Presence of SARS-CoV-2 S-protein specific BMEMORYcells in convalescent COVID-19 patients
Unlabelled SARS-CoV-2 S-protein in class-switched
BMEMORY cells could significantly block binding in
COVID-19 patients, but not healthy donor samples (Figure 2b, Figure 3c).
SARS-CoV-2 specific BMEMORY cells correlated moderately
with anti-S-protein IgG antibodies (Figure 3b). Overall, the frequency
of S-protein specific BMEMORY cells was significantly
higher in the COVID-19 disease cohort compared to healthy individuals
(Figure 3c). The difference between COVID-19 patients and healthy
individuals was restricted to BMEMORY cells and was not
observed for other B cell subsets such as naïve or unswitched
BMEMORY cells (Figure 3d-f). This has two important
implications: First, it demonstrates the specificity of the protocol for
the detection of SARS-CoV-2 specific BMEMORY cells,
since it is expected that only COVID-19 convalescent, but not unexposed
individuals generate SARS‑CoV-2 specific B cell memory. Second, it
demonstrates that the humoral immune response in the analysed patient
cohort could be mediated by long-lived memory B cells. We did not
observe substantial amounts of SARS-CoV-2 specific plasmablasts (Figure
3e).
The longevity of B cell memory can also be demonstrated by analysing the
frequency of SARS-CoV-2 specific BMEMORY cells
concerning the time of sample collection after COVID-19 diagnosis (Fig.
3g). While there was a tendency of lower frequencies in samples
collected at later time points, SARS-CoV-2 specific
BMEMORY cells remained detectable also 6 months after
COVID-19 diagnosis.