ABSTRACT
Background: SARS-CoV-2 vaccines capable of inducing broad and cross-reactive humoral and T cell responses help to fight against emerging variants. In this study we compared the immunogenicity and efficacy of modified vaccinia Ankara (MVA) based SARS-CoV-2 vaccine expressing furin-cleavage site inactivated stabilized spike (SdFCS) and nucleocapsid (N) delivered via intramuscular (IM), buccal or sublingual (SL) routes in rhesus macaques (RMs). Methods: Three groups (n=5/group) of RMs were immunized with MVA/SdFCS-N vaccine on weeks 0 and 4, via IM, buccal, or SL route. An additional group (control) received non-recombinant MVA via IM. IM vaccinations were delivered using needle and SL and buccal vaccinations were delivered using a needle-free injection device. All RMs were challenged with B.1.617.2 strain (Delta) of SARS-CoV-2 at week 8 via intratracheal and intranasal routes simultaneously. Various humoral and cellular immune parameters were determined post vaccination and challenge. SARS-CoV-2 subgenomic RNA (sgRNA) was measured to monitor virus replication in the upper (nose) and lower (lung) respiratory tract. Results: IM vaccination induced strong RBD-specific IgG antibody in serum, nose, throat, lung, and rectum. The serum antibody showed strong live virus neutralizing activity against WA-1/2020 (median of 415) and B.1.617.2 strains (median of 317). Serum from IM vaccinated animals also demonstrated strong non-neutralizing effector functions such as ADCD, ADCP and ADNKA. In addition, IM vaccination induced strong CD4 and CD8 T cell response in the blood that was directed against both S and N. In contrast, the SL and buccal vaccination-induced antibody showed lower neutralization titer against WA-1/2020 (143 and 302, respectively), and showed 4.5-fold lower cross reactivity neutralization titer against B.1.617.2 compared to WA-1/2020. Following challenge with B.1.617.2, the IM group RMs showed superior protection with 3 of the 5 animals being negative in upper and lower respiratory airways at Day 2. In contrast, no significant protection was observed in the SL group. Vaccine induced neutralizing and non-neutralizing antibody effector functions showed direct association with protection. Conclusion: Our findings showed that IM vaccination with improved MVA-based SARS-CoV-2 vaccine elicits cross-reactive antibody and T cell responses and protect against heterologous SARS-CoV-2 Delta challenge in RMs. They also showed IM vaccinations are superior to oral vaccinations.
ABSTRACT
Background: SARS-CoV-2 vaccines have shown promising efficacy in human adult trials, but immunogenicity and efficacy studies in the pediatric population are lagging behind. Here we evaluated the immunogenicity of two prefusion stabilized Spike protein (S-2P) vaccine platforms in infant Rhesus Macaques (RM): an adjuvanted S-P2 subunit and mRNA vaccine. Methods: Infant RMs (2.5 months-old) were immunized intramuscularly at weeks (wks) 0 & 4 with 15 μg S-P2 adjuvanted with the toll-like receptor 7/8 agonist 3M-052 in stable emulsion (n=8), or 30 μg of S-P2 mRNA in lipid nanoparticles (mRNA-LNP, Moderna) (n=8). Blood was collected at wks 0, 4, 6, 8, & 14. Plasma (Spike[S]) and salivary (receptor binding domain [RBD]) IgG responses were measured by ELISA and epitope specificity by multiparameter bead array. Antibody function was assessed by an ACE2 blocking assay and neutralization by pseudovirus (PSVA) and whole virus neutralization assays, both with D614G. Flow cytometry was applied to measure S-specific memory B cells using fluorochrome-conjugated recombinant S, and S-specific IL-2, IL-17, TNF-α, or IFN-γ producing T cells after stimulation with overlapping peptides of full-length S. Results: No adverse effects were observed with either vaccine. Plasma S-specific IgG responses were induced by both vaccines at wk 4, increased after the second dose, and persisted through wk 14 (Fig 1A). All S regions were targeted by plasma IgG (Fig 1B), and RBD-specific IgG was also detected in saliva. Serum antibodies achieved >95% ACE2 blocking by wk 6 (1:10 dilution), remaining >90% at wk 14. Geometric mean ID50 titers of neutralizing antibodies in the PSVA exceeded 10[3] from wk 6 through wk 14 (Fig 1C) and strongly correlated with whole virion neutralization (p<0.0001). In the protein vaccine group, S-specific CD27+ memory B cells peaked at 3.1% (mean) of total memory B cells;and S-specific CD4+ T cell responses were dominated by IL-17 and IFN-γ Mean S-specific CD27+ B cells peaked at 0.9% total memory B cells in mRNA vaccinees and S-specific CD4+ T cells produced IL-2, IFN-γ, IL-17, or TNF-α. Conclusion: The S-2P-3M-052-SE and mRNA-LNP vaccines were well-tolerated and highly immunogenic in infant Rhesus Macaques, with persistent IgG binding and neutralization responses that are comparable to those reported for adult RMs and humans. Our results provide proof-of-concept that a pediatric SARS-CoV-2 vaccine could induce long term protection against SARS-CoV-2.