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Merozoite surface protein 3 (MSP3) is a target of antibody-dependent cellular inhibition (ADCI), a protective mechanism against Plasmodium falciparum malaria. From the C-terminal half of the molecule, 6 overlapping peptides were chosen to characterize human immune responses. Each peptide defined at least 1 non-crossreactive B cell epitope. Distinct patterns of antibody responses, by level and IgG subclass distribution, were observed in inhabitants of a malaria-endemic area. Antibodies affinity purified toward each peptide differed in their functional capacity to mediate parasite killing in ADCI assays: 3 of 6 overlapping peptides had a major inhibitory effect on parasite growth. This result was confirmed by the passive transfer of anti-MSP3 antibodies in vivo in a P. falciparum mouse model. T helper cell epitopes were identified in each peptide. Antigenicity and functional assays identified a 70-amino acid conserved domain of MSP3 as a target of biologically active antibodies to be included in future vaccine constructs based on MSP3

Background: Few data are available about malaria epidemiological situation in Niger. However, implementation of new strategies such as vaccination or seasonal treatment of a target population requires the knowledge of baseline epidemiological features of malaria. A population-based study was conducted to provide better characterization of malaria seasonal variations and population groups the most at risk in this particular area. Methods: From July 2007 to December 2009, presumptive cases of malaria among a study population living in a typical Sahelian village of Niger were recorded, and confirmed by microscopic examination. In parallel, asymptomatic carriers were actively detected at the end of each dry season in 2007, 2008 and 2009. Results: Among the 965 presumptive malaria cases recorded, 29% were confirmed by microscopic examination. The incidence of malaria was found to decrease significantly with age (p < 0.01). The mean annual incidence was 0.254. The results show that the risk of malaria was higher in children under ten years (p < 0.0001). The number of malaria episodes generally followed the temporal pattern of changes in precipitation levels, with a peak of transmission in August and September. One-thousand and ninety subjects were submitted to an active detection of asymptomatic carriage of whom 16% tested positive; asymptomatic carriage decreased with increasing age. A higher prevalence of gametocyte carriage among asymptomatic population was recorded in children aged two to ten years, though it did not reach significance. Conclusions: In Southern Niger, malaria transmission mostly occurs from July to October. Children aged two to ten years are the most at risk of malaria, and may also represent the main reservoir for gametocytes. Strategies such as intermittent preventive treatment in children (IPTc) could be of interest in this area, where malaria transmission is highly seasonal. Based on these preliminary data, a pilot study could be implemented in Zi, France. Ministère des affaires étrangères, Institut Pasteur International Network

Immunity against the pre-erythrocytic stages of malaria is the most promising, as it is strong and fully sterilizing. Yet, the underlying immune effectors against the human Plasmodium falciparum pre-erythrocytic stages remain surprisingly poorly known and have been little explored, which in turn prevents any rational vaccine progress. Evidence that has been gathered in vitro and in vivo, in higher primates and in humans, is reviewed here, emphasizing the significant role of IFN-gamma, either as a critical immune mediator or at least as a valuable surrogate marker of protection. One may hope that these results will trigger investigations in volunteers immunized either by optimally irradiated or over-irradiated sporozoites, to quickly delineate better surrogates of protection, which are essential for the development of a successful malaria vaccine.

BACKGROUND: In a previous Phase 1/2b malaria vaccine trial testing the 3D7 isoform of the malaria vaccine candidate Merozoite surface protein 2 (MSP2), parasite densities in children were reduced by 62%. However, breakthrough parasitemias were disproportionately of the alternate dimorphic form of MSP2, the FC27 genotype. We therefore undertook a dose-escalating, double-blinded, placebo-controlled Phase 1 trial in healthy, malaria-naïve adults of MSP2-C1, a vaccine containing recombinant forms of the two families of msp2 alleles, 3D7 and FC27 (EcMSP2-3D7 and EcMSP2-FC27), formulated in equal amounts with Montanide® ISA 720 as a water-in-oil emulsion. METHODOLOGY/PRINCIPAL FINDINGS: The trial was designed to include three dose cohorts (10, 40, and 80 µg), each with twelve subjects receiving the vaccine and three control subjects receiving Montanide® ISA 720 adjuvant emulsion alone, in a schedule of three doses at 12-week intervals. Due to unexpected local reactogenicity and concern regarding vaccine stability, the trial was terminated after the second immunisation of the cohort receiving the 40 µg dose; no subjects received the 80 µg dose. Immunization induced significant IgG responses to both isoforms of MSP2 in the 10 µg and 40 µg dose cohorts, with antibody levels by ELISA higher in the 40 µg cohort. Vaccine-induced antibodies recognised native protein by Western blots of parasite protein extracts and by immunofluorescence microscopy. Although the induced anti-MSP2 antibodies did not directly inhibit parasite growth in vitro, IgG from the majority of individuals tested caused significant antibody-dependent cellular inhibition (ADCI) of parasite growth. CONCLUSIONS/SIGNIFICANCE: As the majority of subjects vaccinated with MSP2-C1 developed an antibody responses to both forms of MSP2, and that these antibodies mediated ADCI provide further support for MSP2 as a malaria vaccine candidate. However, in view of the reactogenicity of this formulation, further clinical dev

Contains fulltext : 80283.pdf ( ) (Open Access), A 20 year-old healthy female volunteer participated in a clinical Phase I and IIa safety and efficacy trial with candidate malaria vaccine PfLSA-3-rec adjuvanted with aluminium hydroxide. Eleven weeks after the third and last immunization she was experimentally infected by bites of Plasmodium falciparum-infected mosquitoes. When the thick blood smear became positive, at day 11, she was treated with artemether/lumefantrine according to protocol. On day 16 post-infection i.e. two days after completion of treatment, she woke up with retrosternal chest pain. She was diagnosed as acute coronary syndrome and treated accordingly. She recovered quickly and her follow-up was uneventful. Whether the event was related to the study procedures such as the preceding vaccinations, malaria infection or antimalarial drugs remains elusive. However, the relation in time with the experimental malaria infection and apparent absence of an underlying condition makes the infection the most probable trigger. This is in striking contrast, however, with the millions of malaria cases each year and the fact that such complication has never been reported in the literature. The rare occurrence of cardiac events with any of the preceding study procedures may even support a coincidental finding. Apart from acute coronary syndrome, myocarditis can be considered as a final diagnosis, but the true nature and patho-physiological explanation of the event remain unclear.

Contains fulltext : 79604.pdf (publisher's version ) (Closed access), The correct selection of individuals who will benefit from iron supplements in malaria-endemic regions requires improved insight in the effects of malaria on host iron homeostasis and innovative biomarkers. We assessed sequential changes in serum hepcidin and in traditional biochemical iron status indicators during an experimental Plasmodium falciparum malaria infection with five adult volunteers. The haemoglobin content of reticulocytes (Ret-H(e)) and of mature red blood cells (RBC-H(e)) represented iron incorporation into haemoglobin. Low-density parasitaemia and its treatment induced a mild increase in interleukin (IL)-6 and serum hepcidin concentrations. Despite this only mild increase, a marked hypoferraemia with a strong increase in serum ferritin concentrations developed, which was associated with a sharp fall in Ret-H(e), while RBC-H(e) remained unchanged. The ratio of soluble transferrin receptor (sTfR) to log ferritin concentrations decreased to an average nadir of 63% of the baseline value. We concluded that even mild increases in serum hepcidin and IL-6 concentrations result in a disturbed host iron homeostasis. Serum hepcidin, Ret-H(e) and Delta-H(e) (Ret-H(e) minus RBC-H(e)) are promising biomarkers to select those individuals who will benefit from iron supplements in malaria endemic regions, while the sTfR/log ferritin ratio should be used with caution to assess iron status during malaria.

Clinical experiments have shown that the Ab-dependent cell-mediated inhibition of Plasmodium falciparum is a major mechanism controlling malaria parasitemia and thereby symptoms. In this study, we demonstrate that a single merozoite per monocyte (MN) is sufficient to trigger optimal antiparasitic activity. Using particulate Ag as pseudomerozoites, we show that only Ags, and no other parasite-derived factor, are required to trigger MN activation and that a single Ag is as potent as the complex combination of Ags constituting the merozoite surface. Moreover, we found that soluble Ags binding at least two Abs are as effective as the parasite at stimulating MN and that nonmalarial Ags are as efficient provided they are targeted by cytophilic Abs. Indeed, only cytophilic IgGs are potent and, in agreement with immunoepidemiological findings, IgG3 is superior to IgG1. Very low Ab concentrations (>700 pM), i.e., in the range of molecules having a hormonal effect, are effective, in contrast to Abs having a direct, neutralizing effect. Finally, Ab-dependent cell-mediated inhibition proved to require the synergistic activation of both FcgammaRIIa and FcgammaRIIIa which both distinguish it from other Ab-dependent cellular cytotoxicity and implies that all MN are not equally effective. These findings have both fundamental and practical implications, particularly for vaccine discovery.

Item does not contain fulltext, BACKGROUND: The liver stage of the human malaria parasite Plasmodium falciparum is the least known, yet it holds the greatest promise for the induction of sterile immunity and the development of novel drugs. Progress has been severely limited by the lack of adequate in vitro and in vivo models. METHODS: Recently, it was found that immunodeficient mice transgenic for the urokinase plasminogen activator allow survival of differentiated human hepatocytes. We confirm this finding but show that hepatocyte survival is short lived unless nonadaptive defenses are simultaneously depleted. RESULTS: By controlling macrophages and NK cells, we readily effected the long-term secretion of human serum albumin and human alpha-1 antitrypsin in mouse serum (at 3 months, the proportion of repopulated mice increased from 0% to 60% and from 22% to 80%, respectively; P<.0001). P. falciparum sporozoites delivered intravenously into mice readily infected transplanted human hepatocytes and developed into liver schizonts. Their size was twice as large as what was seen in vitro and was comparable to that found in humans and chimpanzees. CONCLUSION: These results emphasize the importance of nonadaptive defenses against xenotransplantation and lead to development of small laboratory models that, because they can harbor human hepatocytes, provide novel opportunities to study intrahepatic pathogens, such as those causing malaria and hepatitis.

Immunoglobulins from individuals with immunity to malaria have a strong antiparasitic effect when transferred to Plasmodium falciparum malaria infected patients. One prominent target of antiparasitic antibodies is the merozoite surface antigen 3 (MSP-3). We have investigated the antibody response against MSP-3 residues 194 to 257 (MSP-3(194-257)) on the molecular level. mRNA from peripheral blood leukocytes from clinically immune individuals was used as a source of Fab (fragment antibody) genes. A Fab-phage display library was made, and three distinct antibodies designated RAM1, RAM2, and RAM3 were isolated by panning. Immunoglobulin G1 (IgG1) and IgG3 full-length antibodies have been produced in CHO cells. Reactivity with the native parasite protein was demonstrated by immunofluorescence microscopy, flow cytometry, and immunoblotting. Furthermore, the antiparasitic effect of RAM1 has been tested in vitro in an antibody-dependent cellular inhibition (ADCI) assay. Both the IgG1 and the IgG3 versions of the antibody show an inhibitory effect on parasite growth.

Udgivelsesdato: 2001-Sep, Antibodies against three long synthetic peptides (LSPs) derived from the glutamate-rich protein (GLURP) of Plasmodium falciparum were analyzed in three cohorts from Liberia, Ghana, and Senegal. Two overlapping LSPs, LR67 and LR68, are derived from the relatively conserved N-terminal nonrepeat region (R0), and the third, LR70, is derived from the R2 repeat region. A high prevalence of antibody responses to each LSP was observed in all three areas of endemic infection. Levels of cytophilic immunoglobulin G (IgG) antibodies against both GLURP regions were significantly correlated with protection from clinical P. falciparum malaria. Protected children from the Ghana cohort possessed predominantly IgG1 antibodies against the nonrepeat epitope and IgG3 antibodies against the repeat epitope. T-cell proliferation responses, studied in the cohort from Senegal, revealed that T-helper-cell epitopes were confined to the nonrepeat region. When used as immunogens, the LR67 and LR68 peptides elicited strong IgG responses in outbred mice and LR67 also induced antibodies in mice of different H-2 haplotypes, confirming the presence of T-helper-cell epitopes in these constructs. Mouse antipeptide antisera recognized parasite proteins as determined by immunofluorescence and immunoblotting. This indicates that synthetic peptides derived from relatively conserved epitopes of GLURP might serve as useful immunogens for vaccination against P. falciparum malaria.

We have compared the reactivities of antibodies developed by individuals frequently exposed to Plasmodium falciparum infections with the epitopes contained within the repeats of the circumsporozoite (CS) protein and their reactivities with the epitopes of a native molecule(s) accessible on the sporozoite surface. Results of direct-binding assays and competition assays between artificial and native molecules or between human antibodies and anti-CS monoclonal antibodies suggest that humans respond preferentially to epitopes not contained within the repeats of the CS protein and probably not contained in the whole CS protein. Human monoclonal antibodies reactive with P. falciparum sporozoite surface antigens were produced by Epstein-Barr virus transformation of human lymphocytes. Their pattern of reactivity with sporozoites from a number of different isolates indicates the existence of several distinct epitopes on the parasite surface. Differences between isolates and between sporozoites within a given sample were observed. No single human monoclonal antibody capable of detecting an epitope expressed in all the parasites studied was found., Pub. in Infection and Immunity, v58 n9 p2995-3001 Sep 1990.

The feasibility of successfully developing a vaccine against sporozoite challenge has rested largely on successes in protecting mice and some humans with irradiated sporozoites. Several studies have indicated that antibodies (5), CD8+ T cells, and cytokines released by immuno-competent cells can interfere with the pre-erythrocytic phase of parasite development. However, information from malaria animal models have demonstrated that antibodies alone, either monoclonal (MAb) or polyclonal, can be fully or partially effective in preventing infection in sporozoite challenged animals., Published in Bulletin of the World Health Organization, v68 (Suppl.) p52-59, 1990.

The liver phase of development of malaria parasites has been studied only recently and remains poorly understood compared to the other stages such as sporozoites, merozoites and gametes. Access to liver forms of Plasmodium falciparum has been improved by the development of in vivo and in vitro propagation methods, but the yield of mature schizonts remains limited and does not allow a detailed antigenic analysis. To date, only immunofluorescence assays (IFA) have permitted a description of a species and liver-stage-specific antigen(s) (LSA; 3). Monospecific antibodies to these antigens have not been obtained due either to difficulty in immunizing mice (against LSA), or to poor stability of human monoclonal antibodies. Therefore, as a means of characterizing the LSA, we used an alternative immunological approach to identify clones of the corresponding LSA genes. We describe here the isolation of a DNA sequence coding for a P. falciparum liver-stage-specific antigen composed of repeats of 17 amino-acids, which is immunogenic in man. We looked for human sera with restricted specificity to the pre-erythrocytic stages of development of P. falciparum by screening individuals living in a malaria endemic area and undergoing continuous drug prophylaxis. Keywords: Chloroquine, Reprints., Pub. in Nature, v329 p164-167, 10 Sep 1987.

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Copyright © American Society for Microbiology, Infection and Immunity, 70(12), 2002, 7182-7184, https://doi.org/10.1128/IAI.70.12.7182-7184.2002., Using monoclonal antibodies and human affinity-purified antibodies specific to the Plasmodium falciparum 126-kDa serine-rich protein, SERP, we found that these antibodies have no direct effect upon merozoite invasion at the concentrations tested but can cooperate with blood monocytes to strongly inhibit P. falciparum in vitro growth.

Copyright © American Society for Microbiology, Infection and Immunity, 70(12), 2002, 7182-7184, https://doi.org/10.1128/IAI.70.12.7182-7184.2002., Using monoclonal antibodies and human affinity-purified antibodies specific to the Plasmodium falciparum 126-kDa serine-rich protein, SERP, we found that these antibodies have no direct effect upon merozoite invasion at the concentrations tested but can cooperate with blood monocytes to strongly inhibit P. falciparum in vitro growth.

Merozoite surface protein 3 (MSP3) is a target of antibody-dependent cellular inhibition (ADCI), a protective mechanism against Plasmodium falciparum malaria. From the C-terminal half of the molecule, 6 overlapping peptides were chosen to characterize human immune responses. Each peptide defined at least 1 non-crossreactive B cell epitope. Distinct patterns of antibody responses, by level and IgG subclass distribution, were observed in inhabitants of a malaria-endemic area. Antibodies affinity purified toward each peptide differed in their functional capacity to mediate parasite killing in ADCI assays: 3 of 6 overlapping peptides had a major inhibitory effect on parasite growth. This result was confirmed by the passive transfer of anti-MSP3 antibodies in vivo in a P. falciparum mouse model. T helper cell epitopes were identified in each peptide. Antigenicity and functional assays identified a 70-amino acid conserved domain of MSP3 as a target of biologically active antibodies to be included in future vaccine constructs based on MSP3