Challenge Trial of PfSPZ-LARC2 Vaccine in Burkina Faso

This is a randomized, double-blind, placebo-controlled, single-center Phase 1 clinical trial. Healthy non-pregnant, non-lactating adults will be enrolled. Women of child-bearing potential must agree to high-efficacy birth control during the period of immunization. Screening tests will include an ECG, hepatitis B and C serology, HIV testing, sickle cell testing, white blood count, neutrophil count, lymphocyte count, hemoglobin, platelets, creatinine, alanine aminotransferase, aspartate aminotransferase, bilirubin, gamma-glutamyl transferase, and a fasting blood glucose to assure overall good health.

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, to prevent the known immunosuppressive effects of parasitemia on the induction of protective immunity and to prevent such infections from recrudescing later in the trial. AL will be administered by study staff using directly observed therapy (DOT). If there are logistical constraints (risk of rainy season overlapping with CHMI follow-up), the interval can be reduced as needed, but there must be at least two weeks between the first dose of AL and immunization.

AL is one of three artemisinin combination therapies (ACTs) used for treating malaria in Burkina Faso. This particular ACT is selected based on the relatively short half-life of the longer-acting lumefantrine compared to piperaquine, the longer-acting drug of the other ACT used in Burkina Faso, dihydroartemisinin/piperaquine (DHA-P) . A short half-life is needed to prevent any potential impact on the PfSPZ in the vaccine and their development as liver stages (although even relatively high levels of lumefantrine should not affect liver stages - it acts only against blood stages).

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.

The justification for assuring negative status before immunization is based on data from two trials of PfSPZ vaccines in Africa where protection was markedly diminished in participants with parasitemia before clearance two weeks before immunization (noting that the negative effect on protection occurred even though they were cleared). For this reason, the interval between pre-treatment and immunization has been extended from 2 weeks, as done in prior trials, to 5-6 weeks, to provide time for the immune system to recover from the effects of parasitemia. However, a shorter interval can be used (two weeks minimum) based on logistical consideration. If this is done, blood draws for pre-immunization immunology studies can be consolidated as needed (same amount of blood drawn in total).

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.

A syringe of vaccine and a syringe of normal saline are indistinguishable, facilitating the double-blind design. All administrations will be by DVI, a nearly painless procedure in which a narrow-gauge needle is inserted into a superficial vein, blood flashback is demonstrated, and the contents of the syringe are rapidly injected.

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. TBS will be made according to Sanaria's SOP which provides for quantification of parasite density.

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) as residual antimalarial drug could otherwise influence CHMI results.

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.

Descriptive statistics including frequencies, means, medians, and ranges will be utilized to characterize adverse events and laboratory abnormalities including breakthrough blood stage infections. Proportions of vaccinees and controls experiencing AEs or laboratory abnormalities will be compared using Chi-squared or Fishers exact test.

Sample size: The sample size of 15 per group was selected to provide 80% power to show a statistically significant difference (alpha = 0.05) in protection between either vaccine group and the placebo group assuming one drop-out from each group (yielding n=14 per group), assuming 13/14 (93%) or 14/14 (100%) vaccinees are protected in the high dose vaccine group and assuming the most conservative (lowest) positivity rate in the control group across all CHMIs conducted in endemic areas of Africa (8/15 positive). The sample size, 14 per group, is increased to 15 to allow one drop-out from each group.

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. The SHD covers an area of 449 km^2 and is in the region of Boulkiemdé with 112,485 inhabitants, according to the district health records, with most people living in small rural villages in houses made of mud or cement walls and thatched or metal roofs. The population is stable and mainly composed of the Mossi ethnic group. Farming is the main activity. The study's field station is based at Sabou town which is the main town in the district. The SHD includes 20 peripheral health facilities which represent the primary point of contact with the health system for the population. It is in a Sudan Sahelian eco-climatic zone. The climate consists of a single rainy season from June to October followed by a long dry season. This defines the highly seasonal malaria transmission with most malaria episodes experienced during or immediately following the rainy season. The study will be conducted during the dry season to minimize the number of wildtype infections.

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 in phosphate buffered saline (PBS) with human serum albumin (HSA) to achieve the correct dosage and is administered by direct venous inoculation (DVI) into a superficial arm or hand vein within 30 minutes of thaw.

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).

The Safety Monitoring Committee (SMC) will consist of the Local Safety Monitor and two additional clinicians. The SMC will meet before vaccinations to review the SMC Charter and the details of the clinical trial. It will meet again after CHMI has been completed and data are unblinded. It will additionally meet if there is an emerging need.

Inclusion criteria

• Healthy males and females, based on clinical and laboratory findings (note: an effort will be made to recruit roughly equal numbers of males and females, although a balanced sex ratio is not required)
• From 18 to 50 years of age
• Adults with a Body Mass Index (BMI) 18 to 30 Kg/m^2
• Residence in the study area for the duration of the study
• Agreement to release medical information and to inform the study doctor concerning contraindications for participation in the study
• Willingness to be attended to by a study clinician and take all necessary medications prescribed during study period
• Agreement to provide contact information of a third-party household member or close friend to study team
• Agreement not to participate in another clinical trial during the study period
• Agreement not to donate blood during the study period (until final clearance is completed)
• Able and willing to complete the study visit schedule over the study follow up period
• Willingness to undergo HIV, hepatitis B (HBV), hepatitis C (HCV), and sickle cell testing
• Able to demonstrate their understanding of the study by responding correctly to 18 out of 20 true/false statements (in a maximum of two repeat attempts for those who failed to pass in the first attempt)
• Signed written informed consent, in accordance with local practice
• Has not been treated with any antimalarial medication for at least two weeks before the initial clearance treatment.
• Female volunteers must be non-pregnant (as demonstrated by a negative urine pregnancy test) and provide consent / assent of their willingness to take protocol-defined measures not to become pregnant during the study and safety follow-up period. Acceptable measures to not become pregnant include oral or implanted contraceptives, IUD, female condom, diaphragm with spermicide, cervical cap, abstinence, use of a condom by the sexual partner, or sterile sexual partner during the entire study. Women with a history of surgical or chemical sterilization (e.g., tubal ligation, hysterectomy, other) must provide written documentation of the procedure from a health care provider.
• Ability to complete pre-vaccination drug clearance without significant untoward effects.

Exclusion criteria

• Unable to provide informed consent including inability to pass the test of understanding
• Receipt of a malaria vaccine in a prior clinical trial
• History of a splenectomy or sickle cell disease.
• History of a neurologic disorder (including non-febrile seizures or complex febrile seizures) or formal history of migraine headache
• Current use of systemic immunosuppressant pharmacotherapy
• Receipt of a live vaccine within 4 weeks of first immunization or of 3 or more non-live vaccines within 2 weeks of first immunization
• Women who are breast-feeding, pregnant or planning to become pregnant during the study period
• Known allergy to artemether-lumefantrine (AL), dihydroartemisinin-piperaquine (DHA-P), or any component of the investigational products
• History of anaphylaxis or other life-threatening reaction to a vaccine
• Participation in any study involving investigational vaccine or drug within 4 weeks before enrollment that in the estimation of the site PI might adversely affect the individual's safety or the quality of data to be collected
• Evidence of increased cardiovascular disease risk; defined as >10% five-year risk by non-laboratory method
• Plan to participate in another investigational vaccine/drug research during the study
• Plan for major surgery between enrollment until last study visit
• Use or planned use of any drug with anti-malarial activity that would precede or coincide with vaccination through to 56 days after controlled human malaria infection (CHMI)
• Anticipated use of medications known to cause drug interactions with DHA-P (antiarrhythmics, neuroleptics, macrolide antibiotics, fluoroquinolones, imidazole and triazole antifungal agents, quinine, halofantrine, pentamidine and saquinavir, certain non-sedating antihistamines, all of which can affect QT intervals ) or AL (the same list of drugs affecting QT intervals plus rifampin, carbamazepine, phenytoin, St. John's wort and antiretroviral drugs)
• Positive HIV, HBsAg or HCV serology
• Positive sickle cell trait or disease testing
• History of or evidence for other chronic disease conditions including cancer, diabetes, renal failure, hypertension, and tuberculosis
• History of arrythmias or cardiac disease, or an abnormal electrocardiogram, defined as one showing prolonged QT interval, pathologic Q waves and significant ST-T wave changes; left ventricular hypertrophy; any non-sinus rhythm including isolated premature ventricular contractions, but excluding isolated premature atrial contractions; right or left bundle branch block; or advanced (secondary or tertiary) A-V heart block; or other clinically significant abnormalities on the electrocardiogram
• Any clinically significant deviation from the normal range in biochemistry or hematology tests measured at screening and not resolving (grade 1 abnormalities are allowed)
• Any medical, psychiatric, social, behavioral or occupational condition or situation (including active alcohol or drug abuse affecting social function) that, in the judgment of the site PI, impairs the participant's ability to give informed consent, increases the risk to the participant of participation in the study, affects the ability of the participant to participate fully in the study, or might negatively impact the quality, consistency, integrity or interpretation of data derived from their participation in the study
• Inability to complete a course of malaria treatment before receipt of investigational product