Single-dose replicating RNA vaccine induces neutralizing antibodies against SARS-CoV-2 in nonhuman primates

Abstract

1The ongoing COVID-19 pandemic, caused by infection with SARS-CoV-2, is having a dramatic and 2 deleterious impact on health services and the global economy. Grim public health statistics highlight the 3 need for vaccines that can rapidly confer protection after a single dose and be manufactured using 4 components suitable for scale-up and efficient distribution. In response, we have rapidly developed 5 repRNA-CoV2S, a stable and highly immunogenic vaccine candidate comprised of an RNA replicon 6 formulated with a novel Lipid InOrganic Nanoparticle (LION) designed to enhance vaccine stability, 7 delivery and immunogenicity. We show that intramuscular injection of LION/repRNA-CoV2S elicits 8 robust anti-SARS-CoV-2 spike protein IgG antibody isotypes indicative of a Type 1 T helper response as 9 well as potent T cell responses in mice. Importantly, a single-dose administration in nonhuman primates 10 elicited antibody responses that potently neutralized SARS-CoV-2. These data support further 11 development of LION/repRNA-CoV2S as a vaccine candidate for prophylactic protection from SARS-CoV-Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) first emerged in December 2019 14 and within 3 months, Coronavirus Disease 2019 (COVID-19), caused by SARS-CoV-2 infection, was 15 declared a worldwide pandemic 1-3 . Coronaviruses are enveloped, single-strand positive-sense RNA 16 viruses with a large genome and open reading frames for four major structural proteins: Spike (S), 17 envelope, membrane, and nucleocapsid. The S protein mediates binding of coronaviruses to angiotensin 18 converting enzyme 2 (ACE2) on the surface of various cell types including epithelial cells of 19 the pulmonary alveolus 4-6 . Protection is thought to be mediated by neutralizing antibodies against the S 20 protein 7,8 , as most of the experimental vaccines developed against the related SARS-CoV incorporated 21 the S protein, or its receptor binding domain (RBD), with the goal of inducing robust, neutralizing 22 responses 9-11 . Indeed, previous reports have shown that human neutralizing antibodies protected mice 23 challenged with SARS-CoV 12-14 and Middle East respiratory syndrome (MERS)-CoV 15 suggesting that 24 protection against SARS-CoV-2 can be mediated through anti-S antibodies. Additionally, SARS vaccines 25 that drive Type 2 T helper (Th2) responses have been associated with enhanced lung immunopathology 26 following challenge with SARS-CoV while those with a Type 1 T helper (Th1)-biased immune response 27 are associated with enhanced protection in the absence of immunopathology 16,17 . Therefore, an 28 effective COVID-19 vaccine will likely need to induce, at the very least, Th1-biased immune responses 29 comprised of SARS-CoV-2-specific neutralizing antibodies.30 Nucleic acid vaccines have emerged as ideal modalities for rapid vaccine design, requiring only 31 the target antigen's gene sequence and removing dependence on pathogen culture (inactivated or live 32 attenuated vaccines) or scaled recombinant protein production. In a...

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“…The single high dose gave NAb ID 50 titers in the range of 20 to 50 after 4 weeks, which increased to the 100 to 450 range at week 6. In the two-dose regimen, NAb titers in the two immunized animals were 220 and 360 at week 6, and NAbs were also detected at similar ID 80 (note, not ID 50 ) titers in an RV assay ( 100 ).…”

“…Another variant of the mRNA vaccine concept involves an RNA replicon expressing the full-length S-protein and formulated as a lipid nanoparticle ( 100 ). The immunogen was given once to mice at 3 different doses.…”

Animal and translational models of SARS-CoV-2 infection and COVID-19

“…A variety of protein, RNA and viral vaccines have been tested in mice and NHPs to induce anti-SARS-CoV-2 antibodies that are neutralizing against infection of human cell lines in vitro. [241][242][243] This provides a rapid screen for potential protective efficacy but these must be tested in challenge models. Recent studies with Chimpanzee adenovirus (ChAdOx1 nCoV-19) 153 and vesicular stomatitis virus (rVSV-ΔG) 244 vaccines expressing the S protein showed protection against SARS-CoV-2 lung disease and inhibited viral replication in NHP and golden hamsters, respectively.…”

Nanomedicine strategies to target coronavirus

“… SARS-CoV-2 Lipid-inorganic NPs composed of superparamagnetic iron oxide NPs within a hydrophobic squalene core RNA (encodes S protein) Pre-clinical Uni. Of Wash., [ 106 ] SARS-CoV-2 Unspecified lipid NP Non-replicating adenovirus type 5 (S protein) Early Stage CanSino Exosomes Vesicles released from cells upon fusion of multivesicular bodies with the plasma membrane. SARS-CoV Exosomes obtained from 293 T cells transfected with CoV S protein-expressing plasmid.…”