ABSTRACT
Background: Measles-Mumps-Rubella (MMR) is an effective live-virus vaccine against measles virus (MeV). However, use of MMR is limited by its inability to boost MeV immunity, lack of immunogenicity in infants, and contraindication in pregnant and immunocompromised persons. Methods: We evaluated a novel recombinant dimeric MeV hemagglutinin protein vaccine (rMeV) in a rhesus macaque model. Sixteen macaques were primed at day 0 and boosted at day 42 by experimental group: 1) MMR x2;2) rMeV x2;3) MMR prime/rMeV boost;4) control;n=4. Macaques were challenged intratracheally with Bilthoven strain wild type MeV 8 months later. Blood, bone marrow (BM), and lymph node (LN) samples were collected over 3–28 days after challenge. Replication-competent MeV was measured in peripheral blood mononuclear cells (PBMC), BM cells, and LN cells by infectious assay;MeV RNA in PBMC and BM cells was determined by quantitative reverse transcriptase polymerase chain reaction. Plasma was evaluated for MeV-specific IgG and plaque reduction neutralization titer (PRNT). Results: Six months after vaccination, mean PRNT was 2,432 in rMeV x2 (standard deviation (SD) 3,840), 3,584 in MMR-prime/rMeV boost (SD 3,072) and 5,120 in MMR x2 groups (SD 3,547). Upon infectious challenge, macaques who received any MeV-containing vaccine developed no clinical signs of measles and had no detectable infectious virus in PBMC, BM cells, or LN cells. All unvaccinated macaques had virus in PBMC that peaked at day 7 (mean 3,162 TCID50/mL, SD 4.1) and resolved by day 14 post challenge, and one macaque developed an extensive rash. Macaques who received any MeV-containing vaccine had no detectable MeV RNA in PBMC or BM cells, whereas all unvaccinated macaques had detectable MeV RNA that peaked at day 7 (1.6e5 copies, SD 10.5) in PBMC. In all experimental groups, MeV-specific IgG titers increased after MeV challenge. Conclusion: Macaques who received rMeV and/or MMR were protected from rash, viremia, and detection of MeV RNA in PBMC and BM cells, unlike unvaccinated macaques. These data suggest that rMeV vaccine generates protective immune responses against measles and may be a novel candidate for future measles vaccine strategies. Study of cellular responses after rMeV vaccination and MeV challenge is warranted. Disclosures: Jessica Rubens, MD, Mevox: Grant/Research Support Guillaume Stewart-Jones, PhD, Moderna: Inventor of SARS-CoV-2 vaccine sequences;Moderna: Stocks/Bonds Michael Watson, MD, MEVOX Ltd: Board Member;MEVOX Ltd: Ownership Interest;MEVOX Ltd: Stocks/Bonds Barney S. Graham, MD, PhD, BSG: BSG is an inventor on patents for the stabilization of the RSV F protein (WO2014160463A1, Prefusion RSV F proteins and their use).;National Institutes of Health: Inventor on patents for RSV vaccines;National Institutes of Health: inventor on patents for measles and other paramyxovirus vaccines Diane Griffin, MD PhD, Gilead: Grant/Research Support;GlaxoSmithKline: Advisor/Consultant;GreenLight Biosciences: Advisor/Consultant;Merck: Advisor/Consultant;MeVox: Grant/Research Support;Takeda Pharmaceuticals: Advisor/Consultant.
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.