4. SARS-CoV-2 SApNP vaccines induce long-term lymph node follicle retention.(A, B) S2GHR2-presenting I3C01v9 SApNP vaccine distribution in a lymph node 12 h after (A) a single-dose or (B) prime-boost footpad injections (10 g/footpad, 40 g/mouse). neutralizing antibody (NAb) responses against emerging variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are essential for combating the coronavirus disease 2019 (COVID-19) pandemic. We demonstrated that mouse plasma induced by self-assembling protein nanoparticles (SApNPs) that present 20 rationally designed S2GHR2 spikes of the ancestral Wuhan-Hu-1 strain can neutralize the B.1.1.7, B.1.351, P.1, and B.1.617 variants with the same potency. The adjuvant effect on vaccine-induced immunity was investigated by testing 16 formulations for the multilayered I3C01v9 SApNP. Using single-cell sorting, Febantel monoclonal antibodies (mAbs) with diverse neutralization breadth and potency were isolated from mice immunized with the receptor binding domain (RBD), S2GHR2 spike, and SApNP vaccines. The mechanism of vaccine-induced immunity was examined in mice. Compared with the soluble spike, the I3C01v9 SApNP showed 6-fold longer retention, 4-fold greater presentation on follicular dendritic cell dendrites, and 5-fold stronger germinal center reactions in lymph node follicles. Keywords: Ancestral strain, broadly neutralizing antibody (bNAb), coronavirus disease 2019 (COVID-19), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), self-assembling protein nanoparticle (SApNP), vaccine, variant of concern (VOC) ONE-SENTENCE SUMMARY With a well-defined mechanism, spike nanoparticle vaccines can effectively counter SARS-CoV-2 variants. INTRODUCTION The COVID-19 Febantel pandemic has led to more than 188 million infection cases and 4 million deaths globally. Antibody responses to SARS-CoV-2 spike antigens can be sustained for several months in most COVID-19 patients after infection (1C4). However, recently identified variants of concern (VOCs) Rabbit Polyclonal to AKR1CL2 exhibit higher transmissibility and resistance to prior immunity as SARS-CoV-2 continues to adapt to the human host (5, 6). One such variant, B.1.1.7 (WHO classification: Alpha), emerged from southeast England in October 2020 and accounted for two-thirds of new infections in London in December 2020, with a higher transmission rate (43C90%) and risk of mortality (32C104%) than previously circulating strains (7, 8). Other variants, such as B.1.351 (Beta) and P.1 (Gamma), also became prevalent in three provinces in South Africa and Manaus, Brazil, respectively (6, 9, 10). The B.1.617.2 (Delta) variant, which was initially identified in India, is becoming a dominant strain in many countries (11, 12) and responsible for the majority of new COVID-19 cases. This variant was found to be ~60% more transmissible than the highly infectious B.1.1.7 variant (12). The rise of SARS-CoV-2 VOCs and their rapid spread worldwide result in more infection cases, hospitalizations, and potentially more deaths, further straining healthcare resources (10). To date, eight COVID-19 vaccines have been approved for emergency use in humans, with more than 90 candidates assessed in various phases of clinical trials (13). With the exception of inactivated whole-virion vaccines, diverse platforms have been used to deliver the recombinant SARS-CoV-2 spike, such as mRNA-encapsulating liposomes (e.g., BNT162b2 and mRNA-1273), adenovirus vectors (e.g., ChAdOx1 nCoV-19 [AZD1222], CTII-nCoV, Sputnik V, and Ad26.COV2.S), and micelle-attached spikes (e.g., NVX-CoV2373). These vaccines demonstrated 65C96% efficacy in Phase 3 trials, with lower morbidity and mortality associated with COVID-19 disease (14C19). However, a notable loss of vaccine efficacy against new SARS-CoV-2 variants was reported, likely caused by spike mutations in the receptor-binding domain (RBD; e.g., K417N, Febantel E484K, and N501Y), N-terminal domain (NTD; e.g., L18F, D80A, D215G, and 242C244), and other regions that are critical to spike stability and function (e.g., D614G and P681R) (6, 11, 20C25). Among circulating VOCs, the B.1.351 lineage appeared to be most resistant to neutralization by convalescent plasma (9.4-fold) and vaccine sera (10.3- to 12.4-fold) (26), whereas a lesser degree of reduction was observed for an early variant, B.1.1.7 (27C29). Based on these findings, it was suggested that vaccines would need to be updated periodically to maintain protection against rapidly evolving SARS-CoV-2 (30C32). However, in a recent study, convalescent sera from B.1.351 or P.1-infected individuals showed a more visible reduction of B.1.617.2 neutralization than convalescent sera from individuals infected with early pandemic strains (33). Together, these issues raise the concern that herd immunity may be difficult to achieve, highlighting the necessity of developing vaccines that can elicit a broadly neutralizing antibody (bNAb) response.