Study Design: VRC 312 is the second study of the PfSPZ Vaccine and the first study to evaluate intravenous (IV) administration of this vaccine. The study is designed as an openlabel evaluation of the safety, tolerability, immunogenicity and protective efficacy of the vaccine at successively higher dosages (2000; 7500; 30,000 and 135,000 SPZ per injection) administered by the IV route. The 3 higher dosages will be evaluated for protection against a malaria challenge after 4 to 6 vaccinations. Control subjects are included in the malaria challenge. The primary objectives of the study are related to the safety and tolerability of the vaccine at the 4 dosage levels when administered IV; the secondary objectives are related to PfSPZ vaccine-mediated protection against Plasmodium falciparum (Pf) challenge at the 3 higher dosage levels; and the exploratory objectives are related to the immunogenicity of the PfSPZ Vaccine and defining an immune correlate of protection.
Product Description: The investigational PfSPZ Vaccine is manufactured by Sanaria, Inc (Rockville, MD) under current Good Manufacturing Practices (cGMP). The vaccine consists of a suspension of purified, metabolically-active, radiation-attenuated cryopreserved Pf sporozoites formulated in cryoprotectant and dispensed in a 0.5 mL screw-cap vial containing a 20 mcL aliquot at a concentration of 150,000 sporozoites (+/-50,000 sporozoites) per 20 mcL. The vaccine is stored in the vapor-phase of liquid nitrogen (LNVP) at -140 to -196 degrees C. The PfSPZ Vaccine is delivered by Sanaria, Inc. to the clinical investigators and diluted in phosphate buffered saline (PBS) with 1% human serum albumin (HSA) to achieve the correct dosage.
Subjects: Healthy subjects, 18-45 years old, who are malaria-naive. The fewest number of subjects needed to complete the study as originally designed was 51; however, with inclusion of study provisions for back-up challenge subjects enrollment of additional vaccinees and options for rechallenge, as added by protocol amendments, the amended accrual allowance is 68 subjects.
Study Plan: Subjects will be enrolled in a step-wise, dose-escalation manner with stringent stopping rules designed for subject safety. The first 12 subjects will be allocated as the pilot subjects that comprise Groups 1, 2a, 3a, 4a; each of which includes 3 pilot subjects. For the pilot subjects, the 1st vaccination (V1) and 2nd vaccination (V2) will be administered no faster than one per pilot subject every 2 hours.
Before administration of the first dose to the subsequent pilot Group (dose escalation), at least 5 weeks of cumulative safety data for the pilot subjects in a dosage group (i.e., 1 week past 2nd vaccination) must be submitted to the Safety Monitoring Committee (SMC) and the FDA, and protocol-specified approval received for the dose escalation.
Subjects in vaccine Groups 2, 3, 4 and the Group 5 controls will be challenged by exposure to Anopheles stephensi mosquitoes infected with Pf sporozoites in a controlled setting, followed by testing for parasitemia at specified intervals through up to 28 days post-challenge. To facilitate intensive daily close monitoring of clinical status and blood smears, 11 overnight stays are required from days 7-18 post-challenge. Subjects who develop blood stage P. falciparum infection will be treated as soon as a case is identified by the protocol criteria. Following treatment, a subject will be considered cured when 2 consecutive daily blood smears are negative. After establishing cure, blood smear checks may end and the subject may discontinue overnight stays.
Challenges occur at specified timepoints in which each challenge includes vaccine recipients and control subjects. Rechallenge options to assess for durability of protective responses and further evaluation of immune correlates of protection are included in the protocol.
Study Duration: The study will take approximately 18 months to complete. The period of follow-up for each vaccinated subject is through at least 24 weeks after the last vaccination. The total duration on study will vary depending upon the schedule assignment and whether or not the subject participates in a rechallenge. The Group 5 (challenge only) subjects and rechallenged subjects will be followed through 8 weeks after last challenge.
