Visceral leishmaniasis: immunology and prospects for a vaccine

Elucidation of conserved multi-epitope vaccine against Leishmania donovani using reverse vaccinology

Visceral leishmaniasis (VL) is a tropical disease that causes severe public health problems in humans when untreated. As no licensed vaccine exists against VL, we aimed to formulate a potential MHC-restricted chimeric vaccine construct against this dreadful parasitic disease. Amastin-like protein derived from L. donovani is considered to be stable, immunogenic and non-allergic. A comprehensive established framework was used to explore the set of immunogenic epitopes with estimated population coverage of 96.08% worldwide. The rigorous assessment revealed 6 promiscuous T-epitopes which can plausibly be presented by more than 66 diverse HLA alleles. Further docking and simulation study of peptide receptor complexes identified a strong and stable binding interaction with better structural compactness. The predicted epitopes were combined with appropriate linkers and adjuvant molecules and their translation efficiency was evaluated in pET28+(a), an bacterial expression vector using in-silico cloning. Molecular docking followed by MD simulation study revealed a stable interaction between chimeric vaccine construct with TLRs. Immune simulation of the chimeric vaccine constructs showed an elevated Th1 immune response against both B and T epitopes. With this, the detailed computational analysis suggested that the chimeric vaccine construct can evoke a robust immune response against Leishmania donovani infection. Future studies are required to validate the role of amastin as a promising vaccine target.Communicated by Ramaswamy H. Sarma.

Immunotherapy and immunochemotherapy in combating visceral leishmaniasis

Visceral leishmaniasis (VL), a vector-borne disease, is caused by an obligate intramacrophage, kinetoplastid protozoan parasite of the genus Leishmania. Globally, VL is construed of diversity and complexity concerned with high fatality in tropics, subtropics, and Mediterranean regions with ~50,000-90,000 new cases annually. Factors such as the unavailability of licensed vaccine(s), insubstantial measures to control vectors, and unrestrained surge of drug-resistant parasites and HIV-VL co-infections lead to difficulty in VL treatment and control. Furthermore, VL treatment, which encompasses several problems including limited efficacy, emanation of drug-resistant parasites, exorbitant therapy, and exigency of hospitalization until the completion of treatment, further exacerbates disease severity. Therefore, there is an urgent need for the development of safe and efficacious therapies to control and eliminate this devastating disease. In such a scenario, biotherapy/immunotherapy against VL can become an alternative strategy with limited side effects and no or nominal chance of drug resistance. An extensive understanding of pathogenesis and immunological events that ensue during VL infection is vital for the development of immunotherapeutic strategies against VL. Immunotherapy alone or in combination with standard anti-leishmanial chemotherapeutic agents (immunochemotherapy) has shown better therapeutic outcomes in preclinical studies. This review extensively addresses VL treatment with an emphasis on immunotherapy or immunochemotherapeutic strategies to improve therapeutic outcomes as an alternative to conventional chemotherapy.

Chronic Systemic Infection of Mice with Leishmania infantum Leads to Increased Bone Mass

Vector-borne infections of humans with the protozoan parasite Leishmania (L.) infantum can cause a systemic and potentially lethal disease termed visceral leishmaniasis. In the corresponding mouse model, an intravenous infection with L. infantum leads to the persistence of parasites in various organs, including bone marrow (BM). Considering the anatomical proximity between the BM and the cortical bone, we investigated whether a chronic infection with L. infantum affected bone homeostasis. Unexpectedly, chronic infection with L. infantum caused an increase in bone mass in mice. In vivo, an increased number of osteoblasts and osteocytes and a decreased maturation of osteoclasts characterized the phenotype. Confocal laser scanning fluorescence microscopy confirmed the infection of BM macrophages but also revealed the presence of parasites in osteoclasts. In vitro, mature osteoclasts took up L. infantum parasites. However, infection of osteoclast progenitors abolished their differentiation and function. In addition, secretory products of infected BM-derived macrophages inhibited the maturation of osteoclasts. Both in vitro and in vivo, infected macrophages and osteoclasts showed an enhanced expression of the anti-osteoclastogenic chemokine CCL5 (RANTES). Neutralization of CCL5 prevented the inhibition of osteoclast generation seen in the presence of culture supernatants from L. infantum-infected macrophages. Altogether, our study shows that chronic infection with Leishmania increases bone mass by inducing bone formation and impairing osteoclast differentiation and function. © 2022 American Society for Bone and Mineral Research (ASBMR).

Host SUMOylation Pathway Negatively Regulates Protective Immune Responses and Promotes Leishmania donovani Survival

SUMOylation is one of the post-translational modifications that have recently been described as a key regulator of various cellular, nuclear, metabolic, and immunological processes. The process of SUMOylation involves the modification of one or more lysine residues of target proteins by conjugation of a ubiquitin-like, small polypeptide known as SUMO for their degradation, stability, transcriptional regulation, cellular localization, and transport. Herein, for the first time, we report the involvement of the host SUMOylation pathway in the process of infection of Leishmania donovani, a causative agent of visceral leishmaniasis. Our data revealed that infection of L. donovani to the host macrophages leads to upregulation of SUMOylation pathway genes and downregulation of a deSUMOylating gene, SENP1. Further, to confirm the effect of the host SUMOylation on the growth of Leishmania, the genes associated with the SUMOylation pathway were silenced and parasite load was analyzed. The knockdown of the SUMOylation pathway led to a reduction in parasitic load, suggesting the role of the host SUMOylation pathway in the disease progression and parasite survival. Owing to the effect of the SUMOylation pathway in autophagy, we further investigated the status of host autophagy to gain mechanistic insights into how SUMOylation mediates the regulation of growth of L. donovani. Knockdown of genes of host SUMOylation pathway led to the reduction of the expression levels of host autophagy markers while promoting autophagosome–lysosome fusion, suggesting SUMOylation-mediated autophagy in terms of autophagy initiation and autophagy maturation during parasite survival. The levels of reactive oxygen species (ROS) generation, nitric oxide (NO) production, and pro-inflammatory cytokines were also elevated upon the knockdown of genes of the host SUMOylation pathway during L. donovani infection. This indicates the involvement of the SUMOylation pathway in the modulation of protective immune responses and thus favoring parasite survival. Taken together, the results of this study indicate the hijacking of the host SUMOylation pathway by L. donovani toward the suppression of host immune responses and facilitation of host autophagy to potentially facilitate its survival. Targeting of SUMOylation pathway can provide a starting point for the design and development of novel therapeutic interventions to combat leishmaniasis.

Visceral Leishmaniasis and the Skin: Dermal Parasite Transmission to Sand Flies

Visceral leishmaniasis is a parasitic disease with significant dermal tropism. The skin is an important site of infection contributing to parasite transmission to naïve sand flies, but understanding how parasitism of host skin and the related immune microenvironment supports or prevents skin parasite replication is now the focus of major investigation in the field of leishmaniasis research. Here, we review dermatoimmunology during visceral leishmaniasis (VL), dermal Leishmania parasite burden, and the role of skin parasitism in transmissibility to sand fly vectors. First, we discuss the epidemiology of VL amongst dogs, the primary zoonotic reservoir for human infection. We explore the association between spatial distribution and the burden of parasites in the skin in driving outward transmission. Factors associated with parasite persistence in the skin are examined. We discuss systemic immunity during VL and what is known about immunological correlates in the skin microenvironment. Finally, we touch on factors egested into the skin during Leishmania inoculation by sand flies. Throughout, we discuss factors associated with the early and chronic establishment of Leishmania parasites in the skin and the role of the dermal immune response.

Leishmania LiHyC protein is immunogenic and induces protection against visceral leishmaniasis

AIMS

Treatment against visceral leishmaniasis (VL) presents problems by toxicity of drugs, high cost and/or emergence of resistant strains. The diagnosis is hampered by variable sensitivity and/or specificity of tests. In this context, prophylactic vaccination could represent a control measure against disease. In this study, the protective efficacy from Leishmania LiHyC protein was evaluated in murine model against Leishmania infantum infection.

METHODS AND RESULTS

LiHyC was used as recombinant protein (rLiHyC) associated with saponin (rLiHyC/S) or Poloxamer 407-based polymeric micelles (rLiHyC/M) to immunize mice. Animals received also saline, saponin or empty micelles as controls. The immunogenicity was evaluated before and after challenge, and results showed that vaccination with rLiHyC/S or rLiHyC/M induced the production of high levels of IFN-γ, IL-12 and GM-CSF in cell culture supernatants, as well as higher IFN-γ expression evaluated by RT-qPCR and involvement from CD4⁺ and CD8⁺ T cell subtypes producing IFN-γ, TNF-α and IL-2. A positive lymphoproliferative response was also found in cell cultures from vaccinated animals, besides high levels of rLiHyC- and parasite-specific nitrite and IgG2a antibodies. Immunological assays correlated with significant reductions in the parasite load in spleens, livers, bone marrows and draining lymph nodes from vaccinated mice, when compared to values found in the controls. The micellar composition showed slightly better immunological and parasitological data, as compared to rLiHyC/S.

CONCLUSION

Results suggest that rLiHyC associated with adjuvants could be considered for future studies as a vaccine candidate against VL.

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.

From infection to vaccination: reviewing the global burden, history of vaccine development, and recurring challenges in global leishmaniasis protection

INTRODUCTION

Leishmaniasis is a major public health problem and the second most lethal parasitic disease in the world due to the lack of effective treatments and vaccines. Even when not lethal, leishmaniasis significantly affects individuals and communities through life-long disabilities, psycho-sociological trauma, poverty, and gender disparity in treatment.

AREAS COVERED

This review discusses the most relevant and recent research available on Pubmed and GoogleScholar highlighting leishmaniasis' global impact, pathogenesis, treatment options, and lack of effective control strategies. An effective vaccine is necessary to prevent morbidity and mortality, lower health care costs, and reduce the economic burden of leishmaniasis for endemic low- and middle-income countries. Since there are several forms of leishmaniasis, a pan-Leishmania vaccine without geographical restrictions is needed. This review also focuses on recent advances and common challenges in developing prophylactic strategies against leishmaniasis.

EXPERT OPINION

Despite advances in pre-clinical vaccine research, approval of a human leishmaniasis vaccine still faces major challenges - including manufacturing of candidate vaccines under Good Manufacturing Practices, developing well-designed clinical trials suitable in endemic countries, and defined correlates of protection. In addition, there is a need to explore Challenge Human Infection Model to avoid large trials because of fluctuating incidence and prevalence of leishmanasis.

Designing of a Novel Fusion Protein Vaccine Candidate Against Human Visceral Leishmaniasis (VL) Using Immunoinformatics and Structural Approaches

Leishmaniasis is caused by an obligate intracellular protozoan parasite. The clinical forms of leishmaniasis differ from cutaneous leishmaniasis, mucocutaneous leishmaniasis and visceral leishmaniasis (VL) which depend on the parasite species and the host’s immune responses. There are significant challenges to the available anti-leishmanial drug therapy, particularly in severe forms of disease, and the rise of drug resistance has made it more difficult. Currently, no licensed vaccines have been introduced to the market for the control and elimination of VL. A potential target for use in candidate vaccines against leishmaniasis has been shown to be leishmania Kinetoplastid membrane protein-11 (KMP-11) antigen. In this study, we chose KMP-11 antigen as target antigen in our vaccine construct. In addition, B-type flagellin (fliC) was used as an adjuvant for enhancing vaccine immunogenicity. The GSGSGSGSGSG linker was applied to link the KMP-11 antigen and fliC (KMP-11-fliC) to construct our fusion protein. Bioinformatics approaches such as; 3D homology modeling, CTL, B-cell, MHC class I and II epitopes prediction, allergenicity, antigenicity evaluations, molecular docking, fast simulations of flexibility of docked complex and in silico cloning were employed to analysis and evaluation of various properties of the designed fusion construct. Computational results showed that our engineered structure has the potential for proper stimulation of cellular and humoral immune responses against VL. Consequently, it could be proposed as a candidate vaccine against VL according to these data and after verifying the efficacy of the candidate vaccine through in vivo and in vitro immunological tests.

Immune response dynamics and Lutzomyia longipalpis exposure characterize a biosignature of visceral leishmaniasis susceptibility in a canine cohort

Background

Reports have shown correlations between the immune response to vector saliva and Leishmaniasis outcome. We followed dogs in an endemic area for two years characterizing resistance or susceptibility to canine visceral leishmaniasis (CVL) according to Leishmania infantum diagnosis and clinical development criteria. Then, we aimed to identify a biosignature based on parasite load, serum biological mediators’ interactions, and vector exposure intensity associated with CVL resistance and susceptibility.

Methodology/Principal findings

A prospective two-year study was conducted in an area endemic for CVL. Dogs were evaluated at 6-month intervals to determine infection, clinical manifestations, immune profile, and sandfly exposure. CVL resistance or susceptibility was determined upon the conclusion of the study. After two years, 78% of the dogs were infected with L. infantum (53% susceptible and 47% resistant to CVL). Susceptible dogs presented higher splenic parasite load as well as persistence of the parasite during the follow-up, compared to resistant ones. Susceptible dogs also displayed a higher number of correlations among the investigated biological mediators, before and after infection diagnosis. At baseline, anti-saliva antibodies, indicative of exposure to the vector, were detected in 62% of the dogs, reaching 100% in one year. Higher sandfly exposure increased the risk of susceptibility to CVL by 1.6 times (CI: 1.11–2.41). We identified a discriminatory biosignature between the resistant and susceptible dogs assessing splenic parasite load, interaction of biological mediators, PGE₂ serum levels and intensity of exposure to sandfly. All these parameters were elevated in susceptible dogs compared to resistant animals.

Conclusions/Significance

The biosignature identified in our study reinforces the idea that CVL is a complex multifactorial disease that is affected by a set of factors which are correlated and, for a better understanding of CVL, should not be evaluated in an isolated way.

Visceral Leishmaniasis (VL) is a disease that can affect humans and dogs, caused by a parasite called Leishmania transmitted through the bite of sandfly insects. During the bite, together with the parasite, the insects also inoculate their saliva into the host. The host immune response produces molecules to the sandfly saliva, such as antibodies and cytokines that can impact VL resistance or susceptibility. The presence of these molecules also indicates if the insects bit the hosts. We followed dogs of a VL endemic area for two years to study Canine Visceral Leishmaniasis (CVL) and immune response to sandfly saliva. Dogs were evaluated at 6-month intervals to determine Leishmania infection, clinical manifestations, parasite load, immune response, and sandfly exposure. CVL resistance or susceptibility was determined upon the conclusion of the study. Dogs living in the endemic area were intensely bitten, as at the beginning of the study, 62% of the dogs present anti-saliva antibodies, reaching 100% after one year. Our findings revealed a biosignature of CVL susceptibility characterized by elevated parasite load, interaction of cytokines, and higher exposure to the sandfly. This data reinforced that CVL is a complex disease affected by several factors related to each other.

Resistance to Experimental Visceral Leishmaniasis in Mice Infected With Leishmania infantum Requires Batf3

Unveiling the protective immune response to visceral leishmaniasis is critical for a rational design of vaccines aimed at reducing the impact caused by this fatal, if left untreated, vector-borne disease. In this study we sought to determine the role of the basic leucine zipper transcription factor ATF-like 3 (Batf3) in the evolution of infection with Leishmania infantum, the causative agent of human visceral leishmaniasis in the Mediterranean Basin and Latin America. For that, Batf3-deficient mice in C57BL/6 background were infected with an L. infantum strain expressing the luciferase gene. Bioluminescent imaging, as well as in vitro parasite titration, demonstrated that Batf3-deficient mice were unable to control hepatic parasitosis as opposed to wild-type C57BL/6 mice. The impaired microbicide capacities of L. infantum-infected macrophages from Batf3-deficient mice mainly correlated with a reduction of parasite-specific IFN-γ production. Our results reinforce the implication of Batf3 in the generation of type 1 immunity against infectious diseases.

Evaluation of transgenic Leishmania infantum expressing mLLO-BAX-SMAC in the apoptosis of the infected macrophages in vitro and in vivo

BACKGROUND

Leishmaniasis is an important infectious disease that develops because of escaping parasite from the host immune system or preventing host macrophages apoptosis. Recently, the development of transgenic methods and the manipulation of the parasite genome has provided many advantages. So, in this study, the effect of the transgenic Leishmania infantum expressing mLLO-BAX-SMAC proteins was examined in accelerating host cell apoptosis.

METHOD

The entire coding sequence of designed codon-optimized mLLO-Bax-Smac was cloned in the pLexyNeo2 vector and integrated downstream of the 18srRNA locus of L infantum genome by homologous recombination. Next, the expression of mLLO-BAX-SMAC fusion protein was evaluated by the Western blotting technique and the pathogenesis of transgenic parasite was surveyed in vitro and in vivo.

RESULTS

The results of PCR and Western blot confirmed proper integration and expression of mLLO-Bax-Smac sequence into the 18srRNA locus of L infantum. Flow cytometry showed accelerating apoptosis of transgenic Leishmania-infected macrophages compared to wild-type parasite. Also, transgenic parasites were less virulent as a fewer parasitic burden was found in the spleen and liver of transgenic-infected mice compared to the control.

CONCLUSION

The data suggested that the transgenic L infantum expressing BAX-SMAC can be used as an experimental model for developing vaccination against leishmaniasis.

Susceptibility to Intracellular Infections: Contributions of TNF to Immune Defense

An interesting puzzle is the fact that an infection of a tumor necrosis factor α (TNF)-deficient host with pathogens such as bacteria or parasites that reside intracellularly inevitably ends fatally. Is this due to one specific role of TNF in the immune defense or are different functions responsible for this outcome? In this review we provide an update of the functions of TNF in the defense against the intracellular pathogens Listeria monocytogenes, Mycobacterium tuberculosis, and Leishmania major. Furthermore, we discuss the role of TNF in the generation of proinflammatory macrophages in mouse models of infection and summarize briefly the potential consequences of anti-TNF treatment for infectious diseases.

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.

Whole Blood Stimulation Assay as a Treatment Outcome Monitoring Tool for VL Patients in Ethiopia: A Pilot Evaluation

Visceral leishmaniasis (VL) is a lethal disease if left untreated. Current treatments produce variable rates of treatment failure and toxicity without sterile cure, rendering treatment efficacy monitoring essential. To avoid repeated invasive tissue aspirates as well as empirical treatment, there is a need for new tools that allow a less-invasive and early assessment of treatment efficacy in the field. Cross-sectional studies have suggested levels of cytokines/chemokines after whole blood stimulation as good markers of cure, but longitudinal studies are lacking. In this study, we followed 13 active VL cases in an endemic area in Ethiopia by measuring the production of IFN-γ, TNF-α, IP-10, IL-2, IL-10, MCP-1, and MIG before, during, and at the end of treatment. After 24 hours of stimulation of whole blood with soluble Leishmania antigen, we observed an early, robust, and incremental increase of IFN-γ, TNF-α, and IP-10 levels in all patients during treatment. Moreover, based on the IFN-γ levels that showed an average 13-fold increase from the time of diagnosis until the end of treatment, we could almost perfectly discriminate active from cured status. Similar concentrations and patterns were found in stimulation assays with the two main Leishmania species. The levels of IFN-γ, IP-10, or TNF-α also seemed to be inversely associated with the parasite load at baseline. Despite a 1/10 drop in concentrations, similar patterns were observed in IFN-γ and IP-10 levels when dried plasma spots were stored at 4°C for an average of 225 days. All the above evidence suggests a detectable restoration of cell-mediated immunity in VL and its association with parasite clearance. With a potential application in rural settings by means of dried plasma spots, we recommend to further explore the early diagnostic value of such assays for treatment efficacy monitoring in large cohort studies including treatment failure cases.

An immunoinformatic approach driven by experimental proteomics: in silico design of a subunit candidate vaccine targeting secretory proteins of Leishmania donovani amastigotes

Background

Visceral leishmaniasis (VL) caused by dimorphic Leishmania species is a parasitic disease with high socioeconomic burden in endemic areas worldwide. Sustaining control of VL in terms of proper and prevailing immunity development is a global necessity amid unavailability of a prophylactic vaccine. Screening of experimental proteome of the human disease propagating form of Leishmania donovani (amastigote) can be more pragmatic for in silico mining of novel vaccine candidates.

Methods

By using an immunoinformatic approach, CD4+ and CD8+ T cell-specific epitopes from experimentally reported L. donovani proteins having secretory potential and increased abundance in amastigotes were screened. A chimera linked with a Toll-like receptor 4 (TLR4) peptide adjuvant was constructed and evaluated for physicochemical characteristics, binding interaction with TLR4 in simulated physiological condition and the trend of immune response following hypothetical immunization.

Results

Selected epitopes from physiologically important L. donovani proteins were found mostly conserved in L. infantum, covering theoretically more than 98% of the global population. The multi-epitope chimeric vaccine was predicted as stable, antigenic and non-allergenic. Structural analysis of vaccine-TLR4 receptor docked complex and its molecular dynamics simulation suggest sufficiently stable binding interface along with prospect of non-canonical receptor activation. Simulation dynamics of immune response following hypothetical immunization indicate active and memory B as well as CD4+ T cell generation potential, and likely chance of a more Th1 polarized response.

Conclusions

The methodological approach and results from this study could facilitate more informed screening and selection of candidate antigenic proteins for entry into vaccine production pipeline in future to control human VL.

Neutrophil elastase promotes Leishmania donovani infection via interferon-β

Visceral leishmaniasis is a deadly illness caused by Leishmania donovani that provokes liver and spleen inflammation and tissue destruction. In cutaneous leishmaniasis, the protein of L. major, named inhibitor of serine peptidases (ISP) 2, inactivates neutrophil elastase (NE) present at the macrophage surface, resulting in blockade of TLR4 activation, prevention of TNF-α and IFN-β production, and parasite survival. We report poor intracellular growth of L. donovani in macrophages from knockout mice for NE (ela^-/-), TLR4, or TLR2. NE and TLR4 colocalized with the parasite in the parasitophorous vacuole. Parasite load in the liver and spleen of ela^-/- mice were reduced and accompanied by increased NO and decreased TGF-β production. Expression of ISP2 was not detected in L. donovani, and a transgenic line constitutively expressing ISP2, displayed poor intracellular growth in macrophages and decreased burden in mice. Infected ela^-/- macrophages displayed significantly lower IFN-β mRNA than background mice macrophages, and the intracellular growth was fully restored by exogenous IFN-β. We propose that L. donovani utilizes the host NE-TLR machinery to induce IFN-β necessary for parasite survival and growth during early infection. Low or absent expression of parasite ISP2 in L. donovani is necessary to preserve the activation of the NE-TLR pathway.-Dias, B. T., Dias-Teixeira, K. L., Godinho, J. P., Faria, M. S., Calegari-Silva, T., Mukhtar, M. M., Lopes, U. G., Mottram, J. C., Lima, A. P. C. A. Neutrophil elastase promotes Leishmania donovani infection via interferon-β.

Novos adjuvantes vacinais: importante ferramenta para imunoterapia da leishmaniose visceral

Atualmente, muitas das vacinas em desenvolvimento são aquelas compostas de proteínas antigênicas individuais de parasitas ou uma combinação de vários antígenos individuais que são produzidos como produtos recombinantes obtidos por técnicas de biologia molecular. Dentre elas a Leish-111f e sua variação Leish-110f tem ganhado destaque na proteção contra a LV e LC e alcançaram estudos de fase II em seres humanos. A eficácia de uma vacina é otimizada pela adição de adjuvantes imunológicos. No entanto, embora os adjuvantes tenham sido usados por mais de um século, até o momento, apenas alguns adjuvantes são aprovados para o uso em humanos, a maioria destinada a melhorar a eficácia da vacina e a produção de anticorpos protetores específicos do antígeno. Os mecanismos de ação dos adjuvantes imunológicos são diversos, dependendo da sua natureza química e molecular sendo capazes de ativar células imunes especificas que conduzem a respostas imunes inatas e adaptativas melhoradas. Embora o mecanismo de ação molecular detalhado de muitos adjuvantes ainda seja desconhecido, a descoberta de receptores Toll-like (TLRs) forneceu informações críticas sobre o efeito imunoestimulador de numerosos componentes bacterianos que envolvem interação com receptores TLRs, mostrando que estes ligantes melhoram tanto a qualidade como a quantidade de respostas imunes adaptativas do hospedeiro quando utilizadas em formulações de vacinais direcionadas para doenças. O potencial desses adjuvantes de TLR em melhorar o design e os resultados de várias vacinas está em constante evolução, à medida que novos agonistas são descobertos e testados em modelos experimentais e estudos clínicos de vacinação. Nesta revisão, é apresentado um resumo do progresso recente no desenvolvimento de proteínas recombinantes de segunda geração e adjuvantes de TLR, sendo o foco principal nos TLR4 e suas melhorias.

Vaccination with a CD4+ and CD8+ T-cell epitopes-based recombinant chimeric protein derived from Leishmania infantum proteins confers protective immunity against visceral leishmaniasis

Vaccination seems to be the best approach to control visceral leishmaniasis (VL). Resistance against infection is based on the development of a Th1 immune response characterized by the production of interferons-γ (IFN-γ), interleukin-12 (IL-12), granulocyte-macrophage-colony-stimulating factor (GM-CSF), and tumor necrosis factor-α (TNF-α), among others. A number of antigens have been tested as potential targets against the disease; few of them are able to stimulate human immune cells. In the present study, 1 prediction of MHC class I and II molecules-specific epitopes in the amino acid sequences of 3 Leishmania proteins: 1 hypothetical, prohibitin, and small glutamine-rich tetratricopeptide repeat-containing proteins, was performed using bioinformatics tools, and a T-cell epitopes-based recombinant chimeric protein was constructed, synthetized and purified to be evaluated in invitro and in vivo experiments. The purified protein was tested regarding its immunogenicity in peripheral blood mononuclear cells (PBMCs) from healthy subjects and VL patients, as well as to its immunogenicity and protective efficacy in a murine model against Leishmania infantum infection. Results showed a Th1 response based on high IFN-γ and low IL-10 levels derived from in chimera-stimulated PBMCs in both healthy subjects and VL patients. In addition, chimera and/or saponin-immunized mice presented significantly lower parasite burden in distinct evaluated organs, when compared to the controls, besides higher levels of IFN-γ, IL-2, IL-12, and GM-CSF, and an IgG2a isotype-based humoral response. In addition, the CD4⁺ and CD8⁺ T-cell subtypes contributed to IFN-γ production in the protected animals. The results showed the immunogenicity in human cells and the protective efficacy against L. infantum in a murine model, and well indicate that this recombinant chimera can be considered as a promising strategy to be used against human disease.

Growth arrested live-attenuated Leishmania infantum KHARON1 null mutants display cytokinesis defect and protective immunity in mice

There is no safe and efficacious vaccine against human leishmaniasis available and live attenuated vaccines have been used as a prophylactic alternative against the disease. In order to obtain an attenuated Leishmania parasite for vaccine purposes, we generated L. infantum KHARON1 (KH1) null mutants (ΔLikh1). This gene was previously associated with growth defects in L. mexicana. ΔLikh1 was obtained and confirmed by PCR, qPCR and Southern blot. We also generate a KH1 complemented line with the introduction of episomal copies of KH1. Although ΔLikh1 promastigote forms exhibited a growth pattern similar to the wild-type line, they differ in morphology without affecting parasite viability. L. infantum KH1-deficient amastigotes were unable to sustain experimental infection in macrophages, forming multinucleate cells which was confirmed by in vivo attenuation phenotype. The cell cycle analysis of ΔLikh1 amastigotes showed arrested cells at G₂/M phase. ΔLikh1-immunized mice presented reduced parasite burden upon challenging with virulent L. infantum, when compared to naïve mice. An effect associated with increased Li SLA-specific IgG serum levels and IL-17 production. Thus, ΔLikh1 parasites present an infective-attenuated phenotype due to a cytokinesis defect, whereas it induces immunity against visceral leishmaniasis in mouse model, being a candidate for antileishmanial vaccine purposes.

Peptide Vaccines for Leishmaniasis

Due to an increase in the incidence of leishmaniases worldwide, the development of new strategies such as prophylactic vaccines to prevent infection and decrease the disease have become a high priority. Classic vaccines against leishmaniases were based on live or attenuated parasites or their subunits. Nevertheless, the use of whole parasite or their subunits for vaccine production has numerous disadvantages. Therefore, the use of Leishmania peptides to design more specific vaccines against leishmaniases seems promising. Moreover, peptides have several benefits in comparison with other kinds of antigens, for instance, good stability, absence of potentially damaging materials, antigen low complexity, and low-cost to scale up. By contrast, peptides are poor immunogenic alone, and they need to be delivered correctly. In this context, several approaches described in this review are useful to solve these drawbacks. Approaches, such as, peptides in combination with potent adjuvants, cellular vaccinations, adenovirus, polyepitopes, or DNA vaccines have been used to develop peptide-based vaccines. Recent advancements in peptide vaccine design, chimeric, or polypeptide vaccines and nanovaccines based on particles attached or formulated with antigenic components or peptides have been increasingly employed to drive a specific immune response. In this review, we briefly summarize the old, current, and future stands on peptide-based vaccines, describing the disadvantages and benefits associated with them. We also propose possible approaches to overcome the related weaknesses of synthetic vaccines and suggest future guidelines for their development.

Recent progress in drug targets and inhibitors towards combating leishmaniasis

Lesihmaniasis is one of the major neglected tropical disease caused by the parasite of the genus Leishmania. The disease has more than one clinical forms and the visceral form is considered fatal. With the lack of potential vaccine, chemotherapy is the major treatment source considered for the control of the disease in the infected people. Drugs including amphotericin B and miltefosine are widely used for the treatment, however, development of resistance by the parasite towards the administered drug and high-toxicity of the drug are of major concern. Hence, more attention has been shown on identifying new targets, effective inhibitors, and better drug delivery system against the disease. This review deals with recent studies on drug targets and exploring their essentiality for the survival of Leishmania. Further, new inhibitors for those targets, novel anti-leishmanial peptides and vaccines against leishmaniasis were discussed. We believe that this pool of information will ease the researchers to gain knowledge and help in choosing right targets and design of new inhibitors against Leishmaniasis.

Canine Leishmaniasis: An Overview of the Current Status and Strategies for Control

Canine leishmaniasis (CanL) is a vector-borne disease caused by Leishmania infantum and is transmitted by female phlebotomine sand flies primarily between animals and secondarily to humans. The course of infection may be different from one individual dog to another, ranging from spontaneous cure to acute evolution that leads to death, if proper management and therapy are not adopted. A parasitological cure is rarely achieved and clinical recurrences in CanL are frequent. Vaccination associated with the use of topical insecticides is undoubtedly the most effective form of prevention and control of the disease. In order to integrate the most important scientific knowledge of the literature in one objective publication, this review proposes a short overview of the main points of CanL.

Infection of Human Monocytes with Leishmania infantum Strains Induces a Downmodulated Response when Compared with Infection with Leishmania braziliensis

Human infection with different species of Leishmania leads to distinct clinical manifestations, ranging from relatively mild cutaneous (Leishmania braziliensis) to severe visceral (Leishmania infantum) forms of leishmaniasis. Here, we asked whether in vitro infection of human monocytes by Leishmania strains responsible for distinct clinical manifestations leads to early changes in immunological characteristics and ability of the host cells to control Leishmania. We evaluated the expression of toll-like receptors and MHC class II molecules, cytokines, and Leishmania control by human monocytes following short-term infection with L. braziliensis (M2904), a reference strain of L. infantum (BH46), and a wild strain of L. infantum (wild). The induction of TLR2, TLR9, and HLA-DR were all lower in L. infantum when compared with L. braziliensis-infected cells. Moreover, L. infantum-infected monocytes (both strains) produced lower TNF-alpha and a lower TNF-alpha/IL-10 ratio, resulting in a weaker inflammatory profile and a 100-fold less effective control of Leishmania than cells infected with L. braziliensis. Our results show that L. infantum strains fail to induce a strong inflammatory response, less activation, and less control of Leishmania from human monocytes, when compared with that induced by L. braziliensis infection. This functional profile may help explain the distinct clinical course observed in patients infected with the different Leishmania species.

Identification of Potential MHC Class-II-Restricted Epitopes Derived from Leishmania donovani Antigens by Reverse Vaccinology and Evaluation of Their CD4+ T-Cell Responsiveness against Visceral Leishmaniasis

Visceral leishmaniasis (VL) is one of the most neglected tropical diseases for which no vaccine exists. In spite of extensive efforts, no successful vaccine is available against this dreadful infectious disease. To support vaccine development, an immunoinformatics approach was applied to screen potential MHC class-II-restricted epitopes that can activate the immune cells. Initially, 37 epitopes derived from six stage-dependent, overexpressed antigens were predicted, which were presented by at least 26 diverse MHC class-II allele. Based on a population coverage analysis and human leukocyte antigen cross-presentation ability, six of the 37 epitopes were selected for further analysis. Stimulation with synthetic peptide alone or as a cocktail triggered intracellular IFN-γ production. Moreover, specific IgG antibodies were detected in the serum of active VL cases against P1, P4, P5, and P6 in order to evaluate the peptide effect on the humoral immune response. Additionally, most of the peptides, except P2, were found to be non-inducers of CD4+ IL-10 against both active VL as well as treated VL subjects. This finding suggests there is no role of these peptides in the pathogenesis of Leishmania. Peptide immunogenicity was validated in BALB/c mice immunized with a cocktail of synthetic peptide emulsified in complete Freund’s adjuvant/incomplete Freund’s adjuvant. The immunized splenocytes induced strong spleen cell proliferation upon parasite re-stimulation. Furthermore, increased IFN-γ, interleukin-12, IL-17, and IL-22 production augmented with elevated nitric oxide (NO) synthesis is thought to play a crucial role in macrophage activation. In this investigation, we identified six MHC class-II-restricted epitope hotspots of Leishmania antigens that induce CD4+ Th1 and Th17 responses, which could be used to potentiate a human universal T-epitope vaccine against VL.

The Eukaryotic Elongation Factor 1 Alpha (eEF1α) from the Parasite Leishmania infantum Is Modified with the Immunomodulatory Substituent Phosphorylcholine (PC)

Proteins and glycolipids have been found to be decorated with phosphorylcholine (PC) both in protozoa and nematodes that parasitize humans and animals. PC epitopes can provoke various effects on immune cells leading to an immunomodulation of the host’s immune system that allows long-term persistence of the parasites. So far, only a limited number of PC-modified proteins, mainly from nematodes, have been identified. Infections caused by Leishmania spp. (e.g., L. infantum in southern Europe) affect about 12 million people worldwide and are characterized by a wide spectrum of clinical forms in humans, ranging from cutaneous to fatal visceral leishmaniasis. To establish and maintain the infection, these protozoa are dependent on the secretion of effector molecules into the host for modulating their immune system. In this project, we analyzed the PC modification of L. infantum promastigotes by 2D-gel based proteomics. Western blot analysis with the PC-specific antibody TEPC-15 revealed one PC-substituted protein in this organism, identified as eEF1α. We could demonstrate that the binding of eEF1α to one of its downstream effectors is dependent on its PC-modification. In this study we provide evidence that in this parasite the modification of eEF1α with PC may be essential for its function as an important virulence factor.

Live Attenuated Leishmania donovani Centrin Gene-Deleted Parasites Induce IL-23-Dependent IL-17-Protective Immune Response against Visceral Leishmaniasis in a Murine Model

No vaccine exists against visceral leishmaniasis. To develop effective vaccines, we have previously reported protective role of live attenuated centrin gene-deleted Leishmania donovani (LdCen^-/- ) parasites through induction of Th1 type immune response in mice, hamsters, and dogs. In this study, we specifically explored the role of Th17 cells in LdCen^-/- -induced host protection in mice. Our results showed that compared with wild-type L. donovani infection, LdCen^-/- parasites induce significantly higher expression of Th17 differentiation cytokines in splenic dendritic cells. There was also induction of IL-17 and its promoting cytokines in total splenocytes and in both CD4 and CD8 T cells following immunization with LdCen^-/- Upon challenge with wild-type parasites, IL-17 and its differentiating cytokines were significantly higher in LdCen^-/- -immunized mice compared with nonimmunized mice that resulted in parasite control. Alongside IL-17 induction, we observed induction of IFN-γ-producing Th1 cells as reported earlier. However, Th17 cells are generated before Th1 cells. Neutralization of either IL-17 or IFN-γ abrogated LdCen^-/- -induced host protection further confirming the essential role of Th17 along with Th1 cytokines in host protection. Treatment with recombinant IL-23, which is required for stabilization and maintenance of IL-17, heightened Th17, and Tc17 responses in immunized mice splenocytes. In contrast, Th17 response was absent in immunized IL-23R^-/- mice that failed to induce protection upon virulent Leishmania challenge suggesting that IL-23 plays an essential role in IL-17-mediated protection by LdCen^-/- parasites. This study unveiled the role of IL-23-dependent IL-17 induction in LdCen^-/- parasite-induced immunity and subsequent protection against visceral leishmaniasis.

Leishmania infantum-specific IFN-γ production in stimulated blood from dogs with clinical leishmaniosis at diagnosis and during treatment

There is limited data regarding Leishmania infantum specific T cell mediated immunity in naturally infected sick dogs at the time of diagnosis and during anti-Leishmania treatment. Our aim was to investigate the kinetics of L. infantum specific IFN-γ production in dogs with leishmaniosis at the time of diagnosis and during treatment and to correlate it with specific L. infantum antibodies, blood parasitemia and clinicopathological findings. Thirty-four dogs were diagnosed with leishmaniosis based on physical examination, routine laboratory tests and L. infantum-specific antibody levels by quantitative ELISA. Heparinized whole blood was stimulated with L. infantum soluble antigen (LSA) and concanavalin A (ConA) and incubated for 5days. IFN-γ concentration was evaluated in supernatants of stimulated blood using a commercial sandwich ELISA. Leishmania real-time PCR was also performed for assessing blood parasitemia. Dogs were treated with meglumine antimoniate and allopurinol. Sixteen dogs were classified as IFN-γ non-producers after LSA stimulation (mean±SD: 0±0pg/mL) and 18 dogs as IFN-γ producers (mean±SD: 2885.3±4436.1pg/mL) at the time of diagnosis (P<0.0001). IFN-γ non-producers were classified in a more severe clinical staging than IFN-γ producers that presented a mild to moderate clinical staging (P=0.03). In the IFN-γ non-producer group, production of IFN-γ after LSA stimulation was significantly increased during treatment especially at day 365 (P=0.018) together with clinical improvement when compared with day 0. In contrast, IFN-γ producers maintained their IFN-γ production after LSA stimulation and no statistically significant changes were found during treatment follow-up. At diagnosis, IFN-γ non-producers showed a significantly higher blood parasitemia versus IFN-γ -producers (P=0.005). IFN-γ non-producers drastically reduced blood parasitemia to minimum values at day 365 when compared with day 0 (P=0.017). No significant differences were found at day 365 in blood parasitemia of IFN-γ producers compared to pre-treatment. At diagnosis, L. infantum specific antibodies were higher in IFN-γ non-producers than IFN-γ producers (P=0.014). A marked reduction of antibody levels was found at day 365 when compared with day 0 in IFN-γ non-producers (P=0.005) and producers (P=0.001). These results demonstrate that IFN-γ concentration increases with long-term anti-Leishmania treatment together with clinical improvement in dogs that do not produce IFN-γ at diagnosis. Together with clinical recovery, reduction in blood parasitemia and L. infantum specific antibodies, tracking IFN-γ concentration could constitute an important prognostic tool for immune monitoring in CanL.

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.

F1 Domain of the Leishmania (Leishmania) donovani Nucleoside Hydrolase Promotes a Th1 Response in Leishmania (Leishmania) infantum Cured Patients and in Asymptomatic Individuals Living in an Endemic Area of Leishmaniasis

The Leishmania (Leishmania) donovani nucleoside hydrolase NH36 is the main antigen of the Leishmune® vaccine and one of the promising candidates for vaccination against visceral leishmaniasis. The antigenicity of the N-terminal (F1), the central (F2), or the C-terminal recombinant domain (F3) of NH36 was evaluated using peripheral blood mononuclear cells (PBMC) from individuals infected with L. (L.) infantum from an endemic area of visceral leishmaniasis of Spain. Both NH36 and F1 domains significantly increased the PBMC proliferation stimulation index of cured patients and infected asymptomatic individuals compared to healthy controls. Moreover, F1 induced a 19% higher proliferative response than NH36 in asymptomatic exposed subjects. In addition, in patients cured from visceral leishmaniasis, proliferation in response to NH36 and F1 was accompanied by a significant increase of IFN-γ and TNF-α secretion, which was 42-43% higher, in response to F1 than to NH36. The interleukin 17 (IL-17) secretion was stronger in asymptomatic subjects, in response to F1, as well as in cured cutaneous leishmaniasis after NH36 stimulation. While no IL-10 secretion was determined by F1, a granzyme B increase was detected in supernatants from cured patients after stimulation with either NH36 or F1. These data demonstrate that F1 is the domain of NH36 that induces a recall cellular response in individuals with acquired resistance to the infection by L. (L.) infantum. In addition, F1 and NH36 discriminated the IgG3 humoral response in patients with active visceral leishmaniasis due to L. (L.) donovani (Ethiopia) and L. (L.) infantum (Spain) from that of endemic and non-endemic area controls. NH36 showed higher reactivity with sera from L. (L.) donovani-infected individuals, indicating species specificity. We conclude that the F1 domain, previously characterized as an inducer of the Th1 and Th17 responses in cured/exposed patients infected with L. (L.) infantum chagasi, may also be involved in the generation of a protective response against L. (L.) infantum and represents a potential vaccine candidate for the control of human leishmaniasis alone, or in combination with other HLA epitopes/antigens.

Probing the efficacy of a heterologous Leishmania/L. Viannia braziliensis recombinant enolase as a candidate vaccine to restrict the development of L. infantum in BALB/c mice

In the present study, the Leishmania braziliensis enolase protein was evaluated as a vaccine candidate against visceral leishmaniasis (VL). The DNA sequence was cloned and the recombinant protein (rEnolase) was evaluated as a vaccine, associated with saponin, as an immune adjuvant. The protective efficacy of the rEnolase plus saponin combination was investigated in BALB/c mice against Leishmania infantum infection. The results revealed that the vaccine induced higher levels of IFN-γ, IL-12, and GM-CSF when a capture ELISA and flow cytometry were performed, as well as an antileishmanial nitrite production after using in vitro stimulation with rEnolase and an antigenic Leishmania preparation. The vaccinated animals, when compared to the control groups, showed a lower parasite burden in the liver, spleen, bone marrow, and paws' draining lymph nodes when both a limiting dilution technique and RT-PCR assay were performed. In addition, these mice showed low levels of antileishmanial IL-4, IL-10, and anti-Leishmania IgG1 isotype antibodies. Partial protection was associated with IFN-γ production, which was mainly mediated by CD4⁺ T cells. In conclusion, the present study's data showed that the L. braziliensis enolase protein could be considered a vaccine candidate that offers heterologous protection against VL.

Novel Areas for Prevention and Control of Canine Leishmaniosis

There have been multiple recent advances regarding tools for the control and prevention of canine leishmaniosis (CanL), including new preventative vaccines. In this review, these advances are evaluated based on control targets, including vector and parasite. Leishvet recommendations are provided for control practices based on the dog's risk of infection. New topical insecticide formulations have proven to be effective in preventing sand fly bites, and subsequently infection. Parasite control occurs through chemotherapeutic or immunologic means, which decrease or prevent transmission to other animals, including humans. Leishmaniosis control programs that include a combination of coordinated measures, either in individuals or for prevention across reservoir populations, are required.

A third generation vaccine for human visceral leishmaniasis and post kala azar dermal leishmaniasis: First-in-human trial of ChAd63-KH

BACKGROUND

Visceral leishmaniasis (VL or kala azar) is the most serious form of human leishmaniasis, responsible for over 20,000 deaths annually, and post kala azar dermal leishmaniasis (PKDL) is a stigmatizing skin condition that often occurs in patients after successful treatment for VL. Lack of effective or appropriately targeted cell mediated immunity, including CD8+ T cell responses, underlies the progression of VL and progression to PKDL, and can limit the therapeutic efficacy of anti-leishmanial drugs. Hence, in addition to the need for prophylactic vaccines against leishmaniasis, the development of therapeutic vaccines for use alone or in combined immuno-chemotherapy has been identified as an unmet clinical need. Here, we report the first clinical trial of a third-generation leishmaniasis vaccine, developed intentionally to induce Leishmania-specific CD8+ T cells.

METHODS

We conducted a first-in-human dose escalation Phase I trial in 20 healthy volunteers to assess the safety, tolerability and immunogenicity of a prime-only adenoviral vaccine for human VL and PKDL. ChAd63-KH is a replication defective simian adenovirus expressing a novel synthetic gene (KH) encoding two Leishmania proteins KMP-11 and HASPB. Uniquely, the latter was engineered to reflect repeat domain polymorphisms and arrangements identified from clinical isolates. We monitored innate immune responses by whole blood RNA-Seq and antigen specific CD8+ T cell responses by IFNγ ELISPOT and intracellular flow cytometry.

FINDINGS

ChAd63-KH was safe at intramuscular doses of 1x1010 and 7.5x1010 vp. Whole blood transcriptomic profiling indicated that ChAd63-KH induced innate immune responses characterized by an interferon signature and the presence of activated dendritic cells. Broad and quantitatively robust CD8+ T cell responses were induced by vaccination in 100% (20/20) of vaccinated subjects.

CONCLUSION

The results of this study support the further development of ChAd63-KH as a novel third generation vaccine for VL and PKDL.

TRIAL REGISTRATION

This clinical trial (LEISH1) was registered at EudraCT (2012-005596-14) and ISRCTN (07766359).

Leishmania donovani Nucleoside Hydrolase (NH36) Domains Induce T-Cell Cytokine Responses in Human Visceral Leishmaniasis

Development of immunoprotection against visceral leishmaniasis (VL) focused on the identification of antigens capable of inducing a Th1 immune response. Alternatively, antigens targeting the CD8 and T-regulatory responses are also relevant in VL pathogenesis and worthy of being included in a preventive human vaccine. We assessed in active and cured patients and VL asymptomatic subjects the clinical signs and cytokine responses to the Leishmania donovani nucleoside hydrolase NH36 antigen and its N-(F1), central (F2) and C-terminal (F3) domains. As markers of VL resistance, the F2 induced the highest levels of IFN-γ, IL-1β, and TNF-α and, together with F1, the strongest secretion of IL-17, IL-6, and IL-10 in DTH+ and cured subjects. F2 also promoted the highest frequencies of CD3+CD4+IL-2+TNF-α-IFN-γ-, CD3+CD4+IL-2+TNF-α+IFN-γ-, CD3+CD4+IL-2+TNF-α-IFN-γ+, and CD3+CD4+IL-2+TNF-α+IFN-γ+ T cells in cured and asymptomatic subjects. Consistent with this, the IFN-γ increase was correlated with decreased spleen (R = -0.428, P = 0.05) and liver sizes (R = -0.428, P = 0.05) and with increased hematocrit counts (R = 0.532, P = 0.015) in response to F1 domain, and with increased hematocrit (R = 0.512, P 0.02) and hemoglobin counts (R = 0.434, P = 0.05) in response to F2. Additionally, IL-17 increases were associated with decreased spleen and liver sizes in response to F1 (R = -0.595, P = 0.005) and F2 (R = -0.462, P = 0.04). Conversely, F1 and F3 increased the CD3+CD8+IL-2+TNF-α-IFN-γ-, CD3+CD8+IL-2+TNF-α+IFN-γ-, and CD3+CD8+IL-2+TNF-α+IFN-γ+ T cell frequencies of VL patients correlated with increased spleen and liver sizes and decreased hemoglobin and hematocrit values. Therefore, cure and acquired resistance to VL correlate with the CD4+-Th1 and Th-17 T-cell responses to F2 and F1 domains. Clinical VL outcomes, by contrast, correlate with CD8+ T-cell responses against F3 and F1, potentially involved in control of the early infection. The in silico-predicted NH36 epitopes are conserved and bind to many HL-DR and HLA and B allotypes. No human vaccine against Leishmania is available thus far. In this investigation, we identified the NH36 domains and epitopes that induce CD4+ and CD8+ T cell responses, which could be used to potentiate a human universal T-epitope vaccine against leishmaniasis.

A Chimera Containing CD4+ and CD8+ T-Cell Epitopes of the Leishmania donovani Nucleoside Hydrolase (NH36) Optimizes Cross-Protection against Leishmania amazonesis Infection

The Leishmania donovani nucleoside hydrolase (NH36) and NH A34480 of Leishmania amazonensis share 93% of sequence identity. In mice, the NH36 induced protection against visceral leishmaniasis is mediated by a CD4+ T cell response against its C-terminal domain (F3). Besides this CD4+ Th1 response, prevention and cure of L. amazonensis infection require also additional CD8+ and regulatory T-cell responses to the NH36 N-terminal (F1 domain). We investigated if mice vaccination with F1 and F3 domains cloned in tandem, in a recombinant chimera, with saponin, optimizes the vaccine efficacy against L. amazonensis infection above the levels promoted by the two admixed domains or by each domain independently. The chimera induced the highest IgA, IgG, and IgG2a anti-NH36 antibody, IDR, IFN-γ, and IL-10 responses, while TNF-α was more secreted by mice vaccinated with F3 or all F3-contaning vaccines. Additionally, the chimera and the F1 vaccine also induced the highest proportions of CD4+ and CD8+ T cells secreting IL-2, TNF-α, or IFN-γ alone, TNF-α in combination with IL-2 or IFN-γ, and of CD4+ multifunctional cells secreting IL-2, TNF-α, and IFN-γ. Correlating with the immunological results, the strongest reductions of skin lesions sizes were determined by the admixed domains (80%) and by the chimera (84%), which also promoted the most pronounced and significant reduction of the parasite load (99.8%). Thus, the epitope presentation in a recombinant chimera optimizes immunogenicity and efficacy above the levels induced by the independent or admixed F1 and F3 domains. The multiparameter analysis disclosed that the Th1-CD4+ T helper response induced by the chimera is mainly directed against its FRYPRPKHCHTQVA epitope. Additionally, the YPPEFKTKL epitope of F1 induced the second most important CD4+ T cell response, and, followed by the DVAGIVGVPVAAGCT, FMLQILDFYTKVYE, and ELLAITTVVGNQ sequences, also the most potent CD8+ T cell responses and IL-10 secretion. Remarkably, the YPPEFKTKL epitope shows high amino acid identity with a multipotent PADRE sequence and stimulates simultaneously the CD4+, CD8+ T cell, and a probable T regulatory response. With this approach, we advanced in the design of a NH36 polytope vaccine capable of inducing cross-protection to cutaneous leishmaniasis.

The leishmanicidal activity of oleuropein is selectively regulated through inflammation- and oxidative stress-related genes

Background

Much research effort has been focused on investigating new compounds derived from low-cost sources, such as natural products, for treating leishmaniasis. Oleuropein derived from numerous plants, particularly from the olive tree, Olea europaea L. (Oleaceae), is a biophenol with many biological activities. Our previous findings showed that oleuropein exhibits leishmanicidal effects against three Leishmania spp. in vitro, and minimizes the parasite burden in L. donovani-infected BALB/c mice. The aim of the present study is to investigate the possible mechanism(s) that mediate this leishmanicidal activity.

Methods

We determined the efficacy of oleuropein in elevating ROS and NO production in L. donovani-infected J774A.1 macrophages and in explanted splenocytes and hepatocytes obtained from L. donovani-infected BALB/c mice. We also assessed the expression of genes that are related to inflammation, T-cell polarization and antioxidant defense, in splenocytes. Finally, we determined the ratios of specific IgG2a/IgG1 antibodies and DTH reactions in L. donovani-infected BALB/c mice treated with oleuropein.

Results

Oleuropein was able to elevate ROS production in both in vitro and in vivo models of visceral leishmaniasis and raised NO production in ex vivo cultures of splenocytes and hepatocytes. The extensive oxidative stress found in oleuropein-treated mice was obviated by the upregulation of the host’s antioxidant enzyme (mGCLC) and the simultaneous downregulation of the corresponding enzyme of the parasite (LdGCLC). Moreover, oleuropein was able to mount a significant Th1 polarization characterized by the expression of immune genes (IL-12β, IL-10, TGF-β1, IFN-γ) and transcription factors (Tbx21 and GATA3). Moreover, this immunomodulatory effect was also correlated with an inhibitory effect on IL-1β gene expression, rather than with the expression of IL-1α, IL-1rn and TNF-α. Furthermore, oleuropein-treated BALB/c mice mounted a delayed-type hypersensitivity (DTH) response and an elevated Leishmania-specific IgG2a/IgG1 ratio that clearly demonstrated an in vivo protective mechanism.

Conclusion

The ability of Oleuropein to promote a Th1 type immune response in L. donovani-infected BALB/c mice points towards the candidacy of this bioactive compound as an immunomodulatory agent that may complement therapeutic approaches to leishmaniasis.

Differential Role of Leptin as an Immunomodulator in Controlling Visceral Leishmaniasis in Normal and Leptin-Deficient Mice

Visceral leishmaniasis (VL) is caused by the protozoan parasite Leishmania donovani. There are no vaccines and available drugs against leishmaniasis are toxic. Immunomodulators that specifically boost the anti-microbial activities of the immune cells could alleviate several of these limitations. Therefore, finding novel immunomodulators for VL therapy is a pressing need. This study is aimed to evaluate the immunomodulatory role of leptin, an adipocyte-derived hormone capable of regulating the immune response, in L. donovani-infected mice. We observed that recombinant leptin treatment reduced splenic parasite burden compared with non-treated infected normal mice. Decrease in parasite burden correlated with an induction of innate immune response in antigen-presenting cells that showed an increase in nitric oxide, enhanced pro-inflammatory cytokine (interferon gamma [IFNγ], interleukin12 [IL]12, and IL1β) response in the splenocytes, indicating host-protecting Th1 response mediated by leptin. Moreover, in infected normal mice, leptin treatment induced IFNγ production from both CD4⁺ and CD8⁺ T cells, compared with non-treated infected mice. Alternatively, leptin-deficient (Ob/Ob) mice had higher splenic and liver parasite burden compared with the infected normal mice. However, leptin treatment failed to reduce the splenic parasite burden and improve a host-protective cytokine response in these mice. In addition, in contrast to dendritic cells (DCs) from a normal mouse, Ob/Ob mouse–derived DCs showed a defect in the induction of innate immune response on Leishmania infection that could not be reversed by leptin treatment. Therefore, our findings reveal that leptin has a differential immunomodulatory effect in controlling VL in normal and Ob/Ob mice.

Regulatory IgDhi B Cells Suppress T Cell Function via IL-10 and PD-L1 during Progressive Visceral Leishmaniasis

During visceral leishmaniasis (VL), Th1-based inflammation is induced to control intracellular parasites. Inflammation-based pathology was shown to be dampened by IL-10 and eventual programmed death 1-mediated T cell exhaustion. Cell type(s) responsible for the initiation of T cell-produced IL-10 during VL are unknown. CD19(+), CD5(-), CD1d(-), IgD(hi) regulatory B cells from healthy controls produced IL-10 in the absence of infection or stimulation, in contrast to IgD(lo/neg) B cells. IgD(hi) B cells may have a de novo versus induced regulatory program. The population of IgD(hi) B cells increased 3-fold as VL progressed. B cells from VL dogs were necessary and sufficient to suppress Th1 cell effector function. IgD(hi) B cells induced IL-10 production by T cells and IgD(lo) B cells. Blockage of B cell-specific PD-L1 restored Th1 responses. IgD(hi) regulatory B cells represent a novel regulatory B cell that may precipitate T cell exhaustion during VL.

Leishmanicidal Activity of Piper nigrum Bioactive Fractions is Interceded via Apoptosis In Vitro and Substantiated by Th1 Immunostimulatory Potential In Vivo

Visceral leishmaniasis (VL) is a life-threatening protozoal infection chiefly impinging the rural and poor population in the tropical and sub-tropical countries. The deadly affliction is rapidly expanding after its association with AIDS, swiftly defying its status of a neglected disease. Despite successful formulation of vaccine against canine leishmaniasis, no licensed vaccine is yet available for human VL, chemotherapy is in appalling state, and the development of new candidate drugs has been painfully slow. In face of lack of proper incentives, immunostimulatory plant preparations owing antileishmanial efficacy bear potential to rejuvenate awful antileishmanial chemotherapy. We have earlier reported profound leishmanicidal activity of Piper nigrum hexane (PNH) seeds and P. nigrum ethanolic (PNE) fractions derived from P. nigrum seeds against Leishmania donovani promastigotes and amastigotes. In the present study, we illustrate that the remarkable anti-promastigote activity exhibited by PNH and PNE is mediated via apoptosis as evidenced by phosphatidylserine externalization, DNA fragmentation, arrest in sub G₀/G₁ phase, loss of mitochondrial membrane potential and generation of reactive oxygen species. Further, P. nigrum bioactive fractions rendered significant protection to L. donovani infected BALB/c mice in comparison to piperine, a known compound present in Piper species. The substantial therapeutic potential of PNH and PNE was accompanied by elicitation of cell-mediated immune response. The bioactive fractions elevated the secretion of Th1 (INF-γ, TNF-α, and IL-2) cytokines and declined IL-4 and IL-10. PNH and PNE enhanced the production of IgG2a, upregulated the expression of co-stimulatory molecules CD80 and CD86, augmented splenic CD4⁺ and CD8⁺ T cell population, induced strong lymphoproliferative and DTH responses and partially stimulated NO production. PNH and PNE were devoid of any hepatic or renal toxicity. These encouraging findings merit further exploration of P. nigrum bioactive fractions as a source of potent and non-toxic antileishmanials.

Uniting mathematics and biology for control of visceral leishmaniasis

The neglected tropical disease (NTD) visceral leishmaniasis (VL) has been targeted by the WHO for elimination as a public health problem on the Indian subcontinent by 2017 or earlier. To date there is a surprising scarcity of mathematical models capable of capturing VL disease dynamics, which are widely considered central to planning and assessing the efficacy of interventions. The few models that have been developed are examined, highlighting the necessity for better data to parameterise and fit these and future models. In particular, the characterisation and infectiousness of the different disease stages will be crucial to elimination. Modelling can then assist in establishing whether, when, and how the WHO VL elimination targets can be met.

Vaccines for visceral leishmaniasis: A review

Visceral leishmaniasis, which is also known as Kala-Azar, is one of the most severely neglected tropical diseases recognized by the World Health Organization (WHO). The threat of this debilitating disease continues due to unavailability of promising drug therapy or human vaccine. An extensive research is undergoing to develop a promising vaccine to prevent this devastating disease. In this review we compiled the findings of recent research with a view to facilitate knowledge on experimental vaccinology for visceral leishmaniasis. Various killed or attenuated parasite based first generation vaccines, second generation vaccines based on antigenic protein or recombinant protein, and third generation vaccines derived from antigen-encoding DNA plasmids including heterologous prime-boost Leishmania vaccine have been examined for control and prevention of visceral leishmaniasis. Vaccines based on recombinant protein and antigen-encoding DNA plasmids have given promising results and few vaccines including Leishmune®, Leishtec, and CaniLeish® have been licensed for canine visceral leishmaniasis. A systematic investigation of these vaccine candidates can lead to development of promising vaccine for human visceral leishmaniasis, most probably in the near future.

From mouse to man: safety, immunogenicity and efficacy of a candidate leishmaniasis vaccine LEISH-F3+GLA-SE

Key antigens of Leishmania species identified in the context of host responses in Leishmania-exposed individuals from disease-endemic areas were prioritized for the development of a subunit vaccine against visceral leishmaniasis (VL), the most deadly form of leishmaniasis. Two Leishmania proteins-nucleoside hydrolase and a sterol 24-c-methyltransferase, each of which are protective in animal models of VL when properly adjuvanted- were produced as a single recombinant fusion protein NS (LEISH-F3) for ease of antigen production and broad coverage of a heterogeneous major histocompatibility complex population. When formulated with glucopyranosyl lipid A-stable oil-in-water nanoemulsion (GLA-SE), a Toll-like receptor 4 TH1 (T helper 1) promoting nanoemulsion adjuvant, the LEISH-F3 polyprotein induced potent protection against both L. donovani and L. infantum in mice, measured as significant reductions in liver parasite burdens. A robust immune response to each component of the vaccine with polyfunctional CD4 TH1 cell responses characterized by production of antigen-specific interferon-γ, tumor necrosis factor and interleukin-2 (IL-2), and low levels of IL-5 and IL-10 was induced in immunized mice. We also demonstrate that CD4 T cells, but not CD8 T cells, are sufficient for protection against L. donovani infection in immunized mice. Based on the sum of preclinical data, we prepared GMP materials and performed a phase 1 clinical study with LEISH-F3+GLA-SE in healthy, uninfected adults in the United States. The vaccine candidate was shown to be safe and induced a strong antigen-specific immune response, as evidenced by cytokine and immunoglobulin subclass data. These data provide a strong rationale for additional trials in Leishmania-endemic countries in populations vulnerable to VL.

Arsenic exposure and outcomes of antimonial treatment in visceral leishmaniasis patients in Bihar, India: a retrospective cohort study

Background

In the late twentieth century, emergence of high rates of treatment failure with antimonial compounds (SSG) for visceral leishmaniasis (VL) caused a public health crisis in Bihar, India. We hypothesize that exposure to arsenic through drinking contaminated groundwater may be associated with SSG treatment failure due to the development of antimony-resistant parasites.

Methods

A retrospective cohort design was employed, as antimony treatment is no longer in routine use. The study was performed on patients treated with SSG between 2006 and 2010. Outcomes of treatment were assessed through a field questionnaire and treatment failure used as a proxy for parasite resistance. Arsenic exposure was quantified through analysis of 5 water samples from within and surrounding the patient’s home. A logistic regression model was used to evaluate the association between arsenic exposure and treatment failure. In a secondary analysis survival curves and Cox regression models were applied to assess the risk of mortality in VL patients exposed to arsenic.

Results

One hundred and ten VL patients treated with SSG were analysed. The failure rate with SSG was 59%. Patients with high mean local arsenic level had a non-statistically significant higher risk of treatment failure (OR = 1.78, 95% CI: 0.7–4.6, p = 0.23) than patients using wells with arsenic concentration <10 μg/L. Twenty one patients died in our cohort, 16 directly as a result of VL. Arsenic levels ≥ 10 μg/L increased the risk of all-cause (HR 3.27; 95% CI: 1.4–8.1) and VL related (HR 2.65; 95% CI: 0.96–7.65) deaths. This was time dependent: 3 months post VL symptom development, elevated risks of all-cause mortality (HR 8.56; 95% CI: 2.5–29.1) and of VL related mortality (HR 9.27; 95% CI: 1.8–49.0) were detected.

Discussion/Conclusion

This study indicates a trend towards increased treatment failure in arsenic exposed patients. The limitations of the retrospective study design may have masked a strong association between arsenic exposure and selection for antimonial resistance in the field. The unanticipated strong correlation between arsenic exposure and VL mortality warrants further investigation.

The parasitic disease visceral leishmaniasis (VL) causes a significant burden of illness and death in India. The main drug used to treat VL, which is based on the chemical element antimony, stopped working well in about half of all patients in the late twentieth century. We hypothesised that arsenic exposure of the Indian population, through contaminated groundwater, was contributing to treatment failure with antimony based drugs. Arsenic and antimony are similar chemical elements and exposure of the parasite to arsenic within the liver of arsenic-exposed patients could allow the parasite to become resistant to treatment with antimony. Using a field-based questionnaire study we retrospectively evaluated whether arsenic exposure was linked to antimonial treatment failure in a cohort of 110 antimonial treated patients. No significant association was found, although this may be because the number of patients in the study was low as antimony use was officially discontinued in 2005 due to high rates of treatment failure. However, arsenic exposure was found to increase risk of mortality from VL particularly if death occurred more than 3 months after the symptoms of VL developed. More research into the relationship between arsenic exposure and mortality in VL is warranted.

Epidemiologic, clinical, diagnostic and therapeutic aspects of visceral leishmaniasis in renal transplant recipients: experience from thirty cases

BACKGROUND

Visceral leishmaniasis is a disease caused by the protozoan Leishmania sp. and is transmitted by Lutzomyia longipalpis (sand fly). In renal transplant recipients, visceral leishmaniasis causes severe damage to the liver, spleen, and hematopoietic system, as well as poor outcomes for patients with transplanted kidneys. This study describes the largest series of cases of visceral leishmaniasis in renal transplant recipients, providing important information about the diagnostic routines and therapeutic strategies in this patient population.

METHODS

A retrospective, descriptive study was performed to analyze the distribution and evaluate the extent of the epidemiologic, clinical, diagnostic and therapeutic aspects of 30 renal transplant recipients from endemic regions who presented with visceral leishmaniasis in the post-transplantation period.

RESULTS

In this study, visceral leishmaniasis was more frequent in men (80%). The mean age of presentation was 40 ± 10.5 years. The majority of patients worked in urban areas (66.7%), cohabitated with domestic animals (90%), and were from low-income households. In 73.3% of cases, diagnosis was made by direct isolation of Leishmania forms. Patients were treated with liposomal amphotericin, resulting in a high degree of disease remission (80%).

CONCLUSIONS

This study describes the largest series of visceral leishmaniasis in renal transplant recipients and expands clinical-epidemiological knowledge for transplantation teams to perform adequate disease management for this specific patient population.

Modular multiantigen T cell epitope-enriched DNA vaccine against human leishmaniasis

The leishmaniases are protozoal diseases that severely affect large populations in tropical and subtropical regions. There are only limited treatment options and preventative measures. Vaccines will be important for prevention, control and elimination of leishmaniasis, and could reduce the transmission and burden of disease in endemic populations. We report the development of a DNA vaccine against leishmaniasis that induced T cell-based immunity and is a candidate for clinical trials. The vaccine antigens were selected as conserved in various Leishmania species, different endemic regions, and over time. They were tested with T cells from individuals cured of leishmaniasis, and shown to be immunogenic and to induce CD4(+) and CD8(+) T cell responses in genetically diverse human populations of different endemic regions. The vaccine proved protective in a rodent model of infection. Thus, the immunogenicity of candidate vaccine antigens in human populations of endemic regions, as well as proof of principle for induction of specific immune responses and protection against Leishmania infection in mice, provides a viable strategy for T cell vaccine development.

Immunoregulation in human American leishmaniasis: balancing pathology and protection

Leishmaniasis covers a broad spectrum of diseases with distinct, and sometimes overlapping, characteristics. The common thread in all forms of leishmaniasis is the infection by the parasite Leishmania belonging to the genus Leishmania. Upon infection of humans, there can be at least three outcomes, (i) control of Leishmania by the host immune response resulting in asymptomatic disease, (ii) patent infection and development of a relatively mild form of leishmaniasis and (iii) patent infection and development of severe clinical forms. The factors that determine the outcome of an initial inoculation with Leishmania are many, with the species of Leishmania representing one of the strongest predictive factors for the development of a given clinical form of disease. This is seen with L. braziliensis and L. amazonensis, infection leading mostly to tegumentary forms of disease, and L. infantum with the potential to induce visceral disease. However, it is also clear that the host immune response is a key factor in disease progression, not only responsible for control of Leishmania, but also playing an important role in disease progression and pathology. This duality between protective and pathogenic immune responses in individuals infected with Leishmania in the Americas is the focus of this review.