Phase 1/2a Study of the Malaria Vaccine Candidate Apical Membrane Antigen-1 (AMA-1) Administered in Adjuvant System AS01B or AS02A

Contains fulltext : 79496.pdf (publisher's version ) (Open Access)BACKGROUND: This Phase 1/2a study evaluated the safety, immunogenicity, and efficacy of an experimental malaria vaccine comprised of the recombinant Plasmodium falciparum protein apical membrane antigen-1 (AMA-1) representing the 3D7 allele formulated with either the AS01B or AS02A Adjuvant Systems. METHODOLOGY/PRINCIPAL FINDINGS: After a preliminary safety evaluation of low dose AMA-1/AS01B (10 microg/0.5 mL) in 5 adults, 30 malaria-naive adults were randomly allocated to receive full dose (50 microg/0.5 mL) of AMA-1/AS01B (n = 15) or AMA-1/AS02A (n = 15), followed by a malaria challenge. All vaccinations were administered intramuscularly on a 0-, 1-, 2-month schedule. All volunteers experienced transient injection site erythema, swelling and pain. Two weeks post-third vaccination, anti-AMA-1 Geometric Mean Antibody Concentrations (GMCs) with 95% Confidence Intervals (CIs) were high: low dose AMA-1/AS01B 196 microg/mL (103-371 microg/mL), full dose AMA-1/AS01B 279 microg/mL (210-369 microg/mL) and full dose AMA-1/AS02A 216 microg/mL (169-276 microg/mL) with no significant difference among the 3 groups. The three vaccine formulations elicited equivalent functional antibody responses, as measured by growth inhibition assay (GIA), against homologous but not against heterologous (FVO) parasites as well as demonstrable interferon-gamma (IFN-gamma) responses. To assess efficacy, volunteers were challenged with P. falciparum-infected mosquitoes, and all became parasitemic, with no significant difference in the prepatent period by either light microscopy or quantitative polymerase chain reaction (qPCR). However, a small but significant reduction of parasitemia in the AMA-1/AS02A group was seen with a statistical model employing qPCR measurements. SIGNIFICANCE: All three vaccine formulations were found to be safe and highly immunogenic. These immune responses did not translate into significant vaccine efficacy in malaria-naive adults employing a primary sporozoite challenge model, but encouragingly, estimation of parasite growth rates from qPCR data may suggest a partial biological effect of the vaccine. Further evaluation of the immunogenicity and efficacy of the AMA-1/AS02A formulation is ongoing in a malaria-experienced pediatric population in Mali. TRIAL REGISTRATION: www.clinicaltrials.gov NCT00385047

Development of a cAdVax-Based Bivalent Ebola Virus Vaccine That Induces Immune Responses against both the Sudan and Zaire Species of Ebola Virus

Ebola virus (EBOV) causes a severe hemorrhagic fever for which there are currently no vaccines or effective treatments. While lethal human outbreaks have so far been restricted to sub-Saharan Africa, the potential exploitation of EBOV as a biological weapon cannot be ignored. Two species of EBOV, Sudan ebolavirus (SEBOV) and Zaire ebolavirus (ZEBOV), have been responsible for all of the deadly human outbreaks resulting from this virus. Therefore, it is important to develop a vaccine that can prevent infection by both lethal species. Here, we describe the bivalent cAdVaxE(GPs/z) vaccine, which includes the SEBOV glycoprotein (GP) and ZEBOV GP genes together in a single complex adenovirus-based vaccine (cAdVax) vector. Vaccination of mice with the bivalent cAdVaxE(GPs/z) vaccine led to efficient induction of EBOV-specific antibody and cell-mediated immune responses to both species of EBOV. In addition, the cAdVax technology demonstrated induction of a 100% protective immune response in mice, as all vaccinated C57BL/6 and BALB/c mice survived challenge with a lethal dose of ZEBOV (30,000 times the 50% lethal dose). This study demonstrates the potential efficacy of a bivalent EBOV vaccine based on a cAdVax vaccine vector design

Identification of Novel Pre-Erythrocytic Malaria Antigen Candidates for Combination Vaccines with Circumsporozoite Protein

<div><p>Malaria vaccine development has been hampered by the limited availability of antigens identified through conventional discovery approaches, and improvements are needed to enhance the efficacy of the leading vaccine candidate RTS,S that targets the circumsporozoite protein (CSP) of the infective sporozoite. Here we report a transcriptome-based approach to identify novel pre-erythrocytic vaccine antigens that could potentially be used in combination with CSP. We hypothesized that stage-specific upregulated genes would enrich for protective vaccine targets, and used tiling microarray to identify <i>P</i>. <i>falciparum</i> genes transcribed at higher levels during liver stage versus sporozoite or blood stages of development. We prepared DNA vaccines for 21 genes using the predicted orthologues in <i>P</i>. <i>yoelii</i> and <i>P</i>. <i>berghei</i> and tested their efficacy using different delivery methods against pre-erythrocytic malaria in rodent models. In our primary screen using <i>P</i>. <i>yoelii</i> in BALB/c mice, we found that 16 antigens significantly reduced liver stage parasite burden. In our confirmatory screen using <i>P</i>. <i>berghei</i> in C57Bl/6 mice, we confirmed 6 antigens that were protective in both models. Two antigens, when combined with CSP, provided significantly greater protection than CSP alone in both models. Based on the observations reported here, transcriptional patterns of <i>Plasmodium</i> genes can be useful in identifying novel pre-erythrocytic antigens that induce protective immunity alone or in combination with CSP.</p></div

Pre-erythrocytic antigens selected for vaccine evaluation.

<p>Pre-erythrocytic antigens selected for vaccine evaluation.</p

GG DNA immunization and reduction of LS parasite burden post-sporozoite challenge.

<p>(A) Experimental design for the immunization and challenge studies. Mice were immunized 3 times at 3 week intervals with VR1020 plasmid DNA carrying the <i>Pb</i> or <i>Py</i> antigen. Two weeks after the last boost mice were challenged with 10,000 <i>Pb</i> or 20,000 <i>Py</i> sporozoites intravenously and livers were harvested 40h post-challenge. *DNA dose is 5 μg (GG), 25 μg + 35 μg GM-CSF DNA (IM) or 20 μg (EP). (B) Meta-analyses of 7 independent immunization experiments and resulting LS parasite burden reduction in <i>Py</i> in BALB/c model by GG immunizations. (C) Meta-analyses of 10 independent immunization experiments and resulting LS parasite burden reduction in <i>Pb</i> in C57Bl/6 model induced by GG immunizations. Each circle represents one mouse. Green color indicates significant difference as compared to EV immunized groups tested in the same immunization studies (p<0.05). Red color indicates p>0.05 and therefore no significant difference in LS parasite burden reduction as compared to EV immunized group. Purple color indicates LS parasite burden reduction by CSP (positive control). A complete statistical analysis is provided in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0159449#pone.0159449.s010" target="_blank">S5 Table</a>.</p

Protein features and transcriptional profiles of selected candidate genes.

<p>Protein features and transcriptional profiles of selected candidate genes.</p

Gene expression profile of <i>Pf</i> genes and selection algorithm used for antigen selection.

<p>(A) Heat map of gene expression by tiling microarray. Red color represents the genes expressing above the 50^th percentile, while green color represents genes expressing below the 50^th. The heat map shows the expression profile of genes across SS, 24h and 48h axenically cultured LS, and BS parasites. (B) Venn diagram shows stage-specific expression of genes by tiling microarray. Color coding of Venn regions matches the color bar provided for the heat map in Panel A. (C) Selection of genes for vaccine evaluation in two rodent models. One hundred and thirty-one genes were selected from among the upregulated genes identified by tiling-microarray, and 124 were confirmed by qPCR to be transcribed at higher levels in LS versus SS and/or BS parasite samples. Twenty-one of these 124 genes were selected for further evaluation as vaccine candidates.</p

Expression of novel antigens by <i>Py</i> LS parasites.

<p>(A) Strategy for generation of myc-tagged <i>Py</i>PF3D7_1241500. (B) Immunofluorescence assay using <i>Py</i>17XNL grown 24h in HepG2-CD81 cells, showing expression of <i>Py</i>PF3D7_1241500 protein detected by Alexa-594 conjugated anti-myc antibody (red). UIS4 (green) was used as a PVM marker and DAPI to identify nuclei. Scale bar represents 10 μm.</p

Novel antigens combined with CSP provide greater protection than CSP alone.

<p>(A) Each C57Bl/6 mouse (circles) was immunized with a combination of <i>Py</i>CSP DNA (2.5 μg) with novel antigen DNA (2.5 μg) by GG, using the schedule described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0159449#pone.0159449.g002" target="_blank">Fig 2</a>. (B) Each BALB/c mouse (triangles) was immunized with a combination of <i>Pb</i>CSP DNA (10 μg) with novel antigen DNA (10 μg) by EP, using the same schedule used for the GG immunizations. Data were compared to the negative control group immunized with a combination of CSP and EV tested in the same immunization study. Significant reduction in LS parasite burden was determined by Kruskal-Wallis test followed by Mann-Whitney test and p<0.05 was considered as significant. Green box indicates p<0.05 and red box indicates p>0.05. A complete statistical analysis is provided in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0159449#pone.0159449.s011" target="_blank">S6 Table</a>.</p