Vaccines in leishmaniasis: advances in the last five years

In vitro anti-leishmanial activity of Prunus armeniaca fractions on Leishmania tropica and molecular docking studies

Prunus armeniaca (L.) is a member of the Rosaceae, subfamily Prunoideae, shows anticancer, antitubercular, antimutagenic, antimicrobial, antioxidant, and cardioprotective activities. Here we fractionated the leaves extract of this highly medicinally important plant for antileishmanial activity. In the current study, the leaves extract was fractionated and characterized using column and thin layer chromatography by n-hexane, ethyl acetate, and methanol solvents. Twelve fractions were isolated and subjected for evaluation of their cytotoxicity and in vitro antileishmanial activity against promastigotes and amastigotes of Leishmania tropica. Among all fractions used, the fraction (F7) exhibited the strongest antileishmanial activity. The bioactive fraction was further characterized by spectroscopy (FTIR, UV-Vis), and GC-MS analysis. The in silico docking was carried out to find the active site of PTR1. All derived fractions exhibited toxicity in the safety range IC₅₀ > 100 μg/ml. The fraction (F7) showed significantly the highest antipromastigotes activity with IC₅₀11.48 ± 0.82 μg/ml and antiamastigotes activity with IC₅₀ 21.03 ± 0.98 μg/ml compared with control i.e. 11.60 ± 0.70 and 22.03 ± 1.02 μg/ml respectively. The UV-Vis spectroscopic analysis revealed the presence of six absorption peaks and the FTIR spectrum revealed the presence of alkane, aldehyde, carboxylic acid, thiols, alkynes, and carbonyls compounds The GC-MS chromatogram exhibited the presence of nine compounds: (a) benzeneethanol, alpha, beta dimethyl, (b)carbazic acid, 3-(1 propylbutylidene)-, ethyl ester, (c)1, 2-benzenedicarboxylic acid, diisooctyl ester, (d)benzeneethanamine a-methyl, (e)2aminononadecane, (f)2-heptanamine-5-methyl, (g)cyclobutanol, (h)cyclopropyl carbine, and (i)nitric acid, nonyl ester. Among all compounds, the 1, 2-benzenedicarboxylic acid, diisooctyl ester bound well to the PTR1 receptor. Fraction (F7) showed acceptable results with no cytotoxicity. However, in vivo studies are required in the future.

Applications of Nanomaterials in Leishmaniasis: A Focus on Recent Advances and Challenges

Leishmaniasis is a widely distributed protozoan vector-born disease affecting almost 350 million people. Initially, chemotherapeutic drugs were employed for leishmania treatment but they had toxic side effects. Various nanotechnology-based techniques and products have emerged as anti-leishmanial drugs, including liposomes, lipid nano-capsules, metal and metallic oxide nanoparticles, polymeric nanoparticles, nanotubes and nanovaccines, due to their unique properties, such as bioavailability, lowered toxicity, targeted drug delivery, and biodegradability. Many new studies have emerged with nanoparticles serving as promising therapeutic agent for anti-leishmanial disease treatment. Liposomal Amphotericin B (AmB) is one of the successful nano-based drugs with high efficacy and negligible toxicity. A new nanovaccine concept has been studied as a carrier for targeted delivery. This review discusses different nanotechnology-based techniques, materials, and their efficacies in leishmaniasis treatment and their futuristic improvements.

Coadminstration of L. major amastigote class I nuclease (rLmaCIN) with LPD nanoparticles delays the progression of skin lesion and the L. major dissemination to the spleen in BALB/c mice-based experimental setting

Human cutaneous leishmaniasis is a disease caused by eukaryotic single-celled Leishmania species, the developmental program of which relies upon blood-feeding adult female sand flies and their dominant mammal blood sources, namely wild rodents in area where human beings exert more or less transient activities. The recourse to model rodents - namely laboratory mice such as C57BL/6 mice - has allowed extracted the immune signatures that account for the healing of the transient cutaneous lesion that develops at the site where Leishmania major promastigotes were delivered. Indeed, if the latter mice are exposed to a second inoculum of L. major promastigotes, no lesion will develop in the secondary skin site remodeled as a niche for a low size intracellular L. major amastigote population. Moreover, IFN-γ dominates over IL-10 in the supernatant of cultures of PBMCs -prepared from blood sampled from human beings who healed from a cutaneous lesion- and incubated with L. major class I Nuclease LmaCIN, a protein highly expressed in the cell-cycling amastigote population which is dominant by macrophages. Altogether, these datasets were strong incentive to promote research aimed to design and monitor efficacy of L. major amastigote protein-based vaccines in pre-clinical settings. Using L. major enzyme class I nuclease (LmaCIN) expressed in the L. major cell-cycling amastigote population hosted by macrophages, BALB/c mice were immunized three times with either rLmaCIN plus LPD nanoparticles (LPD-rLmaCIN), or rLmaCIN-CpG DNA or free rLmaCIN and dextrose. The following parameters: footpad swelling, splenic L. major load, L. major binding IgGs and cytokine profiles of rLmaCIN- reactive T lymphocytes were then compared. Once coadminstered with LPD, rLmaCIN allow BALB/c mice to display delayed onset of skin lesion at the challenge inoculation site and delayed L. major dissemination from the challenged site to the spleen. Thus, the LPD-rLmaCIN is shown to display some promising features out of three formulations inoculated to the BALB/c mouse immunization.

Hairless mice as an experimental model of infection with Leishmania (Leishmania) amazonensis

HRS/J Hairless mice have been investigated as an experimental model in cutaneous leishmaniasis induced by Leishmania (Leishmania) amazonensis. The animals were inoculated with 10(6) promastigotes into the right hind footpad and the course of infection was followed up for 30, 60 and 90 days. BALB/c mice were infected and used as control. Hairless mice were susceptible to L. (L.) amazonensis infection and a progressive increase in number of parasites and footpad thickness was detected over time. Signals of dissemination and visceralization were confirmed by the presence of parasite in the draining lymph node of lesion and spleen, at different times post infection. IL-10 gene expression evaluated by RT-PCR was significantly higher in Hairless mice at 60 days post infection, corroborating the pattern of susceptibility. These results point this inbred strain as a promising susceptible model for the study of experimental infection induced by L. (L.) amazonensis. This model would allow the use of other infection sites that minimize secondary interference and best monitoring the skin lesion, as in the case of in vivo assays of potential drugs for LT.

LBSapSal-vaccinated dogs exhibit increased circulating T-lymphocyte subsets (CD4⁺ and CD8⁺) as well as a reduction of parasitism after challenge with Leishmania infantum plus salivary gland of Lutzomyia longipalpis

BACKGROUND

The development of a protective vaccine against canine visceral leishmaniasis (CVL) is an alternative approach for interrupting the domestic cycle of Leishmania infantum. Given the importance of sand fly salivary proteins as potent immunogens obligatorily co-deposited during transmission of Leishmania parasites, their inclusion in an anti-Leishmania vaccine has been investigated in the last few decades. In this context, we previously immunized dogs with a vaccine composed of L. braziliensis antigens plus saponin as the adjuvant and sand fly salivary gland extract (LBSapSal vaccine). This vaccine elicited an increase in both anti-saliva and anti-Leishmania IgG isotypes, higher counts of specific circulating CD8⁺ T cells, and high NO production.

METHODS

We investigated the immunogenicity and protective effect of LBSapSal vaccination after intradermal challenge with 1 × 10⁷ late-log-phase L. infantum promastigotes in the presence of sand fly saliva of Lutzomyia longipalpis. The dogs were followed for up to 885 days after challenge.

RESULTS

The LBSapSal vaccine presents extensive antigenic diversity with persistent humoral and cellular immune responses, indicating resistance against CVL is triggered by high levels of total IgG and its subtypes (IgG1 and IgG2); expansion of circulating CD5⁺, CD4⁺, and CD8⁺ T lymphocytes and is Leishmania-specific; and reduction of splenic parasite load.

CONCLUSIONS

These results encourage further study of vaccine strategies addressing Leishmania antigens in combination with proteins present in the saliva of the vector.

Th1 Platform Immune Responses Against Leishmania major Induced by Thiol-Specific Antioxidant-Based DNA Vaccines

BACKGROUND

The Thiol-specific antioxidant (TSA) is an antigen of Leishmania major which is believed to be the most promising molecule as a vaccine candidate against leishmaniasis.

OBJECTIVES

In this study, we investigated the protective efficacy of TSA-based DNA vaccine against L. major infection.

MATERIALS AND METHODS

Recombinant plasmid construction TSA (pcTSA) was prepared and transfected into eukaryotic cells and expression was confirmed with western blot and RT-PCR. The mice were assigned to six different groups and DNA immunization was performed with 100 µg intramuscular recombinant plasmid with a two-week interval. Cytokines and lymphocyte proliferation assay, antibody responses and determination of parasite burden were performed following immunization and the challenging infection with L. major.

RESULTS

The antibody and IFN-γ titers were higher in pcTSA + AlPO4 group the immunized mice with pcTSA alone, but there was no statistically significant difference between the two groups. Additionally the IL-4 titer was not statistically different between the groups following immunization and challenge. After infection with L. major promastigotes, the immunized mice with pcTSA and the one immunized with both pcTSA + AlPO4 presented a considerable reduction in diameter of lesion but there was no statistical difference between the two groups. The immunized mice had significantly lower parasite loads. No significant differences were observed between the two vaccinated groups. However the highest reduction in parasite burden was observed in the group immunized with pcDNA + AlPO4. No significant differences were observed in survival rate of the immunized mice after the challenge with L. major.

CONCLUSIONS

In conclusion, TSA-based DNA vaccine induced Th1 platform immune response and aluminum phosphate could improve the efficacy of these vaccines with induction of humoral and cellular immune responses against L. major infection. There were no significant differences observed between pcTSA and pcTSA + AlPO4 groups.

The immunomodulatory effect of plant lectins: a review with emphasis on ArtinM properties

Advances in the glycobiology and immunology fields have provided many insights into the role of carbohydrate-protein interactions in the immune system. We aim to present a comprehensive review of the effects that some plant lectins exert as immunomodulatory agents, showing that they are able to positively modify the immune response to certain pathological conditions, such as cancer and infections. The present review comprises four main themes: (1) an overview of plant lectins that exert immunomodulatory effects and the mechanisms accounting for these activities; (2) general characteristics of the immunomodulatory lectin ArtinM from the seeds of Artocarpus heterophyllus; (3) activation of innate immunity cells by ArtinM and consequent induction of Th1 immunity; (4) resistance conferred by ArtinM administration in infections with intracellular pathogens, such as Leishmania (Leishmania) major, Leishmania (Leishmania) amazonensis, and Paracoccidioides brasiliensis. We believe that this review will be a valuable resource for more studies in this relatively neglected area of research, which has the potential to reveal carbohydrate targets for novel prophylactic and therapeutic strategies.

Performance of LBSap vaccine after intradermal challenge with L. infantum and saliva of Lu. longipalpis: immunogenicity and parasitological evaluation

In the last decade, the search for new vaccines against canine visceral leishmaniasis has intensified. However, the pattern related to immune protection during long periods after experimental infection in vaccine trials is still not fully understood. Herein, we investigated the immunogenicity and parasitological levels after intradermal challenge with Leishmania infantum plus salivary gland extract in dogs immunized with a vaccine composed of L. braziliensis antigens plus saponin as an adjuvant (LBSap vaccine). The LBSap vaccine elicited higher levels of total anti-Leishmania IgG as well as both IgG1 and IgG2. Furthermore, dogs vaccinated had increased levels of lymphocytes, particularly circulating B cells (CD21(+)) and both CD4(+) and CD8(+) T lymphocytes. LBSap also elicited an intense in vitro cell proliferation associated with higher levels of CD4(+) T lymphocytes specific for vaccine soluble antigen and soluble lysate of L. infantum antigen even 885 days after experimental challenge. Furthermore, LBSap vaccinated dogs presented high IFN-γ and low IL-10 and TGF-β1 expression in spleen with significant reduction of parasite load in this tissue. Overall, our results validate the potential of LBSap vaccine to protect against L. infantum experimental infection and strongly support further evaluation of efficiency of LBSap against CVL in natural infection conditions.

Evaluation of TNF-α, IL-4, and IL-10 and parasite density in spleen and liver of L. (L.) chagasi naturally infected dogs

Dogs are the main domestic reservoirs of L. (L.) chagasi. Once in the vertebrate host, the parasite can cause visceral leishmaniasis, which can also be transmitted to humans. Cytokines are key elements of the host immune response against Leishmania spp. To investigate whether tumor necrosis factor (TNF)-α, interleukin (IL)-4 and IL-10 are associated with pattern infection in dogs, these cytokines were quantified in the spleen and liver of dogs naturally infected with L. (L.) chagasi, with or without clinical manifestations, and their levels were correlated with the parasite load verified in these organs. A total of 40 adult dogs naturally infected with L. (L.) chagasi were assessed, together with 12 uninfected control dogs. Samples from spleen and liver were used to determine the cytokine levels by capture ELISA and for quantifying parasite load by real-time PCR. Statistical analysis was performed using the minimum Chi square method and group means were compared using the Tukey test. TNF-α, IL-4 and IL-10 levels in infected dogs were higher than in control groups; the liver was the main cytokine-producing organ during infection. The level of splenic TNF-α showed correlation with parasite load and may represent an important marker for infection process evolution, with the participation of IL-10. These results may contribute to a clearer understanding of the immune response in dogs infected with L. (L.) chagasi, which may lead to the development of prophylactic or preventive measures for these animals.

A killed Leishmania vaccine with sand fly saliva extract and saponin adjuvant displays immunogenicity in dogs

A vaccine against canine visceral leishmaniasis (CVL), comprising Leishmania braziliensis promastigote protein, sand fly gland extract (SGE) and saponin adjuvant, was evaluated in dog model, in order to analyse the immunogenicity of the candidate vaccine. The vaccine candidate elicited strong antigenicity in dogs in respect of specific SGE and Leishmania humoral immune response. The major saliva proteins recognized by serum from immunized dogs exhibited molecular weights of 35 and 45 kDa, and were related to the resistance pattern against Leishmania infection. Immunophenotypic analysis revealed increased circulating CD21⁺ B-cells and CD5⁺ T-cells, reflected by higher counts of CD4⁺ and CD8⁺ T-cells. The observed interaction between potential antigen-presenting cells (evaluated as CD14⁺ monocytes) and lymphocyte activation status indicated a relationship between innate and adaptive immune responses. The higher frequency in L. chagasi antigen-specific CD8⁺ T-lymphocytes, and their positive association with intense cell proliferation, in addition to the progressively higher production of serum nitric oxide levels, showed a profile compatible with anti-CVL vaccine potential. Further studies on immunological response after challenge with L. chagasi may provide important information that will lead to a better understanding on vaccine trial and efficacy.

Immunogenicity of a killed Leishmania vaccine with saponin adjuvant in dogs

Cellular and humoral immune responses of dogs to a candidate vaccine, composed of Leishmania braziliensis promastigote protein plus saponin as adjuvant, have been investigated as a pre-requisite to understanding the mechanisms of immunogenicity against canine visceral leishmaniasis (CVL). The candidate vaccine elicited strong antigenicity related to the increases of anti-Leishmania IgG isotypes, together with higher levels of lymphocytes, particularly of circulating CD8⁺ T-lymphocytes and Leishmania chagasi antigen-specific CD8⁺ T-lymphocytes. As indicated by the intense cell proliferation and increased nitric oxide production during in vitro stimulation by L. chagasi soluble antigens, the candidate vaccine elicited an immune activation status potentially compatible with effective control of the etiological agent of CVL.

Immune response and protection assay of recombinant major surface glycoprotein of Leishmania (rgp63) reconstituted with liposomes in BALB/c mice

In this study the ability of recombinant gp63 entrapped in liposomes to induce immune response and protection against L. major infection in susceptible BALB/c mice was studied. Liposomes containing rgp63 (Lip-rgp63) were prepared from egg lecithin and cholesterol using detergent solubilization method. Immunization of BALB/c mice with rgp63 alone conferred a partial protection while entrapment of rgp63 in liposomes significantly increased the rate of protection (P<0.05). The parasite burden of spleen in mice challenged with L. major was significantly (p<0.001) lower in group of mice immunized with rgp63 alone or Lip-rgp63, however, the least parasite burden was seen in Lip-rgp63 group. Both rgp63 alone and Lip-rgp63 elicited significant delayed-type hypersensitivity (DTH) response compared to controls (p<0.01), however, the DTH response of PBS-rgp63 was less than the Lip-rgp63. Titration of anti-Leishmania IgG isotypes (IgG2a/IgG1) showed a preferential Th1 type of immune response only in mice immunized with Lip-rgp63. The results indicate that liposomes might be used as a suitable immunoadjuvant for development of Leishmania vaccine.

Saliva fromLutzomyia longipalpisInduces CC Chemokine Ligand 2/Monocyte Chemoattractant Protein-1 Expression and Macrophage Recruitment

Saliva of bloodfeeding arthropods has been incriminated in facilitating the establishment of parasite in their host. We report on the leukocyte chemoattractive effect of salivary gland homogenate (SGH) from Lutzomyia longipalpis on saliva-induced inflammation in an air pouch model. SGH (0.5 pair/animal) was inoculated in the air pouch formed in the back of BALB/c or C57BL/6 mice. L. longipalpis SGH induced a significant influx of macrophages in BALB/c but not in C57BL/6 mice. SGH-induced cell recruitment reached a peak at 12 h after inoculation and was higher than that induced by the LPS control. This differential cell recruitment in BALB/c mice was directly correlated to an increase in CCL2/MCP-1 expression in the air pouch lining tissue. In fact, treatment with bindarit, an inhibitor of CCL2/MCP-1 synthesis, and also with a specific anti-MCP-1 mAb resulted in drastic reduction of macrophage recruitment and inhibition of CCL2/MCP-1 expression in the lining tissue. CCL2/MCP-1 production was also seen in vitro when J774 murine macrophages were exposed to L. longipalpis SGH. The SGH effect was abrogated by preincubation with serum containing anti-SGH IgG Abs as well as in mice previously sensitized with L. longipalpis bites. Interestingly, the combination of SGH with Leishmania chagasi induced an increased recruitment of neutrophils and macrophages when compared with L. chagasi alone. Taken together these results suggest that SGH not only induces the recruitment of a greater number of macrophages by enhancing CCL2/MCP-1 production but also synergizes with L. chagasi to recruit more inflammatory cells to the site of inoculation.

Chemokines in host-parasite interactions in leishmaniasis

Crucial to the defense against leishmaniasis is the ability of the host to mount a cell-mediated immune response capable of controlling and/or eliminating the parasite. Cell recruitment to the site of infection is essential to the development of the host cellular immune response. The process is controlled by chemokines, which are chemotactic cytokines produced by leukocytes and tissue cells.

Toward a novel experimental model of infection to study American cutaneous leishmaniasis caused by Leishmania braziliensis

Leishmania spp. cause a broad spectrum of diseases collectively known as leishmaniasis. Leishmania braziliensis is the main etiological agent of American cutaneous leishmaniasis (ACL) and mucocutaneous leishmaniasis. In the present study, we have developed an experimental model of infection that closely resembles ACL caused by L. braziliensis. In order to do so, BALB/c mice were infected in the ear dermis with 10(5) parasites and distinct aspects of the infection were evaluated. Following inoculation, parasite expansion in the ear dermis was accompanied by the development of an ulcerated dermal lesion which healed spontaneously, as seen by the presence of a scar. Histological analysis of infected ears showed the presence of a mixed inflammatory infiltrate consisting of both mononuclear and polymorphonuclear cells. In draining lymph nodes, parasite replication was detected throughout the infection. In vitro restimulation of draining lymph node cells followed by intracellular staining showed an up-regulation in the production of gamma interferon (IFN-gamma) and in the frequency of IFN-gamma-secreting CD4(+) and CD8(+) T cells. Reverse transcription-PCR of ears and draining lymph node cells showed the expression of CC chemokines. The dermal model of infection with L. braziliensis herein is able to reproduce aspects of the natural infection, such as the presence of an ulcerated lesion, parasite dissemination to lymphoid areas, and the development of a Th1-type immune response. These results indicate that this model shall be useful to address questions related to the concomitant immunity to reinfection and parasite persistence leading to mucocutaneous leishmaniasis.

Effect of salivary gland extract of Leishmania vector, Lutzomyia longipalpis, on leukocyte migration in OVA-induced immune peritonitis

Salivary gland extracts (SGE) from Lutzomyia longipalpis potentate L. major infection by inducing a Th2 immune response. However, the effect of SGE on the effector phase of immune response is not known. Herein, we demonstrate that SGE inhibited neutrophil migration in ovalbumin (OVA)-induced peritonitis in immunized mice. SGE pretreatment of mice inhibited OVA-induced CD4+ and CD8+ T lymphocyte migration. The OVA-induced production of TNF-alpha, IL-1beta and leukotriene B4 (LTB4), neutrophil chemotactic mediators in this model, were inhibited by SGE. On the other hand, SGE enhanced production of IL-10 and IL-4. In naive mice, SGE also blocked LTB4-induced neutrophil migration, but not that induced fMLP. Moreover, co-incubation of LTB4 (but not fMLP, TNF-alpha and MIP-1alpha) with SGE inhibited the ability of LTB4 to induce neutrophil migration in vivo and in vitro. Altogether, the results suggest that SGE has anti-inflammatory properties that are associated with inhibition of TNF-alpha and LTB4 production and/or with the neutrophil chemotactic activity of LTB4. The effectiveness of SGE in inhibiting neutrophil migration and inflammatory mediators release in a Th1 immune inflammatory response model reinforces the need for isolation of the compounds responsible for these activities, which could be used as prototypes for the development new anti-inflammatory drugs.

Chromosomal localization of two antihemostatic salivary factors in Simulium vittatum (Diptera: Simuliidae)

The chromosomal locations of two genes encoding the salivary protein products Simulidin (SVAT) and Simulium vittatum erythyma protein (SVEP) were identified using high-resolution cytogenetic mapping. Chromosomal subsection levels were determined from larval and adult salivary gland polytene chromosomes and adult Malphigian tubule chromosomes. Syntenic relationships occurred for both loci from a wild population of Simulium vittatum IIIL-1 collected in central Alabama and the colonized IS-7 S. vittatum sibling. cSVAT mapped to the short arm of chromosomes III, IIIS-72a4.5 and cSVEP mapped to the long arm of chromosome III, IIIL-96b1. cSVAT sits proximal to a common IIIS-2 paracentric inversion, which occurs predominately as the standard sequence in the IIIL-1 sibling and as the inverted sequence in the IS-7 sibling. cSVEP sits close to the differentiated X chromosomes in the IIIL-1 sibling.

Immunization with Leishmania major exogenous antigens protects susceptible BALB/c mice against challenge infection with L. major

The potential of Leishmania major culture-derived soluble exogenous antigens (SEAgs) to induce a protective response in susceptible BALB/c mice challenged with L. major promastigotes was investigated. Groups of BALB/c mice were immunized with L. major SEAgs alone, L. major SEAgs coadministered with either alum (aluminum hydroxide gel) or recombinant murine interleukin-12 (rmIL-12), L. major SEAgs coadministered with both alum and rmIL-12, and L. major SEAgs coadministered with Montanide ISA 720. Importantly and surprisingly, the greatest and most consistent protection against challenge with L. major was seen in mice immunized with L. major SEAgs alone, in the absence of any adjuvant. Mice immunized with L. major SEAgs had significantly smaller lesions that at times contained more than 100-fold fewer parasites. When lymphoid cells from L. major SEAg-immunized mice were stimulated with leishmanial antigen in vitro, they proliferated and secreted a mixed profile of type 1 and type 2 cytokines. Finally, analyses with Western blot analyses and antibodies against three surface-expressed and secreted molecules of L. major (lipophosphoglycan, gp46/M2/PSA-2, and gp63) revealed that two of these molecules are present in L. major SEAgs, lipophosphoglycan and the molecules that associate with it and gp46/M2/PSA-2.

Requirements for Th1-dependent immunity against infection with Leishmania major

Protective immunity against cutaneous leishmaniasis is dependent on the induction of Th1/Tc1 immune responses resulting in efficient parasite elimination. In this review, the mechanisms leading to protection are discussed with special focus on the role of Leishmania major-infected dendritic cells (DC) in induction of Th1-dependent immunity. Murine strain-dependent differences between DC derived from Leishmania-susceptible as compared to resistant mice are highlighted.