Use of a LiESP/QA-21 Vaccine (CaniLeish) Stimulates an Appropriate Th1-Dominated Cell-Mediated Immune Response in Dogs

Canine leishmaniasis is an important zoonotic disease of dogs. The clinical outcome of infection is variable, with the efficiency of the immune response being the key determining factor. There is now a general consensus that a predominant Th1 immune profile in an overall mixed Th1/Th2 response is associated with resistance in dogs, and the absence of a strong Th1 influence is associated with a progression to clinical disease. As a result, there has been a growing demand for vaccines that can induce a specific, strong Th1 response. In this study, we measured the impact of a primary course of a newly available LiESP/QA-21 vaccine on selected humoral and cellular markers of the canine immune response during the onset of immunity. All vaccinated dogs developed a humoral response characterised by IgG2 production. More importantly, vaccinated dogs developed significantly stronger cell-mediated immunity responses than did control dogs. Vaccination induced specific cellular reactivity to soluble Leishmania antigens, with a Leishmania-specific lymphoproliferation (p = 0.0072), characterised by an increased population of T lymphocytes producing IFN-γ (p = 0.0021) and a significant ability of macrophages to reduce intracellular parasite burdens in vitro after co-culture with autologous lymphocytes (p = 0.0014). These responses were correlated with induction of the NOS pathway and production of NO derivatives, which has been shown to be an important leishmanicidal mechanism. These results confirm that vaccination with LiESP/QA-21 induces an appropriate Th1-profile cell-mediated response within three weeks of completing the primary course, and that this response effectively reduces the parasite load in pre-infected macrophages in vitro

Emergence du repertoire des genes des immunoglobulines au cours de l'ontogenese des lymphocytes B humains

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 81379 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

The protective immune response produced in dogs after primary vaccination with the LiESP/QA-21 vaccine (CaniLeish®) remains effective against an experimental challenge one year later

International audienceControl of canine leishmaniasis is an important objective for the benefit of dogs living in or visiting endemic areas and for public health because of the zoonotic nature of this disease. Resistance or susceptibility to developing canine leishmaniasis after exposure to Leishmania infantum is primarily determined by the ability of the immune system to develop an appropriate Th1-dominated specific response to the parasite. For this reason there is a need for effective canine vaccines that can decrease the number of dogs developing progressive infections. In this study, we followed the impact of the LiESP/QA-21 canine vaccine (composed of excreted-secreted proteins of L. infantum and the QA-21 saponin adjuvant), recently launched commercially in Europe, on selected humoral and cellular immune parameters following an infectious intravenous challenge with L. infantum promastigotes administered one year after the primary vaccine course. We also followed parasitological parameters to determine the parasitological status of the challenged dogs. In contrast to controls, vaccinated dogs retained significantly stronger cell-mediated immune responses against the parasite despite a virulent challenge and had significantly lower mean parasite burdens at the end of the study, associated with a lower probability of developing active infections. These results confirm that the immune responses generated by vaccination with LiESP/QA-21 are still effective against an intravenous challenge one year after the primary vaccine course

Primary vaccination with the LiESP/QA-21 vaccine (CaniLeish) produces a cell-mediated immune response which is still present 1 year later

Canine leishmaniasis, an important zoonotic disease of dogs, is the result of an ineffective and inappropriate immune response to infection with Leishmania infantum. It is widely accepted that the appropriate immune response is characterised by a T-helper (Th)1-dominated profile in an overall mixed Th1/Th2 response. The absence of a strong Th1 response is associated with progression to the clinical disease. Thus, there is a need for an effective vaccine that could modulate the immune response to a more appropriate profile against the parasite. In this study we measured the impact of the LiESP/QA-21 canine vaccine, recently launched commercially in Europe, on selected humoral and cellular immune markers for one year after a primary vaccination course. The humoral response to vaccination was characterised by a predominantly IgG2 profile. Vaccinated dogs developed long-lasting cell-mediated immune responses against L. infantum, specifically with a stronger ability of macrophages to reduce intracellular parasite burdens in co-culture with autologous lymphocytes compared to control dogs (p=0.0002), which was correlated with induction of inducible nitric oxide synthase (iNOS) and production of nitric oxide (NO) derivatives. These results confirm that vaccination with LiESP/QA-21 is capable of inducing an appropriate Th1-dominated immune profile which persists for a full year.This study was funded by Virbac, the manufacturer of the vaccine.S

Lymphoproliferation index 3 weeks after the completion of the primary vaccination course.

<p>This assay detects the ability of the specific T cells produced as a result of vaccination to proliferate after being exposed to Soluble <i>Leishmania</i> Antigens (SLA). The lymphoproliferation index is the ratio of the mean optical density obtained for the SLA stimulated samples compared to the mean optical density obtained for the non-stimulated samples using a BrdU specific ELISA system.</p

Progression in log-transformed anti-ESP IgG1 and IgG2 titres during the onset of immunity.

<p>The data presented here are the means of the log-transformed titres. The titre is taken to be the first dilution with an optical density of less than 0.4 measured at 405 nm. The sera were tested using an ESP-coated ELISA at days 0, 21, 42 and 56. The ESP used was identical in profile to the antigen of the vaccine.</p

ELISpot detection of IFN-γ secreting lymphocytes 3 weeks after the completion of the primary course.

<p>This assay detects the ability of lymphocytes to secrete IFN-γ after specific stimulation with SLA by detecting spots (which represent a clone of cells secreting IFN-γ) using specific biotinylated antibodies and an automated ELISpot reader. The data presented here are the number of spots per 2×10⁵ cells after stimulation with SLA minus the equivalent value obtained with the negative control using medium alone.</p

CMLA assay: inhibition of the macrophage parasitic index, iNOS activity and production of NO derivatives.

<p>Panel A is a comparison of the ability of the macrophages to inhibit parasite multiplication before vaccination (D0) and 3 weeks after completion of the primary course (D62). It demonstrates the increase in the inhibition of the macrophage parasite index as a result of vaccination. Panel B Is a comparison of the rate of expression of iNOS in the macrophages before vaccination (D0) and 3 weeks after completion of the primary course (D62). Panel C is a comparison of the rate of production of NO derivatives from the macrophages to before vaccination (D0) and 3 weeks after completion of the primary course (D62). When these three measurements are consistent, this provides evidence of an increased NO-mediated pathway of parasite killing as a result of vaccination.</p

Progression in log-transformed anti-PSA IgG1 and IgG2 titres during the onset of immunity.

<p>The data presented here are the means of the log-transformed titres. The titre is taken to be the first dilution with an optical density of less than 0.4 measured at 405 nm. The sera were tested using a PSA-coated ELISA at days 0, 21, 42 and 56. PSA is a dominant antigen in ESP and therefore a key antigen in the vaccine.</p