Strength and medium-term impact of HisAK70 immunization in dogs: Vaccine safety and biomarkers of effectiveness for ex vivo Leishmania infantum infection

A Tailored Approach to Leishmaniases Vaccination: Comparative Evaluation of the Efficacy and Cross-Protection Capacity of DNA vs. Peptide-Based Vaccines in a Murine Model

Zoonotic leishmaniases are a worldwide public health problem for which the development of effective vaccines remains a challenge. A vaccine against leishmaniases must be safe and affordable and should induce cross-protection against the different disease-causing species. In this context, the DNA vaccine pHisAK70 has been demonstrated to induce, in a murine model, a resistant phenotype against L. major, L. infantum, and L. amazonensis. Moreover, a chimeric multiepitope peptide, HisDTC, has been obtained by in silico analysis from the histone proteins encoded in the DNA vaccine and has showed its ability to activate a potent CD4+ and CD8+ T-cell protective immune response in mice against L. infantum infection. In the present study, we evaluated the plasmid DNA vaccine pHisAK70 in comparison with the peptide HisDTC (with and without saponin) against L. major and L. infantum infection. Our preliminary results showed that both formulations were able to induce a potent cellular response leading to a decrease in parasite load against L. infantum. In addition, the DNA candidate was able to induce better lesion control in mice against L. major. These preliminary results indicate that both strategies are potentially effective candidates for leishmaniases control. Furthermore, it is important to carry out such comparative studies to elucidate which vaccine candidates are the most appropriate for further development.

Transcriptomic Profile of Canine DH82 Macrophages Infected by Leishmania infantum Promastigotes with Different Virulence Behavior

Zoonotic visceral leishmaniosis caused by Leishmania infantum is an endemic disease in the Mediterranean Basin affecting mainly humans and dogs, the main reservoir. The leishmaniosis outbreak declared in the Community of Madrid (Spain) led to a significant increase in human disease incidence without enhancing canine leishmaniosis prevalence, suggesting a better adaptation of the outbreak's isolates by other host species. One of the isolates obtained in the focus, IPER/ES/2012/BOS1FL1 (BOS1FL1), has previously demonstrated a different phenotype than the reference strain MCAN/ES/1996/BCN150 (BCN150), characterized by a lower infectivity when interacting with canine macrophages. Nevertheless, not enough changes in the cell defensive response were found to support their different behavior. Thus, we decided to investigate the molecular mechanisms involved in the interaction of both parasites with DH82 canine macrophages by studying their transcriptomic profiles developed after infection using RNA sequencing. The results showed a common regulation induced by both parasites in the phosphoinositide-3-kinase-protein kinase B/Akt and NOD-like receptor signaling pathways. However, other pathways, such as phagocytosis and signal transduction, including tumor necrosis factor, mitogen-activated kinases and nuclear factor-κB, were only regulated after infection with BOS1FL1. These differences could contribute to the reduced infection ability of the outbreak isolates in canine cells. Our results open a new avenue to investigate the true role of adaptation of L. infantum isolates in their interaction with their different hosts.

A further investigation of the leishmaniosis outbreak in Madrid (Spain): low-infectivity phenotype of the Leishmania infantum BOS1FL1 isolate to establish infection in canine cells

Human leishmaniosis caused by Leishmania infantum is a zoonotic disease, with dogs as the main reservoir in Mediterranean Basin countries. The largest European outbreak of human leishmaniosis declared in the southwestern Madrid region (Spain) is characterized by unusual epidemiological and clinical features, such as the emergence of new wild reservoirs (hares and rabbits), whereas the seroprevalence, infection, and severity of canine leishmaniosis have not substantially changed since the first studies conducted in Madrid before the outbreak. Previous studies reported that L. infantum isolates from the Madrid leishmaniosis focus displayed elevated virulence in in vivo models of infection and increased infectivity in murine target cells. With the aim of studying whether changes in the host-parasite interaction and virulence profile have developed, we first assessed the behaviour of one circulating isolate of the outbreak, IPER/ES/2012/BOS1FL1 (BOS1FL1), compared to that of a well-characterized strain from canine leishmaniosis, MCAN/ES/1996/BCN150 (BCN150), in terms of infection capacity (percentage of infected cells, representing infectivity, and number of amastigotes per infected cell, representing the intensity of infection) in canine monocytes and macrophages. BCN150 displayed significantly higher infectivity (76.82 ± 4.40 vs 38.58 ± 2.19; P <  0.0001) and intensity of infection (3.64 ± 0.13 vs 1.83 ± 0.12; P <  0.0001) than BOS1FL1 when interacting with canine cells. Our ROS induction results did not differ significantly between the two isolates or with the responses previously described for other L. infantum isolates. Paradoxically, increased resilience to hydrogen peroxide exposure was observed for BOS1FL1 (% viability 40.62 ± 5.54 vs 26.37 ± 2.93; P = 0.039). Finally, we demonstrated that a decreased intracellular load of BOS1FL1 was associated with increased IFN-γ (261.21 ± 26.29 vs 69.80 ± 9.02; P = 0.0151) and decreased IL-10 production (165.06 ± 23.87 vs 264.41 ± 30.58; P = 0.0002). In this study, we provide the first detailed insight into the differences between the isolate BOS1FL1 from the outbreak in Madrid and the well-characterized strain BCN150 MON-1 obtained from a dog in their response to interacting with canine cells. However, further studies are necessary to shed light on the immune mechanisms resulting in BOS1FL1 exhibiting less virulent behaviour in canine cells than in cells derived from other host species.

Properties of virulence emergence of Leishmania infantum isolates from Phlebotomus perniciosus collected during the human leishmaniosis outbreak in Madrid, Spain. Hepatic histopathology and immunological parameters as virulence markers in the mouse model

Recent anthropic activity related to the construction of the Bosquesur Green Park in a large urban setting in Madrid (Spain) has resulted in the largest reported community outbreak of human leishmaniosis in Europe. Previous phylogenetic and molecular-typing studies of parasite isolates have implicated the Leishmania infantum ITS-Lombardi genotype in this outbreak. In an unusual scenario, visceral leishmaniosis (VL) is affecting a significant number of individuals, suggesting that an increase in parasite virulence has occurred. In this work, using an in vivo BALB/c model of VL, we aimed to investigate the properties of emergent virulence of the L. infantum POL2FL7 and BOS1FL1 isolates obtained from Phlebotomus perniciosus collected in the outbreak area and compare them with those of the well-characterized strain BCN150 MON-1 isolated from a dog. The P. perniciosus specimens were collected during an entomological survey conducted in the transmission season of 2012. We observed a range of virulence phenotypes from moderately to highly aggressive after 5 weeks of infection. IV challenge of mice with outbreak isolates from sand flies induced higher splenic and liver parasite burdens, higher serological titres of specific anti-Leishmania antibodies and impaired capacities to control infection, as revealed by the arginine metabolism and low ratios of Th1/Th2 cytokine profiles analysed, compared with the corresponding measures evaluated in mice infected with the BCN150 strain. The BOS1FL1 isolate showed the highest degree of virulence among the isolates, superior to that of POL2FL7, as evidenced by the analysed biomarkers and the histopathological severity of liver lesions. These results provide insight into how L. infantum isolates from sand flies collected in the outbreak area have been able to affect not only immunosuppressed patients but also middle-aged people with normal immunocompetence in the largest human VL outbreak in Europe.

Epitope Selection for Fighting Visceral Leishmaniosis: Not All Peptides Function the Same Way

Visceral leishmaniosis (VL) caused by Leishmania infantum is a disease with an increasing prevalence worldwide. Treatments are expensive, toxic, and ineffective. Therefore, vaccination seems to be a promising approach to control VL. Peptide-based vaccination is a useful method due to its stability, absence of local side effects, and ease of scaling up. In this context, bioinformatics seems to facilitate the use of peptides, as this analysis can predict high binding affinity epitopes to MHC class I and II molecules of different species. We have recently reported the use of HisAK70 DNA immunization in mice to induce a resistant phenotype against L. major, L. infantum, and L. amazonensis infections. In the present study, we used bioinformatics tools to select promising multiepitope peptides (HisDTC and AK) from the polyprotein encoded in the HisAK70 DNA to evaluate their immunogenicity in the murine model of VL by L. infantum. Our results revealed that both multiepitope peptides were able to induce the control of VL in mice. Furthermore, HisDTC was able to induce a better cell-mediated immune response in terms of reduced parasite burden, protective cytokine profile, leishmanicidal enzyme modulation, and specific IgG2a isotype production in immunized mice, before and after infectious challenge. Overall, this study indicates that the HisDTC chimera may be considered a satisfactory tool to control VL because it is able to activate a potent CD4+ and CD8+ T-cell protective immune responses.

Dias D, Ribeiro PAF, Roatt BM, Mas A, Carrión J, Coelho EAF, Domínguez-Bernal G. Immunization with the HisAK70 DNA Vaccine Induces Resistance against Leishmania Amazonensis Infection in BALB/c Mice

Leishmania amazonensis is the aetiological agent of a broad spectrum of leishmaniosis in South America. It can cause not only numerous cases of cutaneous leishmaniosis but also diffuse cutaneous leishmaniosis. Considering the diversity of parasite species causing different forms of the disease that coexist in the same region, it is desirable to develop a vaccine capable of eliciting cross-protection. We have previously described the use of HisAK70 DNA vaccine for immunization of mice to assess the induction of a resistant phenotype against Leishmania major and infantum infections. In this study, we extended its application in the murine model of infection by using L. amazonensis promastigotes. Our data revealed that 14 weeks post-infection, HisAK70-vaccinated mice showed key biomarkers of protection, such as higher iNOS/arginase activity, IFN-γ/IL-10, IFN-γ/IL-4, and GM-CSF/IL-10 ratios, in addition to an IgG2a-type response when compared to the control group. These findings correlated with the presentation of lower footpad swelling and parasite burdens in the immunized compared to the control mice. Overall, this study suggests that immunization with HisAK70 may be considered a suitable tool to combat leishmaniosis as it is able to induce a potent cellular immune response, which allows to control the infection caused by L. amazonensis.