Single immunization with genetically attenuated Pf∆mei2 (GA2) parasites by mosquito bite in controlled human malaria infection: a placebo-controlled randomized trial.

Malaria vaccines consisting of metabolically active Plasmodium falciparum (Pf) sporozoites can offer improved protection compared with currently deployed subunit vaccines. In a previous study, we demonstrated the superior protective efficacy of a three-dose regimen of late-arresting genetically attenuated parasites administered by mosquito bite (GA2-MB) compared with early-arresting counterparts (GA1-MB) against a homologous controlled human malaria infection. Encouraged by these results, we explored the potency of a single GA2-MB immunization in a placebo-controlled randomized trial.

Safety and Efficacy of Immunization with a Late-Liver-Stage Attenuated Malaria Parasite.

Background: Currently licensed and approved malaria subunit vaccines provide modest, short-lived protection against malaria. Immunization with live-attenuated malaria parasites is an alternative vaccination strategy that has potential to improve protection.

Methods: We conducted a double-blind, controlled clinical trial to evaluate the safety, side-effect profile, and efficacy of immunization, by means of mosquito bites, with a second-generation genetically attenuated parasite (GA2) - a single knockout NF54 parasite (sporozoite form) with extended development into the liver stage.

Experimental vaccination by single dose sporozoite injection of blood-stage attenuated malaria parasites.

Malaria vaccination approaches using live Plasmodium parasites are currently explored, with either attenuated mosquito-derived sporozoites or attenuated blood-stage parasites. Both approaches would profit from the availability of attenuated and avirulent parasites with a reduced blood-stage multiplication rate. Here we screened gene-deletion mutants of the rodent parasite P.

Variable long-term protection by radiation-, chemo-, and genetically-attenuated Plasmodium berghei sporozoite vaccines.

Long-term protection against malaria remains one of the greatest challenges of vaccination against this deadly parasitic disease. Whole-sporozoite (WSp) malaria vaccine formulations, which target the Plasmodium parasite's pre-erythrocytic stages, include radiation-attenuated sporozoites (RAS), early- and late-arresting genetically-attenuated parasites (EA-GAP and LA-GAP, respectively), and chemoprophylaxis with sporozoites (CPS). Although all these four vaccine formulations induce protective immune responses in the clinic, data on the longevity of the antimalarial protection they afford remain scarce.

The effect of dosage on the protective efficacy of whole-sporozoite formulations for immunization against malaria.

Immunization with Plasmodium sporozoites, either attenuated or administered under the cover of an antimalarial drug, can induce strong protection against malaria in pre-clinical murine models, as well as in human trials. Previous studies have suggested that whole-sporozoite (WSpz) formulations based on parasites with longer liver stage development induce higher protection, but a comparative analysis of four different WSpz formulations has not been reported. We employed a rodent model of malaria to analyze the effect of immunization dosage on the protective efficacy of WSpz formulations consisting of (i) early liver arresting genetically attenuated parasites (EA-GAP) or (ii) radiation-attenuated sporozoites (RAS), (iii) late arresting GAP (LA-GAP), and (iv) sporozoites administered under chemoprophylaxis, that are eliminated upon release into the bloodstream (CPS).

Sporozoite immunization: innovative translational science to support the fight against malaria.

Introduction: Malaria, a devastating febrile illness caused by protozoan parasites, sickened 247,000,000 people in 2021 and killed 619,000, mostly children and pregnant women in sub-Saharan Africa. A highly effective vaccine is urgently needed, especially for (Pf), the deadliest human malaria parasite.

Areas Covered: Sporozoites (SPZ), the parasite stage transmitted by mosquitoes to humans, are the only vaccine immunogen achieving >90% efficacy against Pf infection.

curtails autoimmune nephritis via lasting bone marrow alterations, independent of hemozoin accumulation.

The host response against infection with commonly raises self-reactivity as a side effect, and antibody deposition in kidney has been cited as a possible cause of kidney injury during severe malaria. In contrast, animal models show that infection with the parasite confers long-term protection from lethal lupus nephritis initiated by autoantibody deposition in kidney. We have limited knowledge of the factors that make parasite infection more likely to induce kidney damage in humans, or the mechanisms underlying protection from autoimmune nephritis in animal models.

Glycosylated nanoparticle-based PfCSP vaccine confers long-lasting antibody responses and sterile protection in mouse malaria model.

The development of an effective and durable vaccine remains a central goal in the fight against malaria. Circumsporozoite protein (CSP) is the major surface protein of sporozoites and the target of the only licensed Plasmodium falciparum (Pf) malaria vaccine, RTS,S/AS01. However, vaccine efficacy is low and short-lived, highlighting the need for a second-generation vaccine with superior efficacy and durability.

Exploring expression and immune potency in mice using mRNA encoding the malaria antigen, CelTOS.

The secreted malarial protein, Cell-Traversal protein for Ookinetes and Sporozoites (CelTOS), is highly conserved among species, and plays a role in the invasion of mosquito midgut cells and hepatocytes in the vertebrate host. CelTOS was identified as a potential protective antigen based on a proteomic analysis, which showed that CelTOS stimulated significant effector T cells producing IFN-γ in peripheral blood mononuclear cells (PBMCs) from radiation attenuated sporozoite-immunized, malaria-naïve human subjects. In a rodent malaria model, recombinant full-length CelTOS protein/adjuvant combinations induced sterile protection, and in several studies, functional antibodies were produced that had hepatocyte invasion inhibition and transmission-blocking activities.

A genetically modified Plasmodium berghei parasite as a surrogate for whole-sporozoite vaccination against P. vivax malaria.

Two malaria parasite species, Plasmodium falciparum (Pf) and P. vivax (Pv) are responsible for most of the disease burden caused by malaria. Vaccine development against this disease has focused mainly on Pf.

Creation and preclinical evaluation of genetically attenuated malaria parasites arresting growth late in the liver.

Whole-sporozoite (WSp) malaria vaccines induce protective immune responses in animal malaria models and in humans. A recent clinical trial with a WSp vaccine comprising genetically attenuated parasites (GAP) which arrest growth early in the liver (PfSPZ-GA1), showed that GAPs can be safely administered to humans and immunogenicity is comparable to radiation-attenuated PfSPZ Vaccine. GAPs that arrest late in the liver stage (LA-GAP) have potential for increased potency as shown in rodent malaria models.

Malaria parasite evades mosquito immunity by glutaminyl cyclase-mediated posttranslational protein modification.

Glutaminyl cyclase (QC) modifies N-terminal glutamine or glutamic acid residues of target proteins into cyclic pyroglutamic acid (pGlu). Here, we report the biochemical and functional analysis of QC. We show that sporozoites of QC-null mutants of rodent and human malaria parasites are recognized by the mosquito immune system and melanized when they reach the hemocoel.

Suppression of Plasmodium MIF-CD74 signaling protects against severe malaria.

The deadliest complication of infection by Plasmodium parasites, cerebral malaria, accounts for the majority of malarial fatalities. Although our understanding of the cellular and molecular mechanisms underlying the pathology remains incomplete, recent studies support the contribution of systemic and neuroinflammation as the cause of cerebral edema and blood-brain barrier (BBB) dysfunction. All Plasmodium species encode an orthologue of the innate cytokine, Macrophage Migration Inhibitory Factor (MIF), which functions in mammalian biology to regulate innate responses.

A universal vaccine candidate against Plasmodium vivax malaria confers protective immunity against the three PvCSP alleles.

Malaria is a highly prevalent parasitic disease in regions with tropical and subtropical climates worldwide. Among the species of Plasmodium causing human malaria, P. vivax is the second most prevalent and the most geographically widespread species.

Hemozoin-mediated inflammasome activation limits long-lived anti-malarial immunity.

During acute malaria, most individuals mount robust inflammatory responses that limit parasite burden. However, long-lived sterilizing anti-malarial memory responses are not efficiently induced, even following repeated Plasmodium exposures. Using multiple Plasmodium species, genetically modified parasites, and combinations of host genetic and pharmacologic approaches, we find that the deposition of the malarial pigment hemozoin directly limits the abundance and capacity of conventional type 1 dendritic cells to prime helper T cell responses.

Messenger RNA expressing PfCSP induces functional, protective immune responses against malaria in mice.

Human malaria affects the vast majority of the world's population with the Plasmodium falciparum species causing the highest rates of morbidity and mortality. With no licensed vaccine and leading candidates achieving suboptimal protection in the field, the need for an effective immunoprophylactic option continues to motivate the malaria research community to explore alternative technologies. Recent advances in the mRNA discipline have elevated the long-neglected platform to the forefront of infectious disease research.

Dissection-independent production of sporozoites from whole mosquitoes.

Progress towards a protective vaccine against malaria remains slow. To date, only limited protection has been routinely achieved following immunisation with either whole-parasite (sporozoite) or subunit-based vaccines. One major roadblock to vaccine progress, and to pre-erythrocytic parasite biology in general, is the continued reliance on manual salivary gland dissection for sporozoite isolation from infected mosquitoes.

A Hetero-Multimeric Chitinase-Containing and Ookinete-Secreted Protein Complex Involved in Mosquito Midgut Invasion.

Malaria parasites are transmitted by  mosquitoes. During its life cycle in the mosquito vector the ookinete escapes the proteolytic milieu of the post-blood meal midgut by traversing the midgut wall. This process requires penetration of the chitin-containing peritrophic matrix lining the midgut epithelium, which depends in part on ookinete-secreted chitinases.

Generation of a Genetically Modified Chimeric Parasite Expressing Circumsporozoite Protein for Malaria Vaccine Development.

Chimeric rodent malaria parasites with the endogenous circumsporozoite protein () gene replaced with from the human parasites () and () are used in preclinical evaluation of CSP vaccines. Chimeric rodent parasites expressing CSP have also been assessed as whole sporozoite (WSP) vaccines. Comparable chimeric parasites expressing CSP of could be used both for clinical evaluation of vaccines targeting CSP in controlled human infections and in WSP vaccines targeting and .

Artemisinin exposure at the ring or trophozoite stage impacts sexual conversion differently.

Malaria transmission is dependent on the formation of gametocytes in the human blood. The sexual conversion rate, the proportion of asexual parasites that convert into gametocytes at each multiplication cycle, is variable and reflects the relative parasite investment between transmission and maintaining the infection. The impact of environmental factors such as drugs on sexual conversion rates is not well understood.

Plasmodium berghei sporozoites in nonreplicative vacuole are eliminated by a PI3P-mediated autophagy-independent pathway.

The protozoan parasite Plasmodium, causative agent of malaria, invades hepatocytes by invaginating the host cell plasma membrane and forming a parasitophorous vacuole membrane (PVM). Surrounded by this PVM, the parasite undergoes extensive replication. Parasites inside a PVM provoke the Plasmodium-associated autophagy-related (PAAR) response.

Generation of Novel NF135 and NF54 Lines Expressing Fluorescent Reporter Proteins Under the Control of Strong and Constitutive Promoters.

Transgenic reporter lines of malaria parasites that express fluorescent or luminescent proteins are valuable tools for drug and vaccine screening assays as well as to interrogate parasite gene function. Different ( ) reporter lines exist, however nearly all have been created in the African NF54/3D7 laboratory strain. Here we describe the generation of novel reporter lines, using CRISPR/Cas9 gene modification, both in the standard NF54 background and in a recently described Cambodian NF135.