RESUMEN
Reticulocyte-binding protein homologue 5 (RH5), a leading blood-stage Plasmodium falciparum malaria vaccine target, interacts with cysteine-rich protective antigen (CyRPA) and RH5-interacting protein (RIPR) to form an essential heterotrimeric "RCR-complex". We investigate whether RCR-complex vaccination can improve upon RH5 alone. Using monoclonal antibodies (mAbs) we show that parasite growth-inhibitory epitopes on each antigen are surface-exposed on the RCR-complex and that mAb pairs targeting different antigens can function additively or synergistically. However, immunisation of female rats with the RCR-complex fails to outperform RH5 alone due to immuno-dominance of RIPR coupled with inferior potency of anti-RIPR polyclonal IgG. We identify that all growth-inhibitory antibody epitopes of RIPR cluster within the C-terminal EGF-like domains and that a fusion of these domains to CyRPA, called "R78C", combined with RH5, improves the level of in vitro parasite growth inhibition compared to RH5 alone. These preclinical data justify the advancement of the RH5.1 + R78C/Matrix-M™ vaccine candidate to Phase 1 clinical trial.
Asunto(s)
Anticuerpos Monoclonales , Anticuerpos Antiprotozoarios , Antígenos de Protozoos , Vacunas contra la Malaria , Malaria Falciparum , Plasmodium falciparum , Proteínas Protozoarias , Vacunas contra la Malaria/inmunología , Vacunas contra la Malaria/administración & dosificación , Animales , Plasmodium falciparum/inmunología , Proteínas Protozoarias/inmunología , Femenino , Malaria Falciparum/prevención & control , Malaria Falciparum/inmunología , Malaria Falciparum/parasitología , Antígenos de Protozoos/inmunología , Ratas , Anticuerpos Antiprotozoarios/inmunología , Anticuerpos Monoclonales/inmunología , Humanos , Epítopos/inmunología , Proteínas Portadoras/inmunología , Proteínas Portadoras/metabolismoRESUMEN
Understanding mechanisms of antibody synergy is important for vaccine design and antibody cocktail development. Examples of synergy between antibodies are well-documented, but the mechanisms underlying these relationships often remain poorly understood. The leading blood-stage malaria vaccine candidate, CyRPA, is essential for invasion of Plasmodium falciparum into human erythrocytes. Here we present a panel of anti-CyRPA monoclonal antibodies that strongly inhibit parasite growth in in vitro assays. Structural studies show that growth-inhibitory antibodies bind epitopes on a single face of CyRPA. We also show that pairs of non-competing inhibitory antibodies have strongly synergistic growth-inhibitory activity. These antibodies bind to neighbouring epitopes on CyRPA and form lateral, heterotypic interactions which slow antibody dissociation. We predict that such heterotypic interactions will be a feature of many immune responses. Immunogens which elicit such synergistic antibody mixtures could increase the potency of vaccine-elicited responses to provide robust and long-lived immunity against challenging disease targets.
Asunto(s)
Anticuerpos Monoclonales/inmunología , Anticuerpos Antiprotozoarios/inmunología , Antígenos de Protozoos/inmunología , Vacunas contra la Malaria/inmunología , Malaria Falciparum/prevención & control , Proteínas Protozoarias/inmunología , Animales , Anticuerpos Monoclonales/aislamiento & purificación , Anticuerpos Monoclonales/metabolismo , Anticuerpos Antiprotozoarios/aislamiento & purificación , Anticuerpos Antiprotozoarios/metabolismo , Antígenos de Protozoos/genética , Antígenos de Protozoos/aislamiento & purificación , Antígenos de Protozoos/metabolismo , Línea Celular , Drosophila melanogaster , Epítopos/inmunología , Humanos , Inmunogenicidad Vacunal , Vacunas contra la Malaria/uso terapéutico , Malaria Falciparum/inmunología , Malaria Falciparum/parasitología , Plasmodium falciparum/inmunología , Proteínas Protozoarias/genética , Proteínas Protozoarias/aislamiento & purificación , Proteínas Protozoarias/metabolismo , Desarrollo de VacunasRESUMEN
Plasmodium falciparum malaria continues to evade control efforts, utilizing highly specialized sexual-stages to transmit infection between the human host and mosquito vector. In a vaccination model, antibodies directed to sexual-stage antigens, when ingested in the mosquito blood meal, can inhibit parasite growth in the midgut and consequently arrest transmission. Despite multiple datasets for the Plasmodium sexual-stage transcriptome and proteome, there have been no rational screens to identify candidate antigens for transmission-blocking vaccine (TBV) development. This study characterizes 12 proteins from across the P. falciparum sexual-stages as possible TBV targets. Recombinant proteins are heterologously expressed as full-length ectodomains in a mammalian HEK293 cell system. The proteins recapitulate native parasite epitopes as assessed by indirect fluorescence assay and a proportion exhibits immunoreactivity when tested against sera from individuals living in malaria-endemic Burkina Faso and Mali. Purified IgG generated to the mosquito-stage parasite antigen enolase demonstrates moderate inhibition of parasite development in the mosquito midgut by the ex vivo standard membrane feeding assay. The findings support the use of rational screens and comparative functional assessments in identifying proteins of the P. falciparum transmission pathway and establishing a robust pre-clinical TBV pipeline.
Asunto(s)
Anticuerpos Bloqueadores/inmunología , Malaria Falciparum/inmunología , Malaria Falciparum/transmisión , Plasmodium falciparum/inmunología , Proteínas Protozoarias/inmunología , Proteínas Recombinantes/inmunología , Adulto , Animales , Anopheles/parasitología , Epítopos/inmunología , Femenino , Células HEK293 , Humanos , Inmunoglobulina G/inmunología , Vacunas contra la Malaria/inmunología , Malaria Falciparum/epidemiología , Malaria Falciparum/virología , Masculino , Malí/epidemiología , Ratones , Ratones Endogámicos BALB C , Mosquitos Vectores/parasitología , Fosfopiruvato Hidratasa/inmunología , Proteoma , Proteómica/métodos , VacunaciónRESUMEN
The malaria genome encodes over 5,000 proteins and many of these have also been proposed to be potential vaccine candidates, although few of these have been tested clinically. RH5 is one of the leading blood-stage Plasmodium falciparum malaria vaccine antigens and Phase I/II clinical trials of vaccines containing this antigen are currently underway. Its likely mechanism of action is to elicit antibodies that can neutralize merozoites by blocking their invasion of red blood cells (RBC). However, many other antigens could also elicit neutralizing antibodies against the merozoite, and most of these have never been compared directly to RH5. The objective of this study was to compare a range of blood-stage antigens to RH5, to identify any antigens that outperform or synergize with anti-RH5 antibodies. We selected 55 gene products, covering 15 candidate antigens that have been described in the literature and 40 genes selected on the basis of bioinformatics functional prediction. We were able to make 20 protein-in-adjuvant vaccines from the original selection. Of these, S-antigen and CyRPA robustly elicited antibodies with neutralizing properties. Anti-CyRPA IgG generally showed additive GIA with anti-RH5 IgG, although high levels of anti-CyRPA-specific rabbit polyclonal IgG were required to achieve 50% GIA. Our data suggest that further vaccine antigen screening efforts are required to identify a second merozoite target with similar antibody-susceptibility to RH5.
Asunto(s)
Eritrocitos/inmunología , Eritrocitos/parasitología , Vacunas contra la Malaria/inmunología , Malaria Falciparum/inmunología , Merozoítos/inmunología , Plasmodium falciparum/inmunología , Animales , Anticuerpos Neutralizantes/inmunología , Anticuerpos Antiprotozoarios/inmunología , Especificidad de Anticuerpos/inmunología , Antígenos de Protozoos/genética , Antígenos de Protozoos/inmunología , Femenino , Humanos , Inmunoglobulina G/inmunología , Malaria Falciparum/prevención & control , Ratones , Plasmodium falciparum/genética , Plasmodium falciparum/crecimiento & desarrollo , Polimorfismo Genético , Proteínas Protozoarias/genética , Proteínas Protozoarias/inmunologíaRESUMEN
The Plasmodium falciparum reticulocyte-binding protein homolog 5 (PfRH5) is the leading target for next-generation vaccines against the disease-causing blood-stage of malaria. However, little is known about how human antibodies confer functional immunity against this antigen. We isolated a panel of human monoclonal antibodies (mAbs) against PfRH5 from peripheral blood B cells from vaccinees in the first clinical trial of a PfRH5-based vaccine. We identified a subset of mAbs with neutralizing activity that bind to three distinct sites and another subset of mAbs that are non-functional, or even antagonistic to neutralizing antibodies. We also identify the epitope of a novel group of non-neutralizing antibodies that significantly reduce the speed of red blood cell invasion by the merozoite, thereby potentiating the effect of all neutralizing PfRH5 antibodies as well as synergizing with antibodies targeting other malaria invasion proteins. Our results provide a roadmap for structure-guided vaccine development to maximize antibody efficacy against blood-stage malaria.
Asunto(s)
Anticuerpos Monoclonales/inmunología , Anticuerpos Neutralizantes/inmunología , Anticuerpos Antiprotozoarios/inmunología , Eritrocitos/parasitología , Vacunas contra la Malaria/inmunología , Malaria Falciparum/inmunología , Plasmodium falciparum/inmunología , Adolescente , Adulto , Animales , Sitios de Unión , Proteínas Portadoras/inmunología , Reacciones Cruzadas/inmunología , Epítopos/inmunología , Femenino , Células HEK293 , Voluntarios Sanos , Humanos , Malaria Falciparum/parasitología , Masculino , Merozoítos/fisiología , Persona de Mediana Edad , Plasmodium falciparum/metabolismo , Proteínas Protozoarias/inmunología , Conejos , Ratas , Ratas Sprague-Dawley , Adulto JovenRESUMEN
The Plasmodium falciparum reticulocyte-binding protein homolog 5 (PfRH5) has recently emerged as a leading candidate antigen against the blood-stage human malaria parasite. However it has proved challenging to identify a heterologous expression platform that can produce a soluble protein-based vaccine in a manner compliant with current Good Manufacturing Practice (cGMP). Here we report the production of full-length PfRH5 protein using a cGMP-compliant platform called ExpreS(2), based on a Drosophila melanogaster Schneider 2 (S2) stable cell line system. Five sequence variants of PfRH5 were expressed that differed in terms of mutagenesis strategies to remove potential N-linked glycans. All variants bound the PfRH5 receptor basigin and were recognized by a panel of monoclonal antibodies. Analysis following immunization of rabbits identified quantitative and qualitative differences in terms of the functional IgG antibody response against the P. falciparum parasite. The antibodies induced by one protein variant were shown to be qualitatively similar to responses induced by other vaccine platforms. This work identifies Drosophila S2 cells as a clinically-relevant platform suited for the production of 'difficult-to-make' proteins from Plasmodium parasites, and identifies a PfRH5 sequence variant that can be used for clinical production of a non-glycosylated, soluble full-length protein vaccine immunogen.
Asunto(s)
Proteínas Portadoras/inmunología , Vacunas contra la Malaria/inmunología , Plasmodium falciparum/inmunología , Animales , Anticuerpos Monoclonales/inmunología , Basigina/inmunología , Proteínas Portadoras/genética , Proteínas Portadoras/metabolismo , Línea Celular , Drosophila melanogaster , Inmunoglobulina G/inmunología , Vacunas contra la Malaria/genética , MutaciónRESUMEN
Viral vectors used in heterologous prime-boost regimens are one of very few vaccination approaches that have yielded significant protection against controlled human malaria infections. Recently, protection induced by chimpanzee adenovirus priming and modified vaccinia Ankara boosting using the ME-TRAP insert has been correlated with the induction of potent CD8(+) T cell responses. This regimen has progressed to field studies where efficacy against infection has now been reported. The same vectors have been used pre-clinically to identify preferred protective antigens for use in vaccines against the pre-erythrocytic, blood-stage and mosquito stages of malaria and this work is reviewed here for the first time. Such antigen screening has led to the prioritization of the PfRH5 blood-stage antigen, which showed efficacy against heterologous strain challenge in non-human primates, and vectors encoding this antigen are in clinical trials. This, along with the high transmission-blocking activity of some sexual-stage antigens, illustrates well the capacity of such vectors to induce high titre protective antibodies in addition to potent T cell responses. All of the protective responses induced by these vectors exceed the levels of the same immune responses induced by natural exposure supporting the view that, for subunit vaccines to achieve even partial efficacy in humans, "unnatural immunity" comprising immune responses of very high magnitude will need to be induced.
Asunto(s)
Antígenos de Protozoos/inmunología , Vacunas contra la Malaria/inmunología , Virus Vaccinia/genética , Adenovirus Humanos/genética , Animales , Anticuerpos Antiprotozoarios/sangre , Anticuerpos Antiprotozoarios/inmunología , Linfocitos T CD8-positivos/inmunología , Ensayos Clínicos como Asunto , Humanos , Inmunización Secundaria , Vacunas contra la Malaria/genética , Plasmodium falciparum/genética , Plasmodium falciparum/crecimiento & desarrollo , Plasmodium falciparum/inmunología , Proteínas Protozoarias/inmunología , Vacunación , Vacunas de Subunidad/inmunologíaRESUMEN
Antigenic diversity has posed a critical barrier to vaccine development against the pathogenic blood-stage infection of the human malaria parasite Plasmodium falciparum. To date, only strain-specific protection has been reported by trials of such vaccines in nonhuman primates. We recently showed that P. falciparum reticulocyte binding protein homolog 5 (PfRH5), a merozoite adhesin required for erythrocyte invasion, is highly susceptible to vaccine-inducible strain-transcending parasite-neutralizing antibody. In vivo efficacy of PfRH5-based vaccines has not previously been evaluated. Here, we demonstrate that PfRH5-based vaccines can protect Aotus monkeys against a virulent vaccine-heterologous P. falciparum challenge and show that such protection can be achieved by a human-compatible vaccine formulation. Protection was associated with anti-PfRH5 antibody concentration and in vitro parasite-neutralizing activity, supporting the use of this in vitro assay to predict the in vivo efficacy of future vaccine candidates. These data suggest that PfRH5-based vaccines have potential to achieve strain-transcending efficacy in humans.
Asunto(s)
Proteínas Portadoras/inmunología , Inmunidad Heteróloga , Vacunas contra la Malaria/inmunología , Malaria/prevención & control , Animales , Anticuerpos Neutralizantes/sangre , Anticuerpos Antiprotozoarios/sangre , Antígenos de Protozoos/inmunología , Aotus trivirgatus , Modelos Animales de Enfermedad , Femenino , Malaria/inmunología , Vacunas contra la Malaria/administración & dosificación , Pruebas de NeutralizaciónRESUMEN
BACKGROUND: Circumsporozoite protein (CS) is the antigenic target for RTS,S, the most advanced malaria vaccine to date. Heterologous prime-boost with the viral vectors simian adenovirus 63 (ChAd63)-modified vaccinia virus Ankara (MVA) is the most potent inducer of T-cells in humans, demonstrating significant efficacy when expressing the preerythrocytic antigen insert multiple epitope-thrombospondin-related adhesion protein (ME-TRAP). We hypothesized that ChAd63-MVA containing CS may result in a significant clinical protective efficacy. METHODS: We conducted an open-label, 2-site, partially randomized Plasmodium falciparum sporozoite controlled human malaria infection (CHMI) study to compare the clinical efficacy of ChAd63-MVA CS with ChAd63-MVA ME-TRAP. RESULTS: One of 15 vaccinees (7%) receiving ChAd63-MVA CS and 2 of 15 (13%) receiving ChAd63-MVA ME-TRAP achieved sterile protection after CHMI. Three of 15 vaccinees (20%) receiving ChAd63-MVA CS and 5 of 15 (33%) receiving ChAd63-MVA ME-TRAP demonstrated a delay in time to treatment, compared with unvaccinated controls. In quantitative polymerase chain reaction analyses, ChAd63-MVA CS was estimated to reduce the liver parasite burden by 69%-79%, compared with 79%-84% for ChAd63-MVA ME-TRAP. CONCLUSIONS: ChAd63-MVA CS does reduce the liver parasite burden, but ChAd63-MVA ME-TRAP remains the most promising antigenic insert for a vectored liver-stage vaccine. Detailed analyses of parasite kinetics may allow detection of smaller but biologically important differences in vaccine efficacy that can influence future vaccine development. CLINICAL TRIALS REGISTRATION: NCT01623557.
Asunto(s)
Vacunas contra la Malaria/inmunología , Malaria Falciparum/prevención & control , Plasmodium falciparum/inmunología , Proteínas Protozoarias/inmunología , Adenovirus de los Simios/genética , Adenovirus de los Simios/inmunología , Adolescente , Adulto , Anticuerpos Antiprotozoarios/biosíntesis , Epítopos/inmunología , Femenino , Vectores Genéticos , Humanos , Interferón gamma/inmunología , Hígado/virología , Malaria Falciparum/inmunología , Malaria Falciparum/parasitología , Masculino , Persona de Mediana Edad , Plasmodium falciparum/genética , Proteínas Protozoarias/genética , Adulto JovenRESUMEN
The development of effective vaccines against difficult disease targets will require the identification of new subunit vaccination strategies that can induce and maintain effective immune responses in humans. Here we report on a phase 1a clinical trial using the AMA1 antigen from the blood-stage Plasmodium falciparum malaria parasite delivered either as recombinant protein formulated with Alhydrogel adjuvant with and without CPG 7909, or using recombinant vectored vaccines--chimpanzee adenovirus ChAd63 and the orthopoxvirus MVA. A variety of promising "mixed-modality" regimens were tested. All volunteers were primed with ChAd63, and then subsequently boosted with MVA and/or protein-in-adjuvant using either an 8- or 16-week prime-boost interval. We report on the safety of these regimens, as well as the T cell, B cell, and serum antibody responses. Notably, IgG antibody responses primed by ChAd63 were comparably boosted by AMA1 protein vaccine, irrespective of whether CPG 7909 was included in the Alhydrogel adjuvant. The ability to improve the potency of a relatively weak aluminium-based adjuvant in humans, by previously priming with an adenoviral vaccine vector encoding the same antigen, thus offers a novel vaccination strategy for difficult or neglected disease targets when access to more potent adjuvants is not possible.
Asunto(s)
Adyuvantes Inmunológicos/administración & dosificación , Antígenos de Protozoos/administración & dosificación , Vacunas contra la Malaria/administración & dosificación , Malaria Falciparum/prevención & control , Plasmodium falciparum/inmunología , Adenovirus de los Simios/genética , Adulto , Hidróxido de Aluminio/administración & dosificación , Antígenos de Protozoos/inmunología , Terapia Combinada , Vectores Genéticos/administración & dosificación , Humanos , Inmunización Secundaria , Masculino , Persona de Mediana Edad , Oligodesoxirribonucleótidos/administración & dosificación , Orthopoxvirus/genética , Vacunación , Adulto JovenRESUMEN
Invasion of host erythrocytes is essential to the life cycle of Plasmodium parasites and development of the pathology of malaria. The stages of erythrocyte invasion, including initial contact, apical reorientation, junction formation, and active invagination, are directed by coordinated release of specialized apical organelles and their parasite protein contents. Among these proteins, and central to invasion by all species, are two parasite protein families, the reticulocyte-binding protein homologue (RH) and erythrocyte-binding like proteins, which mediate host-parasite interactions. RH5 from Plasmodium falciparum (PfRH5) is the only member of either family demonstrated to be necessary for erythrocyte invasion in all tested strains, through its interaction with the erythrocyte surface protein basigin (also known as CD147 and EMMPRIN). Antibodies targeting PfRH5 or basigin efficiently block parasite invasion in vitro, making PfRH5 an excellent vaccine candidate. Here we present crystal structures of PfRH5 in complex with basigin and two distinct inhibitory antibodies. PfRH5 adopts a novel fold in which two three-helical bundles come together in a kite-like architecture, presenting binding sites for basigin and inhibitory antibodies at one tip. This provides the first structural insight into erythrocyte binding by the Plasmodium RH protein family and identifies novel inhibitory epitopes to guide design of a new generation of vaccines against the blood-stage parasite.
Asunto(s)
Anticuerpos Bloqueadores/química , Basigina/química , Eritrocitos/química , Malaria , Plasmodium falciparum/química , Anticuerpos Bloqueadores/inmunología , Antígenos de Protozoos/química , Antígenos de Protozoos/inmunología , Basigina/inmunología , Sitios de Unión , Cristalografía por Rayos X , Epítopos/química , Epítopos/inmunología , Interacciones Huésped-Parásitos/inmunología , Humanos , Malaria/parasitología , Modelos Moleculares , Plasmodium falciparum/inmunología , Proteínas Protozoarias/química , Proteínas Protozoarias/inmunologíaRESUMEN
There is intense interest in induction and characterization of strain-transcending neutralizing Ab against antigenically variable human pathogens. We have recently identified the human malaria parasite Plasmodium falciparum reticulocyte-binding protein homolog 5 (PfRH5) as a target of broadly neutralizing Abs, but there is little information regarding the functional mechanism(s) of Ab-mediated neutralization. In this study, we report that vaccine-induced polyclonal anti-PfRH5 Abs inhibit the tight attachment of merozoites to erythrocytes and are capable of blocking the interaction of PfRH5 with its receptor basigin. Furthermore, by developing anti-PfRH5 mAbs, we provide evidence of the following: 1) the ability to block the PfRH5-basigin interaction in vitro is predictive of functional activity, but absence of blockade does not predict absence of functional activity; 2) neutralizing mAbs bind spatially related epitopes on the folded protein, involving at least two defined regions of the PfRH5 primary sequence; 3) a brief exposure window of PfRH5 is likely to necessitate rapid binding of Ab to neutralize parasites; and 4) intact bivalent IgG contributes to but is not necessary for parasite neutralization. These data provide important insight into the mechanisms of broadly neutralizing anti-malaria Abs and further encourage anti-PfRH5-based malaria prevention efforts.
Asunto(s)
Anticuerpos Neutralizantes/inmunología , Anticuerpos Antiprotozoarios/inmunología , Proteínas Portadoras/inmunología , Merozoítos/inmunología , Plasmodium falciparum/inmunología , Secuencia de Aminoácidos , Animales , Anticuerpos Monoclonales/química , Anticuerpos Monoclonales/inmunología , Anticuerpos Monoclonales/metabolismo , Anticuerpos Neutralizantes/metabolismo , Anticuerpos Antiprotozoarios/metabolismo , Proteínas Portadoras/metabolismo , Mapeo Epitopo , Epítopos/química , Epítopos/inmunología , Eritrocitos/inmunología , Eritrocitos/parasitología , Humanos , Cinética , Vacunas contra la Malaria/inmunología , Malaria Falciparum/inmunología , Ratones , Pruebas de Neutralización , Plasmodium falciparum/crecimiento & desarrollo , Unión Proteica/inmunología , ConejosRESUMEN
No vaccine has yet proven effective against the blood-stages of Plasmodium falciparum, which cause the symptoms and severe manifestations of malaria. We recently found that PfRH5, a P. falciparum-specific protein expressed in merozoites, is efficiently targeted by broadly-neutralizing, vaccine-induced antibodies. Here we show that antibodies against PfRH5 efficiently inhibit the in vitro growth of short-term-adapted parasite isolates from Cambodia, and that the EC(50) values of antigen-specific antibodies against PfRH5 are lower than those against PfAMA1. Since antibody responses elicited by multiple antigens are speculated to improve the efficacy of blood-stage vaccines, we conducted detailed assessments of parasite growth inhibition by antibodies against PfRH5 in combination with antibodies against seven other merozoite antigens. We found that antibodies against PfRH5 act synergistically with antibodies against certain other merozoite antigens, most notably with antibodies against other erythrocyte-binding antigens such as PfRH4, to inhibit the growth of a homologous P. falciparum clone. A combination of antibodies against PfRH4 and basigin, the erythrocyte receptor for PfRH5, also potently inhibited parasite growth. This methodology provides the first quantitative evidence that polyclonal vaccine-induced antibodies can act synergistically against P. falciparum antigens and should help to guide the rational development of future multi-antigen vaccines.
Asunto(s)
Anticuerpos Monoclonales de Origen Murino/inmunología , Anticuerpos Antiprotozoarios/inmunología , Antígenos de Protozoos/inmunología , Proteínas Portadoras/inmunología , Eritrocitos/inmunología , Merozoítos/inmunología , Plasmodium falciparum/inmunología , Proteínas Protozoarias/inmunología , Animales , Eritrocitos/parasitología , Humanos , Vacunas contra la Malaria/inmunología , Malaria Falciparum/inmunología , Malaria Falciparum/prevención & control , RatonesRESUMEN
Results from live-cell microscopy suggest that the behaviour of isolated components of the T-cell activation machinery in vitro does not represent the reality inside cells. Understanding the cellular-scale dynamics of microcluster migration can only be accomplished by in situ observation. Developments in 'super-resolution' microscopy have permitted investigators to move beyond tracking the movements of individual molecules, allowing the recognition of protein islands and nanodomains present in quiescent and active T cells. Many high-resolution techniques have their own susceptibilities to artefacts, so it is important to take a multifaceted approach to confirm results. A major challenge for the future will be to integrate all the new information into a coherent model of antigen recognition and T-cell activation.
Asunto(s)
Activación de Linfocitos/inmunología , Microscopía Fluorescente/métodos , Linfocitos T/inmunología , Animales , Transferencia Resonante de Energía de Fluorescencia/métodos , Humanos , Técnicas In Vitro , Cinética , Membrana Dobles de Lípidos , Complejo Mayor de Histocompatibilidad , Receptores de Antígenos de Linfocitos T/metabolismo , Linfocitos T/metabolismoRESUMEN
Current vaccine strategies against the asexual blood stage of Plasmodium falciparum are mostly focused on well-studied merozoite antigens that induce immune responses after natural exposure, but have yet to induce robust protection in any clinical trial. Here we compare human-compatible viral-vectored vaccines targeting ten different blood-stage antigens. We show that the full-length P. falciparum reticulocyte-binding protein homologue 5 (PfRH5) is highly susceptible to cross-strain neutralizing vaccine-induced antibodies, out-performing all other antigens delivered by the same vaccine platform. We find that, despite being susceptible to antibody, PfRH5 is unlikely to be under substantial immune selection pressure; there is minimal acquisition of anti-PfRH5 IgG antibodies in malaria-exposed Kenyans. These data challenge the widespread beliefs that any merozoite antigen that is highly susceptible to immune attack would be subject to significant levels of antigenic polymorphism, and that erythrocyte invasion by P. falciparum is a degenerate process involving a series of parallel redundant pathways.