Safety and Immunogenicity of an Anti-Zika Virus DNA Vaccine

Abstract

Background: Although Zika virus (ZIKV) infection is typically self-limiting, other associated complications such as congenital birth defects and the Guillain-Barré syndrome are well described. There are no approved vaccines against ZIKV infection.

Methods: In this phase 1, open-label clinical trial, we evaluated the safety and immunogenicity of a synthetic, consensus DNA vaccine (GLS-5700) encoding the ZIKV premembrane and envelope proteins in two groups of 20 participants each. The participants received either 1 mg or 2 mg of vaccine intradermally, with each injection followed by electroporation (the use of a pulsed electric field to introduce the DNA sequence into cells) at baseline, 4 weeks, and 12 weeks.

Results: The median age of the participants was 38 years, and 60% were women; 78% were White and 22% Black; in addition, 30% were Hispanic. At the interim analysis at 14 weeks (i.e., after the third dose of vaccine), no serious adverse events were reported. Local reactions at the vaccination site (e.g., injection-site pain, redness, swelling, and itching) occurred in approximately 50% of the participants. After the third dose of vaccine, binding antibodies (as measured on enzyme-linked immunosorbent assay) were detected in all the participants, with geometric mean titers of 1642 and 2871 in recipients of 1 mg and 2 mg of vaccine, respectively. Neutralizing antibodies developed in 62% of the samples on Vero-cell assay. On neuronal-cell assay, there was 90% inhibition of ZIKV infection in 70% of the serum samples and 50% inhibition in 95% of the samples. The intraperitoneal injection of postvaccination serum protected 103 of 112 IFNAR knockout mice (bred with deletion of genes encoding interferon-α and interferon-β receptors) (92%) that were challenged with a lethal dose of ZIKV-PR209 strain; none of the mice receiving baseline serum survived the challenge. Survival was independent of the neutralization titer.

Conclusions: In this phase 1, open-label clinical trial, a DNA vaccine elicited anti-ZIKV immune responses. Further studies are needed to better evaluate the safety and efficacy of the vaccine. (Funded by GeneOne Life Science and others; ZIKA-001 ClinicalTrials.gov number, NCT02809443.).

Figure 1. Screening, Enrollment, Vaccinations, and Follow-up

The 1 and 2 mg groups were enrolled sequentially according to a dose-escalation protocol. After the first 5 participants received the 1 mg dose, a safety committee reviewed the safety profile and agreed to continue with enrollment at 1 mg dose and proceed with 2 mg dose escalation enrollment. The rest of the participants were allocated to the 1 or 2 mg dose sequentially at each site. All available study data and samples were used for study analyses. All participants but 1 completed the study-injection regimen and 24 weeks of follow-up. One participant was lost to follow-up after the second dose of the vaccine.

Figure 2

Local and systemic elicited treatment-emergent adverse events related to the vaccine administration. Table S3 (in the Supplementary Appendix, available at NEJM.org) list includes all treatment-emergent events without regard to relationship to study drug administration.

Figure 3. Antibody response

A. Geometric mean (95% CI) binding antibody titers at weeks 0, 1, 4, 6, 12 and 14 in the 1 mg (red) and the 2 mg (blue) dose groups as measured by ELISA. The antibody responses were statistically different at week 6 (p=0.039) (2 weeks after the second vaccine administration). B. Geometric mean (95% CI) neutralizing antibody titers and proportion of participants (95% CI) with a neutralizing antibody response at each time point by standard 50% micro neutralization (MN50) assay methodology in Vero cells 18. C. Proportion and 95% CI of week 14 individual sera (1:25 dilution) that would produce a 50 and 90% inhibition of cell fluorescence quantified by two independent analyses in glioblastoma cells (U87MG).

Figure 3. Antibody response

A. Geometric mean (95% CI) binding antibody titers at weeks 0, 1, 4, 6, 12 and 14 in the 1 mg (red) and the 2 mg (blue) dose groups as measured by ELISA. The antibody responses were statistically different at week 6 (p=0.039) (2 weeks after the second vaccine administration). B. Geometric mean (95% CI) neutralizing antibody titers and proportion of participants (95% CI) with a neutralizing antibody response at each time point by standard 50% micro neutralization (MN50) assay methodology in Vero cells 18. C. Proportion and 95% CI of week 14 individual sera (1:25 dilution) that would produce a 50 and 90% inhibition of cell fluorescence quantified by two independent analyses in glioblastoma cells (U87MG).

Figure 4. Cellular response

Pre-immunization PBMCs were compared to PBMCs obtained at weeks 0, 4, 6 and 14 by ELISpot to detect IFN-γ-secreting cells in response to stimulation with ZIKV-prME peptides. The number of IFN-γ producing cells obtained per million PBMCs against three peptide pools encompassing the entire prME protein is shown. The values represent median and IQR responses in each group.

Figure 5. Protection of IFNAR^−/− mice following passive transfer of immune sera

Survival of IFNAR^−/− mice following passive transfer of participant’s immune sera. Week 14 sera from participants were administered intraperitoneally (0.1ml/mouse; 7 mice per participant) one hour before an intraperitoneal challenge with ZIKV (10⁵ PFUs/mouse of ZIKV PR209 strain). (A) Proportions of mice surviving at day 14 post challenge given either sera collected pre-vaccination (Week 0) lanes 1-9; or with sera collected post-vaccination (Week 14), lanes 10-25. Participants P4, P8, P25, P37 and P39 had binding antibody titers but no neutralizing titers at week 14 (* bolded in the X axis) (B) Kaplan-Meier curves of survival of mice included in the challenge study and injected with PBS, pre-vaccination (Week 0) sera, or post-vaccination (Week 14) sera. There were no differences between male and female mice.

Figure 5. Protection of IFNAR^−/− mice following passive transfer of immune sera

Survival of IFNAR^−/− mice following passive transfer of participant’s immune sera. Week 14 sera from participants were administered intraperitoneally (0.1ml/mouse; 7 mice per participant) one hour before an intraperitoneal challenge with ZIKV (10⁵ PFUs/mouse of ZIKV PR209 strain). (A) Proportions of mice surviving at day 14 post challenge given either sera collected pre-vaccination (Week 0) lanes 1-9; or with sera collected post-vaccination (Week 14), lanes 10-25. Participants P4, P8, P25, P37 and P39 had binding antibody titers but no neutralizing titers at week 14 (* bolded in the X axis) (B) Kaplan-Meier curves of survival of mice included in the challenge study and injected with PBS, pre-vaccination (Week 0) sera, or post-vaccination (Week 14) sera. There were no differences between male and female mice.