Challenge Trial of PfSPZ-LARC2 Vaccine in Burkina Faso

Overview

This is a randomized, double-blind, placebo-controlled, Phase 1 trial of Plasmodium falciparum (Pf) late liver stage-arresting replication-competent (LARC) sporozoite (SPZ) malaria vaccine (Sanaria® PfSPZ-LARC2 Vaccine) administered to healthy, malaria-exposed adults by direct venous inoculation (DVI) to determine safety, immunogenicity, and efficacy against controlled human malaria infection (CHMI). The PfSPZ comprising PfSPZ-LARC2 Vaccine contain a double deletion of the genes encoding the Mei2 and LINUP proteins, both of which are required for transition from liver to blood stage malaria. As a result, mei2-/linup- parasites undergo developmental arrest in the late liver stages without releasing merozoites into the blood stream. No blood stage parasites are produced, either asexual or sexual, and the parasite life cycle does not progress. CHMI will be performed using PfSPZ Challenge (NF54), composed of PfSPZ that are genetically intact and fully infectious. Because PfSPZ-LARC2 vaccine is also based on the Pf strain NF54, CHMI using PfSPZ Challenge (NF54) is considered homologous to the vaccine. It will be performed 6 weeks after the single administration of PfSPZ-LARC2 Vaccine or normal saline placebo (with an option to shorten the interval to 4 weeks if logistical issues arise, such as a risk that CHMI follow-up will overlap with the rainy season).

This is a randomized, double-blind, placebo-controlled, single-center Phase 1 clinical trial of PfSPZ-LARC2 Vaccine to be conducted in healthy non-pregnant, non-lactating adults in Burkina Faso. PfSPZ-LARC2 Vaccine is composed of aseptic, purified, vialed, cryopreserved, genetically altered PfNF54 sporozoites (SPZ) that are stored in liquid nitrogen vapor phase (LNVP). After thawing, the vaccine is diluted and administered by direct venous inoculation (DVI). The trial will compare a low dose of 2x10\^5 PfSPZ to a high dose of 6x10\^5 PfSPZ. There are three groups: Group 1: one dose of PfSPZ-LARC2 Vaccine (2x10\^5 PfSPZ) Group 2: one dose of PfSPZ-LARC2 Vaccine (6x10\^5 PfSPZ) Group 3: one dose of normal saline placebo The goal is to have one highly protective group (the high dose group) and one modestly protective group (2x10\^5 PfSPZ) so that there are adequate numbers of protected and non-protected participants to support the secondary and exploratory objectives of identifying immunological correlates of protection. Before study start, if evidence emerges that 4x10\^5 PfSPZ would address the aim of the high dose group (providing high level protection) as effectively as 6x10\^5 PfSPZ, the protocol permits using 4x10\^5 PfSPZ as the higher dose instead of 6x10\^5 PfSPZ. All participants will be cleared of any existing parasitemia by a three-day treatment course of artemether/lumefantrine (AL). Before treatment, samples will be collected for thick blood smear (TBS) for real-time reading and dried blood spots (DBS) on filter paper for retrospective PCR. Assessment by rapid diagnostic test (RDT) may be included as an option for information purposes. Drug clearance will be done 5-6 weeks before the first dose of investigational product. AL will be administered by study staff using directly observed therapy (DOT). Following initial clearance, all participants will be checked by TBS two weeks before immunization (DBS sample also collected for retrospective PCR). If a participant is positive by TBS at this timepoint, they will be retreated with the same regimen of AL (or an alternative regimen if clinically appropriate), even if asymptomatic. Because immunization will be done during the dry season when malaria is rarely transmitted, only a few retreatments (if any) may be required two weeks before immunization. Immunization: TBS/DBS will be checked again on the day of immunization for retrospective reading. On study day 1, group 1 will receive one dose of 2x10\^5 PfSPZ, group 2 will receive one dose of 6x10\^5 PfSPZ, and group 3 will receive one dose of normal saline. Safety monitoring: Monitoring for adverse events (AEs) will take place for 28 days after injections. Local (site of injection) AEs will be solicited for two days, systemic AEs will be solicited for 14 days, and unsolicited AEs will be collected for 28 days after immunization. Laboratory tests (white blood count, neutrophil count, lymphocyte count, hemoglobin, platelets, creatinine, alanine aminotransferase and aspartate aminotransferase) will be done on the day of immunization and 7 days after. Medically attended adverse events (MAAEs) and serious adverse events (SAEs) will be monitored throughout the trial. Surveillance and treatment for malaria post immunization: After vaccine or normal saline injection, surveillance for clinical malaria and malaria infection will be conducted. Although there have been no breakthrough blood stage infections to date in the 68 adults and children receiving PfSPZ-LARC2 Vaccine, breakthrough is still possible. Passive surveillance will be done by encouraging all participants to immediately report any signs or symptoms consistent with malaria to the clinical team, who will be available 24/7. Any symptom consistent with malaria will be investigated by TBS, which will be repeated if symptoms are ongoing - daily if the initial TBS is negative and symptoms are grade 1 or 2 in severity, or every 8 to 12 hours if initial TBS is negative and symptoms are grade 3 in severity. Malaria signs and symptoms include fever (axillary temperature in \> 37.5°C \[\>99.5°F\]), subjective fever, headache, dizziness, malaise, fatigue, chills, rigors, sweats, myalgia, arthralgia, nausea, vomiting, diarrhea, abdominal pain, cough and chest pain. TBS will generally be made from finger-prick blood, but venipuncture can be used if preferred by the participant or if venipuncture needs to be done anyway for other tests. In addition to passive surveillance, TBS/DBS will be obtained from all participants two, four and six weeks after immunization. If any participants are positive for malaria by TBS, they will be treated with AL and if this occurs within 21 days of CHMI, CHMI will be postponed for that participant (or the participant will be excluded from CHMI). If parasitemia is detected post immunization and prior to CHMI, an additional 2 mL will be collected before treatment, as a back-up for the DBS to be used for the identity assay to differentiate between breakthrough and wildtype infections (this assay was used successfully in the BFSPZL1 trial using blood eluted from DBS). The 2 mL will enable whole genome sequencing if needed. Surveillance and treatment for malaria post CHMI: Six weeks after vaccine or normal saline injection, participants will undergo CHMI using a dose of 3,200 PfSPZ of PfSPZ Challenge (NF54) administered by DVI. Participants will be followed as outpatients for malaria diagnosis, treatment, and follow-up for four weeks after CHMI until day CHMI+28. Malaria positivity will be determined in real time by TBS microscopy read immediately and with qPCR diagnostics based on concurrent DBS completed retrospectively. Rapid diagnostic tests (RDTs), if available, may be included as an option for information purposes, although do not provide quantitative estimates of parasite density. Samples will be taken daily starting on day +5 after CHMI until day +18, then every other day until day CHMI+28. On these same days, body temperature will be measured, and malaria symptoms will be solicited. Clinical events will also be recorded. Participants who test positive for malaria will be treated with a three-day oral regimen of dihydroartemisinin-piperaquine (DHA-P). As mentioned, DBS will be collected on filter paper with every TBS, for retrospective analysis by PCR. On day CHMI+28, all participants who have not been treated already will be presumptively treated with the same DHA-P regimen. All positive TBS endpoints will require retrospective PCR confirmation of Pf parasitemia before being considered final. If samples are negative by PCR, TBS results (and RDT results, if available) will be reviewed. If TBS results are determined to be correct (positive) while PCR is negative, the participant may be excluded from the efficacy analysis due to conflicting data. If TBS results (or RDT results) are determined to represent a false positive result, the participant will be considered negative at the time of treatment. If the time of treatment is later than that of any other participant developing parasitemia post CHMI, the participant will be classified as protected. If the time of treatment is not later than that of any other participant developing parasitemia post CHMI, the participant may be excluded from the efficacy analysis. Definition of blood stage parasitemia during the immunization up until CHMI: Any positive TBS showing normal appearing malaria parasites at 2/ul or higher will be confirmed by a second reader (with a third reader used to resolve disagreements between the first two). RDT may also be included as an option. TBS will be read in real-time as collected, prioritizing the reading of TBS from symptomatic participants. Following CHMI, the threshold for declaring a TBS positive will be maintained at 2/ul or higher for symptomatic participants; however, for asymptomatic persons, it will be increased to 1000 parasites/ul to reduce the chance of false positives and unneeded treatment (if false positives occur, the participant will be removed from the efficacy analysis data set and the power of the study would be diminished). Any participant not already treated post CHMI will be presumptively treated with DHA-P on days 28, 29 and 30 post CHMI. Last study visit: The last in-person study visit will be 26 weeks after immunization. This will be to record medically significant unsolicited AEs (termed clinical events because the time will be past the 28-day interval for unsolicited AEs) including malaria infections and any medical adverse events. The study will be conducted by the Groupe de Recherche Action Santé (GRAS) in the Sabou Health District (SHD) area located about 100 km to the west of Ouagadougou, the capital city of Burkina Faso. As described above, local solicited adverse events will be monitored for 2 days, systemic solicited adverse events for 14 days, and unsolicited adverse events collected daily until 28 days after vaccination. Local (site of injection) adverse events which will be recorded for 2 days after vaccination. In addition, laboratory testing (white blood count, neutrophil count, lymphocyte count, hemoglobin, platelets, creatinine level, alanine aminotransferase, aspartate aminotransferase) will be conducted before and one week after immunization. Serious adverse events (SAEs) and medically attended adverse events (MAAEs) will be recorded from the time of signing the consent to the end of the trial. Pausing rules are defined in the protocol (e.g., a cluster of grade 3 AEs/laboratory abnormalities or an SAE deemed related to the vaccine).