Cutaneous leishmaniasis: progress towards a vaccine

Cutaneous leishmaniasis presenting with painless ulcer on the right forearm: A case report

BACKGROUND

Leishmaniasis includes a range of chronic infections in humans and animals and can be caused by more than 20 species of Leishmania protozoa. The manifestations of leishmaniasis are diverse and dependent on the immune response capacity of the host and the type of Leishmania. In East Asia, leishmaniasis is relatively rare and prone to misdiagnosis and underdiagnosis.

CASE SUMMARY

We report a case of a 36-year-old male with cutaneous leishmaniasis. The patient had been misdiagnosed with a bacterial skin infection and was given a dressing change and oral levofloxacin, which proved ineffective. Histopathological examination revealed amastigote (Leishman-Donovan body) in the histocytes, and nucleic acid sequencing proved that the pathogen was Leishmania major. The patient was treated successfully by regional injection of sodium gluconate (600 mg) three times. The ulcer healed and did not recur at 1.5-year follow-up.

CONCLUSION

Skin ulcers caused by leishmaniasis are easily misdiagnosed in non-epidemic countries, yet it should not be overlooked.

In Vitro Modulator Effect of Total Extract from the Endophytic Paenibacillus polymyxa RNC-D in Leishmania (Leishmania) amazonensis and Macrophages

Leishmaniases are diseases with high epidemiological relevance and wide geographical distribution. In Brazil, Leishmania (Leishmania) amazonensis is related to the tegumentary form of leishmaniasis. The treatment for those diseases is problematic as the available drugs promote adverse effects in patients. Therefore, it is important to find new therapeutic targets. In this regard, one alternative is the study of biomolecules produced by endophytic microorganisms. In this study, the total extract produced by the endophytic Paenibacillus polymyxa RNC-D was used to evaluate the leishmanicidal, nitric oxide, and cytokines production using RAW 264.7 macrophages. The results showed that, in the leishmanicidal assay with L. amazonensis, EC50 values at the periods of 24 and 48 hours were 0.624 mg/mL and 0.547 mg/mL, respectively. Furthermore, the cells treated with the extract presented approximately 25% of infected cells with an average of 3 amastigotes/cell in the periods of 24 and 48 hours. Regarding the production of cytokines in RAW 264.7 macrophages infected/treated with the extract, a significant increase in TNF-α was observed at the periods of 24 and 48 hours in the treated cells. The concentrations of IFN-γ and IL-12 showed significant increase in 48 hours. A significant decrease in IL-4 was observed in all cells treated with the extract in 24 hours. It was observed in the treated cells that the NO production by RAW 264.7 macrophages increased between 48 and 72 hours. The endophytic Paenibacillus polymyxa RNC-D extract modulates the mediators of inflammation produced by RAW 264.7 macrophages promoting L. amazonensis death. The immunomodulatory effects might be a promising target to develop new immunotherapeutic and antileishmanial drugs.

Apoptotic blebs from Leishmania major-infected macrophages as a new approach for cutaneous leishmaniasis vaccination

We focused on apoptotic blebs from Leishmania major-infected macrophages as a vaccine for cutaneous leishmaniasis. Apoptosis was induced in L. major-infected J774A.1 cells in order to prepare apoptotic blebs. Test groups of BALB/c mice were immunized with these at doses of 1 × 10⁶, 5 × 10⁶ or 1 × 10⁷ blebs. An immunization control group received Leishmania lysate antigens. The results showed that as the number of apoptotic bodies increased, the lymphocyte proliferation index increased, and this was proportional to IFN-γ level in the test groups. Additionally, the difference of IFN-γ, IL-4, IFN-γ/IL-4 ratio, or total IgG (p < 0.0001) in all groups was statistically significant compared to the negative control group. The highest IFN-γ (514.0 ± 40.92 pg/mL) and IFN-γ/IL-4 ratio (2.94 ± 0.22) were observed in the group that received 1 × 10⁷ apoptotic blebs. The highest levels of IL-4 (244.6 ± 38.8 pg/mL) and total IgG (5626 ± 377 μg/mL) were observed in the immunization control group. Reflecting these data, no lesions were observed in any of the groups vaccinated with apoptotic blebs after 12 weeks. In summary, the use of apoptotic blebs from L. major-infected macrophages is protective against the challenge with L. major in this animal model.

Identification of HLA-I restricted epitopes in six vaccine candidates of Leishmania tropica using immunoinformatics and molecular dynamics simulation approaches

In spite of numerous studies on vaccination for various species of Leishmania, research on the development of an effective vaccine for L. tropica is very scarce. In silico epitope prediction is a new way to survey the best vaccine candidates. Here, we predicted the best epitopes of six L. tropica antigens with vaccine capability against this pathogen, using highly frequent HLA-I alleles. Based on the frequent HLA alleles, the protein sequences were screened individually using four different MHC prediction applications, namely SYFPEITHI, ProPredI, BIMAS, and IEDB. Several in silico assays including clustering, human similarity exclusion, epitope conservancy prediction, investigating in experimental records, immunogenicity prediction, and prediction of population coverage were performed to narrow the results and to find the best epitopes. The selected epitopes and their restricted HLA-I alleles were docked and the final epitopes with the lowest binding energy (the highest binding affinity) were chosen. Finally, the stability and the binding properties of the best epitope-HLA-I combinations were analyzed using molecular dynamics simulation studies. We found ten potential peptides with strong binding affinity to highly frequent HLA-I alleles that can be further evaluated as vaccine targets against L. tropica.

Biopharmaceutical Assessment and Irritation Potential of Microemulsions and Conventional Systems Containing Oil from Syagrus cearensis for Topical Delivery of Amphotericin B Using Alternative Methods

The aim of this study was to compare the biopharmaceutical characteristics and irritation potentials of microemulsions (MEs) and conventional systems (CSs) containing oil from Syagrus cearensis for topical delivery of Amphotericin B (AmB). Pseudo-ternary phase diagrams were constructed using a water titration method to develop the MEs, and the CSs were prepared according to the classical technique of phase inversion. In the skin permeation and retention study, dermatomed pig skin without stratum corneum was used as an alternative disturbed skin model. The irritation potential was evaluated using three different methods, chorioallantoic membrane assays (HET-CAM and CAM-TBS), and bovine corneal opacity and permeability (BCOP) test. The optimized formulation (ME1) consisting of 0.1% (w/w) Amphotericin B, 9.1% (w/w) catolé oil, 81% (w/w) Smix (1:1, Tween 20 and Kolliphor EL) possessed droplet size of 31.02 ± 0.9 nm, zeta potential of -23.4 mV, and viscosity 0.63 ± 0.1 Pa.s. ME1 exhibited greater retention of AmB in to skin layers (84.79 ± 2.08 μg cm^-2) than all the others formulations. In general, MEs showed higher drug release and retention than CSs and all of the formulations showed greater retentivity than permeability. Only MEs developed using Labrasol/Plurol Oleique (L/PO) as the surfactant and co-surfactant exhibited a moderate irritation potential; all other MEs and CSs were classified as non-irritants or slight irritants. The results indicate that formulations containing oil from S. cearensis are promising alternatives for the delivery of AmB targeting the treatment of cutaneous leishmaniasis.

Immune and biochemical responses in skin differ between bovine hosts genetically susceptible and resistant to the cattle tick Rhipicephalus microplus

Background

Ticks attach to and penetrate their hosts’ skin and inactivate multiple components of host responses in order to acquire a blood meal. Infestation loads with the cattle tick, Rhipicephalus microplus, are heritable: some breeds carry high loads of reproductively successful ticks, whereas in others, few ticks feed and reproduce efficiently.

Methods

In order to elucidate the mechanisms that result in the different outcomes of infestations with cattle ticks, we examined global gene expression and inflammation induced by tick bites in skins from one resistant and one susceptible breed of cattle that underwent primary infestations with larvae and nymphs of R. microplus. We also examined the expression profiles of genes encoding secreted tick proteins that mediate parasitism in larvae and nymphs feeding on these breeds.

Results

Functional analyses of differentially expressed genes in the skin suggest that allergic contact-like dermatitis develops with ensuing production of IL-6, CXCL-8 and CCL-2 and is sustained by HMGB1, ISG15 and PKR, leading to expression of pro-inflammatory chemokines and cytokines that recruit granulocytes and T lymphocytes. Importantly, this response is delayed in susceptible hosts. Histopathological analyses of infested skins showed inflammatory reactions surrounding tick cement cones that enable attachment in both breeds, but in genetically tick-resistant bovines they destabilized the cone. The transcription data provided insights into tick-mediated activation of basophils, which have previously been shown to be a key to host resistance in model systems. Skin from tick-susceptible bovines expressed more transcripts encoding enzymes that detoxify tissues. Interestingly, these enzymes also produce volatile odoriferous compounds and, accordingly, skin rubbings from tick-susceptible bovines attracted significantly more tick larvae than rubbings from resistant hosts. Moreover, transcripts encoding secreted modulatory molecules by the tick were significantly more abundant in larval and in nymphal salivary glands from ticks feeding on susceptible bovines.

Conclusions

Compared with tick-susceptible hosts, genes encoding enzymes producing volatile compounds exhibit significantly lower expression in resistant hosts, which may render them less attractive to larvae; resistant hosts expose ticks to an earlier inflammatory response, which in ticks is associated with significantly lower expression of genes encoding salivary proteins that suppress host immunity, inflammation and coagulation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1945-z) contains supplementary material, which is available to authorized users.

An 8-hydroxyquinoline-containing polymeric micelle system is effective for the treatment of murine tegumentary leishmaniasis

The current treatment of leishmaniasis has been hampered due to the high toxicity of the available drugs and long duration protocols, which often lead to its abandonment. In the present study, a poloxamer 407-based delivery system was developed, and a molecule, 8-hydroxyquinoline (8-HQN), was incorporated with it, leading to an 8-HQN/micelle (8-HQN/M) composition. Assays were performed to evaluate the in vitro antileishmanial activity of 8-HQN/M against Leishmania amazonensis stationary promastigotes. The cytotoxicity in murine macrophages and in human red cells, as well as the efficacy of the treatment in macrophages infected by parasites, was also assessed. This product was also evaluated for the treatment of murine tegumentary leishmaniasis, using L. amazonensis-infected BALB/c mice. To evaluate the in vivo efficacy of the treatment, the average lesion diameter (area) in the infected tissue, as well as the parasite load at the site of infection (skin), spleen, liver and draining lymph nodes were examined. Non-incorporated micelle (B-8-HQN/M) and the free molecule (8-HQN) were used as controls, besides animals that received only saline. The parasite burden was evaluated by limiting dilution and quantitative real-time PCR (qPCR) techniques, and immunological parameters associated with the treatments were also investigated. In the results, the 8-HQN/M group, when compared to the others, presented more significant reductions in the average lesion diameter and in the parasite burden in the skin and all evaluated organs. These animals also showed significantly higher levels of parasite-specific IFN-γ, IL-12, and GM-CSF, associated with low levels of IL-4 and IL-10, when compared to the saline, 8-HQN/M, and B-8-HQN groups. A predominant IL-12-driven IFN-γ production, against parasite proteins, mainly produced by CD4⁺ T cells, was observed in the treated animals, post-infection. In conclusion, 8-HQN/M was highly effective in treating L. amazonensis-infected BALB/c mice and can be considered alone, or combined with other drugs, as an alternative treatment for tegumentary leishmaniasis. Graphical Abstract Therapeutic scheme and immunological and parasitological parameters developed in the present study.

Enhanced protective efficacy of nonpathogenic recombinant leishmania tarentolae expressing cysteine proteinases combined with a sand fly salivary antigen

BACKGROUND

Novel vaccination approaches are needed to prevent leishmaniasis. Live attenuated vaccines are the gold standard for protection against intracellular pathogens such as Leishmania and there have been new developments in this field. The nonpathogenic to humans lizard protozoan parasite, Leishmania (L) tarentolae, has been used effectively as a vaccine platform against visceral leishmaniasis in experimental animal models. Correspondingly, pre-exposure to sand fly saliva or immunization with a salivary protein has been shown to protect mice against cutaneous leishmaniasis.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we tested the efficacy of a novel combination of established protective parasite antigens expressed by L. tarentolae together with a sand fly salivary antigen as a vaccine strategy against L. major infection. The immunogenicity and protective efficacy of different DNA/Live and Live/Live prime-boost vaccination modalities with live recombinant L. tarentolae stably expressing cysteine proteinases (type I and II, CPA/CPB) and PpSP15, an immunogenic salivary protein from Phlebotomus papatasi, a natural vector of L. major, were tested both in susceptible BALB/c and resistant C57BL/6 mice. Both humoral and cellular immune responses were assessed before challenge and at 3 and 10 weeks after Leishmania infection. In both strains of mice, the strongest protective effect was observed when priming with PpSP15 DNA and boosting with PpSP15 DNA and live recombinant L. tarentolae stably expressing cysteine proteinase genes.

CONCLUSION/SIGNIFICANCE

The present study is the first to use a combination of recombinant L. tarentolae with a sand fly salivary antigen (PpSP15) and represents a novel promising vaccination approach against leishmaniasis.

Plasma membranes as heat stress sensors: from lipid-controlled molecular switches to therapeutic applications

The classic heat shock (stress) response (HSR) was originally attributed to protein denaturation. However, heat shock protein (Hsp) induction occurs in many circumstances where no protein denaturation is observed. Recently considerable evidence has been accumulated to the favor of the "Membrane Sensor Hypothesis" which predicts that the level of Hsps can be changed as a result of alterations to the plasma membrane. This is especially pertinent to mild heat shock, such as occurs in fever. In this condition the sensitivity of many transient receptor potential (TRP) channels is particularly notable. Small temperature stresses can modulate TRP gating significantly and this is influenced by lipids. In addition, stress hormones often modify plasma membrane structure and function and thus initiate a cascade of events, which may affect HSR. The major transactivator heat shock factor-1 integrates the signals originating from the plasma membrane and orchestrates the expression of individual heat shock genes. We describe how these observations can be tested at the molecular level, for example, with the use of membrane perturbers and through computational calculations. An important fact which now starts to be addressed is that membranes are not homogeneous nor do all cells react identically. Lipidomics and cell profiling are beginning to address the above two points. Finally, we observe that a deregulated HSR is found in a large number of important diseases where more detailed knowledge of the molecular mechanisms involved may offer timely opportunities for clinical interventions and new, innovative drug treatments. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

Targeting Leishmania major Antigens to Dendritic Cells In Vivo Induces Protective Immunity

Efficient vaccination against the parasite Leishmania major, the causative agent of human cutaneous leishmaniasis, requires development of type 1 T-helper (Th1) CD4⁺ T cell immunity. Because of their unique capacity to initiate and modulate immune responses, dendritic cells (DCs) are attractive targets for development of novel vaccines. In this study, for the first time, we investigated the capacity of a DC-targeted vaccine to induce protective responses against L. major. To this end, we genetically engineered the N-terminal portion of the stress-inducible 1 protein of L. major (LmSTI1a) into anti-DEC205/CD205 (DEC) monoclonal antibody (mAb) and thereby delivered the conjugated protein to DEC⁺ DCs in situ in the intact animal. Delivery of LmSTI1a to adjuvant-matured DCs increased the frequency of antigen-specific CD4⁺ T cells producing IFN-γ⁺, IL-2⁺, and TNF-α⁺ in two different strains of mice (C57BL/6 and Balb/c), while such responses were not observed with the same doses of a control Ig-LmSTI1a mAb without receptor affinity or with non-targeted LmSTI1a protein. Using a peptide library for LmSTI1a, we identified at least two distinct CD4⁺ T cell mimetopes in each MHC class II haplotype, consistent with the induction of broad immunity. When we compared T cell immune responses generated after targeting DCs with LmSTI1a or other L. major antigens, including LACK (Leishmania receptor for activated C kinase) and LeIF (Leishmania eukaryotic ribosomal elongation and initiation factor 4a), we found that LmSTI1a was superior for generation of IFN-γ-producing CD4⁺ T cells, which correlated with higher protection of susceptible Balb/c mice to a challenge with L. major. For the first time, this study demonstrates the potential of a DC-targeted vaccine as a novel approach for cutaneous leishmaniasis, an increasing public health concern that has no currently available effective treatment.

Vaccination with L. infantum chagasi nucleosomal histones confers protection against new world cutaneous leishmaniasis caused by Leishmania braziliensis

Background

Nucleosomal histones are intracellular proteins that are highly conserved among Leishmania species. After parasite destruction or spontaneous lysis, exposure to these proteins elicits a strong host immune response. In the present study, we analyzed the protective capability of Leishmania infantum chagasi nucleosomal histones against L. braziliensis infection using different immunization strategies.

Methodology/Principal Findings

BALB/c mice were immunized with either a plasmid DNA cocktail (DNA) containing four Leishmania nucleosomal histones or with the DNA cocktail followed by the corresponding recombinant proteins plus CpG (DNA/Protein). Mice were later challenged with L. braziliensis, in the presence of sand fly saliva. Lesion development, parasite load and the cellular immune response were analyzed five weeks after challenge. Immunization with either DNA alone or with DNA/Protein was able to inhibit lesion development. This finding was highlighted by the absence of infected macrophages in tissue sections. Further, parasite load at the infection site and in the draining lymph nodes was also significantly lower in vaccinated animals. This outcome was associated with increased expression of IFN-γ and down regulation of IL-4 at the infection site.

Conclusion

The data presented here demonstrate the potential use of L. infantum chagasi nucleosomal histones as targets for the development of vaccines against infection with L. braziliensis, as shown by the significant inhibition of disease development following a live challenge.

The biology and control of leishmaniasis vectors

Vector control remains a key component of many anti-leishmaniasis programs and probably will remain so until an effective vaccine becomes available. Technologies similar to those used for control of adult mosquitoes, specifically interior residual sprays and insecticide-treated nets, are currently at the forefront as disease control measures. This article provides a review of literature on the biology and control of sand fly vectors of leishmaniasis in the context of changing disease risks and the realities of modern vector control. The Literature Retrieval System of the Armed Forces Pest Management Board, Washington, DC, was the primary search engine used to review the literature.

TLR1/2 activation during heterologous prime-boost vaccination (DNA-MVA) enhances CD8+ T Cell responses providing protection against Leishmania (Viannia)

BACKGROUND

Leishmania (Viannia) parasites present particular challenges, as human and murine immune responses to infection are distinct from other Leishmania species, indicating a unique interaction with the host. Further, vaccination studies utilizing small animal models indicate that modalities and antigens that prevent infection by other Leishmania species are generally not protective.

METHODOLOGY

Using a newly developed mouse model of chronic L. (Viannia) panamensis infection and the heterologous DNA prime - modified vaccinia virus Ankara (MVA) boost vaccination modality, we examined whether the conserved vaccine candidate antigen tryparedoxin peroxidase (TRYP) could provide protection against infection/disease.

RESULTS

Heterologous prime - boost (DNA/MVA) vaccination utilizing TRYP antigen can provide protection against disease caused by L. (V.) panamensis. However, protection is dependent on modulating the innate immune response using the TLR1/2 agonist Pam3CSK4 during DNA priming. Prime-boost vaccination using DNA alone fails to protect. Prior to infection protectively vaccinated mice exhibit augmented CD4 and CD8 IFNγ and memory responses as well as decreased IL-10 and IL-13 responses. IL-13 and IL-10 have been shown to be independently critical for disease in this model. CD8 T cells have an essential role in mediating host defense, as CD8 depletion reversed protection in the vaccinated mice; vaccinated mice depleted of CD4 T cells remained protected. Hence, vaccine-induced protection is dependent upon TLR1/2 activation instructing the generation of antigen specific CD8 cells and restricting IL-13 and IL-10 responses.

CONCLUSIONS

Given the general effectiveness of prime-boost vaccination, the recalcitrance of Leishmania (Viannia) to vaccine approaches effective against other species of Leishmania is again evident. However, prime-boost vaccination modality can with modulation induce protective responses, indicating that the delivery system is critical. Moreover, these results suggest that CD8 T cells should be targeted for the development of a vaccine against infection caused by Leishmania (Viannia) parasites. Further, TLR1/2 modulation may be useful in vaccines where CD8 T cell responses are critical.

Neglected tropical diseases: moving beyond mass drug treatment to understanding the science

Neglected tropical diseases (NTDs) represent a major health burden in many developing countries. To date, global efforts to control thirteen parasitic and bacterial infections that affect more than 1.4 billion people have relied on mass drug administration. This singular approach should now be expanded to a more comprehensive suite of tools including coordinated community-based programs, vector control, local training, education, and environmental change. In addition, an intensive basic research agenda is urgently needed to develop effective diagnostic, preventive, and therapeutic interventions to stay one step ahead of the evolutionary adaptation tactics of disease-causing microbes and parasites.

Changes in membrane fluid state and heat shock response cause attenuation of virulence

So far attenuation of pathogens has been mainly obtained by chemical or heat treatment of microbial pathogens. Recently, live attenuated strains have been produced by genetic modification. We have previously demonstrated that in several prokaryotes as well as in yeasts and mammalian cells the heat shock response is controlled by the membrane physical state (MPS). We have also shown that in Salmonella enterica serovar Typhimurium LT2 (Salmonella Typhimurium) overexpression of a Delta(12)-desaturase gene alters the MPS, inducing a sharp impairment of transcription of major heat shock genes and failure of the pathogen to grow inside macrophage (MPhi) (A. Porta et al., J. Bacteriol. 192:1988-1998, 2010). Here, we show that overexpression of a homologous Delta(9)-desaturase sequence in the highly virulent G217B strain of the human fungal pathogen Histoplasma capsulatum causes loss of its ability to survive and persist within murine MPhi along with the impairment of the heat shock response. When the attenuated strain of H. capsulatum was injected in a mouse model of infection, it did not cause disease. Further, treated mice were protected when challenged with the virulent fungal parental strain. Attenuation of virulence in MPhi of two evolutionarily distant pathogens was obtained by genetic modification of the MPS, suggesting that this is a new method that may be used to produce attenuation or loss of virulence in both other intracellular prokaryotic and eukaryotic pathogens. This new procedure to generate attenuated forms of pathogens may be used eventually to produce a novel class of vaccines based on the genetic manipulation of a pathogen's membrane fluid state and stress response.

Vector transmission of leishmania abrogates vaccine-induced protective immunity

Numerous experimental vaccines have been developed to protect against the cutaneous and visceral forms of leishmaniasis caused by infection with the obligate intracellular protozoan Leishmania, but a human vaccine still does not exist. Remarkably, the efficacy of anti-Leishmania vaccines has never been fully evaluated under experimental conditions following natural vector transmission by infected sand fly bite. The only immunization strategy known to protect humans against natural exposure is “leishmanization,” in which viable L. major parasites are intentionally inoculated into a selected site in the skin. We employed mice with healed L. major infections to mimic leishmanization, and found tissue-seeking, cytokine-producing CD4+ T cells specific for Leishmania at the site of challenge by infected sand fly bite within 24 hours, and these mice were highly resistant to sand fly transmitted infection. In contrast, mice vaccinated with a killed vaccine comprised of autoclaved L. major antigen (ALM)+CpG oligodeoxynucleotides that protected against needle inoculation of parasites, showed delayed expression of protective immunity and failed to protect against infected sand fly challenge. Two-photon intra-vital microscopy and flow cytometric analysis revealed that sand fly, but not needle challenge, resulted in the maintenance of a localized neutrophilic response at the inoculation site, and removal of neutrophils following vector transmission led to increased parasite-specific immune responses and promoted the efficacy of the killed vaccine. These observations identify the critical immunological factors influencing vaccine efficacy following natural transmission of Leishmania.

The generation of vaccines that protect against intracellular pathogens such as malaria, human immunodeficiency virus and leishmaniasis have met with limited success. A perplexing aspect of this failure as it relates to leishmaniasis is the knowledge that individuals typically get the disease only once, and that individuals who are experimentally infected with cultured parasites are protected against sand fly transmitted infection, thereby providing a “gold standard” for vaccine design. Many engineered, non-living vaccines have been developed to mimic the immune response observed in protected individuals and some of these have been shown to provide excellent protection against needle inoculation of Leishmania parasites in mice. However, very similar vaccine formulations adapted for use in people have failed to protect against natural exposure to infected sand fly bites. In the present study, we attempt to reconcile these long-standing differences, and to provide the critical correlates of immunity that will predict vaccination success against natural exposure.