Assessment of SARS-CoV-2 Spike and NCAP antigen-specific memory B cell frequency and Ig class/subclass usage following natural infection and/or COVID-19 mRNA vaccination

An adaptive humoral response can encompass multiple Ig classes/subclasses, each capable of contributing to host defense through different effector functions. Which Ig class/subclass are elicited in response to an antigen encounter is the consequence of context, such as site of antigen contact, presence of immunostimulatory motifs and the cytokine secretion signature of helper T cells. Moreover, the number of antigen encounters and duration of the ensuing immune responses can further diversify the memory B cell compartment’s epitope specificity, affinity and Ig class/subclass usage. Beyond characterization of Ig usage in blood, whether differences also exist in the Bmem compartment following multiple SARS-CoV-2 infections and/or COVID-19 vaccinations is still not well understood. Leveraging multiplexed B cell ImmunoSpot assays, the scope of this work is to characterize SARS-CoV-2 S- and N-specific Bmem and their respective Ig class/subclass usage in the context of complex immune exposure histories. In agreement with recent observations detailing the antibody response elicited following COVID-19 mRNA vaccination and/or breakthrough infection, alterations in the affinity, breadth and IgG subclass usage of S-specific Bmem was also observed. Collectively, our findings demonstrate the feasibility of performing in-depth characterization of Bmem in a streamlined pipeline that requires minimal cell material and serves to motivate usage of the multiplexed FluoroSpot platform.