RESUMEN
Malaria is caused by parasites of the genus Plasmodium, which are transmitted to humans by the bites of Anopheles mosquitoes. After the elimination of Plasmodium falciparum, it is predicted that Plasmodium vivax will remain an important cause of morbidity and mortality outside Africa, stressing the importance of developing a vaccine against P. vivax malaria. In this study, we assessed the immunogenicity and protective efficacy of two P. vivax antigens, apical membrane antigen 1 (AMA1) and the 42-kDa C-terminal fragment of merozoite surface protein 1 (MSP142) in a plasmid recombinant DNA prime/adenoviral (Ad) vector boost regimen in Aotus monkeys. Groups of 4 to 5 monkeys were immunized with plasmid DNA alone, Ad alone, prime/boost regimens with each antigen, prime/boost regimens with both antigens, and empty vector controls and then subjected to blood-stage challenge. The heterologous immunization regimen with the antigen pair was more protective than either antigen alone or both antigens delivered with a single vaccine platform, on the basis of their ability to induce the longest prepatent period and the longest time to the peak level of parasitemia, the lowest peak and mean levels of parasitemia, the smallest area under the parasitemia curve, and the highest self-cure rate. Overall, prechallenge MSP142 antibody titers strongly correlated with a decreased parasite burden. Nevertheless, a significant proportion of immunized animals developed anemia. In conclusion, the P. vivax plasmid DNA/Ad serotype 5 vaccine encoding blood-stage parasite antigens AMA1 and MSP142 in a heterologous prime/boost immunization regimen provided significant protection against blood-stage challenge in Aotus monkeys, indicating the suitability of these antigens and this regimen for further development.
Asunto(s)
Antígenos de Protozoos/inmunología , Vacunas contra la Malaria/inmunología , Malaria Vivax/prevención & control , Proteínas de la Membrana/inmunología , Proteína 1 de Superficie de Merozoito/inmunología , Proteínas Protozoarias/inmunología , Vacunas de ADN/inmunología , Anemia/prevención & control , Animales , Anticuerpos Antiprotozoarios/sangre , Aotidae , Modelos Animales de Enfermedad , Femenino , Vacunas contra la Malaria/administración & dosificación , Malaria Vivax/inmunología , Masculino , Parasitemia/prevención & control , Resultado del Tratamiento , Vacunas de ADN/administración & dosificaciónRESUMEN
BACKGROUND: In this phase 1 clinical trial, healthy adult, malaria-naïve subjects were immunized with radiation-attenuated Plasmodium falciparum sporozoites (PfRAS) by mosquito bite and then underwent controlled human malaria infection (CHMI). The PfRAS model for immunization against malaria had previously induced >90 % sterile protection against homologous CHMI. This study was to further explore the safety, tolerability and protective efficacy of the PfRAS model and to provide biological specimens to characterize protective immune responses and identify protective antigens in support of malaria vaccine development. METHODS: Fifty-seven subjects were screened, 41 enrolled and 30 received at least one immunization. The true-immunized subjects received PfRAS via mosquito bite and the mock-immunized subjects received mosquito bites from irradiated uninfected mosquitoes. Sera and peripheral blood mononuclear cells (PBMCs) were collected before and after PfRAS immunizations. RESULTS: Immunization with PfRAS was generally safe and well tolerated, and repeated immunization via mosquito bite did not appear to increase the risk or severity of AEs. Local adverse events (AEs) of true-immunized and mock-immunized groups consisted of erythaema, papules, swelling, and induration and were consistent with reactions from mosquito bites seen in nature. Two subjects, one true- and one mock-immunized, developed large local reactions that completely resolved, were likely a result of mosquito salivary antigens, and were withdrawn from further participation as a safety precaution. Systemic AEs were generally rare and mild, consisting of headache, myalgia, nausea, and low-grade fevers. Two true-immunized subjects experienced fever, malaise, myalgia, nausea, and rigours approximately 16 h after immunization. These symptoms likely resulted from pre-formed antibodies interacting with mosquito salivary antigens. Ten subjects immunized with PfRAS underwent CHMI and five subjects (50 %) were sterilely protected and there was a significant delay to parasitaemia in the other five subjects. All ten subjects developed humoral immune responses to whole sporozoites and to the circumsporozoite protein prior to CHMI, although the differences between protected and non-protected subjects were not statistically significant for this small sample size. CONCLUSIONS: The protective efficacy of this clinical trial (50 %) was notably less than previously reported (>90 %). This may be related to differences in host genetics or the inherent variability in mosquito biting behavior and numbers of sporozoites injected. Differences in trial procedures, such as the use of leukapheresis prior to CHMI and of a longer interval between the final immunization and CHMI in these subjects compared to earlier trials, may also have reduced protective efficacy. This trial has been retrospectively registered at ISRCTN ID 17372582, May 31, 2016.
Asunto(s)
Anticuerpos Antiprotozoarios/sangre , Culicidae/fisiología , Mordeduras y Picaduras de Insectos , Vacunas contra la Malaria/efectos adversos , Vacunas contra la Malaria/inmunología , Malaria Falciparum/prevención & control , Plasmodium falciparum/inmunología , Adolescente , Adulto , Animales , Efectos Colaterales y Reacciones Adversas Relacionados con Medicamentos/epidemiología , Efectos Colaterales y Reacciones Adversas Relacionados con Medicamentos/patología , Humanos , Vacunas contra la Malaria/administración & dosificación , Masculino , Persona de Mediana Edad , Plasmodium falciparum/efectos de la radiación , Esporozoítos/inmunología , Esporozoítos/efectos de la radiación , Vacunas Atenuadas/administración & dosificación , Vacunas Atenuadas/efectos adversos , Vacunas Atenuadas/inmunología , Adulto JovenRESUMEN
When introduced in the 1990s, immunization with DNA plasmids was considered potentially revolutionary for vaccine development, particularly for vaccines intended to induce protective CD8 T cell responses against multiple antigens. We conducted, in 1997-1998, the first clinical trial in healthy humans of a DNA vaccine, a single plasmid encoding Plasmodium falciparum circumsporozoite protein (PfCSP), as an initial step toward developing a multi-antigen malaria vaccine targeting the liver stages of the parasite. As the next step, we conducted in 2000-2001 a clinical trial of a five-plasmid mixture called MuStDO5 encoding pre-erythrocytic antigens PfCSP, PfSSP2/TRAP, PfEXP1, PfLSA1 and PfLSA3. Thirty-two, malaria-naïve, adult volunteers were enrolled sequentially into four cohorts receiving a mixture of 500 µg of each plasmid plus escalating doses (0, 20, 100 or 500 µg) of a sixth plasmid encoding human granulocyte macrophage-colony stimulating factor (hGM-CSF). Three doses of each formulation were administered intramuscularly by needle-less jet injection at 0, 4 and 8 weeks, and each cohort had controlled human malaria infection administered by five mosquito bites 18 d later. The vaccine was safe and well-tolerated, inducing moderate antigen-specific, MHC-restricted T cell interferon-γ responses but no antibodies. Although no volunteers were protected, T cell responses were boosted post malaria challenge. This trial demonstrated the MuStDO5 DNA and hGM-CSF plasmids to be safe and modestly immunogenic for T cell responses. It also laid the foundation for priming with DNA plasmids and boosting with recombinant viruses, an approach known for nearly 15 y to enhance the immunogenicity and protective efficacy of DNA vaccines.
Asunto(s)
Antígenos de Protozoos/inmunología , Factor Estimulante de Colonias de Granulocitos y Macrófagos/metabolismo , Vacunas contra la Malaria/inmunología , Vacunas contra la Malaria/uso terapéutico , Plasmodium falciparum/inmunología , Plasmodium falciparum/patogenicidad , Esporozoítos/inmunología , Vacunas de ADN/inmunología , Vacunas de ADN/uso terapéutico , Adulto , Femenino , Factor Estimulante de Colonias de Granulocitos y Macrófagos/genética , Humanos , Vacunas contra la Malaria/administración & dosificación , Masculino , Persona de Mediana Edad , Plásmidos/genética , Vacunas de ADN/efectos adversos , Adulto JovenRESUMEN
The present study has evaluated the immunogenicity of single or multiple Plasmodium falciparum (Pf) antigens administered in a DNA prime/poxvirus boost regimen with or without the poloxamer CRL1005 in rhesus monkeys. Animals were primed with PfCSP plasmid DNA or a mixture of PfCSP, PfSSP2/TRAP, PfLSA1, PfAMA1 and PfMSP1-42 (CSLAM) DNA vaccines in PBS or formulated with CRL1005, and subsequently boosted with ALVAC-Pf7, a canarypox virus expressing the CSLAM antigens. Cell-mediated immune responses were evaluated by IFN-gamma ELIspot and intracellular cytokine staining, using recombinant proteins and overlapping synthetic peptides. Antigen-specific and parasite-specific antibody responses were evaluated by ELISA and IFAT, respectively. Immune responses to all components of the multi-antigen mixture were demonstrated following immunization with either DNA/PBS or DNA/CRL1005, and no antigen interference was observed in animals receiving CSLAM as compared to PfCSP alone. These data support the down-selection of the CSLAM antigen combination. CRL1005 formulation had no apparent effect on vaccine-induced T cell or antibody responses, either before or after viral boost. In high responder monkeys, CD4+IL-2+ responses were more predominant than CD8+ T cell responses. Furthermore, CD8+ IFN-gamma responses were detected only in the presence of detectable CD4+ T cell responses. Overall, this study demonstrates the potential for multivalent Pf vaccines based on rational antigen selection and combination, and suggests that further formulation development to increase the immunogenicity of DNA encoded antigens is warranted.
Asunto(s)
Antígenos de Protozoos/inmunología , Inmunización Secundaria/métodos , Vacunas contra la Malaria/administración & dosificación , Malaria Falciparum/inmunología , Plasmodium falciparum/inmunología , Poxviridae/inmunología , Vacunas de ADN/inmunología , Animales , Anticuerpos Antiprotozoarios/biosíntesis , Antígenos de Protozoos/administración & dosificación , Antígenos de Protozoos/genética , Inmunización , Macaca mulatta , Vacunas contra la Malaria/inmunología , Plásmidos , Vacunas de ADN/administración & dosificaciónRESUMEN
A mixture of DNA plasmids expressing five Plasmodium falciparum pre-erythrocyte-stage antigens was administered with or without a DNA plasmid encoding human granulocyte-macrophage colony-stimulating factor (hGM-CSF) as an immune enhancer. After DNA immunization, antigen-specific gamma interferon (IFN-gamma) responses were detected by ELISPOT in 15/31 volunteers to multiple class I- and/or class II-restricted T-cell epitopes derived from all five antigens. Responses to multiple epitopes (=7) were detected simultaneously in some volunteers. By 4 weeks after challenge with P. falciparum parasites, 23/31 volunteers had positive IFN-gamma responses and the magnitude of responses was increased from 2- to 143-fold. Nonetheless, none was protected against malaria. Volunteers who received hGM-CSF had a reduced frequency of IFN-gamma responses to class I peptides compared to those who only received plasmids expressing P. falciparum proteins before challenge (3/23 versus 3/8; P = 0.15) or after parasite challenge (4/23 versus 5/8; P = 0.015) but not to class II peptides before or after challenge. The responses to one antigen (P. falciparum circumsporozoite protein [PfCSP]) were similar among volunteers who received the five-gene mixture compared to volunteers who only received the PfCSP DNA plasmid in a previous study. In summary, DNA-primed IFN-gamma responses were boosted in humans by exposure to native antigen on parasites, coadministration of a plasmid expressing hGM-CSF had a negative effect on boosting of class I-restricted IFN-gamma responses, and there was no evidence that immunization with PfCSP DNA in the mixture reduced T-cell responses to PfCSP compared to when it was administered alone.
Asunto(s)
Antígenos de Protozoos/inmunología , Interferón gamma/sangre , Vacunas contra la Malaria/inmunología , Malaria Falciparum/inmunología , Plasmodium falciparum/inmunología , Vacunas de ADN/inmunología , Animales , Antígenos de Protozoos/administración & dosificación , Antígenos de Protozoos/genética , Mordeduras y Picaduras , Culicidae , Factor Estimulante de Colonias de Granulocitos y Macrófagos/administración & dosificación , Factor Estimulante de Colonias de Granulocitos y Macrófagos/genética , Factor Estimulante de Colonias de Granulocitos y Macrófagos/inmunología , Humanos , Inmunización , Vacunas contra la Malaria/administración & dosificación , Plásmidos , Linfocitos T/inmunología , Resultado del Tratamiento , Vacunas de ADN/administración & dosificaciónRESUMEN
CEL-1000 (derG, DGQEEKAGVVSTGLIGGG) is a small immunomodulatory peptide which delivers demonstrated protective activity in two infectious disease challenge models (HSV and malaria) and an allogenic tumor vaccine model. CEL-1000 and other activators (defensin-beta, CpG ODN, and imiquimod) of the innate immune system promote IFN-gamma-associated protective responses. CEL-1000 is an improved form of peptide G (a peptide from human MHC II beta chain second domain, aa 135-149) known to enhance immune responses of other immunogenic peptides. Since defensin-beta, CpG ODN, and imiquimod have been shown to possess adjuvant activity, we investigated the adjuvant effect of peptide G and CEL-1000 as conjugates with HIV and malaria peptides. Antibody titers and isotypes were evaluated on serum taken from select days following immunization. Results for CEL-1000 and G peptide conjugates were compared with results for KLH conjugates of the same HIV peptide from the p17 molecule (87-116) referred to as HGP-30. Studies demonstrated that comparable titers were seen on day 28, 42, 63, and 77 with either G or KLH-HGP-30 peptide conjugates. In another study, CEL-1000 conjugates (CEL-1000-HGP-30) demonstrated a 4-10-fold higher titer antibody response than seen with several other peptide conjugates of the same HGP-30 peptide. Improved adjuvant activity of CEL-1000 in peptide conjugates was also demonstrated by a shift in the antibody isotypes toward a Th1 response (IgG2a). The IgG2a/IgG1, ratio for G-HGP-30 HIV or KLH-HGP-30 HIV conjugates were lower than for the CEL-1000-HGP-30 HIV conjugate. A similar favoring of the IgG2a/IgG1 ratio was seen for a malaria peptide conjugate (CEL-1000-SF/GF) compared to the un-conjugated peptide (SF-GF). CEL-1000 also showed adjuvant activity in an allogenic tumor vaccine model. As expected for an adjuvant, CEL-1000 or G does not induce detectable self-directed or cross reactive antibodies. CEL-1000 is currently being investigated for use as an adjuvant with conventional vaccines. It is expected that IgG2a antibodies would be preferably generated by CEL-1000 adjuvancy and could enhance in vivo clearance of antigens or pathogens.
Asunto(s)
Adyuvantes Inmunológicos , Péptidos/inmunología , Células TH1/inmunología , Animales , Ensayo de Inmunoadsorción Enzimática , Ratones , Péptidos/efectos adversosRESUMEN
CEL-1000 (DGQEEKAGVVSTGLIGGG) is a novel potential preventative and therapeutic agent. We report that CEL-1000 confers a high degree of protection against Plasmodium sporozoite challenge in a murine model of malaria, as shown by the total absence of blood stage infection following challenge with 100 sporozoites (100% protection) and by a substantial reduction (400-fold) of liver stage parasite RNA following challenge with 50,000 sporozoites. CEL-1000 protection was demonstrated in A/J (H-2(a)) and C3H/HeJ (H-2(k)) mice but not in BALB/c (H-2(d)) or CAF1 (A/J x BALB/c F(1) hybrid) mice. In CEL-1000-treated and protected mice, high levels of gamma interferon (IFN-gamma) in serum and elevated frequencies of hepatic and splenic CD4+ IFN-gamma-positive T cells were detected 24 h after administration of an additional dose of CEL-1000. Treatment of A/J mice that received CEL-1000 with antibodies against IFN-gamma just prior to challenge abolished the protection, and a similar treatment with antibodies against CD4+ T cells partially reduced the level of protection, while treatment with control antibodies or antibodies specific for interleukin-12 (IL-12), CD8+ T cells, or NK cells had no effect. Our data establish that the protection induced by CEL-1000 is dependent on IFN-gamma and is partially dependent on CD4+ T cells but is independent of CD8+ T cells, NK cells, and IL-12 at the effector phase and does not induce a detectable antibody response.
Asunto(s)
Antígenos de Protozoos/inmunología , Antimaláricos/farmacología , Genes MHC Clase II/genética , Malaria/prevención & control , Secuencia de Aminoácidos , Animales , Especificidad de Anticuerpos , Citocinas/sangre , Ensayo de Inmunoadsorción Enzimática , Femenino , Interferón gamma/inmunología , Cinética , Hígado/química , Hígado/parasitología , Malaria/inmunología , Malaria/parasitología , Ratones , Ratones Endogámicos BALB C , Datos de Secuencia Molecular , Plasmodium berghei/inmunología , Plasmodium yoelii/inmunología , ARN/química , ARN/aislamiento & purificación , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
Vaccine-induced protection against diseases like malaria, AIDS, and cancer may require induction of Ag-specific CD8(+) and CD4(+) T cell and Ab responses in the same individual. In humans, a recombinant Plasmodium falciparum circumsporozoite protein (PfCSP) candidate vaccine, RTS,S/adjuvant system number 2A (AS02A), induces T cells and Abs, but no measurable CD8(+) T cells by CTL or short-term (ex vivo) IFN-gamma ELISPOT assays, and partial short-term protection. P. falciparum DNA vaccines elicit CD8(+) T cells by these assays, but no protection. We report that sequential immunization with a PfCSP DNA vaccine and RTS,S/AS02A induced PfCSP-specific Abs and Th1 CD4(+) T cells, and CD8(+) cytotoxic and Tc1 T cells. Depending upon the immunization regime, CD4(+) T cells were involved in both the induction and production phases of PfCSP-specific IFN-gamma responses, whereas, CD8(+) T cells were involved only in the production phase. IFN-gamma mRNA up-regulation was detected in both CD45RA(-) (CD45RO(+)) and CD45RA(+)CD4(+) and CD8(+) T cell populations after stimulation with PfCSP peptides. This finding suggests CD45RA(+) cells function as effector T cells. The induction in humans of the three primary Ag-specific adaptive immune responses establishes a strategy for developing immunization regimens against diseases in desperate need of vaccines.
Asunto(s)
Anticuerpos Antiprotozoarios/biosíntesis , Linfocitos T CD4-Positivos/inmunología , Linfocitos T CD8-positivos/inmunología , Esquemas de Inmunización , Vacunas contra la Malaria/administración & dosificación , Plasmodium falciparum/inmunología , Proteínas Protozoarias/administración & dosificación , Vacunas de ADN/administración & dosificación , Secuencia de Aminoácidos , Animales , Linfocitos T CD4-Positivos/metabolismo , Linfocitos T CD8-positivos/metabolismo , Pruebas Inmunológicas de Citotoxicidad , Epítopos de Linfocito T/administración & dosificación , Epítopos de Linfocito T/inmunología , Anticuerpos contra la Hepatitis B/biosíntesis , Antígenos de Superficie de la Hepatitis B/inmunología , Humanos , Inmunización Secundaria/métodos , Interferón gamma/biosíntesis , Vacunas contra la Malaria/genética , Vacunas contra la Malaria/inmunología , Malaria Falciparum/inmunología , Malaria Falciparum/prevención & control , Datos de Secuencia Molecular , Proteínas Protozoarias/genética , Proteínas Protozoarias/inmunología , Subgrupos de Linfocitos T , Linfocitos T Citotóxicos/inmunología , Linfocitos T Citotóxicos/metabolismo , Células TH1/inmunología , Células TH1/metabolismo , Vacunas de ADN/genética , Vacunas de ADN/inmunologíaRESUMEN
Optimal protection against malaria may require induction of high levels of protective antibody and CD8(+) and CD4(+) T cell responses. In humans, malaria DNA vaccines elicit CD8(+) cytotoxic T cells (CTL) and IFNgamma responses as measured by short-term (ex vivo) ELISPOT assays, and recombinant proteins elicit antibodies and excellent T cell responses, but no CD8(+) CTL or CD8(+) IFNgamma-producing cells as measured by ex vivo ELISPOT. Priming with DNA and boosting with recombinant pox virus elicits much better T cell responses than DNA alone, but not antibody responses. In an attempt to elicit antibodies and enhanced T cell responses, we administered RTS,S/AS02A, a partially protective Plasmodium falciparum recombinant circumsporozoite protein (CSP) vaccine in adjuvant, to volunteers previously immunized with a P. falciparum CSP DNA vaccine (VCL-2510) and to naïve volunteers. This vaccine regimen was well tolerated and safe. The volunteers who received RTS,S/AS02A alone had, as expected, antibody and CD4(+) T cell responses, but no CD8(+) T cell responses. Volunteers who received PfCSP DNA followed by RTS,S/AS02A had antibody and CD8(+) and CD4(+) T cell responses (Wang et al., submitted). Sequential immunization with DNA and recombinant protein, also called heterologous prime-boost, led to enhanced immune responses as compared to DNA or recombinant protein alone, suggesting that it might provide enhanced protective immunity.
Asunto(s)
Anticuerpos Antiprotozoarios/biosíntesis , Vacunas contra la Malaria/inmunología , Plasmodium falciparum/inmunología , Vacunas de ADN/inmunología , Adolescente , Adulto , Animales , Anticuerpos Antiprotozoarios/análisis , Linfocitos B/inmunología , Femenino , Anticuerpos contra la Hepatitis B/biosíntesis , Antígenos de Superficie de la Hepatitis B/inmunología , Humanos , Esquemas de Inmunización , Vacunas contra la Malaria/efectos adversos , Masculino , Esporas Protozoarias/inmunología , Linfocitos T/inmunología , Vacunas de ADN/efectos adversos , Vacunas Sintéticas/efectos adversos , Vacunas Sintéticas/inmunologíaRESUMEN
We describe a novel approach for identifying target antigens for preerythrocytic malaria vaccines. Our strategy is to rapidly test hundreds of DNA vaccines encoding exons from the Plasmodium yoelii yoelii genomic sequence. In this antigen identification method, we measure reduction in parasite burden in the liver after sporozoite challenge in mice. Orthologs of protective P. y. yoelii genes can then be identified in the genomic databases of Plasmodium falciparum and Plasmodium vivax and investigated as candidate antigens for a human vaccine. A pilot study to develop the antigen identification method approach used 192 P. y. yoelii exons from genes expressed during the sporozoite stage of the life cycle. A total of 182 (94%) exons were successfully cloned into a DNA immunization vector with the Gateway cloning technology. To assess immunization strategies, mice were vaccinated with 19 of the new DNA plasmids in addition to the well-characterized protective plasmid encoding P. y. yoelii circumsporozoite protein. Single plasmid immunization by gene gun identified a novel vaccine target antigen which decreased liver parasite burden by 95% and which has orthologs in P. vivax and P. knowlesi but not P. falciparum. Intramuscular injection of DNA plasmids produced a different pattern of protective responses from those seen with gene gun immunization. Intramuscular immunization with plasmid pools could reduce liver parasite burden in mice despite the fact that none of the plasmids was protective when given individually. We conclude that high-throughput cloning of exons into DNA vaccines and their screening is feasible and can rapidly identify new malaria vaccine candidate antigens.
Asunto(s)
Antígenos de Protozoos/genética , Vacunas contra la Malaria/genética , Plasmodium yoelii/genética , Plasmodium yoelii/inmunología , Animales , Anticuerpos Antiprotozoarios/sangre , Secuencia de Bases , Biolística , Clonación Molecular , Cartilla de ADN , ADN Protozoario/genética , Exones , Femenino , Técnica del Anticuerpo Fluorescente Indirecta , Genoma de Protozoos , Humanos , Inyecciones Intramusculares , Hígado/parasitología , Malaria/inmunología , Malaria/parasitología , Malaria/prevención & control , Vacunas contra la Malaria/administración & dosificación , Vacunas contra la Malaria/farmacología , Ratones , Ratones Endogámicos BALB C , Plásmidos/genética , Plasmodium yoelii/crecimiento & desarrollo , Reacción en Cadena de la Polimerasa , Vacunas de ADN/administración & dosificación , Vacunas de ADN/genética , Vacunas de ADN/farmacologíaRESUMEN
Plasmodium sporozoites are transmitted through the bite of infected mosquitoes and invade hepatocytes as a first and obligatory step of the parasite life cycle in man. Hepatocyte invasion involves proteins secreted from parasite vesicles called micronemes, the most characterized being the thrombospondin-related adhesive protein (TRAP). Here we investigated the expression and function of another microneme protein recently identified in Plasmodium falciparum sporozoites, apical membrane antigen 1 (AMA-1). P. falciparum AMA-1 is expressed in sporozoites and is lost after invasion of hepatocytes, and anti-AMA-1 antibodies inhibit sporozoite invasion, suggesting that the protein is involved during invasion of hepatocytes. As observed with TRAP, AMA-1 is initially mostly sequestered within the sporozoite. Upon microneme exocytosis, AMA-1 and TRAP relocate to the sporozoite surface, where they are proteolytically cleaved, resulting in the shedding of soluble fragments. A subset of serine protease inhibitors blocks the processing and shedding of both AMA-1 and TRAP and inhibits sporozoite infectivity, suggesting that interfering with sporozoite proteolytic processing may constitute a valuable strategy to prevent hepatocyte infection.
Asunto(s)
Antígenos de Protozoos/metabolismo , Hepatocitos/parasitología , Proteínas de la Membrana/metabolismo , Plasmodium falciparum/metabolismo , Proteínas Protozoarias/metabolismo , Animales , Células Cultivadas , Hepatocitos/metabolismo , Humanos , Plasmodium falciparum/patogenicidad , Esporozoítos/metabolismo , Esporozoítos/patogenicidadAsunto(s)
Predisposición Genética a la Enfermedad/genética , Inmunidad Innata/genética , Malaria Falciparum/genética , Malaria Falciparum/inmunología , Plasmodium falciparum/genética , Plasmodium falciparum/inmunología , Adulto , Animales , Formación de Anticuerpos/genética , Niño , Interacciones Huésped-Parásitos/genética , Interacciones Huésped-Parásitos/inmunología , Humanos , Indonesia/epidemiología , Indonesia/etnología , Malaria Falciparum/parasitología , Papúa Nueva Guinea/epidemiología , Papúa Nueva Guinea/etnología , Plasmodium falciparum/patogenicidad , Polimorfismo Genético/genéticaRESUMEN
The aim of this study was to determine the exposure of child citizens of the United Arab Emirates (UAE) to Plasmodium vivax, and to elucidate if it was related to place of residence or previous international travel to malaria-endemic areas. Blood samples were collected from 1010 primary schoolchildren resident in 7 out of 9 districts of the UAE during October and November 1999. Plasma samples were tested for antibodies against MAP4 (DGQPAGDR)3P2P30, a multiple antigen peptide containing the repeat amino acid sequences of P. vivax circumsporozoite protein (CSP), conjugated to 2 T-helper epitopes, P2 (QYIKANSKFIGITE) and P30 (FNNFTVSFWLRVPKVSASHLE) from tetanus toxin. For confirmation of P. vivax-specific reactivity, positive samples were further tested against (AGDR)6, a synthetic peptide containing 6 copies of a protective epitope within the CSP, and against a recombinant CSP, designated as NS1(81)V20. Results indicated that 3.3% of the children were seropositive. The seropositivity rates differed significantly in relation to place of residence, whereas travel outside the UAE did not significantly affect the exposure rates to P. vivax.
Asunto(s)
Anticuerpos Antiprotozoarios/sangre , Malaria Vivax/parasitología , Plasmodium vivax/inmunología , Proteínas Protozoarias/inmunología , Animales , Niño , Estudios Transversales , Ensayo de Inmunoadsorción Enzimática/métodos , Humanos , Masculino , Prevalencia , Emiratos Árabes Unidos/epidemiologíaRESUMEN
Introduction of a new vaccine requires choosing a delivery system that provides safe administration and the desired level of immunogenicity. The safety, tolerability, and immunogenicity of three monthly 2.5-mg doses of a PfCSP DNA vaccine were evaluated in healthy volunteers as administered intramuscularly (IM) by needle, IM by jet injection (Biojector or IM/intradermally (ID) by jet injection. Vaccine administration was well-tolerated. Adverse events were primarily mild and limited to the site of injection (98%). Jet injections (either IM or ID) were associated with approximately twice as many adverse events per immunization as needle IM, but nevertheless were strongly and consistently preferred in opinion polls taken during the study. No volunteers had clinically significant biochemical or hematologic changes or detectable anti-dsDNA antibodies. In conclusion, the injection of Plasmodium falciparum circumsporozoite (PfCSP) DNA vaccine appeared to be safe and well-tolerated when administered by any of the three modes of delivery. However, despite improved antibody responses following both jet injection and ID delivery in animal models, no antibodies could be detected in volunteers by immunofluorescence antibody test (IFAT) or enzyme-linked immunosorbent assay (ELISA) after DNA vaccination.
Asunto(s)
Malaria/prevención & control , Vacunas de ADN/administración & dosificación , Animales , Humanos , Inyecciones Intradérmicas , Inyecciones Intramusculares , Malaria/inmunología , Plasmodium falciparum/inmunología , Vacunas de ADN/efectos adversos , Vacunas de ADN/inmunologíaRESUMEN
The persistence of immunity to malaria induced in mice by a heterologous DNA priming and poxvirus boosting regimen was characterized. Mice were immunized by priming with DNA vaccine plasmids encoding the Plasmodium yoelii circumsporozoite protein (PyCSP) and murine granulocyte-macrophage colony-stimulating factor and boosting with recombinant vaccinia encoding PyCSP. BALB/c mice immunized with either high-dose (100 microg of p PyCSP plus 30 microg of pGM-CSF) or low-dose (1 microg of p PyCSP plus 1 microg of pGM-CSF DNA) priming were protected against challenge with 50 P. yoelii sporozoites. Protection 2 weeks after immunization was 70 to 100%, persisted at this level for at least 20 weeks, and declined to 30 to 40% by 28 weeks. Eight of eight mice protected at 20 weeks were still protected when rechallenged at 40 weeks. The antigen (Ag)-specific effector CD8(+)-T-cell population present 2 weeks after boosting had ex vivo Ag-specific cytolytic activity, expressed both gamma interferon (IFN-gamma) and tumor necrosis factor alpha, and constituted 12 to 20% of splenic CD8(+) T cells. In contrast, the memory CD8(+)-Ag-specific-cell population at 28 weeks lacked cytolytic activity and constituted only 6% of splenic CD8(+) T cells, but at the single-cell level it produced significantly higher levels of IFN-gamma than the effectors. High levels of Ag- or parasite-specific antibodies present 2 weeks after boosting had declined three- to sevenfold by 28 weeks. Low-dose priming was similarly immunogenic and as protective as high-dose priming against a 50-, but not a 250-, sporozoite challenge. These results demonstrate that a heterologous priming and boosting vaccination can provide lasting protection against malaria in this model system.