• Vaccine Name: Pfs25/ Montanide ISA 51
• Target Pathogen: Plasmodium spp.
• Target Disease: Malaria
• Type: Live, attenuated vaccine
• Status: Licensed
• Host Species for Licensed Use: None
• Antigen: Pfs25, a protein expressed on the surface of ookinetes of P. falciparum (Wu et al., 2008)
• Pfs25 from P. falciparum 3D7 gene engineering:
  • Type: Recombinant protein preparation
  • Description: Recombinant Pfs25 was used as the vaccine adjuvant. (Wu et al., 2008)
  • Detailed Gene Information: Click Here.
• Preparation: Recombinant proteins Pfs25 were produced in the yeast expression system utilizing Pichia pastoris. A hexa-His tag was added to the C-terminus of the recombinant protein to facilitate purification and characterization. the Pfs25 at a concentration of 320 µg/mL in phosphate-buffered saline (PBS, 155 mM NaCl, 1 mMKH2PO4, 3 mM Na2HPO3) was aseptically emulsified with an equal volume of Montanide ISA 51 to give a final vaccine concentration of 160 µg/mL. The emulsion was achieved by homogenizing the mixture in a volume of 200 mL in a 400-mL vessel at room temperature for 6 min at 6000 rpm using an Omni Mixer-ES homogenizer. (Wu et al., 2008)
• Immunization Route: Intramuscular injection (i.m.)
• Description: The Pfs25/ Montanide ISA 51 uses Pfs25, a P. falciparum ookinete surface protein, as the vaccine antigen emulsified in Montanide ISA 51 as the vaccine adjuvant.

Human Response

• Host Strain: healthy US volunteers
• Vaccination Protocol: Vaccines were administered at three dose levels (5, 20, and 80 µg per dose in 0.5 mL) (Wu et al., 2008)
• Immune Response: Four of 10 volunteers, including the one that developed a leukemoid reaction (Volunteer “C”), had no detectable antibodies against Pfs25 (i.e. <25 ELISA units) by day 120 following the first vaccination. Of the 2 volunteers that developed grade 3 induration, one (Volunteer “H”) had a minimal antibody level of 30 ELISA units on day 90, 30 days after the induration resolved. The other (Volunteer “G”) had 132 ELISA units on day 60. All 5 volunteers (Volunteers “A” through “E”) receiving a second dose of 5 µg Pfs25/ISA 51 developed substantial antibody levels against Pfs25 following the second vaccination (Table 4). The antibody levels reached a peak 30–60 days after the second vaccination and the geometric mean of the peak of this group was 1295 ELISA units. (Wu et al., 2008)
• Side Effects: Local adverse events included erythema, induration, swelling, and tenderness at the site of injection. Solicited systemic adverse events included fever (oral temperature≥37.5°C), headache, nausea, malaise, myalgia, and arthralgia. In the groups receiving antigen with ISA 51, 6 volunteers experienced severe local reaction, 4 experienced moderate local reaction, and 14 experienced mild reaction (maximum severity for each). Four of six volunteers who received the control vaccine (PBS/ISA 51) complained of mild injection site pain lasting up to 4 days and two recipients reported mild erythema for one day. (Wu et al., 2008)
• Efficacy: In ex vivo membrane feeding assays, one antiserum that contained 7322 ELISA units resulted in reduction of the parasite in mosquitoes by >90%. The severity and duration of the local reactions seen in this study, combined with the observed systemic reactions, make further progression of the Montanide ISA 51 formulations unlikely.