Phase 1 randomized trial of a plant-derived virus-like particle vaccine for COVID-19

Abstract

Several severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines are being deployed, but the global need greatly exceeds the supply, and different formulations might be required for specific populations. Here we report Day 42 interim safety and immunogenicity data from an observer-blinded, dose escalation, randomized controlled study of a virus-like particle vaccine candidate produced in plants that displays the SARS-CoV-2 spike glycoprotein (CoVLP: NCT04450004 ). The co-primary outcomes were the short-term tolerability/safety and immunogenicity of CoVLP formulations assessed by neutralizing antibody (NAb) and cellular responses. Secondary outcomes in this ongoing study include safety and immunogenicity assessments up to 12 months after vaccination. Adults (18-55 years, n = 180) were randomized at two sites in Quebec, Canada, to receive two intramuscular doses of CoVLP (3.75 μg, 7.5 μg, and 15 μg) 21 d apart, alone or adjuvanted with AS03 or CpG1018. All formulations were well tolerated, and adverse events after vaccination were generally mild to moderate, transient and highest in the adjuvanted groups. There was no CoVLP dose effect on serum NAbs, but titers increased significantly with both adjuvants. After the second dose, NAbs in the CoVLP + AS03 groups were more than tenfold higher than titers in Coronavirus 2019 convalescent sera. Both spike protein-specific interferon-γ and interleukin-4 cellular responses were also induced. This pre-specified interim analysis supports further evaluation of the CoVLP vaccine candidate.

Fig. 1. Trial profile—participant disposition.

Enrollment and follow-up of study participants vaccinated with 3.75 µg, 7.5 µg or 15 µg CoVLP with or without AS03 or CpG1018 adjuvant after the first and second dose administration. One participant in the 3.75 µg + AS03 treatment group did not receive the second vaccination as per protocol owing to a grade 3 AE (fatigue) after the first dose but agreed to have blood collection for immunogenicity. One participant in the 15 µg + CpG1018 treatment group withdrew consent before the second vaccination and consequently did not have blood collection at Day 21 and Day 42. Both participants were excluded from the per-protocol set. For more details of participant disposition, see Table 1. PP, per-protocol.

Fig. 2. Solicited local and systemic AEs 7 d after the first or second vaccine dose.

Participants were monitored for solicited local (a) and systemic (b) AEs from the time of vaccination through 7 d after vaccine administration. There was no grade 4 (potentially life-threatening) event. Participants who reported no AEs make up the remainder of the 100% calculation (data not shown). If any of the solicited AEs persisted beyond Day 7 after each vaccination (when applicable), it was recorded as an unsolicited AE. Fever was defined as oral temperature ≥38.0 °C.

Fig. 3. Humoral response to CoVLP alone or with adjuvants.

Serum antibodies of participants vaccinated with 3.75 µg, 7.5 µg or 15 µg CoVLP with or without AS03 or CpG1018 adjuvant were measured to S protein by ELISA (a) and in neutralization assays based on a VSV pseudovirus (b) or live virus (c) and presented here as reciprocal titers. Inverted green triangles are used for unadjuvanted CoVLP groups; upright red triangles are used for the CoVLP + AS03 groups; and blue squares are used for the CoVLP + CpG1018 groups. Convalescent sera or plasma were collected at least 14 d after a positive diagnosis of COVID-19 (RT–PCR) from individuals whose illness was classified as mild, moderate or severe/critical (n = 35). These samples were analyzed in the anti-S ELISA and both neutralization assays; results (right panels). Horizontal bars and numbers in the figure indicate geometric means. Error bars indicate 95% CIs. Significant differences among Days 0 and 21 or Days 0 and 42 for each formulation are indicated by a hashtag (#P < 0.05, ##P < 0.01, ###P < 0.001, ####P < 0.0001; paired two-sided t-test of log-transformed values, GraphPad Prism v8.1.1). Significant differences between unadjuvanted and adjuvanted regimens for Days 21 and 42 are indicated by an asterisk (*P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001; two-way ANOVA of log-transformed values, GraphPad Prism v8.1.1). The PsVNA₅₀ is reciprocal of the serum dilution at which a decrease in luminescence ≥50% was observed in the PNA. The PRNT₅₀ is the reciprocal serum dilution at which ≥50% of the cells were free from infection in the MNA.

Fig. 4. Cellular immune response to CoVLP alone or with adjuvants.

Frequencies of S protein-specific production of IFN-γ (a) or IL-4 (b) at baseline (Day 0) and 21 d after the first (Day 21) or second (Day 42) vaccine dose with 3.75-µg, 7.5-µg or 15-µg doses of CoVLP with or without adjuvants (CpG1018 and AS03). PBMCs were stimulated ex vivo with a peptide pool covering the entire S protein (15-mers with 11-amino acid overlap). Bars and numbers in the figure indicate group medians, and error bars indicate 95% CI. The median pre-vaccination values in both assays across all groups was 0. Significant differences between Day 0 and Day 21 or between Day 0 and Day 42 for each vaccine regimen are indicated by a hashtag (^#P < 0.05, ^##P < 0.01, ^###P < 0.001, ^####P < 0.0001; unpaired two-sided t-test; the figure illustrates matched subject data, GraphPad Prism v8.1.1). Significant differences among adjuvanted vaccine and unadjuvanted vaccine regimens at Day 21 and Day 42 are indicated by an asterisk (*P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001; Kruskal–Wallis test, GraphPad Prism v8.1.1). SPC, spot-forming cell.