Antibody targeting of a specific region of Pfs47 blocks Plasmodium falciparum malaria transmission

Abstract

Transmission-blocking vaccines are based on eliciting antibody responses in the vertebrate host that disrupt parasite development in the mosquito vector and prevent malaria transmission. The surface protein Pfs47 is present in Plasmodium falciparum gametocytes and female gametes. The potential of Pfs47 as a vaccine target was evaluated. Soluble full-length recombinant protein, consisting of three domains, was expressed in E. coli as a thioredoxin fusion (T-Pfs47). The protein was immunogenic, and polyclonal and monoclonal antibodies (mAb) were obtained, but they did not confer transmission blocking activity (TBA). All fourteen mAb targeted either domains 1 or 3, but not domain 2 (D2), and immune reactivity to D2 was also very low in polyclonal mouse IgG after T-Pfs47 immunization. Disruption of the predicted disulfide bond in D2, by replacing cysteines for alanines (C230A and C260A), allowed expression of recombinant D2 protein in E. coli. A combination of mAbs targeting D2, and deletion proteins from this domain, allowed us to map a central 52 amino acid (aa) region where antibody binding confers strong TBA (78-99%). This 52 aa antigen is immunogenic and well conserved, with only seven haplotypes world-wide that share 96–98% identity. Neither human complement nor the mosquito complement-like system are required for the observed TBA. A dramatic reduction in ookinete numbers and ookinete-specific transcripts was observed, suggesting that the antibodies are interacting with female gametocytes and preventing fertilization.

Plasmodium PIMMS43 is required for ookinete evasion of the mosquito complement-like response and sporogonic development in the oocyst

“…A recent study has shown that antibodies binding a 52 amino acid region of Pfs47 confer strong transmission blocking of laboratory P. falciparum strains in A. gambiae [42]. In the same study, antibodies binding different regions of the protein showed either weak or no transmission blocking activity, consistent with an earlier study reporting that none of three monoclonal antibodies against Pfs47 could affect P. falciparum infections in A stephensi [43].…”

Transmission-Blocking Vaccines: Old Friends and New Prospects

“…The monoclonal antibodies initially available against Pfs47 did not exhibit TB activity (83), and therefore, Pfs47 had not been the focus of much previous analysis. However, the transmission-blocking potential of Pfs47 has been demonstrated recently (43).…”

“…This problem was overcome by expressing a section of domain 2 (aa 178 to 267) in which the two cysteines were replaced with alanines (mD2). The original MAbs generated against full-length protein did not recognize the recombinant, so mD2 was used to generate additional MAbs, some of which were found to have significant TRA, inhibiting fertilization and subsequent ookinete formation (43). Further analysis of domain 2 identified a smaller, relatively conserved 52-aa region (aa 178 to 229) that elicited TRA antibodies in mice, and this is currently a prospective transmission-blocking vaccine candidate.…”

“…An effective alternative strategy has been to target the P. vivax homologs of P. falciparum TB candidates (21). Polyclonal antibodies targeting the male gamete protein HAP2 and a MAb targeting female-specific Pfs47, a paralog of Pfs48/45, have been shown to reduce transmission significantly (43,44) and are included in the discussion. An Anopheles midgut antigen, AnAPN1, with the potential to block the transmission of malaria in a parasite strain-and species-transcending manner (45), has also been identified and is discussed below.…”

Male-Specific Protein Disulphide Isomerase Function is Essential forPlasmodiumFertilization and Transmission

“…transmission blocking vaccines (TBVs), or transmission blocking drugs (TBDs) against parasitic sexual stages [9]. Antibodies targeted to three of the five currently proven, potent TBV targets have confirmed localization to proteins found on the surface of the plasma membrane of the gametes [10-20], clearly indicating the potential value of targeting this stage of the parasite lifecycle. Additionally, multiple anti-malarial compounds have been demonstrated to have activity against this parasitic stage [21-25].…”