Understanding the underlying molecular mechanisms behind ADE of SARS-CoV-2 is critical for development of safe and effective therapies. Here, we report that two neutralizing mAbs, MW01 and MW05, could enhance the infection of SARS-CoV-2 pseudovirus on FcγRIIB-expressing B cells. X-ray crystal structure determination and S trimer-binding modeling showed that MW01 and MW05 could bind to RBDs in S trimer with both “up” and “down” states. While, the neutralizing mAb MW07, which has no ADE activity only binds to RBD in S trimer with “up” state. Monovalent MW01 and MW05 completely diminished the ADE activity compared with their bivalent counterparts. Moreover, both macropinocytosis and endocytosis are confirmed involving in ADE of SARS-CoV-2 pseudoviral infection. Blocking endosome transportation and lysosome acidification could inhibit the ADE activity mediated by MW05. Together, our results identified a novel ADE mechanism of SARS-CoV-2 pseudovirus in vitro, FcγRIIB-mediated uptake of SARS-CoV-2/mAb complex with bivalent interaction.

The spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mutated continuously and newly emerging variants escape from antibody-mediated neutralization raised great concern. S protein is heavily glycosylated and the glycosylation sites are relatively conserved, thus glycans on S protein surface could be a target for the development of anti-SARS-CoV-2 strategies against variants. Here, we collected 12 plant-derived lectins with different carbohydrate specificity and evaluated their anti-SARS-CoV-2 activity against mutant strains and epidemic variants using a pseudovirus-based neutralization assay. The Lens culinaris-derived lentil lectin which specifically bind to oligomannose-type glycans and GlcNAc at the non-reducing end terminus showed most potent and broad antiviral activity against a panel of mutant strains and variants, including the artificial mutants at N-/O-linked glycosylation site, natural existed amino acid mutants, as well as the epidemic variants B.1.1.7, B.1.351, and P.1. Lentil lectin also showed antiviral activity against SARS-CoV and MERS-CoV. We found lentil lectin could block the binding of ACE2 to S trimer and inhibit SARS-CoV-2 at the early steps of infection. Using structural information and determined N-glycan profile of S trimer, taking together with the carbohydrate specificity of lentil lectin, we provide a basis for the observed broad spectrum anti-SARS-CoV-2 activity. Lentil lectin showed weak haemagglutination activity at 1 mg/mL and no cytotoxicity activity, and no weight loss was found in single injection mouse experiment. This report provides the first evidence that lentil lectin strongly inhibit infection of SARS-COV-2 variants, which should provide valuable insights for developing future anti-SARS-CoV-2 strategies.

Trastuzumab deruxtecan (T-DXd) is a transformative HER2-targeting antibody–drug conjugate (ADC) for treating breast cancer. Unfortunately, T-DXd has also been implicated in causing fatal interstitial lung disease (ILD) in multiple clinical trials. A better understanding of the mechanistic basis of these ADC-induced adverse effects could enable development of strategies to prevent or treat T-DXd–related ILD. In this study, we determined that T-DXd–induced ILD represents an off-target adverse event rather than an on-target off-tumor adverse event. To further investigate this phenomenon, an immunocompetent murine model that recapitulates T-DXd–induced ILD events was developed, facilitating in-depth mechanistic studies. Single-cell RNA sequencing in this model implicated alveolar macrophages (AM) as the primary cell type impacted by T-DXd in the lung microenvironment. Intravital microscopy further revealed that AMs resident in perivascular niches directly engulfed blood-circulating T-DXd via Fc–FcγR engagement. This Fc–FcγR interaction with T-DXd triggered a phenotypic shift in AMs from an immunosuppressive to a pro-ILD state, characterized by inflammation and immune activation, mediated through the SPP1 pathways. Finally, mitigating nonspecific T-DXd uptake in the lung by preconditioning perivascular AMs with IgG1 or the parental antibody of T-DXd significantly reduced unintended ADC absorption. These findings elucidate a mechanism by which T-DXd ignites the lung immune microenvironment and underscore the importance of off-target endocytosis by innate immune cells in the development of ADC-related toxicities. Significance: Preconditioning the perivascular niche can prevent lung inflammation induced by antibody-drug conjugate phagocytosis by alveolar macrophages and subsequent SPP1high macrophage differentiation, providing a clinically viable strategy for mitigating interstitial lung disease.