*Purpose: Lung transplantation (Tx) in ~30% of cases is subject to primary graft dysfunction (PGD), the severe acute lung injury that occurs within 72 hours of surgery and is characterized by pulmonary edema with profound hypoxemia. The pathogenesis of PGD is poorly understood but the initial effects of ischemia-reperfusion injury (IRI) are considered a primary pathophysiological mechanism responsible for hyperactivation of innate and then adaptive immunity.

*Methods: The current study concerned identifiable epigenetic factors pre-Tx that were linked with subsequent development of PGD following lung Tx. Pre-Tx blood samples were collected prospectively from 78 patients, 50 of whom received lung Tx, and 18 of whom developed grade-3 PGD.

*Results: By qPCR, HDAC6 mRNA was the most upregulated epigenetic enzyme in PBMC collected at 2-3 months pre-Tx from patients who developed PGD after Tx. Using PrimeFlow to detect RNA transcripts within cells defined by standard flow cytometry, we found showed that CD14+ monocytes in PGD+ patients, but not PGD- patients or healthy donors, had upregulated HDAC6 mRNA expression pre-Tx. PGD+ monocytes appeared to be trained rather than activated cells since they had normal levels of CD40, CD54, HLA-DR, PDL1, CD80 and CD86, but upon short-term LPS stimulation, upregulated IL-1b and IL-6 mRNA significantly more than PGD- monocytes. RNA-seq showed that PGD+ monocytes upregulated genes associated with antigen processing and presentation (31 genes); cytokine signaling in the immune system (26 genes), cytoskeletal signaling (12 genes), and TLR pathways (12 genes), and 78% of mapped genes were suggested as HDAC6 target genes in ChIP-seq datasets from the ENCODE Transcription Factor Targets dataset. In co-cultures, PGD+ CD14+ monocytes directly stimulated T-effector cell activation and counteracted Treg suppression. Using multiple linear regression and preoperative blood samples, i) HDAC6 mRNA expression (p=0.003), ii) suppressive function of isolated FOXP3+ Tregs (p=0.021), iii) presence of metabolic diseases (p=0.003) and iv) statin therapy (p=0.005) were the main 4 factors influencing PGD development. In murine proof-of-principle studies involving lung IRI, HDAC6-/- mice had significantly decreased inflammatory responses in affected lungs (CXCL1, TNF-a, IL-6, IL-1b) compared with WT mice, and selective pharmacologic inhibition of HDAC6 pre-lung IRI also led to significantly decreased inflammation in WT mice.

*Conclusions: Hence, our studies i) demonstrate factors in pre-Tx peripheral blood that may be used to identify patients at increased risk of developing PGD post-lung Tx, and ii) indicate approaches to significantly reduce the risk of subsequently developing PGD by pharmacologic inhibition of HDAC6.

« Back to 2020 American Transplant Congress