Strong correlation between anti-AMA1 antibody level and the growth-inhibitory activity in AMA1-specific IgGs.

<p>Anti-AMA1(3D7) (A) or anti-AMA1(FVO) (B) antibody levels (µg/ml) in the GIA well (<i>x</i>-axis) are plotted against % inhibition (<i>y</i>-axis) of <i>P. falciparum</i> 3D7 (A) or FVO (B) parasites. Each AMA1-specific IgG was tested at three (for U.S. IgGs) or two (for Mali IgGs) different concentrations. All responses below the limit of detection in ELISA were assigned a value of 2 µg/ml for the analysis.</p

Competition ELISA with US-total IgG and non-AMA1 IgGs.

<p>(A) A fixed amount of US-total IgG, which gives approximately O.D. value of 3, was mixed with 3-fold dilutions of non-AMA1(3D7) IgGs from Malian children. The mixtures were tested by ELISA using an AMA1(3D7)-coated plate and the O.D. values are shown. (B) Similar study was performed using non-AMA(FVO) IgGs and an AMA1(FVO)-coated ELISA plate.</p

Anti-AMA1 antibody level [mg/ml] in test IgGs (40 mg/ml).

a<p>Number of individual IgGs to make total IgG pool.</p>b<p>Antibody level [µg/ml] to AMA1(3D7) ELISA plate.</p>c<p>Antibody level [µg/ml] to AMA1(FVO) ELISA plate.</p>d<p>Less than the minimal detection level of antibody.</p>e<p>N/A, No sample available.</p>f<p>Numbers in parentheses, percent relative to the total IgG.</p>g<p>ND, Percent cannot be determined.</p

Safety and Immunogenicity of Pfs25-EPA/Alhydrogel^®, a Transmission Blocking Vaccine against <i>Plasmodium falciparum</i>: An Open Label Study in Malaria Naïve Adults

<div><p>Transmission-blocking vaccines (TBVs) that target sexual stage parasite development could be an integral part of measures for malaria elimination. Pfs25 is a leading TBV candidate, and previous studies conducted in animals demonstrated an improvement of its functional immunogenicity after conjugation to EPA, a recombinant, detoxified ExoProtein A from <i>Pseudomonas aeruginosa</i>. In this report, we describe results of an open-label, dose-escalating Phase 1 trial to assess the safety and immunogenicity of Pfs25-EPA conjugates formulated with Alhydrogel^®. Thirty malaria-naïve healthy adults received up to four doses of the conjugate vaccine, with 8, 16, or 47 μg of conjugated Pfs25 mass, at 0, 2, 4, and 10 months. Vaccinations were generally well tolerated. The majority of solicited adverse events were mild in severity with pain at the injection site the most common complaint. Anemia was the most common laboratory abnormality, but was considered possibly related to the study in only a minority of cases. No vaccine-related serious adverse events occurred. The peak geometric mean anti-Pfs25 antibody level in the highest dose group was 88 (95% CI 53, 147) μg/mL two weeks after the 4^th vaccination, and declined to near baseline one year later. Antibody avidity increased over successive vaccinations. Transmission blocking activity demonstrated in a standard membrane feeding assay (SMFA) also increased from the second to the third dose, and correlated with antibody titer and, after the final dose, with antibody avidity. These results support the further evaluation of Pfs25-EPA/Alhydrogel^® in a malaria-endemic population.</p></div

Summary of adverse events after each vaccination.

<p>Clinical solicited (A-C) and Laboratory (D-F) adverse events after each vaccination with each dose group are reported in individual graphs: Group 1a (A and D), 1b (B and E) and Group 2 (C and F). All adverse events were mild except when indicated as moderate.</p

Immunofluorescence assays with immune sera.

<p>A. Surface labeling of zygotes with sera from one volunteer (#20) collected on days 0, 314 and 356, with Pfs25 specific mouse mAbs 1G2 and 4B7. B. Recognition of parasite protein in fixed ookinetes with sera from one volunteer (#20) collected on days 0, 314 and 356, with Pfs25 specific mouse mAb 4B7. Magnification 1000X.</p

Transmisison reducing activity of immune sera.

<p>A. Transmission reducing activity of sera collected 2 weeks after each initial vaccination and 8 weeks after the booster vaccination. Each data point represents the average of two results in the SMFA, and lines indicate estimate EC50 and point-wise confidence interval by GEE model. B. Standard deviation (SD) of individual TRA from replica assays. Thick blue line indicates the threshold representing significant biological activity (50% TRA), the black line is a standard loess smooth curve. The green, red, blue, and black dots correspond to the data points on D70, D134, D314 (2 weeks after the second, third, and fourth vaccination respectively), and D356 (8 weeks after the fourth vaccination), as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0163144#pone.0163144.g004" target="_blank">Fig 4A</a>.</p

Study flow chart.

<p>Thirty (30) participants were enrolled, 23 completed the study per protocol.</p

Anti-Pfs25 responses.

<p>A, Groups 1a and 1b participants, receiving conjugated proteins comprising of 8 μg and 16 μg Pfs25H, respectively. B, Group 2 participants, receiving 47 μg Pfs25H. Arrows indicate the day of vaccination. Closed circles represent antibody level and individual participants, and black bars indicate geometric mean of antibody levels and t-distribution 95% confidence interval (CI).</p