A non-pathogenic Leishmania tarentolae vector based- HCV polytope DNA vaccine elicits potent and long lasting Th1 and CTL responses in BALB/c mice model

Towards an HCV vaccine: an overview of the immunization strategies for eliciting an effective B-cell response

INTRODUCTION

Fifty-eight million people worldwide are chronically infected with hepatitis C virus (HCV) and are at risk of developing cirrhosis and hepatocellular carcinoma (HCC). Direct-acting antivirals are highly effective; however, they are burdened by high costs and the unchanged risk of HCC and reinfection, making prophylactic countermeasures an urgent medical need. HCV high genetic diversity is one of the main obstacles to vaccine development. The protective role of the humoral response directed against the HCV E2 glycoprotein is well established, and broadly neutralizing antibodies play a crucial role in effective viral clearance.

AREAS COVERED

This review explores the HCV targets and the different vaccination approaches, encompassing different expression systems, antigen selection strategies, and delivery methods, focusing on those aimed at eliciting a broad and effective humoral response. Our search criteria included the keywords 'HCV,' 'Hepatitis C,' and 'vaccine' using publicly available databases. Following the screening, 54 papers were selected.

EXPERT OPINION

The investigation of novel vaccine platforms beyond traditional approaches is necessary. While progress has been made in this direction, continued investigations on the HCV virology, immunology, and vaccinology are essential to surmount associated obstacles, heling in the development of an HCV vaccine that can benefit the global public health.

Leishmania tarentolae as a platform for the production of vaccines against viral pathogens

Infectious diseases remain a persistent public health problem and a leading cause of morbidity and mortality in both humans and animals. The most effective method of combating viral infections is the widespread use of prophylactic vaccinations, which are administered to both people at risk of disease and animals that may serve as significant sources of infection. Therefore, it is crucial to develop technologies for the production of vaccines that are highly effective, easy to transport and store, and cost-effective. The protein expression system based on the protozoan Leishmania tarentolae offers several advantages, validated by numerous studies, making it a good platform for producing vaccine antigens. This review provides a comprehensive overview into the potential applications of L. tarentolae for the safe production of effective viral antigens.

Exploring T-Cell Immunity to Hepatitis C Virus: Insights from Different Vaccine and Antigen Presentation Strategies

The hepatitis C virus (HCV) is responsible for approximately 50 million infections worldwide. Effective drug treatments while available face access barriers, and vaccine development is hampered by viral hypervariability and immune evasion mechanisms. The CD4+ and CD8+ T-cell responses targeting HCV non-structural (NS) proteins have shown a role in the viral clearance. In this paper, we reviewed the studies exploring the relationship between HCV structural and NS proteins and their effects in contributing to the elicitation of an effective T-cell immune response. The use of different vaccine platforms, such as viral vectors and virus-like particles, underscores their versability and efficacy for vaccine development. Diverse HCV antigens demonstrated immunogenicity, eliciting a robust immune response, positioning them as promising vaccine candidates for protein/peptide-, DNA-, or RNA-based vaccines. Moreover, adjuvant selection plays a pivotal role in modulating the immune response. This review emphasizes the importance of HCV proteins and vaccination strategies in vaccine development. In particular, the NS proteins are the main focus, given their pivotal role in T-cell-mediated immunity and their sequence conservation, making them valuable vaccine targets.

The non-pathogenic protozoon Leishmania tarentolae interferes with the activation of NLRP3 inflammasome in human cells: new perspectives in the control of inflammation

Background

Innate immune responses against infectious agents can act as triggers of inflammatory diseases. On the other hand, various pathogens have developed mechanisms for the evasion of the immune response, based on an inhibition of innate immunity and inflammatory responses. Inflammatory diseases could thus be controlled through the administration of pathogens or pathogen-derived molecules, capable of interfering with the mechanisms at the basis of inflammation. In this framework, the NLRP3 inflammasome is an important component in innate antimicrobial responses and a major player in the inflammatory disease. Parasites of the genus Leishmania are master manipulators of innate immune mechanisms, and different species have been shown to inhibit inflammasome formation. However, the exploitation of pathogenic Leishmania species as blockers of NLRP3-based inflammatory diseases poses safety concerns.

Methods

To circumvent safety issues associated with pathogenic parasites, we focused on Leishmania tarentolae, a species of Leishmania that is not infectious to humans. Because NLRP3 typically develops in macrophages, in response to the detection and engulfment microorganisms, we performed our experiments on a monocyte-macrophage cell line (THP-1), either wild type or knockout for ASC, a key component of NLRP3 formation, with determination of cytokines and other markers of inflammation.

Results

L. tarentolae was shown to possess the capability of dampening the formation of NLRP3 inflammasome and the consequent expression of pro-inflammatory molecules, with minor differences compared to effects of pathogenic Leishmania species.

Conclusion

The non-pathogenic L. tarentolae appears a promising pro-biotic microbe with anti-inflammatory properties or a source of immune modulating cellular fractions or molecules, capable of interfering with the formation of the NLRP3 inflammasome.

Immunomodulatory properties of Leishmania tarentolae extracellular vesicles containing the Spike protein of SARS-CoV-2

Extracellular vesicles released by the protozoan parasite Leishmania display immunomodulatory properties towards mammalian immune cells. In this study, we have evaluated the potential of extracellular vesicles derived from the non-pathogenic protozoan Leishmania tarentolae towards the development of a vaccine adjuvant. As a proof of concept, we expressed in L. tarentolae a codon-optimized SARS-CoV-2 Spike protein fused to the L. mexicana secreted acid phosphatase signal peptide in the N-terminal and to a 6×-His stretch in the C-terminal. Extracellular vesicles released by the engineered L. tarentolae were isolated by ultracentrifugation and fast protein liquid chromatography and were characterized via nanoparticle tracking analysis and transmission electron microscopy. The recombinant S protein was present in extracellular vesicles released by L. tarentolae, as determined by Western blot analyses and immunoelectron microscopy. Next, we evaluated the immunomodulatory potential of extracellular vesicles containing the S protein towards bone-marrow-derived macrophages and bone-marrow-derived dendritic cells. Our data show that in bone-marrow-derived dendritic cells, extracellular vesicles containing the S protein induced an increased expression of proinflammatory genes compared to plain extracellular vesicles whereas the opposite was observed in bone-marrow-derived macrophages. These findings reveal the immunomodulatory potential of L. tarentolae extracellular vesicles and provide a proof of concept that they can be used as adjuvant in the context of dendritic cell stimulation.

A novel mRNA vaccine, TGGT1_278620 mRNA-LNP, prolongs the survival time in BALB/c mice with acute toxoplasmosis

IMPORTANCE

Toxoplasma gondii, an obligate intracellular eukaryotic parasite, can infect about one-third of the world's population. One vaccine, Toxovax, has been developed and licensed commercially; however, it is only used in the sheep industry to reduce the losses caused by congenital toxoplasmosis. Various other vaccine approaches have been explored, including excretory secretion antigen vaccines, subunit vaccines, epitope vaccines, and DNA vaccines. However, current research has not yet developed a safe and effective vaccine for T. gondii. Here, we generated an mRNA vaccine candidate against T. gondii. We investigated the efficacy of vaccination with a novel identified candidate, TGGT1_278620, in a mouse infection model. We screened T. gondii-derived protective antigens at the genome-wide level, combined them with mRNA-lipid nanoparticle vaccine technology against T. gondii, and investigated immune-related factors and mechanisms. Our findings might contribute to developing vaccines for immunizing humans and animals against T. gondii.

Leishmania tarentolae: a vaccine platform to target dendritic cells and a surrogate pathogen for next generation vaccine research in leishmaniases and viral infections

Parasites of the genus Leishmania are unusual unicellular microorganisms in that they are characterized by the capability to subvert in their favor the immune response of mammalian phagocytes, including dendritic cells. Thus, in overt leishmaniasis, dendritic cells and macrophages are converted into a niche for Leishmania spp. in which the parasite, rather than being inactivated and disassembled, survives and replicates. In addition, Leishmania parasites hitchhike onto phagocytic cells, exploiting them as a mode of transport to lymphoid tissues where other phagocytic cells are potentially amenable to parasite colonization. This propensity of Leishmania spp. to target dendritic cells has led some researchers to consider the possibility that the non-pathogenic, reptile-associated Leishmania tarentolae could be exploited as a vaccine platform and vehicle for the production of antigens from different viruses and for the delivery of the antigens to dendritic cells and lymph nodes. In addition, as L. tarentolae can also be regarded as a surrogate of pathogenic Leishmania parasites, this parasite of reptiles could possibly be developed into a vaccine against human and canine leishmaniases, exploiting its immunological cross-reactivity with other Leishmania species, or, after its engineering, for the expression of antigens from pathogenic species. In this article we review published studies on the use of L. tarentolae as a vaccine platform and vehicle, mainly in the areas of leishmaniases and viral infections. In addition, a short summary of available knowledge on the biology of L. tarentolae is presented, together with information on the use of this microorganism as a micro-factory to produce antigens suitable for the serodiagnosis of viral and parasitic infections.

Leishmania tarentolae: A new frontier in the epidemiology and control of the leishmaniases

Leishmaniasis (or the leishmaniases), classified as a neglected tropical parasitic disease, is found in parts of the tropics, subtropics and southern Europe. Leishmania parasites are transmitted by the bite of phlebotomine sand flies and million cases of human infection occur annually. Leishmania tarentolae has been historically considered a non-pathogenic protozoan of reptiles, which has been studied mainly for its potential biotechnological applications. However, some strains of L. tarentolae appear to be transiently infective to mammals. In areas where leishmaniasis is endemic, recent molecular diagnostics and serological positivity to L. tarentolae in humans and dogs have spurred interest in the interactions between these mammalian hosts, reptiles and Leishmania infantum, the main aetiologic agent of human and canine leishmaniasis. In this review, we discuss the systematics and biology of L. tarentolae in the insect vectors and the vertebrate hosts and address questions about evolution of reptilian leishmaniae. Furthermore, we discuss the possible usefulness of L. tarentolae for new vaccination strategies.

Leishmania tarentolae as an Antigen Delivery Platform: Dendritic Cell Maturation after Infection with a Clone Engineered to Express the SARS-CoV-2 Spike Protein

Background: Protozoa of the genus Leishmania are characterized by their capacity to target macrophages and Dendritic Cells (DCs). These microorganisms could thus be exploited for the delivery of antigens to immune cells. Leishmania tarentolae is regarded as a non-pathogenic species; it was previously used as a biofactory for protein production and has been considered as a candidate vaccine or as an antigen delivery platform. However, results on the type of immune polarization determined by L. tarentolae are still inconclusive. Methods: DCs were derived from human monocytes and exposed to live L. tarentolae, using both the non-engineered P10 strain, and the same strain engineered for expression of the spike protein from SARS-CoV-2. We then determined: (i) parasite internalization in the DCs; and (ii) the capacity of the assayed strains to activate DCs and the type of immune polarization. Results: Protozoan parasites from both strains were effectively engulfed by DCs, which displayed a full pattern of maturation, in terms of MHC class II and costimulatory molecule expression. In addition, after parasite infection, a limited release of Th1 cytokines was observed. Conclusions: Our results indicate that L. tarentolae could be used as a vehicle for antigen delivery to DCs and to induce the maturation of these cells. The limited cytokine release suggests L. tarentolae as a neutral vaccine vehicle that could be administered in association with appropriate immune-modulating molecules.

HCV Core/NS3 Protein Immunization with "N-Terminal Heat Shock gp96 Protein (rNT (gp96))" Induced Strong and Sustained Th1-Type Cytokines in Immunized Mice

Feeble cellular responses induced by T cell-based vaccines are a major challenge for the development of an effective vaccine against Hepatitis C virus (HCV) infection. To address this challenge, the potential of N-terminal fragment of gp96 heat shock protein (rNT (gp96) as an adjuvant was evaluated and compared to that of the CpG (as a recognized Th1-type adjuvant) in the formulation of HCV core/NS3 antigens in three immunization strategies of protein/protein, DNA/DNA, and DNA/protein. Immunized mice were evaluated for elicited immune responses in week 3 (W3) and 11 post-immunizations. Our results demonstrated that the protein (subunit) vaccine formulated with rNT (gp96) in protein/protein strategy (core/NS3 + gp96) was significantly more efficient than CpG oligodeoxynucleotides (CpG ODN) formulation and all other immunization strategies in the induction of Th1-type cytokines. This group of mice (core/NS3 + gp96) also elicited a high level of anti-Core-NS3 total immunoglobulin G (IgG) with dominant IgG2a isotype at W3. Thus, the co-administration of recombinant NT (gp96) protein with rHCV proteins might be a promising approach in the formulation of HCV subunit vaccine candidates for induction of high levels of Th1 cytokines and humoral responses.

gB co-immunization with GP96 enhances pulmonary-resident CD8 T cells and exerts a long-term defence against MCMV pneumonitis

Human cytomegalovirus (HCMV) infection in the respiratory tract leads to pneumonitis in immunocompromised hosts without available vaccine. Considering cytomegalovirus (CMV) mainly invades through the respiratory tract, CMV-specific pulmonary mucosal vaccine development that provides a long-lasting protection against CMV challenge gains our attention. In this study, N-terminal domain of GP96 (GP96-NT) was used as a mucosal adjuvant to enhance the induction of pulmonary-resident CD8 T cells elicited by MCMV glycoprotein B (gB) vaccine. Mice were intranasally co-immunized with 50 μg pgB and equal amount of pGP96-NT vaccine 4 times at 2-week intervals, and then i.n. challenged with MCMV at 16 weeks after the last immunization. Compared with pgB immunization alone, co-immunization with pgB/pGP96-NT enhanced a long-lasting protection against MCMV pneumonitis by significantly improved pneumonitis pathology, enhanced bodyweight, reduced viral burdens and increased survival rate. Moreover, the increased CD8 T cells were observed in lung but not spleen from pgB/pGP96-NT co-immunized mice. The increments of pulmonary CD8 T cells might be mainly due to non-circulating pulmonary-resident CD8 T-cell subset expansion but not circulating CD8 T-cell populations that home to inflammation site upon MCMV challenge. Finally, the deterioration of MCMV pneumonitis by depletion of pulmonary site-specific CD8 T cells in mice that were pgB/pGP96-NT co-immunization might be a clue to interpret the non-circulating pulmonary-resident CD8 T subset expansion. These data might uncover a promising long-lasting prophylactic vaccine strategy against MCMV-induced pneumonitis.