Safety and Immunogenicity Study of Plasmodium Vivax CS Derived Synthetic Peptides Formulated in Two Adjuvants

The study corresponds to a clinical trial, randomized double-blind, controlled, dose escalation, Phase IB, which will assess the safety and immunogenicity of a mixture of synthetic peptides derived from CS protein of P. vivax, formulated in adjuvant Montanide ISA 720 and 51; in healthy men and nonpregnant women without previous history of malaria infection.

In order to optimize the vaccine dose, eligible participants were enrolled to receive three doses of vaccine containing peptide mixtures at a dose of 50 ug or 100 ug of each individual peptide, for a final dose of 150 ug or 300 ug respectively, in a volume of 0.5 mL. The previous clinical trial had indicated that doses between 30 ug and 100 ug produced better responses than lower doses. The first immunization dose (given at Month 0) contained the peptides N and C only, whereas the two boosting doses (given at Months 2 and 4) contained all three (N, R, and C) peptides (Table 1). Vaccination was performed by intramuscular injection in the deltoid muscle, alternating arms with each injection.

For safety reasons, participants assigned to the low vaccine dose groups were immunized first and only two weeks after initiation when no serious adverse events (SAE) had occurred, immunization of participants in the high-dose was started. Half of the participants assigned to receive placebo were immunized along with each dose level group. Clinical monitors and the IRBs of the University of Valle and IMC, evaluated the occurrence and severity of adverse events (AE) associated with immunization. The occurrence of more than three AE (severity grade 2 or higher) or one SAE related to the vaccine would have led to study termination. Participants who left the study were not replaced.

Inclusion criteria

• Healthy adults (male and non-pregnant female) 18- 45 years old, without previously malaria infection (naïve volunteers), capable to pass a comprehension test on the study and able to provide written informed consent to participate in the trial.
• Use of adequate contraceptive method since the initiation of the study and until two months after the end of the study.
• No plans to travel to a malaria endemic area during the course of the study.
• Reachable by phone during the study period (1 year).
• No use of other vaccines since 3 months before the beginning of the study and during it.

Exclusion criteria

• Females who intend to become pregnant within the 3 months following the screening visit or who are pregnant at screening time, ascertained by urine or serum pregnancy test (B-HCG). Women who are breast-feeding will also be excluded. Reason for exclusion: The immunological changes accompanying pregnancy and lactation could alter the results of the assays performed. If a pathological condition appear, it could be carried to the vaccine.
• Duffy negative phenotype. Justification: Individuals with this phenotype are refractory to P. vivax infection.
• G-6-PD deficiency or any genetic defect (hemoglobinopathy). Justification: These conditions influence the development of P. vivax infection.
• History of previous experimental malaria vaccination. Justification: Individuals who have been previously immunized may show a response due to the past immunization and not to the present one.
• Clinical or laboratory evidence of significant systemic disease, including hepatic, renal, cardiac, immunologic or hematological disease.

Justification: The results of the study could have a negative impact on the study if volunteers are suffering from any of these diseases.

• Evidence of active hepatitis B or C or HIV infection. Justification: Serious underlying medical condition could affect the immunological responses of volunteers or could increase the risk or severity of adverse events associated with participation in this study.
• Clinically significant laboratory abnormalities as determined by the investigator(s).

Justification: Baseline abnormal laboratory values may indicate a serious underlying medical condition and also will make it difficult to evaluate AE´s during the conduct of the study.

• Known history of autoimmune (including inflammatory bowel disease, rheumatoid arthritis, lupus) or connective tissue disease.

Justification: Autoimmune diseases could affect the immunological responses of volunteers and could increase the risk to the volunteer.

• Individuals receiving treatment with steroids or non-steroidal anti-inflammatory drugs or any immunosuppressive therapy.

Justification: These drugs could affect the immunological responses of volunteers and could increase the risk to the volunteer.

• Known history of drug or alcohol abuse interfering with normal social function. Justification: Pharmaco-dependency alters the capacity of free decision and produce physical or psychiatric undesirable condition that could affect the study.
• Volunteers unable to give written informed consent or with difficulties to understand the study.

Justification: Volunteers must have the capacity to provide informed consent in order to participate in any research involving humans