Fig. 3

Priming of functional S-specific IgG antibodies in aged vs. HSC-transplanted hosts. Young (2–3 months) and old (22–24 months) mice (n = 4–5) (a, b), and DY-HSC and DO-HSC-recipient mice at 18 weeks post transplantation (n = 5–8) (c, d) were immunized subcutaneously twice (at day 0 and 22) with 1 µg recombinant S-antigen (Novaxovid). (a, c) Serum samples were collected 14 days after the second immunization and tested in a quantitative S-specific IgG ELISA (anti-S IgG ng/µl) as described in M&M and (b, d) in a vesicular stomatitis virus (VSV)-based SARS-CoV-2 S-carrying pseudovirus model to determine the neutralizing activity of vaccine-induced antibodies. The results are depicted as serum dilution factors that result in 50% pseudovirus neutralization (PVNT50). Dotted lines represent the detection limit of PVNT50 values (100). Data are derived from two independent experiments and presented as geometric mean±SD. Statistical significance between the groups were determined using the unpaired student’s t-test (p < 0.05*). ns, not significant. Mean values±SD are shown