Baculovirus-Induced Fast-Acting Innate Immunity Kills Liver-Stage Plasmodium

Evaluation of the antiplasmodial and anti-Toxoplasma activities of several Indonesian medicinal plant extracts

ETHNOPHARMACOLOGICAL RELEVANCE

Malaria, caused by Plasmodium parasites, remains a significant global health challenge, particularly in tropical and subtropical regions. At the same time, the prevalence of toxoplasmosis has been reported to be 30% worldwide. Traditional medicines have long played a vital role in discovering and developing novel drugs, and this approach is essential in the face of increasing resistance to current antimalarial and anti-Toxoplasma drugs. In Indonesian traditional medicine, various plants are used for their therapeutic properties. This study focuses on eleven medicinal plants from which nineteen extracts were obtained and screened for their potential medicinal benefits against malaria and toxoplasmosis.

AIMS OF THE STUDY

The aim of this study was to evaluate the efficacy of extracts from Indonesian medicinal plants to inhibit Plasmodium falciparum, a parasite responsible for malaria, and Toxoplasma gondii, an opportunistic parasite responsible for toxoplasmosis.

METHODS

Nineteen extracts from eleven plants were subjected to in vitro screening against P. falciparum 3D7 (a chloroquine-sensitive strain) and the T. gondii RH strain. In vitro treatments were conducted on P. falciparum 3D7 and K1 (multidrug-resistant strains) using the potent extracts, and in vivo assessments were carried out with mice infected with P. yoelii 17XNL. LCMS analysis was also conducted to identify the main components of the most effective extract.

RESULTS

Seven extracts showed significant antiplasmodial activity (>80% inhibition) at a concentration of 100 μg/ml. These extracts were obtained from Dysoxylum parasiticum (Osbeck) Kosterm., Elaeocarpus glaber (Bl.) Bijdr., Eleutherine americana Merr., Kleinhovia hospita L., Peronema canescens Jack, and Plectranthus scutellarioides (L.) R.Br. Notably, the D. parasiticum ethyl acetate extract exhibited high selectivity and efficacy both in vitro and in vivo. Herein, the key active compounds oleamide and erucamide were identified, which had IC50 values (P. falciparum 3D7/K1) of 17.49/23.63 μM and 32.49/51.59 μM, respectively.

CONCLUSIONS

The results of this study highlight the antimalarial potential of plant extracts collected from Indonesia. Particularly, extracts from D. parasiticum EtOH and EtOAc stood out for their low toxicity and strong antiplasmodial properties, with the EtOAc extract emerging as a notably promising antimalarial candidate. Key compounds identified within this extract demonstrate the complexity of extracts' action against malaria, potentially targeting both the parasite and the host. This suggests a promising approach for developing new antimalarial strategies that tackle the multifaceted challenges of drug resistance and disease management. Future investigations are necessary to unlock the full therapeutic potential of these extracts.

A two-dose viral-vectored Plasmodium vivax multistage vaccine confers durable protection and transmission-blockade in a pre-clinical study

Among Plasmodium spp. responsible for human malaria, Plasmodium vivax ranks as the second most prevalent and has the widest geographical range; however, vaccine development has lagged behind that of Plasmodium falciparum, the deadliest Plasmodium species. Recently, we developed a multistage vaccine for P. falciparum based on a heterologous prime-boost immunization regimen utilizing the attenuated vaccinia virus strain LC16m8Δ (m8Δ)-prime and adeno-associated virus type 1 (AAV1)-boost, and demonstrated 100% protection and more than 95% transmission-blocking (TB) activity in the mouse model. In this study, we report the feasibility and versatility of this vaccine platform as a P. vivax multistage vaccine, which can provide 100% sterile protection against sporozoite challenge and >95% TB efficacy in the mouse model. Our vaccine comprises m8Δ and AAV1 viral vectors, both harboring the gene encoding two P. vivax circumsporozoite (PvCSP) protein alleles (VK210; PvCSP-Sal and VK247; -PNG) and P25 (Pvs25) expressed as a Pvs25-PvCSP fusion protein. For protective efficacy, the heterologous m8Δ-prime/AAV1-boost immunization regimen showed 100% (short-term; Day 28) and 60% (long-term; Day 242) protection against PvCSP VK210 transgenic Plasmodium berghei sporozoites. For TB efficacy, mouse sera immunized with the vaccine formulation showed >75% TB activity and >95% transmission reduction activity by a direct membrane feeding assay using P. vivax isolates in blood from an infected patient from the Brazilian Amazon region. These findings provide proof-of-concept that the m8Δ/AAV1 vaccine platform is sufficiently versatile for P. vivax vaccine development. Future studies are needed to evaluate the safety, immunogenicity, vaccine efficacy, and synergistic effects on protection and transmission blockade in a non-human primate model for Phase I trials.

Potential Epha2 Receptor Blockers Involved in Cerebral Malaria from Taraxacum officinale, Tinospora cordifolia, Rosmarinus officinalis and Ocimum basilicum: A Computational Approach

Cerebral malaria (CM) is a severe manifestation of parasite infection caused by Plasmodium species. In 2018, there were approximately 228 million malaria cases worldwide, resulting in about 405,000 deaths. Survivors of CM may live with lifelong post-CM consequences apart from an increased risk of childhood neurodisability. EphA2 receptors have been linked to several neurological disorders and have a vital role in the CM-associated breakdown of the blood-brain barrier. Molecular docking (MD) studies of phytochemicals from Taraxacum officinale, Tinospora cordifolia, Rosmarinus officinalis, Ocimum basilicum, and the native ligand ephrin-A were conducted to identify the potential blockers of the EphA2 receptor. The software program Autodock Vina 1.1.2 in PyRx-Virtual Screening Tool and BIOVIA Discovery Studio visualizer was used for this MD study. The present work showed that blocking the EphA2 receptor by these phytochemicals prevents endothelial cell apoptosis by averting ephrin-A ligand-expressing CD8+ T cell bioadhesion. These phytochemicals showed excellent docking scores and binding affinity, demonstrating hydrogen bond, electrostatic, Pi-sigma, and pi alkyl hydrophobic binding interactions when compared with native ligands at the EphA2 receptor. The comparative MD study using two PDB IDs showed that isocolumbin, carnosol, luteolin, and taraxasterol have better binding affinities (viz. -9.3, -9.0, -9.5, and -9.2 kcal/mol, respectively). Ocimum basilicum phytochemicals showed a lower docking score but more binding interactions than native ligands at the EphA2 receptor for both PDB IDs. This suggests that these phytochemicals may serve as potential drug candidates in the management of CM. We consider that the present MD study provides leads in drug development by targeting the EphA2 receptor in managing CM. The approach is innovative because a role for EphA2 receptors in CM has never been highlighted.

Adeno-associated virus-based malaria booster vaccine following attenuated replication-competent vaccinia virus LC16m8Δ priming

We previously demonstrated that boosting with adeno-associated virus (AAV) type 1 (AAV1) can induce highly effective and long-lasting protective immune responses against malaria parasites when combined with replication-deficient adenovirus priming in a rodent model. In the present study, we compared the efficacy of two different AAV serotypes, AAV1 and AAV5, as malaria booster vaccines following priming with the attenuated replication-competent vaccinia virus strain LC16m8Δ (m8Δ), which harbors the fusion gene encoding both the pre-erythrocytic stage protein, Plasmodium falciparum circumsporozoite (PfCSP) and the sexual stage protein (Pfs25) in a two-dose heterologous prime-boost immunization regimen. Both regimens, m8Δ/AAV1 and m8Δ/AAV5, induced robust anti-PfCSP and anti-Pfs25 antibodies. To evaluate the protective efficacy, the mice were challenged with sporozoites twice after immunization. At the first sporozoite challenge, m8Δ/AAV5 achieved 100% sterile protection whereas m8Δ/AAV1 achieved 70% protection. However, at the second challenge, 100% of the surviving mice from the first challenge were protected in the m8Δ/AAV1 group whereas only 55.6% of those in the m8Δ/AAV5 group were protected. Regarding the transmission-blocking efficacy, we found that both immunization regimens induced high levels of transmission-reducing activity (>99%) and transmission-blocking activity (>95%). Our data indicate that the AAV5-based multistage malaria vaccine is as effective as the AAV1-based vaccine when administered following an m8Δ-based vaccine. These results suggest that AAV5 could be a viable alternate vaccine vector as a malaria booster vaccine.

TLR9 signalling inhibits Plasmodium liver infection by macrophage activation

Recognition of pathogen-associated molecular patterns (PAMPs) through Toll-like receptors (TLRs) plays a pivotal role in first-line pathogen defense. TLRs are also likely triggered during a Plasmodium infection in vivo by parasite-derived components. However, the contribution of innate responses to liver infection and to the subsequent clinical outcome of a blood infection is not well understood. To assess the potential effects of enhanced TLR-signalling on Plasmodium infection, we systematically examined the effect of agonist-primed immune responses to sporozoite inoculation in the P. berghei/C57Bl/6 murine malaria model. We could identify distinct stage-specific effects on the course of infection after stimulation with two out of four TLR-ligands tested. Priming with a TLR9 agonist induced killing of pre-erythrocytic stages in the liver that depended on macrophages and the expression of inducible nitric oxide synthase (iNOS). These factors have previously not been recognized as antigen-independent effector mechanisms against Plasmodium liver stages. Priming with TLR4 and -9 agonists also translated into blood stage-specific protection against experimental cerebral malaria (ECM). These insights are relevant to the activation of TLR signalling pathways by adjuvant systems of antimalaria vaccine strategies. The protective role of TLR4-activation against ECM might also explain some unexpected clinical effects observed with pre-erythrocytic vaccine approaches.

Characterization of the Gene Expression Patterns in the Murine Liver Following Intramuscular Administration of Baculovirus

Intramuscular administration of wild-type baculovirus is able to both protect against Plasmodium sporozoite challenge and eliminate liver-stage parasites via a Toll-like receptor 9-independent pathway. To investigate its effector mechanism(s), the gene expression profile in the liver of baculovirus-administered mice was characterized by cDNA microarray analysis. The ingenuity pathway analysis gene ontology module revealed that the major gene subsets induced by baculovirus were immune-related signaling, such as interferon signaling. A total of 40 genes commonly upregulated in a Toll-like receptor 9-independent manner were included as possible candidates for parasite elimination. This gene subset consisted of NT5C3, LOC105246895, BTC, APOL9a/b, G3BP3, SLC6A6, USP25, TRIM14, and PSMB8 as the top 10 candidates according to the special unit. These findings provide new insight into effector molecules responsible for liver-stage parasite killing and, possibly, the development of a new baculovirus-mediated prophylactic and therapeutic biopharmaceutical for malaria.

Baculoviruses in Gene Therapy and Personalized Medicine

This review will outline the role of baculoviruses in gene therapy and future potential in personalized medicine. Baculoviruses are a safe, non-toxic, non-integrative vector with a large cloning capacity. Baculoviruses are also a highly adaptable, low-cost vector with a broad tissue and host tropism due to their ability to infect both quiescent and proliferating cells. Moreover, they only replicate in insect cells, not mammalian cells, improving their biosafety. The beneficial properties of baculoviruses make it an attractive option for gene delivery. The use of baculoviruses in gene therapy has advanced significantly, contributing to vaccine production, anti-cancer therapies and regenerative medicine. Currently, baculoviruses are primarily used for recombinant protein production and vaccines.  This review will also discuss methods to optimize baculoviruses protein production and mammalian cell entry, limitations and potential for gene therapy and personalized medicine. Limitations such as transient gene expression, complement activation and virus fragility are discussed in details as they can be overcome through further genetic modifications and other methods. This review concludes that baculoviruses are an excllent candidate for gene therapy, personalized medicine and other biotherapeutic applications.

Type I Interferons and Malaria: A Double-Edge Sword Against a Complex Parasitic Disease

Type I interferons (IFN-Is) are important cytokines playing critical roles in various infections, autoimmune diseases, and cancer. Studies have also shown that IFN-Is exhibit 'conflicting' roles in malaria parasite infections. Malaria parasites have a complex life cycle with multiple developing stages in two hosts. Both the liver and blood stages of malaria parasites in a vertebrate host stimulate IFN-I responses. IFN-Is have been shown to inhibit liver and blood stage development, to suppress T cell activation and adaptive immune response, and to promote production of proinflammatory cytokines and chemokines in animal models. Different parasite species or strains trigger distinct IFN-I responses. For example, a Plasmodium yoelii strain can stimulate a strong IFN-I response during early infection, whereas its isogenetic strain does not. Host genetic background also greatly influences IFN-I production during malaria infections. Consequently, the effects of IFN-Is on parasitemia and disease symptoms are highly variable depending on the combination of parasite and host species or strains. Toll-like receptor (TLR) 7, TLR9, melanoma differentiation-associated protein 5 (MDA5), and cyclic GMP-AMP synthase (cGAS) coupled with stimulator of interferon genes (STING) are the major receptors for recognizing parasite nucleic acids (RNA/DNA) to trigger IFN-I responses. IFN-I levels in vivo are tightly regulated, and various novel molecules have been identified to regulate IFN-I responses during malaria infections. Here we review the major findings and progress in ligand recognition, signaling pathways, functions, and regulation of IFN-I responses during malaria infections.

Baculovirus AcMNPV induces type I interferons and NK/NKT cells-mediated protection against foot-and-mouth disease virus in mice

Foot-and-mouth disease is a viral illness that affects cloven-hoofed animals causing serious economic losses. Inactivated vaccines against its causative agent, foot-and-mouth disease virus (FMDV), require approximately seven days to induce protection. Therefore, antiviral strategies are needed to provide earlier protection and to stop the spread of this highly contagious virus during outbreak situations. In this way, our group has previously demonstrated that the baculovirus (BV) Autographa californica multiple nucleopolyhedrovirus (AcMNPV), an insect virus with immunostimulant effects, induces a nonspecific antiviral status that protects C57BL/6 mice against a lethal challenge with FMDV A/Arg/01 at 3 hours or 3 days post inoculation. In this work, we studied the immunological mechanisms involved in this protection. Firstly, we compared the protection elicited by AcMNPV in wild type mice and in knock-out mice lacking the subunit IFNAR1 of the receptor for type I interferons (IFNs). Our results showed that type I IFNs are key to prevent the death of the animals after the FMDV challenge. On the other hand, we evaluated the role of NK and NKT cells by depleting these cell subsets with anti-NK1.1 monoclonal antibody. These cells proved to be necessary for the induction of IFN-γ by AcMNPV and to prevent the onset of a severe disease after the FMDV challenge. We propose BV as a novel tool for the development of antiviral strategies because of the high levels of IFNs induced and the NK/NKT cells-mediated immune response elicited.

Down-selecting circumsporozoite protein-based malaria vaccine: A comparison of malaria sporozoite challenge model

Plasmodium falciparum circumsporozoite protein (PfCSP) is the main target antigen in development of pre-erythrocytic malaria vaccines. To evaluate PfCSP vaccines in animal models, challenge by intravenous sporozoite injection is preferentially used. However, in clinical trials, vaccinated human volunteers are exposed to the bites of malaria-infected mosquitoes. In this study, we down-selected Escherichia coli-produced full-length PfCSP (PfCSP-F) and its three truncated PfCSPs based on their abilities to elicit immune response and protection in mice against two challenge models. We showed that immunization with three doses of PfCSP-F elicited high anti-PfCSP antibody titres and 100% protection against the bites of infected mosquitoes. Meanwhile, three-dose truncated PfCSP induced 60%-70% protection after immunization with each truncated PfCSP. Heterologous prime-boost immunization regimen with adenovirus-PfCSP-F and R32LR greatly induced complete protection against intravenous sporozoite injection. Our results suggest that Abs to both anti-repeat and anti-nonrepeat regions induced by PfCSP-F are required to confer complete protection against challenge by the bites of infected mosquitoes, whereas anti-repeat Abs play an important role in protection against intravenous sporozoite injection. Our findings provide a potential clinical application that PfCSP-F vaccine induces potent Abs capable of neutralizing sporozoites in the dermis inoculated by infected mosquitoes and subsequently sporozoites in the blood circulation.

A Viral-Vectored Multi-Stage Malaria Vaccine Regimen With Protective and Transmission-Blocking Efficacies

Malaria parasites undergo several stages in their complex lifecycle. To achieve reductions in both the individual disease burden and malaria transmission within communities, a multi-stage malaria vaccine with high effectiveness and durability is a more efficacious strategy compared with a single-stage vaccine. Here, we generated viral-vectored vaccines based on human adenovirus type 5 (AdHu5) and adeno-associated virus serotype 1 (AAV1) expressing a fusion protein of the pre-erythrocytic stage Plasmodium falciparum circumsporozoite protein (PfCSP) and the transmission-blocking sexual stage P25 protein (Pfs25). A two-dose heterologous AdHu5-prime/AAV1-boost immunization regimen proved to be highly effective for both full protection and transmission-blocking activity against transgenic P. berghei parasites expressing the corresponding P. falciparum antigens in mice. Remarkably, the immunization regimen induced antibody responses to both PfCSP and Pfs25 for over 9 months after the boosting and also maintained high levels of transmission-reducing activity (TRA: >99%) during that period, as evaluated by a direct feeding assay. If similar efficacies on P. falciparum can be shown following vaccination of humans, we propose that this multi-stage malaria vaccine regimen will be a powerful tool for malaria control, providing greater overall protection and cost-effectiveness than single-stage vaccines.

Adeno-Associated Virus as an Effective Malaria Booster Vaccine Following Adenovirus Priming

An ideal malaria vaccine platform should potently induce protective immune responses and block parasite transmission from mosquito to human, and it should maintain these effects for an extended period. Here, we have focused on vaccine development based on adeno-associated virus serotype 1 (AAV1), a viral vector widely studied in the field of clinical gene therapy that is able to induce long-term transgene expression without causing toxicity in vivo. Our results show the potential utility of AAV1 vectors as an extremely potent booster vaccine to induce durable immunity when combined with an adenovirus-priming vaccine in a rodent malaria model. We generated a series of recombinant AAV1s and human adenovirus type 5 (AdHu5) expressing either Plasmodium falciparum circumsporozoite protein (PfCSP) or P25 (Pfs25) protein. Heterologous two-dose immunization with an AdHu5-prime and AAV1-boost (AdHu5-AAV1) elicited robust and durable PfCSP- or Pfs25-specific functional antibodies over 280 days. Regarding protective efficacy, AdHu5-AAV1 PfCSP achieved high sterile protection (up to 80% protection rate) against challenge with transgenic Plasmodium berghei sporozoites expressing PfCSP. When examining transmission-blocking (TB) efficacy, we found that immunization with AdHu5-AAV1 Pfs25 maintained TB activity in vivo against transgenic P. berghei expressing Pfs25 for 287 days (99% reduction in oocyst intensity, 85% reduction in oocyst prevalence). Our data indicate that AAV1-based malaria vaccines can confer potent and durable protection as well as TB efficacy when administered following an AdHu5 priming vaccine, supporting the further evaluation of this regimen in clinical trials as a next-generation malaria vaccine platform.