Phase 1 trial of AMA1-C1/Alhydrogel plus CPG 7909: an asexual blood-stage vaccine for Plasmodium falciparum malaria

Abstract

Background: Apical Membrane Antigen 1 (AMA1), a polymorphic merozoite surface protein, is a leading blood-stage malaria vaccine candidate. This is the first reported use in humans of an investigational vaccine, AMA1-C1/Alhydrogel, with the novel adjuvant CPG 7909.

Methods: A phase 1 trial was conducted at the University of Rochester with 75 malaria-naive volunteers to assess the safety and immunogenicity of the AMA1-C1/Alhydrogel+CPG 7909 malaria vaccine. Participants were sequentially enrolled and randomized within dose escalating cohorts to receive three vaccinations on days 0, 28 and 56 of either 20 microg of AMA1-C1/Alhydrogel+564 microg CPG 7909 (n = 15), 80 microg of AMA1-C1/Alhydrogel (n = 30), or 80 microg of AMA1-C1/Alhydrogel+564 microg CPG 7909 (n = 30).

Results: Local and systemic adverse events were significantly more likely to be of higher severity with the addition of CPG 7909. Anti-AMA1 immunoglobulin G (IgG) were detected by enzyme-linked immunosorbent assay (ELISA), and the immune sera of volunteers that received 20 microg or 80 microg of AMA1-C1/Alhydrogel+CPG 7909 had up to 14 fold significant increases in anti-AMA1 antibody concentration compared to 80 microg of AMA1-C1/Alhydrogel alone. The addition of CPG 7909 to the AMA1-C1/Alhydrogel vaccine in humans also elicited AMA1 specific immune IgG that significantly and dramatically increased the in vitro growth inhibition of homologous parasites to levels as high as 96% inhibition.

Conclusion/significance: The safety profile of the AMA1-C1/Alhydrogel+CPG 7909 malaria vaccine is acceptable, given the significant increase in immunogenicity observed. Further clinical development is ongoing.

Trial registration: ClinicalTrials.gov NCT00344539.

Figure 1. Participant Flow.

Reasons for exclusion: Abnormal labs (48: 28 positive ANA, 9 positive RF, 1 positive anti-dsDNA, 10 other) Medical history (21) No show (19) Other (21).

Figure 2. Anti-AMA1 antibody responses: Day 42 and 70 AMA1 antibody responses in recipients of the 20 or 80 µg AMA1-C1/Alhydrogel±CPG 7909 vaccines.

Antibody responses against AMA1-3D7 (A) and AMA1-FVO (B) measured by ELISA in sera collected on Day 42 (14 days postvaccination 2) and Day 70 (14 days postvaccination 3). ELISA results are shown as the geometric mean of AMA1-specific antibody (µg/mL) with standard error. The bars represents 80 µg AMA1 (white bar, n = 25), 20 µg AMA1+CPG (grey bar, n = 12), and 80 µg AMA1+CPG (black bar, n = 29).

Figure 3. Longevity of antibody responses: AMA1 antibody responses in recipients of the 20 or 80 µg AMA1-C1/Alhydrogel±CPG 7909 vaccines.

Antibody responses against AMA1-3D7 (A) and AMA1-FVO (B) measured by ELISA in sera collected on Day 0 through to Day 236. ELISA results are shown as the geometric mean of AMA1-specific antibody (µg/mL). The lines represents 80 µg AMA1 (black circles/dashed line), 20 µg AMA1+CPG (black squares/solid line), and 80 µg AMA1+CPG (black triangles/dotted line). Arrows indicate the days of vaccination.

Figure 4. Functional Immunological response: Homologous in vitro parasite growth inhibition in recipients of the 20 or 80 µg AMA1-C1/Alhydrogel±CPG 7909 vaccines.

Day 70 in vitro parasite growth inhibition response against 3D7 parasites measured by GIA using total IgG purified from individual sera. (A) Arithmetic mean of % inhibition against 3D7 parasites is shown with standard error bars. (B) The concentration of Day 70 AMA1-specific antibody (µg/mL) to test wells (x-axis) is plotted against % inhibition (y-axis). The individual data points represent 80 µg AMA1 (black circles, n = 23), 20 µg AMA1+CPG (white squares, n = 10), and 80 µg AMA1+CPG (white circles, n = 25).

Figure 5. Functional Immunological response: Heterologous in vitro parasite growth inhibition.

Ten available samples on Day 70 with high growth-inhibitory activity to homologous parasites (≥68% inhibition to 3D7 parasites) were selected. Volunteers 10, 11 and 46 received 20 µg AMA1+CPG; Volunteers 61, 62, 63, 88, 96 and 97 received 80 µg AMA1+CPG 7909 and Volunteer 66 received 80 µg AMA1. Day 70 in vitro parasite growth inhibition response against 3D7 parasites (white bar), FVO (grey bar) and L32 (black bar) and M24 (hashed bar) measured by GIA using total IgG (10 mg/mL in GIA well) purified from individual sera.