Antigenicity of a whole parasite vaccine as promising candidate against canine leishmaniasis

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.

Drug Discovery for Cutaneous Leishmaniasis: A Review of Developments in the Past 15 Years

Leishmaniasis is a group of vector-borne, parasitic diseases caused by over 20 species of the protozoan Leishmania spp. The three major disease classifications, cutaneous, visceral, and mucocutaneous, have a range of clinical manifestations from self-healing skin lesions to hepatosplenomegaly and mucosal membrane damage to fatality. As a neglected tropical disease, leishmaniasis represents a major international health challenge, with nearly 350 million people living at risk of infection a year. The current chemotherapeutics used to treat leishmaniasis have harsh side effects, prolonged and costly treatment regimens, as well as emerging drug resistance, and are predominantly used for the treatment of visceral leishmaniasis. There is an undeniable need for the identification and development of novel chemotherapeutics targeting cutaneous leishmaniasis (CL), largely ignored by concerted drug development efforts. CL is mostly non-lethal and the most common presentation of this disease, with nearly 1 million new cases reported annually. Recognizing this unaddressed need, substantial yet fragmented progress in early drug discovery efforts for CL has occurred in the past 15 years and was outlined in this review. However, further work needs to be carried out to advance early discovery candidates towards the clinic. Importantly, there is a paucity of investment in the translation and development of therapies for CL, limiting the emergence of viable solutions to deal with this serious and complex international health problem.

Polymeric Delivery Systems as a Potential Vaccine against Visceral Leishmaniasis: Formulation Development and Immunogenicity

Recent studies suggest that the association of antigens in microparticles increases the anti-Leishmania vaccine immunogenicity. This study aims to investigate the in situ effect of the adjuvant performance consisting of chitosan-coated poly(D,L-lactic) acid submicrometric particles (SMP) and analyze the inflammatory profile and toxicity. Two formulations were selected, SMP1, containing poly(D,L-lactide) (PLA) 1% wt/v and chitosan 1% wt/v; and SMP2, containing PLA 5% wt/v and chitosan 5% wt/v. After a single dose of the unloaded SMP1 or SMP2 in mice, the SMPs promoted cell recruitment without tissue damage. In addition, besides the myeloperoxidase (MPO) activity having demonstrated similar results among the analyzed groups, a progressive reduction in the levels of N-acetyl-β-D-glucosaminidase (NAG) until 72 h was observed for SMPs. While IL-6 levels were similar among all the analyzed groups along the kinetics, only the SMPs groups had detectable levels of TNF-α. Additionally, the Leishmania braziliensis antigen was encapsulated in SMPs (SMP1Ag and SMP2Ag), and mice were vaccinated with three doses. The immunogenicity analysis by flow cytometry demonstrated a reduction in NK (CD3-CD49+) cells in all the SMPs groups, in addition to impairment in the T cells subsets (CD3+CD4+) and CD3+CD8+) and B cells (CD19+) of the SMP2 group. The resulting data demonstrate that the chitosan-coated SMP formulations stimulate the early events of an innate immune response, suggesting their ability to increase the immunogenicity of co-administered Leishmania antigens.

Vaccination with Formulation of Nanoparticles Loaded with Leishmania amazonensis Antigens Confers Protection against Experimental Visceral Leishmaniasis in Hamster

Visceral leishmaniasis (VL) is a fatal disease caused by the protozoa Leishmania infantum for which dogs are the main reservoirs. A vaccine against canine visceral leishmaniasis (CVL) could be an important tool in the control of human and CVL by reducing the infection pressure of L. infantum. Despite the CVL vaccine available on the market, the Brazilian Ministry of Health did not implement the use of it in their control programs. In this sense, there is an urgent need to develop more efficient vaccines. In this study, the association between two polymeric nanoformulations, (poly (D, L-lactic) acid (PLA) polymer) loading Leishmania amazonensis antigens, was evaluated as a potential immunobiological agent against VL using golden hamsters as an experimental model. The results indicated that no significant adverse reactions were observed in animals vaccinated with LAPSmP. LAPSmP presented similar levels of total anti-Leishmania IgG as compared to LAPSmG. The LAPSmP and LAPSmG groups showed an intense reduction in liver and spleen parasitic load by qPCR. The LAPSmP and LAPSmG vaccines showed exceptional results, indicating that they may be promising candidates as a VL vaccine.

Live attenuated Leishmania major p27 gene knockout as a novel vaccine candidate: A study on safety, protective immunity and efficacy against canine leishmaniasis caused by Leishmania infantum

Canine leishmaniasis (CanL) is an important parasitic e disease caused by Leishmania infantum and is transmitted by female phlebotomine sand flies primarily between canines and secondarily to humans. Recently, we showed that immunization with Leishmania major p27 gene knockout (Lmp27^-/-) as a live attenuated vaccine was safe, induced immunogenicity, and protected against the development cutaneous and visceral leishmaniasis in mice. The p27 protein is a component of the COX protein complex which is responsible for ATP production. In this study, we analyzed the Lmp27^-/- candidate vaccine potential with this regard to the safety and induction of immunogenicity and protection against CanL. Variables such a clinical manifestation, anti-Leishmania antibodies using direct agglutination test (DAT), lymphocyte proliferation, delayed-type hypersensitivity (DTH), bone marrow aspiration (BMA) and parasite burden using parasitological and molecular examinations were measured. The results demonstrated that the Lmp27^-/- vaccinated group showed no clinical signs after inoculation with Lmp27^-/- mutant during a 12-month follow-up, and had significantly higher T-cell responses (Lymphocyte proliferation and DTH), lower seroconversion and parasite burdens following a challenge inoculation with L. infantum after 6-mounth. In conclusion, vaccination with Lmp27^-/- parasites would be safe and provide significant immunoprotectivity and efficacy against infection with wild type (WT) L. infantum.

Evaluation of Cellular Immune Responses in Dogs Immunized with Alum-Precipitated Autoclaved Leishmania major along with BCG and Imiquimod

Background:

We aimed to investigate the potential effects of BCG and imiquimod on improvement of current experimental L. major vaccine against dogs in an endemic area of Zoonotic visceral leishmaniasis (ZVL) in Iran.

Methods:

During 2012 till 2014, seven mixed-breed shepherd dogs with no anti-Leishmania antibodies and no response to Leishmanin reagent were immunized with 2 doses of alum-precipitated autoclaved L. major (Alum-AML) while BCG and imiquimod (for skin pre-treatment) were used as adjuvants. The productions of a few characteristic cytokines of T-helper immune responses and the development of delayed-type hypersensitivity (DTH) of the immunized animals were then evaluated, up to 300 days. Blood samples were collected at 0, 30, 80 and 300 d post-vaccination and the concentrations of IFN-γ, IL10, IL-12 and TGF-β cytokines secreted from PBMCs at these time-points were quantified by ELISA. DTH was evaluated by Leishmanin skin test (LST).

Results:

Although a similar LST conversion was observed at all time-points, the cytokine measurement results indicated significantly higher levels of IFN-γ at day 80 and elevated levels of IL-10 at days 80 and 300, post-vaccination. Moreover, a significantly higher IFN-γ/IL-10 ratio was observed at day 30 post-vaccination compared to the other time-points.

Conclusion:

Although a Th1-like response could be observed at day 30 post-vaccination, the development of cytokine profiles was inclined toward mixed Th1 and Th2 responses at days 80 and 300 post-vaccination. This situation may indicate the requirement of an additional boosting by this Alum-AML formula, in order to induce long-lasting protection against ZVL.

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.

Live Attenuated Leishmania donovani Centrin Knock Out Parasites Generate Non-inferior Protective Immune Response in Aged Mice against Visceral Leishmaniasis

Background

Visceral leishmaniasis (VL) caused by the protozoan parasite Leishmania donovani causes severe disease. Age appears to be critical in determining the clinical outcome of VL and at present there is no effective vaccine available against VL for any age group. Previously, we showed that genetically modified live attenuated L. donovani parasites (LdCen-/-) induced a strong protective innate and adaptive immune response in young mice. In this study we analyzed LdCen-/- parasite mediated modulation of innate and adaptive immune response in aged mice (18 months) and compared to young (2 months) mice.

Methodology

Analysis of innate immune response in bone marrow derived dendritic cells (BMDCs) from both young and aged mice upon infection with LdCen-/- parasites, showed significant enhancement of innate effector responses, which consequently augmented CD4⁺ Th1 cell effector function compared to LdWT infected BMDCs in vitro. Similarly, parasitized splenic dendritic cells from LdCen-/- infected young and aged mice also revealed induction of proinflammatory cytokines (IL-12, IL-6, IFN-γ and TNF) and subsequent down regulation of anti-inflammatory cytokine (IL-10) genes compared to LdWT infected mice. We also evaluated in vivo protection of the LdCen-/- immunized young and aged mice against virulent L. donovani challenge. Immunization with LdCen-/- induced higher IgG2a antibodies, lymphoproliferative response, pro- and anti-inflammatory cytokine responses and stimulated splenocytes for heightened leishmanicidal activity associated with nitric oxide production in young and aged mice. Furthermore, upon virulent L. donovani challenge, LdCen-/- immunized mice from both age groups displayed multifunctional Th1-type CD4 and cytotoxic CD8 T cells correlating to a significantly reduced parasite burden in the spleen and liver compared to naïve mice. It is interesting to note that even though there was no difference in the LdCen-/- induced innate response in dendritic cells between aged and young mice; the adaptive response specifically in terms of T cell and B cell activation in aged animals was reduced compared to young mice which correlated with less protection in old mice compared to young mice.

Conclusions

Taken together, LdCen-/- immunization induced a significant but diminished host protective response in aged mice after challenge with virulent L. donovani parasites compared to young mice.

Visceral leishmaniasis (VL) is caused by the protozoan parasite Leishmania donovani. There is no effective vaccine available against VL for any age group and importantly, there are no previous studies regarding immune responses against experimental Leishmania vaccines tested in aged animals. We have reported earlier that immunization with a live attenuated L. donovani parasites (LdCen-/-) induced protective immune response in young animals viz, mice, hamsters and dogs. In this study we analyzed LdCen-/- mediated modulation of innate and adaptive responses in aged mice and compared to young mice. We observed that LdCen-/- infected dendritic cells from young and aged mice resulted in enhanced innate effector functions compared to LdWT parasites both in vitro and in vivo. Further, upon virulent challenge, LdCen-/- immunized young and aged mice displayed protective Th1 immune response which correlated with a significantly reduced parasite burden in the visceral organs compared with naïve challenged mice. Although there was no difference in the LdCen-/- induced dendritic cell response between aged and young mice; adaptive response in aged was reduced, compared to young which correlated with less protection in aged compared to young mice. This study supports the potential use of LdCen-/- as vaccine candidate across all age groups against VL.

Impact of LbSapSal Vaccine in Canine Immunological and Parasitological Features before and after Leishmania chagasi-Challenge

Dogs represent the most important domestic reservoir of L. chagasi (syn. L. infantum). A vaccine against canine visceral leishmaniasis (CVL) would be an important tool for decreasing the anxiety related to possible L. chagasi infection and for controlling human visceral leishmaniasis (VL). Because the sand fly salivary proteins are potent immunogens obligatorily co-deposited during transmission of Leishmania parasites, their inclusion in an anti-Leishmania vaccine has been investigated in past decades. We investigated the immunogenicity of the "LbSapSal" vaccine (L. braziliensis antigens, saponin as adjuvant, and Lutzomyia longipalpis salivary gland extract) in dogs at baseline (T0), during the post-vaccination protocol (T3rd) and after early (T90) and late (T885) times following L. chagasi-challenge. Our major data indicated that immunization with "LbSapSal" is able to induce biomarkers characterized by enhanced amounts of type I (tumor necrosis factor [TNF]-α, interleukin [IL]-12, interferon [IFN]-γ) cytokines and reduction in type II cytokines (IL-4 and TGF-β), even after experimental challenge. The establishment of a prominent pro-inflammatory immune response after "LbSapSal" immunization supported the increased levels of nitric oxide production, favoring a reduction in spleen parasitism (78.9%) and indicating long-lasting protection against L. chagasi infection. In conclusion, these results confirmed the hypothesis that the "LbSapSal" vaccination is a potential tool to control the Leishmania chagasi infection.

Application of rapid in vitro co-culture system of macrophages and T-cell subsets to assess the immunogenicity of dogs vaccinated with live attenuated Leishmania donovani centrin deleted parasites (LdCen-/-)

BACKGROUND

Live attenuated Leishmania donovani parasites as LdCen(-/-) were shown to confer protective immunity against Leishmania infection in mice, hamsters, and dogs. Strong immunogenicity in dogs vaccinated with LdCen(-/-) has been previously reported, including increased antibody response favoring Th1 response lymphoproliferative responses, CD4(+) and CD8(+) T-cells activation, increased levels of Th1 and reduction of Th2 cytokines, in addition to a significant reduction in parasite burden after 18 and 24 months post virulent parasite challenge.

METHODS

Aimed at validating a new method using in vitro co-culture systems with macrophages and purified CD4(+) or CD8(+) or CD4(+):CD8(+) T-cells of immunized dogs with both LdCen(-/-) and Leishmune® to assess microbicide capacity of macrophages and the immune response profile as the production of IFN-γ, TNF-α, IL-12, IL-4 and IL-10 cytokines.

RESULTS AND DISCUSSION

Our data showed co-cultures of macrophages and purified T-cells from dogs immunized with LdCen(-/-) and challenged with L. infantum were able to identify high microbicidal activity, especially in the co-culture using CD4(+) T-cells, as compared to the Leishmune® group. Similarly, co-cultures with CD8(+) T-cells or CD4(+):CD8(+) T-cells in both experimental groups were able to detect a reduction in the parasite burden in L. infantum infected macrophages. Moreover, co-cultures using CD4(+) or CD8(+) or CD4(+):CD8(+) T-cells from immunized dogs with both LdCen(-/-) and Leishmune® were able to identify higher levels of IFN-γ and IL-12 cytokines, reduced levels of IL-4 and IL-10, and a higher IFN-γ/IL-10 ratio. While the highest IFN-γ levels and IFN-γ/IL-10 ratio were the hallmarks of LdCen(-/-) group in the co-culture using CD4(+) T-cells, resulting in strong reduction of parasitism, the Leishmune® immunization presented a differential production of TNF-α in the co-culture using CD4(+):CD8(+) T-cells.

CONCLUSION

The distinct conditions of co-culture systems were validated and able to detect the induction of immune protection. The method described in this study applied a new, more accurate approach and was able to yield laboratory parameters useful to test and monitor the immunogenicity and efficacy of Leishmania vaccines in dogs.

Setting the proportion of CD4+ and CD8+ T-cells co-cultured with canine macrophages infected with Leishmania chagasi

New methods for evaluating the canine immune system are necessary, not only to monitor immunological disorders, but also to provide insights for vaccine evaluations and therapeutic interventions, reducing the costs of assays using dog models, and provide a more rational way for analyzing the canine immune response. The present study intended to establish an in vitro toll to assess the parasitological/immunological status of dogs, applicable in pre-clinical trials of vaccinology, prognosis follow-up and therapeutics analysis of canine visceral leishmaniasis. We have evaluated the performance of co-culture systems of canine Leishmania chagasi–infected macrophages with different cell ratios of total lymphocytes or purified CD4⁺ and CD8⁺ T-cells. Peripheral blood mononuclear cells from uninfected dogs were used for the system set up. Employing the co-culture systems of L. chagasi–infected macrophages and purified CD4⁺ or CD8⁺ T-cell subsets we observed a microenvironment compatible with the expected status of the analyzed dogs. In this context, it was clearly demonstrated that, at this selected T-cell:target ratio, the adaptive immune response of uninfected dogs, composed by L. chagasi-unprimed T-cells was not able to perform the in vitro killing of L. chagasi–infected macrophages. Our data demonstrated that the co-culture system with T-cells from uninfected dogs at 1:5 and 1:2 ratio did not control the infection, yielding to patent in vitro parasitism (≥80%), low NO production (≤5 μM) and IL-10 modulated (IFN-γ/IL-10≤2) immunological profile in vitro. CD4⁺ or CD8⁺ T-cells at 1:5 or 1:2 ratio to L. chagasi–infected macrophages seems to be ideal for in vitro assays. This co-culture system may have great potential as a canine immunological analysis method, as well as in vaccine evaluations, prognosis follow-up and therapeutic interventions.

Vaccination using live attenuated Leishmania donovani centrin deleted parasites induces protection in dogs against Leishmania infantum

Live attenuated Leishmania donovani parasites such as LdCen(-/-) have been shown elicit protective immunity against leishmanial infection in mice and hamster models. Previously, we have reported on the induction of strong immunogenicity in dogs upon vaccination with LdCen(-/-) including an increase in immunoglobulin isotypes, higher lymphoproliferative response, higher frequencies of activated CD4(+) and CD8(+) T cells, IFN-γ production by CD8(+) T cells, increased secretion of TNF-α and IL-12/IL-23p40 and, finally, decreased secretion of IL-4. To further explore the potential of LdCen(-/-) parasites as vaccine candidates, we performed a 24-month follow up of LdCen(-/-) immunized dogs after challenge with virulent Leishmania infantum, aiming determination of parasite burden by qPCR, antibody production (ELISA) and cellular responses (T cell activation and cytokine production) by flow cytometry and sandwich ELISA. Our data demonstrated that vaccination with a single dose of LdCen(-/-) (without any adjuvant) resulted in the reduction of up to 87.3% of parasite burden after 18 months of virulent challenge. These results are comparable to those obtained with commercially available vaccine in Brazil (Leishmune(®)). The protection was associated with antibody production and CD4(+) and CD8(+) proliferative responses, as well as T cell activation and significantly higher production of IFN-γ, IL-12/IL-23p40 and TNF-α, which was comparable to responses induced by immunization with Leishmune(®), with significant differences when compared to control animals (Placebo). Moreover, only animals immunized with LdCen(-/-) expressed lower levels of IL-4 when compared to animals vaccinated either with Leishmune(®) or PBS. Our results support further studies aiming to demonstrate the potential of genetically modified live attenuated L. donovani vaccine to control L. infantum transmission in endemic areas for CVL.

Mapping B-cell epitopes for the peroxidoxin of Leishmania (Viannia) braziliensis and its potential for the clinical diagnosis of tegumentary and visceral leishmaniasis

The search toward the establishment of novel serological tests for the diagnosis of leishmaniasis and proper differential diagnosis may represent one alternative to the invasive parasitological methods currently used to identify infected individuals. In the present work, we investigated the potential use of recombinant peroxidoxin (rPeroxidoxin) of Leishmania (Viannia) braziliensis as a potential antigen for the immunodiagnosis of human tegumentary (TL) and visceral leishmaniasis (VL) and canine visceral leishmaniasis (CVL). Linear B-cell epitope mapping was performed to identify polymorphic epitopes when comparing orthologous sequences present in Trypanosoma cruzi, the agent for Chagas disease (CD), and the Homo sapiens and Canis familiaris hosts. The serological assay (ELISA) demonstrated that TL, VL and CVL individuals showed high levels of antibodies against rPeroxidoxin, allowing identification of infected ones with considerable sensitivity and great ability to discriminate (specificity) between non-infected and CD individuals (98.46% and 100%; 98.18% and 95.71%; 95.79% and 100%, respectively). An rPeroxidoxin ELISA also showed a greater ability to discriminate between vaccinated and infected animals, which is an important requirement for the public campaign control of CVL. A depletion ELISA assay using soluble peptides of this B-cell epitope confirmed the recognition of these sites only by Leishmania-infected individuals. Moreover, this work identifies two antigenic polymorphic linear B-cell epitopes of L. braziliensis. Specific recognition of TL and VL patients was confirmed by significantly decreased IgG reactivity against rPeroxidoxin after depletion of peptide-1- and peptide-2-specific antibodies (peptide 1: reduced by 32%, 42% and 5% for CL, ML and VL, respectively; peptide-2: reduced by 24%, 22% and 13% for CL, ML and VL, respectively) and only peptide-2 for CVL (reduced 9%). Overall, rPeroxidoxin may be a potential antigen for the immunodiagnosis of TL, VL or CVL, as it has a higher agreement with parasitological assays and is better than other reference tests that use soluble Leishmania antigens for diagnosing CVL in Brazil (EIE-LVC, Bio-manguinhos, FIOCRUZ).

LBSapSal-vaccinated dogs exhibit increased circulating T-lymphocyte subsets (CD4⁺ and CD8⁺) as well as a reduction of parasitism after challenge with Leishmania infantum plus salivary gland of Lutzomyia longipalpis

BACKGROUND

The development of a protective vaccine against canine visceral leishmaniasis (CVL) is an alternative approach for interrupting the domestic cycle of Leishmania infantum. Given the importance of sand fly salivary proteins as potent immunogens obligatorily co-deposited during transmission of Leishmania parasites, their inclusion in an anti-Leishmania vaccine has been investigated in the last few decades. In this context, we previously immunized dogs with a vaccine composed of L. braziliensis antigens plus saponin as the adjuvant and sand fly salivary gland extract (LBSapSal vaccine). This vaccine elicited an increase in both anti-saliva and anti-Leishmania IgG isotypes, higher counts of specific circulating CD8⁺ T cells, and high NO production.

METHODS

We investigated the immunogenicity and protective effect of LBSapSal vaccination after intradermal challenge with 1 × 10⁷ late-log-phase L. infantum promastigotes in the presence of sand fly saliva of Lutzomyia longipalpis. The dogs were followed for up to 885 days after challenge.

RESULTS

The LBSapSal vaccine presents extensive antigenic diversity with persistent humoral and cellular immune responses, indicating resistance against CVL is triggered by high levels of total IgG and its subtypes (IgG1 and IgG2); expansion of circulating CD5⁺, CD4⁺, and CD8⁺ T lymphocytes and is Leishmania-specific; and reduction of splenic parasite load.

CONCLUSIONS

These results encourage further study of vaccine strategies addressing Leishmania antigens in combination with proteins present in the saliva of the vector.

Cytokine and nitric oxide patterns in dogs immunized with LBSap vaccine, before and after experimental challenge with Leishmania chagasi plus saliva of Lutzomyia longipalpis

In the studies presented here, dogs were vaccinated against Leishmania (Leishmania) chagasi challenge infection using a preparation of Leishmania braziliensis promastigote proteins and saponin as adjuvant (LBSap). Vaccination with LBSap induced a prominent type 1 immune response that was characterized by increased levels of interleukin (IL-) 12 and interferon gamma (IFN-γ) production by peripheral blood mononuclear cells (PBMC) upon stimulation with soluble vaccine antigen. Importantly, results showed that this type of responsiveness was sustained after challenge infection; at day 90 and 885 after L. chagasi challenge infection, PBMCs from LBSap vaccinated dogs produced more IL-12, IFN-γ and concomitant nitric oxide (NO) when stimulated with Leishmania antigens as compared to PBMCs from respective control groups (saponin, LB- treated, or non-treated control dogs). Moreover, transforming growth factor (TGF)-β decreased in the supernatant of SLcA-stimulated PBMCs in the LBSap group at 90 days. Bone marrow parasitological analysis revealed decreased frequency of parasitism in the presence of vaccine antigen. It is concluded that vaccination of dogs with LBSap vaccine induced a long-lasting type 1 immune response against L. chagasi challenge infection.

Analysis using canine peripheral blood for establishing in vitro conditions for monocyte differentiation into macrophages for Leishmania chagasi infection and T-cell subset purification

Canine visceral leishmaniasis (CVL) is a parasitic disease endemic in many countries, and dogs present as the major natural reservoir of the parasite, Leishmania chagasi (syn. L. infantum). Biomarkers in the canine immune system is an important technique in the course of developing vaccines and treatment strategies against CVL. New methodologies for studying the immune response of dogs during Leishmania infection and after receiving vaccines and treatments against CVL would be useful. In this context, we used peripheral blood mononuclear cells (PBMCs) from healthy dogs to evaluate procedures related to (i) establishment of in vitro conditions of monocytes differentiated into macrophages infected with L. chagasi and (ii) purification procedures of T-cell subsets (CD4⁺ and CD8⁺) using microbeads. Our data demonstrated that after 5 days of differentiation, macrophages were able to induce significant phagocytic and microbicidal activity after L. chagasi infection and also showed increased frequency of parasitism and a higher parasite load. Although N-acetyl-β-d-glucosaminidase (NAG) levels presented similar levels of macrophage culture and L. chagasi infection, a progressive decrease in myeloperoxidase (MPO) levels was a hallmark over 5 days of culture. High purity levels (>90%) of CD4 and CD8 T cells were obtained on a magnetic separation column. We concluded that monocytes differentiated into macrophages at 5 days and displayed an intermediate frequency of parasitism and parasite load 72 h after L. chagasi infection. Furthermore, the purification system using canine T-lymphocyte subsets obtained after 5 days of monocyte differentiation proved efficient for CD4 or CD8 T-cell purification (≥90%). The in vitro analysis using L. chagasi-infected macrophages and purified T cells presented a prospective methodology that could be incorporated in CVL vaccine and treatment studies that aim to analyze the microbicidal potential induced by specific CD4⁺ and/or CD8⁺ T cells.

Dogs immunized with LBSap vaccine displayed high levels of IL-12 and IL-10 cytokines and CCL4, CCL5 and CXCL8 chemokines in the dermis

The complex interplay between cytokines and chemokines regulates innate and adaptive immune responses against pathogens; specifically, cytokine and chemokine expression drives activation of immune effector cells and their recruitment to tissue infection sites. Herein, we inoculated dogs with Leishmania braziliensis antigens plus saponin (the LBSap vaccine), as well as with the vaccine components, and then used real-time PCR to evaluate the kinetics of dermal expression of mRNAs of cytokines (IL-12, IFN-γ, TNF-α, IL-4, IL-13, TGF-β and IL-10) and chemokines (CCL2, CCL4, CCL5, CCL21 and CXCL8) 1, 12, 24 and 48 h after inoculation. We also evaluated the correlation between cytokine and chemokine expression and dermal cellularity. The LBSap vaccine induced high levels of IL-12 and IL-10 expression at 12 and 24 h, respectively. Furthermore, we observed positive correlations between IL-12 and IL-13 expression, IFN-γ and IL-13 expression, and IL-13 and TGF-β expression, suggesting that a mixed cytokine microenvironment developed after immunization with the vaccine. Inoculation with the saponin adjuvant alone induced a chemokine and cytokine expression profile similar to that observed in the LBSap group. CCL4 and CXCL8 chemokine expression was up regulated by the LBSap vaccine. CCL5 expression was initially highest in the LBSap group, but at 48 h, expression was highest in the LB group. Information about the kinetics of the immune response to this vaccine gained using this dog model will help to elucidate the mechanisms of and factors involved in a protective response against Leishmania infection and will aid in establishing rational approaches for the development of vaccines against canine visceral leishmaniasis.

Induction of immunogenicity by live attenuated Leishmania donovani centrin deleted parasites in dogs

Zoonotic visceral leishmaniasis, caused by the intracellular protozoan parasite Leishmania infantum, is a neglected tropical disease that is often fatal when untreated. Dogs are considered the main reservoir of L. infantum in zoonotic VL as the presence of infected dogs may increase the risk for human infection. Canine visceral leishmaniasis (CVL) is a major veterinary and public health problem in Southern Europe, Middle East and South America. Control of animal reservoirs relies on elimination of seropositive dogs in endemic areas. However, treatment of infected dogs is not considered a favorable approach as this can lead to emergence of drug resistance since the same drugs are used to treat human infections. Therefore, vaccination against CVL remains the best alternative in control of the animal reservoirs. In this study, we present data on the immunogenicity profile of a live attenuated parasite LdCen(-/-) in a canine infection model and compared it to that of Leishmune(®), a commercially available recombinant vaccine. The immunogenicity of the LdCen(-/-) parasites was evaluated by antibody secretion, production of intracytoplasmic and secreted cytokines, activation and proliferation of T cells. Vaccination with LdCen(-/-) resulted in high immunogenicity as revealed by the higher IgGTotal, IgG1, and IgG2 production and higher lymphoproliferative response. Further, LdCen(-/-) vaccinated dogs showed higher frequencies of activated CD4+ and CD8+ T cells, IFN-γ production by CD8+ T cells, increased secretion of TNF-α and IL-12/IL-23p40 and decreased secretion of IL-4. These results contribute to the understanding of immunogenicity elicited by live attenuated L. donovani parasites and, consequently, to the development of effective vaccines against visceral leishmaniasis.

Performance of LBSap vaccine after intradermal challenge with L. infantum and saliva of Lu. longipalpis: immunogenicity and parasitological evaluation

In the last decade, the search for new vaccines against canine visceral leishmaniasis has intensified. However, the pattern related to immune protection during long periods after experimental infection in vaccine trials is still not fully understood. Herein, we investigated the immunogenicity and parasitological levels after intradermal challenge with Leishmania infantum plus salivary gland extract in dogs immunized with a vaccine composed of L. braziliensis antigens plus saponin as an adjuvant (LBSap vaccine). The LBSap vaccine elicited higher levels of total anti-Leishmania IgG as well as both IgG1 and IgG2. Furthermore, dogs vaccinated had increased levels of lymphocytes, particularly circulating B cells (CD21(+)) and both CD4(+) and CD8(+) T lymphocytes. LBSap also elicited an intense in vitro cell proliferation associated with higher levels of CD4(+) T lymphocytes specific for vaccine soluble antigen and soluble lysate of L. infantum antigen even 885 days after experimental challenge. Furthermore, LBSap vaccinated dogs presented high IFN-γ and low IL-10 and TGF-β1 expression in spleen with significant reduction of parasite load in this tissue. Overall, our results validate the potential of LBSap vaccine to protect against L. infantum experimental infection and strongly support further evaluation of efficiency of LBSap against CVL in natural infection conditions.

Humoral and cellular immune responses in adult geese induced by an inactivated vaccine against new type gosling viral enteritis virus

To assess the immunogenicity of an inactivated new type gosling viral enteritis virus (NGVEV) vaccine, we investigated 3 different doses of the inactivated vaccine and the inactivated vaccine in conjunction with 3 different doses of recombinant goose interleukin-2 (rGoIL-2) adjuvant. A virus concentration of 10(5) 50% embryo infective dose/mL was subcutaneously inoculated into adult geese divided into 6 groups. The dynamic changes of the humoral and cellular immunity responses elicited by the vaccines in the adult geese postvaccination (PV) were investigated using ELISA, virus neutralization test, and lymphocyte proliferation assay. The clearance of virus from the intestines of geese (175 d PV) was studied by histopathological examination and indirect immunofluorescence assay after virulent NGVEV challenge. This study showed that the inactivated NGVEV vaccine elicits strong humoral and cellular responses in the vaccinated adult geese. The absorbance values of specific anti-NGVEV antibodies, the neutralization antibody titer, and the lymphocyte proliferation index rapidly increased, peaked at about 28 d PV, progressed to the plateau stage, and then decreased slightly. The rGoIL-2 adjuvant enhanced the immune response, and this adjuvant in conjunction with the inactivated NGVEV vaccine induces a significantly higher specific anti-NGVEV antibody absorbance value, neutralization antibody titer, and lymphocyte proliferation index than the non-adjuvant-inactivated NGVEV vaccine (P < 0.05). The inactivated NGVEV vaccine conferred adequate efficient ability to clear NGVEV in vaccinated geese even in the last phase of the vaccination period (175 d PV). The inactivated NGVEV vaccine (0.5 mL/goose) with 1,000 units of rGoIL-2 adjuvant/goose is the most effective dose, thereby eliciting the strongest humoral and cellular immunity responses and providing the most efficacious clearance of NGVEV in vivo.

Exacerbation of Leishmania (Viannia) shawi infection in BALB/c mice after immunization with soluble antigen from amastigote forms

The present study aimed to evaluate the effects of immunization with soluble amastigote (AmaAg) and promastigote (ProAg) antigens from Leishmania (Viannia) shawi on the course of infection in BALB/c mice. After immunization with AmaAg, the challenged group showed greater lesion size and parasite load in the skin and lymph nodes, associated with diminished interleukin (IL)-2, IL-4, IL-10, interferon (IFN)-γ and nitrate levels in the supernatant of lymph node cell cultures, together with increases in transforming growth factor (TGF)-β concentrations and humoral immune response. In contrast, immunization with ProAg led to smaller lesion size with reduced numbers of viable parasites in the skin. Protection was associated with increases in IL-12, IFN-γ, TGF-β and nitrates and decreases in IL-4 and IL-10 levels. Concerning humoral immune response, a significant reduction in anti-leishmania immunoglobulin G was verified in the ProAg-challenged group. Analysis of these results suggests that AmaAg induced a suppressive cellular immune response in mice, favouring the spread of infection, whereas ProAg induced partial protection associated with increased cellular immune response.

Immunity to Leishmania and the rational search for vaccines against canine leishmaniasis

The control of infection by Leishmania infantum (syn. Leishmania chagasi) in dogs is essential to stop the current spread of zoonotic visceral leishmaniasis. The past few years have seen significant advances in achieving efficient immunization of dogs and, more than ever before, an effective vaccine against canine leishmaniasis can now be considered a feasible goal. This article summarizes experimental data gathered from recent dog trials aimed at identifying immunological mechanisms implicated in protection against canine infection to discuss their potential to serve as quantitative surrogate markers of immunization and, more importantly, its usefulness to evaluate whether the immunity induced by the vaccine candidate is strong enough to protect against canine leishmaniasis.

Vaccine development against Trypanosoma cruzi and Leishmania species in the post-genomic era

Trypanosoma cruzi and the genus Leishmania are protozoan parasites causing diseases of major public health importance, and the recent completion of the sequencing of their genomes has opened new opportunities to further our understanding of the mechanisms required for protection and the development of vaccines. For example, trans-sialidases, one of the largest protein families from T. cruzi, contain dominant CD8+ T cell epitopes, and their use as preventive or therapeutic vaccines in different animal models has provided encouraging results. A much wider range of antigens and vaccine formulations have been tested against Leishmania, and new correlates for protection are being defined, such as the induction of multifunctional Th1 effector cells capable of producing a complex set of cytokines. Also, while a large number of these vaccine candidates have been rather successful in mouse models, their usefulness in more relevant animal models is still poor, in spite of significant immunogenicity. Novel proteomics and genomics approaches are being used for antigen discovery and the identification of new vaccine candidates, some of which have shown promise for the control of infection. These studies cast little doubt that T. cruzi and Leishmania genomes represent major resources for understanding key aspects of the mechanisms of immune protection against these parasites, and the increasing use of these tools will greatly impact vaccine development.

Kinetics of cell migration to the dermis and hypodermis in dogs vaccinated with antigenic compounds of Leishmania braziliensis plus saponin

The search for new immunobiologicals against canine visceral leishmaniasis (CVL) has intensified in the last decade. However, it still remains to be elucidated that mechanisms of the innate immune response in situ after immunization (a.i.). The aim of this study was to investigate the kinetics of cell migration in the skin dogs with distinct antigenic compounds of the LBSap vaccine. Our major findings indicated that saponin adjuvant alone or combined with Leishmania braziliensis antigen induced strong local acute inflammatory reaction. However, these reactions not progressed to ulcerated lesions. Overall, the cell profile found in Sap and LBSap was composed of neutrophils, lymphocytes and eosinophils. There was also increased production of iNOS in Sap and LBSap groups. Thus, we can conclude that dogs immunized by LBSap and the saponin adjuvant elicited a potential innate-immune activations status compatible with effective control of the resistance to infection by Leishmania and contributing to a better understanding of the innate-immunity events induced by the LBSap vaccine.

A killed Leishmania vaccine with sand fly saliva extract and saponin adjuvant displays immunogenicity in dogs

A vaccine against canine visceral leishmaniasis (CVL), comprising Leishmania braziliensis promastigote protein, sand fly gland extract (SGE) and saponin adjuvant, was evaluated in dog model, in order to analyse the immunogenicity of the candidate vaccine. The vaccine candidate elicited strong antigenicity in dogs in respect of specific SGE and Leishmania humoral immune response. The major saliva proteins recognized by serum from immunized dogs exhibited molecular weights of 35 and 45 kDa, and were related to the resistance pattern against Leishmania infection. Immunophenotypic analysis revealed increased circulating CD21⁺ B-cells and CD5⁺ T-cells, reflected by higher counts of CD4⁺ and CD8⁺ T-cells. The observed interaction between potential antigen-presenting cells (evaluated as CD14⁺ monocytes) and lymphocyte activation status indicated a relationship between innate and adaptive immune responses. The higher frequency in L. chagasi antigen-specific CD8⁺ T-lymphocytes, and their positive association with intense cell proliferation, in addition to the progressively higher production of serum nitric oxide levels, showed a profile compatible with anti-CVL vaccine potential. Further studies on immunological response after challenge with L. chagasi may provide important information that will lead to a better understanding on vaccine trial and efficacy.