AH is a named inventor on the following patent applications on malaria vectored vaccines and immunization regimes (WO2008/122769, Adenoviral vector encoding malaria antigen; and WO 2008/122811 Novel adenovirus vectors). Authors from Okairòs are employees of and/or shareholders in Okairòs, which is developing vectored vaccines for malaria and other diseases. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials.
Project management: PS JM NV RR KG AL EI. Conceived and designed the experiments: CO MGK SS CD JM EI PB KF KE R. Chilengi AH KB. Performed the experiments: CO MGK DK YJ CB KC AS JO EK. Analyzed the data: CO MGK DK YJ SS CB KC NA AS PB BU KF KE KB EK. Contributed reagents/materials/analysis tools: EB SM SG SC R. Cortese AN. Wrote the paper: CO MGK SS AH.
Heterologous prime boost immunization with chimpanzee adenovirus 63 (ChAd63) and Modified vaccinia Virus Ankara (MVA) vectored vaccines is a strategy recently shown to be capable of inducing strong cell mediated responses against several antigens from the malaria parasite. ChAd63-MVA expressing the
We conducted two Phase Ib dose escalation clinical trials assessing the safety and immunogenicity of ChAd63-MVA ME-TRAP in 46 healthy malaria exposed adults in two African countries with similar malaria transmission patterns.
ChAd63-MVA ME-TRAP was shown to be safe and immunogenic, inducing high-level T cell responses (median >1300 SFU/million PBMC).
ChAd63-MVA ME-TRAP is a safe and highly immunogenic vaccine regimen in adults with prior exposure to malaria. Further clinical trials to assess safety and immunogenicity in children and infants and protective efficacy in the field are now warranted.
Pactr.org PACTR2010020001771828
Pactr.org PACTR201008000221638
ClinicalTrials.gov NCT01373879
ClinicalTrials.gov NCT01379430
Malaria caused by
Analysis of the immunological correlates of immunity induced by the RTS,S vaccine in both phase IIa sporozoite challenge studies
Increasing data from animal models, fieldwork and inoculation of volunteers with irradiated sporozoites support an important role for CD8+ T cells in mediating pre-erythrocytic immunity, even in the absence of antibodies
The Jenner Institute has been working to develop a T cell inducing pre-erythrocytic
Multiple vectors for this antigen have been clinically tested including DNA, fowl pox (FP) and the orthopox virus modified vaccinia virus Ankara (MVA)
Most recently, heterologous prime boost immunization with chimpanzee adenovirus 63 (ChAd63) followed by MVA, both expressing ME-TRAP, has been shown to be the most immunogenic vaccine regimen to date, inducing more than 2000 IFNγ producing T cells post MVA boost in malaria naïve volunteers
The safety, immunogenicity and efficacy of malaria vaccines may be affected by the intensity and pattern of local malaria transmission which determine pre-existing natural immunity to malaria and the potential natural ‘boosting’ of the vaccine induced immune responses
The protocols for these trials and supporting CONSORT checklist are available as supporting information; see
The objective of the studies was to assess the safety and immunogenicity of ChAd63 ME-TRAP and MVA ME-TRAP administered in a heterologous prime boost regimen to healthy malaria-exposed adults.
The first trial (Trial A) was conducted at the Medical Research Council (MRC) Unit field site located within Sukuta Health Centre in Kombo North district of The Gambia, West Africa. Sukuta village has an estimated population of 17,000 (2003 census). The climate is typical of sub-Saharan Africa with a long dry season lasting from December–June followed by a relatively short rainy season from July–November when the majority of
The second trial (Trial B) was conducted in Vipingo, Kilifi County, Kenya, East Africa. Participants were recruited from the Rea Vipingo Sisal Plantation Estates in Kilifi which has over 1000 employees and a land area of 3,950 hectares. In Kilifi, there are two seasons of high transmission of
Recent studies have reported a decline in malaria transmission in both sites
Healthy males aged 18–50 years were invited to participate in the studies. There was no selection of participants on the basis of pre-existing neutralizing antibodies (NAb) to the ChAd63 vector prior to enrolment. Volunteers were considered eligible if they were consenting adult males aged 18–50 years in good health who were likely to remain resident in the study area for the study duration. Exclusion criteria included any evidence of any acute or chronic illness or hematological, renal or hepatic pathology. Specific exclusion criteria included; prior receipt of an investigational malaria vaccine, recent or planned use of any investigational drug, vaccine, immunoglobulin or any blood product, confirmed or suspected immunodeficiency, history of surgical splenectomy, concurrent participation in another clinical trial or within 3 months of this study (see
We conducted two Phase Ib open-label, dose-escalation malaria vaccine trials (
Trial A = Phase Ib clinical trial in The Gambia, West Africa. Trial B = Phase Ib clinical trial in Kilifi, Kenya, East Africa. IM = intramuscular administration. ID = intradermal administration. In Trial A, 10 volunteers were excluded following screening for the following reasons: severe thrombocytopenia, severe proteinuria, spastic deformity of arm and withdrawal of consent (seven individuals). In Trial B, 14 volunteers were excluded following screening for the following reasons: hypertension (two individuals), positive serology for HIV (two individuals), positive Hepatitis B surface antigen (four individuals), participation in a previous malaria vaccine trial (2 individuals), peptic ulcer disease, allergic disease, recruitment complete (one participant).
In Trial A, eligible participants were allocated to receive either ChAd63 ME-TRAP 1×1010 viral particles (vp) (group 1; n = 6) or ChAd63 ME-TRAP 5×1010 vp (group 2; n = 10) administered intramuscularly in the deltoid. All participants were subsequently vaccinated in the opposite arm 56 days later with 2×108 plaque forming units (pfu) MVA ME-TRAP administered intramuscularly. The first participant in group 1 to receive ChAd63 ME-TRAP 1×1010 vp was vaccinated in isolation. 48 hours later, two further participants were enrolled in group 1. Prior to dose escalation of ChAd63 ME-TRAP from 1×1010 vp to 5×1010 vp, safety data from group 1 up to 14 days post ChAd63 ME-TRAP was reviewed by the DSMB. There was a protocol-required interval of at least 14 days between immunization of groups 1 and 2. Details of clinical follow-up and safety monitoring are given in
In Trial B, eligible participants were allocated to receive either ChAd63 ME-TRAP 1×1010 viral particles (vp) (group 1; n = 10) or ChAd63 ME-TRAP 5×1010 vp (group 2; n = 20) administered intramuscularly in the deltoid. All participants were subsequently vaccinated in the opposite arm 56 days later with 2×108 plaque forming units (pfu) MVA ME-TRAP. Participants in each group were randomised 1∶1 to receive MVA ME-TRAP administered intramuscularly (IM) or intradermally (ID). The first 3 participants in group 1 were vaccinated with ChAd63 ME-TRAP 1×1010 vp 7 days ahead of the remaining 7 participants in this group. There was an 8 day interval between enrolment of group 1 and group 2. Details of clinical follow-up and safety monitoring are given in
For both trials, a time window ranging between 1 and 28 days depending on the visit was allowed for vaccination and follow-up visits. Throughout the paper, study day refers to the nominal time point for a group and not the actual day of sampling.
30 participants were systematically allocated to receive either 1×1010 vp ChAd63 ME - TRAP or 5×1010 vp dose ChAd63 ME in a ratio of 1∶2. 8 weeks later participants were randomised 1∶1 to receive 2×108 pfu MVA ME-TRAP administered intramuscularly (IM) or intradermally (ID). The randomization sequence was generated by an independent statistician using STATA programme. Group allocations were kept in sealed opaque envelopes stored in a locked cabinet by the study coordinator who gave them to the research nurses on day of vaccination. Participants and clinical study staff were un-blinded to group allocation, however, field workers were blinded to group allocation.
These were observational and descriptive studies to assess the safety and immunogenicity of ChAd63 ME-TRAP and MVA ME-TRAP in malaria exposed adults. The sample sizes were chosen to allow estimation of the magnitude of the primary outcome measures, especially of serious adverse events (AEs) rather than assessment of statistically significant differences between groups.
The clinical trial protocols and associated documents were approved by Gambia Government/MRC Joint Ethics Committee for Trial A and The Kenya Medical Research Institute National Ethics Review Committee for Trial B. Documents for both clinical trials were reviewed and approved by the Oxford Tropical Research Ethics Committee (OXTREC). Regulatory approval was given by the Medicines Board of The Gambia for Trial A and The Pharmacy and Poisons Board of Kenya for Trial B. All participants gave documented informed consent prior to any study procedure being undertaken. The study was conducted according to the principles of the Declaration of Helsinki (2008) and the International Conference on Harmonization (ICH) Good Clinical Practice (GCP) guidelines. An independent DSMB and local safety monitors provided safety oversight and GCP compliance was independently monitored by an external organization at both trial sites (Appledown Clinical Research Ltd, Great Missenden, UK).
Generation of the recombinant vectors has been previously described
The antigen ME-TRAP contains a fusion protein of multiple epitopes (ME) and the
In each trial participants were observed for 1 hour post each immunization. Following each immunization participants in both trials were reviewed at home by a trained field worker and findings recorded on standardised case report forms. Local and systemic vaccine reactogenicity was evaluated and graded for severity, outcome and association to vaccination as per the criteria outlined in
Grade | Diameter (mm) |
0 | 0 |
1 | <50 |
2 | 50–100 |
3 | >100 |
Grade | Diameter (mm) |
0 | 0 |
1 | <20 |
2 | 20–50 |
3 | >50 |
Grade | Description |
0 | No pain at all |
1 | Painful to touch, no restriction in movement of arms, able to work, drive, carry heavy objects as normal |
2 | Painful when limb is moved ( |
3 | Severe pain at rest ( |
Scale | Description | Definition |
0 | Absence of the indicated symptom | |
1 | Mild | Awareness of a symptom but the symptom is easily tolerated |
2 | Moderate | Discomfort enough to cause interference with usual activity |
3 | Severe | Incapacitating; unable to perform usual activities; requires absenteeism or bed rest |
|
|
No temporal relationship to study product |
|
|
Reasonable temporal relationship to study product; |
|
|
Reasonable temporal relationship to study product; |
|
|
Reasonable temporal relationship to study product; |
Blood samples were collected into lithium or sodium heparin-treated vacutainer blood collection tubes (Becton Dickinson, UK). PBMC were isolated and used within 6 hours in fresh assays as previously described
Peptides were purchased from NEO Peptide (Cambridge, MA, USA). The peptides, 20 amino acids (aa) in length and overlapping by 10 aa covered the entire ME-TRAP insert present in the viral vectored vaccines. Peptides were also synthesised for the sequence of TRAP from the 3D7 strain. Peptides were reconstituted in 100% DMSO at 50–200 mg/mL and combined into various pools for ELISPOT and flow cytometry assays. Peptides are listed in
The kinetics and magnitude of the T cell response to ME-TRAP were assessed over time by
Data were analyzed using GraphPad Prism version 5.03 for Windows (GraphPad Software Inc., California, USA) and Stata 10.0 (Statacorp LP, Texas, USA). Geometric mean or median responses for each group are described. Significance testing of differences between two groups used the two-tailed Mann-Whitney U test or Wilcoxon signed rank test as appropriate. Correlations were analyzed using Spearman's rank correlation co-efficient (rs) for non-parametric data. Collated immunology data was analysed by multivariate linear regression using log-transformed ELISPOT results. A value of
Recruitment for Trial A took place in the Gambia between 19th May 2010 and 9th June 2010. Sixteen healthy male adult participants were enrolled, immunized and followed up (
Recruitment for Trial B took place in Kenya between 10th June 2010 and 7th July 2010. Thirty healthy male adult participants were enrolled, immunized and followed up (
No unexpected AEs or SAEs occurred and no volunteers were withdrawn due to AEs. AEs associated with ChAd63 ME-TRAP AEs were all mild in intensity (
Only the highest intensity of each AE per subject is listed. Data are combined for all AEs for all volunteers receiving the same vaccine at the stated dose. There were no immunization related serious AEs. IM = intramuscular.
Only the highest intensity of each AE per subject is listed. Data are combined for all AEs for all volunteers receiving the same vaccine at the stated dose. There were no immunization related serious AEs. IM = intramuscular. ID = Intradermal.
Heterologous prime boost with ChAd63-MVA ME-TRAP induced high frequencies of antigen-specific IFNγ-secreting T cells in both trials as measured by ex-vivo IFNγ ELISPOT. Peak IFNγ ELISPOT responses were detected 7 days post MVA ME-TRAP when a positive response (defined as responses above the lower limit of detection and at least double the response measured at Day 0) was detected in 90% and 100% of recipients in Trial A and Trial B respectively (
(
Trial Site | Kenya | Kenya | Kenya | Kenya | Gambia | Gambia | Oxford | Oxford | Oxford |
Route of Admin | IM | ID | IM | ID | IM | IM | ID | IM | ID |
|
|||||||||
Dose |
1×1010 | 1×1010 | 5×1010 | 5×1010 | 1×1010 | 5×1010 | 1×1010 | 5×1010 | 5×1010 |
(All IM) | |||||||||
Number Participants | 5 | 5 | 10 | 10 | 6 | 9 | 4 | 4 | 4 |
Median | 426 | 906 | 1334 | 1699 | 266 | 1558 | 2465 | 1410 | 1031 |
IQR | 208–945 | 529–1704 | 712–2382 | 1101–2410 | 129–909 | 333–2443 | 910–3138 | 932–1571 | 319–1707 |
Values are SFC per million PBMC for summated peptide pools spanning the length of the ME-TRAP insert tested in duplicate with response to negative (medium) control wells subtracted. IM = intramuscular administration. ID = intradermal administration. Vp = virus particles.
In Trial A there was no statistically significant difference in peak IFNγ ELISPOT response between individuals receiving 1×1010 vp ChAd63 ME-TRAP (median 266 SFC/106 PBMC, 95% CI -208, 1310) and individuals receiving 5×1010 vp ChAd63 ME-TRAP (1558 SFC/106 PBMC, 95% CI 550, 2179) (p = 0.11; Mann Whitney U, 2 tailed test). In contrast in Trial B, the median peak IFNγ ELISPOT response elicited in individuals receiving 5×1010 vp ChAd63 (1536 SFC/106 PBMC (95% CI 1230, 2355) was significantly greater than the peak response in individuals receiving 1×1010 vp ChAd63 ME-TRAP (590 SFC/106 PBMC, 95% CI 399, 1314, p = 0.011 2 tailed Mann Whitney test).
In Trial B there was no significant difference in peak immune response between volunteers receiving MVA administered intramuscularly or intradermally for either dose of ChAd63 ME-TRAP (ChAd63 ME-TRAP 1×1010 vp p = 0.22; ChAd63 ME-TRAP 5×1010 vp p = 0.62, 2-tailed Mann Whitney test) (
ELISPOT data was combined from both trials and analysed using a multivariate linear regression model. Data was stratified by dose of ChAd63 ME-TRAP and trial site. Only dose of ChAd63 ME-TRAP had a significant effect with a 2.3 (95% CI 1.4–3.8) fold increase in mean ELISPOT response in the individuals receiving 5×1010 vp. Of note, route of administration and trial site did not have significant effects on outcome (0.8× fold increase [95% CI 0.4–1.4], p = 0.4 for IM versus ID, 1.6×fold increase [95% CI 0.9–3.0], p = 0.1 for Kenya versus The Gambia).
In these two Phase Ib trials we have shown in healthy, malaria-exposed adult volunteers that a recombinant ChAd63-MVA heterologous prime-boost immunization regimen encoding ME-TRAP is safe as well as very immunogenic for T-cell induction. ChAd63 ME-TRAP demonstrated an excellent safety profile, inducing only a small number of AEs, all of which were mild in intensity. ChAd63 ME-TRAP had a similar reactogenicity profile in our malaria exposed population to that seen in UK volunteers who received comparable doses of ChAd63 ME-TRAP
The safety and immunogenicity of intradermally administered MVA ME-TRAP at doses of up to 1.5×108 pfu MVA ME-TRAP have previously been assessed in malaria exposed adults
In agreement with data from previous clinical studies of ChAd63 vectored vaccines,
Whilst a previous study of vectored malaria vaccines observed a reduction in T-cell immunogenicity in malaria exposed populations compared to UK volunteers
Concerns have been raised that pre-existing anti-vector immunity could limit the immunogenicity or compromise safety of adenoviral vectored vaccines in exposed populations
Chimpanzee adenoviruses were first used as a vaccine in humans in 2007
Future Phase Ib studies will now assess the safety and immunogenicity of ChAd63-MVA ME-TRAP in children and infants. If these data are favourable, field efficacy studies will be undertaken in infants to assess whether strong cellular immunity against ME-TRAP can translate into significant efficacy against naturally acquired
(PDF)
(PDF)
(PDF)
(DOC)
(PDF)
(PDF)
For Trial A we thank the Gambian National Malaria Control Programme and staff of Sukuta Health Centre for their collaboration; J. Adetifa and the Sukuta field team; E. Touray, S. Sanneh, M. Sambou and O. Badjie for field work; M. Cox, A. Drammeh and F. Darboe for laboratory assistance; O. Nyan for safety monitoring; J. Suso for clinical trial supports; M. Sowe and H. Kanyi for help with data management and C. McKenna for study monitoring. For Trial B we thank V. Mwatemo for clinical assistance, and E. Gitau for clinical trials support, REA Vipingo Plantations Ltd for use of their facilities; E. Pembe and A. Mbaru for field work; K Awuondo, S. Gambo, A. Bwika, R. Keya and other Clinical Trials Laboratory staff for laboratory assistance; M. Otieno for data management, E. Etyang for safety monitoring and C. McKenna for study monitoring. We thank the members of the Data Safety Monitoring Board and all the study volunteers in both trials. This study is published with the permission of the Director of the Kenyan Medical Research Institute.