Role of DOCK8 in Hyper-inflammatory Syndromes

Background: Cytokine storm syndromes (CSS), including hemophagocytic lymphohistiocytosis (HLH), are increasingly recognized as hyper-inflammatory states leading to multi-organ failure and death. Familial HLH (FHL) in infancy results from homozygous genetic defects in perforin-mediated cytolysis by CD8 T-lymphocytes and natural killer (NK) cells. Later onset CSS are frequently associated with heterozygous defects in FHL genes, but genetic etiologies for most are unknown. We identified rare DOCK8 variants in CSS patients. Objective: We explore the role of CSS patient derived DOCK8 mutations on cytolytic activity in NK cells. We further study effects of Dock8^-/- in murine models of CSS. Methods: DOCK8 cDNA from 2 unrelated CSS patients with different missense mutations were introduced into human NK-92 NK cells by foamy virus transduction. NK cell degranulation (CD107a), cytolytic activity against K562 target cells, and interferon-gamma (IFNlower case Greek gamma) production were explored by flow cytometry (FCM). A third CSS patient DOCK8 mRNA splice acceptor site variant was explored by exon trapping. Dock8^-/- mice were assessed for features of CSS (weight loss, splenomegaly, hepatic inflammation, cytopenias, and IFNlower case Greek gamma levels) upon challenge with lymphochoriomeningitic virus (LCMV) and excess IL-18. Results: Both patient DOCK8 missense mutations decreased cytolytic function in NK cells in a partial dominant-negative fashion in vitro. The patient DOCK8 splice variant disrupted mRNA splicing in vitro. Dock8^-/- mice tolerated excess IL-18 but developed features of CSS upon LCMV infection. Conclusion: Mutations in DOCK8 may contribute to CSS-like hyper-inflammatory states by altering cytolytic function in a threshold model of disease.