Trial to Evaluate the Safety, Immunogenicity and Protective Efficacy of Three or Five Administrations of GAP3KO Sporozoites
The primary objectives are:
- To assess the safety and reactogenicity of candidate GAP3KO malaria vaccine when administered by the bite of approximately 200 infected mosquitoes on a five dose schedule, with the first four vaccinations given four weeks apart and the fifth vaccination given eight weeks after the fourth vaccination, and on a three dose schedule, with the second vaccination given four weeks after the first vaccination and the third vaccination given eight weeks after the second vaccination, to healthy malaria-naïve adults aged 18 through 50 years.
- To confirm attenuation of GAP3KO parasites by assessing the occurrence of breakthrough peripheral parasitemia from the time of first GAP3KO administration through 28 days after last GAP3KO administration.
The secondary objectives are:
- To assess the efficacy of GAP3KO vaccine given on a five dose schedule and GAP3KO vaccine given on a three dose schedule against malaria challenge four weeks after last vaccination, and re-challenge 26 weeks (six months) after the first challenge, using standard controlled human malaria infection (CHMI) procedures.
- To assess humoral and cell-mediated immune responses to malaria antigens induced by GAP3KO administration and by CHMI.
This Phase 1 non-randomized clinical trial will include 16 subjects in Study Arms 1 and 2 who will receive the Genetically-attenuated p52-/p36-/sap1- Plasmodium falciparum Parasites (GAP3KO) vaccine administered by the bite of approximately 200 infected Anopheles stephensi mosquitoes in a controlled clinical environment and 12 Controlled Human Malaria Infection (CHMI) infectivity controls (six for each of the two CHMIs). Subjects will be observed for adverse events for at least 60 minutes after each GAP3KO administration. Solicited local and systemic Adverse Events (AEs) will be recorded on a memory aid beginning of the day of first vaccine administration and continuing through 28 days after the last administration. During the vaccination phase clinical laboratory evaluations for safety will be performed on venous blood. Unsolicited AEs will be collected from the day of first vaccination through 28 days after last vaccination and serious adverse events (SAEs) will be collected from the day of first GAP3KO administration through the end of study follow-up. Subjects will be monitored for possible breakthrough peripheral parasitemia with qRT-PCR testing. Four weeks after the last GAP3KO administration, all subjects who completed the immunization phase (up to 16) and a group of six malaria-naïve infectivity controls will be challenged on the same day with wild-type Plasmodium falciparum NF54 sporozoites. Approximately twenty-six weeks (six months) after that challenge, all of the protected subjects in Arms 1 and 2 (up to 16) and another six malaria-naïve infectivity controls will receive five infectious An. stephensi mosquito bites on the same day using standard CHMI procedures. For subjects in Study Arms 1 and 2 without documented parasitemia additional post-CHMI follow-ups will occur. For subjects in Study Arms 1 and 2 with documented parasitemia after the first CHMI or who are discontinued for other reasons after the first CHMI, and for the infectivity controls, additional follow ups will occur. Serious Adverse Events (SAEs) will be recorded from the day of CHMI through the end of study follow up and clinical laboratory evaluations for safety will be performed on Day 29 and as clinically indicated (all subjects) and, for subjects with documented parasitemia, on the day malaria treatment is initiated and three days after malaria treatment is initiated.