Chimeric Vaccines Designed by Immunoinformatics-Activated Polyfunctional and Memory T Cells That Trigger Protection against Experimental Visceral Leishmaniasis

Synthetic Peptides Selected by Immunoinformatics as Potential Tools for the Specific Diagnosis of Canine Visceral Leishmaniasis

Diagnosing canine visceral leishmaniasis (CVL) in Brazil faces challenges due to the limitations regarding the sensitivity and specificity of the current diagnostic protocol. Therefore, it is urgent to map new antigens or enhance the existing ones for future diagnostic techniques. Immunoinformatic tools are promising in the identification of new potential epitopes or antigen candidates. In this study, we evaluated peptides selected by epitope prediction for CVL serodiagnosis in ELISA assays. Ten B-cell epitopes were immunogenic in silico, but two peptides (peptides No. 45 and No. 48) showed the best performance in vitro. The selected peptides, both individually and in combination, were highly diagnostically accurate, with sensitivities ranging from 86.4% to 100% and with a specificity of approximately 90%. We observed that the combination of peptides showed better performance when compared to peptide alone, by detecting all asymptomatic dogs, showing lower cross-reactivity in sera from dogs with other canine infections, and did not detect vaccinated animals. Moreover, our data indicate the potential use of immunoinformatic tools associated with ELISA assays for the selection and evaluation of potential new targets, such as peptides, applied to the diagnosis of CVL.

Immunization with recombinant LiHyp1 protein plus adjuvant is protective against tegumentary leishmaniasis

Tegumentary leishmaniasis (TL) is the main clinical manifestation of leishmaniasis, and it can cause the infected hosts to self-healing cutaneous lesions until mutilating scars in mucosal membranes, particularly in the nose and throat. The treatment against disease presents problems, and the diagnosis is hampered by variable sensitivity and/or specificity of the tests. In this context, the development of prophylactic vaccines could be considered as a strategy to control the disease. Previously, we showed that the recombinant LiHyp1 protein plus adjuvant protected mice from infection with Leishmania infantum, which causes visceral leishmaniasis. In the present study, we tested whether rLiHyp1 could induce protection against infection with L. amazonensis, a parasite species able to cause TL. We immunized BALB/c mice with rLiHyp1 plus saponin (rLiHyp1/S) or incorporated in micelles (rLiHyp1/M) as adjuvants and performed parasitological and immunological evaluations before and after infection. Results showed that after in vitro stimulation from spleen cell cultures using rLiHyp1 or a Leishmania antigenic extract (SLA), rLiHyp1/S and rLiHyp1/M groups developed a Th1-type immune response, which was characterized by high levels of IFN-γ, IL-2, TNF-α and IL-12 cytokines, nitrite, and IgG2a isotype antibodies when compared to values found in the control (saline, saponin, micelles alone) groups, which showed higher levels of anti-SLA IL-4, IL-10, and IgG1 antibodies before and after challenge. In addition, mice receiving rLiHyp1/S or rLiHyp1/M presented significant reductions in the lesion average diameter and parasite load in the infected tissue and internal organs. Blood samples were collected from healthy subjects and TL patients to obtain PBMC cultures, which were in vitro stimulated with rLiHyp1 or SLA, and results showed higher lymphoproliferation and IFN-γ production after stimulus using rLiHyp1, as compared to values found using SLA. These results suggest that rLiHyp1 plus adjuvant was protective against experimental TL and could also be considered for future studies as a vaccine candidate against human disease.

Development of a multi-epitope vaccine candidate for leishmanial parasites applying immunoinformatics and in vitro approaches

Leishmaniasis is a neglected tropical disease, and its severity necessitates the development of a potent and efficient vaccine for the disease; however, no human vaccine has yet been approved for clinical use. This study aims to design and evaluate a multi-epitope vaccine against the leishmanial parasite by utilizing helper T-lymphocyte (HTL), cytotoxic T-lymphocyte (CTL), and linear B-lymphocyte (LBL) epitopes from membrane-bound acid phosphatase of Leishmania donovani (LdMAcP). The designed multi-epitope vaccine (LdMAPV) was highly antigenic, non-allergenic, and non-toxic, with suitable physicochemical properties. The three-dimensional structure of LdMAPV was modeled and validated, succeeded by molecular docking and molecular dynamics simulation (MDS) studies that confirmed the high binding affinity and stable interactions between human toll-like receptors and LdMAPV. In silico disulfide engineering provided improved stability to LdMAPV, whereas immune simulation displayed the induction of both immune responses, i.e., antibody and cell-mediated immune responses, with a rise in cytokines. Furthermore, LdMAPV sequence was codon optimized and cloned into the pET-28a vector, followed by its expression in a bacterial host. The recombinant protein was purified using affinity chromatography and subjected to determine its effect on cytotoxicity, cytokines, and nitric oxide generation by mammalian macrophages. Altogether, this report provides a multi-epitope vaccine candidate from a leishmanial protein participating in parasitic virulence that has shown its potency to be a promising vaccine candidate against leishmanial parasites.

Development of chimeric protein as a multivalent vaccine for human Kinetoplastid infections: Chagas disease and leishmaniasis

Leishmania spp. and Trypanosoma cruzi are parasitic kinetoplastids of great medical and epidemiological importance since they are responsible for thousands of deaths and disability-adjusted life-years annually, especially in low- and middle-income countries. Despite efforts to minimize their impact, current prevention measures have failed to fully control their spread. There are still no vaccines available. Taking into account the genetic similarity within the Class Kinetoplastida, we selected CD8+ T cell epitopes preserved among Leishmania spp. and T. cruzi to construct a multivalent and broad-spectrum chimeric polyprotein vaccine. In addition to inducing specific IgG production, immunization with the vaccine was able to significantly reduce parasite burden in the colon, liver and skin lesions from T. cruzi, L. infantum and L. mexicana challenged mice, respectively. These findings were supported by histopathological analysis, which revealed decreased inflammation in the colon, a reduced number of degenerated hepatocytes and an increased proliferation of connective tissue in the skin lesions of the corresponding T. cruzi, L. infantum and L. mexicana vaccinated and challenged mice. Collectively, our results support the protective effect of a polyprotein vaccine approach and further studies will elucidate the immune profile associated with this protection. Noteworthy, our results act as conceptual proof that a single multi-kinetoplastida vaccine can be used effectively to control different infectious etiologies, which in turn can have a profound impact on the development of a new generation of vaccines.

A Tailored Approach to Leishmaniases Vaccination: Comparative Evaluation of the Efficacy and Cross-Protection Capacity of DNA vs. Peptide-Based Vaccines in a Murine Model

Zoonotic leishmaniases are a worldwide public health problem for which the development of effective vaccines remains a challenge. A vaccine against leishmaniases must be safe and affordable and should induce cross-protection against the different disease-causing species. In this context, the DNA vaccine pHisAK70 has been demonstrated to induce, in a murine model, a resistant phenotype against L. major, L. infantum, and L. amazonensis. Moreover, a chimeric multiepitope peptide, HisDTC, has been obtained by in silico analysis from the histone proteins encoded in the DNA vaccine and has showed its ability to activate a potent CD4+ and CD8+ T-cell protective immune response in mice against L. infantum infection. In the present study, we evaluated the plasmid DNA vaccine pHisAK70 in comparison with the peptide HisDTC (with and without saponin) against L. major and L. infantum infection. Our preliminary results showed that both formulations were able to induce a potent cellular response leading to a decrease in parasite load against L. infantum. In addition, the DNA candidate was able to induce better lesion control in mice against L. major. These preliminary results indicate that both strategies are potentially effective candidates for leishmaniases control. Furthermore, it is important to carry out such comparative studies to elucidate which vaccine candidates are the most appropriate for further development.

A New Strategy for Mapping Epitopes of LACK and PEPCK Proteins of Leishmania amazonensis Specific for Major Histocompatibility Complex Class I

Leishmaniasis represents a complex of diseases with a broad clinical spectrum and epidemiological diversity, considered a major public health problem. Although there is treatment, there are still no vaccines for cutaneous leishmaniasis. Because Leishmania spp. is an intracellular protozoan with several escape mechanisms, a vaccine must provoke cellular and humoral immune responses. Previously, we identified the Leishmania homolog of receptors for activated C kinase (LACK) and phosphoenolpyruvate carboxykinase (PEPCK) proteins as strong immunogens and candidates for the development of a vaccine strategy. The present work focuses on the in silico prediction and characterization of antigenic epitopes that might interact with mice or human major histocompatibility complex class I. After immunogenicity prediction on the Immune Epitope Database (IEDB) and the Database of MHC Ligands and Peptide Motifs (SYFPEITHI), 26 peptides were selected for interaction assays with infected mouse lymphocytes by flow cytometry and ELISpot. This strategy identified nine antigenic peptides (pL1-H2, pPL3-H2, pL10-HLA, pP13-H2, pP14-H2, pP15-H2, pP16-H2, pP17-H2, pP18-H2, pP26-HLA), which are strong candidates for developing a peptide vaccine against leishmaniasis.

Recombinant endonuclease III protein from Leishmania infantum associated with Th1-type adjuvants is immunogenic and induces protection against visceral leishmaniasis

Vaccination against visceral leishmaniasis (VL) should be considered as a safe and effective measure to disease control; however, few vaccines are available against canine VL and there is no an approved human vaccine. In this context, in the present study, we evaluated the endonuclease III (ENDO) protein, which was recently showed to be antigenic for human disease, as a vaccine candidate against Leishmania infantum infection. The recombinant protein (rENDO) was administered in BALB/c mice alone or associated with saponin (rENDO/Sap) or micelles (rENDO/Mic) as adjuvants. Controls received saline, saponin or empty micelles. Results showed that both rENDO/Sap and rENDO/Mic compositions induced higher levels of IFN-γ, IL-12, TNF-α, and GM-CSF cytokines, besides nitrite and IgG2a isotype antibodies, before and after challenge infection, which were related to both CD4⁺ and CD8⁺ T cell subtypes. The immunological results contributed to significant reductions in the parasite load found in the spleens, livers, bone marrows and draining lymph nodes of the vaccinated animals. In general, mice immunized with rENDO/Mic presented a slightly higher Th1-type cellular and humoral immune response, as compared to those receiving rENDO/Sap. In addition, saponin caused a slight to moderate inflammatory edema in their vaccinated footpads, which was not observed when micelles were used with rENDO. In addition, a preliminary analysis showed that the recombinant protein was immunogenic to human cells cultures, since PBMCs from treated VL patients and healthy subjects showed higher lymphoproliferation and IFN-γ production in the culture supernatants. In conclusion, data suggest that rENDO could be considered as a candidate to be evaluated in future studies as vaccine to protect against VL.

Immunotherapy Using Immunogenic Mimotopes Selected by Phage Display plus Amphotericin B Inducing a Therapeutic Response in Mice Infected with Leishmania amazonensis

Leishmania amazonensis can cause cutaneous and visceral clinical manifestations of leishmaniasis in infected hosts. Once the treatment against disease is toxic, presents high cost, and/or there is the emergence of parasite-resistant strains, alternative means through which to control the disease must be developed. In this context, immunotherapeutics combining known drugs with immunogens could be applied to control infections and allow hosts to recover from the disease. In this study, immunotherapeutics protocols associating mimotopes selected by phage display and amphotericin B (AmpB) were evaluated in L. amazonensis-infected mice. Immunogens, A4 and A8 phages, were administered alone or associated with AmpB. Other animals received saline, AmpB, a wild-type phage (WTP), or WTP/AmpB as controls. Evaluations performed one and thirty days after the application of immunotherapeutics showed that the A4/AmpB and A8/AmpB combinations induced the most polarized Th1-type immune responses, which reflected in significant reductions in the lesion's average diameter and in the parasite load in the infected tissue and distinct organs of the animals. In addition, the combination also reduced the drug toxicity, as compared to values found using it alone. In this context, preliminary data presented here suggest the potential to associate A4 and A8 phages with AmpB to be applied in future studies for treatment against leishmaniasis.

The Use of an Adjuvant System Improves Innate and Adaptive Immune Response When Associated with a Leishmania (Viannia) braziliensis Antigen in a Vaccine Candidate against L. (Leishmania) infantum Infection

BACKGROUND

The adjuvants' optimal dose and the administration route can directly influence the epitope recognition patterns and profiles of innate response. We aimed to establish the effect and the optimal dose of adjuvant systems for proposing a vaccine candidate to be employed with Leishmania (Viannia) braziliensis.

METHODS

We evaluated the adjuvants saponin (SAP), monophosphoryl lipid A (MPL) and resiquimod (R-848) isolated and combined as adjuvant systems in a lower dose corresponding to 25%, 33%, and 50% of each adjuvant total dose. Male outbred BALB/c mice were divided into 13 groups, SAP, MPL, and R-848 isolated, and the adjuvant systems SAP plus MPL (SM), SAP plus R-848 (SR), and MPL plus R-848 (MR).

RESULTS

SM50 increased levels of all chemokines analyzed and TNF production, while it presented an increased inflammatory cell infiltrate in the skin with macrophage recruitment. Thus, we proposed a vaccine candidate employing L. (V.) braziliensis antigen associated with the SM adjuvant system against experimental L. (Leishmania) infantum challenge. We observed a significant increase in the frequency of cells expressing the central and effector memory CD4⁺ T cells phenotype in immunized mice with the LBSM50. In the liver, there was a decreased parasite load when mice received LBSM50.

CONCLUSIONS

When combined with L. (V.) braziliensis antigen, SM50 increases TNF and IFN-γ, which generates central and effector memory CD4⁺ T cells. Therefore, using an adjuvant system can promote an effective innate immune response with the potential to compose future vaccines.

Immunoinformatics Approach to Design a Multi-Epitope Nanovaccine against Leishmania Parasite: Elicitation of Cellular Immune Responses

Leishmaniasis is a vector-borne disease caused by an intracellular parasite of the genus Leishmania with different clinical manifestations that affect millions of people worldwide, while the visceral form may be fatal if left untreated. Since the available chemotherapeutic agents are not satisfactory, vaccination emerges as the most promising strategy for confronting leishmaniasis. In the present study, a reverse vaccinology approach was adopted to design a pipeline starting from proteome analysis of three different Leishmania species and ending with the selection of a pool of MHCI- and MHCII-binding epitopes. Epitopes from five parasite proteins were retrieved and fused to construct a multi-epitope chimeric protein, named LeishChim. Immunoinformatics analyses indicated that LeishChim was a stable, non-allergenic and immunogenic protein that could bind strongly onto MHCI and MHCII molecules, suggesting it as a potentially safe and effective vaccine candidate. Preclinical evaluation validated the in silico prediction, since the LeishChim protein, encapsulated simultaneously with monophosphoryl lipid A (MPLA) into poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles, elicited specific cellular immune responses when administered to BALB/c mice. These were characterized by the development of memory CD4⁺ T cells, as well as IFNγ- and TNFα-producing CD4⁺ and CD8⁺ T cells, supporting the potential of LeishChim as a vaccine candidate.

A specific Leishmania infantum polyepitope vaccine triggers Th1-type immune response and protects against experimental visceral leishmaniasis

The development of an immunogenic, effective, and safe vaccine is essential as an alternative for disease control. The present study aimed to evaluate the immunogenicity and efficacy potential of a polyepitope T-cell antigen candidate against visceral leishmaniasis in a murine model. BALB/c mice were immunized with three doses subcutaneously with Poly-T Leish alone or adjuvanted with Saponin plus Monophosphoryl lipid A, with 15-day intervals between doses, and challenged with 10⁷ stationary-phase Leishmania infantum promastigotes via tail vein. Immunogenicity and parasitism in spleen and liver of immunized mice were evaluated 45 days post-challenge. Our results revealed that the immunization with Poly-T Leish and Poly-T Leish/SM increases the percentage of specific T (CD4⁺ and CD8⁺) lymphocytes proliferation in vitro after antigen-specific stimulation. Also, Poly-T Leish and Poly-T Leish/SM groups showed a high percentage of IFN-γ and TNF-α-producing T cells, meanwhile, the Poly-T Leish/SM group also showed an increased percentage of multifunctional T cells producing double and triple-positive (IFN-γ⁺TNF-α⁺IL-2⁺) cytokines. The immunization with Poly-T Leish or Poly-T Leish/SM stimulated a decreased IL-4 and IL-10 compared to the Saline and adjuvant group. Poly-T Leish/SM immunized mice exhibit a noteworthy reduction in the parasite burden (spleen and liver) through real-time PCR (96%). Moreover, we observed higher nitrite secretion in 120-hour stimulated-culture supernatant using Griess method. We demonstrated that the Poly-T Leish/SM candidate was potentially immunogenic, providing enhancement of protective immune mechanisms, and conferred protection reducing parasitism. Our candidate was considered potential against visceral leishmaniasis, and eventually, could be tested in phase I and II clinical trials in dogs.

Current leishmaniasis drug discovery

Leishmaniasis is a complex protozoan infectious disease and, associated with malnutrition, poor health services and unavailability of prophylactic control measures, neglected populations are particularly affected. Current drug regimens are outdated and associated with some drawbacks, such as cytotoxicity and resistance, and the development of novel, efficacious and less toxic drug regimens is urgently required. In addition, leishmanial pathogenesis is not well established or understood, and a prophylactic vaccine is an unfulfilled goal. Human kinetoplastid protozoan infections, including leishmaniasis, have been neglected for many years, and in an attempt to overcome this situation, some new drug targets were recently identified, enabling the development of new drugs and vaccines. Compounds from new drug classes have also shown excellent antileishmanial activities, some of the most promising ones included in clinical trials, and could be a hope to control the disease burden of this endemic disease in the near future. In this review, we discuss the limitations of current control methods, explore the wide range of compounds that are being screened and identified as antileishmanial drug prototypes, summarize the advances in identifying new drug targets aiming at innovative treatments and explore the state-of-art vaccine development field, including immunomodulation strategies.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

A Recombinant Chimeric Protein-Based Vaccine Containing T-Cell Epitopes from Amastigote Proteins and Combined with Distinct Adjuvants, Induces Immunogenicity and Protection against Leishmania infantum Infection

Currently, there is no licensed vaccine to protect against human visceral leishmaniasis (VL), a potentially fatal disease caused by infection with Leishmania parasites. In the current study, a recombinant chimeric protein ChimT was developed based on T-cell epitopes identified from the immunogenic Leishmania amastigote proteins LiHyp1, LiHyV, LiHyC and LiHyG. ChimT was associated with the adjuvants saponin (Sap) or monophosphoryl lipid A (MPLA) and used to immunize mice, and their immunogenicity and protective efficacy were evaluated. Both ChimT/Sap and ChimT/MPLA induced the development of a specific Th1-type immune response, with significantly high levels of IFN-γ, IL-2, IL-12, TNF-α and GM-CSF cytokines produced by CD4+ and CD8+ T cell subtypes (p < 0.05), with correspondingly low production of anti-leishmanial IL-4 and IL-10 cytokines. Significantly increased (p < 0.05) levels of nitrite, a proxy for nitric oxide, and IFN-γ expression (p < 0.05) were detected in stimulated spleen cell cultures from immunized and infected mice, as was significant production of parasite-specific IgG2a isotype antibodies. Significant reductions in the parasite load in the internal organs of the immunized and infected mice (p < 0.05) were quantified with a limiting dilution technique and quantitative PCR and correlated with the immunological findings. ChimT/MPLA showed marginally superior immunogenicity than ChimT/Sap, and although this was not statistically significant (p > 0.05), ChimT/MPLA was preferred since ChimT/Sap induced transient edema in the inoculation site. ChimT also induced high IFN-γ and low IL-10 levels from human PBMCs isolated from healthy individuals and from VL-treated patients. In conclusion, the experimental T-cell multi-epitope amastigote stage Leishmania vaccine administered with adjuvants appears to be a promising vaccine candidate to protect against VL.

Development of an immunogen containing CD4+/CD8+ T-cell epitopes for the prophylaxis of tegumentary leishmaniasis

Abstract

Tegumentary leishmaniasis (TL) is a disease of high severity and incidence in Brazil, and Leishmania braziliensis is its main etiological agent. The inefficiency of control measures, such as high toxicity and costs of current treatments and the lack of effective immunoprophylactic strategies, makes the development of vaccines indispensable and imminent. In this light, the present work developed a gene encoding multiple T-cell (CD4⁺/CD8⁺) epitope, derived from conserved proteins found in Leishmania species and associated with TL, to generate a chimeric protein (rMEP/TL) and compose a vaccine formulation. For this, six T-cell epitopes were selected by immunoinformatics approaches from proteins present in the amastigote stage and associated with host-parasite interactions. The following formulations were then tested in an L. braziliensis murine infection model: rMEP/TL in saline or associated with MPLA-PHAD^®. Our data revealed that, after immunization (three doses; 14-day intervals) and subsequent challenging, rMEP/TL and rMEP/TL + MPLA-vaccinated mice showed an increased production of key immunological biomarkers of protection, such as IgG_2a, IgG_2a/IgG₁, NO, CD4⁺, and CD8⁺ T-cells with IFN-γ and TNF-α production, associated with a reduction in CD4⁺IL-10⁺ and CD8⁺IL-10⁺ T-cells. Vaccines also induced the development of central (CD44^highCD62L^high) and effector (CD44^highCD62L^low) memory of CD4⁺ and CD8⁺ T-cells. These findings, associated with the observation of lower rates of parasite burdens in the vaccinated groups, when compared to the control groups, suggest that immunization with rMEP/TL and, preferably, associated with an adjuvant, may be considered an effective tool to prevent TL.

Key points

• Rational design approaches for vaccine development.

• Central and effector memory of CD4+ and CD8+ T-cells.

• Vaccine comprised of rMEP/TL plus MPLA as an effective tool to prevent TL.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-12033-7.

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.

Host–Pathogen Interaction in Leishmaniasis: Immune Response and Vaccination Strategies

Leishmaniasis is a zoonotic and vector-borne infectious disease that is caused by the genus Leishmania belonging to the trypanosomatid family. The protozoan parasite has a digenetic life cycle involving a mammalian host and an insect vector. Leishmaniasisis is a worldwide public health problem falling under the neglected tropical disease category, with over 90 endemic countries, and approximately 1 million new cases and 20,000 deaths annually. Leishmania infection can progress toward the development of species–specific pathologic disorders, ranging in severity from self-healing cutaneous lesions to disseminating muco-cutaneous and fatal visceral manifestations. The severity and the outcome of leishmaniasis is determined by the parasite’s antigenic epitope characteristics, the vector physiology, and most importantly, the immune response and immune status of the host. This review examines the nature of host–pathogen interaction in leishmaniasis, innate and adaptive immune responses, and various strategies that have been employed for vaccine development.

Acarbose presents in vitro and in vivo antileishmanial activity against Leishmania infantum and is a promising therapeutic candidate against visceral leishmaniasis

Treatment against visceral leishmaniasis (VL) is mainly hampered by drug toxicity, long treatment regimens and/or high costs. Thus, the identification of novel and low-cost antileishmanial agents is urgent. Acarbose (ACA) is a specific inhibitor of glucosidase-like proteins, which has been used for treating diabetes. In the present study, we show that this molecule also presents in vitro and in vivo specific antileishmanial activity against Leishmania infantum. Results showed an in vitro direct action against L. infantum promastigotes and amastigotes, and low toxicity to mammalian cells. In addition, in vivo experiments performed using free ACA or incorporated in a Pluronic^® F127-based polymeric micelle system called ACA/Mic proved effective for the treatment of L. infantum-infected BALB/c mice. Treated animals presented significant reductions in the parasite load in their spleens, livers, bone marrows and draining lymph nodes when compared to the controls, as well as the development of antileishmanial Th1-type humoral and cellular responses based on high levels of IFN-γ, IL-12, TNF-α, GM-CSF, nitrite and IgG2a isotype antibodies. In addition, ACA or ACA-treated animals suffered from low organ toxicity. Treatment with ACA/Mic outperformed treatments using either Miltefosine or free ACA based on parasitological and immunological evaluations performed one and 15 days post-therapy. In conclusion, data suggest that the ACA/Mic is a potential therapeutic agent against L. infantum and merits further consideration for VL treatment.

Ivermectin presents effective and selective antileishmanial activity in vitro and in vivo against Leishmania infantum and is therapeutic against visceral leishmaniasis

Treatment for visceral leishmaniasis (VL) is hindered mainly by the toxicity and/or high cost of therapeutic drugs. In addition, parasite resistance has been registered. Thus, there is an urgent need for the identification of novel, effective and low-cost antileishmanial agents. Since drug discovery is a long and expensive process, drug repositioning for treatment of leishmaniasis should be considered. In the present study, Ivermectin (IVE), a broad-spectrum drug used for treatment of parasitic diseases, was evaluated in vitro and in vivo against Leishmania infantum species. Results in vitro showed that IVE presented 50% Leishmania and macrophage inhibitory concentrations (IC₅₀ and CC₅₀, respectively) of 3.64 ± 0.48 μM and 427.50 ± 17.60 μM, respectively, with a selectivity index (SI) of 117.45; whereas Amphotericin B (AmpB), which was used as control, showed IC₅₀ and CC₅₀ values of 0.12 ± 0.05 μM and 1.06 ± 0.23 μM, respectively, with a corresponding SI of 8.90. Treatment with IVE effectively reduced the infection percentage and parasite burden in infected and treated macrophages and displayed a prophylactic activity by inhibiting macrophage infection with pre-treated parasites. Furthermore, preliminary studies suggested that IVE targets the parasite's mitochondria. Activity of IVE in its free format or incorporated into Pluronic® F127-based polymeric micelles (IVE/Mic) was also evaluated in vivo as a treating drug for L. infantum-infected BALB/c mice. Miltefosine was used as a control. Results showed that Miltefosine, IVE and IVE/Mic-treated animals presented significant reductions in the parasite load in their spleens, livers, bone marrows and draining lymph nodes, as well as development of an antileishmanial Th1-type immune response one and 15 days after treatment. Notably, IVE/Mic showed a better parasitological and immunological response in comparison to other alternative treatments. In conclusion, results suggest that IVE/Mic could be considered in future studies as a therapeutic alternative to treat VL.