Dendritic Cells Pulsed with Peptides of GP63 Induce Differential Protection against Experimental Cutaneous Leishmaniasis

Anti-leishmanial therapy: Caught between drugs and immune targets

Leishmaniasis is an enigmatic disease that has very restricted options for chemotherapy and none for prophylaxis. As a result, deriving therapeutic principles for curing the disease has been a major objective in Leishmania research for a long time. Leishmania is a protozoan parasite that lives within macrophages by subverting or switching cell signaling to the pathways that ensure its intracellular survival. Therefore, three groups of molecules aimed at blocking or eliminating the parasite, at least, in principle, include blockers of macrophage receptor- Leishmania ligand interaction, macrophage-activating small molecules, peptides and cytokines, and signaling inhibitors or activators. Macrophages also act as an antigen-presenting cell, presenting antigen to the antigen-specific T cells to induce activation and differentiation of the effector T cell subsets that either execute or suppress anti-leishmanial functions. Three groups of therapeutic principles targeting this sphere of Leishmania-macrophage interaction include antibodies that block pro-leishmanial response of T cells, ligands that activate anti-leishmanial T cells and the antigens for therapeutic vaccines. Besides these, prophylactic vaccines have been in clinical trials but none has succeeded so far. Herein, we have attempted to encompass all these principles and compose a comprehensive review to analyze the feasibility and adoptability of different therapeutics for leishmaniasis.

Host-directed antileishmanial interventions: Harvesting unripe fruits to reach fruition

Leishmaniasis is an exemplary paradigm of immune evasion, fraught with the perils of limited clinical assistance, escalating costs of treatment and made worse with the lack of suitable vaccine. While drugs remain central to large-scale disease control, the growing emergence of parasite resistance necessitates the need for combination therapy involving host-directed immunological agents. Also, since prolonged disease progression is associated with strong immune suppression of the host, augmentation of host immunity via restoration of the immunoregulatory circuit involving antigen-presenting cells and T-cells, activation of macrophage function and/or CD4⁺ T helper 1 cell differentiation may serve as an ideal approach to resolve severe cases of leishmaniasis. As such, therapies that embody a synergistic approach that involve direct killing of the parasite in addition to elevating host immunity are likely to pave the way for widespread elimination of leishmaniasis in the future. With this review, we aim to recapitulate the various immunotherapeutic agents found to hold promise in antileishmanial treatment both in vitro and in vivo. These include parasite-specific antigens, dendritic cell-targeted therapy, recombinant inhibitors of various components intrinsic to immune cell signaling and agonists or antagonists to immune cells and cytokines. We also summarize their abilities to direct therapeutic skewing of the host cell-immune response and review their potential to combat the disease either alone, or as adjunct modalities.

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.

Vaccination in Leishmaniasis: A Review Article

Leishmaniasis is caused by protozoan Leishmania parasites that are transmitted through female sandfly bites. The disease is predominantly endemic to the tropics and semi-tropics and has been reported in more than 98 countries. Due to the side effects of anti-Leishmania drugs and the emergence of drug-resistant isolates, there is currently no encouraging prospect of introducing an effective therapy for the disease. Hence, it seems that the key to disease control management is the introduction of an effective vaccine, particularly against its cutaneous form. Advances in understanding underlying immune mechanisms are feasibale using a variety of candidate antigens, including attenuated live parasites, crude antigens, pure or recombinant Leishmania proteins, Leishmania genes encoding protective proteins, as well as immune system activators from the saliva of parasite vectors. However, there is still no vaccine against different types of human leishmaniasis. In this study, we review the works conducted or being performed in this field.

Evaluation of protection induced by in vitro maturated BMDCs presenting CD8+ T cell stimulating peptides after a heterologous vaccination regimen in BALB/c model against Leishmania major

Leishmaniasis is a complex vector-borne disease mediated by Leishmania parasite and a strong and long-lasting CD4⁺ Th1 and CD8⁺-T cell immunity is required to control the infection. Thus far multivalent subunit vaccines have met this requirement more promisingly. However several full protein sequences cannot be easily arranged in one construct. Instead, new emerging immune-informatics based epitope formulations surpass this restriction. Herein, we aimed to examine the protective potential of a dendritic cell based vaccine presenting epitopes to CD8⁺ and CD4⁺-T cells in combination with DNA vaccine encoding the same epitopes against murine cutaneous leishmaniasis. Immature DCs were loaded with epitopes (selected from parasite proteome) in vitro with or without CpG oligonucleotides and were used to immunize BALB/c mice. Peptide coding DNA was used to boost the system and immunological responses were evaluated after Leishmania (L.) major infectious challenge. The pre-challenge response to included epitopes was Th1 polarized which potentially lowered the infection at early time points post-challenge but not at later weeks. Collectively, DC prime-DNA boost was found to be a promising approach for Th1 polarization however the constituent epitopes undoubtedly make a significant contribution in the protection outcome of the vaccine.

Anti-Leishmanial Vaccines: Assumptions, Approaches, and Annulments

Leishmaniasis is a neglected protozoan parasitic disease that occurs in 88 countries but a vaccine is unavailable. Vaccination with live, killed, attenuated (physically or genetically) Leishmania have met with limited success, while peptide-, protein-, or DNA-based vaccines showed promise only in animal models. Here, we critically assess several technical issues in vaccination and expectation of a host-protective immune response. Several studies showed that antigen presentation during priming and triggering of the same cells in infected condition are not comparable. Altered proteolytic processing, antigen presentation, protease-susceptible sites, and intracellular expression of pathogenic proteins during Leishmania infection may vary dominant epitope selection, MHC-II/peptide affinity, and may deter the reactivation of desired antigen-specific T cells generated during priming. The robustness of the memory T cells and their functions remains a concern. Presentation of the antigens by Leishmania-infected macrophages to antigen-specific memory T cells may lead to change in the T cells' functional phenotype or anergy or apoptosis. Although cells may be activated, the peptides generated during infection may be different and cross-reactive to the priming peptides. Such altered peptide ligands may lead to suppression of otherwise active antigen-specific T cells. We critically assess these different immunological issues that led to the non-availability of a vaccine for human use.

Peptide Vaccines for Leishmaniasis

Due to an increase in the incidence of leishmaniases worldwide, the development of new strategies such as prophylactic vaccines to prevent infection and decrease the disease have become a high priority. Classic vaccines against leishmaniases were based on live or attenuated parasites or their subunits. Nevertheless, the use of whole parasite or their subunits for vaccine production has numerous disadvantages. Therefore, the use of Leishmania peptides to design more specific vaccines against leishmaniases seems promising. Moreover, peptides have several benefits in comparison with other kinds of antigens, for instance, good stability, absence of potentially damaging materials, antigen low complexity, and low-cost to scale up. By contrast, peptides are poor immunogenic alone, and they need to be delivered correctly. In this context, several approaches described in this review are useful to solve these drawbacks. Approaches, such as, peptides in combination with potent adjuvants, cellular vaccinations, adenovirus, polyepitopes, or DNA vaccines have been used to develop peptide-based vaccines. Recent advancements in peptide vaccine design, chimeric, or polypeptide vaccines and nanovaccines based on particles attached or formulated with antigenic components or peptides have been increasingly employed to drive a specific immune response. In this review, we briefly summarize the old, current, and future stands on peptide-based vaccines, describing the disadvantages and benefits associated with them. We also propose possible approaches to overcome the related weaknesses of synthetic vaccines and suggest future guidelines for their development.

Extracellular Expression in Aspergillus niger of an Antibody Fused to Leishmania sp. Antigens

Nucleoside hydrolase and sterol 24-c-methyltransferase, two antigenic proteins of Leishmania sp., were expressed in Aspergillus niger. Genetic transformation of conidia was achieved using underwater shock waves. scFv antibody addressed to DEC205, a receptor of dendritic cells, was fused to two proteins of Leishmania sp. Receptor 205 has a relevant role in the immune system in mammals; it can modulate T cell response to different antigens. Extracellular expression strategy of recombinant antibody was achieved using a fragment of native glucoamylase A (514 aa) as a carrier. Fermentations in shake flasks showed that the recombinant protein (104 kDa) was expressed and secreted only when maltose was used as carbon source; on the contrary, the expression was highly repressed in presence of xylose. Noteworthy, recombinant protein was secreted without glucoamylase-carrier and accumulation at intracellular level was not observed. The results presented here demonstrate the high value of Aspergillus niger as biotechnological platform for recombinant antibodies against Leishmania sp. at low cost. To the best of our knowledge, this is the first report about the recombinant expression of antigenic proteins of Leishmania sp. in filamentous fungi. The protein obtained can be used to explore novel strategies to induce immunity against Leishmania sp. or it can be employed in diagnostic kits to detect this neglected disease.

Overview of dendritic cell-based vaccine development for leishmaniasis

Leishmaniasis is one of the most serious vector-borne diseases in the world and is distributed over 98 countries. It is estimated that 350 million people are at risk for leishmaniasis. There are three different generation of vaccines that have been developed to provide immunity and protection against leishmaniasis. However, their use has been limited due to undesired side effects. These vaccines have also failed to provide effective and reliable protection and, as such, currently, there is no safe and effective vaccine for leishmaniasis. Dendritic cells (DCs) are a unique population of cells that come from bone marrow and become specialized to take up, process and present antigens to helper T cells in a mechanism similar to macrophages. By considering these significant features, DCs stimulated with different kinds of Leishmania antigens have been used in recent vaccine studies for leishmaniasis with promising results so far. In this review, we aim to review and combine the latest studies about this issue after defining potential problems in vaccine development for leishmaniasis and considering the importance of DCs in the immunopathogenesis of the disease.

Dendritic Cells and Leishmania Infection: Adding Layers of Complexity to a Complex Disease

Leishmaniasis is a group of neglected diseases whose clinical manifestations depend on factors from the host and the pathogen. It is an important public health problem worldwide caused by the protozoan parasite from the Leishmania genus. Cutaneous Leishmaniasis (CL) is the most frequent form of this disease transmitted by the bite of an infected sandfly into the host skin. The parasites can be uptook and/or recognized by macrophages, neutrophils, and/or dendritic cells (DCs). Initially, DCs were described to play a protective role in activating the immune response against Leishmania parasites. However, several reports showed a dichotomic role of DCs in modulating the host immune response to susceptibility or resistance in CL. In this review, we discuss (1) the interactions between DCs and parasites from different species of Leishmania and (2) the crosstalk of DCs and other cells during CL infection. The complexity of these interactions profoundly affects the adaptive immune response and, consequently, the disease outcome, especially from Leishmania species of the New World.

Leishmania infantum FML pulsed-dendritic cells induce a protective immune response in murine visceral leishmaniasis

AIM

To investigate the efficacy of FML loaded dendritic cells (DCs) in protection against visceral leishmaniasis.

MATERIALS & METHODS

Mice were immunized with FML- or soluble Leishmania antigen-loaded DCs as well as FML or soluble Leishmania antigen in saponin and challenged with parasite. The levels of cytokines before and after challenge were detected by ELISA. Parasite burden (total Leishman-Donovan unit) was determined after parasite challenge.

RESULTS

FML-saponin induced the highest IFN-γ/IL-4 ratio among vaccinated groups, though this ratio was higher in FML-loaded DCs group subsequent to challenge with Leishmania infantum. Moreover, the greatest reduction in parasite number was detected in mice vaccinated with FML-loaded DCs compared with phosphate-buffered saline-treated mice (p = 0.002).

CONCLUSION

FML-loaded DCs are one of the promising tools for protection against murine visceral leishmaniasis.

Vaccine Development Against Leishmania donovani

Visceral leishmaniasis (VL) caused by Leishmania donovani and Leishmania infantum/chagasi represents the second most challenging infectious disease worldwide, leading to nearly 500,000 new cases and 60,000 deaths annually. Zoonotic VL caused by L. infantum is a re-emergent canid zoonoses which represents a complex epidemiological cycle in the New world where domestic dogs serve as a reservoir host responsible for potentially fatal human infection and where dog culling is the only measure for reservoir control. Life-long immunity to VL has motivated development of prophylactic vaccines against the disease but very few have progressed beyond the experimental stage. No licensed vaccine is available till date against any form of leishmaniasis. High toxicity and increasing resistance to the current chemotherapeutic regimens have further complicated the situation in VL endemic regions of the world. Advances in vaccinology, including recombinant proteins, novel antigen-delivery systems/adjuvants, heterologous prime-boost regimens and strategies for intracellular antigen presentation, have contributed to recent advances in vaccine development against VL. Attempts to develop an effective vaccine for use in domestic dogs in areas of canine VL should be pursued for preventing human infection. Studies in animal models and human patients have revealed the pathogenic mechanisms of disease progression and features of protective immunity. This review will summarize the accumulated knowledge of pathogenesis, immune response, and prerequisites for protective immunity against human VL. Authors will discuss promising vaccine candidates, their developmental status and future prospects in a quest for rational vaccine development against the disease. In addition, several challenges such as safety issues, renewed and coordinated commitment to basic research, preclinical studies and trial design will be addressed to overcome the problems faced in developing prophylactic strategies for protection against this lethal infection.

Cellular vaccination with bone marrow-derived dendritic cells pulsed with a peptide of Leishmania infantum KMP-11 and CpG oligonucleotides induces protection in a murine model of visceral leishmaniasis

The use of dendritic cells (DCs) pulsed with defined Leishmania antigens could be a potential immune intervention tool for the induction of protection against infection. In the present study, bone marrow-derived DCs (BM-DCs) pulsed ex vivo with the peptide 12-31aa portion of kinetoplastid membrane protein (KMP)-11 (KMP-11(12-31aa) peptide) acquired a semimature phenotype expressing IL-12 and IL-10, whereas pulsing with the combination of the peptide and CpG oligodeoxynucleotides (ODNs) resulted in their functional maturation expressing mainly IL-12. Vaccination of genetically susceptible to parasite BALB/c mice with both peptide-pulsed BM-DCs elicited a peptide-specific mixed Th1/Th2 immune response, characterized by the production of IFNγ, IL-10 and IgG1 and IgG2a isotype antibodies. However, only BM-DCs pulsed with the combination of KMP-11(12-31aa) peptide and CpG ODNs induced the differentiation of peptide-specific Th17 cells, indicating the adjuvanticity of CpG ODNs. When BALB/c mice were vaccinated with KMP-11(12-31aa) peptide-pulsed BM-DCs, they exhibited only partial protection against Leishmania infantum challenge, whereas (KMP-11(12-31aa) peptide+CpG ODNs)-pulsed BM-DCs reduced efficiently the parasite load in visceral organs. Protective immunity was correlated with restoration of lymphoproliferative responses and a modulation of parasite-specific cellular responses towards Th1 and Th17 profile, confirmed by the isotype switching towards IgG2a, the enhanced production of IFNγ against IL-10, the absence of TGF-β and the overproduction of IL-17. Thus, ex vivo antigen-pulsed BM-DCs represent a powerful tool for the study of protective immune responses against leishmanial infection. Moreover, these findings suggest the use of BM-DCs as effective tools in antigen and adjuvant screening in the design of a protective vaccine against leishmaniasis and other pathogen-related infections.

Cutaneous leishmaniasis: progress towards a vaccine

Leishmaniases are vector-borne diseases due to the protozoan parasite Leishmania . Since no prevention method is available and as current therapy is costly, often poorly tolerated and not always efficacious, the development of alternative therapies, including vaccines, constitutes the priority in the fight of Leishmania infection. This review focuses on recent advances in the development of vaccines against leishmaniasis, with emphasis on the cutaneous form. Indeed, the fact that recovery from leishmaniasis is associated with immunity against new infection provides a rational basis for the development of vaccination strategy against infection with Leishmania . Evidence from animal studies demonstrate that protection can be achieved following infection with live-attenuated Leishmania as well as through immunization with purified proteins or DNA vaccines. In addition, recent results have shown that immunization against the saliva of the insect vector could have synergistic effects with conventional vaccination. Finally, vaccination using dendritic cells was recently demonstrated as a possible tool for Leishmania vaccination.

Leishmaniavaccines: progress and problems

Leishmaniaare protozoan parasites spread by a sandfly insect vector and causing a spectrum of diseases collectively known as leishmaniasis. The disease is a significant health problem in many parts of the world resulting in an estimated 12 million new cases each year. Current treatment is based on chemotherapy, which is difficult to administer, expensive and becoming ineffective due to the emergence of drug resistance. Leishmaniasis is considered one of a few parasitic diseases likely to be controllable by vaccination. The relatively uncomplicated leishmanial life cycle and the fact that recovery from infection renders the host resistant to subsequent infection indicate that a successful vaccine is feasible. Extensive evidence from studies in animal models indicates that solid protection can be achieved by immunisation with protein or DNA vaccines. However, to date no such vaccine is available despite substantial efforts by many laboratories. Advances in our understanding ofLeishmaniapathogenesis and generation of host protective immunity, together with the completedLeishmaniagenome sequence open new avenues for vaccine research. The major remaining challenges are the translation of data from animal models to human disease and the transition from the laboratory to the field. This review focuses on advances in anti-leishmania vaccine development over the recent years and examines current problems hampering vaccine development and implementation.

Chemokines as markers for parasite-induced inflammation and tumors

Chemokines are a group of small secreted proteins (8-10 kDa) produced and released by a wide variety of cell types. They were originally described as mediators of leukocyte recruitment, which is essential in acute and chronic inflammation. They also play a critical role in many pathophysiological processes such as allergic responses, infections and autoimmune diseases, tumor growth and hematopoietic development. This review introduces the three supergene families of chemokines (CXC, CC and C) with emphasis on their important role in different states in humans and in animal models with parasitic diseases. The concentration of transcription and translation of the cytokines and chemokines in the parasitic diseases may be an important marker for evaluation of the inflammatory state.

In vitro responses of human peripheral blood mononuclear cells to whole-cell, particulate and soluble extracts of Leishmania promastigotes

Whole-cell and soluble extracts of Leishmania promastigotes have both been used as skin test antigens and have also been tested as vaccine candidates. However, the differences in antigenicity between soluble and particulate Leishmania fractions are not known. We evaluated in vitro responses of PBMC from 30 American tegumentary leishmaniasis (ATL) patients and seven noninfected donors to different antigen preparations from Leishmania promastigotes, namely Leishmania amazonensis and L. braziliensis whole-cell extracts, as well as soluble and particulate fractions of L. amazonensis. All Leishmania antigen preparations stimulated significantly higher proliferation and interferon (IFN)-gamma production (but not interleukin (IL)-10 production) in PBMC from the leishmaniasis patients than in cells from the control subjects. The L. braziliensis whole-cell extract stimulated significantly higher cell proliferation and IFN-gamma production than the L. amazonensis whole-cell extract in the group of patients but not in the control group. This result can be explained by the fact that the patients were infected with L. braziliensis. Again in the group of patients, the PBMC proliferative responses as well as the levels of IFN-gamma and IL-10 stimulated by L. amazonensis whole-cell extract were significantly greater than those elicited by the L. amazonensis soluble fraction but were not significantly different from those elicited by the L. amazonensis particulate fraction. We found a higher antigenicity of the particulate fraction as compared to the soluble fraction, what suggests that the antigens present in the particulate fraction account for most of the antigenicity of whole-cell Leishmania promastigote antigen extracts.