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Monoclonal antibodies are highly specific proteins that are cloned from a single B cell and bind to a single epitope on a pathogen. These laboratory-made molecules can serve as prophylactics or therapeutics for infectious diseases and have an impressive capacity to modulate the progression of disease, as demonstrated for the first time on a large scale during the COVID-19 pandemic. The high specificity and natural starting point of monoclonal antibodies afford an encouraging safety profile, yet the high cost of production remains a major limitation to their widespread use. While a monoclonal antibody approach to abrogating malaria infection is not yet available, the unique life cycle of the malaria parasite affords many opportunities for such proteins to act, and preliminary research into the efficacy of monoclonal antibodies in preventing malaria infection, disease, and transmission is encouraging. This review examines the current status and future outlook for monoclonal antibodies against malaria in the context of the complex life cycle and varied antigenic targets expressed in the human and mosquito hosts, and provides insight into the strengths and limitations of this approach to curtailing one of humanity's oldest and deadliest diseases.

Mycoplasma hyorhinis (Mhr) is a pathogen of pigs causing polyserositis and polyarthritis. The most susceptible population are nursery pigs of approximately 7 weeks of age, although we have shown that clinical signs can persist into finishing aged animals after a late-nursery infection. We have previously demonstrated the efficacy of a novel inactivated Mhr vaccine for the reduction of lameness and polyserositis in caesarian-derived colostrum-deprived (CDCD) pigs vaccinated at 3 weeks and challenged with Mhr at 6 weeks of age. Here we evaluated the duration of immunity (DOI) of the same vaccine. Vaccine or placebo was administered to CDCD pigs at 3 weeks of age. Pigs were challenged with Mhr at either 10 weeks of age (=7 week DOI) or 13 weeks of age (=10 week DOI). In the 7 week DOI, vaccination provided significant reductions in lameness (p = 0.0018), arthritis (p = 0.0002), and pericarditis (p = 0.0312) versus the placebo control. In the 10 week DOI, a significant reduction in arthritis (p = 0.0320) was observed in the vaccine group as compared to the placebo group. Both vaccine groups showed a significant increase (p

CD8 T cells have long been known to target infected hepatocytes during the intracellular liver stages of Plasmodium—the causative agent of malaria. Current T cell vaccine strategies are limited by the inability to obtain sufficient amounts of Plasmodium-infected hepatocytes to identify peptides presented on MHC-I (“immunopeptidomics”). Recently, we demonstrated that the blood stages of Plasmodium vivax are also susceptible to CD8 T cell killing and performed immunopeptidomics on Pv-infected reticulocytes. Peptides mapped to proteins conserved across Plasmodium spp. and were common across volunteers. Furthermore, ~50% of the peptides detected are not predicted to bind classical HLA-I molecules and thus could be presented by non-classical HLA. In support of this, blocking HLA-E during in vitro stimulation of PBMCs with a pool of newly-identified peptides substantially reduced the CD8 T cell response. Mechanistic studies conducted in the rhesus macaque/P. cynomolgi malaria model demonstrated that CD8 T cell killing of infected reticulocytes is conserved in this model as are CD8 responses to the newly identified peptides. In vitrostimulation assays showed that CD8 T cell responses to at least 3 of 9 peptides tested are completely restricted to MHC-E. This is supported by in vitro binding assays showing peptide binding to HLA-E. In summary, we demonstrate for the first time that malaria infection induces HLA/MHC-E-restricted CD8 T cell responses to newly identified peptides that are conserved across host and parasite species. Given the extreme conservation of MHC-E, these results pave the way to explore a universal, species-transcending vaccine for malaria based on MHC-E presentation of novel antigens.

BackgroundThe potential benefits of long-acting injectable chemoprotection (LAI-C) against malaria have been recently recognized, prompting a call for suitable candidate drugs to help meet this need. On the basis of its known pharmacodynamic and pharmacokinetic profiles after oral dosing, ELQ-331, a prodrug of the parasite mitochondrial electron transport inhibitor ELQ-300, was selected for study of pharmacokinetics and efficacy as LAI-C in mice.MethodsFour trials were conducted in which mice were injected with a single intramuscular dose of ELQ-331 or other ELQ-300 prodrugs in sesame oil with 1.2% benzyl alcohol; the ELQ-300 content of the doses ranged from 2.5 to 30 mg/kg. Initial blood stage challenges with Plasmodium yoelii were used to establish the model, but the definitive study measure of efficacy was outcome after sporozoite challenge with a luciferase-expressing P.yoelii, assessed by whole-body live animal imaging. Snapshot determinations of plasma ELQ-300 concentration ([ELQ-300]) were made after all prodrug injections; after the highest dose of ELQ-331 (equivalent to 30 mg/kg ELQ-300), both [ELQ-331] and [ELQ-300] were measured at a series of timepoints from 6 hours to 5 ½ months after injection.ResultsA single intramuscular injection of ELQ-331 outperformed four other ELQ-300 prodrugs and, at a dose equivalent to 30 mg/kg ELQ-300, protected mice against challenge with P. yoelii sporozoites for at least 4 ½ months. Pharmacokinetic evaluation revealed rapid and essentially complete conversion of ELQ-331 to ELQ-300, a rapidly achieved (< 6 hours) and sustained (4-5 months) effective plasma ELQ-300 concentration, maximum ELQ-300 concentrations far below the estimated threshold for toxicity, and a distinctive ELQ-300 concentration vs. time profile. Pharmacokinetic modeling indicates a high-capacity, slow-exchange tissue compartment which serves to accumulate and then slowly redistribute ELQ-300 into blood, and this property facilitates an extremely long period during which ELQ-300 concentration is sustained above a minimum fully-protective threshold (60-80 nM).ConclusionsExtrapolation of these results to humans clearly predicts that ELQ-331 should be capable of meeting and far-exceeding currently published duration-of-effect goals for antimalarial LAI-C. Allometric scaling from mice to humans would predict a several-fold enhancement in the relationship between duration-of-effect and dose, and available drug engineering and formulation technologies would be expected to offer significant improvement over the simple powder in sesame oil used here. Furthermore, the distinctive pharmacokinetic profile of ELQ-300 after treatment with ELQ-331 may facilitate durable protection using a variety of delivery and formulation options, and may enable protection for far longer than 3 months. Particularly in light of the favorable pharmacodynamic profile of ELQ-300, ELQ-331 warrants consideration as a leading prototype for LAI-C.

This study investigated the influence of gut microbiome composition in modulating susceptibility toMycoplasma hyopneumoniaein pigs. Thirty-two conventionalM. hyopneumoniaefree piglets were randomly selected from six different litters at 3 weeks of age and were experimentally inoculated withM. hyopneumoniaeat 8 weeks of age. Lung lesion scores (LS) were recorded 4 weeks post-inoculation (12 weeks of age) from piglet lungs at necropsy. Fecal bacterial community composition of piglets at 3, 8 and 12 weeks of age were targeted by amplifying the V3–V4 region of the 16S rRNA gene. The LS ranged from 0.3 to 43% with an evident clustering of the scores observed in piglets within litters. There were significant differences in species richness and alpha diversity in fecal microbiomes among piglets within litters at different time points (p M. hyopneumoniaeassociated lesions were identified. The microbial shift at 3 weeks of age was observed to be driven by the increase in abundance of the indicator family, Ruminococcaceae in piglets with low LS (p Ruminococcus_2 having the highest richness scores, correlated significantly between litters showing stronger associations with the lowest LS (r = −0.49,p = 0.005). These findings suggest that early life gut microbiota can be a potential determinant forM. hyopneumoniaesusceptibility in pigs.

Within the liver, Plasmodium sporozoites traverse cells searching for a "suitable" hepatocyte, invading these cells through a process that results in the formation of a parasitophorous vacuole (PV), within which the parasite undergoes intracellular replication as a liver stage. It was previously established that two members of the Plasmodium s48/45 protein family, P36 and P52, are essential for productive invasion of host hepatocytes by sporozoites as their simultaneous deletion results in growth-arrested parasites that lack a PV. Recent studies point toward a pathway of entry possibly involving the interaction of P36 with hepatocyte receptors EphA2, CD81, and SR-B1. However, the relationship between P36 and P52 during sporozoite invasion remains unknown. Here we show that parasites with a single P52 or P36 gene deletion each lack a PV after hepatocyte invasion, thereby pheno-copying the lack of a PV observed for the P52/P36 dual gene deletion parasite line. This indicates that both proteins are equally important in the establishment of a PV and act in the same pathway. We created a Plasmodium yoelii P36mCherry tagged parasite line that allowed us to visualize the subcellular localization of P36 and found that it partially co-localizes with P52 in the sporozoite secretory microneme organelles. Furthermore, through co-immunoprecipitation studies in vivo, we determined that P36 and P52 form a protein complex in sporozoites, indicating a concerted function for both proteins within the PV formation pathway. However, upon sporozoite stimulation, only P36 was released as a secreted protein while P52 was not. Our results support a model in which the putatively glycosylphosphatidylinositol (GPI)-anchored P52 may serve as a scaffold to facilitate the interaction of secreted P36 with the host cell during sporozoite invasion of hepatocytes.

Within the liver, Plasmodium sporozoites traverse cells searching for a “suitable” hepatocyte, invading these cells through a process that results in the formation of a parasitophorous vacuole (PV), within which the parasite undergoes intracellular replication as a liver stage. It was previously established that two members of the Plasmodium s48/45 protein family, P36 and P52, are essential for productive invasion of host hepatocytes by sporozoites as their simultaneous deletion results in growth-arrested parasites that lack a PV. Recent studies point toward a pathway of entry possibly involving the interaction of P36 with hepatocyte receptors EphA2, CD81, and SR-B1. However, the relationship between P36 and P52 during sporozoite invasion remains unknown. Here we show that parasites with a single P52 or P36 gene deletion each lack a PV after hepatocyte invasion, thereby pheno-copying the lack of a PV observed for the P52/P36 dual gene deletion parasite line. This indicates that both proteins are equally important in the establishment of a PV and act in the same pathway. We created a Plasmodium yoelii P36mCherry tagged parasite line that allowed us to visualize the subcellular localization of P36 and found that it partially co-localizes with P52 in the sporozoite secretory microneme organelles. Furthermore, through co-immunoprecipitation studies in vivo, we determined that P36 and P52 form a protein complex in sporozoites, indicating a concerted function for both proteins within the PV formation pathway. However, upon sporozoite stimulation, only P36 was released as a secreted protein while P52 was not. Our results support a model in which the putatively glycosylphosphatidylinositol (GPI)-anchored P52 may serve as a scaffold to facilitate the interaction of secreted P36 with the host cell during sporozoite invasion of hepatocytes.

Gliding motility and cell traversal by the Plasmodium ookinete and sporozoite invasive stages allow penetration of cellular barriers to establish infection of the mosquito vector and mammalian host, respectively. Motility and traversal are not observed in red cell infectious merozoites, and we have previously classified genes that are expressed in sporozoites but not merozoites (S genes) in order to identify proteins involved in these processes. The S4 gene has been described as criticaly involved in Cell Traversal for Ookinetes and Sporozoites (CelTOS), yet knockout parasites (s4/celtos¯) do not generate robust salivary gland sporozoite numbers, precluding a thorough analysis of S4/CelTOS function during host infection. We show here that a failure of oocysts to develop or survive in the midgut contributes to the poor mosquito infection by Plasmodium yoelii (Py) s4/celtos¯ rodent malaria parasites. We rescued this phenotype by expressing S4/CelTOS under the ookinete-specific circumsporozoite protein and thrombospondin-related anonymous protein-related protein (CTRP) promoter (S4/CelTOSCTRP ), generating robust numbers of salivary gland sporozoites lacking S4/CelTOS that were suitable for phenotypic analysis. Py S4/CelTOSCTRP sporozoites showed reduced infectivity in BALB/c mice when compared to wild-type sporozoites, although they appeared more infectious than sporozoites deficient in the related traversal protein PLP1/SPECT2 (Py plp1/spect2¯). Using in vitro assays, we substantiate the role of S4/CelTOS in sporozoite cell traversal, but also uncover a previously unappreciated role for this protein for sporozoite gliding motility.

The reflection from an array of narrow series slots on the broad face of a rectangular waveguide is used to determine the permittivity of lossy materials. The theoretical study of the electromagnetic field in the vicinity of the slots yields a system of integral equations which takes into account the internal and external coupling between slots. The numerical solution is discussed and an optimization procedure for the array is presented, which provides a simple relationship linking the reflection coefficient to the complex permittivity over a specified range. Computed results are compared to experimental values for air and a lossy dielectric at 10 GHz, showing good agreement. Interpolation from computed data is provided by a polynomial expansion: this allows one to determine the complex permittivity once the reflection factor has been measured.