An update on recombinant vaccines against leishmaniasis

Leishmaniasis is a parasitic disease caused by various species of the Leishmania parasite, manifesting in visceral (VL), cutaneous (CL), and mucocutaneous (MCL) forms. To combat this debilitating disease, various vaccines candidates including proteins, DNA, vectors, adjuvants, and recombinant whole parasites have been developed and tested experimentally and preclinically against several Leishmania species. Some vaccines have already entered human clinical trials. These vaccines aim to induce protective immunity using specific antigens. This review examines all efforts to develop recombinant vaccines against the parasite, analyzing successes including commercially available canine vaccines and the overall challenges faced in the quest to eradicate the disease. Additionally, recent advances in vaccine delivery systems, such as viral vectors and non-pathogenic bacteria, offer promising avenues to enhance immunogenicity and improve the targeted delivery of antigens, potentially leading to more effective and long-lasting immune responses. By understanding past and current efforts, future strategies can be refined to create more effective vaccines and ultimately control or eradicate this parasitic disease.

Leishmania vaccine development: A comprehensive review

Infectious diseases like leishmaniasis, malaria, HIV, tuberculosis, leprosy and filariasis are responsible for an immense burden on public health systems. Among these, leishmaniasis is under the category I diseases as it is selected by WHO (World Health Organization) on the ground of diversity and complexity. High cost, resistance and toxic effects of Leishmania traditional drugs entail identification and development of therapeutic alternative. Since the natural infection elicits robust immunity, consistence efforts are going on to develop a successful vaccine. Clinical trials have been conducted on vaccines like Leish-F1, F2, and F3 formulated using specific Leishmania antigen epitopes. Current strategies utilize individual or combined antigens from the parasite or its insect vector's salivary gland extract, with or without adjuvant formulation for enhanced efficacy. Promising animal data supports multiple vaccine candidates (Lmcen-/-, LmexCen-/-), with some already in or heading for clinical trials. The crucial challenge in Leishmania vaccine development is to translate the research knowledge into affordable and accessible control tools that refines the outcome for those who are susceptible to infection. This review focuses on recent findings in Leishmania vaccines and highlights difficulties facing vaccine development and implementation.

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.

Lipophosphoglycan-3 protein from Leishmania infantum chagasi plus saponin adjuvant: A new promising vaccine against visceral leishmaniasis

Visceral leishmaniasis (VL) is a serious neglected tropical disease that affects humans and dogs in urban areas. There are no vaccines against human VL, and few licensed canine VL vaccines are currently available, which instigates the search for new antigens and vaccine formulations with prophylactic potential against VL in these hosts. In this study, we evaluated the immunization using the native and recombinant Leishmania infantum chagasi (L. chagasi) lipophosphoglycan-3 (LPG3) and the adjuvants saponin (SAP) and incomplete Freund adjuvant (IFA) against L. chagasi infection in BALB/c mice. The native LPG3 vaccine was immunogenic, inducing splenic IFN-γ and IL-10 production, and mixed Th1/Th2 response when associated with IFA. However, only mice vaccinated with LPG3-IFA presented a reduction in the splenic parasite load (96% in comparison to the PBS control group), but without a significant reduction in the hepatic parasitism. On the other hand, mice immunized with the LPG3-SAP vaccine presented a reduction of approximately 98% in both splenic and hepatic parasite load, accompanied by a Th1/Th17 response and IL-10 production by L. chagasi antigen (AgLc)-stimulated splenic cells. Importantly, vaccination with recombinant LPG3 (rLPG3)-SAP presented similar results to the native LPG3-SAP vaccine. Therefore, the rLPG3-SAP vaccine is qualified to be used in future tests in canine and human models, considering the technical and economic advantages of the recombinant protein production compared to the native protein and the results obtained in the murine model.

Therapeutic effects of mesenchymal stem cells on cutaneous leishmaniasis lesions caused by Leishmania major

OBJECTIVES

Leishmania major (L. major) is a cutaneous leishmaniasis causative agent. Current chemotherapeutic methods are not totally effective in treatment of this disease. The immunomodulation and tissue repairing capability of mesenchymal stem cells (MSCs), ease of isolation, detection and in vitro culture, have encouraged biologists to use MSCs for cell therapy in different infections such as cutaneous leishmaniasis.

METHODS

BALB/c mice (6-8 weeks old) were infected with L. major then divided into four groups and treated with MSCs, Glucantime, Glucantime + MSCs, or PBS. Regression of lesions, potency of macrophages for phagocytosis, proliferation of immune cells against Leishmania soluble antigen, reduction of spleen parasite burden and healing of the lesions were evaluated on days 10, 20 and 30 of treatment.

RESULTS

The results indicated that the mice intralesionally injected with MSCs showed significant regression in the lesions produced by L. major by day 30. Proliferation of splenocytes stimulated with SLA (soluble leishmania antigen) in vitro in MSC-treated mice on day 20 was significantly higher than in the other groups. The potency of phagocytosis in macrophages of mice treated with MSCs was significantly higher by day 30 and healing of the lesions in this group of mice showed more progress on histopathological examinations. Spleen parasite burden showed significant reduction in the mice treated with Glucantime + MSCs by day 30.

CONCLUSIONS

The results showed that including MSCs in treatment of cutaneous leishmaniasis caused by L. major is a promising approach.

Lipophosphoglycan-3 recombinant protein vaccine controls hepatic parasitism and prevents tissue damage in mice infected by Leishmania infantum chagasi

AIMS

In this work, we aimed to evaluate the effects of the Leishmania infantum chagasi infection on the liver of vaccinated mice, considering parameters of tissue damage and the inflammatory response elicited by vaccination.

MAIN METHODS

We used recombinant LPG3 protein (rLPG3) as immunogen in BALB/c mice before challenge with promastigote forms of L. infantum chagasi. The animals were separated into five groups: NI: non-infected animals; NV: non-vaccinated; SAP: treated with saponin; rLPG3: immunized with rLPG3; rLPG3 + SAP: immunized with rLPG3 plus SAP. The experiment was conducted in replicate, and the vaccination protocol consisted of three subcutaneous doses of rLPG3 (40 μg + two boosters of 20 μg). The mice were challenged two weeks after the last immunization.

KEY FINDINGS

Our results showed that rLPG3 + SAP immunization decreased the parasite burden in 99 %, conferring immunological protection in the liver of the infected animals. Moreover, the immunization improved the antioxidant defenses, increasing CAT and GST activity, while reducing the levels of oxidative stress markers, such as H₂O₂ and NO₃/NO_2, and carbonyl protein in the organ. As a consequence, rLPG3 + SAP immunization preserved tissue integrity and reduced the granuloma formation, inflammatory infiltrate and serum levels of AST, ALT, and ALP.

SIGNIFICANCE

Taken together, these results showed that rLPG3 vaccine confers liver protection against L. infantum chagasi in mice, while maintaining the liver tissue protected against the harmful inflammatory effects caused by the vaccine followed by the infection.

Analysis of the Antigenic and Prophylactic Properties of the Leishmania Translation Initiation Factors eIF2 and eIF2B in Natural and Experimental Leishmaniasis

Different members of intracellular protein families are recognized by the immune system of the vertebrate host infected by parasites of the genus Leishmania. Here, we have analyzed the antigenic and immunogenic properties of the Leishmania eIF2 and eIF2B translation initiation factors. An in silico search in Leishmania infantum sequence databases allowed the identification of the genes encoding the α, β, and γ subunits and the α, β, and δ subunits of the putative Leishmania orthologs of the eukaryotic initiation factors F2 (LieIF2) or F2B (LieIF2B), respectively. The antigenicity of these factors was analyzed by ELISA using recombinant versions of the different subunits. Antibodies against the different LieIF2 and LieIF2B subunits were found in the sera from human and canine visceral leishmaniasis patients, and also in the sera from hamsters experimentally infected with L. infantum. In L. infantum (BALB/c) and Leishmania major (BALB/c or C57BL/6) challenged mice, a moderate humoral response against these protein factors was detected. Remarkably, these proteins elicited an IL-10 production by splenocytes derived from infected mice independently of the Leishmania species employed for experimental challenge. When DNA vaccines based on the expression of the LieIF2 or LieIF2B subunit encoding genes were administered in mice, an antigen-specific secretion of IFN-γ and IL-10 cytokines was observed. Furthermore, a partial protection against murine CL development due to L. major infection was generated in the vaccinated mice. Also, in this work we show that the LieIF2α subunit and the LieIF2Bβ and δ subunits have the capacity to stimulate IL-10 secretion by spleen cells from naïve mice. B-lymphocytes were identified as the major producers of this anti-inflammatory cytokine. Taking into account the data found in this study, it may be hypothesized that these proteins act as virulence factors implicated in the induction of humoral responses as well as in the production of the down-regulatory IL-10 cytokine, favoring a pathological outcome. Therefore, these proteins might be considered markers of disease.

Immune response to recombinant Leishmania infantum lipophosphoglycan 3 plus CpG oligodeoxynucleotides in BALB/c mice

Development of a protective antileishmanial vaccine is an urgent priority for successful control of different forms of leishmaniasis. The potential of a recombinant lipophosphoglycan 3 (rLPG3) expressed by Leishmania tarentolae was evaluated in combination with CpG oligodeoxynucleotides (CpG-ODN) as a Th1-promoting adjuvant against Leishmania infantum infection in BALB/c mice. First, mice were immunized subcutaneously with rLPG3 either alone or in combination with CpG-ODN. Next, the immunogenic and protective efficacies of this vaccine were analysed in immunized mice. It was observed that coadministration of rLPG3 with CpG-ODN led to enhance in a Th1 response to rLPG3 induced by itself as the IFN-γ production was promoted in association with the predominant presence of IgG2a antibodies in the sera. However, immunization with rLPG3 plus CpG-ODN induced partial protection against infectious challenge in BALB/c mice. Taken together, further studies are required to improve the protective efficacy using either more potent immune enhancers or vaccination strategies.

Possibilities and challenges for developing a successful vaccine for leishmaniasis

Leishmaniasis is a vector-borne disease caused by different species of protozoan parasites of the genus Leishmania. It is a major health problem yet neglected tropical diseases, with approximately 350 million people worldwide at risk and more than 1.5 million infections occurring each year. Leishmaniasis has different clinical manifestations, including visceral (VL or kala-azar), cutaneous (CL), mucocutaneous (MCL), diffuse cutaneous (DCL) and post kala-azar dermal leishmaniasis (PKDL). Currently, the only mean to treat and control leishmaniasis is by rational medications and vector control. However, the number of available drugs is limited and even these are either exorbitantly priced, have toxic side effects or prove ineffective due to the emergence of resistant strains. On the other hand, the vector control methods are not so efficient. Therefore, there is an urgent need for developing a safe, effective, and affordable vaccine for the prevention of leishmaniasis. Although in recent years a large body of researchers has concentrated their efforts on this issue, yet only three vaccine candidates have gone for clinical trial, until date. These are: (i) killed vaccine in Brazil for human immunotherapy; (ii) live attenuated vaccine for humans in Uzbekistan; and (iii) second-generation vaccine for dog prophylaxis in Brazil. Nevertheless, there are at least half a dozen vaccine candidates in the pipeline. One can expect that, in the near future, the understanding of the whole genome of Leishmania spp. will expand the vaccine discovery and strategies that may provide novel vaccines. The present review focuses on the development and the status of various vaccines and potential vaccine candidates against leishmaniasis.

Recombinant Leishmania major lipophosphoglycan 3 activates human T-lymphocytes via TLR2-independent pathway

Leishmaniasis is one of the most common infectious diseases transmitted by an obligate intracellular genus Leishmania. As there is no efficient vaccination strategy for leishmaniasis, new immunostimulatory components may enhance protective immune responses against this parasite. Lipophosphoglycan 3 (LPG3) is an essential protein required for LPG assembling. In this study, the ability of recombinant LPG3 (rLPG) and its fragments to activate isolated healthy human T-cells and cytokine secretion was evaluated in vitro. The results showed that rLPG3 and its N-terminal fragment (rNT-LPG3) enhanced expression of CD69 on the surface of T-cells and promoted differentiation of CD4(+) T-lymphocytes toward a T-helper 1 (T(H)1) phenotype, in part, through up-regulation of interferon (IFN)-γ expression in a TLR2-independent manner. These results indicated the protective effects of LPG3 (particularly NT-LPG3 fragment) as a potent immunostimulatory component of leishmania in vaccination against leishmaniasis. Further investigations in in vivo assays are clearly warranted.