Leishmaniavaccines: progress and problems

Balancing the functions of DNA extracellular traps in intracellular parasite infections: implications for host defense, disease pathology and therapy

The release of DNA to the extracellular milieu is a biological process referred to as etosis, which is involved in both physiological and pathological functions. Although the release of DNA extracellular traps (ETs) was initially attributed to innate immune cells such as neutrophils, eosinophils, and macrophages, recent studies have shown that T cells, as well as non-immune cells, are capable of releasing ETs. These structures were described primarily for their potential to trap and kill pathogens, presenting an important strategy of host defense. Intriguingly, these functions have been associated with intracellular pathogens such as the parasites Leishmania sp. and Trypanosoma cruzi, causative agents of leishmaniasis and Chagas disease, respectively. These are two devastating tropical diseases that lead to thousands of deaths every year. In an apparent contradiction, ETs can also induce and amplify inflammation, which may lead to worsening disease pathology. This has prompted the concept of targeting ETs' release as a means of controlling tissue destruction to treat human diseases. What is the best approach to prevent disease severity: inducing ETs to kill pathogens or preventing their release? In this Perspective article, we will discuss the importance of understanding ETs released by different cell types and the need to balance their potentially complementary functions. In addition, we will explore other functions of ETs and their translational applications to benefit individuals infected with intracellular parasites and other pathogens. Ultimately, a better understanding of the role of ETs in disease pathogenesis will provide valuable insights into developing novel therapies for human diseases.

Deletion of MIF gene from live attenuated LdCen-/- parasites enhances protective CD4+ T cell immunity

Vaccination with live attenuated Leishmania parasites such as centrin deleted Leishmania donovani (LdCen^-/-) against visceral leishmaniasis has been reported extensively. The protection induced by LdCen^-/- parasites was mediated by both CD4⁺ and CD8⁺ T cells. While the host immune mediators of protection are known, parasite determinants that affect the CD4⁺ and CD8⁺ T cell populations remain unknown. Parasite encoded inflammatory cytokine MIF has been shown to modulate the T cell differentiation characteristics by altering the inflammation induced apoptosis during contraction phase in experimental infections with Leishmania or Plasmodium. Neutralization of parasite encoded MIF either by antibodies or gene deletion conferred protection in Plasmodium and Leishmania studies. We investigated if the immunogenicity and protection induced by LdCen^-/- parasites is affected by deleting MIF genes from this vaccine strain. Our results showed that LdCen^-/-MIF^-/- immunized group presented higher percentage of CD4⁺ and CD8⁺ central memory T cells, increased CD8⁺ T cell proliferation after challenge compared to LdCen^-/- immunization. LdCen^-/-MIF^-/- immunized group presented elevated production of IFN-γ⁺ and TNF-α⁺ CD4⁺ T cells concomitant with a reduced parasite load in spleen and liver compared to LdCen^-/-group following challenge with L. infantum. Our results demonstrate the role of parasite induced factors involved in protection and long-term immunity of vaccines against VL.

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.

Immunoinformatics based design and prediction of proteome-wide killer cell epitopes of Leishmania donovani: Potential application in vaccine development

Despite several extensive and exhaustive efforts, search for potential therapy against leishmaniasis has not made much progress. In the present work, we have employed mining strategy to screen Leishmania donovani proteome for identification of promising vaccine candidate. We have screened 21 potential antigenic proteins from 7960 total protein of L. donovani, based on the presence of signal peptide, GPI anchor, antigenicity prediction and substractive proteomic approach. Secondly, we have also performed comprehensive immunogenic epitope prediction from the screened 21 proteins, using IEDB-AR tools. Out of the 21 antigenic proteins, we obtained 11 immunogenic epitopes from 9 proteins. The final results revealed that four predicted epitopes namely; YPAFAALVF, VAVAATVAY, AAAPTEAAL and MYPLVAVVF, have significantly better binding potential with respective alleles and could elicits immune responses. Docking analysis using PATCHDOCK server and molecular dynamic simulation using GROMACS revealed the potential of the sequences as immunogenic epitopes. In silico studies also suggested that the epitopes occupied almost same binding cleft with the respective alleles, when compared with the reference peptides. It is also suggested from the molecular dynamic simulation data that the peptides were intact in the pocket for longer periods of time. Our study was designed to select MHC class I restricted epitopes for the activation of CD8 T cells using immunoinformatics for the prediction of probable vaccine candidate against L. donovani parasites. Communicated by Ramaswamy H. Sarma.

In-silico design of an immunoinformatics based multi-epitope vaccine against Leishmania donovani

BACKGROUND

Visceral Leishmaniasis (VL) is a fatal vector-borne parasitic disorder occurring mainly in tropical and subtropical regions. VL falls under the category of neglected tropical diseases with growing drug resistance and lacking a licensed vaccine. Conventional vaccine synthesis techniques are often very laborious and challenging. With the advancement of bioinformatics and its application in immunology, it is now more convenient to design multi-epitope vaccines comprising predicted immuno-dominant epitopes of multiple antigenic proteins. We have chosen four antigenic proteins of Leishmania donovani and identified their T-cell and B-cell epitopes, utilizing those for in-silico chimeric vaccine designing. The various physicochemical characteristics of the vaccine have been explored and the tertiary structure of the chimeric construct is predicted to perform docking studies and molecular dynamics simulations.

RESULTS

The vaccine construct is generated by joining the epitopes with specific linkers. The predicted tertiary structure of the vaccine has been found to be valid and docking studies reveal the construct shows a high affinity towards the TLR-4 receptor. Population coverage analysis shows the vaccine can be effective on the majority of the world population. In-silico immune simulation studies confirms the vaccine to raise a pro-inflammatory response with the proliferation of activated T and B cells. In-silico codon optimization and cloning of the vaccine nucleic acid sequence have also been achieved in the pET28a vector.

CONCLUSION

The above bioinformatics data support that the construct may act as a potential vaccine. Further wet lab synthesis of the vaccine and in vivo works has to be undertaken in animal model to confirm vaccine potency.

Canine Leishmaniasis: Update on Epidemiology, Diagnosis, Treatment, and Prevention

Dog are the main reservoir of Leishmania infantum, causing canine leishmaniasis, an incurable multisystemic disease that leads to death in symptomatic dogs, when not treated. This parasite causes visceral, cutaneous, and mucosal leishmaniasis in people in the Mediterranean Basin, North Africa, South America, and West Asia. This disease is mostly unknown by veterinarians outside the endemic areas, but the disease is expanding in the Northern Hemisphere due to travel and climate change. New methodologies to study the epidemiology of the disease have found new hosts of leishmaniasis and drawn a completely new picture of the parasite biological cycle. Canine leishmaniasis diagnosis has evolved over the years through the analysis of new samples using novel molecular techniques. Given the neglected nature of leishmaniasis, progress in drug discovery is slow, and the few drugs that reach clinical stages in humans are unlikely to be commercialised for dogs, but several approaches have been developed to support chemotherapy. New-generation vaccines developed during the last decade are now widely used, along with novel prevention strategies. The implications of the epidemiology, diagnosis, treatment, and prevention of canine leishmaniasis are fundamental to public health.

Spatial modeling of zoonotic cutaneous leishmaniasis with regard to potential environmental factors using ANFIS and PCA-ANFIS methods

This study compares two adaptive neuro-fuzzy inference system (ANFIS) and principal component analysis (PCA)-ANFIS techniques for spatial modeling and forecasting of zoonotic cutaneous leishmaniasis (ZCL) cases in rural districts of Golestan province, Iran. We collected and prepared data on ZCL cases and climatic, topographic, vegetation, and human population factors. By applying the PCA algorithm, the parameters affecting the ZCL incidence were decomposed into principal components (PCs), and their dimensions were reduced. Then, PCs were used to train the ANFIS model. To evaluate the proposed approaches in model assessment phase, we used test data in 2016. In this phase, we showed that PCA-ANFIS model with values ​​of R² = 0.791, MAE = 0.681, RMSE = 0.904 compared to ANFIS model with values ​​of R² = 0.705, MAE = 0.827, RMSE = 1.073 has better performance in prediction of the ZCL cases. Actual and predicted maps of ZCL cases in 2016 by both models demonstrated that the high-risk regions of the disease are located in the northeastern, northern parts, and some central rural districts of Golestan province. Sensitivity analysis of the ANFIS model showed that population, vegetation, average wind speed, elevation, and average soil temperature, respectively, are the most significant factors in predicting the ZCL cases. The findings indicated the importance of machine learning (ML) techniques (ANFIS and PCA-ANFIS) in medical geography studies. By using these approaches, with less cost and shorter time, high-risk areas of diseases can be predicted, and the most effective factors on the spatial prediction of diseases can be identified. Public health policymakers can use these useful tools to control and prevent the disease and to allocate resources to disease-prone areas.

An alphavirus-derived self-amplifying mRNA encoding PpSP15-LmSTI1 fusion protein for the design of a vaccine against leishmaniasis

The main aims of the present study were to design a fusion protein of Leishmania major stress-inducible protein 1 (LmSTI1) and Phlebotomus papatasi SP15 (PpSP15), and to express it in the form of alphavirus packaged Self-amplifying mRNA (SAM). Two combinations, PpSP15-LmSTI1 and LmSTI1-PpSP15 fusion forms, were analyzed for folding and minimum free energies of the mRNA. Conformational studies on 3D modeled fusion and native forms were performed, and the Root-Mean-Square-distance (RMSD) of the Cα atomic coordinates were calculated. Antigenicity and stability were predicted using bioinformatics tools. The coding sequences of PpSP15-LmSTI1 fusion, PpSP15, and LmSTI1 were cloned into an alphavirus-based vector and used to produce the SAM constructs. All the subcloned constructs were then subjected to packaging in the form of viral replicon particles (VRPs),and were evaluated for their ability to infect BHK-21 cells and express the recombinant fusion proteins. The in-silico analysis indicated that the PpSP15-LmSTI1 combination could be a promising candidate based on lower folding ΔG of mRNA, higher protein antigenicity and lower instability indexes, and less conformational changes compared to the native proteins and the LmSTI1-PpSP15 fusion form. Packaged SAM encoding fusion and native antigens are used for infection of mammalian cells and for recombinant protein expression. This is the first study on in silico designing and successful packaging of an alphavirus-derived SAM in the form of the VRPs to target leishmaniasis.

Vaccination in Leishmaniasis: A Review Article

Leishmaniasis is caused by protozoan Leishmania parasites that are transmitted through female sandfly bites. The disease is predominantly endemic to the tropics and semi-tropics and has been reported in more than 98 countries. Due to the side effects of anti-Leishmania drugs and the emergence of drug-resistant isolates, there is currently no encouraging prospect of introducing an effective therapy for the disease. Hence, it seems that the key to disease control management is the introduction of an effective vaccine, particularly against its cutaneous form. Advances in understanding underlying immune mechanisms are feasibale using a variety of candidate antigens, including attenuated live parasites, crude antigens, pure or recombinant Leishmania proteins, Leishmania genes encoding protective proteins, as well as immune system activators from the saliva of parasite vectors. However, there is still no vaccine against different types of human leishmaniasis. In this study, we review the works conducted or being performed in this field.

Immunoinformatics Approach to Design a Novel Subunit Vaccine Against Visceral Leishmaniasis

Visceral leishmaniasis (VL) infection is mostly caused by Leishmania donovani and affects countries worldwide. Despite the need for a safe and effective vaccine against leishmaniasis due to the increased drug resistance, however, no vaccine has yet been licensed for clinical use. This study revolves around the immunoinformatics approach to design a multi-epitope vaccine against VL infection. In this case, the proteome of L. donovani has been investigated, and three host non-homologous and antigenic extracellular secretory proteins have been identified as potential vaccine candidates with low transmembrane helices (≤ 1). The multi-epitope subunit vaccine construct consists of T-cell (cytotoxic T-lymphocyte (CTL) and helper T-lymphocyte (HTL)) epitopes accompanied by appropriate adjuvant and linkers. A 372-amino acid vaccine construct has been established with specific characteristics, such as soluble, stable, antigenic, non-allergenic, non-toxic, and non-host homologous. Besides, the tertiary structure of the designed vaccine was modeled and validated. Also, the stability and affinity of the vaccine- TLR4 complex were confirmed by using molecular docking and molecular dynamics (MD) simulation. In addition, in silico immunization assay showed the efficiency of this candidate vaccine to stimulate an effective immune response. Furthermore, the refined vaccine was optimized and cloned in the pET28a (+) vector, and its successful expression was confirmed virtually. However, the experimental validation is required to verify the multi-epitope vaccine efficacy against VL infection.

Potential molecular targets of Leishmania pathways in developing novel antileishmanials

The illness known as leishmaniasis has not become a household name like malaria, although it stands as the second-largest parasitic disease, surpassed only by malaria. As no licensed vaccine is available, treatment for leishmaniasis mostly relies on chemotherapy. Inefficiency and drug resistance are the major impediments in current therapeutics. In this scenario, identification of novel molecular drug candidates is indispensable to develop robust antileishmanials. The exploration of structure-based drugs to target enzymes/molecules of Leishmania which differ structurally/functionally from their equivalents in mammalian hosts not only helps in developing a new class of antileishmanials, but also paves the way to understand Leishmania biology. This review provides a comprehensive overview on possible drug candidates relating to various Leishmania molecular pathways.

Quantitative evaluation of PpSP15-LmSTI1 fusion gene expression following transfection with an alphavirus-derived self-amplifying mRNA and conventional DNA vaccine platforms

New vaccine platforms are crucial to address complex parasitic infections such as cutaneous leishmaniasis. Self-amplifying mRNA (SAM) based vaccines represent the next generation nucleic acid-based platform. In the present study, we compared the expression levels of PpSP15-LmSTI1 fusion gene in BHK-21 cells following transfection with Semliki Forest virus (SFV)-derived SAM, SFV-derived plasmid DNA (pSFV-PD) and conventional plasmid DNA (pcDNA3.1+). PpSP15-LmSTI1 fusion gene expression levels were evaluated at different time points, using quantitative Real-time PCR. All data were validated and normalized by two internal control genes. According to the results, mean values of relative expression were significantly higher for SFV-PD SAM/fusion than pcDNA/fusion and pSFV-PD/fusion at all concentrations and time points. Our results showed that higher levels of PpSp15-LmSTI1 antigen expression could be achieved using a SAM vector than pcDNA and pSFV-PD, making it a valuable and efficient alternative to conventional plasmid DNA-based vaccines against leishmaniasis.

Immunoproteomics characterization of Leishmania panamensis proteins for potential clinical diagnosis of mucosal Leishmaniasis

Diagnosis of leishmaniasis based on antibodies detection represents a challenge due to cross-reaction of sera with other infectious agents, which co-exist in endemic areas of Leishmania sp, especially patients with Trypanosoma cruzi. This work is aimed at searching for immunogenic proteins in sera from patients with cutaneous and mucosal leishmaniasis that may be potential candidates for the development of diagnostic tests and/or vaccines that help control the infection. Total protein extracts of L. panamensis promastigotes were put in contact with sera from patients with cutaneous and mucosal leishmaniasis (immunoblots). Immunoreactive proteins were identified by mass spectrometry and bioinformatics tools. 81 proteins were identified. One of these was uniquely recognized by the sera from patients with ML but not from sera from either CL or Chagas disease patients. MS analysis of this band pointed to the putative leishmanial 3-oxoacyl-(Acylcarrierprotein) reductase.

Genetically modified live attenuated vaccine: A potential strategy to combat visceral leishmaniasis

Visceral leishmaniasis (VL) is caused by a protozoan parasite Leishmania donovani mainly influencing the population of tropical and subtropical regions across the globe. The arsenal of drugs available is limited, and prolonged use of such drugs makes parasite to become resistant. Therefore, it is very imperative to develop a safe, cost-effective and inexpensive vaccine against VL. Although in recent years, many strategies have been pursued by researchers, so far only some of the vaccine candidates reached for clinical trial and more than half of them are still in pipeline. There is now a broad consent among Leishmania researchers that the perseverance of parasite is very essential for eliciting a protective immune response and may perhaps be attained by live attenuated parasite vaccination. For making a live attenuated parasite, it is very essential to ensure that the parasite is deficient of virulence and should further study genetically modified parasites to perceive the mechanism of pathogenesis. So it is believed that in the near future, a complete understanding of the Leishmania genome will explore clear strategies to discover a novel vaccine. This review describes the need for a genetically modified live attenuated vaccine against VL, and obstacles associated with its development.

The immunogenicity and protective immunity of multi-epitopes DNA prime-protein boost vaccines encoding Amastin-Kmp-11, Kmp11-Gp63 and Amastin-Gp63 against visceral leishmaniasis

Visceral leishmaniasis (VL) is the most fatal form of leishmaniasis if left untreated and 50,000 to 90,000 new cases of VL occur worldwide each year. Although various vaccines had been studied in animal models, none of them was eligible to prevent human from infections. In this study, according to the silico analysis of Leishmania Amastin, Kmp-11 and Gp63 protein, dominant epitope sequences of these proteins were selected and linked to construct dominant multi-epitopes DNA and protein vaccines (Amastin-Kmp-11, Amastin-Gp63 and Kmp-11-Gp63) against VL. BALB/c mice were immunized with a DNA prime-protein boost immunization strategy and challenged with a new Leishmania parasite strain isolated from a VL patient. After immunization, the results including specific antibody titers, IL-4 and TNF-α levels, and CD4 and CD8 T cell proportion suggested the potent immunogenicity of the three vaccines. After infection, the results of spleen parasite burdens in the three vaccine groups were significantly lower than those of control groups, and the parasite reduction rates of Amastin-Kmp-11, Amastin-Gp63 and Kmp-11-Gp63 groups were 89.38%, 91.01% and 88.42%, respectively. Spleen smear observation and liver histopathological changes showed that all vaccine groups could produce significant immunoprotection against VL and Amastin-Gp63 vaccine was the best. In conclusion, our work demonstrated that the three dominant multi-epitopes Amastin-Kmp-11, Amastin-Gp63 and Kmp-11-Gp63 DNA prime-protein boost vaccines might be new vaccine candidates for VL, and the Amastin-Gp63 vaccine have best efficacy.

The potential of live attenuated vaccines against Cutaneous Leishmaniasis

Cutaneous Leishmaniasis is a serious public health problem, typically affecting poor populations with limited access to health care. Control is largely dependent on chemotherapies that are inefficient, costly and challenging to deliver. Vaccination is an attractive and feasible alternative because long-term protection is typical in patients who recover from the disease. No human vaccine is yet approved for use, but several candidates are at various stages of testing. Live attenuated parasites, which stimulate long-term immune protection, have potential as effective vaccines, and their challenges relating to safety, formulation and delivery can be overcome. Here we review current data on the potential of live attenuated Leishmania vaccines and discuss possible routes to regulatory approval.

Bioinformatics analyses of immunogenic T-cell epitopes of LeIF and PpSP15 proteins from Leishmania major and sand fly saliva used as model antigens for the design of a multi-epitope vaccine to control leishmaniasis

Leishmaniasis is caused by protozoan parasites belonging to 20 Leishmania species. This infectious disease is transmitted by bites of infected phlebotomine sandflies, and is widespread in 97 countries throughout the world. No preventive or effective vaccine has been developed yet. In this study, diverse computational methods were integrated to calculate evolutionary divergence, immunogenicity, IFN-γ production, epitope conservancy, and population coverage of protein fusion models of LeIF-SP15 namely SaLeish. Immunogenicity of LeIF of Leishmania species and SP15 of sandfly saliva has not been investigated in-silico in fusion form. A complete set of 9-mer MHC class I and 15-mer MHC class II peptides were identified with a high affinity for the antigenic epitopes of SaLeish inducing specific responses of CD8⁺ and CD4⁺ T cells from BALB/c and human. Our preferred approach was determining truncated fragment of SaLeish rather than a whole length bearing the capacity to trigger specific immune response. Phylogenetic analysis showed that LeIF protein is under balancing selection and is conserved between different Leishmania species. Selected SaLeish model contained 19 and 35 antigenic peptides for MHC class I and II, respectively, with strong binding affinity to both highly frequent HLA-I and HLA-II alleles. Analysis of class I CTL epitopes showed that promiscuous peptides of KSLKADIRK, MSCIPHCKY, LQAGVIVAV, and YQYYGFVAM have greater affinity to interact with HLA-A*01:01, HLA-A*02 (03, 06), HLA-A*30:02, HLA-B*40:01, and HLA-B*52:01 molecules. Population coverage with a range of 78-85% confirmed SaLeish-Model4 as an appropriate vaccine candidate among Persian, South Asia, Europe, and North America population. Also, predicted antigenic epitopes of AKPEIRTFSNVLIKY, TRVQDDLRKLQAGVI, and VALFSATMPEEVLEL corresponding to MHC class II were found to provide strong ability to produce IFNγ toward TH(1)-biased-DTH responses. Findings of the current investigation warrant the future experimental assessment of promising SaLeish prophylaxis vaccine that is capable to enhance both innate and specific cellular immune responses.

Leishmanicidal effects of amphotericin B in combination with selenium loaded on niosome against Leishmania tropica

The strategy for improving the treatment of leishmaniasis by the World Health Organization, is the development of new drugs and combination therapy. The aim of this survey was to investigate the effect of amphotericin B (AmB) in combination with selenium, in a simple or niosomal form, on Leishmania tropica (L. tropica) by in vitro advanced assays. In this study, a niosomal formulation of AmB with selenium was prepared and characterized based on size and morphology. Using MTT assay, macrophage model, flow cytometry, and qPCR, the cytotoxicity and efficiency of the niosomal formulation and simple form of combination were evaluated. No toxicity was reported for both the niosomal and simple form of the combination. The niosomal formulation significantly showed higher inhibitory effect on the promastigote and amastigote forms of L. tropica than simple combination form. Interleukin (IL)-10 significantly decreased while the level of IL-12 and metacasoase as Th-1 activator significantly increased (P < 0.001). The findings of this study indicated that niosomes are the stable carriers for this combination, easy to produce and provide promising results as an effective formulation in the inhibition of extracellular and intracellular forms of L. tropica in compared with simple combination form.

Current Visceral Leishmaniasis Research: A Research Review to Inspire Future Study

Visceral leishmaniasis (VL), one of the deadliest parasitic diseases in the world, causes more than 50,000 human deaths each year and afflicts millions of people throughout South America, East Africa, South Asia, and Mediterranean Region. In 2015 the World Health Organization classified VL as a neglected tropical disease (NTD), prompting concentrated study of the VL epidemic using mathematical and simulation models. This paper reviews literature related to prevalence and prevention control strategies. More than thirty current research works were reviewed and classified based on VL epidemic study methods, including modeling approaches, control strategies, and simulation techniques since 2013. A summarization of these technical methods, major findings, and contributions from existing works revealed that VL epidemic research efforts must improve in the areas of validating and verifying VL mathematical models with real-world epidemic data. In addition, more dynamic disease control strategies must be explored and advanced simulation techniques must be used to predict VL pandemics.

Efficacy of Four Solanum spp. Extracts in an Animal Model of Cutaneous Leishmaniasis

Background: Leishmaniasis is a complex protozoa disease caused by Leishmania genus (Trypanosomatidae family). Currently, there have been renewed interests worldwide in plants as pharmaceutical agents. In this study, the in vivo efficacy of Solanum spp. is assessed in an L. amazonensis BALB/c mice model for experimental cutaneous leishmaniasis. Methods: Animals were infected with 5 × 10⁶ metacyclic promastigotes and 30-day post-infection, a treatment with 30 mg/kg of Solanum extracts or Glucantime^® (GTM) was applied intralesionally every four days to complete 5 doses. Results: Neither death nor loss of weight higher than 10% was observed. All the tested extracts were able to control the infection, compared with the infected and untreated group. Solanum havanense Jacq. extract showed the highest efficacy and was superior (p < 0.05) to GTM. Solanum myriacanthum Dunal., S. nudum Dunal. and S. seaforthianum Andr. extracts demonstrated a similar effect (p > 0.05) to GTM. An increase of IFN-γ (p < 0.05) was displayed only by animals treated with S. nudum compared to the group treated with a vehicle, while no differences (p > 0.05) were observed for IL-12. Conclusions:In vivo effects of Solanum extracts were demonstrated, suggesting that this genus could be further explored as a new antileishmanial alternative.

Emerging therapeutic targets for treatment of leishmaniasis

INTRODUCTION

Parasitic diseases that pose a threat to human life include leishmaniasis - caused by protozoan parasite Leishmania species. Existing drugs have limitations due to deleterious side effects like teratogenicity, high cost and drug resistance. This calls for the need to have an insight into therapeutic aspects of disease. Areas covered: We have identified different drug targets via. molecular, imuunological, metabolic as well as by system biology approaches. We bring these promising drug targets into light so that they can be explored to their maximum. In an effort to bridge the gaps between existing knowledge and prospects of drug discovery, we have compiled interesting studies on drug targets, thereby paving the way for establishment of better therapeutic aspects. Expert opinion: Advancements in technology shed light on many unexplored pathways. Further probing of well established pathways led to the discovery of new drug targets. This review is a comprehensive report on current and emerging drug targets, with emphasis on several metabolic targets, organellar biochemistry, salvage pathways, epigenetics, kinome and more. Identification of new targets can contribute significantly towards strengthening the pipeline for disease elimination.

Combined Strategies to Improve the Expression of Recombinant Sterol C24-Methyltransferase from Leishmania braziliensis in E. coli

Among the neglected tropical diseases, leishmaniasis stands out for its worldwide distribution and diversity of symptoms. Cutaneous leishmaniasis (CL), for instance, is endemic in 18 countries, but the available drugs to fight it have high toxicity and low patient adherence. In order to overcome this, dilemma drugs that target enzymes which are absent in the human host, such as Leishmania braziliensis sterol C24-methyltransferase (SMT-C24, EC 2.1.1.41), are needed. However, medicinal chemistry efforts toward this goal have been hampered by the low yield of soluble recombinant SMT-C24 afforded by currently available expression systems. Herein, we show that a combination of molecular biology and chromatographic strategies may increase the yield of LbSMT-C24 in up to fivefold. These results lay the ground for future investigation of this enzyme as a drug target.

Exploring Leishmania secretory proteins to design B and T cell multi-epitope subunit vaccine using immunoinformatics approach

Visceral leishmaniasis (VL) is a fatal form of leishmaniasis which affects 70 countries, worldwide. Increasing drug resistance, HIV co-infection, and poor health system require operative vaccination strategy to control the VL transmission dynamics. Therefore, a holistic approach is needed to generate T and B memory cells to mediate long-term immunity against VL infection. Consequently, immunoinformatics approach was applied to design Leishmania secretory protein based multi-epitope subunit vaccine construct consisting of B and T cell epitopes. Further, the physiochemical characterization was performed to check the aliphatic index, theoretical PI, molecular weight, and thermostable nature of vaccine construct. The allergenicity and antigenicity were also predicted to ensure the safety and immunogenic behavior of final vaccine construct. Moreover, homology modeling, followed by molecular docking and molecular dynamics simulation study was also performed to evaluate the binding affinity and stability of receptor (TLR-4) and ligand (vaccine protein) complex. This study warrants the experimental validation to ensure the immunogenicity and safety profile of presented vaccine construct which may be further helpful to control VL infection.

Meglumine antımoniate-TiO2@Ag nanoparticle combinations reduce toxicity of the drug while enhancing its antileishmanial effect

Currently, the treatment of leishmaniasis is increasingly insufficient as current antileishmanial drugs have many disadvantages such as toxic side effects, high cost, and growing drug resistance. In order to overcome these disadvantages, researchers have recently focused on combination therapy by using pentavalent antimonials in conjunction with other antileihmanial compounds. Our previous study found that TiO2@Ag nanoparticles (TiAgNps) demonstrated significant antileishmanial effects. However, a lethal dose of TiAgNps on L. topica promastigotes was found to be toxic for macrophage cells. Moreover, non-toxic concentrations of TiAgNps were ineffective in inhibiting L. topica promastigotes and amastigotes. Thus, we propose the use of TiAgNps in combination with other antileishmanial compounds like meglumine antimoniate (MA) at non-toxic concentrations, which may increase the efficacies of both agents and decrease their toxicities. Therefore, the aim of this study was to determine in vitro and in vivo antileishmanial efficacies of TiAgNps-MA combinations at non-toxic concentrations and develop a new approach for treatment that lowers the toxicities of pentavalent antimonials to minimal levels and enhances their effectiveness. In vitro screening was performed on L. topica promastigote and amastigote-macropage culture by using MTT assay to determine proliferation, perform infection index analysis, and to conduct a Griess reaction for nitric oxide production, while in vivo antileishmanial assays were applied on Balb/c mice with CL models. The results demonstrated that combinations including TiAgNps and MA at non-toxic concentrations were highly efficacious against both promastigotes and amastigotes, while MA application alone did not show any inhibitory effects. It was determined that combination applications decreased the proliferation of L. topica promastigotes 2- to 5-fold in contrast to use of MA alone, and was dependent on concentrations. Moreover, the use of combinations led to inhibition of L. topica amastigotes at rates ranging between 80% and 95%. Additionally, combinations were found to decrease metabolic activities of each form of the parasite at ranges between 7- to 20-fold, causing programmed-cell death and stimulation of macrophages for intensive production of nitric oxide, which is accepted as an important antileishmanial agent (p<0.05). Furthermore, Σ FIC analysis demonstrated that the tested combinations composed little additive, but mostly synergistic effects for inhibition of promastigotes and amastigotes. According to in vivo screening results, the combinations displayed high antileishmanial activities by successfully healing lesions and significantly reducing parasite burdens. Combined, these results show that TiAgNps-MA combinations were much more effective than use of MA alone at non-toxic concentrations and they possess high potential for development of new antileishmanial drugs to fight against leishmaniasis.

Nanoliposomal Buparvaquone Immunomodulates Leishmania infantum-Infected Macrophages and Is Highly Effective in a Murine Model

Visceral leishmaniasis is a fatal parasitic neglected disease affecting 1.5 million people worldwide. Based on a drug repositioning approach, the aim of this work was to investigate the in vitro immunomodulatory potential of buparvaquone (BPQ) and to establish a safe regimen to evaluate the in vivo efficacy of BPQ entrapped by negatively charged nanoliposomes (BPQ-LP) in Leishmania infantum-infected hamsters. Small-angle X-ray scattering, dynamic light scattering, and the ζ-potential were applied in order to study the influence of BPQ on the liposome structure. Our data revealed that BPQ was located in the polar-apolar interface, snorkeling the polar region, and protected against aggregation inside the lipophilic region. The presence of BPQ also decreased the Z-average hydrodynamic diameter and increased the surface charge. Compared to intravenous and intramuscular administration, a subcutaneous route was a more effective route for BPQ-LP; at 0.4 mg/kg, BPQ-LP reduced infection in the spleen and liver by 98 and 96%, respectively. Treatment for 5 days resulted in limited efficacy, but 10 days of treatment resulted in an efficacy similar to that of a 15-day regimen. The nanoliposomal drug was highly effective, with a mean 50% effective dose of 0.25 mg/kg, reducing the parasite load in bone marrow by 80%, as detected using quantitative PCR analysis. In addition, flow cytometry studies showed that BPQ upregulated cytokines as tumor necrosis factor, monocyte chemoattractant protein 1, interleukin-10 (IL-10), and IL-6 in Leishmania-infected macrophages, eliminating the parasites via a nitric oxide-independent mechanism. This new formulation proved to be a safe and effective treatment for murine leishmaniasis that could be a useful candidate against visceral leishmaniasis.

Gene deleted live attenuated Leishmania vaccine candidates against visceral leishmaniasis elicit pro-inflammatory cytokines response in human PBMCs

Currently no effective vaccine is available for human visceral leishmaniasis(VL) caused by Leishmania donovani. Previously, we showed that centrin1 and p27gene deleted live attenuated Leishmania parasites (LdCen1(-/-) and Ldp27(-/-)) are safe, immunogenic and protective in animal models. Here, to assess the correlates of protection, we evaluated immune responses induced by LdCen1(-/-) and Ldp27(-/-) in human blood samples obtained from healthy, healed VL (HVL), post kala-azar dermal leishmaniasis(PKDL) and VL subjects. Both parasites infected human macrophages, as effectively as the wild type parasites. Further, LdCen1(-/-) and Ldp27(-/-) strongly stimulated production of pro-inflammatory cytokines including, IL-12, IFN-γ, TNF-α, IL-2, IL-6 and IL-17 in the PBMCs obtained from individuals with a prior exposure to Leishmania (HVL and PKDL). There was no significant stimulation of anti-inflammatory cytokines (IL-4 and IL-10). Induction of Th1 biased immune responses was supported by a remarkable increase in IFN-γ secreting CD4(+) and CD8(+) T cells and IL-17 secreting CD4(+) cells in PBMCs from HVL cases with no increase in IL-10 secreting T cells. Hence, LdCen1(-/-) and Ldp27(-/-) are promising as live vaccine candidates against VL since they elicit strong protective immune response in human PBMCs from HVL, similar to the wild type parasite infection, mimicking a naturally acquired protection following cure.

Differences in immune responses against Leishmania induced by infection and by immunization with killed parasite antigen: implications for vaccine discovery

The leishmaniases are a group of diseases caused by different species of the protozoan genus Leishmania and transmitted by sand fly vectors. They are a major public health problem in almost all continents. There is no effective control of leishmaniasis and its geographical distribution is expanding in many countries. Great effort has been made by many scientists to develop a vaccine against leishmaniasis, but, so far, there is still no effective vaccine against the disease. The only way to generate protective immunity against leishmaniasis in humans is leishmanization, consisting of the inoculation of live virulent Leishmania as a means to acquire long-lasting immunity against subsequent infections. At present, all that we know about human immune responses to Leishmania induced by immunization with killed parasite antigens came from studies with first generation candidate vaccines (killed promastigote extracts). In the few occasions that the T cell-mediated immune responses to Leishmania induced by infection and immunization with killed parasite antigens were compared, important differences were found both in humans and in animals. This review discusses these differences and their relevance to the development of a vaccine against leishmaniasis, the major problems involved in this task, the recent prospects for the selection of candidate antigens and the use of attenuated Leishmania as live vaccines.

Immunoprotective responses of T helper type 1 stimulatory protein-S-adenosyl-L-homocysteine hydrolase against experimental visceral leishmaniasis

It is well known that a patient in clinical remission of visceral leishmaniasis (VL) remains immune to reinfection, which provides a rationale for the feasibility of a vaccine against this deadly disease. In earlier studies, observation of significant cellular responses in treated Leishmania patients as well as in hamsters against leishmanial antigens from different fractions led to its further proteomic characterization, wherein S-adenosyl-L-homocysteine hydrolase (AdoHcy) was identified as a helper type 1 (Th1) stimulatory protein. The present study includes immunological characterization of this protein, its cellular responses [lymphoproliferation, nitric oxide (NO) production and cytokine responses] in treated Leishmania-infected hamsters and patients as well as prophylactic efficacy against Leishmania challenge in hamsters and the immune responses generated thereof. Significantly higher cellular responses were noticed against recombinant L. donovani S-adenosyl-L-homocysteine hydrolase (rLdAdoHcy) compared to soluble L. donovani antigen in treated samples. Moreover, stimulation of peripheral blood mononuclear cells with rLdAdoHcy up-regulated the levels of interferon (IFN)-γ, interleukin (IL)-12 and down-regulated IL-10. Furthermore, vaccination with rLdAdoHcy generated perceptible delayed-type hypersensitivity response and exerted considerably good prophylactic efficacy (∼70% inhibition) against L. donovani challenge. The efficacy was confirmed by the increased expression levels of inducible NO synthase and Th1-type cytokines, IFN-γ and IL-12 and down-regulation of IL-4, IL-10 and transforming growth factor (TGF)-β. The results indicate the potentiality of rLdAdoHcy protein as a suitable vaccine candidate against VL.

Cutaneous Leishmaniasis Vaccination: A Matter of Quality

There have been exhaustive efforts to develop an efficient vaccine against leishmaniasis. Factors like host and parasite genetic characteristics, virulence, epidemiological scenarios, and, mainly, diverse immune responses triggered by Leishmania species make the achievement of this aim a complex task. It is already clear that the induction of a Th1, pro-inflammatory response, is important in the protection against Leishmania infection. However, many questions must still be answered to fully understand Leishmania immunopathology, especially regarding Leishmania-specific Th1 response induction, regulation, and persistence. A large number of Leishmania antigens able to induce pro-inflammatory response have been selected so far, but none of them demonstrated efficiency in protection assays. A possible explanation is that CD4 T cells display marked heterogeneity at a single-cell level especially regarding the production of Th1-defining cytokines and multifunctionality. It has been established in the literature that Th1 cells undergo a differentiation process, which can generate cells with diverse phenotypes and survival capabilities. Despite that, only a few studies evaluate this heterogenic response and the amount of multifunctional CD4 T cells induced by Leishmania vaccine candidates, missing what can be a crucial point in defining a correlate of protection after vaccination. Moreover, most of the knowledge involving the development of cutaneous leishmaniasis (CL) vaccines comes from the mouse model of infection with Leishmania major, which cannot be fully applied to New World Leishmaniasis. For this reason, the immune response triggered by infection with New World Leishmania species, as well as vaccine candidates, need further studies. In this review, we will reinforce the importance of evaluating the quality of immune response against Leishmania, using a multiparametric analysis in order to understand better this complex host-parasite interaction, discussing the differences in the responses triggered by different New World Leishmania species, as well as the impact on the development of an effective vaccine against CL.

Zoonotic visceral leishmaniasis transmission: modeling, backward bifurcation, and optimal control

Visceral leishmaniasis (VL), a vector-borne disease caused by protozoan flagellates of the genus Leishmania, is transmitted by sand flies. After malaria, VL is the second-largest parasitic killer, responsible for an estimated 500,000 infections and 51,000 deaths annually worldwide. Mathematical models proposed for VL have included the impact of dogs versus wild canids in disease dissemination and models developed to assist in control approaches. However, quantitative conditions that are required to control or eradicate VL transmission are not provided and there are no mathematical methods proposed to quantitatively calculate optimal control strategies for VL transmission. The research objective of this work was to model VL disease transmission system (specifically Zoonotic VL), perform bifurcation analysis to discuss control conditions, and calculate optimal control strategies. Three time-dependent control strategies involving dog populations, sand fly population, and humans are mainly discussed. Another strategy sometimes used in attempts to control zoonotic VL transmission, dog culling, is also evaluated in this paper.

Attenuated Leishmania induce pro-inflammatory mediators and influence leishmanicidal activity by p38 MAPK dependent phagosome maturation in Leishmania donovani co-infected macrophages

Promastigote form of Leishmania, an intracellular pathogen, delays phagosome maturation and resides inside macrophages. But till date limited study has been done to manipulate the phagosomal machinery of macrophages to restrict Leishmania growth. Attenuated Leishmania strain exposed RAW 264.7 cells showed a respiratory burst and enhanced production of pro-inflammatory mediators. The augmentation of pro-inflammatory activity is mostly attributed to p38 MAPK and p44/42 MAPK. In our study, these activated macrophages are found to induce phagosome maturation when infected with pathogenic Leishmania donovani. Increased co-localization of carboxyfluorescein succinimidyl ester labeled pathogenic L. donovani with Lysosome was found. Moreover, increased co-localization was observed between pathogenic L. donovani and late phagosomal markers viz. Rab7, Lysosomal Associated Membrane Protein 1, Cathepsin D, Rab9, and V-ATPase which indicate phagosome maturation. It was also observed that inhibition of V-type ATPase caused significant hindrance in attenuated Leishmania induced phagosome maturation. Finally, it was confirmed that p38 MAPK is the key player in acidification and maturation of phagosome in attenuated Leishmania strain pre-exposed macrophages. To our knowledge, this study for the first time reported an approach to induce phagosome maturation in L. donovani infected macrophages which could potentiate short-term prophylactic response in future.

HisAK70: progress towards a vaccine against different forms of leishmaniosis

BACKGROUND

Leishmania major and Leishmania infantum are among the main species that are responsible for cutaneous leishmaniosis (CL) and visceral leishmaniosis (VL), respectively. The leishmanioses represent the second-largest parasitic killer in the world after malaria. Recently, we succeeded in generating a plasmid DNA (pCMV-HISA70m2A) and demonstrated that immunized mice were protected against L. major challenge. The efficacy of the DNA-vaccine was further enhanced by the inclusion of KMP-11 antigen into the antibiotic-free plasmid pVAX1-asd.

METHODS

Here, we describe the use of a HisAK70 DNA-vaccine encoding seven Leishmania genes (H2A, H2B, H3, H4, A2, KMP11 and HSP70) for vaccination of mice to assess the induction of a resistant phenotype against VL and CL.

RESULTS

HisAK70 was successful in vaccinated mice, resulting in a high amount of efficient sterile hepatic granulomas associated with a hepatic parasite burden fully resolved in the VL model; and resulting in 100% inhibition of parasite visceralization in the CL model.

CONCLUSIONS

The results suggest that immunization with the HisAK70 DNA-vaccine may provide a rapid, suitable, and efficient vaccination strategy to confer cross-protective immunity against VL and CL.

Genome-Wide Prediction of Vaccine Candidates for Leishmania major: An Integrated Approach

Despite the wealth of information regarding genetics of the causative parasite and experimental immunology of the cutaneous leishmaniasis, there is currently no licensed vaccine against it. In the current study, a two-level data mining strategy was employed, to screen the Leishmania major genome for promising vaccine candidates. First, we screened a set of 25 potential antigens from 8312 protein coding sequences, based on presence of signal peptides, GPI anchors, and consensus antigenicity predictions. Second, we conducted a comprehensive immunogenic analysis of the 25 antigens based on epitopes predicted by NetCTL tool. Interestingly, results revealed that candidate antigen number 1 (LmjF.03.0550) had greater number of potential T cell epitopes, as compared to five well-characterized control antigens (CSP-Plasmodium falciparum, M1 and NP-Influenza A virus, core protein-Hepatitis B virus, and PSTA1-Mycobacterium tuberculosis). In order to determine an optimal set of epitopes among the highest scoring predicted epitopes, the OptiTope tool was employed for populations susceptible to cutaneous leishmaniasis. The epitope (127SLWSLLAGV) from antigen number 1, found to bind with the most prevalent allele HLA-A⁎0201 (25% frequency in Southwest Asia), was predicted as most immunogenic for all the target populations. Thus, our study reasserts the potential of genome-wide screening of pathogen antigens and epitopes, for identification of promising vaccine candidates.

Skin-resident memory CD4+ T cells enhance protection against Leishmania major infection

While people infected with Leishmania can become refractory to reinfection, human vaccines have not yet been achieved. Glennie et al. identify a population of skin-resident Leishmania-specific memory T cells that produce IFN-γ and recruit circulating T cells to the skin in response to a subsequent parasitic infection. The findings indicate that a successful vaccine may be dependent on generating skin-resident memory T cells for an effective immune response.

Leishmaniasis causes a significant disease burden worldwide. Although Leishmania-infected patients become refractory to reinfection after disease resolution, effective immune protection has not yet been achieved by human vaccines. Although circulating Leishmania-specific T cells are known to play a critical role in immunity, the role of memory T cells present in peripheral tissues has not been explored. Here, we identify a population of skin-resident Leishmania-specific memory CD4⁺ T cells. These cells produce IFN-γ and remain resident in the skin when transplanted by skin graft onto naive mice. They function to recruit circulating T cells to the skin in a CXCR3-dependent manner, resulting in better control of the parasites. Our findings are the first to demonstrate that CD4⁺ T_RM cells form in response to a parasitic infection, and indicate that optimal protective immunity to Leishmania, and thus the success of a vaccine, may depend on generating both circulating and skin-resident memory T cells.

Evaluation of Live Recombinant Nonpathogenic Leishmania tarentolae Expressing Cysteine Proteinase and A2 Genes as a Candidate Vaccine against Experimental Canine Visceral Leishmaniasis

Canine Visceral Leishmaniasis (CVL) is a major veterinary and public health problem caused by Leishmania infantum (L. infantum) in many endemic countries. It is a severe chronic disease with generalized parasite spread to the reticuloendothelial system, such as spleen, liver and bone marrow and is often fatal when left untreated. Control of VL in dogs would dramatically decrease infection pressure of L. infantum for humans, since dogs are the main domestic reservoir. In the past decade, various subunits and DNA antigens have been identified as potential vaccine candidates in experimental animal models, but none has been approved for human use so far. In this study, we vaccinated outbreed dogs with a prime-boost regimen based on recombinant L. tarentolae expressing the L. donovani A2 antigen along with cysteine proteinase genes (CPA and CPB without its unusual C-terminal extension (CPB^-CTE) and evaluated its immunogenicity and protective immunity against L. infantum infectious challenge. We showed that vaccinated animals produced significantly higher levels of IgG2, but not IgG1, and also IFN-γ and TNF-α, but low IL-10 levels, before and after challenge as compared to control animals. Protection in dogs was also correlated with a strong DTH response and low parasite burden in the vaccinated group. Altogether, immunization with recombinant L. tarentolae A2-CPA-CPB^-CTE was proven to be immunogenic and induced partial protection in dogs, hence representing a promising live vaccine candidate against CVL.

Recombinant Leishmania major lipophosphoglycan 3 activates human T-lymphocytes via TLR2-independent pathway

Leishmaniasis is one of the most common infectious diseases transmitted by an obligate intracellular genus Leishmania. As there is no efficient vaccination strategy for leishmaniasis, new immunostimulatory components may enhance protective immune responses against this parasite. Lipophosphoglycan 3 (LPG3) is an essential protein required for LPG assembling. In this study, the ability of recombinant LPG3 (rLPG) and its fragments to activate isolated healthy human T-cells and cytokine secretion was evaluated in vitro. The results showed that rLPG3 and its N-terminal fragment (rNT-LPG3) enhanced expression of CD69 on the surface of T-cells and promoted differentiation of CD4(+) T-lymphocytes toward a T-helper 1 (T(H)1) phenotype, in part, through up-regulation of interferon (IFN)-γ expression in a TLR2-independent manner. These results indicated the protective effects of LPG3 (particularly NT-LPG3 fragment) as a potent immunostimulatory component of leishmania in vaccination against leishmaniasis. Further investigations in in vivo assays are clearly warranted.

Vaccination using live attenuated Leishmania donovani centrin deleted parasites induces protection in dogs against Leishmania infantum

Live attenuated Leishmania donovani parasites such as LdCen(-/-) have been shown elicit protective immunity against leishmanial infection in mice and hamster models. Previously, we have reported on the induction of strong immunogenicity in dogs upon vaccination with LdCen(-/-) including an increase in immunoglobulin isotypes, higher lymphoproliferative response, higher frequencies of activated CD4(+) and CD8(+) T cells, IFN-γ production by CD8(+) T cells, increased secretion of TNF-α and IL-12/IL-23p40 and, finally, decreased secretion of IL-4. To further explore the potential of LdCen(-/-) parasites as vaccine candidates, we performed a 24-month follow up of LdCen(-/-) immunized dogs after challenge with virulent Leishmania infantum, aiming determination of parasite burden by qPCR, antibody production (ELISA) and cellular responses (T cell activation and cytokine production) by flow cytometry and sandwich ELISA. Our data demonstrated that vaccination with a single dose of LdCen(-/-) (without any adjuvant) resulted in the reduction of up to 87.3% of parasite burden after 18 months of virulent challenge. These results are comparable to those obtained with commercially available vaccine in Brazil (Leishmune(®)). The protection was associated with antibody production and CD4(+) and CD8(+) proliferative responses, as well as T cell activation and significantly higher production of IFN-γ, IL-12/IL-23p40 and TNF-α, which was comparable to responses induced by immunization with Leishmune(®), with significant differences when compared to control animals (Placebo). Moreover, only animals immunized with LdCen(-/-) expressed lower levels of IL-4 when compared to animals vaccinated either with Leishmune(®) or PBS. Our results support further studies aiming to demonstrate the potential of genetically modified live attenuated L. donovani vaccine to control L. infantum transmission in endemic areas for CVL.

Identifying vaccine targets for anti-leishmanial vaccine development

Leishmaniasis is a neglected tropical disease spread by an arthropod vector. It remains a significant health problem with an incidence of 0.2–0.4 million visceral leishmaniasis and 0.7–1.2 million cutaneous leishmaniasis cases each year. There are limitations associated with the current therapeutic regimens for leishmaniasis and the fact that after recovery from infection the host becomes immune to subsequent infection therefore, these factors force the feasibility of a vaccine for leishmaniasis. Publication of the genome sequence of Leishmania has paved a new way to understand the pathogenesis and host immunological status therefore providing a deep insight in the field of vaccine research. This review is an effort to study the antigenic targets in Leishmania to develop an anti-leishmanial vaccine.

Characterization of cross-protection by genetically modified live-attenuated Leishmania donovani parasites against Leishmania mexicana

Previously, we showed that genetically modified live-attenuated Leishmania donovani parasite cell lines (LdCen(-/-) and Ldp27(-/-)) induce a strong cellular immunity and provide protection against visceral leishmaniasis in mice. In this study, we explored the mechanism of cross-protection against cutaneous lesion-causing Leishmania mexicana. Upon challenge with wild-type L. mexicana, mice immunized either for short or long periods showed significant protection. Immunohistochemical analysis of ears from immunized/challenged mice exhibited significant influx of macrophages, as well as cells expressing MHC class II and inducible NO synthase, suggesting an induction of potent host-protective proinflammatory responses. In contrast, substantial inhibition of IL-10, IL-4, and IL-13 expression and the absence of degranulated mast cells and less influx of eosinophils within the ears of immunized/challenged mice suggested a controlled anti-inflammatory response. L. mexicana Ag-stimulated lymph node cell culture from the immunized/challenged mice revealed induction of IFN-γ secretion by the CD4 and CD8 T cells compared with non-immunized/challenged mice. We also observed suppression of Th2 cytokines in the culture supernatants of immunized/challenged lymph nodes compared with non-immunized/challenged mice. Adoptively transferred total T cells from immunized mice conferred strong protection in recipient mice against L. mexicana infection, suggesting that attenuated L. donovani can provide protection against heterologous L. mexicana parasites by induction of a strong T cell response. Furthermore, bone marrow-derived dendritic cells infected with LdCen(-/-) and Ldp27(-/-) parasites were capable of inducing a strong proinflammatory response leading to the proliferation of Th1 cells. These studies demonstrate the potential of live-attenuated L. donovani parasites as pan-Leishmania species vaccines.

Short-term protection conferred by Leishvacin® against experimental Leishmania amazonensis infection in C57BL/6 mice

To date, there is no vaccine available against human leishmaniasis. Although some vaccination protocols can induce immunity in murine models, they fail to induce protection in humans. The reasons for that remain unclear. The aim of the present study was to characterize the changes in the pattern of the immune response during subcutaneous vaccination with Leishvacin® in mice. We also investigated whether IFN-γ and nitric oxide synthase are indispensable for the protection elicited by the vaccine. C57BL/6 WT vaccinated mice showed smaller lesions and fewer numbers of parasites in footpads until 8 weeks post-infection. Up to this time, they produced higher levels of IFN-γ, IL-2, IL-4, IL-17A and IL-10 and higher specific antibody response than control non-vaccinated mice. Moreover, we showed that IFN-γ, most likely by induction of iNOS expression, is essential for immunity. However, after 12 weeks of infection, we observed loss of difference in lesion size and parasite burden between the groups. Loss of resistance was associated with the disappearance of differences in cytokine patterns between vaccinated and control mice, but not of antibody response, which remained different until a later time of infection. The reversal of resistance to L. amazonensis could not be explained by upregulation of regulatory cytokines. Our data point to a subversion of the host immune response by L. amazonensis even when a protective response was previously induced.

Immune responses during cutaneous and visceral leishmaniasis

SUMMARY Leishmania are protozoan parasites spread by a sandfly insect vector and causing a spectrum of diseases collectively known as leishmaniasis. The disease is a significant health problem in many parts of the world, resulting in an estimated 1·3 million new cases and 30 000 deaths annually. Current treatment is based on chemotherapy, which is difficult to administer, expensive and becoming ineffective in several endemic regions. To date there is no vaccine against leishmaniasis, although extensive evidence from studies in animal models indicates that solid protection can be achieved upon immunization. This review focuses on immune responses to Leishmania in both cutaneous and visceral forms of the disease, pointing to the complexity of the immune response and to a range of evasive mechanisms utilized by the parasite to bypass those responses. The amalgam of innate and acquired immunity combined with the paucity of data on the human immune response is one of the major problems currently hampering vaccine development and implementation.

Immune regulation during chronic visceral leishmaniasis

Visceral leishmaniasis is a chronic parasitic disease associated with severe immune dysfunction. Treatment options are limited to relatively toxic drugs, and there is no vaccine for humans available. Hence, there is an urgent need to better understand immune responses following infection with Leishmania species by studying animal models of disease and clinical samples from patients. Here, we review recent discoveries in these areas and highlight shortcomings in our knowledge that need to be addressed if better treatment options are to be developed and effective vaccines designed.