• Vaccine Name: PfRipr5/ CAF01
• Target Pathogen: Plasmodium spp.
• Target Disease: Malaria
• Type: Protein Subunit Vaccine
• Status: Research
• Host Species for Licensed Use: Baboon
• Antigen: PfRipr5: a protein fragment of PfRipr complex considered to play one of the central roles in the sequential molecular events leading to P. falciparum merozoite invasion. PfRipr5 is a protein fragment inducing the most potent growth inhibitory antibodies as comparable level to the antibodies against full-length PfRip. (Takashima et al., 2022)
• Preparation: PfRipr5 recombinant protein was produced in a 50 L stirred-tank bioreactor by infecting insect High Five cells at 2 ×106 cell/mL with a recombinant baculovirus encoding pfripr5 nucleotide sequence and His6-tag for purification, using a multiplicity of infection of 0.1 virus per cell. cell culture bulk was clarified using a Sartopore 2 30’’ 0.45 µm + 0.2 µm filter, loaded on a Histrap HP column, and protein was eluted with a linear Imidazole gradient. The eluate was concentrated using a Vivaflow 200 Hydrosart 10 kDa and loaded into a Superdex 75 prep grade XK50/100 gel size-exclusion chromatography column, from which fractions corresponding to monomeric PfRipr5 were collected. The collected fractions were loaded in a HiPrep desalting 26/10 column, the eluate was concentrated as mentioned above, and then sterile-filtered (0.2 μm). The final sample was formulated in 16 mM sodium phosphate buffer, 250 mM NaCl, at pH 8.0, aliquoted and stored at -80°C. The PfRipr5 was diluted in 10 mM Tris buffer with 2% glycerol (pH=7.0) to the target concentration in each vaccine formulation. CAF01 vaccine formulations containing CAF®01 (1250 µg/mL DDA and 250 µg/mL TDB), and either 100 µg/mL (low dose) or 400 µg/mL (high dose) of PfRipr5.
• Immunization Route: Intramuscular injection (i.m.)
• Description: PfRipr5/ CAF01 is a asexual-blood stage malaria vaccine that uses the PfRipr5 protien segment as the vaccine antigen and a CAF01 adjuvant.

Rabbit Response

• Host Strain: Japanese white rabbits
• Vaccination Protocol: apanese white rabbits (n=6 per group) were subcutaneously immunized with the PfRipr5 protein alone (50 µg/shot) or with PfRipr5 antigen (0, 50, and 200 µg/shot) formulated with the aforementioned adjuvants at the specific concentrations in 500 µL injection, twice at three-week intervals (Day 0 and Day 21). Antisera were collected two weeks after the last immunization (Day 35). (Takashima et al., 2022)
• Immune Response: Formulation of PfRipr5 with CAF®01 induced statistically significant higher levels of antibodies in most low dose (50 µg) (Mean ELISA titers: CAF = 1.0 ×105 (P<0.01)) and in all high dose groups (200 µg) (Mean ELISA titers: CAF = 1.1 ×105 (P<0.001)). The GIA activities of IgG induced by PfRipr5 CAF®01 formulations were higher in the high dose (200 µg) (Mean %GIA: CAF = 49.4%) than in the low dose (50 µg) (Mean %GIA: CAF = 38%) groups. (Takashima et al., 2022)
• Description: The PfRipr5/CAF®01 formulation was identified as the most promising vaccine candidate for further development because of its higher immunogenicity. (Takashima et al., 2022)