Leishmania Immunity: Advancing Immunotherapy and Vaccine Development

An overview of host immune responses against Leishmania spp. infections

Leishmania spp. infections pose a significant global health challenge, affecting approximately 1 billion people across more than 88 endemic countries. This unicellular, obligate intracellular parasite causes a spectrum of diseases, ranging from localized cutaneous lesions to systemic visceral infections. Despite advancements in modern medicine and increased understanding of the parasite's etiology and associated diseases, treatment options remain limited to pentavalent antimonials, liposomal amphotericin B, and miltefosine. A deeper understanding of the interactions between immune and non-immune cells involved in the clearance of Leishmania spp. infections could uncover novel therapeutic strategies for this debilitating disease. This review highlights recent progress in elucidating how various cell types contribute to the regulation and resolution of Leishmania spp. infections.

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.

Putrescine Depletion in Leishmania donovani Parasites Causes Immediate Proliferation Arrest Followed by an Apoptosis-like Cell Death

The polyamine pathway in Leishmania parasites has emerged as a promising target for therapeutic intervention, yet the functions of polyamines in parasites remain largely unexplored. Ornithine decarboxylase (ODC) and spermidine synthase (SPDSYN) catalyze the sequential conversion of ornithine to putrescine and spermidine. We previously found that Leishmania donovani Δodc and Δspdsyn mutants exhibit markedly reduced growth in vitro and diminished infectivity in mice, with the effect being most pronounced in putrescine-depleted Δodc mutants. Here, we report that, in polyamine-free media, ∆odc mutants arrested proliferation and replication, while ∆spdsyn mutants showed a slow growth and replication phenotype. Starved ∆odc parasites also exhibited a marked reduction in metabolism, which was not observed in the starved ∆spdsyn cells. In contrast, both mutants displayed mitochondrial membrane hyperpolarization. Hallmarks of apoptosis, specifically DNA fragmentation and membrane modifications, were observed in Δodc mutants incubated in polyamine-free media. These results show that putrescine depletion had an immediate detrimental effect on cell growth, replication, and mitochondrial metabolism and caused an apoptosis-like death phenotype. Our findings establish ODC as the most promising therapeutic target within the polyamine biosynthetic pathway for treating leishmaniasis.

Unleashing the role of potential adjuvants in leishmaniasis

Leishmaniasis is amongst one of the most neglected tropical disease, caused by an intracellular protozoan of genus Leishmania. Currently, the most promising strategy to combat leishmaniasis, relies on chemotherapy but the toxicity and increasing resistance of the standard drugs, presses the demand for new alternatives. Immunization is arguably the best strategy for cure because an individual once infected becomes immune to the disease. Yet, there is no efficient vaccine capable of providing enduring immunity against the parasite. Achieving the goal of developing highly efficacious and durable vaccine is limited due to lack of an appropriate adjuvant. Adjuvants are recognized as 'immune potentiators' which redirect or amplify the immune response. A number of adjuvants like alum, MPL-A, CpG ODN, GLA-SE, imiquimod, saponins etc. have been used in combination with various classes of Leishmania antigens. However, only few have reached clinical trials. Thus, the choice of an adjuvant is critically dependent on many factors such as the route of administration, the nature of antigen, formulation, the type of required immune response, their mode of action and the immunization schedule. This review provides an updated status on the types of adjuvants used in leishmaniasis so far and their mechanism of action if known.

Antibody dynamics in dogs submitted to different canine visceral leishmaniasis treatment protocols

This study evaluated dynamics of antibodies in dogs treated for canine visceral leishmaniasis (CVL). Twenty-one dogs naturally infected by Leishmania spp. were grouped based on the treatment protocol: G1 (n=4) received allopurinol; G2 (n=10) allopurinol with miltefosine; and G3 (n=7) allopurinol, miltefosine and Leish-Tec® vaccine. The dogs were monitored monthly for a period of one year. To verify serum antibody titers, an indirect immunofluorescence reaction was performed. We found that dogs from G1 and G2 had lower clinical scores and antibody titers, when compared to the parameters evaluated in pre-treatment; however, clinical relapses were observed in three animals. In G3, clinical scores were lower than pre-treatment; however, they presented relatively stable antibody titers and no clinical relapse was observed. All animals submitted to the evaluated treatment protocols showed relative improvement in clinical signs. Furthermore, the immune response of animals must be considered, given the challenges of parasitic loads in infections. Therefore, it is necessary to complement the methods of clinical and therapeutic monitoring of dogs with CVL in order to establish the risk of transmissibility of the agent in infected and treated dogs.

In silico and in vitro evaluation of the immunogenic potential of Leishmania donovani ascorbate peroxidase and its derived peptides

The control and eradication of any infectious disease is only possible with a potential vaccine, which has not been accomplished for human visceral leishmaniasis (VL). The lack of vaccines may increase the risk of VL outbreaks periodically in endemic zones. Identifying a reliable vaccine candidate for Leishmania is a major challenge. Here, we considered Leishmania donovani ascorbate peroxidase (LdAPx) for its in vitro evaluation with the hope of future vaccine candidates for VL. LdAPx was selected based on its unique presence in Leishmania and virulence in VL pathogenesis. Initially, we found antibodies against recombinant LdAPx (rLdAPx) in the serum of VL patients. Therefore, using bioinformatics, we predicted and selected ten (MHC class I and II) peptides. These peptides, evaluated in vitro with PBMCs from healthy, active VL, and treated VL individuals induced PBMC proliferation, IFN-γ secretion, and Nitric Oxide (NO) production, indicating host-protective immune responses. Among them, three peptides (PEP6, PEP8, and PEP9) consistently elicited a Th1-type immune response in PBMCs. Treated VL individuals showed a stronger Th1 response compared to active VL patients and healthy subjects, highlighting these peptides' potential as vaccine candidates. Further studies are on the way toward evaluating the LdAPx-derived peptides or sub-unit vaccine in animal models against the L. donovani challenge.

Immunoinformatic approach to the design of a novel multi-epitope vaccine against Leishmania major fused to human IgG-Fc

Background and purpose

Cutaneous leishmaniasis poses significant health and socioeconomic challenges, making vaccine development a top priority, especially in endemic regions. Cysteine proteases, KMP-11, and HASPB proteins are promising candidates for leishmaniasis vaccine development owing to their immunogenic properties and capacity to provoke robust immune responses, as evidenced by different investigations. This study aimed to design a recombinant chimeric protein (MEV-Fc) vaccine using multi-epitopes from these Leishmania major proteins.

Experimental approach

The antigens were subjected to immunoinformatic prediction and screening of HTL, CTL, and B-cell epitopes. The multi-epitope protein was designed with significantly high-scoring epitopes and suitable linkers. Natural adjuvants were then added to enhance immunogenicity. Vaccine potency was innovatively improved by covalently fusing human IgG1 Fc with multi-epitope protein. To investigate how the MEV-Fc vaccine interacts with Toll-like receptors, molecular docking, multi-scale normal mode analysis simulation, and computational immune simulation were employed to study humoral and cellular immune responses.

Findings/Results

The results demonstrated the vaccine's antigenicity, stability, and nontoxicity. The structural validation confirmed the accuracy of the 3D models, indicating robust interactions with TLR2 and TLR4, with binding free energies of -1269.9 and -1128.7 (kcal/mol), respectively. Immune simulation results showed significant increases in IgM and IgG antibody levels following three vaccinations, along with enhanced activation of B cells, helper T cells, and cytotoxic T lymphocytes.

Conclusion and implications

These findings provide novel insights for developing effective candidates for cutaneous leishmaniasis vaccines. However, laboratory experiments are necessary to evaluate its protective effects.

A systematic review and meta-analysis of the association between neglected tropical diseases and malnutrition: more research needed on diseases other than intestinal parasites, leishmaniasis and leprosy

Background. According to the World Health Organization, neglected tropical diseases (NTDs) affect over two billion people worldwide. While the links between nutrition and many diseases have become clear over recent decades, NTDs have lagged behind and the linkage with nutrition is largely unknown. We conducted this systematic review with meta-analysis to determine the current knowledge on the association between NTDs and malnutrition. Methodology. PubMed, Embase, Scopus and African Journals Online databases were searched using predefined search terms. We included all original articles with a case-control design and at least one NTD. The studies had to compare nutritional parameters between infected cases and control participants. Articles that did not report original data were excluded. The quality of the studies was assessed using the Newcastle-Ottawa scale. Pooled estimates were conducted using the random effect model. The publication bias of the studies was determined by funnel plots. Q and I 2 statistics were used to assess the heterogeneity of the studies. Results. After screening 1294 articles, only 16 qualified for the systematic review and 12 for meta-analysis. These predominately had a focus on soil-transmitted helminthiasis (ascariasis, hookworm diseases and trichuriasis) and schistosomiasis, with a minority concerning leishmaniasis and leprosy. Pooled estimates showed an association between intestinal parasites and stunting in children [odds ratio (OR) = 1.38, 95% confidence interval (CI): 1.14-1.66, I 2 = 0%, tau2 = 0]. We also identified a moderate association established between serum iron deficiency (OR = 4.67, 95% CI: 1.91-11.44, tau2 = 0) and intestinal parasites. Conclusions/significance. Of the 20 NTDs, the links between diet and disease have been explored for only 4. There is a paucity of data from low- and middle-income countries and least-developed countries where the NTD burden is high. Therefore, more research into the role of malnutrition in NTDs other than intestinal parasites, leishmaniasis and leprosy is needed.

Advances in Leishmania Vaccines: Current Development and Future Prospects

Leishmaniasis is a neglected tropical disease caused by parasites of the genus Leishmania. As approved human vaccines are not available, treatment and prevention rely heavily on toxic chemotherapeutic agents, which face increasing resistance problems. The development of effective vaccines against human leishmaniasis is of utmost importance for the control of the disease. Strategies that have been considered for this purpose range from whole-killed and attenuated parasites to recombinant proteins and DNA vaccines. The ideal vaccine must be safe and effective, ensuring lasting immunity through a robust IL-12-driven Th1 adaptive immune response. Despite some success and years of effort, human vaccine trials have encountered difficulties in conferring durable protection against Leishmania, a problem that may be attributed to the parasite's antigenic diversity and the intricate nature of the host's immune response. The aim of this review is to provide a thorough overview of recent advances in Leishmania vaccine development, ranging from initial trials to recent achievements, such as the ChAd63-KH DNA vaccine, which underscores the potential for effective control of leishmaniasis through continued research in this field.

PLGA nanoparticle-delivered Leishmania antigen and TLR agonists as a therapeutic vaccine against cutaneous leishmaniasis in BALB/c mice

Leishmaniasis, caused by Leishmania (L.) species, remains a neglected infection. Therapeutic vaccination presents a promising strategy for its treatment. In this study, we aimed to develop a therapeutic vaccine candidate using Leishmaniaantigens (SLA) and Toll-like receptor (TLR) 7/8 agonist (R848) encapsulated into the poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs). Moreover, TLR1/2 agonist (Pam3CSK4) was loaded onto the NPs. The therapeutic effects of these NPs were evaluated in L. major-infected BALB/c mice. Footpad swelling, parasite load, cellular and humoral immune responses, and nitric oxide (NO) production were analyzed. The results demonstrated that the PLGA NPs (SLA-R848-Pam3CSK4) therapeutic vaccine effectively stimulated Th1 cell responses, induced humoral responses, promoted NO production, and restricted parasite burden and lesion size.Our findings suggest that vaccination with SLA combined with TLR1/2 and TLR7/8 agonists in PLGA NPs as a therapeutic vaccine confers strong protection againstL. majorinfection. These results represent a novel particulate therapeutic vaccine against Old World cutaneous leishmaniasis.

Effect of Leishmania infantum infection on B cell lymphopoiesis and memory in the bone marrow and spleen

Visceral leishmaniasis (VL) is characterized by an uncontrolled infection of internal organs such as the spleen, liver and bone marrow (BM) and can be lethal when left untreated. No effective vaccination is currently available for humans. The importance of B cells in infection and VL protective immunity has been controversial, with both detrimental and protective effects described. VL infection was found in this study to increase not only all analyzed B cell subsets in the spleen but also the B cell progenitors in the BM. The enhanced B lymphopoiesis aligns with the clinical manifestation of polyclonal hypergammaglobulinemia and the occurrence of autoantibodies. In line with earlier reports, flow cytometric and microscopic examination identified parasite attachment to B cells of the BM and spleen without internalization, and transformation of promastigotes into amastigote morphotypes. The interaction appears independent of IgM expression and is associated with an increased detection of activated lysosomes. Furthermore, the extracellularly attached amastigotes could be efficiently transferred to infect macrophages. The observed interaction underscores the potentially crucial role of B cells during VL infection. Additionally, using immunization against a fluorescent heterologous antigen, it was shown that the infection does not impair immune memory, which is reassuring for vaccination campaigns in VL endemic areas.

Targeting and activation of macrophages in leishmaniasis. A focus on iron oxide nanoparticles

Macrophages play a pivotal role as host cells for Leishmania parasites, displaying a notable functional adaptability ranging from the proinflammatory, leishmanicidal M1 phenotype to the anti-inflammatory, parasite-permissive M2 phenotype. While macrophages can potentially eradicate amastigotes through appropriate activation, Leishmania employs diverse strategies to thwart this activation and redirect macrophages toward an M2 phenotype, facilitating its survival and replication. Additionally, a competition for iron between the two entities exits, as iron is vital for both and is also implicated in macrophage defensive oxidative mechanisms and modulation of their phenotype. This review explores the intricate interplay between macrophages, Leishmania, and iron. We focus the attention on the potential of iron oxide nanoparticles (IONPs) as a sort of immunotherapy to treat some leishmaniasis forms by reprogramming Leishmania-permissive M2 macrophages into antimicrobial M1 macrophages. Through the specific targeting of iron in macrophages, the use of IONPs emerges as a promising strategy to finely tune the parasite-host interaction, endowing macrophages with an augmented antimicrobial arsenal capable of efficiently eliminating these intrusive microbes.

The non-pathogenic protozoon Leishmania tarentolae interferes with the activation of NLRP3 inflammasome in human cells: new perspectives in the control of inflammation

Background

Innate immune responses against infectious agents can act as triggers of inflammatory diseases. On the other hand, various pathogens have developed mechanisms for the evasion of the immune response, based on an inhibition of innate immunity and inflammatory responses. Inflammatory diseases could thus be controlled through the administration of pathogens or pathogen-derived molecules, capable of interfering with the mechanisms at the basis of inflammation. In this framework, the NLRP3 inflammasome is an important component in innate antimicrobial responses and a major player in the inflammatory disease. Parasites of the genus Leishmania are master manipulators of innate immune mechanisms, and different species have been shown to inhibit inflammasome formation. However, the exploitation of pathogenic Leishmania species as blockers of NLRP3-based inflammatory diseases poses safety concerns.

Methods

To circumvent safety issues associated with pathogenic parasites, we focused on Leishmania tarentolae, a species of Leishmania that is not infectious to humans. Because NLRP3 typically develops in macrophages, in response to the detection and engulfment microorganisms, we performed our experiments on a monocyte-macrophage cell line (THP-1), either wild type or knockout for ASC, a key component of NLRP3 formation, with determination of cytokines and other markers of inflammation.

Results

L. tarentolae was shown to possess the capability of dampening the formation of NLRP3 inflammasome and the consequent expression of pro-inflammatory molecules, with minor differences compared to effects of pathogenic Leishmania species.

Conclusion

The non-pathogenic L. tarentolae appears a promising pro-biotic microbe with anti-inflammatory properties or a source of immune modulating cellular fractions or molecules, capable of interfering with the formation of the NLRP3 inflammasome.

Multi-epitope vaccine design against leishmaniasis using IFN-γ inducing epitopes from immunodominant gp46 and gp63 proteins

There is no currently approved human vaccine against leishmaniasis. Utilization of immunogenic antigens and their epitopes capable of enhancing immune responses against leishmaniasis is a crucial step for rational in silico vaccine design. The objective of this study was to generate and evaluate a potential vaccine candidate against leishmaniasis, designed by immunodominant proteins from gp46 and gp63 of Leishmania major, which can stimulate helper T-lymphocytes (HTL) and cytotoxic T-lymphocytes (CTL). For this aim, the IFN-γ-inducing MHC-I and MHC-II binders were predicted for each examined protein (gp46 and gp63) and connected with appropriate linkers, along with an adjuvant (Mycobacterium tuberculosis L7/L12) and a histidine tag. The vaccine's stability, antigenicity, structure, and interaction with the TLR-4 receptor were evaluated in silico. The resulting chimeric vaccine was composed of 344 amino acids and had a molecular weight of 35.64 kDa. Physico-chemical properties indicated that it was thermotolerant, soluble, highly antigenic, and non-allergenic. Predictions of the secondary and tertiary structures were made, and further analyses confirmed that the vaccine construct could interact with the human TLR-4 receptor. Virtual immune simulation demonstrated strong stimulation of T-cell responses, particularly by an increase in IFN-γ, following vaccination. In summary, the in silico data indicated that the vaccine candidate showed high antigenicity in humans. It was also found to trigger significant levels of clearance mechanisms and other components of the cellular immune profile. Nevertheless, further wet experiments are required to properly assess the efficacy of this multi-epitope vaccine candidate against leishmaniasis.

Phenotypic screening reveals a highly selective phthalimide-based compound with antileishmanial activity

Pharmacophores such as hydroxyethylamine (HEA) and phthalimide (PHT) have been identified as potential synthons for the development of compounds against various parasitic infections. In order to further advance our progress, we conducted an experiment utilising a collection of PHT and HEA derivatives through phenotypic screening against a diverse set of protist parasites. This approach led to the identification of a number of compounds that exhibited significant effects on the survival of Entamoeba histolytica, Trypanosoma brucei, and multiple life-cycle stages of Leishmania spp. The Leishmania hits were pursued due to the pressing necessity to expand our repertoire of reliable, cost-effective, and efficient medications for the treatment of leishmaniases. Antileishmanials must possess the essential capability to efficiently penetrate the host cells and their compartments in the disease context, to effectively eliminate the intracellular parasite. Hence, we performed a study to assess the effectiveness of eradicating L. infantum intracellular amastigotes in a model of macrophage infection. Among eleven L. infantum growth inhibitors with low-micromolar potency, PHT-39, which carries a trifluoromethyl substitution, demonstrated the highest efficacy in the intramacrophage assay, with an EC50 of 1.2 +/- 3.2 μM. Cytotoxicity testing of PHT-39 in HepG2 cells indicated a promising selectivity of over 90-fold. A chemogenomic profiling approach was conducted using an orthology-based method to elucidate the mode of action of PHT-39. This genome-wide RNA interference library of T. brucei identified sensitivity determinants for PHT-39, which included a P-type ATPase that is crucial for the uptake of miltefosine and amphotericin, strongly indicating a shared route for cellular entry. Notwithstanding the favourable properties and demonstrated efficacy in the Plasmodium berghei infection model, PHT-39 was unable to eradicate L. major infection in a murine infection model of cutaneous leishmaniasis. Currently, PHT-39 is undergoing derivatization to optimize its pharmacological characteristics.

Evaluation of the in vitro schistosomicidal, leishmanicidal, and trypanocidal activities of the capsaicin metabolite, Capsicum frutescens, and Capsicum baccatum extracts and of their analysis of the main constituents by HPLC/UV and CG/MS

Neglected tropical diseases are significant causes of death and temporary or permanent disability for millions living in developing countries. Unfortunately, there is no effective treatment for these diseases. Thus, this work aimed to conduct a chemical analysis using HPLC/UV and GC/MS to identify the major constituents of the hydroalcoholic extracts of Capsicum frutescens and Capsicum baccatum fruits, evaluating these extracts and their constituents' schistosomicidal, leishmanicidal and trypanocidal activities. The results obtained for the extracts of C. frutescens are better when compared to those obtained for C. baccatum, which can be related to the different concentrations of capsaicin (1) present in the extracts. The lysis of trypomastigote forms results for capsaicin (1) led to a significant value of IC50 = 6.23 µM. Thus, the results point to capsaicin (1) as a possible active constituent in these extracts.

In silico and in vitro potentials of crocin and amphotericin B on Leishmania major: Multiple synergistic mechanisms of actions

A significant barrier to optimal antileishmanial treatment is low efficacy and the emergence of drug resistance. Multiple approaches were used to monitor and assess crocin (a central component of saffron) mixed with amphotericin B (AmpB) potential in silico and in vitro consequences. The binding behavior of crocin and iNOS was the purpose of molecular docking. The results showed that crocin coupled with AmpB demonstrated a safe combination, extremely antileishmanial, suppressed Leishmania arginase absorption, and increased parasite death. This natural flower component is a robust antioxidant, significantly promoting the expression of the Th1-connected cytokines (IL12p40, IFN-γ, and TNF- α), iNOS, and transcription factors (Elk-1, c-Fos, and STAT-1). In comparison, the expression of the Th2-associated phenotypes (IL-10, IL-4, and TGF-β) was significantly reduced. The leishmanicidal effect of this combination was also mediated through programmed cell death (PCD), as confirmed by the manifestation of phosphatidylserine and cell cycle detention at the sub-GO/G1 phase. In conclusion, crocin with AmpB synergistically exerted in vitro antileishmanial action, generated nitric oxide and reactive oxygen species, modulated Th1, and Th2 phenotypes and transfer factors, enhanced PCD profile and arrested the cell cycle of Leishmania major promastigotes. The main action of crocin and AmpB involved wide-ranging mechanistic insights for conducting other clinical settings as promising drug candidates for cutaneous leishmaniasis. Therefore, this combination could be esteemed as a basis for a potential bioactive component and a logical source for leishmanicidal drug development against CL in future advanced clinical settings.

Immunotherapy and immunochemotherapy in combating visceral leishmaniasis

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

Immunotherapies against human bacterial and fungal infectious diseases: A review

Nations' ongoing struggles with a number of novel and reemerging infectious diseases, including the ongoing global health issue, the SARS-Co-V2 (severe acute respiratory syndrome coronavirus 2) outbreak, serve as proof that infectious diseases constitute a serious threat to the global public health. Moreover, the fatality rate in humans is rising as a result of the development of severe infectious diseases brought about by multiple drug-tolerant pathogenic microorganisms. The widespread use of traditional antimicrobial drugs, immunosuppressive medications, and other related factors led to the establishment of such drug resistant pathogenic microbial species. To overcome the difficulties commonly encountered by current infectious disease management and control processes, like inadequate effectiveness, toxicities, and the evolution of drug tolerance, new treatment solutions are required. Fortunately, immunotherapies already hold great potential for reducing these restrictions while simultaneously expanding the boundaries of healthcare and medicine, as shown by the latest discoveries and the success of drugs including monoclonal antibodies (MAbs), vaccinations, etc. Immunotherapies comprise methods for treating diseases that specifically target or affect the body's immune system and such immunological procedures/therapies strengthen the host's defenses to fight those infections. The immunotherapy-based treatments control the host's innate and adaptive immune responses, which are effective in treating different pathogenic microbial infections. As a result, diverse immunotherapeutic strategies are being researched more and more as alternative treatments for infectious diseases, leading to substantial improvements in our comprehension of the associations between pathogens and host immune system. In this review we will explore different immunotherapies and their usage for the assistance of a broad spectrum of infectious ailments caused by various human bacterial and fungal pathogenic microbes. We will discuss about the recent developments in the therapeutics against the growing human pathogenic microbial diseases and focus on the present and future of using immunotherapies to overcome these diseases. Graphical AbstractThe graphical abstract shows the therapeutic potential of different types of immunotherapies like vaccines, monoclonal antibodies-based therapies, etc., against different kinds of human Bacterial and Fungal microbial infections.

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.

Chromosome-Scale Assembly of the Complete Genome Sequence of Leishmania (Mundinia) procaviensis Isolate 253, Strain LV425

Leishmania (Mundinia) procaviensis is a parasitic kinetoplastid that was first isolated from a rock hyrax in Namibia in 1975. We present the complete genome sequence of Leishmania (Mundinia) procaviensis isolate 253, strain LV425, sequenced using combined short- and long-read technologies. This genome will contribute to our understanding of hyraxes as a Leishmania reservoir.

In Vitro Determination of Antileshmanial Activities of Benzimidazolium Derivatives on L. major Promastigotes and Amastigotes

PURPOSE

Leishmaniasis is a serious public health problem infecting millions of people worldwide. An effective and reliable treatment method to be used in the treatment of the disease has not been developed yet.

METHODS

In this article, the anti-leishmanial activities of two benzimidazolium derivatives (B.A and B.B) against Leishmania major promastigotes and amastigotes, which are known to cause cutaneous leishmaniasis, were investigated for the first time. The immunostimulatory activity of the developed formulations was determined using the J774 murine macrophage cell line.

RESULTS

B.A and B.B compounds were found to have a much higher cytotoxic effect than Amphotericin B (IC₅₀ value 0.75 μM ± 0.03), which is used as the reference drug. The IC₅₀ value was determined as 2.02 µM ± 0.52 for B.A and 1.83 µM ± 0.71 for B.B in Leishmania promastigotes. In addition, IC₅₀ values of B. A and B.B Leishmania amastigotes were found to be 1.01 µM and 0.67 µM, respectively. It was found that B.B was 81.12 times more selective than Amphotericin B and showed the highest selectivity against L. major promastigotes (359.09) and amastigotes (980.80). Considering the selectivity indices (SI) of B.A and B.B, both compounds tested are more promising than Amphotericin B.

CONCLUSION

The results showed that benzimidazolium derivatives have anti-leishmanial potential against L. major, which is the causative agent of cutaneous leishmaniasis. Thus, we can say that the obtained results will help the development of effective and safe antileishmanial drug formulations against cutaneous leishmaniasis.

In vitro and in vivo therapeutic antileishmanial potential of ellagic acid against Leishmania donovani in murine model

Parasite of genus Leishmania viz. L. donovani and L. infantum cause visceral leishmaniasis (VL) or Kala-azar, systemic disease with significant enlargement of the liver and spleen, weight loss, anemia, fever and immunosuppression. The silent expansion of vectors, reservoir hosts and resistant strains is also of great concern in VL control. Considering all these issues, the present study focused on in vitro and in vivo antileishmanial screening of ellagic acid (EA) against L. donovani. The in vitro study was performed against the protozoan parasite L. donovani and a 50% inhibitory concentration was calculated. The DNA arrest in the sub-G0/G1 phase of the cell cycle was studied. In vivo studies included the assessment of parasite burden and immunomodulation in response to treatment of ellagic acid in BALB/c mice. The levels of Th1 and Th2 cytokines and isotype antibodies were assessed in different groups of mice. EA showed in vitro parasiticidal activity with IC₅₀ 18.55 µg/mL and thwarted cell-cycle progression at the sub-G0/G1 phase. Administration of ellagic acid to the BALB/c mice reported diminution of splenic and hepatic parasite burden coupled with an expansion of CD4⁺ and CD8⁺ T lymphocytes. EA further potentiated a protective immune response with augmentation of Th1 type immune response evidenced by elevation of serum IgG2a levels and DTH response. EA was reported to be safe and non-toxic to the THP-1 cell line as well as to the liver and kidneys of mice. These findings endorse the therapeutic potential of EA with significant immunomodulation and can serve as a promising agent against this debilitating parasitic disease.

Unraveling the role of natural killer cells in leishmaniasis

NK cells are known as frontline responders that are efficient in combating several maladies as well as leishmaniasis caused by Leishmania spp. As such they are being investigated to be used for adoptive transfer therapy and vaccine. In spite of the lack of antigen-specific receptors at their surface, NK cells can selectively recognize pathogens, accomplished by the activation of the receptors on the NK cell surface and also as the result of their effector functions. Activation of NK cells can occur through interaction between TLR-2 expressed on NK cells and. LPG of Leishmania parasites. In addition, NK cell activation can occur by cytokines (e.g., IFN-γ and IL-12) that also lead to producing cytokines and chemokines and lysis of target cells. This review summarizes several evidences that support NK cells activation for controlling leishmaniasis and the potentially lucrative roles of NK cells during leishmaniasis. Furthermore, we discuss strategies of Leishmania parasites in inhibiting NK cell functions. Leishmania LPG can utilizes TLR2 to evade host-immune responses. Also, Leishmania GP63 can directly binds to NK cells and modulates NK cell phenotype. Finally, this review analyzes the potentialities to harness NK cells effectiveness in therapy regimens and vaccinations.

Leishmania Vaccines: the Current Situation with Its Promising Aspect for the Future

Leishmaniasis is a serious parasitic disease caused by Leishmania spp. transmitted through sandfly bites. This disease is a major public health concern worldwide. It can occur in 3 different clinical forms: cutaneous, mucocutaneous, and visceral Leishmaniasis (CL, MCL, and VL, respectively), caused by different Leishmania spp. Currently, licensed vaccines are unavailable for the treatment of human Leishmaniasis. The treatment and prevention of this disease rely mainly on chemotherapeutics, which are highly toxic and have an increasing resistance problem. The development of a safe, effective, and affordable vaccine for all forms of vector-borne disease is urgently needed to block transmission of the parasite between the host and vector. Immunological mechanisms in the pathogenesis of Leishmaniasis are complex. IL-12-driven Th1-type immune response plays a crucial role in host protection. The essential purpose of vaccination is to establish a protective immune response. To date, numerous vaccine studies have been conducted using live/attenuated/killed parasites, fractionated parasites, subunits, recombinant or DNA technology, delivery systems, and chimeric peptides. Most of these studies were limited to animals. In addition, standardization has not been achieved in these studies due to the differences in the virulence dynamics of the Leishmania spp. and the feasibility of the adjuvants. More studies are needed to develop a safe and effective vaccine, which is the most promising approach against Leishmania infection.

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.

Immunotherapy for visceral leishmaniasis: A trapeze of balancing counteractive forces

The protozoan parasite Leishmania donovani, residing and replicating within the cells of the monocyte-macrophage (mono-mac) lineage, causes visceral leishmaniasis (VL) in humans. While, Leishmania infantum, is the main causative agent for zoonotic VL, where dogs are the main reservoirs of the disease. The chemotherapy is a serious problem because of restricted repertoire of drugs, drug-resistant parasites, drug-toxicity and the requirement for parenteral administration, which is a problem in resource-starved countries. Moreover, immunocompromised individuals, particularly HIV-1 infected are at higher risk of VL due to impairment in T-helper cell and regulatory cell responses. Furthermore, HIV-VL co-infected patients report poor response to conventional chemotherapy. Recent efforts are therefore directed towards devising both prophylactic and therapeutic immunomodulation. As far as prophylaxis is concerned, although canine vaccines for the disease caused by Leishmania infantum or Leishmania chagasi are available, no vaccine is available for use in humans till date. Therefore, anti-leishmanial immunotherapy triggering or manipulating the host's immune response is gaining momentum during the last two decades. Immunomodulators comprised of small molecules, anti-leishmanial peptides, complex ligands for host receptors, cytokines or their agonists and antibodies have been given trials both in experimental models and in humans. However, the success of immunotherapy in humans remains a far-off target. We, therefore, propose that devising a successful immunotherapy is an act of balancing enhanced beneficial Leishmania-specific responses and deleterious immune activation/hyperinflammation just as the swings in a trapeze.

Homology Modeling, de Novo Design of Ligands, and Molecular Docking Identify Potential Inhibitors of Leishmania donovani 24-Sterol Methyltransferase

The therapeutic challenges pertaining to leishmaniasis due to reported chemoresistance and toxicity necessitate the need to explore novel pathways to identify plausible inhibitory molecules. Leishmania donovani 24-sterol methyltransferase (LdSMT) is vital for the synthesis of ergosterols, the main constituents of Leishmania cellular membranes. So far, mammals have not been shown to possess SMT or ergosterols, making the pathway a prime candidate for drug discovery. The structural model of LdSMT was elucidated using homology modeling to identify potential novel 24-SMT inhibitors via virtual screening, scaffold hopping, and de-novo fragment-based design. Altogether, six potential novel inhibitors were identified with binding energies ranging from −7.0 to −8.4 kcal/mol with e-LEA3D using 22,26-azasterol and S1–S4 obtained from scaffold hopping via the ChEMBL, DrugBank, PubChem, ChemSpider, and ZINC15 databases. These ligands showed comparable binding energy to 22,26-azasterol (−7.6 kcal/mol), the main inhibitor of LdSMT. Moreover, all the compounds had plausible ligand efficiency-dependent lipophilicity (LELP) scores above 3. The binding mechanism identified Tyr92 to be critical for binding, and this was corroborated via molecular dynamics simulations and molecular mechanics Poisson–Boltzmann surface area (MM-PBSA) calculations. The ligand A1 was predicted to possess antileishmanial properties with a probability of activity (Pa) of 0.362 and a probability of inactivity (Pi) of 0.066, while A5 and A6 possessed dermatological properties with Pa values of 0.205 and 0.249 and Pi values of 0.162 and 0.120, respectively. Structural similarity search via DrugBank identified vabicaserin, daledalin, zanapezil, imipramine, and cefradine with antileishmanial properties suggesting that the de-novo compounds could be explored as potential antileishmanial agents.

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.

Mechanobiology of immune cells: Messengers, receivers and followers in leishmaniasis aiding synthetic devices

Cytokines are influential molecules which can direct cells behavior. In this review, cytokines are referred as messengers, immune cells which respond to cytokine stimulus are referred as receivers and the immune cells which gets modulated due to their plasticity induced by infectious pathogen leishmania, are referred as followers. The advantage of plasticity of cells is taken by the parasite to switch them from parasite eliminating form to parasite survival favoring form through a process called as reciprocity which is undergone by cytokines, wherein pro-inflammatory to anti-inflammatory switch occur rendering immune cell population to switch their phenotype. Detailed study of this switch can help in identification of important targets which can help in restoring the phenotype to parasite eliminating form and this can be done through synthetic circuit, finding its wider applicability in therapeutics.

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Cytokines as messengers for governing reciprocity in infection.

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Leishmania induces reciprocity modulating the immune cells plasticity.

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Reciprocity of cytokines identifies important target for therapeutics.

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Therapeutic targets aiding the design of synthetic devices to combat infection.

Chromosome-Scale Assembly of the Complete Genome Sequence of Leishmania (Mundinia) orientalis, Isolate LSCM4, Strain LV768

Leishmania (Mundinia) orientalis is a kinetoplastid parasite first isolated in 2014 in Thailand. We report the complete genome sequence of L. (M.) orientalis, sequenced using combined short-read and long-read technologies. This will facilitate greater understanding of this novel pathogen and its relationship to other members of the subgenus Mundinia.

Exploring Innovative Leishmaniasis Treatment: Drug Targets from Pre-Clinical to Clinical Findings

Leishmaniasis is a group of tropical diseases caused by parasitic protozoa belonging to the genus Leishmania. The disease is categorized in cutaneous leishmaniasis (CL), mucocutaneous leishmaniasis (MCL), and visceral leishmaniasis (VL). The conventional treatment is complex and can present high toxicity and therapeutic failures. Thus, there is a continuing need to develop new treatments. In this review, we focus on the novel molecules described in the literature with potential leishmanicidal activity, categorizing them in pre-clinical (in vitro, in vivo), drug repurposing and clinical research.

Identification of 3-Methoxycarpachromene and Masticadienonic Acid as New Target Inhibitors against Trypanothione Reductase from Leishmania Infantum Using Molecular Docking and ADMET Prediction

Polyphenolic and Terpenoids are potent natural antiparasitic compounds. This study aimed to identify new drug against Leishmania parasites, leishmaniasis’s causal agent. A new in silico analysis was accomplished using molecular docking, with the Autodock vina program, to find the binding affinity of two important phytochemical compounds, Masticadienonic acid and the 3-Methoxycarpachromene, towards the trypanothione reductase as target drugs, responsible for the defense mechanism against oxidative stress and virulence of these parasites. There were exciting and new positive results: the molecular docking results show as elective binding profile for ligands inside the active site of this crucial enzyme. The ADMET study suggests that the 3-Methoxycarpachromene has the highest probability of human intestinal absorption. Through this work, 3-Methoxycarpachromene and Masticadienonic acid are shown to be potentially significant in drug discovery, especially in treating leishmaniasis. Hence, drug development should be completed with promising results.

Adjuvant effects of TLR agonist gardiquimod admixed with Leishmania vaccine in mice model of visceral leishmaniasis

Tropical and subtropical areas of the world are affected by leishmaniasis, which is caused by Leishmania spp. It has been categorized as an NTD (neglected tropical disease) because of its negligence. The sand fly of genus Phlebotomus acts as the vector for the transmission of the promastigote form of this protozoan parasite to the mammalian host where it converts to amastigote form in the macrophages. Visceral form of leishmaniasis (VL) is a deadly infection in the endothelial system of the human and other mammals. Only a few chemotherapeutic agents are available for the treatment of this infectious disease whereas no vaccine is available for the control of leishmanial infection. Therefore in the current study, we have tested the effects of gardiquimod (a TLR agonist) as an adjuvant in combination with the formalin-killed antigen of L. donovani as a vaccine. The mice were vaccinated thrice at an interval of 2 weeks and challenged with L. donovani promastigotes after 2 weeks of the last vaccination. We assessed the parasite load, delayed-type hypersensitivity (DTH) responses, humoral and cell-mediated immune response in BALB/c mice before and after challenge infection with L. donovani. Immunized mice were found to have the least parasite load, high DTH response, elevated levels of Th1 cytokines, IgG2a, and nitric oxide than non-immunized and infected control mice. The efficacy of the vaccine was boosted with the use of adjuvant gardiquimod that depicts its potential as an adjuvant in this study. Our study is reporting the adjuvant effects of gardiquimod for the first time. Further studies using other Leishmania species can be performed to signify its role.

Visualizing the In Vivo Dynamics of Anti-Leishmania Immunity: Discoveries and Challenges

Intravital microscopy, such as 2-photon microscopy, is now a mainstay in immunological research to visually characterize immune cell dynamics during homeostasis and pathogen infections. This approach has been especially beneficial in describing the complex process of host immune responses to parasitic infections in vivo, such as Leishmania. Human-parasite co-evolution has endowed parasites with multiple strategies to subvert host immunity in order to establish chronic infections and ensure human-to-human transmission. While much focus has been placed on viral and bacterial infections, intravital microscopy studies during parasitic infections have been comparatively sparse. In this review, we will discuss how in vivo microscopy has provided important insights into the generation of innate and adaptive immunity in various organs during parasitic infections, with a primary focus on Leishmania. We highlight how microscopy-based approaches may be key to providing mechanistic insights into Leishmania persistence in vivo and to devise strategies for better parasite control.

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

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

Immunotherapy in treatment of leishmaniasis

Leishmaniasis caused by various species of protozoan transmitted by sand fly vectors occurs as a spectrum of clinical features including cutaneous, mucocutaneous and visceral forms. It is a geographically distributed parasitic disease and a major public health problem in the world. The clinical syndromes are highly variable depending on the parasite species, host genetics, vectors and environment. To date, there is no effective vaccine and traditional treatments are toxic, expensive with long administration duration and many adverse side effects and/or drug resistance. Instead of treatments based on chemotherapy, certain strategies aim to recover leishmaniasis and reduce the parasitic burden. Immunotherapy has focused on the induction of effective immune response to rapidly control the disease. Recent studies have indicated that a single dose of a suitable therapeutic vaccine induces a quick and lasting recovery in patients. Immunotherapy reduces the toxicity of drug and the emergence of resistance dramatically. It could be an effective addition to chemotherapy with a safe and potent drug compared with monotherapy, resulting in a prophylactic and therapeutic cure of leishmaniasis. This review has focused on treatment of leishmaniasis with particular emphasis on immunotherapy as an alternative to conventional drug treatment.

Recent advances in immunotherapies against infectious diseases

Immunotherapies are disease management strategies that target or manipulate components of the immune system. Infectious diseases pose a significant threat to human health as evidenced by countries continuing to grapple with several emerging and re-emerging diseases, the most recent global health threat being the SARS-CoV2 pandemic. As such, various immunotherapeutic approaches are increasingly being investigated as alternative therapies for infectious diseases, resulting in significant advances towards the uncovering of pathogen-host immunity interactions. Novel and innovative therapeutic strategies are necessary to overcome the challenges typically faced by existing infectious disease prevention and control methods such as lack of adequate efficacy, drug toxicity, and the emergence of drug resistance. As evidenced by recent developments and success of pharmaceuticals such as monoclonal antibodies (mAbs), immunotherapies already show abundant promise to overcome such limitations while also advancing the frontiers of medicine. In this review, we summarize some of the most notable inroads made to combat infectious disease, over mainly the last 5 years, through the use of immunotherapies such as vaccines, mAb-based therapies, T-cell-based therapies, manipulation of cytokine levels, and checkpoint inhibition. While its most general applications are founded in cancer treatment, advances made towards the curative treatment of human immunodeficiency virus, tuberculosis, malaria, zika virus and, most recently COVID-19, reinforce the role of immunotherapeutic strategies in the broader field of disease control. Ultimately, the comprehensive specificity, safety, and cost of immunotherapeutics will impact its widespread implementation.

Central and local controls of monocytopoiesis influence the outcome of Leishmania infection

Leishmaniases represent a complex of tropical and subtropical diseases caused by an intracellular protozoon of the genus Leishmania. The principal cells controlling the interaction between the host and the parasite Leishmania are monocytes and macrophages, as these cells play a decisive role in establishing the pathogenesis or cure. These cells are involved in controlling the growth of Leishmania and in modulating the adaptive immune responses. The heterogeneity and extensive plasticity of monocytes allow these cells to adjust their functional phenotypes in response to the pathogen-directed immunological cues. In Leishmania-infected host, the rate of myelopoiesis is augmented by enhanced monocytic lineage commitment and proliferation of myeloid progenitor cells both in the BM and at the site of infection. These newly generated monocytes play as "safe haven" for the parasite and also as the antigen-presenting cells for T cells to cause deregulated cytokine production. This altered monocytopoiesis is characterized by tissue-specific immune responses, spatiotemporal dynamics of immunoregulation and functional heterogeneity. In the presence of Th1 cytokines, monocytes exhibit a pro-inflammatory phenotype that protects the host from Leishmania. By contrast, in an environment of Th2 cytokines, monocytes display anti-inflammatory phenotype with pro-parasitic functions. In this review, we summarize the involvement of cytokines in the regulation of monocytopoiesis and differentiation of macrophages during leishmanial infection. Understanding the role of cytokines in regulating interactions between Leishmania and the host monocytes is key to developing new therapeutic interventions against leishmaniases.