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WO1990011772A1 - Antigenes du stade merozoite localises a l'extremite apicale du parasite - Google Patents

Antigenes du stade merozoite localises a l'extremite apicale du parasite Download PDF

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Publication number
WO1990011772A1
WO1990011772A1 PCT/US1990/001849 US9001849W WO9011772A1 WO 1990011772 A1 WO1990011772 A1 WO 1990011772A1 US 9001849 W US9001849 W US 9001849W WO 9011772 A1 WO9011772 A1 WO 9011772A1
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Prior art keywords
erythrocytes
vivax
duffy
protein
maep
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PCT/US1990/001849
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English (en)
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John W. Barnwell
Mary R. Galinski
Samuel P. Wertheimer
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New York University
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Publication of WO1990011772A1 publication Critical patent/WO1990011772A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K16/00—Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies
    • C07K16/18—Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans
    • C07K16/20—Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans from protozoa
    • C07K16/205—Plasmodium
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
    • C07K14/435—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans
    • C07K14/44—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans from protozoa
    • C07K14/445—Plasmodium
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K38/00—Medicinal preparations containing peptides
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K39/00—Medicinal preparations containing antigens or antibodies
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K2319/00—Fusion polypeptide
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K2319/00—Fusion polypeptide
    • C07K2319/40—Fusion polypeptide containing a tag for immunodetection, or an epitope for immunisation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/30—Against vector-borne diseases, e.g. mosquito-borne, fly-borne, tick-borne or waterborne diseases whose impact is exacerbated by climate change

Definitions

  • This invention relates to antigens of malarial merozoite origin localized at the apical end of the parasite; and to synthetic versions, fragments and derivatives of such antigens which (a) are immunochemically reactive with antibodies recognizing the native merozoite apical end protein, and/or (b) can be used to elicit monoclonal or polyclonal antibodies that recognize the native apical antigen, and/or (c) bind with receptor-like specificity to a Duffy blood group antigen present on the surface of red blood cells (said Duffy antigen serving as the ligand); and/or (d) recognize erythrocyte surface structures involved in parasite invasion of erythrocytes.
  • the antigens of the invention are necessary in the process of invasion of red blood cells by the merozoites.
  • This invention also relates to peptides and polypeptides comprising synthetic versions, fragments, derivatives or analogs of the native malarial polypeptides that have the foregoing properties.
  • This invention also relates to nucleic acids encoding such antigens and to nucleic acids hybridizing therewith.
  • this invention also relates to compositions and methods for inhibiting invasion of susceptible primate (including simian) cells by malarial merozoites and inhibiting the propagation of a malarial organism in the red blood cells of a mammal.
  • compositions and methods employ the antigens of the invention or antibodies immunochemically reactive with these antigens.
  • the invention further relates to vaccine and drug compositions useful for inhibiting the propagation of a malarial organism in the red blood cells of a mammal.
  • the malarial species P.vivax one of the four species infective to humans, is a particularly difficult target for such efforts.
  • This parasite is in. short supply and cannot be cultured in vitro, as has been possible with P. knowlesi (a simian malaria parasite) and P. falciparum (another human malaria parasite).
  • P.vivax bears substantial phylogenetic similarity to P. knowlesi, the two species are different in many important respects. For example, P.vivax is not infective at all to many simian species and infection is poorly established in others, whereas P. knowlesi is poorly infective to humans while readily infecting many simian species.
  • the preinvasion orientation of malarial merozoites indicates that the apical end plays an important role in the invasion process but this role is complex and is not yet clearly understood. Therefore, identification of proteins or other structural features specific to the apical end will provide a better understanding of the molecular mechanism of the invasion process.
  • antigens specifically associated with the apical end are likely to play an important role in apical-end functions, including but not limited to the invasion process and particularly its substages (3) and (4) mentioned above, and therefore at least some such antigens may constitute targets for new antimalarial drugs and/or potential candidates for new vaccines against malaria.
  • Antibodies raised against an apical end-associated antigen would be useful in studies of parasite morphology and structure; could be used in diagnostic or other serological assays designed to determine infection and measure its extent; and could be also used to inhibit invasion by interfering with erythrocyte binding of the apical antigen or otherwise impeding the function of an apical antigen indispensable to the invasion process.
  • the present invention is directed to antigens localized at the apical end of the malarial merozoite surface said antigens being involved in the invasion process and being immunochemically reactive with antibodies raised against malaria (particularly including P.vivax) blood stage parasites; and to synthetic proteins (including but not limited to fusion proteins) polypeptides and peptide fragments and analogs of such antigens that are themselves immunochemically reactive with antibodies raised against the apical-end localized malarial antigens.
  • One particular subgroup of antigens within the invention concerns polypeptides of malarial merozoite origin that bind specifically to a Duffy blood group antigen (said antigen being present on the surface of susceptible mammalian red blood cells) and are necessary in the process of invasion of red blood cells by merozoites; and compounds comprising synthetic versions, fragments, derivatives or analogs of these polypeptides which maintain the ability to bind to the erythrocyte Duffy antigen.
  • the present invention is directed to nucleic acids encoding such antigens, proteins and peptides and to nucleic acids hybridizing therewith.
  • the present invention is directed to materials (including vaccines) and methods for inhibiting the intraerythrocytic propagation of malaria; and to materials (e.g. antibodies, including monoclonal antibodies) recognizing the immunochemically reactive compounds on the surface of P.vivax merozoites and useful inter alia in qualitative and quantitative diagnostic assays for assessing the presence and extent of malarial parasitemia.
  • This invention also provides a method for inhibiting invasion of susceptible mammalian blood cells by malarial merozoites which comprises exposing said merozoites to the presence of an invasion-inhibiting effective amount of antibodies recognizing a parasite polypeptide binding to a Duffy blood group antigen.
  • This invention also provides a method of inhibiting the propagation of a malarial organism in the red blood cells of a susceptible mammal in need of such treatment which comprises administering to said mammal an effective amount of an apicalend-derived peptide or polypeptide (capable of raising antibodies against the parasite antigen from which it was derived and/or inhibiting the binding between said parasite antigen and its erythrocyte receptor).
  • an apicalend-derived peptide or polypeptide capable of raising antibodies against the parasite antigen from which it was derived and/or inhibiting the binding between said parasite antigen and its erythrocyte receptor.
  • One subgroup of this method involves use of a peptide capable of binding to a human Duffy blood group antigen, in an amount effective to inhibit the invasion of said red blood cells by said malarial organism.
  • the invention also provides a composition (such as a vaccine) useful for inhibiting the propagation of a malarial organism in the red blood cells of a susceptible mammal, the composition comprising an effective amount of a peptide within the scope of this invention (e.g. a peptide capable of binding to a human Duffy blood group antigen) and optionally comprising a pharmaceutically acceptable carrier or diluent.
  • a composition such as a vaccine
  • a composition useful for inhibiting the propagation of a malarial organism in the red blood cells of a susceptible mammal
  • the composition comprising an effective amount of a peptide within the scope of this invention (e.g. a peptide capable of binding to a human Duffy blood group antigen) and optionally comprising a pharmaceutically acceptable carrier or diluent.
  • Figures 1A and IB depict the nucleotide and amino acid sequences of a merozoite apical-end-localized protein in accordance with the invention. These sequences correspond to two different portions of the native MAEP (insert 5.3:Fig. 1A; insert 7.2:Fig. 1B).
  • Figure 2 shows SDS-PAGE gels
  • lane a molecular weight m ⁇ rkers
  • lane b purified native MAEP antigen which was isolated by binding to rabbit erythrocytes
  • lane c native MAEP antigen, as a 250 kD protein band, immunoprecipitated by hyperimmune monkey antibodies specifically recognizing the fusion protein from phage clone 5.3.
  • lane b shows SDS-PAGE gels of native MAEP antigen (previously immunoprecipitated with specific antibody) binding to rabbit erythrocytes and compared with total culture supernatants from infected monkey erythrocytes (lane a).
  • Figure 4 shows that hyperimmune monkey antibody specifically recognizing the fusion protein from clone 7.2 also recognizes the native 250 kD MAEP (lane b); rabbit antibodies raised against the fusion protein from clone 5.3 also recognize the native MAEP (lane c) and immunoprecipitate native MAEP (lane d); native purified MAEP binds to human erythrocytes (lane e) and to rabbit erythrocytes (lane f) (lane a contains total supernatant samples).
  • Figure 5 shows an ethidium bromide-stained agarose gel containing parasite DNA (lanes 2 and 7) coding for portions of the native MAEP and DNA size markers (lanes 1 and 8).
  • Figure 6 (also containing SDS-PAGE gels) lane a, shows that hyperimmune monkey antibody specifically recognizes the 7.2 fusion protein and (lane c) monkey antibody specifically recognizes the 5.3 fusion protein and also recognizes native MAEP. Lane b is a control to show that these antibodies do not recognize phage proteins.
  • Figure 7 is an autoradiograph of an SDS-PAGE gel of biosynthetically ( 35 S-methionine) labeled P. vivax proteins which bind to erythrocytes: Total culture supernatant diluted 1:20 with sample buffer (lane 1); proteins binding to human Fy(a + b + 6+), Fy(a + b-6 + ), Fy(a-b+6+) and Fy(a-b-6-) erythrocytes (lanes 2-5); Aotus . Saimiri, Rhesus and Cebus erythrocytes (lanes 6-9); and rabbit erythrocytes (lane 10).
  • the 135 to 140 kilodalton (kD) P. vivax Duffy-associating protein, PvDAP is indicated by the open arrow and molecular weight markers are indicated on the left.
  • Figure 8 is an autoradiograph of an SDS-PAGE gel of metabolically labeled P. knowlesi proteins eluted from (i.e. binding to) mouse and rabbit erythrocytes (lanes 1 and 2); Cebus. Aotus. Saimiri and Rhesus erythrocytes (lanes 3-6); human Fy(a-b-6-), Fy(a + b-6 + ), Fy(a-b + 6 + ) and Fy(a + b + 6 + ) erythrocytes (lanes 7-10).
  • the 135kD P. knowlesi Duffyassociating protein, Pkl35 is indicated by the closed arrow on the right.
  • Figure 9A depicts a gel of silver stained SDS-PAGE affinity-purified human Duffy glycoprotein (seen as the band closest to m.w. marker 42). Duffy glycoprotein aggregates appear as a smear and extra bands in immunoblots with the anti- Fy 6 monoclonal antibody (mAb).
  • mAb monoclonal antibody
  • Figure 9B is an autoradiograph of an SDS-PAGE gel showing inhibition of protein binding to Duffy-positive human erythrocytes by prein ⁇ ubating purified human Duffy glycoprotein erythrocyte binding assay culture supernatant from an erythrocyte binding assay: inhibition of PvDAP or Pkl35 to either human Fy(a + b + 6 + ) or Fy(a-b + 6 + ) erythrocytes (lanes 2 and 5); controls with ho protein added to the culture supernatants (lanes 1 and 4) or with addition of an unrelated sialoglycoprotein, orosomucoid (lanes 3 and 6).
  • PvDAP is indicated by the open arrow and Pk135 is indicated by the closed arrow.
  • Figure 9C shows inhibition of protein binding to human Fy(a + b + 6 + ) or Fy(a-b + 6 + ) erythrocytes presensitized with the anti-Fy° mAb before doing an erythrocyte binding assay with either P. vivax or P. knowlesi culture supernatants (lanes 1 and 4, respectively). Controls include withholding of the antibody (lanes 2 and 5) or use of an unrelated (anti-glycophorin) mAb (lanes 3 and 6). PvDAP is indicated by the open arrow and Pkl35 is indicated by the closed arrow.
  • Figure 10 is an SDS-PAGE autoradiograph showing the effect of protease treatment of erythrocytes on the ability of parasite proteins to bind: P. vivax proteins binding to human Fy(a + b + 6 + ) erythrocytes treated with either no enzymes, trypsin, or chymotrypsin (lanes 1-3); human Fy(a-b + 6 + ) erythrocytes treated with either no enzyme or V-8 protease (lanes 4 and 5); P. knowlesi proteins binding to human Fy(a-b + 6 + ) erythrocytes treated with no enzymes or with V-8 protease (lanes 6 and 7).
  • PvDAP and Pk135 are indicated by the open and closed arrows, respectively.
  • Figure 11A represents the SDS-PAGE analysis of the
  • Saimiri monkey antiserum P. knowlesi proteins binding to Rhesus monkey erythrocytes (lane 1); P. knowlesi proteins eluted from Rhesus erythrocytes and immunoprecipitated with the Saimiri antiserum (lane 2); proteins immunoprecipitated from a P. knowlesi culture supernatant or a detergent extract (lanes 3 and 4); immunoprecipitation of a 135 to 140kD protein from a P. vivax detergent extract (lane 5).
  • Pre-immune Saimiri serum used to immunoprecipitate proteins from detergent extracts of either P. knowlesi or P. vivax as controls (lanes 6 and 7, respectively).
  • Figure 11B is an SDS-PAGE gel autoradiograph showing the results of immunoprecipitation using the Saimiri monkey antiserum of proteins from a P. knowlesi detergent extract incubated at 37°C without protease inhibitors for 0, 2, 5, 10, 20, 40 and 60 minutes (lanes 1-7).
  • the 160kD protein and the 135kD P. knowlesi proteins are indicated by the arrow head and the closed arrow, respectively.
  • Figure 12 depicts the amino acid and encoding nucleotide sequences of a 1.8kb cloned insert of the Pk DAP gene.
  • immunochemically reactive refers to the ability of a peptide or protein to recognize (i.e. bind to) an antibody and vice versa (i.e. the ability of an antibody to recognize a peptide or protein);
  • antigen means a peptide or protein that either elicits antibodies in mammals or is "immunochemically reactive" (as defined above) with antibodies elicited by immunization with another antigen;
  • MAEP or "merozoite apical-end protein” means any natural or synthetic peptide, protein or antigen which is immunochemically reactive with antibodies recognizing a native merozoite protein localized at the apical end of malarial parasites;
  • DAP or "Duffy-associating protein” (PvDAP) means a particular malarial MAEP which specifically binds to the Duffy blood group antigen of primate erythrocytes such that in the absence of this protein invasion of the erythrocytes by the parasite cannot be accomplished.
  • MAEP-based peptide means a peptide, polypeptide or antigen that comprises a synthetic version, or a derivative, fragment or analog of MAEP; accordingly a “DAP-based peptide” is a particular MAEP based peptide that binds to the Duffy blood group of primate erythrocytes;
  • compound comprising MAEP or a MAEP-based peptide means a compound or conjugate or synthetic construct which is or comprises an amino acid sequence corresponding to MAEP or a MAEP-based peptide (both as defined above);
  • parasitemia in malarial infection is defined as the presence of at least one parasite in 10,000 blood cells of the host.
  • peptide shall be deemed to include polypeptides, antigens or proteins except if the context requires otherwise; and the term “synthetic” shall be deemed to encompass substances synthesized by classical chemical techniques and substances synthesized by recombinant DNA techniques.
  • the invention is directed to a surface 250 kD protein isolated from P.vivax merozoites which is localized (on the merozoite surface) at the apical end of the parasite and has the property of binding to human reticulocytes (i.e. non-nucleated immature erythrocytes) and consequently is involved (and is potentially important) in erythrocyte invasion by P.vivax.
  • P.vivax is known to invade reticulocytes almost exclusively.
  • Another important property of this protein is that it is specifically recognized by antibodies elicited against whole blood stage parasites and in turn elicits antibodies recognizing the native protein on the merozoite surface.
  • the MAEP antigens of this invention constitute potential components for a malaria vaccine.
  • More embodiments of this invention include synthetic versions of this protein as well as fragments, deriva tives and analogs thereof having the same immunogenic, immunorecognition and/or inhibiting properties.
  • this protein includes a molecular weight of about 250 kD; a highly hydrophilic, highly charged region which extends over at least 50% of its amino acid sequence; the total absence of repetitive sequences (in contrast to other known blood-stage and sporozoite-stage antigens); a probable largely alpha-helix secondary structure with beta turns as determined by algorithms for deducing protein secondary structure (Chou-Fasman and Robson-Garnier); and at least 15 potential N-linked glycosylation sites.
  • This MAEP protein binds to the surface of susceptible erythrocytes (reticulocytes) from P.vivax susceptible humans and primates and also binds to rabbit erythrocytes (despite the fact that rabbits are not susceptible to P.vivax).
  • P. knowlesi Based on the phylogenetic similarity between P.vivax. P. cynomolgi. and P. knowlesi. it is likely that a corresponding MAEP will be found to be present in P. knowlesi and P. cynomolgi. Whether such a P. knowlesi protein exists can be determined by the same methods described herein and variations thereof within the skill of the art.
  • antibodies specifically recognizing P. vivax MAEP can be used to extract P. knowlesi MAEP based on the extensive cross-reactivity of antibodies against each of those species.
  • anti ⁇ era against P. knowlesi can be separated based on their ability to bind fusion proteins expressed from a genomic P. knowlesi DNA library and antibodies binding each P.
  • knowlesi fusion protein can be used in immunofluorescence assays for localization of their antigenic determinants at the apical end of P. knowlesi merozoites.
  • Other malarial species such as P. falciparum. may also possess MAEP's which can be identified and sequenced using no more than ordinary skill in the art in light of the present description, and hence the present invention is not limited to P.vivax.
  • MAEPs can be used as described in the Background section to design potential drugs and antigens for combatting malaria and to gain a better understanding of the biology and pathology of this disease.
  • a native P. vivax MAEP was identified by screening a lambda gt 11 genomic P. vivax DNA expression library with sera from Saimiri sciureus monkeys hyperimmunized with P. vivax schizonts, a procedure which yielded a restricted antibody response (directed against 12 antigens).
  • Monkey antibodies reacting specifically with expression products from two clones of the genomic library (the clones being designated 5.3 and 7.2, respectively) recognized this native MAEP by immunofluorescence and were used to immunoprecipitate it from P. vivax merozoite 35 S-methionine labeled extracts.
  • DNA from the positive clones (5.3 and 7.2) was expressed to yield MAEP's as beta-galactosidase fusion proteins. Both fusion proteins elicited antibodies which also recognized the native MAEP. Accordingly, such fusion proteins are fully within the scope of this invention. Moreover the results of these experiments show that the native MAEP (or synthetic versions thereof) and antigenic fragments thereof are immunogenic and elicit antibodies which recognize the native MAEP on the merozoite apical surface. Hence, MAEPs which comprise less than the entire sequence of the native MAEP are antigenic and (as will be shown below) can be used to elicit antibodies that inhibit the binding of native MAEP to mammalian (including human) erythrocytes.
  • synthetic antigens will be constructed containing one or more subsequences (optionally with further deletions or substitutions of one or more amino acids) of the native MAEP such that the synthetic constructs will bear one or preferably more antigenic determinants of the native MAEP and/or maintain the ability of eliciting antibodies that recognize the native MAEP.
  • heterologous sequences can also be added or interposed in such constructs (as can amino acid or subsequence dilution or substitutions) to enhance their immunogenic ability (and/or activity of the resulting antibodies in inhibiting binding of the merozoite MAEP to erythrocytes and/or the invasion of erythrocytes by the parasite).
  • peptides based on these antigens and having desired immunochemical properties can be synthesized, e.g. as described in Merrifield, R.B. Fed. Proc. Am. Soc. Ex. Biol. 21: 412, 1962 and J. Am. Chem. Soc. 85: 2149, 1963; Mitchel, A.R. et al., J. Am. Chem. Soc. 98: 7357, 1976; Tarn, J. et al., J. Am. Chem. Soc. 105: 6442, 1983.
  • Genomic library (phage) clone 5.3 contained approximately 3.8 kb of P. vivax DNA; phage clone 7.2 contained approximately 1.9 kb of P. vivax DNA; DNA from these clones did not cross-hybridize, indicating that essentially different portions of MAEP are encoded by each fragment.
  • the MAEP-encoding nucleotide sequence for P. vivax clone 5.3 (in which the sequence is present in an open reading frame) was determined and is set forth in Fig. 1A, along with the amino acid sequence it encodes. To obtain this DNA sequence the P.
  • vivax DNA insert from the lambda gt 11 recombinant clone 5.3 was isolated and subcloned into the plasmid pBluescript (obtained from Stratagene) and a series of clones containing overlapping deletions of the 5.3 insert were created using the exonuclease-III/mung-bean-nuclease deletion kit obtained from Stratagene and the supplier's protocol slightly modified to use 1 microgram of DNA per deletion as opposed to 5 micrograms as suggested by the supplier.
  • the inserts contained within the series of clones were sequenced using the well-known Sanger et al. technique (Proc. Nat'l Acad. Sci.
  • the P. vivax DNA inserts from the 5.3 and 7.2 clones have been isolated, labelled with 32 P dCTP using a random-primed labeling kit (Boeringer-Mannheim) and used to screen a nonexpression lambda-Fix/genomic P. vivax DNA library (lambda-Fix and other lambda replacement vectors suitable to clone fragments of DNA in the 9-23 kb range can be obtained from Stratagene) to identify the entire gene encoding this P . vivax MAEP. Hybridization of 32 p-labeled 5.3 and 7.2 inserts to P.
  • vivax Bam Hl-restricted DNA reveals in both cases a single hybridizing band.
  • a lambda-Fix/P. vivax genomic library was made using Bam Hl-digested P. vivax DNA.
  • the library was packaged using GIGAPACK IITM packaging extracts and accompanying protocols from Stratagene. Additionally, a portion of this library may be packaged using GIGAPACK XLTM extracts from Stratagene which preferentially package large DNA fragments, thus increasing the likelihood that the gene encoding the MAEP and contained in P. vivax DNA fragments of 20-23 kb will be cloned.
  • the MAEP-encoding gene may alternatively be identified in other P. vivax libraries constructed according to known methods, or otherwise available, provided the inserted P. vivax DNA contains the MAEP gene in its entirety.
  • positive phage can be plaquepurified, prepared in large liquid lysate cultures (Kern, J., Brenner, S., and Barnett, H.L., Meth. Enzymol. 101:3-19. 1981) and purified using, e.g., LAMBDASORBTM (Promega).
  • the entire gene and its flanking sequences can then be characterized; initially a restriction map can be obtained in which inserts 5.3 and 7.2 can be placed accordingly and appropriate subclones can be placed accordingly and appropriate subclones can be prepared in order to obtain the remaining sequence of MAEP, i.e., the segment not encoded within the inserts of these two clones.
  • the MAEP's of the present invention can be extracted from merozoites by immunoprecipitation and other well-known techniques in the art including chromatographic techniques e.g., using a suitable polysaccharide as the adsorbent and ionic, nonionic and/or affinity chromatography conditions (including but not limited to high performance liquid chromatography).
  • immunoaffinity chromatography using as the adsorbent polyclonal or monoclonal antibodies to the MAEP protein bound to a suitable support, such as a polysaccharide support
  • a specific MAEP immunoaffinity purification protocol is the following:
  • Monoclonal antibodies specific for MAEP are immobilized on a cross-linked agarose support (such as a chromatography column), the MAEP-containing extracts or fluids (e.g. serum from an infected individual) are contacted with the immobilized antibody and the purified MAEP is thereafter eluted from the immune complex formed.
  • a cross-linked agarose support such as a chromatography column
  • ion-exchange chromatography e.g. anion-exchange chromatography on e.g. DEAE-Sepharose (Pharmacia Fine Chemicals, Piscataway, NJ) or molecular sizing FPLC (high-performance liquid chromatography from Pharmacia) can be used alone or sequentially with (before or after) the immunoaffinity column.
  • DEAE-Sepharose Pulcoa Fine Chemicals, Piscataway, NJ
  • molecular sizing FPLC high-performance liquid chromatography from Pharmacia
  • the MAEP's of the present invention can also be produced by recombinant DNA techniques.
  • MAEP DNA can be expressed in any known expression system preferably in a glycosylation-providing expression system such as yeast (European Pat. Appln. Ser. No. A 3 175261 of Chiron Corporation published March 26, 1986 corresponding to U.S. Pat. Appln. Ser. No. 650,323, filed September 12, 1984) or in mammalian cells.
  • the MAEP's of the. present invention are useful in understanding the mechanism of erythrocyte invasion by the blood stage of P.vivax (and possibly also by the blood stage of other malarial species). Also, monoclonal antibodies raised using synthetic or native MAEP's as the immunogen and recognizing the native MAEP can be used in sensitive serologic diagnostic assays, given that the native MAEP is localized in the apical region of the blood stage P.vivax parasite.
  • Monoclonal antibodies against MAEP's can be raised using e.g. the now classical Kohler, G. & Milstein, C. technique (Nature 256:495-497. 1975). Such monoclonal antibodies can then be used in diagnostic assays as follows:
  • Serum from infected or susceptible individuals can be screened for the presence of MAEP antigen or antibody to MAEP antigen, using well-known Enzyme-Linked Immunosolvent Assay (ELISA) or another assay system.
  • ELISA Enzyme-Linked Immunosolvent Assay
  • a first monoclonal anti-MAEP can be bound to a solid support; incubated with sera from the individual to be tested (unbound sera will be washed with PBS or another suitable buffer); and incubated with a second labelled monoclonal anti-MAEP directed to a different MAEP epitope. After washing to remove unbound second antibody, the complexes can be detected and counted. See McDougall, J.S. et al. J. Immunol. Meth. 76:171-183, 1985.
  • antibody to MAEP circulating in the individual's serum can be detected by ELISA according to the method of Engevall, E., Methods in Enzvmology. 70:419-439, 1981. Briefly, MAEP is bound to a solid support (e.g. on a microtiter plate) unbound antigen is removed; the plate is incubated with sera from the individual to be tested; unbound sera are removed; and an anti-immunoglobulin antibody (suitably labelled) (e.g. goat-anti-human IgG) is used to reveal the bound antigen-antibody complexes.
  • an anti-immunoglobulin antibody suitably labelled
  • an anti-immunoglobulin antibody e.g. goat-anti-human IgG
  • assays can also be performed using MAEPs from parasites infective to other species, e.g. monkeys.
  • the MAEP's of the present invention will be used in immunogenically effective amounts alone or in combination with other vaccine components (in fact, MAEP's for this purpose can be made by recombinant DNA techniques and can be co-expressed with such other active vaccine components) with or without any suitable carrier, an adjuvant or a diluent all of which should be pharmaceutically acceptable. Repeat immunizations may be necessary to enable the host to mount an immune response. Both amounts of immunogen and immunization protocols can be determined experimentally, as is well-known in the art, using animal (e.g. primate) models followed by clinical testing in humans. Information on vaccine compositions and immunization is described for example in U.S. Patent No.
  • this invention is directed to a purified DAP of malarial origin (or a synthetic version or fragment thereof) capable of binding to a Duffy blood group antigen with a receptor-like specificity (wherein the Duffy antigen serves as a ligand and DAP serves as a receptor).
  • Duffy blood group antigen is present in primate red blood cells, especially including human red blood cells, specifically the human red blood cells and other primate erythrocytes susceptible to P.vivax having the Fy 6 determinant or phenotype (Nichols, M.E. et al, J. EXP. Med. 166:776. 1987).
  • Such an Fy 6 phenotype may comprise Fy(a-b + ), Fy(a + b + ) and Fy(a + b-) phenotypes of human erythrocytes but not Duffy negative human erythrocytes (Fya-b-).
  • Duffy-positive red blood cells also include simian cells, e.g., Aotus monkey erythrocytes and erythrocytes of other simians and apes susceptible to P. knowlesi or P. vivax malaria.
  • the Duffy glycoprotein human Duffy positive erythrocytes is present in approximately 13,000 copies per cell.
  • DAP of P. vivax origin has been designated P. vivax
  • Duffy-associating protein (PvDAP) and has been determined to possess an apparent molecular weight (by SDS-PAGE) in the range from about 135,000 to about 140,000 daltons (135-140kD); DAP from P. knowlesi is designated herein PkDAP (or Pkl35) and has a molecular weight (by SDS-PAGE) of about 135kD.
  • SDS-PAGE was performed by the method of Laemli, U.K., Nature 227:680-685. 1970, as a discontinuous buffer system and at a polyacrylamide concentration of 7.5%.
  • DAP proteins include immunologic relatedness between PvDAP and PkDAP in that antibodies raised against one recognize (and bind to) the other; the possibility that the DAP proteins are products of proteolysis of higher-molecular weight parasite protein structures; the fact that the receptor-ligand interaction between DAP and the Duffy antigen is essential for erythrocyte invasion by merozoites; the inability of DAP to bind to erythrocytes from P. vivax-insusceptible host red blood cells; and the inability of PkDAP to bind to erythrocytes from P. knowlesi-insusceptible hosts.
  • PvDAP binds with equal affinity to all Duffy-positive human phenotypes and to Aotus erythrocytes but PkDAP binds with higher affinity to human Fy(a-b + ) erythrocytes than to other Duffy positive human erythrocytes, yet all human Duffy-positive erythrocytes are equally susceptible to P. vivax invasion.
  • PvDAP appears to interact with different determinants on the Duffy glycoprotein than PkDAP, which may account for the different erythrocyte host specificities of the two parasites.
  • the PvDAP and PkDAP bind to erythrocytes with different specificities (which can be only partially explained by known characteristics of Duffy antigens).
  • the DAP proteins from the two malarial species are distinct although they both recognize and bind to Duffy antigen.
  • the DAP proteins may be isolated from natural sources, i.e. parasite material (preferably previously selected for ability to bind to erythrocytes) by immunoprecipitation with antibodies raised against P. knowlesi merozoites, regardless of the malarial species provenance of the DAP (since the P. knowlesi antisera recognizing PkDAP cross-react with PvDAP).
  • DAP may be isolated by chromatographic techniques, including affinity chromatography e.g., using purified Duffy antigen as the affinity adsorbent immobilized on a polysaccharide support as described above for MAEPs followed by immunoaffinity chromatography, e.g., using polyclonal anti- P.
  • purified DAP can be used to elicit monoclonal antibodies to DAP (e.g., according to the well-known technique of Kohler, G. and Milstein, C., Nature 256:495-497, 1975) and the monoclonal antibodies can be used as the immunoaffinity adsorbent (bound to a polysaccharide or cellulose support) in subsequent purification of DAP from natural sources.
  • high-performance liquid chromatography (HPLC) including reverse-phase HPLC can be used.
  • DAP and DAP-based peptides can also be prepared by synthetic techniques including chemical peptide synthesis and recombinant DNA techniques, as described further below.
  • DAP and DAP-based peptides may be used as immunogens to raise antibodies in the host (or in another host or in vitro, as in passive immunization) which will recognize and bind to the native DAP protein on the merozoite surface.
  • immunogenic compounds comprising DAP and DAP-based peptides may be used in vaccine preparations to confer prophylactic immunity against the blood stage of malaria or to confer therapeutic immunity by preventing (totally or partially) further intraerythrocytic propagation of the disease in the host through interference with the binding of DAP with the Duffy antigen.
  • the necessity of DAP binding to its ligand for invasion to occur can be shown in vitro.
  • Pk DAP antisera inhibit in vitro invasion of human erythrocytes by P.
  • DAP-based peptide is not immunogenic, its structure may be altered to confer immunogenic properties to it such that the resulting construct will elicit antibodies recognizing native DAP.
  • 100% inhibition of merozoiteerythrocyte binding by a compound (or vaccine containing it, or antibody) according to the present invention is not necessary for these materials to be useful. Any substantial decrease in the extent of infection (as measured, e.g. by the extent of parasitemia) would substantially attenuate the clinical symptoms and substantially increase the probability for survival and recovery of the host. For example, a 50% inhibition of erythrocyte-parasite binding would produce a substantial decrease in parasitemia.
  • DAP-based peptides may be used in drug design to design antagonists to the DAP receptor (i.e. molecules that bind to but do not activate DAP) and thus prevent Duffy-native DAP ligand-receptor interactions or may be used as competitive inhibitors of the Duffy ligand-DAP receptor binding.
  • DAP-based peptides preferably of relatively short length (e.g. molecular weight 5,000 or less) comprising fragments or derivatives of the amino acid sequence DAP protein and binding to the Duffy blood group antigen (preferably with at least substantially the same affinity as the native DAP on the merozoite surface) can be used to inhibit the receptor-ligand binding and thus prevent invasion of erythrocytes.
  • peptides corresponding to various fragments of DAP can be synthesized (optionally derivatized, e.g. incompletely deprotected peptides or peptides also containing non-DAP amino acid sequences or sequence-terminated, i.e. deletion, peptides) using, e.g., the well-known automated peptide-synthesis procedures based on Merrifield, R.B., Fed. Proc. Fed. Am. Soc. Ex. Biol. 21:412, 1962; J. Chem. Soc. 85:2149, 1963 or recombinant DNA methods, also well-known and widely used.
  • peptides can be then tested for their ability to bind Duffy antigen or block DAP binding, e.g. by the erythrocyte binding assay of Example 1, and/or by the erythrocyte invasion of Example 8.
  • competitive versions of these assays in microtiter plates can be used as follows; known quantities of native DAP or recombinant DAP (1.0-100 nanograms) are mixed with candidate peptides (1.0-100 ug)to determine if peptides inhibit binding of DAP to purified Duffy antigen (or Fy 6 ) .
  • the Duffy glycoprotein (or Fy 6 ) could be plated in microtiter wells or to native Duffy antigen on erythrocytes.
  • DAP inhibits peptide binding to Duffy antigen Either DAP or peptides could be radiolabled (125 I or 35 S) to provide a means of detecting functional activity.
  • Nonlimiting examples of recombinant DNA techniques that can be used include those disclosed in U.S. Patents Nos. 4,419,450; 4,418,194; 4,414,150; 4,399,216; 4,394,443; 4,356,270; 4,351,901 and 4,237,224.
  • synthetic DNA sequences may be prepared encoding the desired amino acid sequences, such DNA sequences can be inserted in suitable cloning vectors, and the vectors used to transform various organisms which will then express the desired product. See U.S. Patents Nos. 4,273,875; 4,304,863; 4,332,901; 4,403,036; 4,363,877; and 4,349,629. See also European Application No.
  • the DAP-based synthetic peptides can thus be tested using, e.g., the assay system of Example 1 for inhibition of the DAP-Duffy binding. Successful inhibitors can then be incorporated in drug and vaccine preparations using methods and formulations well-known in the art.
  • DAP-peptide amino acid sequences as well as other components are within the scope of the invention.
  • DAP-peptide sequences can be co-expressed (e.g., in the manner of fusion proteins) with (or bound or ligated or conjugated to) other immunogenic or immune-response enhancing heterologous or malarial-derived peptides and proteins, or nonpeptide entities such as carriers, adjuvants, immunogens mimicking other parasite antigens etc.
  • compositions in accordance with the present inventions can comprise mixtures of such ingredients as separate chemical species.
  • nucleic acid comprising nucleotide sequences encoding DAP or DAP-based peptides described above and nucleic acid hybridizing therewith.
  • This invention further provides cDNA, i.e., nucleic acid which is complementary to the nucleic acids described in the preceding sentence. Methods for preparing such nucleic acid molecules are well-known in the art and the references cited above for preparation of the instant compounds can be used to prepare the nucleic acids encoding for them.
  • Yet another aspect of this invention provides a method for inhibiting invasion of susceptible primate blood cells by malarial merozoites which comprises exposing said merozoites to the presence of an invasion-inhibiting effective amount of antibodies raised against a compound comprising DAP or a DAP- based peptide and binding to primate Duffy blood group antigen.
  • the step of exposing the malarial merozoites to the presence of an invasion inhibiting effective amount of antibodies recognizing a DAP or a DAP-based peptide binding to primate Duffy blood group antigen can be carried out in vitro. Alternatively, this step is carried out in vivo by immunization (or passive immunization) of a susceptible (or infected) host with DAP, or with a DAP-based peptide or a compound comprising either.
  • This invention also provides a method of inhibiting the propagation of a malarial organism in the red blood cells of a susceptible mammal which comprises administering to the mammal an immunogenically effective amount of a compound or composition comprising DAP or DAP-based peptide (or another MAEP or MAEP-based peptide), such an amount being effective to elicit antibodies that inhibit invasion of the red blood cells by the malarial organism.
  • the compound or composition may be administered to a mammal which has been previously exposed to the malarial organism.
  • the polypeptide may be administered to a mammal prior to exposure of the mammal to the malarial organism.
  • Vaccine preparations in accordance with the invention can be prepared as generally described in Voller, et al. (Ed) New Trends and Developments in Vaccines, University Park Press, Baltimore, MD, 1978.
  • Conjugation of DAP-based peptides and DAP to macromolecules can be made as is well-known in the art, e.g. as disclosed in U.S. Patent No. 4,372,945 or 4,474,757
  • conjugation to multiple antigen peptide systems can be accomplished, e.g., as disclosed in Tarn, J., Proc. Nat'l. Acad. Sci. (USA), 85:5409, 1988 using techniques described therein and in Mitchell, A.R. et al., J. Am. Chem. Soc. 98:7357, 1976.
  • encapsulation in liposomes can be accomplished, e.g., as described in U.S. Patent No. 4,235,877.
  • the DAP or DAP-based peptide compounds and constructs or mixtures thereof will be typically formulated in vaccine compositions comprising a pharmaceutically acceptable medium or diluent (e.g. an aqueous solution, preferably at physiological pH).
  • a pharmaceutically acceptable medium or diluent e.g. an aqueous solution, preferably at physiological pH.
  • the immunogenic ingredient or ingredients can be admixed with or adsorbed to any known pharmaceutically acceptable carrier (e.g. a macromolecule) or adjuvant, such as killed Bordetella. tetanus toxoid, diphtheria toxoid, muramyl dipeptide, aluminum hydroxide, saponin, etc.
  • the amount of DAP or DAP-based peptide will vary depending upon the specific immunogen, the response it elicits in various subjects, and the presence or absence of heterologous carrier or adjuvant. Generally, amounts within the range from about 1 to about 1,000 micrograms of DAP or peptide are contemplated. Optimal amounts can be ascertained by routine experimentation involving measurement of antibody titers and other parameters of primate immune response, as is well-known in the art. Repeat immunizations are preferred. The foregoing vaccine discussion is also applicable to other MAEPs.
  • a lambda gt 11/P. vivax genomic DNA expression library was constructed simply by ligating P. vivax DNA predigested with Eco Rl into the Eco Rl cloning site of lambda gt 11 (Young, R.A., and Davis, R.W., Proc. Nat'l Acad. Sci. USA 80:1194, 1983) and packaging the resulting ligation mix using PackageneTM extracts purchased from Promega (lambda gt 11 was also purchased from Promega).
  • Another mode of construction of a genomic DNA library could have been used with optional suitable modification of the subsequent expression strategy.
  • a Saimiri sciureus monkey was hyperimmunized with P.vivax schizonts, by intravenous infection with schizontinfected erythrocytes from an infected Saimiri monkey. The injection was repeated three times.
  • the monkey was injected intramuscularly with inactivated schizonts twice in complete Freund's adjuvant and once in incomplete Freund's adjuvant.
  • a four- to six-week waiting period was interposed between successive injections.
  • the resulting antisera contained a very restricted antibody response (directed against 12 antigens).
  • the antisera were used to screen the lambda gt 11/P. vivax genomic DNA library, expressed in E. coli cells Y1090 (obtained from Stratagene). Lambda gt 11 recombinant phage expressing proteins that reacted positively with this hyperimmune serum were individually reacted with the hyperimmune serum, and those antibodies that reacted specifically with each recombinant, protein-expressing phage were purified as is well known in the art using a plaque adsorption and elution methodology (Hall et al., Nature 311:374, London, 1984).
  • phage plaques expressing individual recombinant proteins were overlayed with a nitrocellulose filter that had been impregnated with Isopropyl beta-D-thiogalactopyranoside (Sigma Chemical Company) and incubated for 3 hours at 37°C to allow the expression of the proteins and their adherence to the nitrocellulose filters.
  • the specific-reacting monkey antibodies were purified by adsorption of the monkey immune sera to the protein of these filters, followed by extensive washes in a Tris Borate Saline/Tween solution and elution with 0.2 M glycine, pH 2.5. These antibody preparations were dialyzed against phosphate buffered saline.
  • Antibodies purified in this manner from the lambda gt 11 clones 5.3 and 7.2 recognized the apical end of P. vivax merozoites by immunofluorescence and immunoprecipitated the 250 kd MAEP antigen from 35 S-methionine labeled parasite extracts ( Figure 3).
  • the 5.3 and 7.2 lambda gt 11 recombinant phage were used to infect Y1088 cells (obtained from Stratagene) to obtain lysogens suitable for the growth of large recombinant phage preparations. Phage were prepared from these lysogens essentially as described for the production of lambda gt 11 phage in DNA Cloning 1: A Practical Approach, Glover, D.M., Editor, IRL Press 1986, Vol. 1, Chapter 2, Huynh, T.V., Young, R.A. , and Davis, R.W. and the phage and their DNAs were purified using LambdasorbTM and accompanying protocols from Promega.
  • Fig. 5 shows an aliquot of both 5.3 and 7.2 purified insert DNAs run next to DNA markers and stained with ethidium bromide. Their insert sizes are estimated at 3.8 kb and 1.9 kb, respectively (Fig. 5).
  • the fusion proteins corresponding to positive clones 5.3 and 7.2 were affinity purified on anti- beta-galactosidase columns and used to immunize rabbits.
  • Antibodies from the immune sera elicited with each fusion protein were shown to recognize the native MAEP antigen (see Figure 4 lanes B and C wherein lane B shows proteins (including the MAEP) recognized by the whole immune rabbit sera and lane C shows the result of immunoprecipitation of MAEP with purified anti-5.3 antibody from the rabbit immune sera).
  • Im munoprecipitation was conducted as described below,
  • Parasite extracts were prepared from purified P.vivax trophozoite-infected erythrfecytes that were washed in RPMI-1640 tissue culture medium and incubated in RPMI-1640 medium which was 90% methionine-deficient (as described in Trager, W. et al., Science 193: 673, 1976) but supplemented with 35 S- methionine (100 microcurie/ml) and 10% human AB serum. The parasites were then allowed to mature to schizonts at 37°C.
  • the cells were then extracted in 1% Triton X-100 at 4°C preferably in the presence of protease inhibitors (50 micrograms/ml each chymostatin and leupeptin, both from Sigma Chemical Co., St. Louis, MO). The cells were extracted for 0.5 hr. with agitation. After extraction, the solution was centrifuged to remove any particulate material.
  • protease inhibitors 50 micrograms/ml each chymostatin and leupeptin, both from Sigma Chemical Co., St. Louis, MO.
  • the complexes were dissociated by addition of an equal volume of SDS sample buffer containing mercaptoethanol, boiled and applied to a 7.5% SDS-PAGE (sodium dodecyl phosphate polyacrylamide gel electrophoresis).
  • SDS-PAGE sodium dodecyl phosphate polyacrylamide gel electrophoresis
  • Example 3 Immunofluorescence Studies Antibodies specifically recognizing the fusion protein from clone 5.3 were incubated with smears of air-dried P. vivax schizonts and merozoites from an infected Saimiri monkey. Unbound antibody was washed with PBS. Anti-immunoglobulin antibodies were labelled with fluorescein isothiocyanate and were incubated with the smear-antibody complex. Unbound labelled antibody was again removed by washing. Fluorescence was detected using a Leitz epifluorescence microscope with a UV light source.
  • MAEP-containing total culture supernatants in which biosynthetically labeled infected erythrocytes were allowed to form merozoites which rupture naturally and release parasite proteins into the medium
  • erythrocytes (1 X 10 9 ) were washed three times with PBS and then incubated with 300 microliters of labelled MAEP for 30 minutes at room temperature with rocking. The erythrocytes were then washed to remove unbound parasite proteins by centrifugation through silicone oil (550 Silicone oil, Dow Chemical Corp., Midland, MI) in an Eppendorf microfuge.
  • silicone oil 550 Silicone oil, Dow Chemical Corp., Midland, MI
  • the pellet was resuspended in 500 microliters RPMI-1640 and centrifuged through oil a second time.
  • the erythrocyte pellet was then incubated with fifty microliters of 1M NaCl for 20 min., and centrifuged.
  • the supernatant was mixed with an equal volume of SDS sample buffer containing mercaptoethanol.
  • the samples were electrophoresed on a 7.5% SDS-PAGE and autoradiographed after impregnation with EnHance scintillation enhancer (NEN/Dupont, Wilmington, DE). The result for rabbit erythrocytes is shown in Fig. 2, lane A.
  • the 250kD MAEP is clearly indicated by the arrow and is specifically immunoprecipitated by rabbit anti-5.3 fusion protein antibodies in lane B.
  • the results of similar binding experiments using human erythrocytes were consistent: they are depicted in lane F of Figure 4.
  • the binding experiment with the rabbit erythrocytes was repeated using immunoprecipitation-purified MAEP instead of total culture supernatants.
  • the results are shown in Figure 3 run on SDS-PAGE side-by-side with a gel containing total culture supernatants.
  • the 250kD MAEP is clearly present in both lane A (total supernatants) and lane B (rabbit erythrocytes).
  • Polyclonal antibodies were raised against the fusion protein expressed from clone 5.3 (which were found to specifically react with antisera from P.vivax immunized Saimiri monkey. These antisera were then used to immunoprecipitate P. vivax protein bands from biosynthetically labeled ruptured erythrocyte culture supernatants. The results are shown in
  • P. vivax (Belem strain) or P. knowlesi (H strain) infected blood drawn from Saimiri or Rhesus monkeys was purified and enriched as follows: P. knowlesi (H strain) parasites were cryopreserved in liquid nitrogen as ring-stage infected erythrocytes from Rhesus monkeys according to Barnwell, J.W., et al., Infect. & Immun. 40(3):985, 1983.
  • Cryopreserved infected erythrocytes for use in invasion assays in vitro were thawed and cultured to the schizont stage in tissue culture medium RPMI-1640 supplemented with 30 mM HEPES, 2 gm/L D-glucose, hypoxanthine 50 mg/1, and 15% horse serum (Hyclone ) , or 15% human AB serum (complete medium) in an atmosphere of 5% CO 2 /5% O 2 /90% N 2 at 37°C for 18-20 hours.
  • P. vivax (Belem) parasites were obtained from squirrel monkeys with synchronous infections when the majority of parasites were at the trophozoite stage.
  • the heparinized blood with added ADP adenosine diphosphate (1 mg/ml) was passed sequentially over acid washed glass beads (0.11 mm diameter) and Whatman CF11 cellulose columns to remove platelets and leukocytes and then centrifuged on 54% Percoll (Pharmacia Fine Chemicals, Piscataway, NJ) to concentrate parasitized erythrocytes to >90% purity (Barnwell, J.W., et al., 1983, supra).
  • Maturation of the parasites to mature schizonts was accomplished in RPMI-1640 supplemented with hypoxanthine (50 mg/1), D-glucose (2 mg/1) (Hyclone), HEPES or TES (35 mM), 10% human AB serum, and 10% fetal calf or horse serum (Hyclone) as above for P. knowlesi.
  • Erythrocytes (1x10 9 ) from human or various simian origins (see Figs. 7 and 8) were washed 3 times with phosphate buffered saline (PBS) and then incubated with 250 ul of culture supernatant for 30 minutes at room temperature with rocking. The erythrocytes were washed by centrifugation through silicone oil (550 Silicone oil, Dow Chemical Corp., Midland, MI) in an Eppendorf microfuge. The pellet was resuspended in 250 u1 RPMI-1640 with 15% horse serum and centrifuged through oil a second time.
  • silicone oil 550 Silicone oil, Dow Chemical Corp., Midland, MI
  • the erythrocyte pellet was then incubated with 50 ul of 1 M NaCl for 20 minutes, centrifuged and the supernatant mixed with an equal volume of 2x SDS sample buffer containing mercaptoethanol.
  • the samples were electrophoresed on a 7.5% SDS polyacrylamide gel and autodiographed after impregnation with EnHance scintillation enhancer (NEN/Du Pont, Wilmington, DE).
  • the results for P. vivax DAP are shown in Fig. 7.
  • Those for PkDAP are shown in Fig. 8.
  • the native DAP polypeptide from P. vivax was first identified using an assay in which biosynthetically labeled parasite proteins from culture supernatant were incubated with intact erythrocytes (Haynes, J.D., et al., J. Exp. Med. 167:1873-1881. 1988; Camus, D., et al., Science 230:553-556. 1985) PvDAP was eluted from these erythrocytes and isolated on SDS-PAGE (see Figure 7). PvDAP has been determined to possess an apparent molecular weight in the range from about
  • P. vivax proteins released into culture supernatant after erythrocyte rupture.
  • DAP is a minor component of the total parasite proteins present in the culture supernatant.
  • PvDAP binds strongly to all three phenotypes of Duffy positive human erythrocytes, chimpanzee, and to Aotus (squirrel) monkey erythrocytes, which are also susceptible to P. vivax invasion.
  • PvDAP does not, however, bind to erythrocytes from Duffy-negative humans or to simian erythrocytes from Rhesus and Cebus monkeys, which are not themselves susceptible to invasion by P. vivax. Erythrocytes from non- primates, such as mice and rabbits, also do not bind to PvDAP.
  • P. knowlesi culture supernatant instead of P. vivax.
  • Pkl35 or PkDAP 135kD parasite protein
  • This P. knowlesi derived protein binds to Duffy-positive human erythrocytes but not to Duffy-negative erythrocytes.
  • PkDAP binds most intensely to Fy(a-b + ) human erythrocytes, less intensely to Fy(a + b + ) cells and poorly to Fy(a + b-) cells (see Fig. 8).
  • PkDAP (all of which have at least one Duffy determinant) bound to cells from Cebus monkeys which are not themselves susceptible to P. knowlesi invasion.
  • the Pkl35 protein does not bind to erythrocytes from other mammals, such as mice or rabbits.
  • Example 7 Purification of Human Duffy Glycoprotein.
  • Duffy-positive human erythrocyte membrane ghosts (1 unit) were extracted with 1% NP-40. The extract was centrifuged and the supernatant passed over an anti-Fy 6 mAb (NYBC-BG6, Nichols, M.E., et al., J. Exp. Med 166:776-785, 1987) affinity column. The column was washed extensively and sequentially with 1% NP-40, 1% NP-40/0.5 M NaC1 and finally with PBS.
  • DAPs Proteins
  • Duffy glycoprotein or orosomucoid (1 mg/ml, Sigma Chemicals, St. Louis, MO) were incubated with 250 u1 of parasite culture supernatant for 1 hour at room temperature.
  • Human Fy(a + b + ) cells were incubated with anti-Fy 6 mAb purified from ascites (10 ug/ml) or with 500 ul of an anti- glycophorin (En a ) mAb culture supernatant (mAb 10-22, 20-25 ug/ml of antibody, Perkins, M.E., et al, J. Immunol. 141:3190- 3196, 1988).
  • F(ab) fragments of the anti-Fy 6 mAb were obtained by treating the affinity purified antibody with cysteine-ac- tivated papain conjugated to agarose (Sigma). After digestion, the papain was centrifuged away and the supernatant was passed over a protein A-affigel column (Bio-Rad, Richmond, CA) to remove the Fc portion. The purity of the F(ab) preparation was checked by SDS-PAGE and silver stain analysis.
  • Anti-Fy 6 antisera partially inhibited the binding of PvDAP to Fy(a + b-) human erythrocytes while antibodies against a common glycophorin determinant (En a , see, Darnbrough, J., et al., Vox. Sang. 17:241-255, 1969) unrelated to Duffy had no effect on the binding of PvDAP (Fig. 9C, lane 3).
  • the binding of Pkl35 to human erythrocytes is also specifically inhibited by both purified Duffy glycoprotein and the anti-Fy 6 mAb (Fig. 9B, lane 5 and Fig. 9C, lane 4, respectively).
  • Duffy glycoprotein as a ligand in the invasion of human erythrocytes by P. vivax (Barnwell, J.W., et al, J. Exp. Med. (in press) supra) and P. knowlesi (Mason, S.J., et al, supra) has been demonstrated by the inhibition of invasion into erythrocytes treated with specific proteases. In addition, these experiments confirm the specificity of the binding between DAP and Duffy antigens.
  • 1x10 9 washed erythrocytes were treated with enzymes at 37°C as follows: 0.5 ml trypsin (1 mg/ml, Sigma) for 0.5 hr; 0.5 ml chymotrypsin (1 mg/ml, Calbiochem-Behring, LaJolla, CA) and 0.5 ml V-8 protease (0.2 mg/ml. Boehringer Mannheim Biochemicals, Indianapolis, IN) in PBS, pH 7.2 for 2 hr. Reactions were stopped with 1 mM soybean trypsin inhibitor (Sigma), 0.05 mg chymostatin (Sigma) and 1 mM PMSF (Sigma), respectively. The cells were then washed 3 times with RPMI- 1640.
  • V-8 protease on either the Fy b or the Fy 6 determinant was measured by the inability to agglutinate Fy (a ⁇ b + ) erythrocytes with an indirect hemagglutination assay using anti-Fyk sera or a change in specific counts per minute when iodinated anti-Fy 6 mAb was incubated with the cells.
  • the binding of the parasite proteins, PvDAP and Pkl35 to protease treated erythrocytes correlates with both the susceptibility of the Duffy glycoprotein to these proteases and the ability of P. vivax and P. knowlesi to invade the protease treated human erythrocytes.
  • the Fy b determinant on intact human erythrocytes can be removed or disrupted by V-8 protease, however, this protease has no effect on the Fy 6 determinant.
  • human Fy(a-b + ) erythrocytes were treated with V-8 protease PvDAP still bound to these erythrocytes (Fig. 10, lane 5).
  • V-8 protease treatment of human Fy(a-b + ) erythrocytes prevents the binding of Pkl35 (Fig. 10, lane 7) indicating that, unlike PvDAP, PkDAP-Duffy interaction requires the involvement of the Fy b determinant of the Duffy protein.
  • Saimiri monkey antiserum to the 135kD P. knowlesi protein was developed.
  • Saimiri monkey Pkl35 antiserum was produced by incubating Saimiri erythrocytes (4x10 10 ) and non-radioactive P. knowlesi culture supernatant (40 ml ). Half of these erythrocytes were then injected intravenously into the Saimiri monkey from which they had been drawn. The other half were eluted in 0.5 M NaC1, the eluate was mixed in Freund's incomplete adjuvant and injected intramuscularly. This procedure was repeated three times over a period of five months before a positive response was detected.
  • the thus developed antisera which include antibodies that recognize PkDAP, could be used to isolate PvDAP by virtue of cross-reactivity with PvDAP.
  • mice were immunized with purified native DAPs.
  • DAP was purified by incubating human Fya-b + erythrocytes (5x10 10 ) with either P.knowlesi or P.vivax culture supernatants (50 ml). After passage of the erythrocytes twice through silicone oil, the bound proteins were eluted with 0.5M NaC1. The eluate was then mixed with SDS sample buffer and subjected to SDS-PAGE (7.5% polyacrylamide). The separated proteins were then electro-blotted onto nitrocellulose sheet.
  • Radioactive-labeled ( 35 S-methionine) eluted proteins were run in the end lanes to mark the exact position of DAP on the nitrocellulose which was revealed by autoradiography.
  • a thin strip (2-3 mm) of the (unlabelled) nitrocellulose was cut out at the position of the blotted and radioactively-labeled DAP proteins.
  • Portions of the nitrocellulose strip were then implanted into the spleens and peritoneal cavities of mice. This procedure was repeated three times with the same mice to generate an antibody response.
  • the antibodies react exclusively at the very apical end of both P.vivax and P.knowlesi merozoites.
  • Culture supernatants are screened for positive clones secreting the appropriate antibodies by indirect immunofluorescence on air-dried P.vivax and P.knowlesi merozoites and immunoprecipitation of 35 S-methionine labeled culture supernatants and detergent extracts of merozoites.
  • Example 1 late schizont parasitized erythrocytes were washed 3 times with PBS. The cells were extracted in 1% Triton X-100 at
  • Antisera from Example 5 were incubated with labeled parasite proteins, either culture supernatant or detergent extract, for 2 hours at 4°C with rocking. Material eluted from an erythrocyte binding assay was diluted with an equal volume of PBS before the antisera were added. Antigen-antibody complexes were precipitated by adding Protein A Sepharose (Pharmacia) and incubating an additional 2 hours. The Sepharose was washed by centrifugation with Tris buffered saline containing 0.5% Triton X-100 and 5mM EDTA (NETT) and NETT with 0.5 M NaC1. The complexes were dissociated by the addition of an equal volume of double-strength SDS sample buffer containing mercaptoethanol, boiled and applied to a 7.5% SDS-PAGE .
  • the P. knowlesi 135kD protein is a proteolytic product of the 160kD protein immunoprecipitated by the antiserum.
  • an immunoprecipitation was performed with the anti-Pkl35 antiserum and P. knowlesi schizonts which had been extracted in the absence of protease inhibitors. (Fig. 11B). Equal aliquots of this inhibitor-free extract were incubated at 37°C for various times ranging from 0 to 60 minutes. Any proteolysis was stopped by the addition of protease inhibitors leupeptin and chymostatin and by placing the aliquots at 4°C. The anti- Pkl35 antiserum was then used to precipitate proteins from these samples.
  • Example 12 Inhibition of P. knowlesi merozoite
  • the antisera from Example 5 were used in an in-vitro invasion assay to determine the effect of such seraa on merozoite invasion of human erythrocytes.
  • P. falciparum late trophozoite- and early schizont-infected erythrocytes were concentrated to 80% parasitemia on plasmagel and adjusted to 10 8 /ml in medium.
  • Target cells at 10 8 /ml were mixed with parasitized erythrocytes at a ratio of 10:1 and cultured in 0.5 ml volumes in 24-well tissue culture plates.
  • P. knowlesi schizont-infected erythrocytes were concentrated to > 95% parasitemia on a 54% Percoll cushion (Barnwell, J.W., et al.
  • the less dense erythrocytes at the Percoll interface were used as target cells in assays of invasion.
  • P. falciparum cultures were harvested after 12 hours for blood film preparation.
  • P. knowlesi and P. vivax cultures were harvested after 8-10 hours.
  • Giemsa staining of thin film smears 1,000-2,000 erythrocytes were examined by light microscopy and the number of ring stage parasites was deter- mined. Smears of the infected erythrocytes/target cell mixtures were also made at the start of the invasion assays and the number of ring stage parasites were determined. Any background invasion rates found in these wells were subtracted from the invasion rates determined in the test wells after 8-10 hours of incubation.
  • Example 1 The erythrocyte binding assay of Example 1 was used to determine whether other merozoite antigens recognize the Duffy blood group glycoprotein.
  • the reuslts are summarized in Table 1.
  • a P. vivax protein of 205 kD bound to all human erythrocytes, regardless of their Duffy phenotype, and also to Aotus and Saimiri erythrocytes (Fig. 7).
  • a 220-230 kD P. knowlesi protein binds to Rhesus erythrocytes (Fig. 8) and on occasion to human erythrocytes.
  • the erythrocyte proteins recognized by these parasite proteins or their role in the invasion process are not known. These proteins probably are not involved in the initial recognition and attachment of the merozoite to the host erythrocyte as their binding is prevented by trypsin treatment of erythrocytes which does not inhibit invasion.
  • Duffy-associating protein binds to erythrocytes as the 160 kD protein and then undergoes proteolytic degradation to the 135 kD protein, then the appearance of the 155 kD protein on some simian erythrocytes could reflect incomplete degradation that does not occur on human or Cebus erythrocytes.
  • Lambda ZAP® (Strategene, LaJolla, CA) genomic DNA expression libraries were constructed essentially as described for cDNA expression libraries in DNA Cloning - A Practical Approach, Glover, D.M., Editor, IRL Press, 1986, Vol. 1 , Chapter 2 , Huynh, T.V. , Young, R.A. , and Davis , R.W. (lambda gt 11 can be purchased from Stratagene, LaJolla, CA) or in Young, R.A., et al., Proc. Nat'l. Acad. Sci. 80:1194, 1983; and Young, R.A., et al., Proc. Nat'l. Acad. Sci.
  • genomic DNA was sheared to obtain fragments averaging 2-7 kb in size or restricted with mung bean nuclease in 42.5% formamide.
  • EcoRI linkers Biolabs
  • EcoRI linkers Biolabs
  • Recombinant DNA was packaged using commercial phage packaging extracts from Strategene with the accompanying manufacturer's protocols, and they were plated on XL1 BLUE cells (Stratagene) for immunoscreening.
  • Another mode of construction of a genomic DNA library could have been used with optional suitable modification of the subsequent expression strategy.
  • Other variations or methods for constructing genomic libraries can be gleaned, e.g., from U.S. Patent No. 4,693,994 or 4,707,357, but such methods are well-known.
  • P.knowlesi Pk 135 antisera from Example 5 were used to screen the genomic libraries, which were expressed in Y1090 cells. Positive clones have been identified and confirmed by 3 rounds of plaque purification. These are being sequenced as follows (by way of nonlimiting example):
  • Phage will be prepared from these clones essentially as described for the production of lambda gtll phage in DNA Cloning 1: A Practical Approach, Glover, D.M. , Editor, IRL Press, 1986, Vol. 1, Chapter 2, Huynh, T.V., Young, R.A., and Davis, R.W. using protocols from the manufacturer (Sttategene), and the phage and their DNAs were purified using LAMBDASORBTM phage adsorbent and accompanying protocols from Promega.
  • Phage DNA inserts can then be released by restricting the DNA with EcoRI or Kpnl and SacI, and cloned into and sequenced from the commercially available plasmid BLUESCRIPTTM (Stratagene) or pGEM ® (Promega).
  • XLl-Blue cells obtained from Stratagene will be transformed using the well-known procedures of Hanahan, D., 1983, J. Mol. Biol., 166:557-580. and large preparations of plasmid DNA will be obtained using the standard alkaline lysis protocol and CsC1 gradient purification (Maniatis, T., Molecular Cloning. A Laboratory Manual, p. 90- 93, Cold Spring Harbor Laboratories, New York 1982).
  • Clones comprising a set of nested deletions will be prepared using standard exonuclease III/mung bean nuclease digestion methodology in accordance with protocols supplied with Stratagene's exonuclease III/mung bean nuclease deletion kit. Subsequently generated clones will be sequenced using the technique of Sanger, F., et al., Proc. Nat'l Acad. Sci. 74:5463-5467, 1977, reagents supplied in U.S. Biochemical Corps. SEQUENASETM sequencing kit and protocols modified to optimize sequencing reactions performed in double stranded DNA using the enzyme SEQUENASETM. Sequence information will be analyzed using IBI's Pustell DNA sequence analysis programs and Genbank for comparative studies.
  • the protein expressed as a beta-galactosidase or other appropriate fusion protein can be purified and used to raise antisera in rabbits and/or mice. These antisera can be used to immunoprecipitate, or can otherwise be used to show specific reactivity with the native DAP antigen from P. vivax or P. knowlesi. Positive results will thus confirm that the appropriate DNA has been cloned and the appropriate product has been expressed. (Alternatively, polyclonal or preferably monoclonal antibodies to natural purified DAP can be raised (Example 10) and used to confirm the nature of the expressed protein).
  • the entire recovered DNA insert can be used for screening a nonexpression genomic P.vivax library (e.g. in an appropriate lambda replacement vector available from Stratagene, LaJolla, CA) to identify the entire gene for P.vivax native DAP. Once identified, the entire gene can be extracted from the genomic DNA library, purified, sequenced and duplicated in accordance with known techniques.
  • a nonexpression genomic P.vivax library e.g. in an appropriate lambda replacement vector available from Stratagene, LaJolla, CA
  • the entire gene can be extracted from the genomic DNA library, purified, sequenced and duplicated in accordance with known techniques.
  • DAP can be elucidated and the corresponding amino acid sequence can be determined. Construction of fragments, derivatives or analogs and hybrid constructs (i.e. comprising moieties or sequences of non-malarial origin) can then proceed as discussed above.
  • a lambda gt11/P.vivax genomic DNA expression library was constructed from mRNA obtained from P.knowlesi mature schizonts essentially as described for cDNA expression libraries in DNA Cloning - A Practical Approach, Glover, D.M., Editor, IRL Press, 1986, Vol. 1, Chapter 2, Huynh, T.V., Young, R.A., and Davis, R.W. (lambda gt 11 can be purchased from Stratagene, LaJolla, CA) or in Young, R.A. , et al., Proc. Nat'l. Acad. Sci. 80:1194, 1983; and Young, R.A., et al., Proc. Nat' l . Acad.
  • Y1090 cells from which large preparations of phage and their DNAs were made
  • Y1089 cells for the production of large quantities of beta-galactosidase fusion proteins. Fusion proteins were prepared from the Y1089 lysogens essentially as described in protocols available from Promega. Lysogens were prepared by first producing a large plaque of each recombinant on bacterial lawns of Y1090 and 1089 and then streaking cells from the center of each large plaque. Colonies which grew were tested for lysogeny by their ability to grow at 32 and 42°C.
  • P. knowlesi Pk 135 antisera from Example 5 were used to screen the cDNA library, which was expressed in Y1090 cells. A positive clone was identified and confirmed by 3 rounds of plaque purification. This clone was sequenced as follows (by way of nonlimiting example):
  • Phage were prepared from these clones essentially as described for the production of lambda gtll phage in DNA Cloning 1: A Practical Approach, Glover, D.M., Editor, IRL Press, 1986, Vol. 1, Chapter 2, Huynh, T.V., Young, R.A., and Davis, R.W., and the phage and their DNAs were purified using LAMBDASORBTM phage adsorbent and accompanying protocols from Promega.
  • the phage DNA insert was then released by restricting the DNA with EcoRI or Kpnl and Sad, and cloned into and sequenced from the commercially available plasmid BLUESCRIPTTM (Stratagene).
  • XL1-Blue cells obtained from Stratagene were transformed using the well-known procedures of Hanahan, D., 1983, J. Mol. Biol., 166:557-580, and large preparations of plasmid DNA were obtained using the standard alkaline lysis protocol and CsC1 gradient purification (Maniatis, T., Molecular Cloning, A Laboratory Manual, p. 90-93, Cold Spring Harbor Laboratories, New York 1982).
  • Clones comprising a set of nested deletions were prepared using standard exonuclease III/mung bean nuclease digestion methodology in accordance with protocols supplied with Stratagene's exonuclease III/mung bean nuclease deletion kit. Subsequently, generated clones were sequenced using the technique of Sanger, F., et al., Proc. Nat'l Acad. Sci. 74:5463-5467, 1977, reagents supplied in U.S. Biochemical Corps. SEQUENASETM sequencing kit and protocols modified to optimize sequencing reactions performed in double stranded DNA using the enzyme SEQUENASETM. Sequence information was analyzed using IBI's Pustell DNA sequence analysis programs and Genbank for comparative studies. The nucleic and deduced amino acid sequences of the cloned 1.8 kD insert is depicted in Figure 12.
  • the lambda gt 11 phage beta-galactosidase fusion protein was purified by affinity chromatography on a rabbit anti-beta galactosidase-Sepharose 4B column and used to raise antisera in mice.
  • the resulting antisera reacted exclusively with the apical end of P.knowlesi and P.vivax air-dried merozoites by indirect immunofluorescence and immunoprecipitated a 135kD band from detergent extracts of P.vivax and P.knowlesi mature schizonts and merozoites radiolabeled biosynthetically with 35 S-methionine (data not shown).
  • These positive results confirm that the appropriate DNA for the PkDAP gene has been cloned and expressed.
  • Monoclonal antibodies to natural purified Pk DAP are being raised and can be used to confirm the nature of the expressed protein.
  • the entire recovered DNA insert can be used for screening a nonexpression genomic P.knowlesi library (e.g. in an appropriate lambda replacement vector available from Stratagene, LaJolla, CA) to identify the entire gene for P.knowlesi native DAP. Once identified, the entire gene can be extracted from the genomic DNA library, purified, sequenced and duplicated in accordance with known techniques.
  • a nonexpression genomic P.knowlesi library e.g. in an appropriate lambda replacement vector available from Stratagene, LaJolla, CA
  • the entire gene can be extracted from the genomic DNA library, purified, sequenced and duplicated in accordance with known techniques.
  • P.knowlesi DAP can be elucidated and the corresponding amino acid sequence can be determined. Construction of fragments, derivatives or analogs and hybrid constructs (i.e. comprising moieties or sequences of non-malarial origin) can then proceed as discussed above.

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Abstract

On décrit des composés comprenant une séquence en acides aminés, choisie dans le groupe se composant de protéines du stade mérozoïte de la malaria localisées à l'extrémité apicale des mérozoïtes, et des peptides, lesdits peptides comprenant des versions synthétiques, des dérivés, des structures analogues et des fragments de protéines de mérozoïte. Certains de ces composés se caractérisent par la capacité de se lier à un antigène de groupe sanguin Duffy provenant des globules rouges de primate. On décrit également des acides nucléiques comprenant une séquence en nucléotides, qui code pour lesdites protéines ou lesdits peptides et les acides nucléiques avec lesquels ils sont hybridés. Ces composés et les anticorps reconnaissant ces composés sont utiles pour inhiber l'invasion des globules rouges susceptibles de primate par les mérozoïtes de la malaria.
PCT/US1990/001849 1989-04-05 1990-04-03 Antigenes du stade merozoite localises a l'extremite apicale du parasite WO1990011772A1 (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0516721A1 (fr) * 1990-02-22 1992-12-09 THE UNITED STATES OF AMERICA as represented by the Secretary UNITED STATES DEPARTMENT OF COMMERCE Proteines antigeniques de plasmodium

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Title
AMERICAN JOURNAL OF TROPICAL MEDICINE AND HYGIENE, Volume 40, No. 6, issued June 1989, C. WANIDWORANUN et al.: "Cross-reacting Antigens to Pc 96, A Protective Antigen of Plasmodium chabaudi, in P. falciparum, P. vivax, and P. cynomolgi", see the abstract and the Discussion (page 582). *
BIOLOGY OF THE CELL, Volume 64, issued 1988, P.H. DAVID et al.: "Plasmodium vivax Malaria: Parasite Biology Defines Potential Targets for Vaccine Development", see the abstract, page 251. *
CIBA FOUNDATION SYMPOSIUM, Volume 94, issued 1983, M. AIKAWA et al.: "Structural Alternation of the Erythrocyte Membrane During Malarial Parasite Invasion and Intraerythrocytic Development", see pages 46-47. *
JOURNAL OF EXPERIMENTAL MEDICINE, Volume 167, issued June 1988, J.D. HAYNES et al.: "Receptor-like Specificity of a Plasmodium Knowlesi Malarial Protein that Binds to Duffy Antigen Ligands on Erythrocytes", see the Abstract and Summary (pages 1879-1880). *
JOURNAL OF IMMUNOLOGY, Volume 127, No. 1, issued July 1981, N. EPSTEIN et al.: "Monoclonal Antibodies Against a Specific Surface Determinant on Malarial (Plasmodium Knowlesi) Morozoites Block Erythrocyte Invasion", see the Abstract and the Discussion (pages 215-216). *
JOURNAL OF IMMUNOLOGY, Volume 132, No. 1, issued January 1984, L.H. MILLEN et al.: "Monoclonal Antibodies to a 140,000-mw Protein on Plasmodium Knowlesi Menozoites Inhibit their Invasion of Rhesus Erythrocytes", see page 438. *
MOLECULAR AND BIOCHEMICAL PARASITOLOGY, Volume 31, issued December 1988, L.H. MILLER et al.: "Identification of Plasmodium Knowlesi Erythrocyte Binding Proteins", See the Discussion pages 219-221. *
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCE, Volume 85, issued January 1988, J.M. BURNS et al.: "The 3' Portion of a Gene for a Plasmodium yoelii Menozoite Surface Antigens Encodes the Epitope Recognized by a Protective Monoclonal Antibody", See the Abstract, page 602. *
PROGRESS IN ALLERGY, Volume 41, issued 1988, T.J. HADLEY et al.: "Invasion of Erythrocyted by Malaria Parasites: Erythrocyte Ligands and Parasite Receptors", see pages 61-63. *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0516721A1 (fr) * 1990-02-22 1992-12-09 THE UNITED STATES OF AMERICA as represented by the Secretary UNITED STATES DEPARTMENT OF COMMERCE Proteines antigeniques de plasmodium
EP0516721A4 (en) * 1990-02-22 1993-02-17 Us Health Antigenic proteins of plasmodium

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