Results of vaccination against canine visceral leishmaniasis (Leishmania infantum) in enzootic areas

Protection against canine leishmaniasis was evaluated in dogs living in enzootic areas in the south of France, and vaccinated with a candidate vaccine, LiESP with the adjuvant MDP. A double-blind field study was carried out in a large number of dogs (n = 414) over two years. At the end of the study, infection rate was 0% in vaccinated dogs versus 5.14% in the placebo group. The candidate vaccine induced an effective and lasting immunity against canine leishmaniasis.La protection contre la leishmaniose canine est évaluée chez des chiens vivant en zone d'enzootie dans le sud de la France, vaccinés par un candidat LiESP adjuvé par MDP. Une étude de terrain randomisée en double aveugle est conduite dans une large population de chiens (n = 414), durant une période de deux années. À l'issue de l'étude, le taux d'infection est de 0 % chez les chiens vaccinés et de 5,14 % chez les chiens du groupe placebo. Le candidat vaccinal a induit une immunité efficace, durable contre la leishmaniose canine

Canine leishmaniosis due to Leishmania infantum: immunotherapy trials

As most methods currently available to treat and control canine leishmaniasis have a limited efficacy, researchers are testing immunotherapeutic methods with great interest. Excreted–secreted antigens (ES Ag) of promastigotes of Leishmania infantum cultured in a defined medium were selected. Three Leishmania–infected dogs received two intradermal injections of 25 mg of ES Ag, at 3 weeks interval. This treatment was the first ever in one of the dogs, whereas the other two had previously received a standard treatment with Glucantime® and Zyloric®. Marked clinical improvement was noted as of Day 15 after the first injection, as well as an intense leishmanicide activity in collected monocytes, and a significant decrease of antibody titres. No clinical relapse was recorded over two years later.La plupart des méthodes disponibles aujourd'hui de traitement et de contrôle de la leishmaniose canine sont d'une efficacité limitée, aussi le développement de méthodes immunothérapeutiques est-il d'un grand intérêt. Des antigènes d'excrétion-sécrétion (Ag ES) de promastigotes de Leishmania infantum cultivés en milieu défini sont retenus. Trois chiens leishmaniens en reçoivent 25 μg, 2 fois à 3 semaines d'intervalle, par la voie intra-dermique: un chien est traité pour la première fois selon ce protocole, les 2 autres avaient été traités antérieurement selon un protocole classique à base de glucantime et de zyloric. Une nette amélioration clinique est observée dès J15 après la première injection, ainsi qu'une forte activité leishmanicide des monocytes récoltés et une diminution significative des titres en anticorps. Aucune rechute clinique n'est enregistrée plus de 2 ans plus tard

Recombinant forms of Leishmania amazonensis excreted/secreted promastigote surface antigen (PSA) induce protective immune responses in dogs

International audiencePreventive vaccination is a highly promising strategy for interrupting leishmaniasis transmission that can, additionally, contribute to elimination. A vaccine formulation based on naturally excreted secreted (ES) antigens was prepared from L. infantum promastigote culture supernatant. This vaccine achieved successful results in Phase III trials and was licensed and marketed as CaniLeish. We recently showed that newly identified ES promastigote surface antigen (PSA), from both viable promastigotes and axenically-grown amastigotes, represented the major constituent and the highly immunogenic antigen of L. infantum and L. amazonensis ES products. We report here that three immunizations with either the recombi-nant ES LaPSA-38S (rPSA) or its carboxy terminal part LaPSA-12S (Cter-rPSA), combined with QA-21 as adjuvant, confer high levels of protection in naive L. infantum-infected Beagle dogs, as checked by bone marrow parasite absence in respectively 78.8% and 80% of vaccinated dogs at 6 months post-challenge. The parasite burden in infected vaccinated dogs was significantly reduced compared to placebo group, as measured by q-PCR. Moreover, our results reveal humoral and cellular immune response clear-cut differences between vaccinated and control dogs. An early increase in specific IgG2 antibodies was observed in rPSA/QA-21-and Cter-rPSA/QA-21-immunized dogs only. They were found functionally active in vitro and were highly correlated with vaccine protection. In vaccinated protected dogs, IFN-γ and NO productions, as well as anti-leishmanial macrophage activity, were increased. These data strongly suggest that ES PSA or its carboxy-terminal part, in recom-binant forms, induce protection in a canine model of zoonotic visceral leishmaniasis by inducing a Th1-dominant immune response and an appropriate specific antibody response. These data suggest that they could be considered as important active components in vaccine candidates

In Vitro Evaluation of a Soluble Leishmania Promastigote Surface Antigen as a Potential Vaccine Candidate against Human Leishmaniasis

International audiencePSA (Promastigote Surface Antigen) belongs to a family of membrane-bound and secreted proteins present in severalLeishmania (L.) species. PSA is recognized by human Th1 cells and provides a high degree of protection in vaccinated mice.We evaluated humoral and cellular immune responses induced by a L. amazonensis PSA protein (LaPSA-38S) produced in aL. tarentolae expression system. This was done in individuals cured of cutaneous leishmaniasis due to L. major (CCLm) or L.braziliensis (CCLb) or visceral leishmaniasis due to L. donovani (CVLd) and in healthy individuals. Healthy individuals weresubdivided into immune (HHR-Lm and HHR-Li: Healthy High Responders living in an endemic area for L. major or L. infantuminfection) or non immune/naive individuals (HLR: Healthy Low Responders), depending on whether they produce high orlow levels of IFN-c in response to Leishmania soluble antigen. Low levels of total IgG antibodies to LaPSA-38S were detectedin sera from the studied groups. Interestingly, LaPSA-38S induced specific and significant levels of IFN-c, granzyme B and IL-10 in CCLm, HHR-Lm and HHR-Li groups, with HHR-Li group producing TNF-a in more. No significant cytokine response wasobserved in individuals immune to L. braziliensis or L. donovani infection. Phenotypic analysis showed a significant increasein CD4+ T cells producing IFN-c after LaPSA-38S stimulation, in CCLm. A high positive correlation was observed between thepercentage of IFN-c-producing CD4+ T cells and the released IFN-c. We showed that the LaPSA-38S protein was able toinduce a mixed Th1 and Th2/Treg cytokine response in individuals with immunity to L. major or L. infantum infectionindicating that it may be exploited as a vaccine candidate. We also showed, to our knowledge for the first time, the capacityof Leishmania PSA protein to induce granzyme B production in humans with immunity to L. major and L. infantum infectio

Peptide-based vaccine successfully induces protective immunity against canine visceral leishmaniasis

International audienceDogs are the main reservoir of zoonotic visceral leishmaniasis. Vaccination is a promising approach to help control leishmaniasis and to interrupt transmission of the Leishmania parasite. The promastigote surface antigen (PSA) is a highly immunogenic component of Leishmania excretory/secretory products. A vaccine based on three peptides derived from the carboxy-terminal part of Leishmania amazonensis PSA and conserved among Leishmania species, formulated with QA-21 as adjuvant, was tested on naive Beagle dogs in a preclinical trial. Four months after the full course of vaccination, dogs were experimentally infected with Leishmania infantum promastigotes. Immunization of dogs with peptide-based vaccine conferred immunity against experimental infection with L. infantum. Evidence for macrophage nitric oxide production and anti-leishmanial activity associated with IFN-y production by lymphocytes was only found in the vaccinated group. An increase in specific IgG2 antibodies was also measured in vaccinated dogs from 2 months after immunization. Additionally, after challenge with L. infantum, the parasite burden was significantly lower in vaccinated dogs than in the control group. These data strongly suggest that this peptide-based vaccine candidate generated cross-protection against zoonotic leishmaniasis by inducing a Th1-type immune response associated with production of specific IgG2 antibodies. This preclinical trial including a peptide-based vaccine against leishmaniasis clearly demonstrates effective protection in a natural host. This approach deserves further investigation to enhance the immunogenicity of the peptides and to consider the possible engineering of a vaccine targeting several Leishmania species

Anti-leishmanial activity of canine monocyte-derived macrophages in non-immune and immune dogs.

<p>The ability of pre-infected canine monocyte-derived macrophages to kill <i>Leishmania</i> parasites when they were exposed to autologous peripheral lymphocytes derived from PBMC was expressed as the percentage of parasitic index inhibition after <i>in vitro</i> infection with <i>Leishmania infantum</i> promastigotes (MHOM/MA/67/ITMAP-263) and 72 h incubation with and without autologous lymphocytes. Anti-leishmanial activity of co-cultured canine macrophages was evaluated immediately before immunization and two months after the third dose. Values represent means +/- standard deviation of duplicate experiments (* <i>p</i>< 0.05, ** <i>p</i><0.01, *** <i>p</i><0.001).</p

Parasitological evaluation of placebo and vaccinated dogs.

<p>The presence of (A) live <i>Leishmania</i> parasites was highlighted by subculture analysis of bone marrow aspirates isolated from dogs of placebo (n = 5), rPSA/QA-21 (n = 9) and Cter-rPSA (n = 5) groups at 2, 4 and 6 months post-challenge (PC). A sample was considered as positive when <i>Leishmania</i> parasites were detected during the seeding or subculture analysis. The presence of (B) <i>Leishmania</i> DNA and (C) the parasite load in bone marrow aspirates of dogs of each group were assessed by quantitative PCR. Dogs were considered as positive when the titer was superior to 40 parasites per mL. Data are expressed as (B) the number of dogs with positive PCR at each time points post-challenge and (C) the mean number of parasites per mL of bone marrow aspirates at different times post-challenge (4 and 6 months) (* <i>p</i><0.05, ** <i>p</i><0.01, *** <i>p</i><0.001).</p

Vaccine specific serological responses as detected by Enzyme-Like Immunosorbent Assay (ELISA).

<p>Evolution of levels of (A) anti-rPSA, (B) anti-Cter-rPSA and (C) anti-<i>Li</i>ESAp specific IgG2 antibodies was assessed in serum samples isolated from dogs of each group immediately before immunization and at different times post-immunization: first month after the second dose and two months after the third dose. Each serum sample was tested in triplicates. Cut-off value was calculated using the following formula: mean OD in sera from all dogs before immunization + 3 standard deviations. Values represent means OD +/- standard deviation of triplicate experiments (* <i>p</i>< 0.05, ** <i>p</i><0.01, *** <i>p</i><0.001).</p