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

Why Functional Pre-Erythrocytic and Bloodstage Malaria Vaccines Fail: A Meta-Analysis of Fully Protective Immunizations and Novel Immunological Model

Background: Clinically protective malaria vaccines consistently fail to protect adults and children in endemic settings, and at best only partially protect infants. Methodology/Principal Findings: We identify and evaluate 1916 immunization studies between 1965-February 2010, and exclude partially or nonprotective results to find 177 completely protective immunization experiments. Detailed reexamination reveals an unexpectedly mundane basis for selective vaccine failure: live malaria parasites in the skin inhibit vaccine function. We next show published molecular and cellular data support a testable, novel model where parasite-host interactions in the skin induce malaria-specific regulatory T cells, and subvert early antigen-specific immunity to parasite-specific immunotolerance. This ensures infection and tolerance to reinfection. Exposure to Plasmodium-infected mosquito bites therefore systematically triggers immunosuppression of endemic vaccine-elicited responses. The extensive vaccine trial data solidly substantiate this model experimentally. Conclusions/Significance: We conclude skinstage-initiated immunosuppression, unassociated with bloodstage parasites, systematically blocks vaccine function in the field. Our model exposes novel molecular and procedural strategies to significantly and quickly increase protective efficacy in both pipeline and currently ineffective malaria vaccines, and forces fundamental reassessment of central precepts determining vaccine development. This has major implications fo

Major surface proteins and antigens on the different in vivo and in vitro forms of Trypanosoma cruzi.

The surface proteins of six stages of Trypanosoma cruzi were labeled by Iodogen-catalized surface iodination and analyzed by one and two dimensional polyacrylamide gel electrophoresis. These stages included bloodstream trypomastigotes, culture-form trypomastigotes, amastigotes, staphylomastigotes, epimastigotes, and metacyclic trypomastigotes. Antigens recognized by serum antibodies were detected by Western blotting against serum from mice hyperimmunized against bloodstream trypomastigotes. Bloodstream trypomastigotes, culture-form trypomastigotes and staphylomastigotes contained several surface proteins of molecular weight (Mr) 90 000 and isoelectric points (pI) between 5.0 and 7.5. Western blotting reveals that at least two proteins of 90 000 Mr represent the major antigens seen on bloodstream trypomastigotes, culture-form trypomastigotes, staphylomastigotes and amastigotes. However, a 90 000 Mr protein was not detected by either Western blotting or surface iodination on epimastigotes or metacyclic trypomastigotes. The major surface proteins on these latter two stages were represented by several 72 000 Mr proteins with pI values between 5.2 and 5.8. An interesting result of this survey is that a 90 000 Mr surface antigen was present on staphylomastigotes, a stage which can be grown in cell free medium

Complexity and content of the DNA and RNA in Trypanosoma cruzi.

The content and sequence complexity of the nuclear DNA and messenger RNA for epimastigotes of Trypanosoma cruzi were determined. From analysis of nuclear DNA reassociation studies and microspectrofluorometric measurements of laser induced fluorescence of cellular DNA, T. cruzi is found to be a diploid organism with a nuclear DNA content of 2.5 x 10(8) nucleotide pairs (2.8 x 10(-13) g) and a kinetoplast DNA content of 4.9 x 10(7) nucleotide pairs (5.4 x 10(-14) g). Reassociation kinetics of nuclear DNA of average length 0.4 kb reveals three kinetic components: a moderately repetitive component with a reiteration frequency of 5.1 x 10(3) present in 9% of the fragments, a lowly repetitive component with a reiteration frequency of 32 present in 51% of the fragments, and a single-copy component present in 23% of the fragments. By saturation hybridization of total polysomal RNA to 3H-labeled single-copy DNA, it was determined that 68% of the single-copy DNA was represented in the epimastigote polysomal RNA. This corresponds to ca. 12 000 different mRNA species. Of these, ca. 9000 are present as poly(A)+-RNA, while the remaining 3000 appear not to be polyadenylated. Kinetic analysis of the poly(A)+-RNA population indicates it is composed of at least three classes of RNA's of different abundancy levels: two sequences which occur ca. 3000 per cell, ca. 750 sequences which occur about 20 times per cell, and ca. 15 500 sequences which occur 1-2 times per cell

Complexity and content of the DNA and RNA in Trypanosoma cruzi.

The content and sequence complexity of the nuclear DNA and messenger RNA for epimastigotes of Trypanosoma cruzi were determined. From analysis of nuclear DNA reassociation studies and microspectrofluorometric measurements of laser induced fluorescence of cellular DNA, T. cruzi is found to be a diploid organism with a nuclear DNA content of 2.5 x 10(8) nucleotide pairs (2.8 x 10(-13) g) and a kinetoplast DNA content of 4.9 x 10(7) nucleotide pairs (5.4 x 10(-14) g). Reassociation kinetics of nuclear DNA of average length 0.4 kb reveals three kinetic components: a moderately repetitive component with a reiteration frequency of 5.1 x 10(3) present in 9% of the fragments, a lowly repetitive component with a reiteration frequency of 32 present in 51% of the fragments, and a single-copy component present in 23% of the fragments. By saturation hybridization of total polysomal RNA to 3H-labeled single-copy DNA, it was determined that 68% of the single-copy DNA was represented in the epimastigote polysomal RNA. This corresponds to ca. 12 000 different mRNA species. Of these, ca. 9000 are present as poly(A)+-RNA, while the remaining 3000 appear not to be polyadenylated. Kinetic analysis of the poly(A)+-RNA population indicates it is composed of at least three classes of RNA's of different abundancy levels: two sequences which occur ca. 3000 per cell, ca. 750 sequences which occur about 20 times per cell, and ca. 15 500 sequences which occur 1-2 times per cell

Two alleles of the 175-kilodalton Plasmodium falciparum erythrocyte binding antigen.

EBA-175, erythrocyte binding antigen 175, is a 175-kDa antigen of Plasmodium falciparum which has been shown to be involved in the recognition of erythrocytes by merozoites and may be involved in the process of erythrocyte invasion. Invasion of erythrocytes by Camp strain merozoites is inhibited by pre-treatment of red blood cells by EBA-175 from the heterologous strain, FCR-3. The sequence of the Camp strain has been published and we report here the sequence of the FCR-3 strain. The sequences are nearly identical except for a 423-bp segment in the FCR-3 strain, F-segment, that is not found in the Camp strain and a 342-bp segment, C-segment, present in the Camp strain but not in the FCR-3 strain. The locations of these two segments are different in Camp and FCR-3 EBA-175 genes and there is little DNA or amino acid sequence homology between them. The essentially dimorphic alleles, F-segment and C-segment, are conserved in all isolates examined to date. Evidence of genetic cross-over between the FCR-3 and the Camp EBA-175 genes was not observed in the analysis of a limited number of wild isolates. The continued study of the biological relevance of these sequence divergences in EBA-175 may further elucidate the sequence of events resulting in merozoite invasion of erythrocytes