The spillovers of β-coronaviruses in humans and the emergence of SARS-CoV-2 variants highlight the need for broad coronavirus countermeasures. We describe five monoclonal antibodies (mAbs) cross-reacting with the stem helix of multiple β-coronavirus spike glycoproteins isolated from COVID-19 convalescent individuals. Using structural and functional studies we show that the mAb with the greatest breadth (S2P6) neutralizes pseudotyped viruses from three different subgenera through inhibition of membrane fusion and delineate the molecular basis for its cross-reactivity. S2P6 reduces viral burden in hamsters challenged with SARS-CoV-2 through viral neutralization and Fc-mediated effector functions. Stem helix antibodies are rare, oftentimes of narrow specificity and can acquire neutralization breadth through somatic mutations. These data provide a framework for structure-guided design of pan-β-coronavirus vaccines eliciting broad protection.

SUMMARY The intestinal mucosal barrier controlling the resident microbiome is dependent on a protective mucus layer generated by goblet cells, impairment of which is a hallmark of the inflammatory bowel disease Ulcerative Colitis. Here we show that IL-18 is critical in driving the pathologic breakdown of barrier integrity in a model of colitis. Deletion of Il18 or its receptor Il18r1 in intestinal epithelial cells (Δ/EC) conferred protection from colitis and mucosal damage in mice. In contrast, deletion of the IL-18 negative regulator Il18bp resulted in severe colitis associated with loss of mature goblet cells. Colitis and goblet cell loss were rescued in Il18bp−/−;Il18rΔ/EC mice, demonstrating that colitis severity is controlled at the level of IL-18 signaling in intestinal epithelial cells. IL-18 inhibited goblet cell maturation by regulating the transcriptional program instructing goblet cell development. These results inform on the mechanism of goblet cell dysfunction which underlies the pathology of Ulcerative Colitis.

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The coronavirus spike (S) glycoprotein attaches to host receptors and mediates viral fusion. Using a broad screening approach, we isolated from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immune donors seven monoclonal antibodies (mAbs) that bind to all human-infecting coronavirus S proteins. This class of mAbs recognize the fusion peptide and acquire affinity and breadth through somatic mutations. Despite targeting a conserved motif, only some mAbs show broad neutralizing activity in vitro against alpha- and beta-coronaviruses, including animal coronavirus WIV-1 and PDF-2180. Two selected mAbs also neutralize Omicron BA.1 and BA.2 authentic viruses and reduce viral burden and pathology in vivo. Structural and functional analyses show that the fusion peptide-specific mAbs bind with different modalities to a cryptic epitope, which is hidden in prefusion stabilized S, and becomes exposed upon binding of angiotensin-converting enzyme 2 (ACE2) or ACE2-mimicking mAbs.