Pluripotent stem cell models of Blau syndrome reveal an IFN-γ–dependent inflammatory response in macrophages

Background Blau syndrome, or early-onset sarcoidosis, is a juvenile-onset systemic granulomatosis associated with a mutation in nucleotide-binding oligomerization domain 2 ( NOD2) . The underlying mechanisms of Blau syndromeleading to autoinflammation are still unclear, and there is currently no effective specific treatment for Blau syndrome. Objectives To elucidate the mechanisms of autoinflammation in patients with Blau syndrome, we sought to clarify the relation between disease-associated mutant NOD2and the inflammatory response in human samples. Methods Blau syndrome–specific induced pluripotent stem cell(iPSC) lines were established. The disease-associated NOD2mutation of iPSCs was corrected by using a CRISPR- Cas9system to precisely evaluate the in vitro phenotype of iPSC-derived cells. We also introduced the same NOD2mutation into a control iPSC line. These isogenic iPSCs were then differentiated into monocytic cell lineages, and the statuses of nuclear factor κB pathway and proinflammatory cytokinesecretion were investigated. Results IFN-γ acted as a priming signal through upregulation of NOD2. In iPSC-derived macrophages with mutant NOD2, IFN-γ treatment induced ligand-independent nuclear factor κB activation and proinflammatory cytokineproduction. RNA sequencing analysis revealed distinct transcriptional profiles of mutant macrophages both before and after IFN-γ treatment. Patient-derived macrophages demonstrated a similar IFN-γ–dependent inflammatory response. Conclusions Our data support the significance of ligand-independent autoinflammation in the pathophysiology of Blau syndrome. Our comprehensive isogenic disease-specific iPSC panel provides a useful platform for probing therapeutic and diagnostic clues for the treatment of patients with Blau syndrome.