Ad26 vector-based COVID-19 vaccine encoding a prefusion-stabilized SARS-CoV-2 Spike immunogen induces potent humoral and cellular immune responses

Abstract

Development of effective preventative interventions against SARS-CoV-2, the etiologic agent of COVID-19 is urgently needed. The viral surface spike (S) protein of SARS-CoV-2 is a key target for prophylactic measures as it is critical for the viral replication cycle and the primary target of neutralizing antibodies. We evaluated design elements previously shown for other coronavirus S protein-based vaccines to be successful, e.g., prefusion-stabilizing substitutions and heterologous signal peptides, for selection of a S-based SARS-CoV-2 vaccine candidate. In vitro characterization demonstrated that the introduction of stabilizing substitutions (i.e., furin cleavage site mutations and two consecutive prolines in the hinge region of S2) increased the ratio of neutralizing versus non-neutralizing antibody binding, suggestive for a prefusion conformation of the S protein. Furthermore, the wild-type signal peptide was best suited for the correct cleavage needed for a natively folded protein. These observations translated into superior immunogenicity in mice where the Ad26 vector encoding for a membrane-bound stabilized S protein with a wild-type signal peptide elicited potent neutralizing humoral immunity and cellular immunity that was polarized towards Th1 IFN-γ. This optimized Ad26 vector-based vaccine for SARS-CoV-2, termed Ad26.COV2.S, is currently being evaluated in a phase I clinical trial (ClinicalTrials.gov Identifier: NCT04436276).

A Single Immunization with Spike-Functionalized Ferritin Vaccines Elicits Neutralizing Antibody Responses against SARS-CoV-2 in Mice

“… 70 , 71 Some vaccine candidates against SARS-CoV were found to cause pulmonary immunopathology potentially due to Th2-type responses in small animal models, 74 − 77 and thus one focus for SARS-CoV-2 vaccine development has been to favor a Th1-type response. 72 , 73 A comparison of the ratio of IgG2a/IgG1 antibody titers among antigen groups demonstrated that, except for the RBD, the antigens exhibit a balanced IgG2a and IgG1 response, which was slightly skewed toward IgG2a for both the SΔC-Fer and S-GCN4 groups ( Figure S8A,B ). Notably, the RBD elicited a substantially higher IgG1 response as compared to both IgG2a and IgG2b, suggesting that this antigen in combination with Quil-A/MPLA caused a Th2-biased immune response ( Figure S8B,C ).…”

SARS-CoV-2: vaccines in the pandemic era

“…The induced cell response was Th1-biased rather than Th2-biased, which also demonstrating the safety of the vaccine. Immunogenicity and antigenicity tests in mice revealed that optimization of the S protein (with furin and two proline mutations) increased the proportion of neutralizing antibody binding to nonneutralizing antibody binding [ 41 ]. This study confirmed that optimization of the S protein improved the protective effect of the vaccine.…”

“… mRNA-1273 Moderna LNP-mRNA S-full length (pre-fusion) Mice [ 22 ] Monkeys [ 31 ] (Challenge: Yes) Phase 1 [ 27 ]: 45 18–55 0/28 25, 100, 250 μg 112, 343, 373 109 PRNT phase 1 [ 28 ]: 20 56–70 0/28 25, 100 μg 116, 402 106 20 > 71 25, 100 μg 121, 317 phase 3: NCT04470427 Viral vector vaccine Ad5-nCoV CanSino Ad5 S-full length Mice [ 38 ] (Challenge: Yes) Phase 1 [ 36 ]: 108 18–60 1 dose 5 × 10 10 , 1 × 10 11 , 1.5 × 10 11 vp 14.5, 16.2, 34 N.A. live virus neutralisation, pseudovirus neutralisation tests Phase 2 [ 37 ]: 508 18–60 1 dose 5 × 10 10 , 1 × 10 11 vp 18.3, 19.5 Phase 3: NCT04526990, NCT04540419 Ad26.COV2.S Janssen Ad26 S-full length (pre-fusion) Mice [ 41 ] Monkeys [ 40 ] (Challenge: Yes) Phase 1/2a [ 42 ]: 402 18–55 0/56 5 × 10 10 vp; 1 × 10 11 vp 214, 243 522 wild-type virus neutralization assay 394 …”

Immunogenicity and protective efficacy of one- and two-dose regimens of the Ad26.COV2.S COVID-19 vaccine candidate in adult and aged rhesus macaques

“…The full-length spike protein used for immunization (COR200099) (Bos et al, 2020) was produced on Expi293F cells. COR200099 is based on the Wuhan-Hu-1 SARS-CoV-2 strain (MN908947) and stabilized by two point mutations (R682A, R685G) in the S1/S2 junction that knocks out the furin cleavage site, and by two consecutive prolines (K986P, V987P) in the hinge region in S2.…”

“…Neutralization assays against live SARS-CoV-2 were performed using the microneutralization assay as previously described (Bos et al, 2020), with the modification of a different strain used.…”