Safety and Immunogenicity of Malaria Vectored Vaccines Given with Routine Expanded Program on Immunization Vaccines in Gambian Infants and Neonates: A Randomized Controlled Trial

Abstract

Background: Heterologous prime-boost vaccination with chimpanzee adenovirus 63 (ChAd63) and modified vaccinia virus Ankara (MVA) encoding multiple epitope string thrombospondin-related adhesion protein (ME-TRAP) has shown acceptable safety and promising immunogenicity in African adult and pediatric populations. If licensed, this vaccine could be given to infants receiving routine childhood immunizations. We therefore evaluated responses to ChAd63 MVA ME-TRAP when co-administered with routine Expanded Program on Immunization (EPI) vaccines.

Methods: We enrolled 65 Gambian infants and neonates, aged 16, 8, or 1 week at first vaccination and randomized them to receive either ME-TRAP and EPI vaccines or EPI vaccines only. Safety was assessed by the description of vaccine-related adverse events (AEs). Immunogenicity was evaluated using IFNγ enzyme-linked immunospot, whole-blood flow cytometry, and anti-TRAP IgG ELISA. Serology was performed to confirm all infants achieved protective titers to EPI vaccines.

Results: The vaccines were well tolerated in all age groups with no vaccine-related serious AEs. High-level TRAP-specific IgG and T cell responses were generated after boosting with MVA. CD8+ T cell responses, previously found to correlate with protection, were induced in all groups. Antibody responses to EPI vaccines were not altered significantly.

Conclusion: Malaria vectored prime-boost vaccines co-administered with routine childhood immunizations were well tolerated. Potent humoral and cellular immunity induced by ChAd63 MVA ME-TRAP did not reduce the immunogenicity of co-administered EPI vaccines, supporting further evaluation of this regimen in infant populations.

Clinical trial registration: The clinical trial was registered on http://Clinicaltrials.gov (NCT02083887) and the Pan-African Clinical Trials Registry (PACTR201402000749217).

Keywords: cellular immune response; clinical trials; cytokines; malaria; vaccines.

Figures

Figure 1

Flow of study design and volunteer enrollment. Seventy-two infants and neonates were screened for eligibility across the three age groups and 65 eligible infants were enrolled, randomized, vaccinated according to randomization list and followed up for 252 days. Of 24 infants screened in the 16-week-old group, mothers of 3 infants withdrew consent before enrollment while 1 infant was excluded due to markedly raised alanine transaminase. Among those randomized to the vaccine arm, one infant had fatal SAE that was non-related to the study vaccines and another was lost to follow-up due to relocation of mother, while only one infant did not complete the follow-up in the control arm. Twenty-two infants were screened for the 8-week-old cohort and all were eligible. Only the first 20 were randomized into 15 vaccine group and 5 controls. Similarly, 26 mother-newborn pairs were screened for the 1-week-old group. A mother withdrew consent before enrollment and the remaining 25 neonates were randomized into 15 vaccinees and 10 controls. All study infants in the 8- and 1-week-old groups completed the study follow-up. SAE, serious adverse event.

Figure 2

Ex vivo IFNγ enzyme-linked immunospot responses to multiple epitope string thrombospondin-related adhesion protein (ME-TRAP) pre- and post-vaccination with ChAd63 and MVA ME-TRAP in Gambian infants. (A–C) Scatter plots show individual responses to ME-TRAP in both vaccinees (in black) and controls (in white) of each age group. (A) 16-week-old; (B) 8-week-old; (C) 1-week-old infants. (D) Geometric mean ME-TRAP responses in each age group over period of follow-up. LLD, lower limit of detection of the assay. Increases in responses over the time course were analyzed using two-tailed Friedman test. Responses between individual time points were compared within each age group using two-tailed Wilcoxon analysis, *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001. Lines and numbers in blue denote geometric mean. Numbers shown in black represent the percentage of responders among the vaccinated infants for each time point.

Figure 3

Peak enzyme-linked immunospot (ELISpot) responses to multiple epitope string thrombospondin-related adhesion protein (ME-TRAP) at D63, 7 days post-MVA. (A) Peak responses from vaccinated infants expressed per million PBMC. (B) Lymphocyte counts per milliliter of blood at D63. (C) ELISpot responses expressed per ml of blood. LLD, lower limit of detection of the assay. Peak responses and cell counts were compared across groups using Kruskal–Wallis test with Dunn’s multiple comparison post-test, *p < 0.05. Lines and numbers indicate geometric mean.

Figure 4

T cells induced by vaccination with thrombospondin-related adhesion protein (TRAP) antigen from P. falciparum T9/96 strain are highly cross-reactive. Scatter plots show individual ex vivo IFNγ enzyme-linked immunospot responses to TRAP peptides from T9/96 and 3D7 strains, respectively. (A) Responses pre-vaccination. (B) Responses 3 weeks post-prime with ChAd63 multiple epitope string thrombospondin-related adhesion protein (ME-TRAP). (C,D) Responses at day 63 and day 168, 7 and 112 days post-boost with MVA ME-TRAP, respectively. Numbers indicate the percentage of positive responses for each age group at each time point for both parasite strains. LLD, lower limit of detection of the assay. Lines represent geometric mean.

Figure 5

CD4+ and CD8+ T cell contribution to total IFNγ response to thrombospondin-related adhesion protein (TRAP). Pie charts display the proportion of IFNγ produced by CD4+ (black) and CD8+ (gray) T cells as a fraction of the total IFNγ response to TRAP post-prime and post-boost vaccination. Here, any negative response was excluded from analysis.

Figure 6

Multifunctionality of peak CD4+ and CD8+ T cell responses to thrombospondin-related adhesion protein (TRAP) at day 63 (1 week post-boosting). Cytokine production from CD4+(A) and CD8+(B) T cells was analyzed using Boolean gating analysis. Pie charts illustrate the relative frequency of each combination of cytokines, indicated in the bar chart below, as a fraction of the total cytokine response. Bar charts show the absolute frequency of each subset in response to stimulation with TRAP peptides, compared between each age group. Bars show median responses in this case as geometric mean is not available in SPICE. Any response which was less than or equal to the background (unstimulated) response was replaced by lower limit of detection value in bar chart and excluded from pie charts.

Figure 7

Antibody responses to Expanded Program on Immunization (EPI) and multiple epitope string thrombospondin-related adhesion protein (ME-TRAP) vaccination. (A) IgG responses to vaccination with ChAd63 ME-TRAP (day 0) and MVA ME-TRAP (day 56). Scatter plots show peak responses post-prime (day 21) and post-boost (day 63). Group 1—16 weeks, group 2—8 weeks, and group 3—1 week old at first vaccination. All comparisons use Kruskal–Wallis with Dunn’s post-test, comparing responses at day 0 with post-vaccination responses for groups 1–3 combined. No significant differences between groups were observed at any time point. (B) Comparison of peak IgG responses with data from previous trials (14). Responses in all groups combined from the present study were compared to those from a study in the same population that received the same dose and vaccine regimen in the absence of EPI coadministration. (C,D) Responses to EPI vaccination at 24 weeks, 8 weeks after last primary EPI, among ME-TRAP vaccinees and controls for diphtheria, tetanus, pertussis, Haemophilus influenza B, Hepatitis B, and polio serotypes 1–3 (C) and pneumococcal immunization (PCV 13) by serotype (D). No significant differences between groups were observed (*p < 0.05, **p < 0.01, ****p < 0.001).