DNA priming and influenza vaccine immunogenicity: two phase 1 open label randomised clinical trials

Abstract

Background: Because the general population is largely naive to H5N1 influenza, antibodies generated to H5 allow analysis of novel influenza vaccines independent of background immunity from previous infection. We assessed the safety and immunogenicity of DNA encoding H5 as a priming vaccine to improve antibody responses to inactivated influenza vaccination.

Methods: In VRC 306 and VRC 310, two sequentially enrolled phase 1, open-label, randomised clinical trials, healthy adults (age 18-60 years) were randomly assigned to receive intramuscular H5 DNA (4 mg) at day 0 or twice, at day 0 and week 4, followed by H5N1 monovalent inactivated vaccine (MIV; 90 μg) at 4 or 24 weeks, and compared with a two-dose regimen of H5N1 MIV with either a 4 or 24 week interval. Antibody responses were assessed by haemagglutination inhibition (HAI), ELISA, neutralisation (ID(80)), and immunoassays for stem-directed antibodies. T cell responses were assessed by intracellular cytokine staining. After enrolment, investigators and individuals were not masked to group assignment. VRC 306 and VRC 310 are registered with ClinicalTrials.gov, numbers NCT00776711 and NCT01086657, respectively.

Findings: In VRC 306, 60 individuals were randomly assigned to the four groups (15 in each) and 59 received the vaccinations. In VRC 310, of the 21 individuals enrolled, 20 received the vaccinations (nine received a two-dose regimen of H5N1 MIV and 11 received H5 DNA at day 0 followed by H5N1 MIV at week 24). H5 DNA priming was safe and enhanced H5-specific antibody titres following an H5N1 MIV boost, especially when the interval between DNA prime and MIV boost was extended to 24 weeks. In the two studies, DNA priming with a 24-week MIV boost interval induced protective HAI titres in 21 (81%) of 26 of individuals, with an increase in geometric mean titre (GMT) of more than four times that of individuals given the MIV-MIV regimen at 4 or 24 weeks (GMT 103-206 vs GMT 27-33). Additionally, neutralising antibodies directed to the conserved stem region of H5 were induced by this prime-boost regimen in several individuals. No vaccine-related serious adverse events were recorded.

Interpretation: DNA priming 24 weeks in advance of influenza vaccine boosting increased the magnitude of protective antibody responses (HAI) and in some cases induced haemagglutinin-stem-specific neutralising antibodies. A DNA-MIV vaccine regimen could enhance the efficacy of H5 or other influenza vaccines and shows that anti-stem antibodies can be elicited by vaccination in man.

Funding: National Institutes of Health.

Figure 1

Trial profile for VRC 306 (A) and VRC 310 (B)

Figure 2

Effect of prime boost immunisation on induction of homologous H5-specific antibodies HAI=haemagglutination inhibition assays. Mean titres with standard error of the mean are shown at 2–4 weeks after boost for groups 1–4 and A and B. VRC 306 group 1 received H5N1 MIV at day 0 and week 4. Group 2 received H5 DNA at day 0 followed by H5N1 MIV at week 4. Group 3 received H5 DNA at day 0 followed by H5N1 MIV at week 24. Group 4 received H5 DNA at day 0 and week 4 followed by H5N1 MIV at week 24 (A, B, C). VRC 310 group A received H5N1 MIV at day 0 and week 24 and group B received H5 DNA at day 0 followed by H5N1 MIV at week 24 (D, E, F): (A, D) HAI titres, (B, E) ELISA, and (C, F) neutralisation (ID₈₀).

Figure 3

Induction of stem-specific cross-neutralising antibodies after vaccination mAb=monoclonal antibody. WT=wild-type. (A) Three representative individuals are shown for neutralisation of A/Indonesia/05/2005 (H5N1). (B) Neutralisation of heterlogous virus, A/mallard/Pennsylvania/12180/1984 (1984 Penn H5N2), is shown for three representative individuals. (C) Neutralisation of heterologous virus, A/Hong Kong/1074/1999 (1999 HK H9N2), is shown for two representative individuals.

Figure 4

Analysis of the H5 HAI mean reciprocal antibody titre in relation to the boost interval (VRC 306 and VRC 310) Antibody titres are shown with standard error of the mean. Response at 2–4 weeks after boost is shown for every regimen across both trials. Individuals were dosed at 4-week (A) or 24-week (B) boost intervals. Reference line represents protective HAI titre (1:40).