A multi-stage vaccine antigen for malaria

Abstract

The present disclosure provides a recombinant antigen which is capable of eliciting protective immunity against all three stages of the Plasmodium life cycle, as well as compositions for and methods of preventing or inhibiting primary infection, disease severity, and transmission of malaria.

Description

[0001]SCRI.512WO / / VHPM 00819.003WO1 A MULTI-STAGE VACCINE ANTIGEN FOR MALARIA CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to United States Provisional Application Number 63 / 469,320 that was filed on May 26, 2023. The entire content of the applications referenced above is hereby incorporated by reference herein. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH This invention was made with government support under AI137234 awarded by National Institutes of Health. The government has certain rights in the invention. SEQUENCE LISTING The instant application contains a Sequence Listing which has been submitted in XML format via Patent Center and is hereby incorporated by reference in its entirety. Said XML copy, created on May 14, 2024, is named 00819003WO1 and is 20,058 Bytes in size. BACKGROUND Malaria remains a major public health concern and burden on society resulting in 619,000 deaths worldwide in 2021, the majority (~80%) of which were children under the age of 51. Plasmodium falciparum (P. falciparum) and P. vivax, the major parasites that cause human malaria, account for most infections in sub-Saharan Africa and outside Africa, respectively. Despite implementing strict counter interventions and vector control measures, the total number of malaria infections stood at 247 million in 20211, an increase of 2 million from 2020, reflecting the dire need for disease prevention through effective vaccine modalities. SUMMARY The present invention provides a recombinant antigen which is capable of eliciting protective immunity against all three stages of the Plasmodium life cycle, as well as compositions for and methods of preventing or inhibiting primary infection, disease severity, and transmission of malaria. Accordingly, certain embodiments provide a recombinant antigen comprising: SCRI.512WO / / VHPM 00819.003WO1 a pre-erythrocytic (PE) fragment comprising a central repeat domain of a Plasmodium Circumsporozite Protein (CSP) or a fragment thereof; a blood stage (BS) fragment comprising at least one of a Plasmodium Merozoite Surface Protein 1 (MSP-1), a Plasmodium Reticulocyte Binding Protein Homologue 5 (RH5), or fragments thereof; and a transmission stage (TS) fragment comprising at least one of a Plasmodium HAP2 paralog (HAP2p) protein, a Plasmodium s230 protein, a Plasmodium s48 / 45 protein, or fragments thereof. In certain embodiments, the recombinant antigen is a single antigen. In certain embodiments, the recombinant antigen is configured to be expressed in a eukaryotic cell. In certain embodiments, at least one of the CSP, MSP-1, RH5, HAP2p, s230 and s48 / 45 proteins is a Plasmodium falciparum protein. In certain embodiments, recombinant antigen comprises an amino acid sequence having at least 80% sequence identity to SEQ ID NO:1, 2, 3, 4, 5, or 6. In certain embodiments, the recombinant antigen comprises an amino acid sequence having at least 85%, at least 90%, or at least 95% sequence identity to SEQ ID NO:1, 2, 3, 4, 5, or 6. Certain embodiments provide an immunogenic composition comprising the recombinant antigen and a pharmaceutically acceptable carrier. In certain embodiments, the immunogenic composition further comprises an adjuvant in an amount sufficient to enhance an immune response. Certain embodiments provide an immunogenic composition comprising a mRNA comprising a coding sequence encoding the recombinant antigen. In certain embodiments, the mRNA is self-amplifying. In certain embodiments, the immunogenic composition further comprises a lipid nanoparticle carrier. Certain embodiments provide a method of preventing or inhibiting transmission of a Plasmodium from an infected or susceptible host, the method comprising administering to the host an immunologically effective amount of the recombinant antigen or an immunologically effective amount of the immunogenic composition. In certain embodiments, the Plasmodium is Plasmodium falciparum. In certain embodiments, the susceptible host is a human. SCRI.512WO / / VHPM 00819.003WO1 Certain embodiments provide an antibody or antigen-binding derivative thereof that binds to at least one immunogenic fragment of the recombinant antigen. In certain embodiments, the antibody or antigen-binding derivative thereof inhibits at least one of PE, BS, and TS stage Plasmodium falciparum parasitic functional activity in vitro. In certain embodiments, the antibody or antigen-binding derivative thereof inhibits at least two of PE, BS, and TS stage Plasmodium falciparum parasitic functional activity in vitro. In certain embodiments, the antibody or antigen-binding derivative thereof inhibits all three of PE, BS, and TS stage Plasmodium falciparum parasitic functional activity in vitro. Certain embodiments provide a method of preventing or inhibiting transmission of a Plasmodium from an infected or susceptible host, the method comprising administering to the host an immunologically effective amount of the antibody or antigen binding derivative thereof. In certain embodiments, the Plasmodium is Plasmodium falciparum and the susceptible host is a human. Other objects, features, and advantages of the present invention will be apparent to one of ordinary skill in the art from the following detailed description and drawings. BRIEF DESCRIPTION OF DRAWINGS The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawings will be provided by the Office upon request and payment of the necessary fee. Figure 1. The P. falciparum life cycle and its multiple opportunities for intervention by a multistage vaccine. Figure 2. Design, expression, and serology of PyMS vaccine. Schematic (A) and expression SDS-gel and anti-HIS tag Western blot (B) of PyMS vaccine. ELISA showing the total IgG responses of the PyMS antigen-immunized mouse polyclonal sera (n=8) to individual antigens (C) and lysed Py sporozoites (5000 cells / well) (D). IFA images showing the binding of PyMS polyclonal antibodies (green) to fixed Py sporozoites (E). Figure 3. Test expression of PfMS (version 4). (A) Identification of PfMS (version 4) antigen expression by Western blot using anti-His tag antibody. (B) PfMS (version 4) SCRI.512WO / / VHPM 00819.003WO1 antigen-coated ELISA and PfMS (version 4) antigen-loaded NiNTA probed Octet-BLI (C) confirming the binding of PfHAP2p (red) and PfCSP (blue) mAbs (B10 and 2A10, respectively) to PfMS antigen (version 4). Figure 4. Design and concept of Pf multistage mRNA and Self-Amplifying mRNA vaccine. SS=secretion signal, TM=transmembrane. Figure 5. PvCSP-TM mRNA surface expression on HEK293 cells by confocal microscope. Figure 6. TBA of PfHAP2p cd-fusion antibodies in immunized rabbits, compared to controls (PBS and pre- immune). DETAILED DESCRIPTION The present disclosure relates to a single-recombinant antigen multistage (MS) malaria vaccine targeting the three life stages of P. falciparum at the same time. The disclosed MS vaccine can be combined with successfully adopted mRNA-lipid nanoparticle vaccine technology2. The MS vaccine design and concept are illustrated in Figure 1, further described below. The tri-stage vaccine prevents primary infection, and also blocks disease progression during the blood stage and transmission. The vaccine has the potential to significantly impact the malaria epidemic and open a new frontier for eradication efforts. The complex life cycle of Plasmodium is classified into pre-erythrocytic (PE), Blood (BS), and transmission stages (TS). The infection initiates when an infected female Anopheles mosquito injects the sporozoite form of the parasite into the human host during a blood meal. The sporozoites readily migrate to the liver and establish liver stage infection and development into schizonts. After the rapid development in the liver, the schizont bearing hepatocytes rupture and release the highly infective form of the parasite, the merozoite. The merozoite invades the host red blood cells (RBCs), multiplies rapidly, matures to trophozoites and BS schizonts, and releases merozoites that keep the infection cycle continuous by repeated infections of fresh RBCs, resulting in severe disease-related symptoms. Some of the early trophozoites develop to the sexual stages, i.e., male and female gametocytes, that circulate in the bloodstream and transmit to mosquito vectors during a blood meal. Fertilization occurs in the mosquito midgut, ultimately resulting in the development of sporozoites that migrate to mosquito salivary glands, and life cycle of the pathogen renews. SCRI.512WO / / VHPM 00819.003WO1 Plasmodium has evolved and adapted several escape strategies to avoid host immunity3–5. Malaria vaccine development is currently at a brisk pace targeting the different stages of the parasite, i.e., PE, BS, and TS, but to date there are no efficacious licensed vaccines that provide sterile protection. In October 2021, the WHO approved RTS,S / AS01, a PE subunit vaccine, for broad use in children that has shown a strong safety profile and significantly reduced (30%) the disease severity but did not render sterile protection6–9. Additionally, R21 and the whole sporozoite vaccine (PfSPZ), the other two clinically advanced PE vaccines, have shown promising efficacy in early clinical trials and the data from advanced clinical trials is underway10–14. Considering the pre-existing immunity in the malaria endemic regions and escape strategies of Plasmodium, sterile protection and eradication of malaria is most likely only possible by attacking all the major different stages of Plasmodium at the same time. Presently, there are several vaccine candidates at different phases of clinical development targeting a specific stage of the pathogen. Whole sporozoite vaccines and Circumsporozoite Protein (CSP)-based vaccines are the most advanced PE vaccines, Merozoite Surface Protein 1 (MSP-1) and Reticulocyte Binding Protein Homologue 5 (RH5)-based vaccines are advancing as BS vaccine candidates, as well as Pfs25 as a TS candidate. The PE and BS vaccines are aimed at preventing primary infection and disease severity, respectively, while the TS vaccine blocks vector-borne transmission. To contribute to the 15-year WHO strategy to eradicate malaria by 2030, a combinatorial and inclusive approach aiming at both blocking infection and transmission at the same time is likely the most promising way forward. To date, there are no licensed PE, BS or TS blocking vaccines that induce sterile protection and block disease transmission, indicating that the pathogen has evolved by finding escape routes from the host immune system to continue its life cycle in humans and mosquito vectors3–5. Completely preventing malaria will likely require intervention at all of the major stages in its lifecycle. A multistage vaccine has been a desirable goal for many years but has met with limited success. Two basic approaches have been pursued: vaccine cocktail (i.e., two or more single vaccines mixed) and multi-component antigen, in which a single vaccine expresses multiple genes. Mixed formulation has been most extensively pursued, where monovalent vaccines or multiple antigens are combined in a regimen or formulation to achieve cross-stage immunity and can include both recombinant and vectored antigens. For example, efforts are under way to combine R21 with a vectored anti- SCRI.512WO / / VHPM 00819.003WO1 Thrombospondin-related adhesive protein (TRAP) vaccine (ME-TRAP), and eventually blood stage antigens. Other preclinical studies have combined blood stage and transmission blocking vaccines to reasonable effect16,17. However, the long-term viability of this approach is unclear, given the obvious drawbacks with such products; chief among them producing, testing, and licensing multiple vaccines to be used together at a cost and scale that will be impactful to the epidemic. Multi-component fusion protein antigens have been less well studied, with most efforts involving synthetic peptides or viral vectors of chimeric gene fragments. Progress on this front has likely been hampered by the extreme difficulty of expressing P. falciparum proteins as recombinant forms, which is only exacerbated by attempting to produce designer chimeric antigens. Thus, there is a need for a malaria vaccine that can induce sterile protection, e.g., by targeting all three major stages of Plasmodium, and that can cost-effectively broaden existing vaccine efficacy by preventing primary infection, disease severity, and disease transmission. The presently disclosed P. falciparum multistage (PfMS) malaria vaccine blocks the known escape routes of the pathogen by targeting the three life stages of P. falciparum with a single vaccine antigen. The vaccine prevents infection, disease, and transmission by educating the host immune system with the potent antigens targeting the three major Plasmodium life stages at the same time in a single recombinant antigen format. A major novel aspect of this invention is the combination of genes and domains that are all known to elicit potent anti-parasitic responses as stand-alone antigens into a single antigen that is produced in eukaryotic production systems to ensure proper folding and disulfide bonding. This modular format is highly useful in testing different combinations of epitopes and genes, and it can be adapted for nanoparticle vaccine formats. Further, the use of PfHAP2p is novel, as it was only very recently discovered15and has not been evaluated as a transmission blocking vaccine, although the present inventors have verified that anti-PfHAP2p antibodies confer potent transmission blocking activity (TBA). See International Application Number PCT / US2021 / 048047, which is incorporated herein by reference. Additionally, the disclosed vaccine can be used in conjunction with advanced mRNA vaccine technologies2, which have not been tested in a multistage format but are known to elicit high titer antibody responses. Finally, a major novel aspect of the disclosed multistage malaria vaccine is that it confers sterile protection against infection (PE stage), reduces disease severity of any breakthrough infection (BS stage), and prevents transmission of any residual blood stage infection to the SCRI.512WO / / VHPM 00819.003WO1 mosquito vector (TS stage). This three-pronged approach attacks all three potential major intervention points in the life cycle of the parasite, creating a powerful tool for eradication. The present inventors have gained extensive experience in expressing Plasmodium proteins in mammalian expression systems and studying their antigenic and immunogenic properties18–25, leading to the development of the disclosed multistage recombinant vaccine antigen. They have shown that developing a PfMS vaccine antigen is feasible, and they have created and optimized several variants expressing leading stage-specific vaccine candidates. The development of a single vaccine antigen that can elicit protective cross-stage protection represents a major leap forward for malaria eradication efforts. The disclosed vaccine antigens combine components of PE, BS, and TS antigens. Pre-erythrocytic fragment of MS vaccine Circumsporozoite Protein (CSP), the predominant protein on the sporozoite surface, mediates binding of the pathogen to hepatocytes, establishing primary liver-stage infection26. The domain organization of CSP includes a central repeat domain that is sandwiched by conserved N’ and C’-terminal domains where the N and central repeat domains facilitate sporozoite binding to hepatocytes while the C-terminal domain promotes hepatocyte invasion26–28. A tight interplay between these domains establishes sporozoite liver-stage infection. CSP is highly conserved, both functionally and structurally, especially in the N and C-terminal domains, across different Plasmodium species. However, the central repeat domain is unique and immunodominant for each Plasmodium species. The PfCSP repeat domain is composed of three different tetrapeptides (NPDP (SEQ ID NO: 12), NVDP (SEQ ID NO: 13), NANP (SEQ ID NO: 14)) that induce neutralizing antibodies27. These three protective tetrapeptide epitopes of PfCSP are used in the presently disclosed PfMS antigen as the PE antigen fragment. This domain can be placed in between the TS and BS target fragments, as shown in Figure 1. Blood stage fragment of MS vaccine Merozoite Surface Protein 1 (MSP-1), the most abundant protein on merozoite surface and a leading blood stage vaccine candidate, is required for merozoite formation and for erythrocyte infection. Merozoites multiply in the parasitophorous vacuole (PV) and egress by the rupture of PV membrane and host erythrocyte membrane, releasing merozoites that SCRI.512WO / / VHPM 00819.003WO1 immediately infect new erythrocytes. Clinical studies have confirmed the presence of MSP-1 antibodies in subjects living in endemic regions and these antibodies confer partial protection29–31. MSP-1 functions as 4 subunit (p30, p38, p42 and p83) proteins that are non- covalently attached to form a complex structure. MSP-1 interacts with other MSPs (MSP-3, MSP-6, MSP7, and MSP-9) and Duffy-binding proteins (DBL-1 and DBL-2), forming a network on the merozoite cell surface31. The present PfMS vaccine employs the p42 fragment of the PfMSP-1 protein as a BS fragment in the vaccine. Another BS antigen, Reticulocyte Binding Protein Homologue 5 (RH5), can be included in the PfMS antigen. See Figures 1 and 2, and Table 1 (below). PfRH5 binds to the basigin (BSG) protein present on the surface of human erythrocytes and helps in merozoite invasion32. Both PfMSP-1 and PfRH5 are structurally conserved proteins with well-defined domains and stable conformations, making them ideal BS antigens for the PfMS vaccine. Transmission stage fragment of MS vaccine Transmission blocking vaccines (TBVs) target gametocyte-specific proteins and prevent development of the parasite inside the mosquito vector, thereby preventing transmission. There are several TBV candidates (e.g., Pfs25 and Pfs230) in different stages of clinical trials and several (e.g., Pfs47 and PfHAP2) in preclinical studies15,33–40. HAP2, a fusion protein present on male gametocytes, is also being investigated as a TBV candidate15,41,42. Recently, a novel paralog of HAP2, HAP2p, has been identified, which is expressed on the late stage-V male gametocytes and is crucial for gametocyte fusion15. Antibodies raised against the PfHAP2p cd-fusion loop (aa 51-135) inhibit the oocyst formation in standard membrane feeding assays15. The present PfMS antigen can include PfHAP2p-cd-fusion loop region as one of the TS fragments (Table 1, version 1 and 4) in the PfMS vaccine. Additionally, Pfs48 / 45 and Pfs230 can be included as the TS component in the PfMS chimeric antigen. Pfs230, a 6-cysteine (SEQ ID NO: 15)-rich protein with fourteen 6-cysteine (SEQ ID NO: 15) domains, is expressed on both male and female gametocytes33,43, and in a clinical study, it was shown to elicit higher transmission-blocking activity antibodies than Pfs2537. The present PfMS antigen can include Pfs230 prodomain and domain I regions, extending from residues 443 to 736, as the TS component (Table 1, version 2 and 5)43. Finally, Pfs48 / 45, another antigen expressed on the surface of both male and female gametes, has an essential role in the fertility of male gametocytes44. A stabilized fragment of SCRI.512WO / / VHPM 00819.003WO1 Pfs48 / 45 C-terminal six cysteine (SEQ ID NO: 15) domain (6C) (SEQ ID NO: 15), residues 291-428, has demonstrated potent transmission blocking activity (TBA)34,43. The present PfMS antigen can include the Pfs48 / 45-6C (SEQ ID NO: 15) protein as the TS fragment in the PfMS vaccine (Table 1, version 3 and 6). Table 1. PfMS antigen designs As indicated in Table 1, versions 1-6 of the PfMS antigen have substantial identity with SEQ ID NOs 1-6, respectively. In certain embodiments, the PfMS antigen comprises a transmission stage (TS) protein or fragment thereof, a blood stage (BS) protein or fragment thereof, and a pre-erythrocytic (PE) stage protein or fragment thereof as described in Table 1. In certain embodiments, the PfMS antigen comprises an amino acid sequence that is at least 80% (e.g., 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100%) identical to any one of SEQ ID NOs:1-6. Certain embodiments provide that SEQ ID NOs 1-6 have the following amino acid sequences: SEQ ID NO:1 KYYEYFKSYKKKDIDNKNLKQFCNIIKEQHEINNEQQKCFCCYCRQDDMVFPLFSHFNYKKA KFKCNKKEQEEDIVLTLSCLKKKGGGGSGGGGSKLKQPADGNPDPNANPNVDPNANPNVDPN ANPNVDPNANPNKNNQGNGQGHNMPNDPNRNVDEKNIFTFNLNLNDILNSRLKKRKYFLDVL ESDLMQFKHISSNEYIIEDSFKLLNSEQKNTLLKSYKYIKESVENDIKFAQEGISYYEKVLA KYKDDLESIKKVIKEEKEFPSSPPTTPPSPAKTDEQKKESKFLPFLTNIETLYNNLVNKIDD YLINLKAKINDCNVEKDEAHVKITKLSDLKAIDDKIDLFKNPYDFEAIKKLINDDTKKDMLG KLLSTGLVQNFPNTIISKLIEGKFQDMLNISQHQCVKKQCPQNSGCFRHLDEREECKCLLNY KQEGDKCVENPNPTCNENNGGCDADAKCTEEDSGSNGKKITCECTKPDSYPLFDGIFCSGGG GSGGGGSHHHHHHHHGLNDIFEAQKIEWHE SCRI.512WO / / VHPM 00819.003WO1 SEQ ID NO:2 EYVDEKERQGEIYPFGDEEEKDEGGESFTYEKSEVDKTDLFKFIEGGEGDDVYKVDGSKVLL DDDTISRVSKKHTARDGEYGEYGEAVEDGENVIKIIRSVLQSGALPSVGVDELDKIDLSYET TESGDTAVSEDSYDKYASNNTNKEYVCDFTDQLKPTESGPKVKKCEVKVNEPLIKVKIICPL KGSVEKLYDNIEYVPKKSPYVVLTKEETKLKEKLLSKLIYGLLISPTVNEKENNFKEGVIEF TLPPVVHKATVFYFICDNSKTEDDNKKGNRGIVEVYVEPYGNKINGGGGGSGGGGSKLKQPA DGNPDPNANPNVDPNANPNVDPNANPNVDPNANPNKNNQGNGQGHNMPNDPNRNVDEKNIFT FNLNLNDILNSRLKKRKYFLDVLESDLMQFKHISSNEYIIEDSFKLLNSEQKNTLLKSYKYI KESVENDIKFAQEGISYYEKVLAKYKDDLESIKKVIKEEKEFPSSPPTTPPSPAKTDEQKKE SKFLPFLTNIETLYNNLVNKIDDYLINLKAKINDCNVEKDEAHVKITKLSDLKAIDDKIDLF KNPYDFEAIKKLINDDTKKDMLGKLLSTGLVQNFPNTIISKLIEGKFQDMLNISQHQCVKKQ CPQNSGCFRHLDEREECKCLLNYKQEGDKCVENPNPTCNENNGGCDADAKCTEEDSGSNGKK ITCECTKPDSYPLFDGIFCSGGGGSGGGGSHHHHHHHHGLNDIFEAQKIEWHE SEQ ID NO: 3 EKKVIHGCNFSSNVSSKHTFTDSLDISLVDDSAHISCNVHLSEPKYNHLVGLNCPGDIIPDC FFQVYQPESEELEPSNIVYLDSQINIGDIEYYEDAEGDDKIKLFGIVGSIPKTTSFTCICKK DKKSAYMTVTIDSAGGGGSGGGGSKLKQPADGNPDPNANPNVDPNANPNVDPNANPNVDPNA NPNKNNQGNGQGHNMPNDPNRNVDEKNIFTFNLNLNDILNSRLKKRKYFLDVLESDLMQFKH ISSNEYIIEDSFKLLNSEQKNTLLKSYKYIKESVENDIKFAQEGISYYEKVLAKYKDDLESI KKVIKEEKEFPSSPPTTPPSPAKTDEQKKESKFLPFLTNIETLYNNLVNKIDDYLINLKAKI NDCNVEKDEAHVKITKLSDLKAIDDKIDLFKNPYDFEAIKKLINDDTKKDMLGKLLSTGLVQ NFPNTIISKLIEGKFQDMLNISQHQCVKKQCPQNSGCFRHLDEREECKCLLNYKQEGDKCVE NPNPTCNENNGGCDADAKCTEEDSGSNGKKITCECTKPDSYPLFDGIFCSGGGGSGGGGSHH HHHHHHGLNDIFEAQKIEWHE SEQ ID NO:4 KYYEYFKSYKKKDIDNKNLKQFCNIIKEQHEINNEQQKCFCCYCRQDDMVFPLFSHFNYKKA KFKCNKKEQEEDIVLTLSCLKKKGGGGSGGGGSKLKQPADGNPDPNANPNVDPNANPNVDPN ANPNVDPNANPNKNNQGNGQGHNMPNDPNRNVDFENAIKKTKNQENNLTLLPIKSTEEEKDD IKNGKDIKKEIDNDKENIKTNNAKDHSTYIKSYLNTNVNDGLKYLFIPSHNSFIKKYSVFNQ INDGMLLNEKNDVKNNEDYKNVDYKNVNFLQYHFKELSNYNIANSIDILQEKEGHLDFVIIP HYTFLDYYKHLSYNSIYHKSSTYGKCIAVDAFIKKINETYDKVKSKCNDIKNDLIATIKKLE HPYDINNKNDDSYRYDISEEIDDKSEETDDETEEVEDSIQDTDSNHTPSNKKKNDLMNRTFK KMMDEYNTKKKKLIKCIKNHENDFNKICMDMKNYGTNLFEQLSCYNNNFCNTNGIRYHYDEY IHKLILSVKSKNLNKDLSDMTNILQQSELLLTNLNKKMGSYIYIDTIKFIHKEMKHIFNRIE YHTKIINDKTKIIQDKIKLNIWRTFQKDELLKRILDMSNEYSLFITSDHLRQMLYNTFYSKE KHLNNIFHHLIYVLQMKFNDVPIKMEYFQTYKKNKPLTQGSGGGSHHHHHHHHGLNDIFEAQ KIEWHE SEQ ID NO:5 EYVDEKERQGEIYPFGDEEEKDEGGESFTYEKSEVDKTDLFKFIEGGEGDDVYKVDGSKVLL DDDTISRVSKKHTARDGEYGEYGEAVEDGENVIKIIRSVLQSGALPSVGVDELDKIDLSYET TESGDTAVSEDSYDKYASNNTNKEYVCDFTDQLKPTESGPKVKKCEVKVNEPLIKVKIICPL KGSVEKLYDNIEYVPKKSPYVVLTKEETKLKEKLLSKLIYGLLISPTVNEKENNFKEGVIEF TLPPVVHKATVFYFICDNSKTEDDNKKGNRGIVEVYVEPYGNKINGGGGGSGGGGSKLKQPA DGNPDPNANPNVDPNANPNVDPNANPNVDPNANPNKNNQGNGQGHNMPNDPNRNVDFENAIK KTKNQENNLTLLPIKSTEEEKDDIKNGKDIKKEIDNDKENIKTNNAKDHSTYIKSYLNTNVN DGLKYLFIPSHNSFIKKYSVFNQINDGMLLNEKNDVKNNEDYKNVDYKNVNFLQYHFKELSN SCRI.512WO / / VHPM 00819.003WO1 YNIANSIDILQEKEGHLDFVIIPHYTFLDYYKHLSYNSIYHKSSTYGKCIAVDAFIKKINET YDKVKSKCNDIKNDLIATIKKLEHPYDINNKNDDSYRYDISEEIDDKSEETDDETEEVEDSI QDTDSNHTPSNKKKNDLMNRTFKKMMDEYNTKKKKLIKCIKNHENDFNKICMDMKNYGTNLF EQLSCYNNNFCNTNGIRYHYDEYIHKLILSVKSKNLNKDLSDMTNILQQSELLLTNLNKKMG SYIYIDTIKFIHKEMKHIFNRIEYHTKIINDKTKIIQDKIKLNIWRTFQKDELLKRILDMSN EYSLFITSDHLRQMLYNTFYSKEKHLNNIFHHLIYVLQMKFNDVPIKMEYFQTYKKNKPLTQ GSGGGSHHHHHHHHGLNDIFEAQKIEWHE SEQ ID NO:6 EKKVIHGCNFSSNVSSKHTFTDSLDISLVDDSAHISCNVHLSEPKYNHLVGLNCPGDIIPDC FFQVYQPESEELEPSNIVYLDSQINIGDIEYYEDAEGDDKIKLFGIVGSIPKTTSFTCICKK DKKSAYMTVTIDSAGGGGSGGGGSKLKQPADGNPDPNANPNVDPNANPNVDPNANPNVDPNA NPNKNNQGNGQGHNMPNDPNRNVDFENAIKKTKNQENNLTLLPIKSTEEEKDDIKNGKDIKK EIDNDKENIKTNNAKDHSTYIKSYLNTNVNDGLKYLFIPSHNSFIKKYSVFNQINDGMLLNE KNDVKNNEDYKNVDYKNVNFLQYHFKELSNYNIANSIDILQEKEGHLDFVIIPHYTFLDYYK HLSYNSIYHKSSTYGKCIAVDAFIKKINETYDKVKSKCNDIKNDLIATIKKLEHPYDINNKN DDSYRYDISEEIDDKSEETDDETEEVEDSIQDTDSNHTPSNKKKNDLMNRTFKKMMDEYNTK KKKLIKCIKNHENDFNKICMDMKNYGTNLFEQLSCYNNNFCNTNGIRYHYDEYIHKLILSVK SKNLNKDLSDMTNILQQSELLLTNLNKKMGSYIYIDTIKFIHKEMKHIFNRIEYHTKIINDK TKIIQDKIKLNIWRTFQKDELLKRILDMSNEYSLFITSDHLRQMLYNTFYSKEKHLNNIFHH LIYVLQMKFNDVPIKMEYFQTYKKNKPLTQGSGGGSHHHHHHHHGLNDIFEAQKIEWHE Certain Definitions As used herein, the terms "Plasmodium" or "parasite" refer to any parasite that belongs to the genus Plasmodium. In some embodiments, the Plasmodium organism can infect human hosts, such as, for example, P. falciparum, P. vivax, P. ovale, P. malariae, and P. knowlesi. In some embodiments, the Plasmodium organism is P. falciparum. In some embodiments, the Plasmodium organism is P. vivax or P. ovale. In other embodiments, the Plasmodium organism can infect other vertebrate hosts, such as nonhuman primates and rodents. Examples of such Plasmodium organisms include P. yoelii, P. berghei, P. chabaudi, P. vinckei, and P. cynomolgi. As used herein, the term "antigen" refers to a molecule capable of being bound by an antibody. An antigen is additionally capable of being recognized by the immune system and / or being capable of inducing a humoral immune response and / or cellular immune response leading to the activation of B- and / or T-lymphocytes. An antigen can have one or more epitopes (B- and / or T-cell epitopes). Antigens as used herein may also be mixtures of several individual antigens. The term "antibody" is used herein in the broadest sense and specifically encompass monoclonal antibodies (including full length monoclonal antibodies), polyclonal antibodies, multispecific antibodies (e.g., bispecific antibodies), and antibody fragments such as variable SCRI.512WO / / VHPM 00819.003WO1 domains and other portions of antibodies that exhibit a desired biological activity, e.g., PfHAP2p binding and or neutralizing. An "immune response" refers to a humoral immune response and / or cellular immune response leading to the activation or proliferation of B- and / or T-lymphocytes and / or and antigen presenting cells. In some instances, however, the immune responses may be of low intensity and become detectable only when using at least one substance in accordance with the invention. "Immunogenic" or “immunogen” refers to an agent used to stimulate the immune system of a living organism, so that one or more functions of the immune system are increased and directed towards the immunogenic agent. An "immunogenic polypeptide" is a polypeptide that elicits a cellular and / or humoral immune response, whether alone or linked to a carrier. Preferably, antigen presenting cell may be activated. A substance that "enhances" an immune response refers to a substance in which an immune response is observed that is greater or intensified or deviated in any way with the addition of the substance when compared to the same immune response measured without the addition of the substance. For example, the lytic activity of cytotoxic T cells can be measured, e.g. using a51Cr release assay, in samples obtained with and without the use of the substance during immunization. The amount of the substance at which the CTL lytic activity is enhanced as compared to the CTL lytic activity without the substance is said to be an amount sufficient to enhance the immune response of the animal to the antigen. In certain embodiments, the immune response in enhanced by a factor of at least about 2, such as by a factor of about 3 or more. The amount or type of cytokines secreted may also be altered. Alternatively, the amount of antibodies induced or their subclasses may be altered. The terms "immunize" or "immunization" or related terms refer to conferring the ability to mount a substantial immune response (comprising antibodies and / or cellular immunity) against a target antigen or epitope. These terms do not require that complete immunity be created, but rather that an immune response be produced which is substantially greater than baseline. For example, a mammal may be considered to be immunized against a target antigen if the cellular and / or humoral immune response to the target antigen occurs following the application of methods of the invention. The term "immunotherapeutic" refers to a composition for the treatment of diseases, disorders or conditions. More specifically, the term is used to refer to a method of treatment wherein a beneficial immune response is generated by vaccination or by transfer of immune SCRI.512WO / / VHPM 00819.003WO1 molecules. An "immunologically effective amount" refers to an amount of a composition sufficient to induce an immune response in an individual when introduced into that individual. In the context of active immunization, the term is synonymous with "immunogenically effective amount." The amount of a composition necessary to be immunologically effective varies according many factors including to the composition, the presence of other components in the composition, the antigen, the route of immunization, the individual, the prior immune or physiologic state etc. The term "epitope" refers to basic element or smallest unit of recognition by an individual antibody or T-cell receptor, and thus the particular domain, region or molecular structure to which said antibody or T-cell receptor binds. An antigen may consist of numerous epitopes while a hapten, typically, may possess few epitopes. As used herein "correspond essentially to" refers to an epitope that will elicit an immunological response at least substantially equivalent to the response generated by the native epitope. An immunological response to a composition or vaccine is the development in the host of a cellular and / or antibody-mediated immune response to the polypeptide or vaccine of interest. Usually, such a response consists of the subject producing antibodies, B cell, helper T cells, suppressor T cells, and / or cytotoxic T cells directed specifically to an antigen or antigens included in the composition or vaccine of interest. The term "adjuvant" as used herein refers to non-specific stimulators of the immune response or substances that allow generation of a depot in the host, which when combined with the vaccine and pharmaceutical composition, respectively, of the present invention may provide for an even more enhanced immune response. Vaccines commonly contain two components: antigen and adjuvant. The antigen is the molecular structure encoded by the pathogen against which the immune response is directed. To activate an antigen-specific immune response, the antigen must be presented in the appropriate immunostimulatory microenvironment. In certain embodiments, adjuvants establish such microenvironments by stimulating the production of immune-activating molecules such as proinflammatory cytokines. Vaccine efficacy depends on the types of antigen and adjuvant, and how they are administered. Immunogenic compositions as described herein also comprise, in certain embodiments, one or more adjuvants. An adjuvant is a substance that enhances the immune response when administered together with an immunogen or antigen. A number of cytokines SCRI.512WO / / VHPM 00819.003WO1 or lymphokines have been shown to have immune modulating activity, and thus are useful as adjuvants, including, but not limited to, the interleukins 1-α, 1-β, 2, 4, 5, 6, 7, 8 and 10, 12 (see, e.g., U.S. Pat. No.5,723,127), 13, 14, 15, 16, 17 and 18 (and its mutant forms); the interferons-α, β and γ; granulocyte-macrophage colony stimulating factor (GM-CSF) (see, e.g., U.S. Pat. No.5,078,996 and ATCC Accession Number 39900); macrophage colony stimulating factor (M-CSF); granulocyte colony stimulating factor (G-CSF); and the tumor necrosis factors α and β. Still other adjuvants that are useful with the immunogenic compositions described herein include chemokines, including without limitation, MCP-1, MIP-1α, MIP-1β, and RANTES; adhesion molecules, such as a selectin, e.g., L-selectin, P- selectin and E-selectin; mucin-like molecules, e.g., CD34, GlyCAM-1 and MadCAM-1; a member of the integrin family such as LFA-1, VLA-1, Mac-1 and p150.95; a member of the immunoglobulin superfamily such as PECAM, ICAMs, e.g., ICAM-1, ICAM-2 and ICAM-3, CD2 and LFA-3; co-stimulatory molecules such as CD40 and CD40L; growth factors including vascular growth factor, nerve growth factor, fibroblast growth factor, epidermal growth factor, B7.2, PDGF, BL-1, and vascular endothelial growth factor; receptor molecules including Fas, TNF receptor, Flt, Apo-1, p55, WSL-1, DR3, TRAMP, Apo-3, AIR, LARD, NGRF, DR4, DR5, KILLER, TRAIL-R2, TRICK2, and DR6; and Caspase (ICE). Still other adjuvants include muramyl peptides, such as N-acetyl-muramyl-L- threonyl-D-isoglutamine (thr-MDP), N-acetyl-normuramyl-L-alanine-2-(1’-2’ dipalmitoyl- sn-glycero-3-hydroxyphosphoryloxy)-ethylamine (MTP-PE); oil-in-water emulsions, such as MF59 (U.S. Pat. No.6,299,884) (containing 5% Squalene, 0.5% Tween 80, and 0.5% Span 85 (optionally containing various amounts of MTP-PE) formulated into submicron particles using a microfluidizer such as Model 110Y microfluidizer (Microfluidics, Newton, MA)), and SAF (containing 10% Squalene, 0.4% Tween 80, 5% pluronic-blocked polymer L121, and thr-MDP, either microfluidized into a submicron emulsion or vortexed to generate a larger particle size emulsion); aluminum salts (alum), such as aluminum hydroxide, aluminum phosphate, aluminum sulfate; Amphigen; Avridine; L121 / squalene; D-lactide- polylactide / glycoside; pluronic polyols; killed Bordetella; saponins, such as Stimulon™ QS- 21 (Antigenics, Framingham, MA.), described in U.S. Pat. No.5,057,540, ISCOMATRIX (CSL Limited, Parkville, Australia), described in U.S. Pat. No.5,254,339, and immunostimulating complexes (ISCOMS); Mycobacterium tuberculosis; bacterial lipopolysaccharides; synthetic polynucleotides such as oligonucleotides containing a CpG SCRI.512WO / / VHPM 00819.003WO1 motif (e.g., U.S. Pat. No.6,207,646); IC-31 (Intercell AG, Vienna, Austria), described in European Patent Nos. 1,296,713 and 1,326,634; a pertussis toxin (PT) or mutant thereof, a cholera toxin or mutant thereof (e.g., U.S. Pat. Nos. 7,285,281, 7,332,174, 7,361,355 and 7,384,640); or an E. coli heat-labile toxin (LT) or mutant thereof, particularly LT-K63, LT- R72 (e.g., U.S. Pat. Nos. 6,149,919, 7,115,730 and 7,291,588). Suitable adjuvants used to enhance an immune response further include, without limitation, MPL™ (3-O-deacylated monophosphoryl lipid A, Corixa, Hamilton, MT), which is described in U.S. Pat. No.4,912,094. Also suitable for use as adjuvants are synthetic lipid A analogs or aminoalkyl glucosamine phosphate compounds (AGP), or derivatives or analogs thereof, which are available from Corixa (Hamilton, MT), and which are described in U.S. Pat. No.6,113,918. One such AGP is 2-[(R)-3- Tetradecanoyloxytetradecanoylamino] ethyl 2-Deoxy-4-O-phosphono-3-O-[(R)-3- tetradecanoyoxytetradecanoyl]-2-[(R)-3-tetradecanoyloxytetradecanoyl-amino]-b-D- glucopyranoside, which is also known as 529 (formerly known as RC529). This 529 adjuvant is formulated as an aqueous form (AF) or as a stable emulsion (SE). Suitable adjuvants also include, but are not limited to, surfactants, e.g., hexadecylamine, octadecylamine, lysolecithin, dimethyldioctadecylammonium bromide, N,N-dioctadecyl-N'-N-bis(2-hydroxyethyl-propane di-amine), methoxyhexadecyl-glycerol, and pluronic polyols; polanions, e.g., pyran, dextran sulfate, poly IC, polyacrylic acid, carbopol; peptides, e.g., muramyl dipeptide, MPL, aimethylglycine, tuftsin, oil emulsions, alum, and mixtures thereof. Other potential adjuvants include the B peptide subunits of E. coli heat labile toxin or of the cholera toxin. McGhee, J.R., et al., "On vaccine development," Sem. Hematol., 30:3-15 (1993). Finally, the immunogenic product may be incorporated into liposomes for use in a vaccine formulation, or may be conjugated to proteins such as keyhole limpet hemocyanin (KLH) or human serum albumin (HSA) or other polymers. In certain embodiments, the adjuvant comprises aluminum salt (e.g., aluminum hydroxide, aluminum phosphate, alum (e.g., potassium aluminum sulfate), or mixed aluminum salts). In certain embodiments, the adjuvant comprises a Toll like receptor agonist (e.g., monophosphoryl lipid A (MPL-A), a lipopeptide, and a synthetic nucleic acid sequence such as CpG and poly(I:C)). In certain embodiments, the adjuvant comprises squalene. In certain embodiments, the adjuvant comprises AS04. In certain embodiments, the adjuvant comprises Complete Freund’s Adjuvant (CFA). SCRI.512WO / / VHPM 00819.003WO1 In certain embodiments, the adjuvant comprises Incomplete Freund's Adjuvant (IFA). In certain embodiments, the adjuvant comprises aluminum salt (e.g., Alum). In certain embodiments, the adjuvant comprises monophosphoryl lipid A. In certain embodiments, the adjuvant comprises aluminum salt (e.g., Alum) and monophosphoryl lipid A. A polypeptide described herein can be conjugated or linked to another peptide or to a polysaccharide. For example, immunogenic proteins well-known in the art, also known as “carriers,” may be employed. Useful immunogenic proteins include keyhole limpet hemocyanin (KLH), bovine serum albumin (BSA), ovalbumin, human serum albumin, human gamma globulin, chicken immunoglobulin G and bovine gamma globulin. Useful immunogenic polysaccharides include polysaccharides from other pathogens, such as those that are effective as vaccines. The immunogenic polysaccharides or proteins of other pathogens can be conjugated to, linked to, or mixed with the polypeptide described herein. To prepare a vaccine, a polypeptide described herein can be isolated, lyophilized and stabilized. The polypeptide described herein may then be adjusted to an appropriate concentration, optionally combined with a suitable vaccine adjuvant, and packaged for use. In certain embodiments, the composition (e.g., immunogenic composition) is a liquid composition. In certain embodiments, the composition (e.g., immunogenic composition) is a solid composition (e.g., lyophilized) that may be reconstituted with suitable solvent (e.g., saline or Dextrose 5% in water) prior to administration. In certain embodiments, the present invention comprises two or more immunogenic polypeptides. In certain embodiments, one or more polypeptides are adjusted to an appropriate concentration and can be formulated with any suitable adjuvant, diluent, pharmaceutically acceptable carrier, or any combination thereof. As used herein the phrase "pharmaceutically acceptable carrier" is intended to include any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, excipients and the like, compatible with pharmaceutical administration. The use of such media and agents for pharmaceutically active substances is well known in the art. Physiologically acceptable vehicles may be used as carriers and / or diluents. A pharmaceutically acceptable vehicle is understood to designate a compound or a combination of compounds entering into a pharmaceutical or immunogenic composition which does not cause side effects and which makes it possible, for example, to facilitate the administration of the active compound, to increase its life and / or its efficacy in the body, to increase its SCRI.512WO / / VHPM 00819.003WO1 solubility in solution or alternatively to enhance its preservation. These pharmaceutically acceptable vehicles are well known and will be adapted by persons skilled in the art according to the nature and the mode of administration of the active compound chosen. These include, but are not limited to, water, Ringer’s solution, an appropriate isotonic medium, glycerol, ethanol and other conventional solvents, phosphate buffered saline, and the like. The term "nucleic acid" refers to deoxyribonucleotides or ribonucleotides and polymers thereof in either single- or double-stranded form, composed of monomers (nucleotides) containing a sugar, phosphate and a base which is either a purine or pyrimidine. Unless specifically limited, the term encompasses nucleic acids containing known analogs of natural nucleotides that have similar binding properties as the reference nucleic acid and are metabolized in a manner similar to naturally occurring nucleotides. Unless otherwise indicated, a particular nucleic acid sequence also implicitly encompasses conservatively modified variants thereof (e.g., degenerate codon substitutions) and complementary sequences as well as the sequence explicitly indicated. Specifically, degenerate codon substitutions may be achieved by generating sequences in which the third position of one or more selected (or all) codons is substituted with mixed-base and / or deoxyinosine residues (Batzer et al. (1991) Nucl. Acids Res.,19:508; Ohtsuka et al. (1985) JBC, 260:2605; Rossolini et al. (1994) Mol. Cell. Probes, 8:91. A "nucleic acid fragment" is a fraction of a given nucleic acid molecule. Deoxyribonucleic acid (DNA) in the majority of organisms is the genetic material while ribonucleic acid (RNA) is involved in the transfer of information contained within DNA into proteins. The term "nucleotide sequence" refers to a polymer of DNA or RNA that can be single- or double-stranded, optionally containing synthetic, non-natural or altered nucleotide bases capable of incorporation into DNA or RNA polymers. The terms "nucleic acid," "nucleic acid molecule," "nucleic acid fragment," "nucleic acid sequence or segment," or "polynucleotide" may also be used interchangeably with gene, cDNA, DNA and RNA encoded by a gene. By “portion” or “fragment,” as it relates to a nucleic acid molecule, sequence or segment of the invention, when it is linked to other sequences for expression, is meant a sequence having at least 80 nucleotides, more preferably at least 150 nucleotides, and still more preferably at least 400 nucleotides. If not employed for expressing, a “portion” or “fragment” means at least 9, preferably 12, more preferably 15, even more preferably at least SCRI.512WO / / VHPM 00819.003WO1 20, consecutive nucleotides, e.g., probes and primers (oligonucleotides), corresponding to the nucleotide sequence of the nucleic acid molecules of the invention. The term “amino acid” includes the residues of the natural amino acids (e.g. Ala, Arg, Asn, Asp, Cys, Glu, Gln, Gly, His, Hyl, Hyp, Ile, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Tyr, and Val) in Dextrorotary or Levorotary stereoisomeric forms, as well as unnatural amino acids (e.g., phosphoserine, phosphothreonine, phosphotyrosine, hydroxyproline, and gamma-carboxyglutamate; hippuric acid, octahydroindole-2-carboxylic acid, statine, 1,2,3,4,-tetrahydroisoquinoline-3-carboxylic acid, penicillamine, ornithine, citruline, alpha-methyl-alanine, para-benzoylphenylalanine, phenylglycine, propargylglycine, sarcosine, and tert-butylglycine). The term also comprises natural and unnatural amino acids (Dextrorotary and Levorotary stereoisomers) bearing a conventional amino protecting group (e.g. acetyl or benzyloxycarbonyl), as well as natural and unnatural amino acids protected at the carboxy terminus (e.g., as a (C1-C6)alkyl, phenyl or benzyl ester or amide; or as an α- methylbenzyl amide). Other suitable amino and carboxy protecting groups are known to those skilled in the art (See for example, Greene, T.W.; Wutz, P.G.M., Protecting Groups In Organic Synthesis; second edition, 1991, New York, John Wiley & sons, Inc, and documents cited therein). An amino acid can be linked to the remainder of a compound through the carboxy terminus, the amino terminus, or through any other convenient point of attachment, such as, for example, through the sulfur of cysteine. The terms "protein," "peptide" and "polypeptide" are used interchangeably herein. Polypeptide sequences specifically recited herein are written with the amino terminus on the left and the carboxy terminus on the right. As used herein, the terms “protein,” “peptide” and "polypeptide" refer to a polymer in which the monomers are amino acid residues that are joined together through amide bonds. When the amino acids are alpha-amino acids, either the L-optical isomer or the D-optical isomer can be used, the L-isomers being preferred. The term polypeptide or protein as used herein encompasses any amino acid sequence and includes modified sequences such as glycoproteins. The term polypeptide is specifically intended to cover naturally occurring proteins, as well as those that are recombinantly or synthetically produced. The phrase “recombinant protein” or “chimeric protein” includes proteins, in particular recombinant fusion proteins that are prepared, expressed, created or isolated by SCRI.512WO / / VHPM 00819.003WO1 recombinant means, such as proteins expressed using a recombinant expression vector transfected into a host cell. The term “recombinant fusion protein” refers to a protein produced by recombinant technology which comprises segments, i.e. amino acid sequences, from heterologous sources, such as different proteins or different organisms. The segments are joined either directly or indirectly to each other via peptide bonds. By indirect joining it is meant that an intervening amino acid sequence, such as a peptide linker is juxtaposed between segments forming the fusion protein. A recombinant fusion protein is encoded by a nucleotide sequence, which is obtained by genetically joining nucleotide sequences derived from different regions of one gene and / or by joining nucleotide sequences derived from two or more separate genes. These nucleotide sequences can be derived from P. falciparum, but they may also be derived from other organisms, the plasmids used for the cloning procedures or from other nucleotide sequences. The invention encompasses isolated or substantially purified protein compositions. In the context of the present invention, an "isolated" or "purified" polypeptide is a polypeptide that exists apart from its native environment and is therefore not a product of nature. A polypeptide may exist in a purified form or may exist in a non-native environment such as, for example, a transgenic host cell. For example, an "isolated" or "purified" protein, or biologically active portion thereof, is substantially free of other cellular material, or culture medium when produced by recombinant techniques, or substantially free of chemical precursors or other chemicals when chemically synthesized. A protein that is substantially free of cellular material includes preparations of protein or polypeptide having less than about 30%, 20%, 10%, 5%, (by dry weight) of contaminating protein. When the protein of the invention, or biologically active portion thereof, is recombinantly produced, preferably culture medium represents less than about 30%, 20%, 10%, or 5% (by dry weight) of chemical precursors or non-protein-of- interest chemicals. Fragments and variants of the disclosed proteins or partial-length proteins encoded thereby are also encompassed by the present invention. By "fragment" or "portion" or “segment” or “domain” is meant a full length or less than full length of the amino acid sequence of, a polypeptide or protein. "Naturally occurring" is used to describe an object that can be found in nature as distinct from being artificially produced. For example, a protein or nucleotide sequence present in an SCRI.512WO / / VHPM 00819.003WO1 organism (including a virus), which can be isolated from a source in nature and which has not been intentionally modified by man in the laboratory, is naturally occurring. A "variant" of a molecule is a sequence that is substantially similar to the sequence of the native molecule. The term “gene” is used broadly to refer to any segment of nucleic acid associated with a biological function. Genes include coding sequences and / or the regulatory sequences required for their expression. For example, gene refers to a nucleic acid fragment that expresses mRNA, functional RNA, or a specific protein, including its regulatory sequences. Genes also include nonexpressed DNA segments that, for example, form recognition sequences for other proteins. Genes can be obtained from a variety of sources, including cloning from a source of interest or synthesizing from known or predicted sequence information, and may include sequences designed to have desired parameters. In addition, a “gene” or a “recombinant gene” refers to a nucleic acid molecule comprising an open reading frame and including at least one exon and (optionally) an intron sequence. The term “intron” refers to a DNA sequence present in a given gene which is not translated into protein and is generally found between exons. "Expression" refers to the transcription and / or translation in a cell of an endogenous gene, transgene, as well as the transcription and stable accumulation of sense (mRNA) or functional RNA. In the case of antisense constructs, expression may refer to the transcription of the antisense DNA only. Expression may also refer to the production of protein. A “vector" is defined to include, inter alia, any viral vector, plasmid, cosmid, phage or binary vector in double or single stranded linear or circular form which may or may not be self-transmissible or mobilizable, and which can transform prokaryotic or eukaryotic host either by integration into the cellular genome or exist extrachromosomally (e.g., autonomous replicating plasmid with an origin of replication). The terms "operably linked," or “linked,” as used in a protein, refer to a structural linkage, covalent or non-covalent, of two or more fragments (e.g., a TS fragment, a BS fragment, and a PE fragment) in a fusion protein. In certain embodiments, a fusion protein comprises optional linker(s) (e.g., GS, GGS, GGGS (SEQ ID NO: 7), or GGGGS (SEQ ID NO: 8)) between fragments. In certain embodiments, a PfMS antigen or fragment may be operably linked to another immunogenic carrier that retains the peptide (e.g., the immunogenic fragment of a Plasmodium HAP2 paralog (HAP2p) protein) and immunogenic SCRI.512WO / / VHPM 00819.003WO1 carrier (e.g., KLH) in close proximity such that the carrier facilitates an immune response to the immunogen. Various technologies for linking immunogenic peptides to carrier proteins are known and are encompassed by this disclosure. "Isolated" means altered or removed from the natural state. For example, a nucleic acid or a peptide naturally present in a living animal is not "isolated." but the same nucleic acid or peptide partially or completely separated from the coexisting materials of its natural state is "isolated." An isolated nucleic acid or protein can exist in substantially purified form, or can exist in a non-native environment such as, for example, a host cell. Unless it is particularly specified otherwise herein, the proteins, virion complexes, antibodies and other biological molecules forming the subject matter of the present invention are isolated, or can be isolated. As used herein, "sequence identity" or "identity" in the context of two nucleic acid or polypeptide sequences makes reference to a specified percentage of residues in the two sequences that are the same when aligned for maximum correspondence over a specified comparison window, as measured by sequence comparison algorithms or by visual inspection. When percentage of sequence identity is used in reference to proteins it is recognized that residue positions which are not identical often differ by conservative amino acid substitutions, where amino acid residues are substituted for other amino acid residues with similar chemical properties (e.g., charge or hydrophobicity) and therefore do not change the functional properties of the molecule. When sequences differ in conservative substitutions, the percent sequence identity may be adjusted upwards to correct for the conservative nature of the substitution. Sequences that differ by such conservative substitutions are said to have "sequence similarity" or "similarity." Means for making this adjustment are well known to those of skill in the art. Typically this involves scoring a conservative substitution as a partial rather than a full mismatch, thereby increasing the percentage sequence identity. Thus, for example, where an identical amino acid is given a score of 1 and a non-conservative substitution is given a score of zero, a conservative substitution is given a score between zero and 1. The scoring of conservative substitutions is calculated, e.g., as implemented in the program PC / GENE (Intelligenetics, Mountain View, California). As used herein, "percentage of sequence identity" means the value determined by comparing two optimally aligned sequences over a comparison window, wherein the portion SCRI.512WO / / VHPM 00819.003WO1 of the sequence in the comparison window may comprise additions or deletions (i.e., gaps) as compared to the reference sequence (which does not comprise additions or deletions) for optimal alignment of the two sequences. The percentage is calculated by determining the number of positions at which the identical nucleic acid base or amino acid residue occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the window of comparison, and multiplying the result by 100 to yield the percentage of sequence identity. The term "substantial identity" in the context of a protein indicates that a protein comprises a sequence with at least 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, or 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, or 89%, at least 90%, 91%, 92%, 93%, or 94%, or 95%, 96%, 97%, 98% or 99%, sequence identity to a reference sequence over a specified comparison window. Optimal alignment is conducted using the homology alignment algorithm of Needleman and Wunsch, J. Mol. Biol.48:443 (1970). An indication that two protein sequences are substantially identical is that one protein is immunologically reactive with antibodies raised against the second protein. Thus, a protein is substantially identical to a second protein, for example, where the two proteins differ only by a conservative substitution. As used herein, a “subject” is an animal, e.g., a mammal, e.g., a human, monkey, dog, cat, horse, cow, pig, goat, rabbit, or mouse. The invention will now be illustrated by the following non-limiting Examples. EXAMPLE 1 Design, development, and optimization of PfMS vaccine To establish proof of concept for the construction and optimization of each PfMS antigen variant, the present inventors have designed a codon-optimized P. yoelii (a rodent malaria model) MS antigen with the D2 domain of PyHAP2p, 4 major (QGPGAP (SEQ ID NO: 10)) and 4 minor (QQPP (SEQ ID NO: 11)) repeats of PyCSP, and the P42 domain of PyMSP-1 (Figure 2A). A signal sequence and a (His)8 (SEQ ID NO: 9)-Avi tag were included in the N and C-termini, respectively, to facilitate protein secretion and purification. Each antigen fragment of the PyMS antigen was intervened by two G4S (SEQ ID NO: 17) (GGGGS) (SEQ ID NO: 8) linkers. The PyMS antigen (Figure 2B) was successfully SCRI.512WO / / VHPM 00819.003WO1 expressed and purified, and it was demonstrated that the PyMS vaccine could elicit robust IgG responses in immunized BALB / cJ mice to all of the individual antigens (Figures 2C, 2D). It was verified that the vaccine-elicited polyclonal antibodies (pAbs) from immunized animals bound to Py sporozoites-associated CSP by sporozoite lysate ELISA and IFA (Figures 2D, 2E). In certain embodiments, several versions of PfMS antigen bearing domain combinations are codon optimized and expressed in HEK293 cells as single PfMS chimeric antigens (Table 1). Except for CSP, all other antigen amino acid boundaries were determined from previous studies showing pathogen inhibitory properties15,31–34,43,45. The CSP repeats include known motifs targeted by potent anti-PfCSP antibodies, such as CIS4327,46. A secretion signal and affinity tags (His-Avi) are included in the design at the N and C-termini, respectively, to facilitate protein secretion, purification, and to support functional assays, and any N-linked glycosylation sites (NXS / T) are mutated to NXA to prevent glycosylation20,21. The individual domains (or segments) are separated by G4S (SEQ ID NO: 8) linkers (the exact number is optimized for each antigen) to allow for flexibility and to relieve potential steric clashes. The PfMS antigen versions are purified from the culture supernatants using NiNTA affinity and size-exclusion chromatography and characterized by SDS PAGE, Octet BLI, and WB. In certain embodiments, the antigenic integrity of neutralizing epitopes in the PfMS antigens is verified with monoclonal antibodies (mAbs) that bind to each antigen using Octet- BLI and ELISA, as shown in Figures 2 and 3. For PfCSP, 2A10 and CIS43 mAbs are used; and for PfHAP2p, mAb B10 (a murine mAb developed in the lab) is used. For other antigens, mAbs are either commercially available or produced from known sequences, such as α- PfRH5 mAbs R5.003, R5.14 and R5.1547. The individual domains of each antigen are also expressed as single recombinant antigens to assess domain-specific antibody responses. To evaluate the feasibility of a P. falciparum multistage antigen, PfMS antigen version 4 (HAP2P / CSP / Rh5, Table 1) was developed by the present inventors. Using Anti-his tag antibody Western blot analysis, the PfMS.V4 has been identified from the culture supernatants of transfected HEK293 cells, confirming the protein expression and secretion (Figure 3A). Further, using PfHAP2p mAb B10 and PfCSP repeat-specific mab 2A10, PfMS.V4 conformation and accessibility of epitopes on the PfMS antigen surface have been validated by ELISA and Ni-NTA Octet-BLI analysis (Figures 3B, 3C). The sequence SCRI.512WO / / VHPM 00819.003WO1 identity of PfMS.V4 was verified by Mass Spectrometry, confirming the feasibility of this approach with P. falciparum. EXAMPLE 2 Formulation of PfMS vaccines as mRNAs After optimization of the protein variants, certain embodiments include selection of the best producing and stable antigens for development as lipid nanoparticle (LNP)-delivered mRNA vaccines. mRNA vaccines have been demonstrated to be highly immunogenic, and have many advantages over recombinant proteins, such as the ease of production (both rapidly and robustly) and time and cost-effectiveness48. Additionally, certain embodiments include testing PfMS self-amplifying mRNA vaccines (SAMs), which could significantly increase the abundance of the antigen and amplify host immune responses. The design of both PfMS mRNA and PfMS SAMs are depicted in Figure 4. The general design of PfMS mRNA vaccine includes a 5’ CAP structure followed by Untranslated regions (UTR’s) and the codon optimized coding sequence of the PfMS antigen with secretion signal, UTR’s and a 3’ 120 nucleotide long Poly-A tail (SEQ ID NO: 16). Additionally, a transmembrane sequence is added in both PfMS mRNA and SAMs in order to display the translated PfMS antigen on the surface of the expressing cells, which increases the duration and bioavailability of the PfMS antigen, thereby inducing high immune responses. For PfMS SAMs, a viral replicase sequence is inserted before the PfMS coding sequence. To ensure the purity of the PfMS mRNA vaccines and to reduce the innate sensing of the mRNA and SAMs, these vaccines can be produced in a GMP facility using the CleanCap technology procured from Trilink® BioTechnologies. The significance of each component and the mode of function of mRNA and SAMs has been recently reviewed49. Both mRNA and SAMs are formulated using LNPs to facilitate internalization and endosomal escape of PfMS mRNA. Briefly, cationic lipid DODMA (1,2-dioleyloxy-3-dimethylaminopropane), DSPC (1,2-distearoyl-sn-glycero-3-phosphocholine), Cholesterol, and DMP-PEG 2000 (1,2- dimyristoyl-rac-glycero-3-methoxypolyethylene glycol) are formulated in 40:10:40:10 ratio in ethanol phase and mixed with aqueous PfMS antigen using NanoGeneratorTMFlex device from PreciGenome. The mRNA and SAMs are initially characterized for protein expression by transfecting HEK293 cells, and the expression is confirmed by using fluorescently tagged SCRI.512WO / / VHPM 00819.003WO1 antibodies in fluorescence microscopy. The present inventors have used this method to validate the expression and localization of the PvCSPvk210 antigen (with transmembrane fragment), which showed robust surface expression in HEK293 cells (Figure 5). EXAMPLE 3 Immunogenicity of PfMS antigens To evaluate antibody responses elicited by the PfMS vaccine antigens, mice are immunized with recombinant protein or mRNA formulations. Groups of ten BALB / cJ mice (balanced for females and males, 6-8 weeks old) receive an immunization protocol with vaccinations at weeks 1, 3, and 7, with blood and spleen harvested at week 8. Using balanced numbers of sexes accounts for sex as a biological variable in immune response measurements. For PfMS protein immunizations, animals receive 20 μg per vaccination intramuscularly (IM) formulated in 50% AddaS03 (an AS03-like adjuvant from Invivogen®). For the mRNA immunizations, 5 and 30 μg mRNA doses are administered. Splenocytes are isolated by Ficoll gradient and stored in liquid nitrogen. PBS plus AS03 or LNPs are used as experimental controls. Polyclonal antibody (pAb) responses for reactivity against each component are assessed, and evaluation of whether they recognize the native antigen in the context of the parasite is performed by whole sporozoite lysate ELISA. The total IgG responses for the PfMS antigen, as well as IgG titers to each antigen fragment of PfMS, are assayed by direct ELISA following standard protocols18,20,21. Serum is titrated across a dynamic range of 1:50- 1:4X106and detected with an anti-mouse IgG secondary antibody. Titers are determined as the lowest dilution at which signal is 2-fold above background. Alternatively, the 50% effective concentration (EC50) can be extrapolated. IgG subclass distribution are evaluated by direct ELISA, but with IgG subclass-specific secondary antibodies20,21. Binding is compared between groups and to the single antigen subunits by ANOVA. To assess antibody avidity, a chaotrope-modified ELISA is used, in which bound antibodies are treated with ammonium thiocyanate, which disrupts binding proportionally to the strength of binding, allowing the derivation of an avidity index20,21. Additionally, an apparent affinity (KD) is derived with purified pAbs by Octet BLI21. Finally, confirmation that pAbs recognize the native antigen in the context of the parasite is performed by IFA. Parasites corresponding to the appropriate stage are adhered to glass slides and probed with pAbs, and then detected by SCRI.512WO / / VHPM 00819.003WO1 fluorophore conjugated secondary antibodies (e.g., Figure 2E). DAPI and a control surface- localized stain are used to provide a reference for cellular localization15,19–21,50. EXAMPLE 4 Efficacy and anti-parasitic functional activity of vaccine-elicited antibody responses The ability of vaccine-elicited pAbs to mediate anti-parasitic functional activity is characterized in standardized in vitro assays. Confirming the ability to inhibit all three lifecycle stages is a critical milestone in the development of an effective PfMS vaccine and can provide the rationale for further development. To assess the anti-parasitic function of vaccine-elicited antibodies, standardized in vitro assays are deployed against all three stages. The production of P. falciparum is conducted in specialized insectary facilities and under strict biosafety regulations. The pAbs are purified from the sera of PfMS-immunized animals by protein-G affinity chromatography and the specific concentrations to be tested are determined using canonical mAbs as guides. The stages-specific in vitro assays are: Pre-erythrocytic infection (i.e., anti-CSP) antibodies are tested in the Inhibition of Sporozoite Traversal and Invasion (ISTI) assay.104freshly isolated salivary gland Pf sporozoites are added to wells of HC-04 cells, seeded 24 hours prior, in the presence or absence of immune serum. FITC-dextran is added to detect cell traversal. After 90 mins, the wells are washed, fixed, permeabilized, and stained with fluoro-conjugated anti-CSP antibodies. The cells are analyzed by flow cytometry, where CSP positivity denotes invaded cells, and for FITC signal, denoting cell traversal18. Reduction in invasion is defined as a decrease in the number of CSP-positive cells, compared to non-immune serum controls. Reductions in traversal is defined as the decrease in FITC-positive cells compared to non- immune serum controls. Experiments are performed three times, each including three technical replicate wells18. Blood stage-specific inhibition (i.e., anti-RH5 or MSP-1) is measured by the Growth Inhibition Assay (GIA). Briefly, the purified total IgG from PfMS immune sera and control non-immune sera at defined concentrations are added to synchronized P. falciparum cultures at the late schizont stage (0.6% parasitemia, 4% hematocrit). The cells are returned to culture for 40 h and harvested to determine the lactate dehydrogenase (LDH) activity, which is an indicator of parasite development, at a wavelength of 650 nm, using the microplate reader29,30. All experiments are performed a minimum of three times in triplicate. SCRI.512WO / / VHPM 00819.003WO1 Transmission blocking activity (TBA) (i.e., anti-HAP2p, anti s230, anti-s48 / 45) is measured in the Standard Membrane Feeding Assay (SMFA). The culture method for mature gametocytes of P. falciparum NF54 and SMFA methodology are described earlier51–53. The purified pAbs from the sera of PfMS-immunized animals is diluted to desired test concentrations to a mixture of 0.3% P. falciparum gametocytes, normal human sera and human RBCs (50% hematocrit) and fed to ~40, 4-6-day old Anopheles stephensi mosquitoes that were starved (8 h) using glass membrane feeders controlled at 37°C for 15 mins. Excluding the unfed mosquitoes, the blood-fed ones are held at 27°C with 70% relative humidity for 8 days followed by dissection of midguts and quantification of oocysts. TBA is the reduction in oocysts per mosquito midgut (averaged from 20 mosquitos) between the PfMS IgG-fed and control IgG-fed groups (as shown in Figure 6 for HAP2p). To ensure scientific rigor, all assays are performed with both experimental and technical replicates, and each assay has rigorous positive and negative controls to ensure assay performance. Assays are designed to enable statistical comparisons, and a group size of 10 is powered to detect a 0.5 Log10 difference in EC50 between antigen groups. Specific comparisons among groups are performed by ANOVA, and analyses including multiple variables, such as biological sex and antigen variant, are evaluated by MANOVA or other multivariate analyses. Although the foregoing specification and examples fully disclose and enable the present invention, they are not intended to limit the scope of the invention, which is defined by the claims appended hereto. All publications, patents and patent applications are incorporated herein by reference. While in the foregoing specification this invention has been described in relation to certain embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein may be varied considerably without departing from the basic principles of the invention. The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. As used herein, the term “about” means ± 10%. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to”) unless SCRI.512WO / / VHPM 00819.003WO1 otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. Embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. REFERENCES 1. Malaria [Internet]. [cited 2021 Aug 27]. 2. Mallory, K.L., Taylor, J.A., Zou, X. et al. Messenger RNA expressing PfCSP induces functional, protective immune responses against malaria in mice. npj Vaccines 6, 84 (2021). 3. Rénia L, Goh YS. Malaria Parasites: The Great Escape. 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Claims

SCRI.512WO / / VHPM 00819.003WO1 CLAIMS What is claimed is:

1. A recombinant antigen comprising: a pre-erythrocytic (PE) fragment comprising a central repeat domain of a Plasmodium Circumsporozite Protein (CSP) or a fragment thereof; a blood stage (BS) fragment comprising at least one of a Plasmodium Merozoite Surface Protein 1 (MSP-1), a Plasmodium Reticulocyte Binding Protein Homologue 5 (RH5), or fragments thereof; and a transmission stage (TS) fragment comprising at least one of a Plasmodium HAP2 paralog (HAP2p) protein, a Plasmodium s230 protein, a Plasmodium s48 / 45 protein, or fragments thereof.

2. The recombinant antigen of claim 1, wherein the recombinant antigen is a single antigen.

3. The recombinant antigen of claim 1 or claim 2, wherein the recombinant antigen is configured to be expressed in a eukaryotic cell.

4. The recombinant antigen of any one of claims 1 to 3, wherein at least one of the CSP, MSP-1, RH5, HAP2p, s230 and s48 / 45 proteins is a Plasmodium falciparum protein.

5. The recombinant antigen of any one of claims 1 to 4, wherein the recombinant antigen comprises an amino acid sequence having at least 80% sequence identity to SEQ ID NO:1, 2, 3, 4, 5, or 6.

6. The recombinant antigen of claim 5, wherein the recombinant antigen comprises an amino acid sequence having at least 85%, at least 90%, or at least 95% sequence identity to SEQ ID NO:1, 2, 3, 4, 5, or 6.

7. An immunogenic composition comprising the recombinant antigen of any one of claims 1 to 6, and a pharmaceutically acceptable carrier.SCRI.512WO / / VHPM 00819.003WO1 8. The immunogenic composition of claim 7, further comprising an adjuvant in an amount sufficient to enhance an immune response.

9. An immunogenic composition comprising a mRNA comprising a coding sequence encoding the recombinant antigen of any one of claims 1 to 6.

10. The immunogenic composition of claim 9, wherein the mRNA is self-amplifying.

11. The immunogenic composition of claim 9 or claim 10, further comprising a lipid nanoparticle carrier.

12. A method of preventing or inhibiting transmission of a Plasmodium from an infected or susceptible host, comprising administering to the host an immunologically effective amount of the recombinant antigen of any one of claims 1 to 6 or an immunologically effective amount of the immunogenic composition of any one of claims 7 to 11.

13. The method of claim 12, wherein the Plasmodium is Plasmodium falciparum.

14. The method of claim 12 or claim 13, wherein the susceptible host is a human.

15. An antibody or antigen-binding derivative thereof that binds to at least one immunogenic fragment of the recombinant antigen of any one of claims 1 to 6.

16. The antibody or antigen-binding derivative thereof of claim 15, wherein the antibody or antigen-binding derivative thereof inhibits at least one of PE, BS, and TS stage Plasmodium falciparum parasitic functional activity in vitro.

17. The antibody or antigen-binding derivative thereof of claim 16, wherein the antibody or antigen-binding derivative thereof inhibits at least two of PE, BS, and TS stage Plasmodium falciparum parasitic functional activity in vitro.

18. The antibody or antigen-binding derivative thereof of claim 17, wherein the antibody or antigen-binding derivative thereof inhibits all three of PE, BS, and TS stage Plasmodium falciparum parasitic functional activity in vitro.SCRI.512WO / / VHPM 00819.003WO1 19. A method of preventing or inhibiting transmission of a Plasmodium from an infected or susceptible host, comprising administering to the host an immunologically effective amount of the antibody or antigen binding derivative thereof according to any one of claims 15 to 18.

20. The method of claim 19, wherein the Plasmodium is Plasmodium falciparum and the susceptible host is a human.

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