鼻内ブースターは粘膜IgA応答のためにクラススイッチとメモリーB細胞のホーミングを駆動する

Mucosal secretory IgA (sIgA) plays a central role in protecting against the invasion of respiratory pathogen via the upper respiratory tract. To understand how intranasal booster induces mucosal sIgA response in humans, we first used liquid chromatography-tandem mass spectrometry for peptide identification of immunoglobulin (MS Ig-Seq) and single-cell B-cell receptor sequencing (scBCR-seq) to identify mucosal spike-specific sIgA monoclonal antibodies (mAbs) after intranasal booster. These mucosal sIgA mAbs exhibited enhanced neutralization up to 100-fold against SARS-CoV-2 variants compared to their monomeric IgG and IgA isotypes. Deep sequencing and longitudinal analysis of B-cell receptor repertoires revealed that nasal booster re-stimulates memory B cells primed by intramuscularly vaccination to undergo IgA class switching, somatic hypermutation, and clonal expansion. Single-cell sequencing revealed that intranasal booster upregulated the expression of mucosal homing receptors in spike-specific IgA-expressing B cells. This increase coincided with a transient increase of cytokines and chemokines that facilitate B cell recruitment in the nasal mucosa. Our findings demonstrate that intranasal booster can be an effective strategy for inducing upper respiratory mucosal sIgA and establishing mucosal immune protection.