Pam3CSK4 adjuvant given intranasally boosts anti-Leishmania immunogenicity but not protective immune responses conferred by LaAg vaccine against visceral 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.

Intranasal delivery of LaAg vaccine improves immunity of aged mice against visceral Leishmaniasis

There are no approved vaccines yet for human visceral leishmaniasis (VL), the most severe form of the leishmaniasis clinical manifestations that is fatal in over 95 % of untreated cases. It is well-accepted that immunological changes during aging have deleterious impact on the efficacy of vaccines and response to infections. In this work, we compared the response of young and aged mice to intranasal vaccination with killed Leishmania amazonensis promastigote antigens (LaAg) that were then challenged with L. infantum infection, a species that causes visceral leishmaniasis. Intranasal vaccination with LaAg induced a similar reduction in parasitism and hepatosplenomegaly in both young and aged mice compared to their unvaccinated counterparts. Following infection, there was also a less prominent inflammatory profile particularly in the vaccinated aged group, with lower production of TNF-α and nitrite compared to the respective unvaccinated group. Interestingly, the LaAg intranasal vaccination promoted increased production of IFN-γ that was observed in both young- and aged vaccinated groups. Additionally, CD4+ and CD8+T cells from both vaccinated groups presented decreased expression of the inhibitory receptors PD-1 and KLRG1 compared to their unvaccinated controls. Interestingly, a strong positive correlation was observed between the expression of both inhibitory receptors PD-1 and KLRG1 and parasitism, which was more conspicuous in the unvaccinated-aged mice than in the others. Overall, this study helps define new strategies to improve vaccine effectiveness and provides a perspective for prophylactic alternatives against leishmaniasis.

Enhancing Control of Leishmania infantum Infection: A Multi-Epitope Nanovaccine for Durable T-Cell Immunity

Canine leishmaniosis (CanL) is a growing health problem for which vaccination is a crucial tool for the control of disease. The successful development of an effective vaccine against this disease relies on eliciting a robust and enduring T-cell immune response involving the activation of CD4+ Th1 and CD8+ T-cells. This study aimed to evaluate the immunogenicity and prophylactic efficacy of a novel nanovaccine comprising a multi-epitope peptide, known as HisDTC, encapsulated in PLGA nanoparticles against Leishmania infantum infection in the murine model. The encapsulation strategy was designed to enhance antigen loading and sustain release, ensuring prolonged exposure to the immune system. Our results showed that mice immunized with PLGA-encapsulated HisDTC exhibited a significant reduction in the parasite load in the liver and spleen over both short and long-term duration. This reduction was associated with a cellular immune profile marked by elevated levels of pro-inflammatory cytokines, such as IFN-γ, and the generation of memory T cells. In conclusion, the current study establishes that PLGA-encapsulated HisDTC can promote effective and long-lasting T-cell responses against L. infantum in the murine model. These findings underscore the potential utility of multi-epitope vaccines, in conjunction with appropriate delivery systems, as an alternative strategy for CanL control.

TLR-2 agonist Pam3CSK4 has no therapeutic effect on visceral leishmaniasis in BALB/c mice and may enhance the pathogenesis of the disease

Most of the existing Leishmania-related research about TLR-2 agonists was focusing on their role as adjuvants in the vaccine, few studied its therapeutic effect. This paper aims to explore the therapeutic effect of TLR-2 agonist Pam3CSK4 on Leishmania-infected mice and the underlying immune molecular mechanisms. In L. donovani-infected BALB/c mice, one group was treated with Pam3CSK4 after infection and the other group was not treated. Normal uninfected mice treated with Pam3CSK4 or untreated were used as controls. Parasite load, hepatic pathology and serum antibodies were detected to assess the severity of the infection. The expression of immune-related genes, spleen lymphocyte subsets and liver RNA-seq were employed to reveal possible molecular mechanisms. The results showed that the liver and spleen parasite load of infected mice in Pam3CSK4 treated and untreated groups had no statistical difference, indicating Pam3CSK4 might have no therapeutic effect on visceral leishmaniasis. Infected mice treated with Pam3CSK4 possessed more hepatic inflammation focus, lower IgG and IgG2a antibody titers, and a lower proportion of spleen CD3+CD4+ T cells. Transcriptome analysis revealed that Th1/Th2 differentiation, NK cells, Th17 cell, complement system and calcium signaling pathways were down-regulated post-treatment of Pam3CSK4. In this study, TLR-2 agonist Pam3CSK4 showed no therapeutic effect on visceral leishmaniasis in BALB/c mice and might enhance the pathogenesis of the disease possibly due to the down-regulation of several immune-related pathways, which can improve our understanding of the role of TLR-2 in both treatment and vaccine development.

Adjuvant Pam3CSk4 does not improve the immunization against Cryptococcus gattii infection in C57BL/6 mice

Background

Cryptococcosis is a relevant invasive fungal infection that affects immunocompromised and immunocompetent individuals when caused by Cryptococcus gattii. Host innate and adaptive immune responses can be subverted by C. gattii, that blocks the differentiation of T helper (Th) 1 and Th17 cells, which are involved in the protection against cryptococcosis. Moreover, the macrophage polarization is modulated by C. gattii infection that requires a balance in the macrophage subsets to control the C. gattii infection. Toll-like receptor (TLR) 2 agonists are important immunomodulators favoring a pro-inflammatory response with potential fungicidal activity, and TLR2 agonists have been used as adjuvants in vaccines against infections caused by bacteria or viruses. Therefore, this work aimed to evaluate the immunomodulatory effect of the tripalmitoyl lipopeptide S-glycerol cysteine (Pam3CSK4 or P3C4), a TLR2 agonist, as an adjuvant in the vaccination against C. gattii infection.

Methods and Results

C57BL/6 mice were immunized with 2 × 10⁷ inactivated yeasts of C. gattii via intranasal route on day 1, 14 and 28 (Immunized group). Immunization was associated with 1µg or 10µg of adjuvant P3C4 (Immunized+P3C4-1µg or Immunized+P3C4-10 µg), followed by C. gattii infection on day 42 after the immunization protocol. Immunized+P3C4-1 µg group had reduced levels of IgG1, IgG2a and IgA and no significant difference in the IgG and IgM anti-GXM antibody titer was detected, compared to the Immunized group. High levels of IL-17 and IL-1β in lung tissue of mice from the Immunized+P3C4-1µg group did not promote a predominance of Th17 cells, in contrast, the frequency of TLR2⁺ cells was increased in immunized mice that received 1 µg of P3C4. The reduction in the relative expression of T-bet and high levels of Foxp3 detected in the lungs of the Immunized+P3C4-1µg group suggest a prevalence of regulatory T cells in the tissue, which did not contribute to the control of C. gattii infection. The immunization protocol associated with 10 µg of adjuvant P3C4 induced high levels of IL-17 in the lung tissue, whereas the levels of pro-inflammatory cytokines were downregulated. To evaluate the effect of adjuvant P3C4 in the control of C. gattii infection, quantification of the fungal burden in the lungs was performed by the CFU assay, and the groups with adjuvant P3C4 showed a pulmonary C. gattii burden that was not significantly altered when compared with the immunized group. The mice that received 1 µg of adjuvant P3C4 had a lower percentage of inflammatory infiltrate in the lungs.

Conclusion

The immunomodulatory effect of P3C4, associated with the immunization protocol, plays an imbalance between pro- and anti-inflammatory response in the lungs that did not favor a protection against C. gattii infection, which is related to the immune response characterized by a suppressive/regulatory profile in the pulmonary microenvironment after C. gattii infection.

Intranasal vaccine from whole Leishmania donovani antigens provides protection and induces specific immune response against visceral leishmaniasis

Visceral leishmaniasis is a protozoan disease associated with high fatality rate in developing countries. Although the drug pipeline is constantly improving, available treatments are costly and live-threatening side effects are not uncommon. Moreover, an approved vaccine against human leishmaniasis does not exist yet. Using whole antigens from Leishmania donovani promastigotes (LdAg), we investigated the protective potential of a novel adjuvant-free vaccine strategy. Immunization of mice with LdAg via the intradermal or the intranasal route prior to infection decreases the parasitic burden in primary affected internal organs, including the liver, spleen, and bone marrow. Interestingly, the intranasal route is more efficient than the intradermal route, leading to better parasite clearance and remarkable induction of adaptive immune cells, notably the helper and cytotoxic T cells. In vitro restimulation experiments with Leishmania antigens led to significant IFN-γ secretion by splenocytes; therefore, exemplifying specificity of the adaptive immune response. To improve mucosal delivery and the immunogenic aspects of our vaccine strategy, we used polysaccharide-based nanoparticles (NP) that carry the antigens. The NP-LdAg formulation is remarkably taken up by dendritic cells and induces their maturation in vitro, as revealed by the increased expression of CD80, CD86 and MHC II. Intranasal immunization with NP-LdAg does not improve the parasite clearance in our experimental timeline; however, it does increase the percentage of effector and memory T helper cells in the spleen, suggesting a potential induction of long-term memory. Altogether, this study provides a simple and cost-effective vaccine strategy against visceral leishmaniasis based on LdAg administration via the intranasal route, which could be applicable to other parasitic diseases.

Visceral leishmaniasis is a neglected tropical disease caused by specific species of Leishmania parasites that affect internal organs including spleen, liver, and bone marrow. The infective stage called promastigote, is transmitted into the host skin via sandfly bites. Visceral leishmaniasis is usually associated with high mortality rate in poor and developing countries, lacking proper health assistance. Moreover, treatments are expensive while no approved vaccines exist to prevent infection and avoid disease outbreaks. This study suggests an affordable and adjuvant-free vaccine formulation made from the total lysate of promastigotes. Vaccine administration via the intranasal route, ensures a remarkable clearance of Leishmania parasites from the internal organs of infected experimental mice. In particular, intranasal route known to be not invasive, is efficient in inducing adequate immune response against the infective form of the parasite. Further studies are now required to improve this prophylactic vaccine and provide therefore the basis for a promising translational approach.

Evaluation of different total Leishmania amazonensis antigens for the development of a first-generation vaccine formulated with a Toll-like receptor-3 agonist to prevent cutaneous leishmaniasis

BACKGROUND

Unfortunately, no any vaccine against leishmaniasis has been developed for human use. Therefore, a vaccine based on total Leishmania antigens could be a good and economic approach; and there are different methodologies to obtain these antigens. However, it is unknown whether the method to obtain the antigens affects the integrity and immune response caused by them.

OBJECTIVES

to compare the protein profile and immune response generated by total L. amazonensis antigens (TLA) produced by different methods, as well as to analyse the immune response and protection by a first-generation vaccine formulated with sonicated TLA (sTLA) and polyinosinic:polycytidylic acid [Poly (I:C)].

METHODS

TLA were obtained by four different methodologies and their integrity and immune response were evaluated. Finally, sTLA was formulated with Poly (I:C) and their protective immune response was measured.

FINDINGS

sTLA presented a conserved protein profile and induced a strong immune response. In addition, Poly (I:C) improved the immune response generated by sTLA. Finally, sTLA + Poly (I:C) formulation provided partial protection against L. amazonensis infection.

MAIN CONCLUSIONS

The protein profile and immune response depend on the methodology used to obtain the antigens. Also, the formulation sTLA + Poly (I:C) provides partial protection against cutaneous leishmaniasis in mice.

The Combinations Chitosan-Pam3CSK4 and Chitosan-Monophosphoryl Lipid A: Promising Immune-Enhancing Adjuvants for Anticaries Vaccine PAc

We previously demonstrated that recombinant protein PAc could be administered as an anticaries vaccine. However, the relatively weak immunogenicity of PAc limits its application. In the present study, we investigated the effect of two adjuvant combinations of chitosan plus Pam₃CSK₄ (chitosan-Pam₃CSK₄) and of chitosan plus monophosphoryl lipid A (chitosan-MPL) in the immune responses to the PAc protein in vivo and in vitro PAc-chitosan-Pam₃CSK₄ or PAc-chitosan-MPL promoted significantly higher PAc-specific antibody titers in serum and saliva, inhibited Streptococcus mutans colonization onto the tooth surfaces, and endowed better protection effect with significantly less caries activities than PAc alone. Chitosan-Pam₃CSK₄ and chitosan-MPL showed no statistically significant differences. In conclusion, our study demonstrated that the chitosan-Pam₃CSK₄ and chitosan-MPL combinations are promising for anticaries vaccine development.