Safety and Immunogenicity of the Placental Malaria Vaccine Candidate PAMVAC Variously Adjuvanted

Overview

Despite having developed robust acquired immunity against complications of malaria, women can return to a susceptible state during their first pregnancies and contribute significantly to the burden of severe malaria in highly endemic areas. Naturally acquired protection against placental malaria correlates with the presence of high concentration of immunoglobulin G molecules (IgGs) against VAR2CSA, a parasite protein of the var gene family that is essential for the binding of infected erythrocytes to CSA in the placenta. To induce high concentrations of specific IgGs, subjects will receive escalating doses of PAMVAC vaccine antigen adjuvanted with Alhydrogel, Glucopyranosyl Lipid Adjuvant-Stable Emulsion (GLA-SE) or Glucopyranosyl Lipid Adjuvant-Liposome-QS-21 Formulation (GLA-LSQ). Three injections with the same dosage and adjuvant will be done, each 28 days apart (Day 0, 28 and 56). Control subjects will receive physiological saline instead of the vaccine and dose escalation will be staggered to ensure safety during the trial.

Phase 1, staggered, two-center, dose-escalation trial. The trial will be conducted in two stages. The first in Germany (first in man and dose escalation) and the second in a malaria-endemic area in the target group (randomized, controlled, dose-finding). First in man administration and dose escalation from 20 to 50 μg per injection of PAMVAC adjuvanted with Alhydrogel, GLA-SE and GLA-LSQ will be done in healthy, malaria-naïve adults in Germany (Stage 1). Subsequently, PAMVAC will be administered to healthy, lifelong malaria-exposed nulligravid women in Benin at doses of 50 and 100 μg, adjuvanted with Alhydrogel and GLA-SE (Stage 2). The PAMVAC vaccine is a VAR2CSA protein-based vaccine, aiming to protect fetus and mother against the adverse effects of placental malaria during pregnancy. As the interaction between the parasite protein VAR2CSA and CSA in the human placenta is a key element in the pathogenesis of placental malaria, a vaccine should elicit the type of immunoglobulins that block the binding of VAR2CSA to CSA. A small sub-unit of the VAR2CSA protein (ID1-ID2a) has been selected as the PAMVAC vaccine antigen. In animal models IgGs induced by immunization with the recombinant PAMVAC antigen are able to inhibit homologous parasite-infected erythrocyte adhesion to CSA in vitro. The three adjuvants are Alhydrogel, an aluminum hydroxide gel widely used as adjuvant in this trial; GLA-SE and GLA-LSQ, synthetic TLR-4 agonists with a strong immune stimulatory effect formulated either in a stable oil-in-water emulsion (SE) or together with QS-21 (Saponin derived from the Quillaja saponaria tree) as liposome (LSQ). In Benin, one group will receive a placebo control (physiological saline). Allocation to placebo, PAMVAC+Alhydrogel or PAMVAC+GLA-SE, will be randomized and the trial team as well as the participants will be kept blinded (double-blinded) to their allocation. All participants (Stage 1+2) will receive three intramuscular injections in four-week intervals. Each dose-escalation is conditional on a positive safety assessment by an independent Safety Monitoring Board (SMB) and sponsor approval. One individual of each PAMVAC-adjuvant combination will serve as sentinel. The sentinel will be injected one day before the rest of the group. There will be a minimum of 4 weeks stagger between the first immunization of Groups 1A-3A and Groups 4A-6A. Group 1A (n = 3) - 20 µg PAMVAC+Alhydrogel Group 2A (n = 3) - 20 µg PAMVAC+GLA-SE Group 3A (n = 3) - 20 µg PAMVAC+GLA-LSQ Group 4A (n = 9) - 50 µg PAMVAC+Alhydrogel Group 5A (n = 9) - 50 µg PAMVAC+GLA-SE Group 6A (n = 9) - 50 µg PAMVAC+GLA-LSQ Following safety assessment by the SMB after the first dose in Groups 4A-6A and approval by the sponsor, Stage 2 (in Benin) will be initiated. Here, the target population of PAMVAC (healthy nulligravid women in a malaria-endemic area) will be vaccinated. Upon SMB review and approval by the sponsor Groups 1B-2B and half the subjects from the control Group 5B will receive vaccinations. One participant allocated to group 1B, 2B and 5B will receive the first immunization at least one day before the rest of the group. Group 1B (n=9) - 50 µg PAMVAC+Alhydrogel Group 2B (n=9) - 50 µg PAMVAC+GLA-SE Group 3B (n=3) - 100 µg PAMVAC+Alhydrogel Group 4B (n=3) - 100 µg PAMVAC+GLA-SE Group 5B (n=6) - Placebo (physiological saline solution) There will be a 4 weeks stagger between Groups 1B-2B and Group 3B-4B and the remaining subjects of the control Group 5B to allow for safety evaluation by the SMB. Here, the same system of sentinel vaccination as for the lower dose will be used; one participant allocated to group 3B, 4B and 5B will receive the first immunization at least one day before the rest of the group.