NLRP3 inflammasome-driven hemophagocytic lymphohistiocytosis occurs independent of IL-1β and IL-18 and is targetable by BET inhibitors.

Hemophagocytic lymphohistiocytosis (HLH) is a potentially fatal cytokine storm syndrome. Its high mortality rate reflects limited therapeutic options and a poor understanding of disease-causing signaling. We show that the NLRP3 inflammasome is responsible for increased mortality in a model of secondary HLH (sHLH). Unexpectedly, neither deletion of the NLRP3-activated pyroptotic effector GSDMD nor combined deletion of the inflammasome-activated cytokines interleukin-1β (IL-1β) and IL-18 conferred strong protection from sHLH. Instead, co-deletion of GSDMD and caspase-8-activated GSDME limited sHLH-driven lethality, demonstrating redundancy in the pyroptotic machinery required to induce sHLH. We also found that bromodomain and extraterminal domain (BET) inhibitors prevent NLRP3-driven pyroptosis, which acted by blocking inflammasome priming. BET inhibitors prevented increased NLRP3 levels in diseased tissue, limited the production of sHLH-associated IL-1β, interferon-γ, and tumor necrosis factor, and protected from sHLH pathogenesis. These findings suggest that targeting NLRP3 could limit sHLH and identify clinically relevant bromodomain-selective BET inhibitors capable of eliminating NLRP3-driven pyroptosis and the sHLH cytokine storm.