Identification of Plasmodium falciparum reticulocyte binding protein homologue 5-interacting protein, PfRipr, as a highly conserved blood-stage malaria vaccine candidate.
Genetic variability in Plasmodium falciparum malaria parasites hampers current malaria vaccine development efforts. Here, we hypothesize that to address the impact of genetic variability on vaccine efficacy in clinical trials, conserved antigen targets should be selected to achieve robust host immunity across multiple falciparum strains. Therefore, suitable vaccine antigens should be assessed for levels of polymorphism and genetic diversity. Using a total of one hundred and two clinical isolates from a region of high malaria transmission in Uganda, we analyzed extent of polymorphism and genetic diversity in four recently reported novel blood-stage malaria vaccine candidate proteins: Rh5 interacting protein (PfRipr), GPI anchored micronemal antigen (PfGAMA), rhoptry-associated leucine zipper-like protein 1 (PfRALP1) and Duffy binding-like merozoite surface protein 1 (PfMSPDBL1). In addition, utilizing the wheat germ cell-free system, we expressed recombinant proteins for the four candidates based on P. falciparum laboratory strain 3D7 sequences, immunized rabbits to obtain specific antibodies (Abs) and performed functional growth inhibition assay (GIA). The GIA activity of the raised Abs was demonstrated using both homologous 3D7 and heterologous FVO strains in vitro. Both pfripr and pfralp1 are less polymorphic but the latter is comparatively more diverse, with varied number of regions having insertions and deletions, asparagine and 6-mer repeats in the coding sequences. Pfgama and pfmspdbl1 are polymorphic and genetically diverse among the isolates with antibodies against the 3D7-based recombinant PfGAMA and PfMSPDBL1 inhibiting merozoite invasion only in the 3D7 but not FVO strain. Moreover, although Abs against the 3D7-based recombinant PfRipr and PfRALP1 proteins potently inhibited merozoite invasion of both 3D7 and FVO, the GIA activity of anti-PfRipr was much higher than that of anti-PfRALP1. Thus, PfRipr is regarded as a promising blood-stage vaccine candidate for next-generation vaccines against P. falciparum.
Division of Malaria Research, Proteo-Science Center, Ehime University, Matsuyama, Ehime 790-8577, Japan.
Edward H
EH
Ntege
Department of Molecular Protozoology, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka 565-0871, Japan.
Nobuko
N
Arisue
Division of Malaria Research, Proteo-Science Center, Ehime University, Matsuyama, Ehime 790-8577, Japan.
Daisuke
D
Ito
Division of Malaria Research, Proteo-Science Center, Ehime University, Matsuyama, Ehime 790-8577, Japan.
Tomoyuki
T
Hasegawa
Department of Molecular Protozoology, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka 565-0871, Japan.
Nirianne M Q
NMQ
Palacpac
Med Biotech Laboratories, P.O. Box 9364, Plot 4-6 Bell Close, Port Bell Road Luzira, Kampala, Uganda.
Thomas G
TG
Egwang
Department of Molecular Protozoology, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka 565-0871, Japan.
Toshihiro
T
Horii
Division of Malaria Research, Proteo-Science Center, Ehime University, Matsuyama, Ehime 790-8577, Japan.
Eizo
E
Takashima
Division of Malaria Research, Proteo-Science Center, Ehime University, Matsuyama, Ehime 790-8577, Japan. Electronic address: tsuboi.takafumi.mb@ehime-u.ac.jp.
Takafumi
T
Tsuboi
D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood; D000953:Antigens, Protozoan / Q000008:administration & dosage / Q000737:chemistry / Q000276:immunology; D002352:Carrier Proteins / Q000235:genetics* / Q000276:immunology*; D003429:Cross Reactions; D004912:Erythrocytes / Q000469:parasitology*; D017780:Malaria Vaccines / Q000276:immunology*; D016778:Malaria, Falciparum / Q000517:prevention & control; D020066:Merozoite Surface Protein 1 / Q000008:administration & dosage / Q000276:immunology / Q000302:isolation & purification; D052940:Merozoites / Q000502:physiology; D010963:Plasmodium falciparum / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification; D011110:Polymorphism, Genetic; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D011817:Rabbits; D011994:Recombinant Proteins / Q000737:chemistry / Q000276:immunology; D012156:Reticulocytes / Q000378:metabolism / Q000469:parasitology; D014454:Uganda
D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D002352:Carrier Proteins; D017780:Malaria Vaccines; D020066:Merozoite Surface Protein 1; D015800:Protozoan Proteins; D011994:Recombinant Proteins; C000622046:Ripr protein, Plasmodium falciparum
Growth inhibition; Malaria blood-stage vaccine; PfRipr; Plasmodium falciparum; Polymorphism