Next-generation B cell ImmunoSpot™ assays permit in-depth assessment of the B cell response elicited by SARS-CoV-2 infection and/or COVID-19 mRNA vaccination

The affinity distribution of antigen-specific Bmem in the body is a critical variable that defines an individual’s ability to rapidly generate protective antibody specificities. Moreover, defining the Ig class/subclass usage of such antigen-specific Bmem is also critical since it forecasts the anamnestic response to be engaged upon antigen re-encounter. Here, we leveraged multiplexed ImmunoSpot to comprehensively define the magnitude and Ig class/subclass usage of the SARS-CoV-2 S-specific Bmem following infection and/or multiple COVID-19 mRNA vaccinations. Beyond evidencing past SARS-CoV-2 infection more reliably than assessment of plasma IgG reactivity against the nucleocapsid protein, direct assessment of Bmem provided insights into their affinity distribution and cross-reactivity profiles against emerging variants such as Delta and Omicron. Following stimulation of PBMC to transition resting Bmem into antibody-secreting cells, our studies entailed tracking of the S-specific Bmem compartment in subjects as their immune histories became increasingly more complex. Of note, our next-generation ImmunoSpot assay approaches evidenced improved functional affinity at single-cell resolution. Collectively, such B cell ImmunoSpot assays offer tremendous value for future B cell immune monitoring efforts owing to their ease of implementation, applicability to essentially any antigenic system, economy of PBMC utilization and suitability for regulated testing.