Summary
background
Licensed vaccines against SARS-CoV-2 effectively protect against severe disease, but show incomplete protection against transmission of the virus. Mucosal vaccines that elicit immune responses in the upper respiratory tract are one strategy to protect against transmission.
methods
We administered Spike HexaPro trimer formulated in a cationic liposomal adjuvant as a parenteral (subcutaneous – sc) intranasal boost regimen to elicit airway mucosal immune responses and evaluated this in a Syrian hamster virus transmission model.
discoveries
Parenteral Primer: Intranasal boost elicited high-magnitude serum neutralizing antibody responses and IgA responses in the upper airways. The vaccine strategy protected against virus in the lower respiratory tract and lung pathology, but the virus could still be detected in the upper respiratory tract. Despite this, parenteral intranasal booster vaccine effectively protected against further transmission of SARS-CoV-2.
interpretation
This study suggests that primary parenteral mucosal augmentation is an effective strategy to protect against SARS-CoV-2 infection and highlights that protection against virus transmission can be obtained despite incomplete virus clearance from the upper respiratory tract. It should be noted that protection against advanced transmission was not compared with standard parenteral boost, which should be a focus for future studies.
financing
This work was principally supported by the European Union’s Horizon 2020 research and innovation program under grant agreement no. 101003653.
Introduction
Licensed vaccines for acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that are based on new technologies, including messenger RNA vaccines,1
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An mRNA vaccine against SARS-CoV-2 – preliminary report.2
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An Alphavirus-derived replicon RNA vaccine induces SARS-CoV-2 neutralizing antibody and T-cell responses in mice and nonhuman primates.3
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Safety and efficacy of the BNT162b2 Covid-19 mRNA vaccine. have proven to be very effective against severe COVID-19. However, a major limitation of these vaccines is that they are less effective at protecting against transmission of the virus than against disease. Parenteral vaccines primarily induce systemic IgG antibody responses, but respiratory viruses with pandemic potential, including coronaviruses, are primarily transmitted person-to-person through respiratory droplets and infect the upper respiratory tract, which is not effectively protected by the Circulating IgG.4 The human antibody response to influenza A virus infection and vaccination.,5
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SARS-CoV-2 reverse genetics reveals a variable infection gradient in the respiratory tract. Failure to elicit sterilizing immunity can lead to local viral replication in respiratory tissues and possible further transmission, allowing the development and spread of resistant variants. Mucosal vaccination is an established strategy for the induction of secretory IgA (sIgA) on mucosal surfaces that, by blocking the virus at the portal of entry, can prevent initial viral replication and thus provide immunity sterilizing Compared to monomeric IgG, sIgA is multimeric, providing greater avidity, and sIgA may therefore be better at neutralizing SARS-CoV-2 than IgG.6.
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IgA dominates the early neutralizing antibody response to SARS-CoV-2.,7
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Enhanced neutralization of SARS-CoV-2 by dimeric IgA. Intranasal (in) immunization also elicits local tissue-resident CD4 and CD8 T-cell (TRM) responses in the nose-associated lymphoid tissue (NALT).8
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Resident memory CD8(+) T cells in the upper respiratory tract prevent infection by pulmonary influenza virus.,9
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Vaccine-generated lung tissue-resident memory T cells provide heterosubtypic protection against influenza infection. For SARS-CoV-1, a vaccine induced respiratory CD4 T cells that recruited protective CD8 T cells to NALT through an IFN-γ-dependent mechanism.10
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Airway memory CD4(+) T cells mediate protective immunity against emerging respiratory coronaviruses. The Th17 cell subset has received particular focus in mucosal immune responses11
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Vaccine-induced Th17 cells become established as resident memory cells in the lung and promote local IgA responses. and Th17-produced IL-17A upregulates the polymeric immunoglobulin receptor (pIgR) to promote IgA secretory responses.12
Jaffar Z, Ferrini ME, Fau – Herritt LA, Herritt La Fau – Roberts K, Roberts K. Cutting edge: lung mucosal Th17-mediated responses induce polymeric Ig receptor expression by airway epithelium and raise secretory levels of IgA. (1550–6606 (electronic)).
13
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High-affinity IgA requires functional plasticity of TH17 cells.14
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Plasticity of Th17 cells in Peyer’s patches is responsible for the induction of T-cell-dependent IgA responses. A strategy to facilitate both systemic immunity and mucosal immune responses in the upper respiratory tract is through a parenteral first, in a booster regimen.11
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Vaccine-induced Th17 cells become established as resident memory cells in the lung and promote local IgA responses.,15
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Safety and immunogenicity of the chlamydial vaccine candidate CTH522 adjuvanted with CAF01 liposomes or aluminum hydroxide: a phase 1, randomized, double-blind, placebo-controlled, first-in-human trial.16
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Immunization of prim-pull with a CAF(R)01 liposome-adjuvanted CAF(R)01 spy-peptide and M-protein bivalent vaccine induces both mucosal and peripheral protection from covR/S Mutant Streptococcus pyogenes.17
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Protection against SARS-CoV-2 infection by a mucosal vaccine in rhesus macaques. We tested this strategy for SARS-CoV-2, using a cationic liposome-adjuvanted spike subunit vaccine (CAF®01). Parenteral priming immunization: on SARS-CoV-2 neutralizing antibody and anti-spike IgG responses induced in serum and IgA responses elicited in the upper respiratory tract. In a transmission model in which vaccinated contacts were co-housed with SARS-CoV-2-infected index hamsters, the parenteral prime mucosal boost strategy reduced virus titers in the upper respiratory tract and protected of the subsequent transmission. In general, a parenteral booster vaccine strategy can be an effective means of limiting the spread of the virus in the population.
methods
ethics
Animal studies were conducted in accordance with Directive 2010/63/EU of the European Community. The experiments were approved and performed in accordance with the government Animal Experimentation Inspection under licenses 2017-15-0201-01363 and 2020-15-0201-00554.
Antigens and adjuvants
Spike ectodomain stabilized by recombinant SARS-CoV-2 prefusion (S-2P18
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Cryo-EM structure of the 2019-nCoV spike in prefusion conformation. and HexaPro trimer19
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Structure-based design of prefusion-stabilized SARS-CoV-2 spikes.), and the RBD domain (RVQ-VNF) of the Wuhan-Hu-1 strain was produced by transient expression in free-style 293-F cells, as previously reported.20
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Beta RBD boost extends antibody-mediated protection against SARS-CoV-2 variants in animal models.21
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An alpaca nanobody neutralizes SARS-CoV-2 by blocking receptor interaction. CAF®01 (250 μg DDA/ 50 μg TDB) in 10 mM TRIS buffer with 2.2% glycerol (pH 7.0) was produced as previously described.22
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Characterization of cationic liposomes based on dimethyldioctadecylammonium and M. tuberculosis synthetic cord factor (trehalose 6,6′-dibehenate)—a novel adjuvant that induces both strong CMI and antibody responses.
Characterization of the formulations
A compatibility study of the Spike HexaPro trimer was performed in CAF®01 at room temperature. Formulations were visually analyzed for possible flocculation and then characterized for particle size and polydispersity index (PDI) by dynamic light scattering, using the photon correlation spectroscopy technique . Zeta potential was measured by laser-Doppler electrophoresis. For size measurements, samples were diluted 10-fold, while for zeta potential measurements, samples were diluted 100-fold in milli-Q water. Measurements were performed at 25 °C, using a Zetasizer Nano ZS (Malvern Instruments, Worcestershire, UK) with a 633 nm laser and 173° detection optics. Malvern Zetasizer v.8.01 software was used for analysis.
Animals
Female wild-type C57Bl/6 (C57BL/6JOlaHsd) mice, 7 to 9 weeks of age, were obtained from Envigo (The Netherlands). Nine-week-old male Syrian golden hamsters (Mesocricetus auratus) were obtained from Janvier. Both species were housed in the animal facilities of the Statens Serum Institut, Denmark during the studies and maintained in rooms with a controlled environment (20–23 °C; relative humidity 52 ± 10%; light cycle/ darkness of 12/12 h). Mice were randomly assigned to cages (type III polycarbonate cages (820 cm2)) with up to eight mice per cage and hamsters were housed in type IV polycarbonate cages (1820 cm2) with high lids (total approx. 30 cm high). ) with up to four animals/cage. A total of 28 mice and 51 hamsters were used for the studies. All animals were offered bedding and Aspen (Tapvei), Sizzelnest (Datesand) bricks and polycarbonate tunnels or houses. In addition, mice were offered DesRes paper houses (LBS) while hamsters had twisted paper rolls (“Diamond Twist” Envigo Teclad) hung from their cage lids. Sunflower seeds, corn kernels and peanuts or irradiated pieces…