Given that the IRE1α/XBP1 pathway augments cytokine production in response to IL-23 by human ILC3s and that IL-23 blockers have been proven effective in CD, we investigated whether the level of pretreatment XBP1s in ILC3s correlates with the response of patients with CD to the nonselective anti–IL-23 antibody ustekinumab. Here, ERN1 is linked to Cowden disease.