Dendritic cell-based vaccination strategies: induction of protective immunity against leishmaniasis

Targeting the P10 Peptide in Maturing Dendritic Cells via the DEC205 Receptor In Vivo: A New Therapeutic Strategy against Paracoccidioidomycosis

Paracoccidioidomycosis (PCM) is a systemic mycosis caused by Paracoccidioides brasiliensis, a thermally dimorphic fungus, which is the most frequent endemic systemic mycosis in many Latin American countries, where ~10 million people are believed to be infected. In Brazil, it is ranked as the tenth most common cause of death among chronic infectious diseases. Hence, vaccines are in development to combat this insidious pathogen. It is likely that effective vaccines will need to elicit strong T cell-mediated immune responses composed of IFNγ secreting CD4⁺ helper and CD8⁺ cytolytic T lymphocytes. To induce such responses, it would be valuable to harness the dendritic cell (DC) system of antigen-presenting cells. To assess the potential of targeting P10, which is a peptide derived from gp43 secreted by the fungus, directly to DCs, we cloned the P10 sequence in fusion with a monoclonal antibody to the DEC205 receptor, an endocytic receptor that is abundant on DCs in lymphoid tissues. We verified that a single injection of the αDEC/P10 antibody caused DCs to produce a large amount of IFNγ. Administration of the chimeric antibody to mice resulted in a significant increase in the levels of IFN-γ and IL-4 in lung tissue relative to control animals. In therapeutic assays, mice pretreated with αDEC/P10 had significantly lower fungal burdens compared to control infected mice, and the architecture of the pulmonary tissues of αDEC/P10 chimera-treated mice was largely normal. Altogether, the results obtained so far indicate that targeting P10 through a αDEC/P10 chimeric antibody in the presence of polyriboinosinic: polyribocytidylic acid is a promising strategy in vaccination and therapeutic protocols to combat PCM.

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.

Humoral Immunity to Allogeneic Immunoproteasome-Expressing Mesenchymal Stromal Cells Requires Efferocytosis by Endogenous Phagocytes

The extensive use of mesenchymal stromal cells (MSCs) over the last decade has revolutionized modern medicine. From the delivery of pharmacological proteins to regenerative medicine and immune modulation, these cells have proven to be highly pleiotropic and responsive to their surrounding environment. Nevertheless, their role in promoting inflammation has been fairly limited by the questionable use of interferon-gamma, as this approach has also been proven to enhance the cells' immune-suppressive abilities. Alternatively, we have previously shown that de novo expression of the immunoproteasome (IPr) complex instills potent antigen cross-presentation capabilities in MSCs. Interestingly, these cells were found to express the major histocompatibility class (MHC) II protein, which prompted us to investigate their ability to stimulate humoral immunity. Using a series of in vivo studies, we found that administration of allogeneic ovalbumin (OVA)-pulsed MSC-IPr cells elicits a moderate antibody titer, which was further enhanced by the combined use of pro-inflammatory cytokines. The generated antibodies were functional as they blocked CD4 T-cell activation following their co-culture with OVA-pulsed MSC-IPr and mitigated E.G7 tumor growth in vivo. The therapeutic potency of MSC-IPr was, however, dependent on efferocytosis, as phagocyte depletion prior to vaccination abrogated MSC-IPr-induced humoral responses while promoting their survival in the host. In contrast, antibody-mediated neutralization of CD47, a potent "do not eat me signal", enhanced antibody titer levels. These observations highlight the major role played by myeloid cells in supporting antibody production by MSC-IPr and suggest that the immune outcome is dictated by a net balance between efferocytosis-stimulating and -inhibiting signals.

Cloning, high-level gene expression and bioinformatics analysis of SP15 and LeIF from Leishmania major and Iranian Phlebotomus papatasi saliva as single and novel fusion proteins: a potential vaccine candidate against leishmaniasis

BACKGROUND

Early exacerbation of cutaneous leishmaniasis is mainly affected by both the salivary and Leishmania parasite components. Little is known of the vaccine combination made by immunogenic proteins of sandfly saliva (SP15) with Leishmania parasites (LeIF) as a single prophylactic vaccine, namely SaLeish. Also, there are no data available to determine the species-specific sequence of SP15 isolated from the Iranian Phlebotomus papatasi.

METHODS

Integrated bioinformatics and genetic engineering methods were employed to design, optimize and obtain a vector-parasite-based vaccine formulation in a whole-length fusion form of LeIF-SP15 against leishmaniasis. Holistic gene optimization was initially performed to obtain a high yield of pure 'whole-SaLeish' expression using bioinformatics analyses. Genomic and salivary gland RNAs of wild-caught P. papatasi were extracted and their complementary DNA was amplified and cloned into pJET vector.

RESULTS

The new chimeric protein of whole-SaLeish and randomly selected transcripts of native PpIRSP15 (GenBank accession nos. MT025054 and MN938854, MN938855 and MN938856) were successfully expressed, purified and validated by immunoblotting assay. Furthermore, despite the single amino acid polymorphisms of PpIRSP15 found at positions Y23 and E73 within the population of wild Iranian sandflies, antigenicity and conservancy of PpIRSP15 epitopes remained constant to activate T cells.

CONCLUSIONS

The SaLeish vaccine strategy takes advantage of a plethora of vector-parasite immunogenic proteins with potential protective efficacy to stimulate both the innate and specific cellular immune responses against Leishmania parasites.

Leishmania lipophosphoglycan components: A potent target for synthetic neoglycoproteins as a vaccine candidate for leishmaniasis

Leishmania is an obligate intracellular pathogen that invades phagocytic host cells. Due to its high morbidity and mortality rates, leishmaniasis attracts significant attention. The disease, which is caused by Leishmania parasites, is distributed worldwide, particularly among developing communities, and causes fatal complications if not treated expediently. Unfortunately, the existing treatments are not preventive and do not impede Leishmania infection. Many drugs available for leishmaniasis are becoming less effective due to emerging resistance in some Leishmania species. Other drugs have drawbacks such as low cost-effectiveness, toxicity, and side effects. The World Health Organization (WHO) considers leishmaniasis to be a major public health problem and suggests that the best prevention is to develop a vaccine for this dangerous disease. In this review, we focus on the unique components of lipophosphoglycan (LPG), a component of the Leishmania cell wall, particularly [Galp(1 → 4)-β-[Manp-(1 → 2)-α-Manp-(1 → 2)-α]-Manp] in the cryptic tetrasaccharide cap, and on synthetic approaches as a potent candidate for a leishmaniasis vaccine.

Assessment of Vaccine-Induced Immunity Against Canine Visceral Leishmaniasis

Canine visceral leishmaniasis is an increasingly important public health problem. Dogs infected by Leishmania infantum are the main domestic reservoir of the parasite and play a key role in its transmission to humans. Recent findings have helped in the development of novel diagnostic methods, and of control measures such as vaccines, some of which are already commercially available. However, quantitative procedures should be followed to confirm whether these vaccines elicit a cell-mediated immune response. The present work describes the need for this evaluation, and the techniques available for confirming this type of immune response.

Leishmania infantum LeIF and its recombinant polypeptides induce the maturation of dendritic cells in vitro: An insight for dendritic cells based vaccine

We previously showed that recombinant Leishmania infantum eukaryotic initiation factor (LieIF) was able to induce the secretion of cytokines IL-12, IL-10 and TNF-α by human monocytes. In this study, we explored in vitro the potential of LieIF to induce phenotypic maturation and functional differentiation of murine bone-marrow derived dendritic cells (BM-DCs). Moreover, in order to identify potential immunnomodulatory regions of LieIF, eight recombinant overlapping protein fragments covering the whole amino acid sequence of protein, were constructed and assessed in vitro for their ability to induce maturation of BM-DCs. Our data showed that LieIF and some of its recombinant polypeptides were able to induce elevated expression of CD40, CD80 and CD86 co-stimulatory molecules with concurrent IL-12 production. Moreover, we used an in vivo experimental model of cutaneous leishmaniasis consisted of susceptible Leishmania major-infected BALB/c mice and we demonstrated that LieIF-pulsed-BM-DCs adoptively transferred in mice were capable to confer protection against a high dose parasite challenge. This study further describes the immunomodulatory properties of LieIF and its polypeptides bringing relevant information for their exploitation as candidate molecules for vaccine development against leishmaniasis.

Age-Related Differential Stimulation of Immune Response by Babesia microti and Borrelia burgdorferi During Acute Phase of Infection Affects Disease Severity

Lyme disease is the most prominent tick-borne disease with 300,000 cases estimated by CDC every year while ~2,000 cases of babesiosis occur per year in the United States. Simultaneous infection with Babesia microti and Borrelia burgdorferi are now the most common tick-transmitted coinfections in the U.S.A., and they are a serious health problem because coinfected patients show more intense and persisting disease symptoms. B. burgdorferi is an extracellular spirochete responsible for systemic Lyme disease while B. microti is a protozoan that infects erythrocytes and causes babesiosis. Immune status and spleen health are important for resolution of babesiosis, which is more severe and even fatal in the elderly and splenectomized patients. Therefore, we investigated the effect of each pathogen on host immune response and consequently on severity of disease manifestations in both young, and 30 weeks old C3H mice. At the acute stage of infection, Th1 polarization in young mice spleen was associated with increased IFN-γ and TNF-α producing T cells and a high Tregs/Th17 ratio. Together, these changes could help in the resolution of both infections in young mice and also prevent fatality by B. microti infection as observed with WA-1 strain of Babesia. In older mature mice, Th2 polarization at acute phase of B. burgdorferi infection could play a more effective role in preventing Lyme disease symptoms. As a result, enhanced B. burgdorferi survival and increased tissue colonization results in severe Lyme arthritis only in young coinfected mice. At 3 weeks post-infection, diminished pathogen-specific antibody production in coinfected young, but not older mice, as compared to mice infected with each pathogen individually may also contribute to increased inflammation observed due to B. burgdorferi infection, thus causing persistent Lyme disease observed in coinfected mice and reported in patients. Thus, higher combined proinflammatory response to B. burgdorferi due to Th1 and Th17 cells likely reduced B. microti parasitemia significantly only in young mice later in infection, while the presence of B. microti reduced humoral immunity later in infection and enhanced tissue colonization by Lyme spirochetes in these mice even at the acute stage, thereby increasing inflammatory arthritis.

NH36 and F3 Antigen-Primed Dendritic Cells Show Preserved Migrating Capabilities and CCR7 Expression and F3 Is Effective in Immunotherapy of Visceral Leishmaniasis

Physical contact between dendritic cells (DCs) and T cell lymphocytes is necessary to trigger the immune cell response. CCL19 and CCL21 chemokines bind to the CCR7 receptor of mature DCs, and of T cells and regulate DCs migration to the white pulp (wp) of the spleen, where they encounter lymphocytes. In visceral leishmaniasis (VL), cellular immunosuppression is mediated by impaired DC migration due to the decreased chemokine secretion by endothelium and to the reduced DCs CCR7 expression. The Leishmania (L.) donovani nucleoside hydrolase NH36 and its C-terminal domain, the F3 peptide are prominent antigens in the generation of preventive immunity to VL. We assessed whether these vaccines could prevent the migrating defect of DCs by restoring the expression of CCR7 receptors. C57Bl6 mice were vaccinated with NH36 and F3 and challenged with L. (L.) infantum chagasi. The F3 vaccine induced a 100% of survival and a long-lasting immune protection with an earlier CD4+Th1 response, with secretion of higher IFN-γ and TNF-α/IL-10 ratios, and higher frequencies of CD4+ T cells secreting IL-2+, TNF-α+, or IFN-γ+, or a combination of two or the three cytokines (IL-2+TNF-α+IFN-γ+). The CD8+ T cell response was promoted earlier by the NH36-vaccine, and later by the F3-vaccine. Maximal number of F3-primed DCs migrated in vitro in response to CCL19 and showed a high expression of CCR7 receptors (26.06%). Anti-CCR7 antibody treatment inhibited DCs migration in vitro (90%) and increased parasite load in vivo. When transferred into 28-day-infected mice, only 8% of DCs from infected, 59% of DCs from NH36-vaccinated, and 84% of DCs from F3-vaccinated mice migrated to the wp. Consequently, immunotherapy of infected mice with F3-primed DCs only, promoted increases in corporal weight and reductions of spleen and liver parasite loads and relative weights. Our findings indicate that vaccination with F3-vaccine preserves the maturation, migration properties and CCR7 expression of DCs, which are essential processes for the generation of cell-mediated immunity. The F3 vaccine is more potent in reversing the migration defect that occurs in VL and, therefore, more efficient in immunotherapy of VL.

Modulation of dendritic cell by pathogen antigens: Where do we stand?

Dendritic cells (DCs) are essential players in the activation of T cells and in the development of adaptive immune response towards invading pathogens. Upon antigen (Ag) recognition of Pathogen Associated Molecular Patterns (PAMPs) by their receptors (PRRs), DCs are activated and acquire an inflammatory profile. DCs have the ability to direct the profile of helper T (Th) cells towards Th1, Th2, Th17, Th9 and regulatory (Treg) cells. Each subset of Th cells presents a unique gene expression signature and is endowed with the ability to conduct or suppress effector cells in inflammation. Pathogens target DCs during infection. Many studies demonstrated that antigens and molecules derived from pathogens have the ability to dampen DC maturation and activation, leading these cells to a permissive state or tolerogenic profile (tolDCs). Although tolDCs may represent a hindrance in infection control, they could be positively used to modulate inflammatory disorders, such as autoimmune diseases. In this review, we focus on discussing findings that use pathogen-antigen modulated DCs and tolDCs in prophylactics and therapeutics approaches for vaccination against infectious diseases or inflammatory disorders.

Leishmaniasis in humans: drug or vaccine therapy?

Leishmania is an obligate intracellular pathogen that invades phagocytic host cells. Approximately 30 different species of Phlebotomine sand flies can transmit this parasite either anthroponotically or zoonotically through their bites. Leishmaniasis affects poor people living around the Mediterranean Basin, East Africa, the Americas, and Southeast Asia. Affected regions are often remote and unstable, with limited resources for treating this disease. Leishmaniasis has been reported as one of the most dangerous neglected tropical diseases, second only to malaria in parasitic causes of death. People can carry some species of Leishmania for long periods without becoming ill, and symptoms depend on the form of the disease. There are many drugs and candidate vaccines available to treat leishmaniasis. For instance, antiparasitic drugs, such as amphotericin B (AmBisome), are a treatment of choice for leishmaniasis depending on the type of the disease. Despite the availability of different treatment approaches to treat leishmaniasis, therapeutic tools are not adequate to eradicate this infection. In the meantime, drug therapy has been limited because of adverse side effects and unsuccessful vaccine preparation. However, it can immediately make infections inactive. According to other studies, vaccination cannot eradicate leishmaniasis. There is no perfect vaccine or suitable drug to eradicate leishmaniasis completely. So far, no vaccine or drug has been provided to induce long-term protection and ensure effective immunity against leishmaniasis. Therefore, it is necessary that intensive research should be performed in drug and vaccine fields to achieve certain results.

In silico analysis and in vitro evaluation of immunogenic and immunomodulatory properties of promiscuous peptides derived from Leishmania infantum eukaryotic initiation factor

It is generally considered as imperative the ability to control leishmaniasis through the development of a protective vaccine capable of inducing long-lasting and protective cell-mediated immune responses. In this current study, we demonstrated potential epitopes that bind to H2 MHC class I and II molecules by conducting the in silico analysis of Leishmania infantum eukaryotic Initiation Factor (LieIF) protein, using online available algorithms. Moreover, we synthesized five peptides (16-18 amino acids long) which are part of the N-terminal portion of LieIF and contain promising MHC class I and II-restricted epitopes and afterwards, their predicted immunogenicity was evaluated in vitro by monitoring peptide-specific T-cell responses. Additionally, the immunomodulatory properties of these peptides were investigated in vitro by exploring their potential of inducing phenotypic maturation and functional differentiation of murine Bone-Marrow derived Dendritic Cells (BM-DCs). It was revealed by our data that all the synthetic peptides predicted for H2 alleles; present the property of immunogenicity. Among the synthetic peptides which contained T-cell epitopes, the peptide 52-68 aa (LieIF_2) exhibited immunomodulatory properties with the larger potential. LieIF_2-pulsed BM-DCs up-regulated the expression of the co-stimulatory surface molecules CD80 and CD86, as well as the production of the proinflammatory cytokine TNF-α and of the Th1-polarizing cytokines IL-12 and IFN-γ. The aforementioned data suggest that selected parts of LieIF could be used to develop innovative subunit protective vaccines able to induce effective immunity mediated by MHC class I-restricted as well as class II-restricted T-cell responses.

A Vaccine Therapy for Canine Visceral Leishmaniasis Promoted Significant Improvement of Clinical and Immune Status with Reduction in Parasite Burden

Herein, we evaluated the treatment strategy employing a therapeutic heterologous vaccine composed of antigens of Leishmania braziliensis associated with MPL adjuvant (LBMPL vaccine) for visceral leishmaniasis (VL) in symptomatic dogs naturally infected by Leishmania infantum. Sixteen dogs received immunotherapy with MPL adjuvant (n = 6) or with a vaccine composed of antigens of L. braziliensis associated with MPL (LBMPL vaccine therapy, n = 10). Dogs were submitted to an immunotherapeutic scheme consisting of 3 series composed of 10 subcutaneous doses with 10-day interval between each series. The animals were evaluated before (T0) and 90 days after treatment (T90) for their biochemical/hematological, immunological, clinical, and parasitological variables. Our major results showed that the vaccine therapy with LBMPL was able to restore and normalize main biochemical (urea, AST, ALP, and bilirubin) and hematological (erythrocytes, hemoglobin, hematocrit, and platelets) parameters. In addition, in an ex vivo analysis using flow cytometry, dogs treated with LBMPL vaccine showed increased CD3⁺ T lymphocytes and their subpopulations (TCD4⁺ and TCD8⁺), reduction of CD21⁺ B lymphocytes, increased NK cells (CD5^-CD16⁺) and CD14⁺ monocytes. Under in vitro conditions, the animals developed a strong antigen-specific lymphoproliferation mainly by TCD4⁺ and TCD8⁺ cells; increasing in both TCD4⁺IFN-γ⁺ and TCD8⁺IFN-γ⁺ as well as reduction of TCD4⁺IL-4⁺ and TCD8⁺IL-4⁺ lymphocytes with an increased production of TNF-α and reduced levels of IL-10. Concerning the clinical signs of canine visceral leishmaniasis, the animals showed an important reduction in the number and intensity of the disease signs; increase body weight as well as reduction of splenomegaly. In addition, the LBMPL immunotherapy also promoted a reduction in parasite burden assessed by real-time PCR. In the bone marrow, we observed seven times less parasites in LBMPL animals compared with MPL group. The skin tissue showed a reduction in parasite burden in LBMPL dogs 127.5 times higher than MPL. As expected, with skin parasite reduction promoted by immunotherapy, we observed a blocking transmission to sand flies in LBMPL dogs with only three positive dogs after xenodiagnosis. The results obtained in this study highlighted the strong potential for the use of this heterologous vaccine therapy as an important strategy for VL treatment.

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

The need for a vaccine against Leishmania spp., a major cause of worldwide morbidity and mortality, is urgent. We tested the efficacy of an experimental vaccination in murine models of cutaneous leishmaniasis, using dendritic cells (DCs) pulsed with synthetic or native parasite antigens. DCs pulsed with peptide 154–169aa of gp63 or soluble promastigote lysate (SPL) triggered antigen-specific immune responses and efficiently reduced lesion formation and parasite load of genetically susceptible BALB/c mice infected with Leishmania major. This effect was accompanied by a modulation of the cellular immune response towards a Th1 profile. Vaccination of genetically resistant CBA mice with DCs pulsed with peptide 154–169aa or SPL did not affect the course of the disease, whereas pulsing with the epitope 467–482aa of gp63 resulted in disease exacerbation, accompanied by a switch to a Th2 profile. In view of our continuously growing knowledge about the immunobiology of DCs, these findings suggest that vaccination with DCs pulsed with defined peptides could be a strategy against infectious diseases. Peptide selection is a prerequisite as they can differentially regulate the type of immune response in susceptible or resistant hosts.

Modulation of Innate Immune Mechanisms to Enhance Leishmania Vaccine-Induced Immunity: Role of Coinhibitory Molecules

No licensed human vaccines are currently available against any parasitic disease including leishmaniasis. Several antileishmanial vaccine formulations have been tested in various animal models, including genetically modified live-attenuated parasite vaccines. Experimental infection studies have shown that Leishmania parasites utilize a broad range of strategies to undermine effector properties of host phagocytic cells, i.e., dendritic cells (DCs) and macrophages (MΦ). Furthermore, Leishmania parasites have evolved strategies to actively inhibit T_H1 polarizing functions of DCs and to condition the infected MΦ toward anti-inflammatory/alternative/M2 phenotype. The altered phenotype of phagocytic cells is characterized by decreased production of antimicrobial reactive oxygen, nitrogen molecules, and pro-inflammatory cytokines, such as IFN-γ, IL-12, and TNF-α. These early events limit the activation of T_H1-effector cells and set the stage for pathogenesis. Furthermore, this early control of innate immunity by the virulent parasites results in substantial alteration in the adaptive immunity characterized by reduced proliferation of CD4⁺ and CD8⁺ T cells and T_H2-biased immunity that results in production of anti-inflammatory cytokines, such as TGF-β, and IL-10. More recent studies have also documented the induction of coinhibitory ligands, such as CTLA-4, PD-L1, CD200, and Tim-3, that induce exhaustion and/or non-proliferation in antigen-experienced T cells. Most of these studies focus on viral infections in chronic phase, thus limiting the direct application of these results to parasitic infections and much less to parasitic vaccines. However, these studies suggest that vaccine-induced protective immunity can be modulated using strategies that enhance the costimulation that might reduce the threshold necessary for T cell activation and conversely by strategies that reduce or block inhibitory molecules, such as PD-L1 and CD200. In this review, we will focus on the polarization of antigen-presenting cells and subsequent role of costimulatory and coinhibitory molecules in mediating vaccine-induced immunity using live-attenuated Leishmania parasites as specific examples.

The role of dendritic cells during infection

The skin and the mucosa of the respiratory and gastrointestinal tracts are continuously exposed to microorganisms, but only a limited number of these enter the body and cause disease. To resist microbial infection, the host has developed a multitude of defense mechanisms involving the innate and adaptive immune systems. Dendritic cells (DCs) provide the link between these arms of the immune system. The initiation of an immune response is critically dependent on the activation of DCs, which can discriminate between different classes of microorganisms and elicit tailored antimicrobial immune responses. They have an extraordinary capacity to stimulate naive T cells and initiate primary immune responses. In turn, some pathogens interfere with DC function to block or delay their elimination by the host. Progress in understanding the role of DCs in the host response to microbes is reviewed.

Immunotherapy and Immunochemotherapy in Visceral Leishmaniasis: Promising Treatments for this Neglected Disease

Leishmaniasis has several clinical forms: self-healing or chronic cutaneous leishmaniasis or post-kala-azar dermal leishmaniasis; mucosal leishmaniasis; visceral leishmaniasis (VL), which is fatal if left untreated. The epidemiology and clinical features of VL vary greatly due to the interaction of multiple factors including parasite strains, vectors, host genetics, and the environment. Human immunodeficiency virus infection augments the severity of VL increasing the risk of developing active disease by 100–2320 times. An effective vaccine for humans is not yet available. Resistance to chemotherapy is a growing problem in many regions, and the costs associated with drug identification and development, make commercial production for leishmaniasis, unattractive. The toxicity of currently drugs, their long treatment course, and limited efficacy are significant concerns. For cutaneous disease, many studies have shown promising results with immunotherapy/immunochemotherapy, aimed to modulate and activate the immune response to obtain a therapeutic cure. Nowadays, the focus of many groups centers on treating canine VL by using vaccines and immunomodulators with or without chemotherapy. In human disease, the use of cytokines like interferon-γ associated with pentavalent antimonials demonstrated promising results in patients that did not respond to conventional treatment. In mice, immunomodulation based on monoclonal antibodies to remove endogenous immunosuppressive cytokines (interleukin-10) or block their receptors, antigen-pulsed syngeneic dendritic cells, or biological products like Pam3Cys (TLR ligand) has already been shown as a prospective treatment of the disease. This review addresses VL treatment, particularly immunotherapy and/or immunochemotherapy as an alternative to conventional drug treatment in experimental models, canine VL, and human disease.

CXCL10 is critical for the generation of protective CD8 T cell response induced by antigen pulsed CpG-ODN activated dendritic cells

The visceral form of leishmaniasis is the most severe form of the disease and of particular concern due to the emerging problem of HIV/visceral leishmaniasis (VL) co-infection in the tropics. Till date miltefosine, amphotericin B and pentavalent antimony compounds remain the main treatment regimens for leishmaniasis. However, because of severe side effects, there is an urgent need for alternative improved therapies to combat this dreaded disease. In the present study, we have used the murine model of leishmaniasis to evaluate the potential role played by soluble leishmanial antigen (SLA) pulsed-CpG-ODN stimulated dendritic cells (SLA-CpG-DCs) in restricting the intracellular leishmanial growth. We found that mice vaccinated with a single dose of SLA-pulsed DC stimulated by CpG-ODN were protected against a subsequent leishmanial challenge and had a dramatic reduction in parasite burden along with the generation of parasite specific cytotoxic T lymphocytes. Moreover, we demonstrate that the induction of protective immunity conferred by SLA-CpG-DCs depends entirely on the CXC chemokine IFN-γ-inducible protein 10 (CXCL10; IP-10). CXCL10 is directly involved in the generation of a parasite specific CD8⁺ T cell-mediated immune response. We observed significant reduction of CD8⁺ T cells in mice depleted of CXCL10 suggesting a direct role of CXCL10 in the generation of CD8⁺ T cells in SLA-CpG-DCs vaccinated mice. CXCL10 also contributed towards the generation of perforin and granzyme B, two important cytolytic mediators of CD8⁺ T cells, following SLA-CpG-DCs vaccination. Together, these findings strongly demonstrate that CXCL10 is critical for rendering a protective cellular immunity during SLA-CpG-DC vaccination that confers protection against Leishmania donovani infection.

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.

Development of Vaccines against Visceral Leishmaniasis

Leishmaniasis is a neglected disease resulting in a global morbidity of 2,090 thousand Disability-Adjusted Life Years and a mortality rate of approximately 60,000 per year. Among the three clinical forms of leishmaniasis (cutaneous, mucosal, and visceral), visceral leishmaniasis (VL) accounts for the majority of mortality, as if left untreated VL is almost always fatal. Caused by infection with Leishmania donovani or L. infantum, VL represents a serious public health problem in endemic regions and is rapidly emerging as an opportunistic infection in HIV patients. To date, no vaccine exists for VL or any other form of leishmaniasis. In endemic areas, the majority of those infected do not develop clinical symptoms and past infection leads to robust immunity against reinfection. Thus the development of vaccine for Leishmania is a realistic public health goal, and this paper summarizes advances in vaccination strategies against VL.

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.

Dendritic cells transfected with scFv from Mab 7.B12 mimicking original antigen gp43 induces protection against experimental Paracoccidioidomycosis

Paracoccidioidomycosis (PCM), endemic in Latin America, is a progressive systemic mycosis caused by Paracoccidioides brasiliensis (P. brasiliensis), which primarily attacks lung tissue. Dendritic cells (DCs) are able to initiate a response in naïve T cells, and they also participate in Th-cell education. Furthermore, these cells have been used for therapy in several disease models. Here we transfected DCs with a plasmid (pMAC/PS-scFv) encoding a single chain variable fragment (scFv) of an anti-Id antibody that is capable of mimicking gp43, the main antigenic component of P. brasiliensis. First, Balb/c mice were immunized subcutaneously with pMAC/PS-scFv and, after seven days, scFv protein was presented to the regional lymph nodes cells. Moreover, we showed that the DCs transfected with scFv were capable of efficiently activating proliferation of total lymph node cells and inducing a decrease in lung infection. Therefore, our results suggested that the use of scFv-transfected DCs may be a promising therapy in the paracoccidioidomycosis (PCM) model.

Mutual helper effect in copulsing of dendritic cells with 2 antigens: a novel approach for improvement of dendritic-based vaccine efficacy against tumors and infectious diseases simultaneously

To develop an efficient dendritic cell (DC)-based immunotherapy protocol, we examined whether simultaneous pulsing of DCs with a given antigen and a third-party antigen could enhance their antigen presentation capacity. Purified splenic DCs of Balb/c mice were pulsed separately with immunoglobulin G, ovalbumin, conalbumin, P15 peptide of Mycobacterium tuberculosis, and prostate-specific antigen or double combinations of the aforementioned antigens. In some settings, DCs pulsed with 1 antigen were mixed equally with those pulsed with another antigen. Antigen-pulsed DCs were injected into the footpad of syngeneic mice and proliferation of whole, CD4 and CD8 depleted lymph node cells was measured after restimulation with cognate antigen. Antigen-specific production of interferon-gamma (IFNgamma) was tested in culture supernatants. Frequency of responding lymph node cells was determined by IFNgamma enzyme-linked immunosorbent spot assay. Our results showed that copulsing of DCs with 2 unrelated antigens increased the capacity of DCs to induce antigen-specific T-cell proliferation against both antigens up to 16-fold. Injection of 2 populations of DCs each pulsed with a different antigen, increased proliferation of primed T cells significantly as well. Both CD4 and CD8 depleted populations showed vigorous proliferative response in copulsing system. In addition, copulsing of DCs with 2 antigens resulted in higher frequency of antigen-specific responding cells and significantly more IFNgamma production. Our results clearly showed that unrelated peptides and proteins could be used to enhance efficacy of DC-based vaccines and in this system, each antigen served to help the other one, a condition that we termed as "mutual helper effect."

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.

Induction of specific immune responses against the Plasmodium vivax liver-stage via in vitro activation by dendritic cells

Due to chronic morbidity, the risk of increasing drug resistance and the existence of the hypnozoite stage in Plasmodium vivax malaria, there is a need to find out how hosts develop immunity to compromise the malaria parasites. Here we focused on an in vitro model for immunotherapy and vaccine development. Immunosuppressive mechanisms in malaria include inhibition of T cell response and suppression of dendritic cell function. Using in vitro activation of lymphocytes by malaria antigen-pulsed dendritic cells could overcome the limitation of antigen presentation during acute infections. Here we showed that the sporozoite-pulsed dendritic cell could elicit cytotoxicity against liver stage of P. vivax. Analysis using immunophenotypic markers showed maturation of the dendritic cells and stimulation of cytotoxic T cells. Functional assay of the in vitro-activated cytotoxic T cells showed enhancement of specific killing of the P. vivax exoerythrocytic stages within infected hepatocytes. This model may be useful for vaccine development against human malaria.

Dendritic cells pulsed with hepatitis C virus NS3 protein induce immune responses and protection from infection with recombinant vaccinia virus expressing NS3

Infections with Hepatitis C virus (HCV) pose a serious health problem worldwide. In this study, the hypothesis that adoptive transfer of dendritic cells (DCs) pulsed with HCV NS3 protein and matured with an oligodeoxynucleotide (ODN) containing CpG motifs (CpG) ex vivo would initiate potent HCV-specific protective immune responses in vivo was tested. NS3 protein was efficiently transduced into DCs and treatment of DCs with CpG ODN induced phenotypic maturation and specifically increased the expression of CD40. DCs matured with CpG ODN produced higher interleukin 12 levels and a stronger allogeneic T-cell response compared with untreated DCs. Notably, there were no differences between NS3-pulsed DCs and DCs pulsed with a control protein with respect to phenotype, cytokine production or mixed lymphocyte reaction, indicating that transduction with NS3 protein did not impair DC functions. Compared with the untreated NS3-pulsed DCs, the NS3-pulsed DCs matured with CpG ODN induced stronger cellular immune responses including enhanced cytotoxicity, higher interferon-gamma production and stronger lymphocyte proliferation. Upon challenge with a recombinant vaccinia virus expressing NS3, all mice immunized with NS3-pulsed DCs showed a significant reduction in vaccinia virus titres when compared with mock-immunized mice. However, the NS3-pulsed DCs matured with CpG ODN induced higher levels of protection compared with the untreated NS3-pulsed DCs. These data are the first to show that NS3-pulsed DCs induce specific immune responses and provide protection from viral challenge, and also demonstrate that CpG ODNs, which have a proven safety profile, would be useful in the development of DC vaccines.

Leishmania major modulates chemokine and chemokine receptor expression by dendritic cells and affects their migratory capacity

Dendritic cells (DC) both produce and respond to chemokines. We examined the profiles of chemokines and chemokine receptors expressed by DC and their chemotactic response after interaction with Leishmania major. Expression of the chemokine receptors CCR2 and CCR5 by DC and their responsiveness to the respective ligands, CCL2 and CCL3, were downregulated, while the level of CCR7 and the DC response to its ligand CCL21 were enhanced. These parasite-induced alterations were observed with DC from L. major-resistant and -susceptible mice. In contrast, expression of the chemokine CXCL10 was elicited only in DC from L. major-resistant mice.

Recent advances in vaccines for leishmaniasis

The observation that recovery from infection with Leishmania confers immunity to reinfection suggests that control of leishmaniasis by vaccination may be possible. However, there are no vaccines available at present to control any form of leishmaniasis, despite considerable efforts. Studies of the immunopathogenesis and mechanisms of protective immunity, mainly derived from animal models of experimental leishmaniasis, have defined a number of features that should be met by an effective vaccine. In addition, several antigens have been identified that may be potential vaccine candidates, and molecular biological techniques have made them available as recombinant proteins for second-generation vaccines. Furthermore, molecules present in the saliva of Leishmania-transmitting vectors have been demonstrated as valuable candidates for the development of anti-Leishmania vaccines. This review concentrates on the most promising vaccine candidates and highlights new approaches for the development of vaccines. Finally, based on present knowledge, the future prospects for developing an effective vaccine against the different clinical forms of leishmaniasis are discussed.

Adoptive transfer of dendritic cells modulates immunogenesis and tolerogenesis in a neonatal model of murine cutaneous leishmaniasis

We evaluated the adoptive transfer of DCs on Leishmania (L.) mexicana-infected neonatal BALB/c mice. DCs were isolated and purified from the spleens of the following donor groups: a) Adult BALB/c mice infected during adulthood with L. (L) mexicana; b) Adult BALB/c mice infected during neonatal life; c) Healthy neonatal BALB/c mice; d) Healthy adult BALB/c mice. A neonatal model of infection, generated after inoculation with 5 × 105 promastigotes of L. (L) mexicana, was used as the infection control group. Sixteen hours after intraperitoneal transfer of DCs (1 × 103, 1 × 105, or 1 × 106 cells/ml), neonatal recipient BALB/c mice were infected. The adoptive transfer of DCs diminished disease progression in neonatal mice. This reduction depends on the quantity and provenance of transferred DCs, since the effect was more evident with high numbers of DCs from adult mice infected during adulthood and healthy neonatal mice. Protection was significantly reduced in animals receiving DCs from healthy adult mice but it was absent in mice receiving DCs from adult mice infected during neonatal life. These results suggest that genetic susceptibility to Leishmania infection can be modified during neonatal life, and that the period of life when antigens are encountered is crucial in influencing the capacity of DCs to induce resistance or tolerance.

Shaping the immune response to parasites: role of dendritic cells

Parasites represent a diverse group of pathogens that often trigger highly polarized immune responses that become tightly regulated during chronic infection. Recent studies have implicated the parasite-dendritic-cell interaction as a key determinant of the host response to these eukaryotic invaders. Dendritic cells appear to be pivotal in the initiation of cellular immunity against parasites as well as in directing Th1/Th2 effector choice. Moreover, there is increasing evidence that parasites regulate dendritic-cell function for the purposes of evading host immunity. This regulation also benefits parasites by protecting their host niche from the potentially lethal consequences of an uncontrolled inflammatory response.

Dendritic cell-based immunotherapy

Dendritic cell (DC)-based vaccinations represent a promising approach for the immunotherapy of cancer and infectious diseases as DCs play an essential role in initiating cellular immune responses. A number of clinical trials using ex vivo-generated DCs have been performed so far and only minor toxicity has been reported. Both the induction of antigen-specific T cells and clinical responses have been observed in vaccinated cancer patients. Nevertheless, DC-based immunotherapy is still in its infancy and there are many issues to be addressed such as antigen loading procedures, DC source and maturational state, migration properties, route, frequency, and dosage of DC vaccination. The increasing knowledge of DC biology should be used to improve the efficacy of this new therapy.

Prevention of allograft rejection by in vitro generated tolerogenic dendritic cells

Achieving immunological tolerance in transplantation has been a long sought-after goal since the 1960s. It is, therefore, interesting that the dendritic cells (DC), which are classically known as the most potent stimulators of T cell activation, are now also considered putative tools for tolerance induction. In line with this, much work has been performed using DC for vaccination and immune stimulation. Recently, great interest has been generated regarding the ability of DC to act as immune regulatory cells. Specific subsets of DC or immature DC (iDC) appear to be responsible for maintaining self-tolerance. In this review we will highlight our efforts at elucidating the contribution of DC in transplant tolerant in mice. Specifically, four strategies will be outlined that are currently being used for the generation of DC that have tolerogenic properties in the prevention of allograft rejection. The present study demonstrates that modulated iDC with blunted T cell stimulatory or antigen presentation abilities can afford transplant tolerance by minimizing T cell activation and proinflammatory cytokine production. Moreover, in an alternate strategy, normally matured DC have also been modulated such that alloreactive T cells are specifically targeted for deletion.

Skewing of cytokine profiles towards T helper cell type 2 response in visceral leishmaniasis patients unresponsive to sodium antimony gluconate

Thirty-two parasitologically confirmed visceral leishmanisis (VL) patients and 23 healthy, age- and gender-matched controls were recruited between April 2001 and March 2002 and studied for intracellular cytokine production after stimulation in vitro using a Fluorescence Activated Cell Sorter-based intracellular cytokine assay. The VL patients were given i.m. sodium antimony gluconate at a dose of 20 mg/kg bodyweight daily for 28 d and were grouped as responders (n = 11) or non-responders (no response after 28 d of treatment; n = 21). Clinically, the non-responders had longer duration of illness (P < 0.05), larger spleen size (P < 0.05), and higher parasite load (P < 0.05) than responders. The percentage of T helper (Th) cells producing interferon-gamma (IFN-gamma) was significantly higher (P < 0.001) in responders than non-responders. Non-responders had higher IFN-gamma production than control subjects (P < 0.001). The percentage of Th cells producing interleukin-4 (IL-4) was significantly higher in non-responders than responders (P = 0.003) as well as in healthy subjects (P < 0.001). The frequency of IL-4 producing cells in responders and control subjects was similar (P= 0.65). The cytokine polarization index, as calculated by the formula loge IFN-gamma producing cells/loge IL-4 producing cells, was significantly lower in non-responders compared with both responders and control subjects (P = 0.003 and P < 0.001, respectively). The overall cytokine bias in non-responders was skewed towards a IL-4 dominance or Th2-like response and this was primarily due to induction of IL-4.

Dendritic cell-based immunotherapy combined with antimony-based chemotherapy cures established murine visceral leishmaniasis

Dendritic cells (DCs) have been proposed to play a critical role as adjuvants in vaccination and immunotherapy. In this study we evaluated the combined effect of soluble Leishmania donovani Ag (SLDA)-pulsed syngeneic bone marrow-derived DC-based immunotherapy and antimony-based chemotherapy for the treatment of established murine visceral leishmaniasis. Three weekly injections of SLDA-pulsed DCs into L. donovani-infected mice reduced liver and splenic parasite burden significantly, but could not clear parasite load from these organs completely. Strikingly, the conventional antileishmanial chemotherapy (sodium antimony gluconate) along with injections of SLDA-pulsed DCs resulted in complete clearance of parasites from both these organs. Repetitive in vitro stimulation of splenocytes from uninfected or L. donovani-infected mice with SLDA-pulsed DCs led to the emergence of CD4(+) T cells with characteristics of Th1 cells. Our data indicate that DC-based immunotherapy enhances the in vivo antileishmanial potential of antimony or vice versa.

Leishmania model for microbial virulence: the relevance of parasite multiplication and pathoantigenicity

Leishmanial mechanisms of virulence have been proposed previously to involve two different groups of parasite molecules. One group consists of largely surface and secretory products, and the second group includes intracellular molecules, referred to as 'pathoantigens'. In the first group are invasive/evasive determinants, which protect not only parasites themselves, but also infected host cells from premature cytolysis. These determinants help intracellular amastigotes maintain continuous infection by growing at a slow rate in the parasitophorous vacuoles of host macrophages. This is illustrated in closed in vitro systems, e.g. Leishmania amazonensis in macrophage cell lines. Although individual macrophages may become heavily parasitized at times, massive destruction of macrophages has not been observed to result from uncontrolled parasite replication. This is thus unlikely to be the direct cause of virulence manifested as the clinical symptoms seen in human leishmaniasis. Of relevance is likely the second group of immunopathology-causing parasite 'pathoantigens'. These are highly conserved cytoplasmic proteins, which have been found to contain Leishmania-unique epitopes immunologically active in leishmaniasis. How these intracellular parasite antigens become exposed to the host immune system is accounted for by periodic cytolysis of the parasites during natural infection. This event is notable with a small number of parasites, even as they grow in an infected culture. The cytolysis of these parasites to release 'pathoantigens' may be inadvertent or medicated by specific mechanisms. Information on the pathoantigenic epitopes is limited. T-cell epitopes have long been recognized, albeit ill-defined, as important in eliciting CD4+ cell development along either the Th1 or Th2 pathway. Their operational mechanisms in suppressing or exacerbating cutaneous disease are still under intensive investigation. However, immune response to B-cell epitopes of such 'pathoantigens' is clearly futile and counterproductive. Their intracellular location within the parasites renders them inaccessible to the specific antibodies generated. One example is the Leishmania K39 epitope, against which antibodies are produced in exceedingly high titers, especially in Indian kala-azar. Here, we consider the hypothetical emergence of this pathoantigenicity and its potential contributions to the virulent phenotype in the form of immunopathology. Microbial virulence may be similarly explained in other emerging and re-emerging infectious diseases. Attenuation of microbial virulence may be achieved by genetic elimination of pathoantigenicity, thereby providing mutants potentially useful as avirulent live vaccines for immunoprophylasis of infectious diseases.