• Vaccine Name: PfRipr5/ Alhydrogel
• Target Pathogen: Plasmodium spp.
• Target Disease: Malaria
• Type: Protein Subunit Vaccine
• Status: Research
• Host Species for Licensed Use: None
• 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. (Takashima et al., 2022)
• Immunization Route: Intramuscular injection (i.m.)
• Description: PfRipr5/ Alhydrogel is a asexual-blood stage malaria vaccine that uses the PfRipr5 protien segment as the vaccine antigen and an Alhydrogel adjuvant. (Takashima et al., 2022)

Rabbit Response

• Host Strain: Japanese white rabbits
• Vaccination Protocol: Japanese 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 Alhydrogel® induced statistically significant higher levels of antibodies in most low dose (50 µg) (Mean ELISA titers: Alum = 1.0 ×105 (P<0.01)); and in all high dose groups (200µg) (Mean ELISA titers: Alum = 8.8 ×104 (P<0.05)). The GIA activity of IgG induced by PfRipr5 Alhydrogel® formulation was higher in the low dose (50 µg) (Mean %GIA = 37%) than in the high dose (200 µg) (Mean %GIA = 19.9%) groups. (Takashima et al., 2022)
• Description: The current study shows that PfRipr5 antigen alone was immunogenic to rabbits without any adjuvant, although the generated antibodies could not induce significant GIA activities.(Takashima et al., 2022)