A Randomized Placebo-Controlled Phase Ia Malaria Vaccine Trial of Two Virosome-Formulated Synthetic Peptides in Healthy Adult Volunteers

Abstract

Background and ObjectivesInfluenza virosomes represent an innovative human-compatible antigen delivery system that has already proven its suitability for subunit vaccine design. The aim of the study was to proof the concept that virosomes can also be used to elicit high titers of antibodies against synthetic peptides. The specific objective was to demonstrate the safety and immunogenicity of two virosome-formulated P. falciparum protein derived synthetic peptide antigens given in two different doses alone or in combination.Methodology/Principal FindingsThe design was a single blind, randomized, placebo controlled, dose-escalating study involving 46 healthy Caucasian volunteers aged 18–45 years. Five groups of 8 subjects received virosomal formulations containing 10 µg or 50 µg of AMA 49-CPE, an apical membrane antigen-1 (AMA-1) derived synthetic phospatidylethanolamine (PE)-peptide conjugate or 10 ug or 50 ug of UK39, a circumsporozoite protein (CSP) derived synthetic PE-peptide conjugate or 50 ug of both antigens each. A control group of 6 subjects received unmodified virosomes. Virosomal formulations of the antigens (designated PEV301 and PEV302 for the AMA-1 and the CSP virosomal vaccine, respectively) or unmodified virosomes were injected i. m. on days 0, 60 and 180. In terms of safety, no serious or severe adverse events (AEs) related to the vaccine were observed. 11/46 study participants reported 16 vaccine related local AEs. Of these 16 events, all being pain, 4 occurred after the 1st, 7 after the 2nd and 5 after the 3rd vaccination. 6 systemic AEs probably related to the study vaccine were reported after the 1st injection, 10 after the 2nd and 6 after the 3rd. Generally, no difference in the distribution of the systemic AEs between either the doses applied (10 respectively 50 µg) or the synthetic antigen vaccines (PEV301 and PEV302) used for immunization was found. In terms of immunogenicity, both PEV301 and PEV302 elicited already after two injections a synthetic peptide-specific antibody response in all volunteers immunized with the appropriate dose. In the case of PEV301 the 50 µg antigen dose was associated with a higher mean antibody titer and seroconversion rate than the 10 µg dose. In contrast, for PEV302 mean titer and seroconversion rate were higher with the lower dose. Combined delivery of PEV301 and PEV302 did not interfere with the development of an antibody response to either of the two antigens. No relevant antibody responses against the two malaria antigens were observed in the control group receiving unmodified virosomes.ConclusionsThe present study demonstrates that three immunizations with the virosomal malaria vaccine components PEV301 or/and PEV302 (containing 10 µg or 50 µg of antigen) are safe and well tolerated. At appropriate antigen doses seroconversion rates of 100% were achieved. Two injections may be sufficient for eliciting an appropriate immune response, at least in individuals with pre-existing anti-malarial immunity. These results justify further development of a final mult...

Preclinical profiling of the immunogenicity of a two-component subunit malaria vaccine candidate based on virosome technology

“…The induced antibody responses were long-lived, as measured one year after the third immunization. The immunogenicity results 38,40 (Okitsu et al, submitted) closely followed the animal results presented in this report, validating the mouse and rabbit model for immunogenicity studies of virosomally formulated vaccine candidates.…”

“…Results presented in this report were confirmed by results from a phase I clinical trial in adult Caucasians, 38 where the same vaccine proved to be well tolerated, safe and immunogenic. The induced antibody responses were long-lived, as measured one year after the third immunization.…”

“…Again, similar observations have been made in a phase 1 clinical trial, where we found 100% seroconversion with both peptides at an appropriate dose. 38 UK-39 induced IgG was cross-reactive with P. falciparum sporozoites in IFA and stained a band corresponding to CSP in Western blot analyses in mice and rabbits. IFA titers closely followed anti-peptide ELISA titers, indicating a close relationship between peptide UK-39 and the natural conformation of the CSP repeats.…”

“…This potential has been confirmed in a phase 1 trial with the same two peptides, where highest antibody titers were measured after combined delivery of the two peptides. 38 The fact that all outbred rabbits immunized with UK-39 and AMA49-C1 mounted a strong peptide-specific immune response, including a T cell dependent immunoglobulin class-switch, shows the possibility to use the IRIV system in individuals with different immunogenetic backgrounds. Again, similar observations have been made in a phase 1 clinical trial, where we found 100% seroconversion with both peptides at an appropriate dose.…”

Passive Immunoprotection of Plasmodium falciparum-Infected Mice Designates the CyRPA as Candidate Malaria Vaccine Antigen

“…Human serum samples were derived from healthy Swiss adults with no history of malaria exposure (66) and from healthy individuals between 5 and 20 y of age living in the malaria endemic (67) Kassena-Nankana District in northern Ghana. ELISA plates (Maxisorp; Nunc) were coated with 10 mg/ml purified recombinant CyRPA protein produced in HEK cells or purified recombinant MSP-1 (aa 34-595) or MSP-1 (aa 1250-1563) produced in Escherichia coli (68).…”