Induction of Parasite Growth-Inhibitory Antibodies by a Virosomal Formulation of a Peptidomimetic of Loop I from Domain III of Plasmodium falciparum Apical Membrane Antigen 1

Abstract

Apical membrane antigen 1 (AMA-1) of Plasmodium falciparum is a leading candidate antigen for inclusion in a malaria subunit vaccine. Its ectodomain can be divided into three subdomains, each with disulfide bond-stabilized structures. Since the majority of antibodies raised against the ectodomain appear to recognize strain-specific epitopes in domain I, we attempted to develop a vaccine formulation which directs the immune response to a region that contains more conserved epitopes. Here we demonstrate that a virosomal formulation of a peptide that mimics the semiconserved loop I of domain III elicits parasite growth-inhibitory antibodies. A synthetic peptide comprising residues 446 to 490 of AMA-1 (AMA-1 446-490 ) was conjugated through the N terminus to a derivative of phosphatidylethanolamine and the phosphatidylethanolamine-peptide conjugate was incorporated into immunopotentiating reconstituted influenza virosomes as a human-compatible antigen delivery system. Both cyclized and linear versions of the peptide antigen elicited antibodies which specifically bound to parasite-expressed AMA-1 in Western blotting with parasite lysates as well as in immunofluorescence assays with blood stage parasites. All 11 peptidomimetic-specific monoclonal antibodies generated were cross-reactive with parasite-expressed AMA-1. Antigen binding assays with a library of overlapping cyclic peptides covering the target sequence revealed differences in the fine specificity of these monoclonal antibodies and provided evidence that at least some of them recognized discontinuous epitopes.

Preclinical profiling of the immunogenicity of a two-component subunit malaria vaccine candidate based on virosome technology

“…The IgG response in mice against both peptide vaccines was dominated by the IgG1 subclass (data not shown). This IgG1 bias in mice has been observed before for AMA49-C1 27 and other virosomally formulated vaccines such as a SERA5-derived malaria peptide, 37 diphtheria, tetanus and hepatitis B (unpublished). Combined delivery of separate IRIV preparations carrying UK-39 and AMA49-C1 did not interfere with the immune response against one of the components.…”

Preclinical profiling of the immunogenicity of a two-component subunit malaria vaccine candidate based on virosome technology

“…The IgG response in mice against both peptide vaccines was dominated by the IgG1 subclass (data not shown). This IgG1 bias in mice has been observed before for AMA49-C1 27 and other virosomally formulated vaccines such as a SERA5-derived malaria peptide, 37 diphtheria, tetanus and hepatitis B (unpublished). Combined delivery of separate IRIV preparations carrying UK-39 and AMA49-C1 did not interfere with the immune response against one of the components.…”

Functional Analysis of Plasmodium falciparum Apical Membrane Antigen 1 Utilizing Interspecies Domains

“…Two studies have been published which specifically demonstrate the importance of domain III epitopes in protective immunity (23,24). Our finding that parasites expressing an AMA1 chimera containing PfAMA1 domain III were relatively resistant to the inhibitory effects of the neutralizing antibody appears to contradict the assertion that domain III contains immunologically important residues.…”

“…Since the parasites expressing a chimeric protein which included PfAMA1 domain III were relatively resistant to the inhibitory antibodies, we conclude that domain III in this context is not a major target of these inhibitory antibodies. Two studies have been published which specifically demonstrate the importance of domain III epitopes in protective immunity (23,24). Our finding that parasites expressing an AMA1 chimera containing PfAMA1 domain III were relatively resistant to the inhibitory effects of the neutralizing antibody appears to contradict the assertion that domain III contains immunologically important residues.…”

Design and pre-clinical profiling of a Plasmodium falciparum MSP-3 derived component for a multi-valent virosomal malaria vaccine

“…In vitro growth inhibition assays with blood stage parasites were performed to assess a parasite inhibitory effect of the anti-FB-12 mAbs. In contrast to the growth-inhibitory mAb DV5 specific for apical membrane antigen 1 [ 7 ], no growth inhibition was found in this test system with any of the anti-FB-12 mAbs tested (Figure 3 ). Previous reports have shown that anti-MSP-3 antibodies have no direct effect upon merozoite invasion but can cooperate with blood monocytes to inhibit P. falciparum in vitro growth [ 16 , 18 ].…”

Preclinical profiling of the immunogenicity of a two-component subunit malaria vaccine candidate based on virosome technology

“…The IgG response in mice against both peptide vaccines was dominated by the IgG1 subclass (data not shown). This IgG1 bias in mice has been observed before for AMA49-C1 27 and other virosomally formulated vaccines such as a SERA5-derived malaria peptide, 37 diphtheria, tetanus and hepatitis B (unpublished). Combined delivery of separate IRIV preparations carrying UK-39 and AMA49-C1 did not interfere with the immune response against one of the components.…”

Functional Analysis of Plasmodium falciparum Apical Membrane Antigen 1 Utilizing Interspecies Domains

“…Two studies have been published which specifically demonstrate the importance of domain III epitopes in protective immunity (23,24). Our finding that parasites expressing an AMA1 chimera containing PfAMA1 domain III were relatively resistant to the inhibitory effects of the neutralizing antibody appears to contradict the assertion that domain III contains immunologically important residues.…”

“…Since the parasites expressing a chimeric protein which included PfAMA1 domain III were relatively resistant to the inhibitory antibodies, we conclude that domain III in this context is not a major target of these inhibitory antibodies. Two studies have been published which specifically demonstrate the importance of domain III epitopes in protective immunity (23,24). Our finding that parasites expressing an AMA1 chimera containing PfAMA1 domain III were relatively resistant to the inhibitory effects of the neutralizing antibody appears to contradict the assertion that domain III contains immunologically important residues.…”

Design and pre-clinical profiling of a Plasmodium falciparum MSP-3 derived component for a multi-valent virosomal malaria vaccine

“…In vitro growth inhibition assays with blood stage parasites were performed to assess a parasite inhibitory effect of the anti-FB-12 mAbs. In contrast to the growth-inhibitory mAb DV5 specific for apical membrane antigen 1 [ 7 ], no growth inhibition was found in this test system with any of the anti-FB-12 mAbs tested (Figure 3 ). Previous reports have shown that anti-MSP-3 antibodies have no direct effect upon merozoite invasion but can cooperate with blood monocytes to inhibit P. falciparum in vitro growth [ 16 , 18 ].…”

Preclinical profiling of the immunogenicity of a two-component subunit malaria vaccine candidate based on virosome technology

“…The IgG response in mice against both peptide vaccines was dominated by the IgG1 subclass (data not shown). This IgG1 bias in mice has been observed before for AMA49-C1 27 and other virosomally formulated vaccines such as a SERA5-derived malaria peptide, 37 diphtheria, tetanus and hepatitis B (unpublished). Combined delivery of separate IRIV preparations carrying UK-39 and AMA49-C1 did not interfere with the immune response against one of the components.…”

Functional Analysis of Plasmodium falciparum Apical Membrane Antigen 1 Utilizing Interspecies Domains

“…Two studies have been published which specifically demonstrate the importance of domain III epitopes in protective immunity (23,24). Our finding that parasites expressing an AMA1 chimera containing PfAMA1 domain III were relatively resistant to the inhibitory effects of the neutralizing antibody appears to contradict the assertion that domain III contains immunologically important residues.…”

“…Since the parasites expressing a chimeric protein which included PfAMA1 domain III were relatively resistant to the inhibitory antibodies, we conclude that domain III in this context is not a major target of these inhibitory antibodies. Two studies have been published which specifically demonstrate the importance of domain III epitopes in protective immunity (23,24). Our finding that parasites expressing an AMA1 chimera containing PfAMA1 domain III were relatively resistant to the inhibitory effects of the neutralizing antibody appears to contradict the assertion that domain III contains immunologically important residues.…”

Design and pre-clinical profiling of a Plasmodium falciparum MSP-3 derived component for a multi-valent virosomal malaria vaccine

“…In vitro growth inhibition assays with blood stage parasites were performed to assess a parasite inhibitory effect of the anti-FB-12 mAbs. In contrast to the growth-inhibitory mAb DV5 specific for apical membrane antigen 1 [ 7 ], no growth inhibition was found in this test system with any of the anti-FB-12 mAbs tested (Figure 3 ). Previous reports have shown that anti-MSP-3 antibodies have no direct effect upon merozoite invasion but can cooperate with blood monocytes to inhibit P. falciparum in vitro growth [ 16 , 18 ].…”