A candidate vaccine for human visceral leishmaniasis based on a specific T cell epitope-containing chimeric protein protects mice against Leishmania infantum infection

Leishmania vaccine development: A comprehensive review

Infectious diseases like leishmaniasis, malaria, HIV, tuberculosis, leprosy and filariasis are responsible for an immense burden on public health systems. Among these, leishmaniasis is under the category I diseases as it is selected by WHO (World Health Organization) on the ground of diversity and complexity. High cost, resistance and toxic effects of Leishmania traditional drugs entail identification and development of therapeutic alternative. Since the natural infection elicits robust immunity, consistence efforts are going on to develop a successful vaccine. Clinical trials have been conducted on vaccines like Leish-F1, F2, and F3 formulated using specific Leishmania antigen epitopes. Current strategies utilize individual or combined antigens from the parasite or its insect vector's salivary gland extract, with or without adjuvant formulation for enhanced efficacy. Promising animal data supports multiple vaccine candidates (Lmcen-/-, LmexCen-/-), with some already in or heading for clinical trials. The crucial challenge in Leishmania vaccine development is to translate the research knowledge into affordable and accessible control tools that refines the outcome for those who are susceptible to infection. This review focuses on recent findings in Leishmania vaccines and highlights difficulties facing vaccine development and implementation.

Proteome profile of Leishmania donovani Centrin1-/- parasite-infected human macrophage cell line and its implications in determining possible mechanisms of protective immunity

Our developed cell division-specific 'centrin' gene deleted Leishmania donovani (LdCen1-/-) the causative parasite of the fatal visceral-leishmaniasis (VL), exhibits a selective growth arrest at the intracellular stage and is anticipated as a live attenuated vaccine candidate against VL. LdCen1-/- immunization in animals has shown increased IFN-γ secreting CD4+ and CD8+ T cells along with protection conferred by a protective proinflammatory immune response. A label-free proteomics approach has been employed to understand the physiology of infection and predict disease interceptors during Leishmania-host interactions. Proteomic modulation after infection of human macrophage cell lines suggested elevated annexin A6, implying involvement in various biological processes such as membrane repair, transport, actin dynamics, cell proliferation, survival, differentiation, and inflammation, thereby potentiating its immunological protective capacity. Additionally, S100A8 and S100A9 proteins, known for maintaining homeostatic balance in regulating the inflammatory response, have been upregulated after infection. The inhibitory clade of serpins, known to inhibit cysteine proteases (CPs), was upregulated in host cells after 48 h of infection. This is reflected in the diminished expression of CPs in the parasites during infection. Such proteome analysis confirms LdCen1-/- efficacy as a vaccine candidate and predicts potential markers in future vaccine development strategies against infectious diseases.

Prediction of an immunogenic peptide ensemble and multi-subunit vaccine for Visceral leishmaniasis using bioinformatics approaches

Visceral Leishmaniasis (VL) is a neglected tropical disease of public health importance in the Indian subcontinent. Despite consistent elimination initiatives, the disease has not yet been eliminated and there is an increased risk of resurgence from active VL reservoirs including asymptomatic, post kala azar dermatitis leishmaniasis (PKDL) and HIV-VL co-infected individuals. To achieve complete elimination and sustain it in the long term, a prophylactic vaccine, which can elicit long lasting immunity, is desirable. In this study, we employed immunoinformatic tools to design a multi-subunit epitope vaccine for the Indian population by targeting antigenic secretory proteins screened from the Leishmania donovani proteome. Out of 8014 proteins, 277 secretory proteins were screened for their cellular location and proteomic evidence. Through NCBI BlastP, unique fragments of the proteins were cropped, and their antigenicity was evaluated. B-cell, HTL and CTL epitopes as well as IFN-ɣ, IL-17, and IL-10 inducers were predicted, manually mapped to the fragments and common regions were tabulated forming a peptide ensemble. The ensemble was evaluated for Class I MHC immunogenicity and toxicity. Further, immunogenic peptides were randomly selected and used to design vaccine constructs. Eight vaccine constructs were generated by linking random peptides with GS linkers. Synthetic TLR-4 agonist, RS09 was used as an adjuvant and linked with the constructs using EAAK linkers. The predicted population coverage of the constructs was ∼99.8 % in the Indian as well as South Asian populations. The most antigenic, nontoxic, non-allergic construct was chosen for the prediction of secondary and tertiary structures. The 3D structures were refined and analyzed using Ramachandran plot and Z-scores. The construct was docked with TLR-4 receptor. Molecular dynamic simulation was performed to check for the stability of the docked complex. Comparative in silico immune simulation studies showed that the predicted construct elicited humoral and cell-mediated immunity in human host comparable to that elicited by Leish-F3, which is a promising vaccine candidate for human VL.

Intramuscular Immunization with a Liposomal Multi-Epitope Chimeric Protein Induces Strong Cellular Immune Responses against Visceral Leishmaniasis

Control of the intracellular parasite Leishmania (L.) requires the activation of strong type 1 cellular immune responses. Towards this goal, in the present study, a multiepitope chimeric protein named LiChimera was encapsulated into cationic liposomes and its protective efficacy against experimental visceral leishmaniasis was investigated. Liposomal LiChimera conferred significant protection against L. infantum as evidenced by the significantly reduced parasite loads in the spleen and liver. Protection detected in Lipo:LiChimera-immunized mice was dependent on the differentiation of long-lasting cellular immune responses and particularly the induction of antigen-specific multifunctional memory CD4+ TH1 and CD8+ T cells that persisted during infection, as evidenced by the persistent high production of IFN-γ and IL-2 and proliferation activity. Notably, protected mice were also characterized by significantly low numbers of non-regulatory CD4+ T cells able to co-produce IFN-γ and IL-10, an important population for disease establishment, as compared to non-immunized control group. Collectively, these results demonstrate that cationic liposomes containing LiChimera can be considered an effective candidate vaccine against visceral leishmaniasis.

Cloning, expression and in vitro validation of chimeric multi epitope vaccine candidate against visceral leishmaniasis infection

Visceral Leishmaniasis or Kala-Azar is one of the most severe and deadly neglected tropical disease caused by the Leishmania parasite. A few number of vaccines are going through different phases in clinical trial but failing of these vaccines in successive phase trial or less efficacy, urge to develop highly immunogenic and cost-effective treatment to get rid of deadly VL. This study focuses on the development of more potent vaccine candidate against VL. The recombinant vaccine candidate LeiSp was expressed in Pichia pastoris, followed by purification and characterization. The purified protein was also tested for any post-translation modification, which favors being a potent immunogenic candidate. Further, the expression modulation of different pro-inflammatory and anti-inflammatory cytokines was evaluated in THP1 cell lines. A significant upregulation in the expression of pro-inflammatory cytokines while no significant changes were observed in the expression of anti-inflammatory cytokines. The impact of recombinant vaccine protein candidates in infected conditions were determined. Here, upon treatment with chimeric vaccine protein candidate, we observed a considerable recovery in the expression level of pro-inflammatory cytokines, which were downregulated upon infection alone. In addition to this, we found a significant decrease in the expression of anti-inflammatory cytokines, which were upregulated during infection alone. We further validated our findings in infected hPBMCs and observed similar expression modulation of pro-inflammatory and anti-inflammatory cytokines with and without treatment. Thus, the present study indicates that the chimeric LeiSp protein which was designed using bioinformatics approaches shows a potential inductive efficacy for pro-inflammatory cytokines in Leishmania-infected cells.

rMELEISH: A Novel Recombinant Multiepitope-Based Protein Applied to the Serodiagnosis of Both Canine and Human Visceral Leishmaniasis

BACKGROUND

visceral leishmaniasis (VL) is a critical public health problem in over ninety countries. The control measures adopted in Brazil have been insufficient when it comes to preventing the spread of this overlooked disease. In this context, a precise diagnosis of VL in dogs and humans could help to reduce the number of cases of this disease. Distinct studies for the diagnosis of VL have used single recombinant proteins in serological assays; however, the results have been variable, mainly in relation to the sensitivity of the antigens. In this context, the development of multiepitope-based proteins could be relevant to solving such problem.

METHODS

a chimeric protein (rMELEISH) was constructed based on amino acid sequences from kinesin 39 (k39), alpha-tubulin, and heat-shock proteins HSP70 and HSP 83.1, and tested in enzyme-linked immunosorbent (ELISA) for the detection of L. infantum infection using canine (n = 140) and human (n = 145) sera samples.

RESULTS

in the trials, rMELEISH was able to discriminate between VL cases and cross-reactive diseases and healthy samples, with sensitivity and specificity values of 100%, as compared to the use of a soluble Leishmania antigenic extract (SLA).

CONCLUSIONS

the preliminary data suggest that rMELEISH has the potential to be tested in future studies against a larger serological panel and in field conditions for the diagnosis of canine and human VL.

Present and future: infectious tropical travel rashes and the impact of climate change

In this article, we discuss pertinent cutaneous findings with which patients may present after travel to tropical destinations. We address arthropod-borne infectious diseases such as cutaneous leishmaniasis, Chagas disease, cutaneous larva migrans, and myiasis. We discuss other relevant diseases with cutaneous signs such as monkey pox and severe acute respiratory syndrome coronavirus 2. We provide clinicians with information regarding the background, diagnosis, treatment, and prevention of these tropical rashes. In addition, we address the impact that climate change will have on the temporal and geographic incidence of these rashes. Viral, fungal, and vector-borne diseases have seen a geographic expansion into more northern latitudes. Among these are tick-borne Lyme disease, aquatic snail-related seabather's eruption, and atopic dermatitis. As these diseases spread, we believe that the updated information within this article is significant to the practicing physician in today's warming world.

Validating Immunomodulatory Responses of r-LdODC Protein and Its Derived HLA-DRB1 Restricted Epitopes against Visceral Leishmaniasis in BALB/c Mice

Vaccination is considered the most appropriate way to control visceral leishmaniasis (VL). With this background, the r-LdODC protein as well as its derived HLA-DRB1-restricted synthetic peptides (P1: RLMPSAHAI, P2: LLDQYQIHL, P3: GLYHSFNCI, P4: AVLEVLSAL, and P5: RLPASPAAL) were validated in BALB/c mice against visceral leishmaniasis. The study was initiated by immunization of the r-LdODC protein as well as its derived peptides cocktail with adjuvants (r-CD2 and MPL-A) in different mice groups, separately. Splenocytes isolated from the challenged and differentially immunized mice group exhibited significantly higher IFN-γ secretion, which was evidenced by the increase in the expression profile of intracellular CD4+IFN-γ T cells. However, the IL-10 secretion did not show a significant increase against the protein and peptide cocktail. Subsequently, the study confirmed the ability of peptides as immunoprophylactic agents, as the IE-I/AD-I molecule overexpressed on monocytes and macrophages of the challenged mice group. The parasitic load in macrophages of the protein and peptides cocktail immunized mice groups, and T cell proliferation rate, further established immunoprophylactic efficacy of the r-LdODC protein and peptide cocktail. This study suggests that the r-LdODC protein, as well as its derived HLA-DRB1-restricted synthetic peptides, have immunoprophylactic potential and can activate other immune cells' functions towards protection against visceral leishmaniasis. However, a detailed study in a humanized mice model can explore its potential as a vaccine candidate.

Leishmania Vaccines: the Current Situation with Its Promising Aspect for the Future

Leishmaniasis is a serious parasitic disease caused by Leishmania spp. transmitted through sandfly bites. This disease is a major public health concern worldwide. It can occur in 3 different clinical forms: cutaneous, mucocutaneous, and visceral Leishmaniasis (CL, MCL, and VL, respectively), caused by different Leishmania spp. Currently, licensed vaccines are unavailable for the treatment of human Leishmaniasis. The treatment and prevention of this disease rely mainly on chemotherapeutics, which are highly toxic and have an increasing resistance problem. The development of a safe, effective, and affordable vaccine for all forms of vector-borne disease is urgently needed to block transmission of the parasite between the host and vector. Immunological mechanisms in the pathogenesis of Leishmaniasis are complex. IL-12-driven Th1-type immune response plays a crucial role in host protection. The essential purpose of vaccination is to establish a protective immune response. To date, numerous vaccine studies have been conducted using live/attenuated/killed parasites, fractionated parasites, subunits, recombinant or DNA technology, delivery systems, and chimeric peptides. Most of these studies were limited to animals. In addition, standardization has not been achieved in these studies due to the differences in the virulence dynamics of the Leishmania spp. and the feasibility of the adjuvants. More studies are needed to develop a safe and effective vaccine, which is the most promising approach against Leishmania infection.

Evolutionary consequences of vector-borne transmission: how using vectors shapes host, vector and pathogen evolution

Transmission mode is a key factor that influences host–parasite coevolution. Vector-borne pathogens are among the most important disease agents for humans and wildlife due to their broad distribution, high diversity, prevalence and lethality. They comprise some of the most important and widespread human pathogens, such as yellow fever, leishmania and malaria. Vector-borne parasites (in this review, those transmitted by blood-feeding Diptera) follow unique transmission routes towards their vertebrate hosts. Consequently, each part of this tri-partite (i.e. parasite, vector and host) interaction can influence co- and counter-evolutionary pressures among antagonists. This mode of transmission may favour the evolution of greater virulence to the vertebrate host; however, pathogen–vector interactions can also have a broad spectrum of fitness costs to the insect vector. To complete their life cycle, vector-borne pathogens must overcome immune responses from 2 unrelated organisms, since they can activate responses in both vertebrate and invertebrate hosts, possibly creating a trade-off between investments against both types of immunity. Here, we assess how dipteran vector-borne transmission shapes the evolution of hosts, vectors and the pathogens themselves. Hosts, vectors and pathogens co-evolve together in a constant antagonistic arms race with each participant's primary goal being to maximize its performance and fitness.

Current leishmaniasis drug discovery

Leishmaniasis is a complex protozoan infectious disease and, associated with malnutrition, poor health services and unavailability of prophylactic control measures, neglected populations are particularly affected. Current drug regimens are outdated and associated with some drawbacks, such as cytotoxicity and resistance, and the development of novel, efficacious and less toxic drug regimens is urgently required. In addition, leishmanial pathogenesis is not well established or understood, and a prophylactic vaccine is an unfulfilled goal. Human kinetoplastid protozoan infections, including leishmaniasis, have been neglected for many years, and in an attempt to overcome this situation, some new drug targets were recently identified, enabling the development of new drugs and vaccines. Compounds from new drug classes have also shown excellent antileishmanial activities, some of the most promising ones included in clinical trials, and could be a hope to control the disease burden of this endemic disease in the near future. In this review, we discuss the limitations of current control methods, explore the wide range of compounds that are being screened and identified as antileishmanial drug prototypes, summarize the advances in identifying new drug targets aiming at innovative treatments and explore the state-of-art vaccine development field, including immunomodulation strategies.

A Recombinant Chimeric Protein-Based Vaccine Containing T-Cell Epitopes from Amastigote Proteins and Combined with Distinct Adjuvants, Induces Immunogenicity and Protection against Leishmania infantum Infection

Currently, there is no licensed vaccine to protect against human visceral leishmaniasis (VL), a potentially fatal disease caused by infection with Leishmania parasites. In the current study, a recombinant chimeric protein ChimT was developed based on T-cell epitopes identified from the immunogenic Leishmania amastigote proteins LiHyp1, LiHyV, LiHyC and LiHyG. ChimT was associated with the adjuvants saponin (Sap) or monophosphoryl lipid A (MPLA) and used to immunize mice, and their immunogenicity and protective efficacy were evaluated. Both ChimT/Sap and ChimT/MPLA induced the development of a specific Th1-type immune response, with significantly high levels of IFN-γ, IL-2, IL-12, TNF-α and GM-CSF cytokines produced by CD4+ and CD8+ T cell subtypes (p < 0.05), with correspondingly low production of anti-leishmanial IL-4 and IL-10 cytokines. Significantly increased (p < 0.05) levels of nitrite, a proxy for nitric oxide, and IFN-γ expression (p < 0.05) were detected in stimulated spleen cell cultures from immunized and infected mice, as was significant production of parasite-specific IgG2a isotype antibodies. Significant reductions in the parasite load in the internal organs of the immunized and infected mice (p < 0.05) were quantified with a limiting dilution technique and quantitative PCR and correlated with the immunological findings. ChimT/MPLA showed marginally superior immunogenicity than ChimT/Sap, and although this was not statistically significant (p > 0.05), ChimT/MPLA was preferred since ChimT/Sap induced transient edema in the inoculation site. ChimT also induced high IFN-γ and low IL-10 levels from human PBMCs isolated from healthy individuals and from VL-treated patients. In conclusion, the experimental T-cell multi-epitope amastigote stage Leishmania vaccine administered with adjuvants appears to be a promising vaccine candidate to protect against VL.

Vaccine Preventable Zoonotic Diseases: Challenges and Opportunities for Public Health Progress

Zoonotic diseases represent a heavy global burden, causing important economic losses, impacting animal health and production, and costing millions of human lives. The vaccination of animals and humans to prevent inter-species zoonotic disease transmission is an important intervention. However, efforts to develop and implement vaccine interventions to reduce zoonotic disease impacts are often limited to the veterinary and agricultural sectors and do not reflect the shared burden of disease. Multisectoral collaboration, including co-development opportunities for human and animal vaccines, expanding vaccine use to include animal reservoirs such as wildlife, and strategically using vaccines to interrupt complex transmission cycles is needed. Addressing zoonoses requires a multi-faceted One Health approach, wherein vaccinating people and animals plays a critical role.

Identification of Immunodominant Antigens From a First-Generation Vaccine Against Cutaneous Leishmaniasis

Leishmaniasis is a neglected tropical disease (NTD) caused by parasites belonging to the Leishmania genus for which there is no vaccine available for human use. Thus, the aims of this study are to evaluate the immunoprotective effect of a first-generation vaccine against L. amazonensis and to identify its immunodominant antigens. BALB/c mice were inoculated with phosphate buffer sodium (PBS), total L. amazonensis antigens (TLAs), or TLA with Poly (I:C) and Montanide ISA 763. The humoral and cellular immune response was evaluated before infection. IgG, IgG1, and IgG2a were measured on serum, and IFN-γ, IL-4, and IL-10 cytokines as well as cell proliferation were measured on a splenocyte culture from vaccinated mice. Immunized mice were challenged with 10⁴ infective parasites of L. amazonensis on the footpad. After infection, the protection provided by the vaccine was analyzed by measuring lesion size, splenic index, and parasite load on the footpad and spleen. To identify immunodominant antigens, total proteins of L. amazonensis were separated on 2D electrophoresis gel and transferred to a membrane that was incubated with serum from immunoprotected mice. The antigens recognized by the serum were analyzed through a mass spectrometric assay (LC-MS/MS-IT-TOF) to identify their protein sequence, which was subjected to bioinformatic analysis. The first-generation vaccine induced higher levels of antibodies, cytokines, and cell proliferation than the controls after the second dose. Mice vaccinated with TLA + Poly (I:C) + Montanide ISA 763 showed less footpad swelling, a lower splenic index, and a lower parasite load than the control groups (PBS and TLA). Four immunodominant proteins were identified by mass spectrometry: cytosolic tryparedoxin peroxidase, an uncharacterized protein, a kinetoplast-associated protein-like protein, and a putative heat-shock protein DNAJ. The identified proteins showed high levels of conserved sequence among species belonging to the Leishmania genus and the Trypanosomatidae family. These proteins also proved to be phylogenetically divergent to human and canine proteins. TLA + Poly (I:C) + Montanide ISA 763 could be used as a first-generation vaccine against leishmaniasis. The four proteins identified from the whole-protein vaccine could be good antigen candidates to develop a new-generation vaccine against leishmaniasis.

Recombinant guanosine-5'-triphosphate (GTP)-binding protein associated with Poloxamer 407-based polymeric micelles protects against Leishmania infantum infection

Leishmania virulence proteins should be considered as vaccine candidates against disease, since they are involved in developing infection in mammalian hosts. In a previous study, a Leishmania guanosine-5'-triphosphate (GTP)-binding protein was identified as a potential parasite virulence factor. In the present work, the gene encoding GTP was cloned and the recombinant protein (rGTP) was evaluated as a vaccine candidate against Leishmania infantum infection. The protein was associated with saponin (rGTP/Sap) or Poloxamer 407-based micelles (rGTP/Mic) as adjuvants, and protective efficacy was investigated in BALB/c mice after parasite challenge. Both rGTP/Sap and rGTP/Mic compositions induced a Th1-type immune response in vaccinated animals, with significantly higher levels of IFN-γ, IL-12, IL-2, TNF-α, GM-CSF, nitrite, specific IgG2a isotype antibody and positive lymphoproliferation, when compared to the control groups. This response was accompanied by significantly lower parasite load in the spleens, livers, bone marrows and draining lymph nodes of the animals. Immunological and parasitological evaluations indicated that rGTP/Mic induced a more polarized Th1-type response and higher reduction in the organ parasitism, and with lower hepatotoxicity, when compared to the use of rGTP/Sap. In conclusion, our preliminary data suggest that rGTP could be considered for further development as a vaccine candidate to protect against VL.

Long-Term In Vitro Passaging Had a Negligible Effect on Extracellular Vesicles Released by Leishmania amazonensis and Induced Protective Immune Response in BALB/c Mice

Depending on Leishmania species and the presence/absence of virulence factors, Leishmania extracellular vesicles (EVs) can differently stimulate host immune cells. This work is aimed at characterizing and evaluating the protective role of EVs released by Leishmania amazonensis promastigotes under different maintenance conditions. Initially, using a control strain, we standardized 26°C as the best release temperature to obtain EVs with a potential protective role in the experimental leishmaniasis model. Then, long-term (LT-P) promastigotes of L. amazonensis were obtained after long-term in vitro culture (100 in vitro passages). In vivo-derived (IVD-P) promastigotes of L. amazonensis were selected after 3 consecutive experimental infections in BALB/c mice. Those strains developed similar lesion sizes except for IVD-P at 8 weeks post infection. No differences in EV production were detected in both strains. However, the presence of LPG between LT-P and IVD-P EVs was different. Groups of mice immunized with EVs emulsified in the adjuvant and challenged with IVD-P parasites showed decreased lesion size and parasitic load compared with the nonimmunized groups. The immunization regimen with two doses showed high IFN-γ and IgG2a titers in challenged mice with either IVD-P or LT-P EVs. IL-4 and IL-10 were detected in immunized mice, suggesting a mixed Th1/Th2 profile. EVs released by either IVD-P or LT-P induced a partial protective effect in an immunization model. Thus, our results uncover a potential protective role of EVs from L. amazonensis for cutaneous leishmaniasis. Moreover, long-term maintenance under in vitro conditions did not seem to affect EV release and their immunization properties in mice.

Possibility of Leishmania Transmission via Lutzomyia spp. Sand Flies Within the USA and Implications for Human and Canine Autochthonous Infection

Purpose of Review

Leishmaniasis is a leading cause of parasitic death, with incidence rising from decreased resources to administer insecticide and anti-leishmanial treatments due to the COVID-19 pandemic. Leishmaniasis is nonendemic in the United States (U.S.), but enzootic canine populations and potentially competent vectors warrant monitoring of autochthonous disease as a fluctuating climate facilitates vector expansion. Recent studies concerning sand fly distribution and vector capacity were assessed for implications of autochthonous transmission within the U.S.

Recent Findings

Climate change and insecticide resistance provide challenges in sand fly control. While most Leishmania-infected dogs in the U.S. were infected via vertical transmission or were imported, autochthonous vector-borne cases were reported. Autochthonous vector-borne human cases have been reported in four states. Further vaccine research could contribute to infection control.

Summary

Both cutaneous and visceral leishmaniasis cases in the U.S. are increasingly reported. Prevention measures including vector control and responsible animal breeding are critical to halt this zoonotic disease.

Determinants of Innate Immunity in Visceral Leishmaniasis and Their Implication in Vaccine Development

Leishmaniasis is endemic to the tropical and subtropical regions of the world and is transmitted by the bite of an infected sand fly. The multifaceted interactions between Leishmania, the host innate immune cells, and the adaptive immunity determine the severity of pathogenesis and disease development. Leishmania parasites establish a chronic infection by subversion and attenuation of the microbicidal functions of phagocytic innate immune cells such as neutrophils, macrophages and dendritic cells (DCs). Other innate cells such as inflammatory monocytes, mast cells and NK cells, also contribute to resistance and/or susceptibility to Leishmania infection. In addition to the cytokine/chemokine signals from the innate immune cells, recent studies identified the subtle shifts in the metabolic pathways of the innate cells that activate distinct immune signal cascades. The nexus between metabolic pathways, epigenetic reprogramming and the immune signaling cascades that drive the divergent innate immune responses, remains to be fully understood in Leishmania pathogenesis. Further, development of safe and efficacious vaccines against Leishmaniasis requires a broader understanding of the early interactions between the parasites and innate immune cells. In this review we focus on the current understanding of the specific role of innate immune cells, the metabolomic and epigenetic reprogramming and immune regulation that occurs during visceral leishmaniasis, and the strategies used by the parasite to evade and modulate host immunity. We highlight how such pathways could be exploited in the development of safe and efficacious Leishmania vaccines.

Murine Susceptibility to Leishmania amazonensis Infection Is Influenced by Arginase-1 and Macrophages at the Lesion Site

Cutaneous leishmaniasis is a zoonotic infectious disease broadly distributed worldwide, causing a range of diseases with clinical outcomes ranging from self-healing infections to chronic disfiguring disease. The effective immune response to this infection is yet to be more comprehensively understood and is fundamental for developing drugs and vaccines. Thus, we used experimental models of susceptibility (BALB/c) and partial resistance (C57BL/6) to Leishmania amazonensis infection to investigate the local profile of mediators involved in the development of cutaneous leishmaniasis. We found worse disease outcome in BALB/c mice than in C57BL/6 mice, with almost 15 times higher parasitic load, ulcerated lesion formation, and higher levels of IL-6 in infected paws. In contrast, C57BL/6 presented higher levels of IFN-γ and superoxide anion (•O2−) after 11 weeks of infection and no lesion ulcerations. A peak of local macrophages appeared after 24 h of infection in both of the studied mice strains, followed by another increase after 240 h, detected only in C57BL/6 mice. Regarding M1 and M2 macrophage phenotype markers [iNOS, MHC-II, CD206, and arginase-1 (Arg-1)], we found a pronounced increase in Arg-1 levels in BALB/c after 11 weeks of infection, whereas C57BL/6 showed an initial predomination of markers from both profiles, followed by an M2 predominance, coinciding with the second peak of macrophage infiltration, 240 h after the infection. Greater deposition of type III collagen and lesion resolution was also observed in C57BL/6 mice. The adoptive transfer of macrophages from C57BL/6 to infected BALB/c at the 11th week showed a reduction in both edema and the number of parasites at the lesion site, in addition to lower levels of Arg-1. Thus, C57BL/6 mice have a more effective response against L. amazonensis, based on a balance between inflammation and tissue repair, while BALB/c mice have an excessive Arg-1 production at late infection. The worst evolution seems to be influenced by recruitment of Arg-1 related macrophages, since the adoptive transfer of macrophages from C57BL/6 mice to BALB/c resulted in better outcomes, with lower levels of Arg-1.

Feline Leishmaniasis Caused by Leishmania infantum: Parasite Sequencing, Seropositivity, and Clinical Characterization in an Endemic Area From Brazil

Zoonotic leishmaniasis caused by Leishmania infantum is a disease of One Health concern since human and animal cases and environmental damage are interconnected. L. infantum has a complex epidemiological cycle with multiple hosts, including mammals-humans, domestic, and wild animals-and arthropod vectors. Knowledge on mammal infections in endemic areas is crucial for developing control strategies. This work aimed to detect and characterize L. infantum infection in domestic cats from areas where human and canine leishmaniasis cases occur. No cases of feline leishmaniasis (FeL) had been previously reported in those areas. Five municipalities from Bahia state were chosen, comprising 2,480.8 km² with 1,103,866 inhabitants. Ninety domiciliated and/or sheltered cats underwent clinical examination and serology by a rapid reference test recommended by the Brazilian government. Cytology, PCR, and parasite DNA sequencing were performed in bone marrow samples. Rapid tests detected antibodies in 5.6% (5/90) of the cats. Leishmania infantum infection was confirmed in 7.8% (7/90) of the cats by PCR, sequencing, and parasite isolation. Three out of the five municipalities (60%) had infected cats, and PCR positivity varied from 6.9 to 29%. One cat was categorized as harboring active L. infantum infection with amastigote forms in bone marrow smears. No clinical signs were detected at the first clinical exam, but 1 month later the cat developed severe FeL. The cat isolate was grown in culture, typed and its DNA sequence was homologous to the L. infantum reference strain (PP75). In conclusion, cats are potential hosts and may acquire L. infantum in endemic areas where canine and human cases occur. For cats, the need for surveillance, differential diagnosis and clinical care is highly recommended since a fast clinical progression of FeL developed in a subclinical animal. An accurate standardized immunodiagnostic assay for FeL is warranted.

Intranasal vaccine from whole Leishmania donovani antigens provides protection and induces specific immune response against visceral leishmaniasis

Visceral leishmaniasis is a protozoan disease associated with high fatality rate in developing countries. Although the drug pipeline is constantly improving, available treatments are costly and live-threatening side effects are not uncommon. Moreover, an approved vaccine against human leishmaniasis does not exist yet. Using whole antigens from Leishmania donovani promastigotes (LdAg), we investigated the protective potential of a novel adjuvant-free vaccine strategy. Immunization of mice with LdAg via the intradermal or the intranasal route prior to infection decreases the parasitic burden in primary affected internal organs, including the liver, spleen, and bone marrow. Interestingly, the intranasal route is more efficient than the intradermal route, leading to better parasite clearance and remarkable induction of adaptive immune cells, notably the helper and cytotoxic T cells. In vitro restimulation experiments with Leishmania antigens led to significant IFN-γ secretion by splenocytes; therefore, exemplifying specificity of the adaptive immune response. To improve mucosal delivery and the immunogenic aspects of our vaccine strategy, we used polysaccharide-based nanoparticles (NP) that carry the antigens. The NP-LdAg formulation is remarkably taken up by dendritic cells and induces their maturation in vitro, as revealed by the increased expression of CD80, CD86 and MHC II. Intranasal immunization with NP-LdAg does not improve the parasite clearance in our experimental timeline; however, it does increase the percentage of effector and memory T helper cells in the spleen, suggesting a potential induction of long-term memory. Altogether, this study provides a simple and cost-effective vaccine strategy against visceral leishmaniasis based on LdAg administration via the intranasal route, which could be applicable to other parasitic diseases.

Visceral leishmaniasis is a neglected tropical disease caused by specific species of Leishmania parasites that affect internal organs including spleen, liver, and bone marrow. The infective stage called promastigote, is transmitted into the host skin via sandfly bites. Visceral leishmaniasis is usually associated with high mortality rate in poor and developing countries, lacking proper health assistance. Moreover, treatments are expensive while no approved vaccines exist to prevent infection and avoid disease outbreaks. This study suggests an affordable and adjuvant-free vaccine formulation made from the total lysate of promastigotes. Vaccine administration via the intranasal route, ensures a remarkable clearance of Leishmania parasites from the internal organs of infected experimental mice. In particular, intranasal route known to be not invasive, is efficient in inducing adequate immune response against the infective form of the parasite. Further studies are now required to improve this prophylactic vaccine and provide therefore the basis for a promising translational approach.

Current status of nanoscale drug delivery and the future of nano-vaccine development for leishmaniasis - A review

The study of tropical diseases like leishmaniasis, a parasitic disease, has not received much attention even though it is the second-largest infectious disease after malaria. As per the WHO report, a total of 0.7-1.0 million new leishmaniasis cases, which are spread by 23 Leishmania species in more than 98 countries, are estimated with an alarming 26,000-65,000 death toll every year. Lack of potential vaccines along with the cost and toxicity of amphotericin B (AmB), the most common drug for the treatment of leishmaniasis, has raised the interest significantly for new formulations and drug delivery systems including nanoparticle-based delivery as anti-leishmanial agents. The size, shape, and high surface area to volume ratio of different NPs make them ideal for many biological applications. The delivery of drugs through liposome, polymeric, and solid-lipid NPs provides the advantage of high biocomatibilty of the carrier with reduced toxicity. Importantly, NP-based delivery has shown improved efficacy due to targeted delivery of the payload and synergistic action of NP and payload on the target. This review analyses the advantage of NP-based delivery over standard chemotherapy and natural product-based delivery system. The role of different physicochemical properties of a nanoscale delivery system is discussed. Further, different ways of nanoformulation delivery ranging from liposome, niosomes, polymeric, metallic, solid-lipid NPs were updated along with the possible mechanisms of action against the parasite. The status of current nano-vaccines and the future potential of NP-based vaccine are elaborated here.

A Chimera of Th1 Stimulatory Proteins of Leishmania donovani Offers Moderate Immunotherapeutic Efficacy with a Th1-Inclined Immune Response against Visceral Leishmaniasis

Immunotherapy, a treatment based on host immune system activation, has been shown to provide a substitute for marginally effective conventional chemotherapy in controlling visceral leishmaniasis (VL), the deadliest form of leishmaniasis. As the majority of endemic inhabitants exhibit either subclinical or asymptomatic infection which often develops into the active disease state, therapeutic intervention seems to be an important avenue for combating infections by stimulating the natural defense system of infected individuals. With this perspective, the present study focuses on two immunodominant Leishmania (L.) donovani antigens (triosephosphate isomerase and enolase) previously proved to be potent prophylactic VL vaccine candidates, for generating a recombinant chimeric antigen. This is based on the premise that in a heterogeneous population, a multivalent antigen vaccine would be required for an effective response against leishmaniasis (a complex parasitic disease). The resulting molecule rLdT-E chimeric protein was evaluated for its immunogenicity and immunotherapeutic efficacy. A Th1 stimulating adjuvant BCG was employed with the protein which showed a remarkable 70% inhibition of splenic parasitic multiplication positively correlated with boosted Th1 dominant immune response against lethal L. donovani challenge in hamsters as evidenced by high IFN-γ and TNF-α and low IL-10. In addition, immunological analysis of antibody subclass presented IgG2-based humoral response besides considerable delayed-type hypersensitivity and lymphocyte proliferative responses in rLdT-E/BCG-treated animals. Our observations indicate the potential of the chimera towards its candidature for an effective vaccine against Leishmania donovani infection.