Immunization with extracellular sexual stages of the malaria parasites can induce the production ... more Immunization with extracellular sexual stages of the malaria parasites can induce the production of antibodies which block the development of the parasites in the midgut of a mosquito after a blood meal. We have generated a number of monoclonal antibodies against gametes and zygotes of the human malaria Plasmodium falciparum. Two monoclonal antibodies (mAb) reacting with a 230-kDa gamete surface protein (mAb 1B3 and 2B4 both isotype IgG2a) were found to block transmission of P. falciparum to mosquitoes. Blocking was complement dependent and this was verified in vitro by the rapid lysis of newly formed gametes and zygotes in the presence of the mAb and active complement. Both mAb reacted by immunofluorescence with the surface of gametes and zygotes from isolates of P. falciparum from various geographical areas. Each mAb immunoprecipitated a 230-kDa protein from 125I-labeled surface proteins of newly formed gametes and zygotes and immunoblotted a protein doublet of about molecular mas...
Malaria is a deadly disease responsible for between 550,000 and 627,000 deaths annually. There is... more Malaria is a deadly disease responsible for between 550,000 and 627,000 deaths annually. There is a pressing need to develop vaccines focused on malaria elimination. The complex lifecycle of Plasmodium falciparum provides opportunities not only to target the infectious sporozoite stage, introduced by anopheline mosquitoes, but also the sexual stages, which are ingested by mosquitoes during blood feeding, leading to parasite transmission. It is widely recognized that a vaccine targeting multiple stages would induce efficacious transmission reducing immunity. Technological advancements offer new vaccine platforms, such as mRNA-LNPs, which can be used to develop highly effective malarial vaccines. We evaluated the immunogenicity of two leading P. falciparum vaccine candidates, Pfs25 and PfCSP, delivered as mRNA-LNP vaccines. Both vaccines induced extremely potent immune responses when administered alone or in combination, which were superior to Pfs25 and PfCSP DNA vaccine formulations....
Plasmodium falciparum circumsporozoite protein (PfCSP) and Pfs25 are leading candidates for the d... more Plasmodium falciparum circumsporozoite protein (PfCSP) and Pfs25 are leading candidates for the development of pre-erythrocytic and transmission-blocking vaccines (TBV), respectively. Although considerable progress has been made in developing PfCSP- and Pfs25-based vaccines, neither have elicited complete protection or transmission blocking in clinical trials. The combination of antigens targeting various life stages is an alternative strategy to develop a more efficacious malaria vaccine. In this study, female and male mice were immunized with DNA plasmids encoding PfCSP and Pfs25, administered alone or in combination via intramuscular in vivo electroporation (EP). Antigen-specific antibodies were analyzed for antibody titers, avidity and isotype by ELISA. Immune protection against sporozoite challenge, using transgenic P. berghei expressing PfCSP and a GFP-luciferase fusion protein (PbPfCSP-GFP/Luc), was assessed by in vivo bioluminescence imaging and blood-stage parasite growth. ...
By use of the parental hybridoma cell line 63F2A2 that produces specific antibodies of immunoglob... more By use of the parental hybridoma cell line 63F2A2 that produces specific antibodies of immunoglobulin isotype G1 (IgG1; 63F2A2.1) against Pfs230, we attempted to enrich for the synthesis of the downstream switch variant IgG2b and IgG2a monoclonal antibodies (MAbs) of the hybridoma cell line (63F2A2.2b and 63F2A2.2a, respectively). The parental IgG1 did not reduce the Plasmodium falciparum transmission in a bioassay irrespective of the presence of complement. MAbs 63F2A2.2b and 63F2A2.2a were effective in reducing the infectivity of P. falciparum parasites to Anopheles gambiae mosquitoes in membrane-feeding experiments. A transmission reduction of 91% was accomplished by the 63F2A2.2b switch variant, and a reduction of greater than 99% was accomplished by the 63F2A2.2a switch variant, but only in the presence of active human complement. Subsequently, the transmission-reducing effect of MAb 63F2A2.2b or 63F2A2.2a was confirmed in vitro by the rapid lysis of newly formed macrogametes o...
γδ T cells accumulate during Plasmodium infections in both murine and human malarias. The biologi... more γδ T cells accumulate during Plasmodium infections in both murine and human malarias. The biological role of these cells and the antigens that they recognize are not clearly understood, although recent findings indicate that γδ T cells in general influence both innate and antigen-specific adaptive host responses. We examined the accumulation of γδ T cells elicited during infection with virulent and avirulent Plasmodium yoelii parasites in relatively susceptible and resistant strains of mice. Our results indicated that in nonlethal malaria infections, γδ T cells comprise a larger proportion of splenic T cells than in lethal infections and that only a live infection is capable of inducing an increase in the percentage of γδ T cells in vivo. Furthermore, we demonstrate that γδ T cells elicited during a P. yoelii infection respond by proliferation in vitro to P. falciparum heat shock proteins (HSPs) of 60 and 70 kDa, suggesting a possible immunological involvement of parasite HSPs in th...
We have characterized HLA-DR-restricted T-cell epitopes on the 27-kDa protein (Pfg27), a sexual s... more We have characterized HLA-DR-restricted T-cell epitopes on the 27-kDa protein (Pfg27), a sexual stage-specific antigen, of the human malaria parasite Plasmodium falciparum in subjects with a history of malaria. Pfg27, expressed early in the sexual stages, is recognized by monoclonal antibodies capable of reducing the infectivity of gametocytes in mosquitoes. By using 16 Pfg27-specific CD4 + -T-cell clones derived from three donors, seven different T-cell epitopes were identified. Among them, P11 (amino acids 191 to 210 of the Pfg27 sequence, IDVVDSYIIKPIPALPVTPD) was found to contain a previously described binding motif for multiple HLA-DR allotypes. Indeed, P11 was found to be promiscuous in that it could be recognized by T cells in the context of at least five different HLA-DR molecules. The cytokine profile of the clones was mixed. Seven of nine T-cell clones exhibited a Th0-like cytokine profile, producing high levels of gamma interferon (IFN-γ) and interleukin-4 (IL-4) upon sti...
Sexual-stage proteins have a distinct function in the mosquito vector during transmission and als... more Sexual-stage proteins have a distinct function in the mosquito vector during transmission and also represent targets for the development of malaria transmission-blocking vaccine. P48/45, a leading vaccine candidate, is critical for male gamete fertility and shows >50% similarity across various species of We evaluated functional conservation of P48/45 in and with the motivation to establish transgenic strains expressing P48/45 (Pvs48/45) in an assay to evaluate the transmission-blocking activity of antibodies elicited by Pvs48/45. Homologous recombination was employed to target / (/) for knockout (KO) or for its replacement by two different forms of / (/) (the full-length gene and a chimeric gene consisting of / 5' signal and 3' anchor sequences flanking /). Expression of Pvs48/45 in transgenic parasites and lack of expression of any P48/45 in KO parasites were confirmed by reverse transcription-PCR (RT-PCR) and Western blotting. Both transgenic and knockout parasites reve...
Antibodies recognizing conformational epitopes in Pfs48/45, an antigen expressed on the surface o... more Antibodies recognizing conformational epitopes in Pfs48/45, an antigen expressed on the surface of Plasmodium falciparum gametes and zygotes, have firmly established Pfs48/45 as a promising transmission blocking vaccine (TBV) candidate. However, it has been difficult to reproducibly express Pfs48/45 in a variety of recombinant expression systems. The goal of our studies was to evaluate functional immunogenicity of Pfs48/45 using DNA vaccine format in rhesus macaques. An additional goal was to ensure that when used in combination with another malarial antigen, specific immunity to both antigens was not compromised. For testing combination vaccines, we employed Pfs25 DNA plasmids that have previously undergone evaluations in rodents and nonhuman primates. Pfs25 is expressed on the surface of parasites after fertilization and is also a lead TBV candidate. DNA plasmids based on codon-optimized sequences of Pfs48/45 and Pfs25 were administered by in vivo electroporation, followed by a fi...
Pfs48/45 and Pfs25 are leading candidates for the development of Plasmodium falciparum transmissi... more Pfs48/45 and Pfs25 are leading candidates for the development of Plasmodium falciparum transmission blocking vaccines (TBV). Expression of Pfs48/45 in the erythrocytic sexual stages and presentation to the immune system during infection in the human host also makes it ideal for natural boosting. However, it has been challenging to produce a fully folded, functionally active Pfs48/45, using various protein expression platforms. In this study, we demonstrate that full-length Pfs48/45 encoded by DNA plasmids is able to induce significant transmission reducing immune responses. DNA plasmids encoding Pfs48/45 based on native (WT), codon optimized (SYN), or codon optimized and mutated (MUT1 and MUT2), to prevent any asparagine (N)-linked glycosylation were compared with or without intramuscular electroporation (EP). EP significantly enhanced antibody titers and transmission blocking activity elicited by immunization with SYN Pfs48/45 DNA vaccine. Mosquito membrane feeding assays also reve...
In general, malaria immunity has been suggested to be species specific with very little, if any, ... more In general, malaria immunity has been suggested to be species specific with very little, if any, known cross-reactivity between Plasmodium vivax and P. falciparum, both of which are responsible for >90% of human malaria, and co-endemic in many countries. It is therefore believed that species-specific immunity may be needed to target different species of Plasmodium. Pfs48/45 and Pvs48/45 are well established targets in the sexual stages of the malaria parasites, and are being pursued for the development of transmission blocking vaccines. Comparison of their sequences reveals 61% and 55% identity at the DNA and protein level, respectively raising the possibility that these two target antigens might share cross-reacting epitopes. Having succeeded in expressing recombinant Pfs48/45 and Pvs48/45 proteins, we hypothesized that these proteins will not only exhibit immunological cross-reactivity but also cross-boost immune responses. Mice were immunized with purified recombinant proteins...
Malaria transmission-blocking vaccines (TBV) targeting sexual stages of the parasite represent an... more Malaria transmission-blocking vaccines (TBV) targeting sexual stages of the parasite represent an ideal intervention to reduce the burden of the disease and eventual elimination at the population level in endemic regions. Immune responses against sexual stage antigens impair the development of parasite inside the mosquitoes. Target antigens identified in Plasmodium falciparum include surface proteins Pfs230 and Pfs48/45 in male and female gametocytes and Pfs25 expressed in zygotes and ookinetes. The latter has undergone extensive evaluation in pre-clinical and phase I clinical trials and remains one of the leading target antigens for the development of TBV. Pfs25 has a complex tertiary structure characterized by four EGF-like repeat motifs formed by 11 disulfide bonds, and it has been rather difficult to obtain Pfs25 as a homogenous product in native conformation in any heterologous expression system. Recently, we have reported expression of codon-harmonized recombinant Pfs25 in Esc...
Plasmodium falciparum sexual stage surface antigen Pfs25 is a well-established candidate for mala... more Plasmodium falciparum sexual stage surface antigen Pfs25 is a well-established candidate for malaria transmission-blocking vaccine development. Immunization with DNA vaccines encoding Pfs25 has been shown to elicit potent antibody responses in mice and non-human primates. Studies aimed at further optimization have revealed improved immunogenicity by the application of in vivo electroporation and using a heterologous prime-boost approach. The goal of studies reported here was to systematically evaluate impact of codon optimization, in vivo electroporation and N-linked glycosylation, on the immunogenicity of Pfs25 encoded by DNA vaccines. The results from this study demonstrate that while both codon optimization and in vivo electroporation greatly improved functional immunogenicity of Pfs25 DNA vaccines, the presence or absence of N-linked glycosylation did not significantly impact vaccine efficacy. These findings suggest that N-glycosylation of Pfs25 encoded by DNA vaccines is not de...
To evaluate functional immunogenicity of CHrPfs25. a malaria transmission blocking vaccine antige... more To evaluate functional immunogenicity of CHrPfs25. a malaria transmission blocking vaccine antigen, using nanoemulsion and porous polymeric PLGA nanoparticles. CHrPfs25 was formulated with nanoemulsions (NE) and poly(D,L-lactide-co-glycolide) nanoparticles (PLGA-NP) and evaluated via IM route in mice. Transmission blocking efficacy of antibodies was evaluated by standard mosquito membrane feeding assay using purified IgG from immune sera. Physicochemical properties and stability of various formulations were evaluated by measuring poly-dispersity index, particle size and zeta potential. Mice immunized with CHrPfs25 using alum via IP and IM routes induced comparable immune responses. The highest antibody response was obtained with CHrPfs25 formulated in 4% NE as compared to 8% NE and PLGA-NP. No further increases were observed by combining NE with MPL-A and chitosan. One hundred percent transmission blocking activity was demonstrated at 400 μg/ml of IgG for alum groups (both routes IP...
Proceedings of the National Academy of Sciences, 1991
Identification of continuous epitopes in the target antigens of Plasmodium falciparum transmissio... more Identification of continuous epitopes in the target antigens of Plasmodium falciparum transmission-blocking antibodies is likely to facilitate the production of a subunit peptide vaccine. Two such epitopes shared among several sexual-stage antigens were identified with murine monoclonal antibodies. An epitope recognized by four monoclonal antibodies capable of blocking infectivity of gametocytes in the mosquitoes is shared among three antigens (230, 48/45 doublet, and 27 kDa). These antigens are synthesized at different times during the development and maturation of gametocytes, and the blocking epitope appears conserved among parasites from diverse geographical locations. Immune response against such a unique epitope (continuous, cross-reacting, and conserved) is likely to be boosted by natural infection. The 27-kDa protein is reported here as a target of malaria transmission-blocking monoclonal antibodies, and the cross-reacting epitope represents an attractive candidate for a tra...
Immunization with extracellular sexual stages of the malaria parasites can induce the production ... more Immunization with extracellular sexual stages of the malaria parasites can induce the production of antibodies which block the development of the parasites in the midgut of a mosquito after a blood meal. We have generated a number of monoclonal antibodies against gametes and zygotes of the human malaria Plasmodium falciparum. Two monoclonal antibodies (mAb) reacting with a 230-kDa gamete surface protein (mAb 1B3 and 2B4 both isotype IgG2a) were found to block transmission of P. falciparum to mosquitoes. Blocking was complement dependent and this was verified in vitro by the rapid lysis of newly formed gametes and zygotes in the presence of the mAb and active complement. Both mAb reacted by immunofluorescence with the surface of gametes and zygotes from isolates of P. falciparum from various geographical areas. Each mAb immunoprecipitated a 230-kDa protein from 125I-labeled surface proteins of newly formed gametes and zygotes and immunoblotted a protein doublet of about molecular mas...
Malaria is a deadly disease responsible for between 550,000 and 627,000 deaths annually. There is... more Malaria is a deadly disease responsible for between 550,000 and 627,000 deaths annually. There is a pressing need to develop vaccines focused on malaria elimination. The complex lifecycle of Plasmodium falciparum provides opportunities not only to target the infectious sporozoite stage, introduced by anopheline mosquitoes, but also the sexual stages, which are ingested by mosquitoes during blood feeding, leading to parasite transmission. It is widely recognized that a vaccine targeting multiple stages would induce efficacious transmission reducing immunity. Technological advancements offer new vaccine platforms, such as mRNA-LNPs, which can be used to develop highly effective malarial vaccines. We evaluated the immunogenicity of two leading P. falciparum vaccine candidates, Pfs25 and PfCSP, delivered as mRNA-LNP vaccines. Both vaccines induced extremely potent immune responses when administered alone or in combination, which were superior to Pfs25 and PfCSP DNA vaccine formulations....
Plasmodium falciparum circumsporozoite protein (PfCSP) and Pfs25 are leading candidates for the d... more Plasmodium falciparum circumsporozoite protein (PfCSP) and Pfs25 are leading candidates for the development of pre-erythrocytic and transmission-blocking vaccines (TBV), respectively. Although considerable progress has been made in developing PfCSP- and Pfs25-based vaccines, neither have elicited complete protection or transmission blocking in clinical trials. The combination of antigens targeting various life stages is an alternative strategy to develop a more efficacious malaria vaccine. In this study, female and male mice were immunized with DNA plasmids encoding PfCSP and Pfs25, administered alone or in combination via intramuscular in vivo electroporation (EP). Antigen-specific antibodies were analyzed for antibody titers, avidity and isotype by ELISA. Immune protection against sporozoite challenge, using transgenic P. berghei expressing PfCSP and a GFP-luciferase fusion protein (PbPfCSP-GFP/Luc), was assessed by in vivo bioluminescence imaging and blood-stage parasite growth. ...
By use of the parental hybridoma cell line 63F2A2 that produces specific antibodies of immunoglob... more By use of the parental hybridoma cell line 63F2A2 that produces specific antibodies of immunoglobulin isotype G1 (IgG1; 63F2A2.1) against Pfs230, we attempted to enrich for the synthesis of the downstream switch variant IgG2b and IgG2a monoclonal antibodies (MAbs) of the hybridoma cell line (63F2A2.2b and 63F2A2.2a, respectively). The parental IgG1 did not reduce the Plasmodium falciparum transmission in a bioassay irrespective of the presence of complement. MAbs 63F2A2.2b and 63F2A2.2a were effective in reducing the infectivity of P. falciparum parasites to Anopheles gambiae mosquitoes in membrane-feeding experiments. A transmission reduction of 91% was accomplished by the 63F2A2.2b switch variant, and a reduction of greater than 99% was accomplished by the 63F2A2.2a switch variant, but only in the presence of active human complement. Subsequently, the transmission-reducing effect of MAb 63F2A2.2b or 63F2A2.2a was confirmed in vitro by the rapid lysis of newly formed macrogametes o...
γδ T cells accumulate during Plasmodium infections in both murine and human malarias. The biologi... more γδ T cells accumulate during Plasmodium infections in both murine and human malarias. The biological role of these cells and the antigens that they recognize are not clearly understood, although recent findings indicate that γδ T cells in general influence both innate and antigen-specific adaptive host responses. We examined the accumulation of γδ T cells elicited during infection with virulent and avirulent Plasmodium yoelii parasites in relatively susceptible and resistant strains of mice. Our results indicated that in nonlethal malaria infections, γδ T cells comprise a larger proportion of splenic T cells than in lethal infections and that only a live infection is capable of inducing an increase in the percentage of γδ T cells in vivo. Furthermore, we demonstrate that γδ T cells elicited during a P. yoelii infection respond by proliferation in vitro to P. falciparum heat shock proteins (HSPs) of 60 and 70 kDa, suggesting a possible immunological involvement of parasite HSPs in th...
We have characterized HLA-DR-restricted T-cell epitopes on the 27-kDa protein (Pfg27), a sexual s... more We have characterized HLA-DR-restricted T-cell epitopes on the 27-kDa protein (Pfg27), a sexual stage-specific antigen, of the human malaria parasite Plasmodium falciparum in subjects with a history of malaria. Pfg27, expressed early in the sexual stages, is recognized by monoclonal antibodies capable of reducing the infectivity of gametocytes in mosquitoes. By using 16 Pfg27-specific CD4 + -T-cell clones derived from three donors, seven different T-cell epitopes were identified. Among them, P11 (amino acids 191 to 210 of the Pfg27 sequence, IDVVDSYIIKPIPALPVTPD) was found to contain a previously described binding motif for multiple HLA-DR allotypes. Indeed, P11 was found to be promiscuous in that it could be recognized by T cells in the context of at least five different HLA-DR molecules. The cytokine profile of the clones was mixed. Seven of nine T-cell clones exhibited a Th0-like cytokine profile, producing high levels of gamma interferon (IFN-γ) and interleukin-4 (IL-4) upon sti...
Sexual-stage proteins have a distinct function in the mosquito vector during transmission and als... more Sexual-stage proteins have a distinct function in the mosquito vector during transmission and also represent targets for the development of malaria transmission-blocking vaccine. P48/45, a leading vaccine candidate, is critical for male gamete fertility and shows >50% similarity across various species of We evaluated functional conservation of P48/45 in and with the motivation to establish transgenic strains expressing P48/45 (Pvs48/45) in an assay to evaluate the transmission-blocking activity of antibodies elicited by Pvs48/45. Homologous recombination was employed to target / (/) for knockout (KO) or for its replacement by two different forms of / (/) (the full-length gene and a chimeric gene consisting of / 5' signal and 3' anchor sequences flanking /). Expression of Pvs48/45 in transgenic parasites and lack of expression of any P48/45 in KO parasites were confirmed by reverse transcription-PCR (RT-PCR) and Western blotting. Both transgenic and knockout parasites reve...
Antibodies recognizing conformational epitopes in Pfs48/45, an antigen expressed on the surface o... more Antibodies recognizing conformational epitopes in Pfs48/45, an antigen expressed on the surface of Plasmodium falciparum gametes and zygotes, have firmly established Pfs48/45 as a promising transmission blocking vaccine (TBV) candidate. However, it has been difficult to reproducibly express Pfs48/45 in a variety of recombinant expression systems. The goal of our studies was to evaluate functional immunogenicity of Pfs48/45 using DNA vaccine format in rhesus macaques. An additional goal was to ensure that when used in combination with another malarial antigen, specific immunity to both antigens was not compromised. For testing combination vaccines, we employed Pfs25 DNA plasmids that have previously undergone evaluations in rodents and nonhuman primates. Pfs25 is expressed on the surface of parasites after fertilization and is also a lead TBV candidate. DNA plasmids based on codon-optimized sequences of Pfs48/45 and Pfs25 were administered by in vivo electroporation, followed by a fi...
Pfs48/45 and Pfs25 are leading candidates for the development of Plasmodium falciparum transmissi... more Pfs48/45 and Pfs25 are leading candidates for the development of Plasmodium falciparum transmission blocking vaccines (TBV). Expression of Pfs48/45 in the erythrocytic sexual stages and presentation to the immune system during infection in the human host also makes it ideal for natural boosting. However, it has been challenging to produce a fully folded, functionally active Pfs48/45, using various protein expression platforms. In this study, we demonstrate that full-length Pfs48/45 encoded by DNA plasmids is able to induce significant transmission reducing immune responses. DNA plasmids encoding Pfs48/45 based on native (WT), codon optimized (SYN), or codon optimized and mutated (MUT1 and MUT2), to prevent any asparagine (N)-linked glycosylation were compared with or without intramuscular electroporation (EP). EP significantly enhanced antibody titers and transmission blocking activity elicited by immunization with SYN Pfs48/45 DNA vaccine. Mosquito membrane feeding assays also reve...
In general, malaria immunity has been suggested to be species specific with very little, if any, ... more In general, malaria immunity has been suggested to be species specific with very little, if any, known cross-reactivity between Plasmodium vivax and P. falciparum, both of which are responsible for >90% of human malaria, and co-endemic in many countries. It is therefore believed that species-specific immunity may be needed to target different species of Plasmodium. Pfs48/45 and Pvs48/45 are well established targets in the sexual stages of the malaria parasites, and are being pursued for the development of transmission blocking vaccines. Comparison of their sequences reveals 61% and 55% identity at the DNA and protein level, respectively raising the possibility that these two target antigens might share cross-reacting epitopes. Having succeeded in expressing recombinant Pfs48/45 and Pvs48/45 proteins, we hypothesized that these proteins will not only exhibit immunological cross-reactivity but also cross-boost immune responses. Mice were immunized with purified recombinant proteins...
Malaria transmission-blocking vaccines (TBV) targeting sexual stages of the parasite represent an... more Malaria transmission-blocking vaccines (TBV) targeting sexual stages of the parasite represent an ideal intervention to reduce the burden of the disease and eventual elimination at the population level in endemic regions. Immune responses against sexual stage antigens impair the development of parasite inside the mosquitoes. Target antigens identified in Plasmodium falciparum include surface proteins Pfs230 and Pfs48/45 in male and female gametocytes and Pfs25 expressed in zygotes and ookinetes. The latter has undergone extensive evaluation in pre-clinical and phase I clinical trials and remains one of the leading target antigens for the development of TBV. Pfs25 has a complex tertiary structure characterized by four EGF-like repeat motifs formed by 11 disulfide bonds, and it has been rather difficult to obtain Pfs25 as a homogenous product in native conformation in any heterologous expression system. Recently, we have reported expression of codon-harmonized recombinant Pfs25 in Esc...
Plasmodium falciparum sexual stage surface antigen Pfs25 is a well-established candidate for mala... more Plasmodium falciparum sexual stage surface antigen Pfs25 is a well-established candidate for malaria transmission-blocking vaccine development. Immunization with DNA vaccines encoding Pfs25 has been shown to elicit potent antibody responses in mice and non-human primates. Studies aimed at further optimization have revealed improved immunogenicity by the application of in vivo electroporation and using a heterologous prime-boost approach. The goal of studies reported here was to systematically evaluate impact of codon optimization, in vivo electroporation and N-linked glycosylation, on the immunogenicity of Pfs25 encoded by DNA vaccines. The results from this study demonstrate that while both codon optimization and in vivo electroporation greatly improved functional immunogenicity of Pfs25 DNA vaccines, the presence or absence of N-linked glycosylation did not significantly impact vaccine efficacy. These findings suggest that N-glycosylation of Pfs25 encoded by DNA vaccines is not de...
To evaluate functional immunogenicity of CHrPfs25. a malaria transmission blocking vaccine antige... more To evaluate functional immunogenicity of CHrPfs25. a malaria transmission blocking vaccine antigen, using nanoemulsion and porous polymeric PLGA nanoparticles. CHrPfs25 was formulated with nanoemulsions (NE) and poly(D,L-lactide-co-glycolide) nanoparticles (PLGA-NP) and evaluated via IM route in mice. Transmission blocking efficacy of antibodies was evaluated by standard mosquito membrane feeding assay using purified IgG from immune sera. Physicochemical properties and stability of various formulations were evaluated by measuring poly-dispersity index, particle size and zeta potential. Mice immunized with CHrPfs25 using alum via IP and IM routes induced comparable immune responses. The highest antibody response was obtained with CHrPfs25 formulated in 4% NE as compared to 8% NE and PLGA-NP. No further increases were observed by combining NE with MPL-A and chitosan. One hundred percent transmission blocking activity was demonstrated at 400 μg/ml of IgG for alum groups (both routes IP...
Proceedings of the National Academy of Sciences, 1991
Identification of continuous epitopes in the target antigens of Plasmodium falciparum transmissio... more Identification of continuous epitopes in the target antigens of Plasmodium falciparum transmission-blocking antibodies is likely to facilitate the production of a subunit peptide vaccine. Two such epitopes shared among several sexual-stage antigens were identified with murine monoclonal antibodies. An epitope recognized by four monoclonal antibodies capable of blocking infectivity of gametocytes in the mosquitoes is shared among three antigens (230, 48/45 doublet, and 27 kDa). These antigens are synthesized at different times during the development and maturation of gametocytes, and the blocking epitope appears conserved among parasites from diverse geographical locations. Immune response against such a unique epitope (continuous, cross-reacting, and conserved) is likely to be boosted by natural infection. The 27-kDa protein is reported here as a target of malaria transmission-blocking monoclonal antibodies, and the cross-reacting epitope represents an attractive candidate for a tra...
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