First Report of a Phase 1 Randomised Trial of Molecular Clamp-Stabilised Spike Protein-Based and MF59-Adjuvanted Vaccine for SARS-CoV-2 (preprint)

Background: We assessed the safety and immunogenicity of an MF59-adjuvanted subunit vaccine for COVID-19 based on recombinant SARS-CoV-2 spike glycoprotein stabilised in a prefusion conformation by a novel molecular clamp (Sclamp).Methods: Phase 1, double-blind, placebo-controlled trial conducted in Australia (July 2020–ongoing; ClinicalTrials.gov NCT04495933). Healthy adults (18-55 years) received two doses of placebo, 5-μg, 15-μg, or 45-μg SARS-CoV-2 Sclamp, or one 45-μg dose of SARS-CoV-2 Sclamp followed by placebo, 28 days apart (n=120; 24 per group). Safety, humoral immunogenicity (ELISA, microneutralisation, pseudovirus neutralisation), and cellular immunogenicity (antigen-specific CD4+/CD8+ T-cells, antibody-secreting cells) were assessed up to 56 days after the first dose.Findings: The SARS-CoV-2 Sclamp vaccine was very well tolerated with few systemic reactions. All two-dose regimens elicited robust, broadly neutralising humoral responses. Geometric mean titres were higher than in sera from convalescent COVID-19 patients and strongly neutralised spike variants of concern, including N501Y. Moreover, humoral and cellular responses were highly correlated. However, antibodies elicited to a peptide sequence used in the molecular clamp derived from human immunodeficiency virus-1 (HIV-1) gp41 cross-reacted weakly with some HIV diagnostic screening tests.Interpretation: These first-in-human results demonstrate that a subunit vaccine comprising mammalian cell culture-derived, molecular clamp-stabilised recombinant spike protein formulated in a squalene-in-oil adjuvant elicits strong immune responses with an excellent safety profile. However, the gp41 peptide induced diagnostic interference, creates a likely barrier to widespread use and highlights the criticality of potential off-target immunogenicity during vaccine development. Studies are ongoing with alternative molecular clamp trimerisation domains to ameliorate this response.Clinical Trial Registration: ClinicalTrials.gov (NCT04495933).Funding: Coalition for Epidemic Preparedness Innovations; National Health and Medical Research Council, Queensland Government, and philanthropic sources.Declaration of Interests: KJC and DW report grants from the Coalition for Epidemic Preparedness Innovations, the National Health and Medical Research Council of Australia, and the Queensland Government, during the conduct of the study; other from ViceBio Limited, outside the submitted work; and has patents pending (AU 2018241252; BR112019019813.0; CA 3057171; CH 201880022016.9; EP 18775234.0; IN 201917038666; ID P00201909145; IL 269534; JP 2019-553883; MX/a/2019/011599; NZ 757178; KR 0-2019-7031415; SG 11201908280S; US 16/498865). JB reports personal fees from CSL Limited, during the conduct of the study, and other from CSL Limited, outside the submitted work. WZ reports grants from the National Health and Medical Research Council of Australia, the Research Grants Council of the Hong Kong Special Administrative Region, China, and the Jack Ma Foundation, during the conduct of the study. SM-H reports grants from Canarian Foundation Doctor Manuel Morales, during the conduct of the study. KJS reports grants from the the Australian Medical Research Future Fund, during the conduct of the study. AWC reports grants from the Australian Medical Research Future Fund and a National Health and Medical Research Council of Australia Career Development Fellowship, during the conduct of the study. BDW reports grants from the National Health and Medical Research Council of Australia, the Australian Medical Research Future Fund, and the Victorian State Government, during the conduct of the study. PMH reports grants from the Australian Medical Research Future Fund, during the conduct of the study. DP reports grants from the National Health and Medical Research Council of Australia, the A2 Milk Foundation, and the Jack Ma Foundation, during the conduct of the study. CR reports grants from the Coalition for Epidemic Preparedness Innovations, during the conduct of the study. PRY reports grants from the Coalition for Epidemic Preparedness Innovations, the National Health and Medical Research Council of Australia, and the Queensland Government, during the conduct of the study; grants from ViceBio Limited, outside the submitted work; and a patent issued (US 2020/0040042). FLM, Zl, DKW, PE, JAL, STMC, NM, SA, CLH, KH, PG, LH, THON, MHT, PT, JB, PCR, SN, SC, TH, KK, KS, and TPM have nothing to disclose.Ethics Approval Statement: The protocol was approved by the Alfred Health Human Research Ethics Committee (2020001376/334/20).

Rapid Application of the Molecular Clamp Platform for SARS-CoV-2 (preprint)

Efforts to develop and deploy effective vaccines against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) continue at pace. Here we describe rational antigen design through to manufacturability and vaccine efficacy, of a prefusion-stabilised Spike (S) protein, Sclamp. This strategy uses an orthogonal stabilisation approach compared to canonical vaccines, in combination with the licensed adjuvant MF59 (Seqirus). In mice, the Sclamp vaccine elicits high levels of neutralising antibodies, as well as broadly reactive and polyfunctional S-specific CD4+ and cytotoxic CD8+ T cells in vivo. In the Syrian hamster challenge model (n = 70), vaccination results in reduced viral load within the lung, protection from pulmonary disease, and decreased viral shedding in daily throat swabs which correlated strongly with the neutralising antibody level. The Sclamp vaccine candidate is currently completing Phase 1 clinical evaluation, in parallel with large-scale commercial manufacture for pivotal efficacy trials and potential widespread distribution.Funding: This work was funded by CEPI.Conflict of Interest: K.J.C., D.W. and P.R.Y. are inventors of the “Molecular Clamp” patent, US 2020/0040042.

Molecular clamp stabilised Spike protein for protection against SARS-CoV-2 (preprint)

Efforts to develop and deploy effective vaccines against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) continue at pace with more than 30 candidate vaccines now in clinical evaluation. Here we describe the preclinical development of an adjuvanted, prefusion-stabilised Spike (S) protein “Sclamp” subunit vaccine, from rational antigen design through to assessing manufacturability and vaccine efficacy. In mice, the vaccine candidate elicits high levels of neutralising antibodies to epitopes both within and outside the receptor binding domain (RBD) of S, as well as broadly reactive and polyfunctional S-specific CD4+ and cytotoxic CD8+ T cells. We also show protection in Syrian hamsters, which has emerged as a robust animal model for pulmonary SARS-CoV-2 infection. No evidence of vaccine enhanced disease was observed in animal challenge studies and pre-clinical safety was further demonstrated in a GLP toxicology study in rats. The Sclamp vaccine candidate is currently progressing rapidly through clinical evaluation in parallel with large-scale manufacture for pivotal efficacy trials and potential widespread distribution.