ProC6C, a novel multi-stage malaria vaccine, elicits functional antibodies against the minor and central repeats of the Circumsporozoite Protein in human adults.

Introduction: ProC6C is a multi-stage malaria vaccine which includes Circumsporozoite Protein (PfCSP), Pfs48/45 and Pfs230 sequences, designed to elicit functional antibodies that prevent sporozoite invasion of human hepatocytes (PfCSP) and parasite development in mosquitoes (Pfs48/45 and Pfs230). ProC6C formulated on Alhydrogel was evaluated in combination with Matrix-M in a Phase 1 trial in Burkina Faso. The PfCSP antibody responses were assessed for magnitude, specificity, avidity and functionality.

Virus-like particle-based vaccines targeting the mosquito salivary protein, TRIO.

Malaria is a highly lethal infectious disease caused by parasites. These parasites are transmitted to vertebrate hosts when mosquitoes of the genus probe for a blood meal. Sporozoites, the infectious stage of , transit to the liver within hours of injection into the dermis.

Immature dendritic cell-targeting mRNA vaccine expressing PfCSP enhances protective immune responses against liver infection.

Resurgence in malaria has been noted in 2022 with 249 million clinical cases resulting in 608,000 deaths, mostly in children under five. Two vaccines, RTS, S, and more recently R21, targeting the circumsporozoite protein (CSP) are recommended by the WHO but are not yet widely available. Strong humoral responses to neutralize sporozoites before they can infect the hepatocytes are important for vaccine-mediated protection.

Hemozoin-induced IFN-γ production mediates innate immune protection against sporozoite infection.

Hemozoin is a crystal synthesized by Plasmodium parasites during hemoglobin digestion in the erythrocytic stage. The hemozoin released when the parasites egress from the red blood cell, which is complexed with parasite DNA, is cleared from the circulation by circulating and tissue-resident monocytes and macrophages, respectively. Recently, we reported that intravenous administration of purified hemozoin complexed with Plasmodium berghei DNA (Hz) resulted in an innate immune response that blocked liver stage development of sporozoites that was dose-dependent and time-limited.

Vaccines and monoclonal antibodies: new tools for malaria control.

SUMMARYMalaria remains one of the biggest health problems in the world. While significant reductions in malaria morbidity and mortality had been achieved from 2000 to 2015, the favorable trend has stalled, rather significant increases in malaria cases are seen in multiple areas. In 2022, there were 249 million estimated cases, and 608,000 malaria-related deaths, mostly in infants and children aged under 5 years, globally.

A candidate antibody drug for prevention of malaria.

Over 75% of malaria-attributable deaths occur in children under the age of 5 years. However, the first malaria vaccine recommended by the World Health Organization (WHO) for pediatric use, RTS,S/AS01 (Mosquirix), has modest efficacy. Complementary strategies, including monoclonal antibodies, will be important in efforts to eradicate malaria.

Molecular determinants of cross-reactivity and potency by VH3-33 antibodies against the Plasmodium falciparum circumsporozoite protein.

IGHV3-33-encoded antibodies are prevalent in the human humoral response against the Plasmodium falciparum circumsporozoite protein (PfCSP). Among VH3-33 antibodies, cross-reactivity between PfCSP major repeat (NANP), minor (NVDP), and junctional (NPDP) motifs is associated with high affinity and potent parasite inhibition. However, the molecular basis of antibody cross-reactivity and the relationship with efficacy remain unresolved.

Affinity-matured homotypic interactions induce spectrum of PfCSP structures that influence protection from malaria infection.

The generation of high-quality antibody responses to Plasmodium falciparum (Pf) circumsporozoite protein (PfCSP), the primary surface antigen of Pf sporozoites, is paramount to the development of an effective malaria vaccine. Here we present an in-depth structural and functional analysis of a panel of potent antibodies encoded by the immunoglobulin heavy chain variable (IGHV) gene IGHV3-33, which is among the most prevalent and potent antibody families induced in the anti-PfCSP immune response and targets the Asn-Ala-Asn-Pro (NANP) repeat region. Cryo-electron microscopy (cryo-EM) reveals a remarkable spectrum of helical antibody-PfCSP structures stabilized by homotypic interactions between tightly packed fragments antigen binding (Fabs), many of which correlate with somatic hypermutation.

Cytotoxicity of human antibodies targeting the circumsporozoite protein is amplified by 3D substrate and correlates with protection.

Human monoclonal antibodies (hmAbs) targeting the Plasmodium falciparum circumsporozoite protein (PfCSP) on the sporozoite surface are a promising tool for preventing malaria infection. However, their mechanisms of protection remain unclear. Here, using 13 distinctive PfCSP hmAbs, we provide a comprehensive view of how PfCSP hmAbs neutralize sporozoites in host tissues.

Plasmodium berghei Purified Hemozoin Associated with DNA Strongly Inhibits P. berghei Liver-Stage Development in BALB/c Mice after Intravenous Inoculation.

In the acidic lysosome-like digestive vacuole, parasites crystallize heme from hemoglobin into hemozoin, or malaria pigment. Upon release of progeny merozoites, the residual hemozoin is phagocytized by macrophages principally in the liver and spleen where the heme crystals can persist for months to years, as heme oxygenase does not readily degrade the crystal. Previous studies demonstrated hemozoin modulation of monocytes and macrophages.

Engineered DNA-encoded monoclonal antibodies targeting Plasmodium falciparum circumsporozoite protein confer single dose protection in a murine malaria challenge model.

Novel approaches for malaria prophylaxis remain important. Synthetic DNA-encoded monoclonal antibodies (DMAbs) are a promising approach to generate rapid, direct in vivo host-generated mAbs with potential benefits in production simplicity and distribution coupled with genetic engineering. Here, we explore this approach in a malaria challenge model.

A vaccine targeting the L9 epitope of the malaria circumsporozoite protein confers protection from blood-stage infection in a mouse challenge model.

Pre-erythrocytic malaria vaccines that induce high-titer, durable antibody responses can potentially provide protection from infection. Here, we engineered a virus-like particle (VLP)-based vaccine targeting a recently described vulnerable epitope at the N-terminus of the central repeat region of the Plasmodium falciparum circumsporozoite protein that is recognized by the potently inhibitory monoclonal antibody L9 and show that immunization with L9 VLPs induces strong antibody responses that provide protection from blood-stage malaria in a mouse infection model.

The light chain of the L9 antibody is critical for binding circumsporozoite protein minor repeats and preventing malaria.

L9 is a potent human monoclonal antibody (mAb) that preferentially binds two adjacent NVDP minor repeats and cross-reacts with NANP major repeats of the Plasmodium falciparum circumsporozoite protein (PfCSP) on malaria-infective sporozoites. Understanding this mAb's ontogeny and mechanisms of binding PfCSP will facilitate vaccine development. Here, we isolate mAbs clonally related to L9 and show that this B cell lineage has baseline NVDP affinity and evolves to acquire NANP reactivity.

Chemoprophylaxis vaccination with a Plasmodium liver stage autophagy mutant affords enhanced and long-lasting protection.

Genetically attenuated sporozoite vaccines can elicit long-lasting protection against malaria but pose risks of breakthrough infection. Chemoprophylaxis vaccination (CVac) has proven to be the most effective vaccine strategy against malaria. Here, we demonstrate that a liver stage-specific autophagy mutant of Plasmodium berghei (ATG8 overexpressor), when used as a live vaccine under a CVac regimen, provides superior long-lasting protection, in both inbred and outbred mice, as compared to WT-CVac.

Structural and biophysical correlation of anti-NANP antibodies with in vivo protection against P. falciparum.

The most advanced P. falciparum circumsporozoite protein-based malaria vaccine, RTS,S/AS01 (RTS,S), confers partial protection but with antibody titers that wane relatively rapidly, highlighting the need to elicit more potent and durable antibody responses. Here, we elucidate crystal structures, binding affinities and kinetics, and in vivo protection of eight anti-NANP antibodies derived from an RTS,S phase 2a trial and encoded by three different heavy-chain germline genes.

Enhancing durability of CIS43 monoclonal antibody by Fc mutation or AAV delivery for malaria prevention.

CIS43 is a potent neutralizing human mAb that targets a highly conserved "junctional" epitope in the Plasmodium falciparum (Pf) circumsporozoite protein (PfCSP). Enhancing the durability of CIS43 in vivo will be important for clinical translation. Here, 2 approaches were used to improve the durability of CIS43 in vivo while maintaining potent neutralization.

A Potent Anti-Malarial Human Monoclonal Antibody Targets Circumsporozoite Protein Minor Repeats and Neutralizes Sporozoites in the Liver.

Discovering potent human monoclonal antibodies (mAbs) targeting the Plasmodium falciparum circumsporozoite protein (PfCSP) on sporozoites (SPZ) and elucidating their mechanisms of neutralization will facilitate translation for passive prophylaxis and aid next-generation vaccine development. Here, we isolated a neutralizing human mAb, L9 that preferentially bound NVDP minor repeats of PfCSP with high affinity while cross-reacting with NANP major repeats. L9 was more potent than six published neutralizing human PfCSP mAbs at mediating protection against mosquito bite challenge in mice.

A high-affinity antibody against the CSP N-terminal domain lacks Plasmodium falciparum inhibitory activity.

Malaria is a global health concern, and research efforts are ongoing to develop a superior vaccine to RTS,S/AS01. To guide immunogen design, we seek a comprehensive understanding of the protective humoral response against Plasmodium falciparum (Pf) circumsporozoite protein (PfCSP). In contrast to the well-studied responses to the repeat region and the C-terminus, the antibody response against the N-terminal domain of PfCSP (N-CSP) remains obscure.

Mapping functional humoral correlates of protection against malaria challenge following RTS,S/AS01 vaccination.

Vaccine development has the potential to be accelerated by coupling tools such as systems immunology analyses and controlled human infection models to define the protective efficacy of prospective immunogens without expensive and slow phase 2b/3 vaccine studies. Among human challenge models, controlled human malaria infection trials have long been used to evaluate candidate vaccines, and RTS,S/AS01 is the most advanced malaria vaccine candidate, reproducibly demonstrating 40 to 80% protection in human challenge studies in malaria-naïve individuals. Although antibodies are critical for protection after RTS,S/AS01 vaccination, antibody concentrations are inconsistently associated with protection across studies, and the precise mechanism(s) by which vaccine-induced antibodies provide protection remains enigmatic.