A2 and other visceralizing proteins of Leishmania: role in pathogenesis and application for vaccine development

Characterization of a novel Leishmania antigen containing a repetitive domain and its potential use as a prophylactic and therapeutic vaccine

Human visceral leishmaniasis (HVL) is the second most lethal tropical parasitic disease. Currently, no prophylactic or therapeutic vaccines exist for HVL. Thus, the development of an efficacious vaccine is still needed. We previously performed an immunoproteomics analysis on Leishmania amazonensis parasite extracts to identify immunodominant antigens recognized by the sera of vaccinated and protected mice. Among the identified antigens, we discovered a novel, previously unstudied repetitive protein, initially annotated in Leishmania genomes as a kinetoplast-associated protein-like protein from Leishmania infantum (LinKAP), containing conserved domains (trichohyalin-plectin-homology [TPH] and TolA) that are associated with other mitochondrial proteins. LinKAP sequences are conserved across trypanosomatids, including Endotrypanum, Leishmania, and Trypanosoma species. Using differential centrifugation of Leishmania subcellular structures, we showed that LinKAP was enriched in fractions colocalizing with other mitochondrial proteins. mNeonGreen labeling at the endogenous locus using CRISPR-Cas9 and confocal microscopy confirmed that LinKAP is a mitochondrial-associated protein in Leishmania but not specifically colocalized with kDNA. We cloned and expressed a truncated version of LinKAP (rLinKAP), containing part (15) of the several LinKAP amino acid repeats, demonstrating over 85% homology across L. infantum, L. amazonensis, L. braziliensis, and L. mexicana species. An adjuvanted formulation of LinKAP with Poly ICLC, a polyinosinic-polycytidylic acid (Poly I:C) stabilized with carboxymethylcellulose and polylysine, was used to vaccinate mice and hamsters as a prophylactic vaccine for visceral leishmaniasis. Animals immunized with rLinKAP showed a potent cellular and humoral response and a significant decrease in tissue parasitism when challenged with L. infantum. We also tested rLinKAP as a therapeutic vaccine in mice. Following therapeutic vaccination, antibody responses were enhanced, and cellular responses became apparent. Our treatment protocol inhibited splenic parasite burden by 75% in treated mice. In conclusion, our antigen discovery strategy and the observed protective effect highlight rLinKAP as a promising vaccine candidate for leishmaniasis.

IMPORTANCE

A previous reverse vaccinology study identified kinetoplast-associated protein-like protein from Leishmania infantum (LinKAP) as a potential new vaccine target, as this protein was recognized by the sera of protected mice in extracts of Leishmania promastigotes. Interestingly, LinKAP is a repetitive protein containing trichohyalin-plectin-homology (TPH) and TolA domains and was initially annotated as a kinetoplast-associated protein. We further characterized LinKAP as a mitochondrial-associated protein highly conserved among trypanosomatids. We also validated LinKAP as a promising vaccine antigen by using a truncated version of LinKAP (rLinKAP) as both a prophylactic and therapeutic vaccine, adjuvanted with Poly ICLC, to immunize animals against visceral leishmaniasis (VL). This disease, caused by the Leishmania parasite, affects several populations globally and still lacks highly effective vaccines. Identifying LinKAP and its preliminary characterization also provides new perspectives for studying its role in the parasite's biology.

Leishmania (Sauroleishmania) tarentolae versus pathogenic species: comparative evaluation of protease activity, glycoconjugates, resistance to complement and metabolome composition

BACKGROUND

Leishmania tarentolae is a non-pathogenic species found in lizards representing an important model for Leishmania biology. However, several aspects of this Sauroleishmania remain unknown to explain its low level of virulence.

OBJECTIVES

We reported several aspects of L. tarentolae biology including glycoconjugates, proteolytic activities and metabolome composition in comparison to pathogenic species (Leishmania amazonensis, Leishmania braziliensis, Leishmania infantum and Leishmania major).

METHODS

Parasites were cultured for extraction and purification of lipophosphoglycan (LPG), immunofluorescence probing with anti-gp63 and resistance against complement. Parasite extracts were also tested for proteases activity and metabolome composition.

FINDINGS

Leishmania tarentolae does not express LPG on its surface. It expresses gp63 at lower levels compared to pathogenic species and, is highly sensitive to complement-mediated lysis. This species also lacks intracellular/extracellular activities of proteolytic enzymes. It has metabolic differences with pathogenic species, exhibiting a lower abundance of metabolites including ABC transporters, biosynthesis of unsaturated fatty acids and steroids, TCA cycle, glycine/serine/threonine metabolism, glyoxylate/dicarboxylate metabolism and pentose-phosphate pathways.

MAIN CONCLUSIONS

The non-pathogenic phenotype of L. tarentolae is associated with alterations in several biochemical and molecular features. This reinforces the need of comparative studies between pathogenic and non-pathogenic species to elucidate the molecular mechanisms of virulence during host-parasite interactions.

A non-replicative antibiotic resistance-free DNA vaccine delivered by the intranasal route protects against canine leishmaniasis

Leishmania infantum is the etiological agent of zoonotic visceral leishmaniasis (ZVL). The disease is endemic in Central and South America, Central and South East Asia, and the Mediterranean basin. Dogs are the main reservoir, with an estimated prevalence of approximately 2.5 million dogs in Southern Europe. Current treatments cause side effects, disease recurrence, and drug resistance. Therefore, the development of vaccines against canine leishmaniasis is necessary. We have generated a DNA vaccine based on the non-replicative antibiotic resistance marker-free plasmid vector pPAL that contains the encoding gene for the L. infantum activated protein kinase C receptor analog (LACK). Homologous pPAL-LACK prime-boost intranasal administration confers efficacious protection in Beagle dogs with a reduction of clinical signs and a statistically significant reduction of the parasite burden in the bone marrow of more than 90% of dogs after experimental infection with highly infective promastigotes. This DNA vaccine elicits a robust cellular immune response skewed towards the Th1 profile.

Identification of Immunodominant Proteins of the Leishmania (Viannia) naiffi SubProteome as Pan-Specific Vaccine Targets against Leishmaniasis

Leishmaniasis is a wide-spectrum disease caused by parasites from Leishmania genus. A well-modulated immune response that is established after the long-lasting clinical cure of leishmaniasis can represent a standard requirement for a vaccine. Previous studies demonstrated that Leishmania (Viannia) naiffi causes benign disease and its antigens induce well-modulated immune responses in vitro. In this work we aimed to identify the immunodominant proteins present in the soluble extract of L. naiffi (sLnAg) as candidates for composing a pan-specific anti-leishmaniasis vaccine. After immunoblotting using cured patients of cutaneous leishmaniasis sera and proteomics approaches, we identified a group of antigenic proteins from the sLnAg. In silico analyses allowed us to select mildly similar proteins to the host; in addition, we evaluated the binding potential and degree of promiscuity of the protein epitopes to HLA molecules and to B-cell receptors. We selected 24 immunodominant proteins from a sub-proteome with 328 proteins. Homology analysis allowed the identification of 13 proteins with the most orthologues among seven Leishmania species. This work demonstrated the potential of these proteins as promising vaccine targets capable of inducing humoral and cellular pan-specific immune responses in humans, which may in the future contribute to the control of leishmaniasis.

The Pathogenicity and Virulence of Leishmania - interplay of virulence factors with host defenses

Leishmaniasis is a group of disease caused by the intracellular protozoan parasite of the genus Leishmania. Infection by different species of Leishmania results in various host immune responses, which usually lead to parasite clearance and may also contribute to pathogenesis and, hence, increasing the complexity of the disease. Interestingly, the parasite tends to reside within the unfriendly environment of the macrophages and has evolved various survival strategies to evade or modulate host immune defense. This can be attributed to the array of virulence factors of the vicious parasite, which target important host functioning and machineries. This review encompasses a holistic overview of leishmanial virulence factors, their role in assisting parasite-mediated evasion of host defense weaponries, and modulating epigenetic landscapes of host immune regulatory genes. Furthermore, the review also discusses the diagnostic potential of various leishmanial virulence factors and the advent of immunomodulators as futuristic antileishmanial drug therapy.

Phenotypical and genotypical differences among Leishmania (Leishmania) amazonensis isolates that caused different clinical frames in humans and dogs: A systematic review

Leishmania (Leishmania) amazonensis is an important etiological agent of American cutaneous leishmaniasis (ACL) in Brazil. The species causes a large spectrum of clinical manifestations in humans and dogs, ranging from cutaneous, cutaneous diffuse, mucocutaneous, and visceral involvement, however, the factors that drive the development of different disease forms by the same species are not yet fully known. In the present work, it was systematically reviewed the studies addressing phenotypic and genotypic characteristics of Leishmania (L.) amazonensis isolates causing cutaneous and visceral clinical frames in humans and dogs, comparing the results observed. For this, four research databases were searched for the following keywords: (Leishmania amazonensis AND visceral leishmaniasis) AND (tropism OR virulence OR visceralization OR adaptations OR mutation OR clinical presentation OR resistance OR survival OR wide spectrum). The results revealed that the complexity disease seems to involve the combination of genetic factors of the parasite (as modifications in molecules related to the virulence and metabolism) and also of the host's immune background and status. Nonetheless, the exact mechanism that leads to different clinical manifestations between strains of the same species is still uncertain and future studies must be developed to better elucidate this phenomenon.

Comparative analysis of the transcriptional responses of five Leishmania species to trivalent antimony

BACKGROUND

Leishmaniasis is a neglected tropical disease caused by several species of Leishmania. The resistance phenotype of these parasites depends on the characteristics of each species, which contributes to increased therapeutic failures. Understanding the mechanism used by the parasite to survive under treatment pressure in order to identify potential common and specific therapeutic targets is essential for the control of leishmaniasis. The aim of this study was to investigate the expression profiles and potential shared and specific resistance markers of the main Leishmania species of medical importance [subgenus L. (Leishmania): L. donovani, L. infantum and L. amazonensis; subgenus L. (Viannia): L. panamensis and L. braziliensis)] resistant and sensitive to trivalent stibogluconate (SbIII).

METHODS

We conducted comparative analysis of the transcriptomic profiles (only coding sequences) of lines with experimentally induced resistance to SbIII from biological replicates of five Leishmania species available in the databases of four articles based on ortholog attribution. Simultaneously, we carried out functional analysis of ontology and reconstruction of metabolic pathways of the resulting differentially expressed genes (DEGs).

RESULTS

Resistant lines for each species had differential responses in metabolic processes, compound binding, and membrane components concerning their sensitive counterpart. One hundred and thirty-nine metabolic pathways were found, with the three main pathways comprising cysteine and methionine metabolism, glycolysis, and the ribosome. Differentially expressed orthologous genes assigned to species-specific responses predominated, with 899 self-genes. No differentially expressed genes were found in common among the five species. Two common upregulated orthologous genes were found among four species (L. donovani, L. braziliensis, L. amazonensis, and L. panamensis) related to an RNA-binding protein and the NAD(P)H cytochrome-B5-oxidoreductase complex, associated with transcriptional control and de novo synthesis of linoleic acid, critical mechanisms in resistance to antimonials.

CONCLUSION

Herein, we identified potential species-specific genes related to resistance to SbIII. Therefore, we suggest that future studies consider a treatment scheme that is species-specific. Despite the limitations of our study, this is the first approach toward unraveling the pan-genus genetic mechanisms of resistance in leishmaniasis.

Development of dominant epitope-based vaccines encoding Gp63, Kmp-11 and Amastin against visceral leishmaniasis

The most dangerous form of leishmaniasis is Visceral leishmaniasis (VL). The elimination of VL depends not only on agent treatments but also on effective vaccines against Leishmania parasites. Epitope-based vaccines composed of alternative short antigenic epitopes have the advantages of MHC epitope easy designing, which has broad application prospects. In a previous study, we analyzed Leishmania Gp63, Kmp-11 and Amastin protein sequence in silico, and found that the amino acid fragments of Gp63 (138-360aa), Kmp-11 (1-91aa) and Amastin (1-72aa) were rich in dominant epitopes. In this study, we used the three amino acid fragments as multi-epitope vaccine candidates to construct DNA and protein vaccines. BALB/c mice were vaccinated with the DNA and protein vaccines by DNA prime-protein boost strategy and challenged with Leishmania promastigotes. To evaluate vaccine immunogenicity and immunoprotection, serum specific antibody titers and cytokines were detected using ELISA, splenic CD3⁺, CD4⁺ and CD8⁺ cells were analyzed by flow cytometry, livers were made into pathological sections to observe pathological changes, and splenic parasitic loads were quantified using qPCR. The results showed that the increased specific IgG titers from vaccinated mice supported the vaccine immunogenicity. The increased cytokines (IFN-γ, IL-12 and TNF-α), splenic CD3⁺, CD4⁺ and CD8⁺ T cells and hepatic granulomas, and the decreased splenic parasitic loads (parasite reduction rates of Gp63, Kmp-11 and Amatin groups were 89%, 86% and 79%, respectively) from immunized mice post-infection were suggested the good immunoprotection of the vaccines. Our study demonstrated that vaccines based on the dominant epitopes of Gp63, Kmp-11 and Amastin with DNA prime-protein boost vaccination strategy showed significant immune effects against Leishmania, especially the Gp63 group showed a nearly 90% parasites reduction rate. This study will provide references for visceral leishmaniasis epitope vaccine design and immune strategy selection.

A Leishmania amastigote-specific hypothetical protein evaluated as recombinant protein plus Th1 adjuvant or DNA plasmid-based vaccine to protect against visceral leishmaniasis

Most studies evaluating vaccine candidates against visceral leishmaniasis (VL) have used parasite promastigote-expressed antigens; however, Leishmania proteins expressed in the amastigote forms should be considered, since few hours after infection this stage comes into contact with the host immune system and is responsible for the development of the disease. In this context, in the present study, a Leishmania amastigote-specific hypothetical protein, called LiHyJ, was evaluated as a recombinant protein plus saponin as an adjuvant or DNA vaccine to protect against VL. The vaccine effect was evaluated by means of the evaluation of immunological and parasitological analyses performed in BALB/c mice against Leishmania infantum infection. Results showed that rLiHyJ/saponin and DNA LiHyJ induced significantly higher levels of anti-protein and anti-parasite IFN-γ, IL-12, GM-CSF, and IgG2a isotype antibodies, which were associated with a low presence of IL-4 and IL-10. DNA vaccination induced higher IFN-γ production, mainly by CD8⁺ T cells, while rLiHyJ/saponin stimulated the production of this cytokine, mainly by CD4⁺ T cells. The parasite load evaluated in distinct organs showed that both immunization schedules significantly reduced organic parasitism, when compared to the controls. Similar results were found in the immunological and parasitological assays when using the recombinant protein or DNA, although the vaccination with rLiHyJ plus saponin induced a slightly higher Th1 response and lower parasite load, when compared to the use of DNA plasmid. The protein also proved to be immunogenic when peripheral blood mononuclear cells of treated VL patients and healthy subjects were in vitro stimulated, since higher IFN-γ and lower IL-4 and IL-10 levels were found in the culture supernatants. In conclusion, LiHyJ should be considered in future studies as a vaccine candidate to protect against VL.

Genomic insights into virulence mechanisms of Leishmania donovani: evidence from an atypical strain

Background

Leishmaniasis is a neglected tropical disease with diverse clinical phenotypes, determined by parasite, host and vector interactions. Despite the advances in molecular biology and the availability of more Leishmania genome references in recent years, the association between parasite species and distinct clinical phenotypes remains poorly understood. We present a genomic comparison of an atypical variant of Leishmania donovani from a South Asian focus, where it mostly causes cutaneous form of leishmaniasis.

Results

Clinical isolates from six cutaneous leishmaniasis patients (CL-SL); 2 of whom were poor responders to antimony (CL-PR), and two visceral leishmaniasis patients (VL-SL) were sequenced on an Illumina MiSeq platform. Chromosome aneuploidy was observed in both groups but was more frequent in CL-SL. 248 genes differed by 2 fold or more in copy number among the two groups. Genes involved in amino acid use (LdBPK_271940) and energy metabolism (LdBPK_271950), predominated the VL-SL group with the same distribution pattern reflected in gene tandem arrays. Genes encoding amastins were present in higher copy numbers in VL-SL and CL-PR as well as being among predicted pseudogenes in CL-SL. Both chromosome and SNP profiles showed CL-SL and VL-SL to form two distinct groups. While expected heterozygosity was much higher in VL-SL, SNP allele frequency patterns did not suggest potential recent recombination breakpoints. The SNP/indel profile obtained using the more recently generated PacBio sequence did not vary markedly from that based on the standard LdBPK282A1 reference. Several genes previously associated with resistance to antimonials were observed in higher copy numbers in the analysis of CL-PR. H-locus amplification was seen in one cutaneous isolate which however did not belong to the CL-PR group.

Conclusions

The data presented suggests that intra species variations at chromosome and gene level are more likely to influence differences in tropism as well as response to treatment, and contributes to greater understanding of parasite molecular mechanisms underpinning these differences. These findings should be substantiated with a larger sample number and expression/functional studies.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5271-z) contains supplementary material, which is available to authorized users.

Down Modulation of Host Immune Response by Amino Acid Repeats Present in a Trypanosoma cruzi Ribosomal Antigen

Several antigens from Trypanosoma cruzi, the causative agent of Chagas disease (CD), contain amino acid repeats identified as targets of the host immune response. Ribosomal proteins containing an Ala, Lys, Pro-rich repeat domain are among the T. cruzi antigens that are strongly recognized by antibodies from CD patients. Here we investigated the role of amino acid repeats present in the T. cruzi ribosomal protein L7a, by immunizing mice with recombinant versions of the full-length protein (TcRpL7a), as well as with truncated versions containing only the repetitive (TcRpL7aRep) or the non-repetitive domains (TcRpL7aΔRep). Mice immunized with full-length TcRpL7a produced high levels of IgG antibodies against the complete protein as well as against the repeat domain, whereas mice immunized with TcRpL7aΔRep or TcRpL7aRep produced very low levels or did not produce IgG antibodies against this antigen. Also in contrast to mice immunized with the full-length TcRpL7a, which produced high levels of IFN-γ, only low levels of IFN-γ or no IFN-γ were detected in cultures of splenocytes derived from mice immunized with truncated versions of the protein. After challenging with trypomastigotes, mice immunized with the TcRpL7a were partially protected against the infection whereas immunization with TcRpL7aΔRep did not alter parasitemia levels compared to controls. Strikingly, mice immunized with TcRpL7aRep displayed an exacerbated parasitemia compared to the other groups and 100% mortality after infection. Analyses of antibody production in mice that were immunized with TcRpL7aRep prior to infection showed a reduced humoral response to parasite antigens as well as against an heterologous antigen. In vitro proliferation assays with mice splenocytes incubated with different mitogens in the presence of TcRpL7aRep resulted in a drastic inhibition of B-cell proliferation and antibody production. Taken together, these results indicate that the repeat domain of TcRpL7a acts as an immunosuppressive factor that down regulates the host B-cell response against parasite antigens favoring parasite multiplication in the mammalian host.