This Phase 1 study, conducted in malaria-naïve adults living in the United States, evaluated the safety, immunogenicity, and transmission-blocking activity of the Pfs25-VLP (Plasmodium falciparum virus-like particle) vaccine. The Pfs25-VLP vaccine was produced in Nicotiana benthamiana plants, using a tobacco mosaic virus-derived launch vector delivered by vacuum infiltration of recombinant Agrobacterium tumefaciens.
Volunteers were divided into four dose-escalating groups (2 µg, 10 µg, 30 µg, and 100 µg total VLP), each receiving three intramuscular immunizations formulated with the aluminum hydroxide adjuvant Alhydrogel® (manufactured by Brenntag Biosector A/S) on a 0,56,168-day schedule.
The study was designed with two objectives:
- Assess the safety and immunogenicity of the Pfs25-VLP vaccine in malaria-naive adults by monitoring for occurrence of solicited signs and symptoms, occurrence of unsolicited symptoms, and the occurrence of serious adverse events during the study period.
- Assess anti-Pfs25 antibody response, and assess transmission-blocking activity.
Outcomes/Next steps: Findings were presented at the American Society of Tropical Medicine and Hygiene Annual Meeting in 2015. Data are in the study record; a publication summarizing the data is not available.
A variety of local and systemic reactions were noted in subjects; however, these were found to be in line with reactogenicity experienced in previous studies. No functional transmission-reducing activity was observed in sera obtained after the second and third immunizations.
Based on the outcomes of this study, the PATH Malaria Vaccine Initiative did not make any further investments.