Phase I and II Clinical Trial Comparing the LBSap, Leishmune®, and Leish-Tec® Vaccines against Canine Visceral Leishmaniasis

LmCen-/- based vaccine is protective against canine visceral leishmaniasis following three natural exposures in Tunisia

Dogs are the main reservoir host of Leishmania infantum, etiological agent of zoonotic visceral leishmaniasis (ZVL). An effective vaccine against Canine Visceral Leishmaniasis (CVL) will help the control and elimination of ZVL. In this study, we evaluated in dogs the safety, immunogenicity, and efficacy of a live attenuated Leishmania major Centrin gene-deleted (LmCen-/-) as a vaccine. Two doses (106 or 107) of LmCen-/- vaccine were administered intradermally in a prime-boost regimen. Both vaccine doses induced equally high level of IgG anti-Leishmania and exhibited strong antigen-specific cellular responses with IFN-γ production by CD4 + T cells one-month post-immunization. A second cohort of dogs was vaccinated with 106 LmCen-/- parasites one month prior to their transfer to a CVL endemic focus in Northern Tunisia for exposure to sand fly bites during three successive transmission seasons. Dogs were exposed to bite from naturally infected sandflies for 3-5 months per year. Our results showed that only 1/11 vaccinated dogs became PCR positive for Leishmania and developed clinical signs of CVL. In contrast, 4/11 unvaccinated dogs were tested PCR positive for Leishmania and displayed oligosymptomatic CVL, demonstrating that immunization with LmCen-/- vaccine confers long-term protection with an efficacy of 82.5% against CVL in natural transmission settings.

Efficacy of LaAg Vaccine Associated with Saponin Against Leishmania amazonensis Infection

BACKGROUND/OBJECTIVES

The total lysate of Leishmania amazonensis (LaAg) is one of the most extensively studied vaccine formulations against leishmaniasis. Despite demonstrating safety and immunogenicity when administered intramuscularly, LaAg has failed to show efficacy in clinical trials and, in some cases, has even been associated with an enhanced susceptibility to infection. Adjuvants, which are molecules or compounds added to antigens to enhance the immunogenicity or modulate the immune response, are frequently employed in vaccine studies. This study aimed to evaluate different adjuvants to improve the protective efficacy of LaAg in L.amazonensis infection using a BALB/c mouse model.

METHODS

BALB/c mice were immunized with LaAg in combination with various adjuvants. The delayed-type hypersensitivity (DTH) test was assessed by measuring the infected paw and was used to evaluate the immunogenicity and to determine the most effective adjuvant. The immune response was analyzed through flow cytometry, focusing on cytokine production, immune cell recruitment and lesion size, alongside the control of parasite load at the infection site. The expression levels of iNOS and TGF-β were quantified using RT-qPCR, while IgG1, IgG2a and IgE antibody levels were determined via ELISA.

RESULTS

Among the adjuvants tested, only saponin (SAP) elicited a significant DTH response following LaAg challenge. SAP enhanced the immunogenicity of LaAg, as evidenced by increased IFN-γ-producing CD4+ and CD8+ T cells in the draining lymph nodes at 18 h post-challenge. Additionally, SAP facilitated the recruitment of lymphocytes, macrophages, neutrophils and eosinophils to the infection site.

CONCLUSIONS

The LaAg + SAP combination conferred partial protection, as demonstrated by a reduction in lesion size and the partial control of parasite load. In conclusion, the addition of SAP as an adjuvant to LaAg effectively modulates the immune response, enhancing the vaccine's protective efficacy. These findings provide valuable insights into the development of improved vaccines against L.amazonensis infection.

Application of the Sponge Model Implants in the Study of Vaccine Memory in Mice Previously Immunized with LBSap

BACKGROUND/OBJECTIVES

Considering the large number of candidates in vaccine-testing studies against different pathogens and the amount of time spent in the preclinical and clinical trials, there is a pressing need to develop an improved in vivo system to quickly screen vaccine candidates. The model of a polyester-polyurethane sponge implant provides a rapid analysis of the specific stimulus-response, allowing the study of a compartmentalized microenvironment. The sponge implant's defined measurements were standardized as a compartment to assess the immune response triggered by the vaccinal antigen. The LBSap vaccine (composed of Leishmania braziliensis antigens associated with saponin adjuvant) was used in the sponge model to assess the antigen-specific immunological biomarker, including memory generation after initial contact with the antigen.

METHODS

Mice strains (Swiss, BALB/c, and C57BL/6) were previously immunized using LBSap vaccine, followed by an antigenic booster performed inside the sponge implant. The sponge implants were assessed after 72 h, and the immune response pattern was analyzed according to leukocyte immunophenotyping and cytokine production.

RESULTS

After LBSap vaccination, the innate immune response of the antigenic booster in the sponge implants demonstrated higher levels in the Ly+ neutrophils and CD11c+ dendritic cells with reduced numbers of F4/80+ macrophages. Moreover, the adaptive immune response in Swiss mice demonstrated a high CD3+CD4+ T-cell frequency, consisting of an effector memory component, in addition to a cytoxicity response (CD3+CD8+ T cells), displaying the central memory biomarker. The major cell surface biomarker in the BALB/c mice strain was related to CD3+CD4+ effector memory, while the increased CD3+CD8+ effector memory was highlighted in C57/BL6. The cytokine profile was more inflammatory in Swiss mice, with the highest levels of IL-6, TNF, IFN-g, and IL-17, while the same cytokine was observed in in C57BL/6 yet modulated by enhanced IL-10 levels. Similar to Swiss mice, BALB/c mice triggered an inflammatory environment after the antigenic booster in the sponge implant with the increased levels in the ILL-6, TNF, and IFN-g.

CONCLUSIONS

The findings emphasized the impact of genetic background on the populations engaged in immune responses, suggesting that this model can be utilized to enhance and track both innate and adaptive immune responses in vaccine candidates. Consequently, these results may inform the selection of the most suitable experimental model for biomolecule testing, taking into account how the unique characteristics of each mouse strain affect the immune response dynamics.

Synthetic Peptides Selected by Immunoinformatics as Potential Tools for the Specific Diagnosis of Canine Visceral Leishmaniasis

Diagnosing canine visceral leishmaniasis (CVL) in Brazil faces challenges due to the limitations regarding the sensitivity and specificity of the current diagnostic protocol. Therefore, it is urgent to map new antigens or enhance the existing ones for future diagnostic techniques. Immunoinformatic tools are promising in the identification of new potential epitopes or antigen candidates. In this study, we evaluated peptides selected by epitope prediction for CVL serodiagnosis in ELISA assays. Ten B-cell epitopes were immunogenic in silico, but two peptides (peptides No. 45 and No. 48) showed the best performance in vitro. The selected peptides, both individually and in combination, were highly diagnostically accurate, with sensitivities ranging from 86.4% to 100% and with a specificity of approximately 90%. We observed that the combination of peptides showed better performance when compared to peptide alone, by detecting all asymptomatic dogs, showing lower cross-reactivity in sera from dogs with other canine infections, and did not detect vaccinated animals. Moreover, our data indicate the potential use of immunoinformatic tools associated with ELISA assays for the selection and evaluation of potential new targets, such as peptides, applied to the diagnosis of CVL.

Transmission-Blocking Vaccines for Canine Visceral Leishmaniasis: New Progress and Yet New Challenges

Dogs with visceral leishmaniasis play a key role in the transmission cycle of Leishmania infantum to humans in the urban environment. There is a consensus regarding the importance of developing a vaccine to control this disease. Despite many efforts to develop a protective vaccine against CVL, the ones currently available, Leish-tec® and LetiFend®, have limited effectiveness. This is due, in part, to the complexity of the immune response of the naturally infected dogs against the parasite and the complexity of the parasite transmission cycle. Thus, strategies, such as the development of a transmission-blocking vaccines (TBVs) already being applied to other vector-borne diseases like malaria and dengue, would be an attractive alternative to control leishmaniasis. TBVs induce the production of antibodies in the vertebrate host, which can inhibit parasite development in the vector and/or interfere with aspects of vector biology, leading to an interruption of parasite transmission. To date, there are few TBV studies for CVL and other leishmaniasis forms. However, the few studies that exist show promising results, thus justifying the further development of this approach.

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.

Immunoprophylaxis using polypeptide chimera vaccines plus adjuvant system promote Th1 response controlling the spleen parasitism in hamster model of visceral leishmaniasis

In recent years, several advances have been observed in vaccinology especially for neglected tropical diseases (NTDs). One of the tools employed is epitope prediction by immunoinformatic approaches that reduce the time and cost to develop a vaccine. In this scenario, immunoinformatics is being more often used to develop vaccines for NTDs, in particular visceral leishmaniasis (VL) which is proven not to have an effective vaccine yet. Based on that, in a previous study, two predicted T-cell multi-epitope chimera vaccines were experimentally validated in BALB/c mice to evaluate the immunogenicity, central and effector memory and protection against VL. Considering the results obtained in the mouse model, we assessed the immune response of these chimeras inMesocricetus auratushamster, which displays, experimentally, similar pathological status to human and dog VL disease. Our findings indicate that both chimeras lead to a dominant Th1 response profile, inducing a strong cellular response by increasing the production of IFN-γ and TNF-α cytokines associated with a decrease in IL-10. Also, the chimeras reduced the spleen parasite load and the weight a correlation between protector immunological mechanisms and consistent reduction of the parasitic load was observed. Our results demonstrate that both chimeras were immunogenic and corroborate with findings in the mouse model. Therefore, we reinforce the use of the hamster as a pre-clinical model in vaccination trials for canine and human VL and the importance of immunoinformatic to identify epitopes to design vaccines for this important neglected disease.

Host–Pathogen Interaction in Leishmaniasis: Immune Response and Vaccination Strategies

Leishmaniasis is a zoonotic and vector-borne infectious disease that is caused by the genus Leishmania belonging to the trypanosomatid family. The protozoan parasite has a digenetic life cycle involving a mammalian host and an insect vector. Leishmaniasisis is a worldwide public health problem falling under the neglected tropical disease category, with over 90 endemic countries, and approximately 1 million new cases and 20,000 deaths annually. Leishmania infection can progress toward the development of species–specific pathologic disorders, ranging in severity from self-healing cutaneous lesions to disseminating muco-cutaneous and fatal visceral manifestations. The severity and the outcome of leishmaniasis is determined by the parasite’s antigenic epitope characteristics, the vector physiology, and most importantly, the immune response and immune status of the host. This review examines the nature of host–pathogen interaction in leishmaniasis, innate and adaptive immune responses, and various strategies that have been employed for vaccine development.

Nutritional Modulation of the Immune Response Mediated by Nucleotides in Canine Leishmaniosis

Leishmaniasis is an emerging, uncontrolled, and neglected zoonotic disease. Climate change is contributing to its ongoing global expansion. The dog is the main reservoir; hence the importance of implementing effective treatment, prevention, and control measures in this animal species to protect public health. However, although the standard treatment for canine leishmaniosis (CanL) is effective, it does not provide full parasitological clearance, and side effects and drug resistance have been described. The host's immune system plays a key role in the establishment and evolution of leishmaniasis. Dietary nucleotides modulate the immune response and, given their reported efficacy and safety in sick and clinically healthy Leishmania-infected dogs and because they represent a sustainable option with no associated side effects or resistance, they could be included within the prevention, treatment, and control strategies for leishmaniasis. This article briefly summarizes the scientific literature on CanL management, including unresolved issues, and reviews the scientific evidence on immunomodulatory effects of dietary nucleotides in different animal species. It also proposes a CanL management algorithm, including nucleotides. It is concluded that nutritional modulation of the immune response with nucleotides can contribute to better management of leishmaniasis following a One Health approach, especially in the COVID-19 era.