Novel immunologic mechanisms for Fontan-associated liver disease.

Introduction: Single ventricle congenital heart disease resulting in Fontan palliation has led to improved survival, however, Fontan-associated liver disease (FALD) is ubiquitous in this population by adulthood. While lymphopenia has been associated with the degree of FALD, potential immunologic mechanisms remain unstudied, and were the focus of this study. Methods: Single-nuclei RNA-seq (snRNA-seq) data from liver samples of adolescent Fontan and control patients were analyzed with specific focus on lymphocytes and natural killer (NK) and T-cell fractions. Results: Liver samples from Fontan patients demonstrated upregulation of endothelial cells (ECs: 4.2 ± 1.0 vs. 13.6 ± 3.4 %, p = 0.037) and total lymphocytes (0.7 ± 0.1 vs. 3.6 ± 0.7 %, p = 0.007), more specifically in NK and T-cells (NK: 0.29 ± 0.16 vs. 1.40 ± 0.64 %, p = 0.028 and T-cell: 0.28 ± 0.04 vs. 1.80 ± 1.01 %, p = 0.034). Enhanced genes important in T-cell activation and differentiation were demonstrated, as well as those involved in cell-to-cell adhesion and lymphocyte migration. Supporting lymphocyte trafficking, ECs demonstrated amplification of critical chemotactic and lymphocyte recruitment genes. Increased time from Fontan palliation was associated with more dramatic lymphocytic transcriptomic changes. Conclusions: Hepatic changes in adolescent Fontan patients suggest that T-cells are contributing to the early development and possible progression of FALD.