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 S1) 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).

Safety and immunogenicity of the Ad26.COV2.S COVID-19 vaccine candidate: interim results of a phase 1/2a, double-blind, randomized, placebo-controlled trial

“…Ad26.COV2.S is a recombinant, replication-incompetent Ad26 vector 12 encoding the full length and stabilized SARS-CoV-2 S protein 7 derived from the first clinical isolate of the Wuhan strain (Wuhan, 2019, whole genome sequence NC_045512). The study is performed at multiple clinical sites in Belgium and the United States.…”

“…This candidate was selected based on its immunogenicity and manufacturability profile. 7 The Ad26 vector is also used for our Ebola vaccine, and RSV, HIV and Zika vaccine candidates and Ad26-based vaccines are generally well tolerated and highly immunogenic. 10…”

Induced pluripotent stem cell-based disease modeling and prospective immune therapy for coronavirus disease 2019

“…Vaccines against chickenpox are being made using MRC5, a human fibroblast cell line [91]. The human embryonic kidney (HEK)-293, a cell line generated from aborted foetus in the 1970s is the cell substrate of choice for many COVID-19 vaccines manufactures [93,94]. The immortalized HEK cells are harnessed for making the spike proteins of SARS-COV-2 [95] or for cultivating the recombinant packaging viruses needed towards vaccine manufacturing [96].…”

Key Considerations for the Development of Safe and Effective SARS‐CoV‐2 Subunit Vaccine: A Peptide‐Based Vaccine Alternative

“…[137,138] A correlation (R = −0.69) between neutralizing anti-RBD Ab titers and viral RNA titer reduction in bronchoalveolar lavage fluid was recently established in rhesus monkeys infected with SARS-2. [139,140] In convalescent patients, anti-RBD IgG titers were at the level of 10 5 , the titers levels correlated (R = 0.64) with 50% neutralization capacity of sera, which were 50% neutralizing in outpatients from as low as about 40-fold dilutions. [141] This substantiates the major contribution and protective potential of humoral immunity though Ab neutralization mechanism.…”