The primary outcome was iALAD-decline which occurred if this criteria was not met. Univariable logistic regression identified factors associated with iALAD-decline. Proteomic analysis using mass spectrometry was performed on all iALAD TBBx and compared with 10 control surveillance biopsies from stable recipients. Bioinformatics and pathways analyses using Scaffold software V5 identified significantly expressed proteins.
Results: From 1109 archived TBBx, a total 379 ALAD TBBx from 221 patients were identified. iALAD occurred in 30/379 TBBx (8%); 11/30 (37%) with subsequent decline. Significantly higher median (IQR) HLA-DR+DQ eplet mismatch scores were measured in iALAD-decline [48.0(29) vs. 24.5(15), p=0.03]. Pneumocyte hypertrophy/reactive changes on LASHA (OR 5.8, 95%CI 1.1–29.8, p=0.04) and sub-therapeutic calcineurin inhibitor (CNI) blood concentrations (OR 7.1, 95%CI 1.1–46.7, p=0.04) were significantly associated with iALAD-decline (Table 1). Of 913 tissue proteins extracted, significant upregulation of 33 (including IGKC, PSMB9, HLA-A, EPX) and downregulation of 15 (including FLNB, IQGAP1, CDH5, P4HB) proteins occurred exclusively in iALAD-decline (Table 2). Unique overexpression of CD55, SUSD2, RACK1 and HLA-DRA indicates potential as candidate biomarkers in iALAD-decline. Mechanistic pathways of upregulated proteins related to immune activation, while downregulated proteins reflected impaired epithelial maintenance, cell–cell communication and tissue homeostasis. Conversely, upregulation of structural cytoskeletal proteins (COL1A1, COL3A1, VIM, FLNA) in iALAD-recovery revealed enhanced extracellular matrix remodelling and cellular integrity. Multiplex immunofluorescence validation is underway.
Conclusion: Higher HLA-DR+DQ eplet scores, subtherapeutic CNI levels, and histologic pneumocyte hypertrophy are associated with poor recovery after iALAD. Pro-inflammatory immune pathway activation and impaired structural repair mechanisms are evident in iALAD-decline. Protein validation is a future priority to identify prognostic tissue biomarkers.