Immunization with merozoite surface protein 2 fused to a Plasmodium-specific carrier protein elicits strain-specific and strain-transcending, opsonizing antibody

Sci Rep. 2019 Jun 21;9(1):9022. doi: 10.1038/s41598-019-45440-4.

Abstract

Vaccine trials and cohort studies in Plasmodium falciparum endemic areas indicate that naturally-acquired and vaccine-induced antibodies to merozoite surface protein 2 (MSP2) are associated with resistance to malaria. These data indicate that PfMSP2 has significant potential as a component of a multi-antigen malaria vaccine. To overcome challenges encountered with subunit malaria vaccines, we established that the use of highly immunogenic rPfMSP8 as a carrier protein for leading vaccine candidates rPfMSP119 and rPfs25 facilitated antigen production, minimized antigenic competition and enhanced induction of functional antibodies. We applied this strategy to optimize a rPfMSP2 (3D7)-based subunit vaccine by producing unfused rPfMSP2 or chimeric rPfMSP2/8 in Escherichia coli. rPfMSP2 formed fibrils, which induced splenocyte proliferation in an antigen receptor-independent, TLR2-dependent manner. However, fusion to rPfMSP8 prevented rPfMSP2 amyloid-like fibril formation. Immunization of rabbits elicited high-titer anti-PfMSP2 antibodies that recognized rPfMSP2 of the 3D7 and FC27 alleles, as well as native PfMSP2. Competition assays revealed a difference in the specificity of antibodies induced by the two rPfMSP2-based vaccines, with evidence of epitope masking by rPfMSP2-associated fibrils. Rabbit anti-PfMSP2/8 was superior to rPfMSP2-elicited antibody at opsonizing P. falciparum merozoites for phagocytosis. These data establish rPfMSP8 as an effective carrier for a PfMSP2-based subunit malaria vaccine.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Antibodies, Protozoan / immunology*
  • Antibody Specificity / immunology
  • Antigens, Protozoan / chemistry
  • Antigens, Protozoan / immunology*
  • Humans
  • Malaria Vaccines / administration & dosage
  • Malaria Vaccines / chemistry
  • Malaria Vaccines / immunology
  • Malaria, Falciparum / immunology*
  • Malaria, Falciparum / prevention & control
  • Merozoites / immunology
  • Opsonin Proteins / immunology*
  • Phagocytosis / immunology
  • Protozoan Proteins / chemistry
  • Protozoan Proteins / immunology*
  • Rabbits
  • Species Specificity
  • THP-1 Cells
  • Vaccination / methods*

Substances

  • Antibodies, Protozoan
  • Antigens, Protozoan
  • Malaria Vaccines
  • Opsonin Proteins
  • Protozoan Proteins
  • merozoite surface protein 2, Plasmodium
  • merozoite surface protein 8, Plasmodium