Identification of a conserved region of plasmodium falciparum msp3 targeted by biologically active antibodies

Abstract

Antigenic and immunogenic determinants of Merozoite surface protein 3 (MSP3). Antigenicity and functional assays identified a 68-amino acid conserved domain of MSP3 as a target of biologically active antibodies. A peptide comprising amino acid residues 184-251 of SEQ ID NO: 2, may also be employed as may peptides consisting of different combinations of the MSP3 a, b, c, d, e and f peptides. Particular non-overlapping or overlapping segments of MSP3 a, b, c, d, e and f peptides may also be used. The various overlapping segments and nonoverlapping segments among the different MSP3 peptides are shown in FIG. 6. MSP3 determinants include targets of antibody-dependent cellular inhibition (ADCI) which is a protective mechanism against Plasmodium falciparum malaria. Six overlapping peptides were derived from the C-terminal end of the MSP3 polypeptide. Each of these peptides defined at least 1 non-crossreactive B cell epitope and contained T helper epitopes. Distinct patterns of antibody responses, by level and IgG subclass distribution, were observed to MSP3 peptides in inhabitants of a malaria-endemic area. Antibodies affinity purified toward each peptide differed in their functional capacity to mediate parasite killing in ADCI assays: 3 of 6 overlapping peptides had a major inhibitory effect on parasite growth. Passive transfer of anti-MSP3 antibodies in vivo in a P. falciparum mouse model confirmed the functional properties of antibodies to these MSP3 determinants.

1 - 45 . (canceled) 
     
     
         46 . An isolated or purified polypeptide that is at least 95% homologous to the C-terminal residues of MSP3 (SEQ ID NO: 2), to the C-terminal residues of MSP3 beginning at residue 1 and ending at residue 251, to fragment of MSP3 consisting of residues 167-354 of SEQ ID NO: 2, or to a fragment of MSP3 consisting of amino acid residues 184-251 of SEQ ID NO: 2; or that is at least 95% homologous to MSP3a (SEQ ID NO: 4), MSP3b (SEQ ID NO: 6), MSP3c (SEQ ID NO: 8), MSP3d (SEQ ID NO: 10), MSP3e (SEQ ID NO: 12) or MSP3f (SEQ ID NO: 14); or an immunogenic peptide fragment having at least 5 contiguous amino acid residues of said polypeptide. 
     
     
         47 . The isolated or purified polypeptide of  claim 46  that is at least 95% homologous to the C-terminal residues of MSP3 (SEQ ID NO: 2). 
     
     
         48 . The isolated or purified polypeptide of  claim 46 , that is at least 95% homologous to the C-terminal residues of MSP3 beginning at residue 1 and ending at residue 251 of SEQ ID NO: 2. 
     
     
         49 . The isolated or purified polypeptide of  claim 46  that is at least 95% homologous to a fragment of MSP3 consisting of residues 167-354 of SEQ ID NO: 2. 
     
     
         50 . The isolated or purified polypeptide of  claim 46  that is at least 95% homologous to a fragment of MSP3 consisting of amino acid residues 184-251 of SEQ ID NO: 2. 
     
     
         51 . The isolated or purified polypeptide of  claim 46  that is at least 95% homologous to MSP3a (SEQ ID NO: 4). 
     
     
         52 . The isolated or purified polypeptide of  claim 46  that is at least 95% homologous to MSP3b (SEQ ID NO: 6). 
     
     
         53 . The isolated or purified polypeptide of  claim 46  that is at least 95% homologous to MSP3c (SEQ ID NO: 8). 
     
     
         54 . The isolated or purified polypeptide of  claim 46  that is at least 95% homologous to MSP3d (SEQ ID NO: 10). 
     
     
         55 . The isolated or purified polypeptide of  claim 46  that is at least 95% homologous to MSP3e (SEQ ID NO: 12). 
     
     
         56 . The isolated or purified polypeptide of  claim 46  that is at least 95% homologous to MSP3f (SEQ ID NO: 14). 
     
     
         57 . The isolated or purified polypeptide of  claim 46  that does not include the C-terminal sequence up to the beginning of third heptad repeat (residue 163 of SEQ ID NO: 2). 
     
     
         58 . The isolated or purified polypeptide of  claim 46  that does not include the C-terminal sequence up to and including the first two C-terminal heptad repeats. 
     
     
         59 . A method for inducing an immune response against  Plasmodium  comprising administering an immunogenic amount of the isolated or purified polypeptide of  claim 46  to a subject in need thereof. 
     
     
         60 . An isolated or purified polynucleotide that encodes the polypeptide of  claim 46 . 
     
     
         61 . A method for inducing an immune response against  Plasmodium  comprising administering an immunogenic amount of the isolated or purified polynucleotide of  claim 58  to a subject in need thereof. 
     
     
         62 . The method of  claim 61 , which comprises:
 administering an amount of at least polynucleotide to a mammal effective to induce an immune response against  Plasmodium falciparum ; wherein said polynucleotide encodes a peptide comprising the 68 amino acid segment covered by peptides Msp3b and Msp3d (residues 184-252 of SEQ ID NO: 2), but which does not include the amino acid segments of Msp3a (residues 167-191) or Msp3f (residues 302-354 of SEQ ID NO: 2); or encodes a peptide that consists essentially of the 68 amino acid segment covered by peptides Msp3b and Msp3d (residues 184-252 of SEQ ID NO: 2).   
     
     
         63 . The method of  claim 61 , wherein the mammal is a human. 
     
     
         64 . The method of  claim 61 , wherein said immune response is sufficient to reduce the severity of disease caused by  Plasmodium falciparum  or sufficient to reduce the incidence of  Plasmodium falciparum  infection in an immunized mammal. 
     
     
         65 . An antibody which binds to the isolated or purified polypeptide of  claim 46 . 
     
     
         66 . The antibody of  claim 65 , wherein the isolated or purified polypeptide it binds to is selected from the group consisting of MSP3 (residues 167-354 of SEQ ID NO: 2), MSP3a (SEQ ID NO: 4), MSP3b (SEQ ID NO: 6), MSP3c (SEQ ID NO: 8), MSP3d (SEQ ID NO: 10), MSP3e (SEQ ID NO: 12) and MSP3f (SEQ ID NO: 14). 
     
     
         67 . The antibody of  claim 65 , which is an affinity purified antibody. 
     
     
         68 . The antibody of  claim 65 , which is a monoclonal antibody. 
     
     
         69 . The antibody of  claim 65 , which is a human antibody. 
     
     
         70 . The antibody of  claim 65 , which inhibits growth of  Plasmodium falciparum.    
     
     
         71 . A method for preventing or treating a  Plasmodium falciparum  infection comprising administering to a subject in need thereof an effective amount of at least one antibody according to  claim 65 .