b Naive WT C57BL/6 mice ( em n /em ?=?5) were subcutaneously immunized, boosted and bled at the indicated time points. The poor antibody persistence after natural SARS-CoV-2 contamination raised issues about whether a vaccine could induce a long-lasting antibody response and whether a memory recall response would be induced upon reinfection.1,2 Currently, over 200 vaccine candidates have been documented, some of which have advanced to clinical trials with encouraging results. However, to the best of our knowledge, the extent of antibody persistence and long-term memory post vaccination is still unclear. Here, we report that a ferritin nanoparticle (NP)-based SARS-CoV-2 receptor-binding domain name (RBD) vaccine induced an efficient antibody response in mice that lasted for at least 7 months post immunization. A high number of memory B cells (MBCs) were managed and recalled significantly upon antigen challenge. The SpyTag/SpyCatcher technique-based click vaccine platform was developed in our laboratory and has been widely used.3C5 The same strategy was applied for Jujuboside A the construction of a ferritin NP-based SARS-CoV-2 RBD vaccine (Fig.?1a). Ferritin-NP-RBD was prepared as explained in the supplementary information (Supplemental Fig.?S1). Open in a separate windows Fig. 1 The ferritin-NP-RBD vaccine induces a persistent antibody response and long-term memory. a Schematic illustration of ferritin-NP-RBD vaccine construction. b Naive WT C57BL/6 mice ( em n /em ?=?5) were subcutaneously immunized, Jujuboside A boosted and bled at the indicated time points. c Anti-RBD responses were monitored and analyzed by ELISA. The reddish arrows indicate the immunization time points. d, e Live SARS-CoV-2 neutralization assay for sera collected from ferritin-NP-RBD- or RBD-SpyTag-immunized mice on day 35 or WT unimmunized mice. The inhibition (d) and MN50 titer (e) were calculated. f, g At 6 months after the first immunization, memory B cells in the peripheral blood were present (f) and statistically analyzed (g). Numbers adjacent to the layed out areas indicate the percentage Rabbit Polyclonal to Bax (phospho-Thr167) of each gate. Data are shown as the mean??SEM. h, i Live SARS-CoV-2 neutralization assay for sera collected from ferritin-NP-RBD- or RBD-SpyTag-immunized mice on day 217 and day 231 or WT unimmunized mice. The inhibition (h) and MN50 titer (i) were calculated To assess the immunogenicity of ferritin-NP-RBD, naive wild-type (WT) C57BL/6 mice were immunized with a ferritin-NP-RBD vaccine or equimolar RBD-SpyTag as a control in the presence of CpG-1826 adjuvant at days 0, 14, and 28 (Fig.?1b). The ferritin-NP-RBD vaccine induced an approximately 100-fold higher antibody level than soluble RBD-SpyTag at day 28 (Fig.?1c). After the third immunization, the control vaccine group reached antibody titers of ~105 on day 35, and the ferritin-NP-RBD group reached antibody titers of ~106 (Fig.?1c). Thus, the RBD conjugated to ferritin NPs elicited a dramatically enhanced RBD-specific antibody response. To test whether the antiserum induced by the ferritin-NP-RBD vaccine could provide protection against live SARS-CoV-2 in vitro, Vero cells were infected with live SARS-CoV-2 (C-Tan-nCoV strain 04) in the presence of day 35 sera from different immunization groups. The results showed that four out of five mice from your RBD-SpyTag group neutralized over 50% of the live computer virus at serum dilutions ranging from only 1 1:100 to 1 1:400, Jujuboside A with an average 50% microneutralization Jujuboside A (MN50) titer of 103.8/ml (Fig.?1d, e). Strikingly, all five mice from your ferritin-NP-RBD vaccine group experienced neutralizing effects at serum dilutions ranging from 1:1600 to 1 1:3200, with an average MN50 of 104.8/ml (Fig.?1d, e). These results confirm that the antiserum to the RBD elicited by the ferritin-NP-RBD vaccine can prevent in Jujuboside A vitro SARS-CoV-2 contamination much more effectively than antiserum elicited by the RBD-SpyTag vaccine. To determine the antibody persistence induced by the ferritin-NP-RBD vaccine in mice, we continued to monitor the antibody responses. The anti-RBD level at 5 months was comparable to that at day 35 (Fig.?1c). At 6 and 7 months, while the antibody endpoint titers of both groups gradually decreased, the ferritin-NP-RBD vaccine group still managed significantly higher anti-RBD levels than the RBD-SpyTag control vaccine group (Fig.?1c), confirming the benefit of ferritin NPs for.