Recovery of antigen-specific T cell responses from dogs infected with Leishmania (L.) infantum by use of vaccine associated TLR-agonist adjuvant

Abstract

Visceral leishmaniasis (VL), caused by infection with the obligate intracellular protozoan parasite Leishmania infantum, is a fatal disease of dogs and humans. Protection against VL requires a T helper 1 (Th1) skewed CD4+ T response, but despite this knowledge, there are currently no approved-to-market vaccines for humans and only three veterinary-use vaccines globally. As VL progresses from asymptomatic to symptomatic, L. infantum–specific interferon gamma (IFNγ) driven- Th1 responses become dampened and a state of immune exhaustion established. T cell exhaustion and other immunoregulatory processes, starting during asymptomatic disease, are likely to hinder vaccine-induced responses if vaccine is administered to infected, but asymptomatic and seronegative, individuals. In this study we evaluated how immune exhaustion, shown previously by our group to worsen in concert with VL progression, effected the capacity of vaccine candidate antigen/toll-like receptor (TLR) agonist combinations to promote protective CD4+ T cell responses during progressive VL. In conjunction with Th1 responses, we also evaluated concomitant stimulation of immune-balanced IL-10 regulatory cytokine production by these vaccine products in progressive VL canine T cells. Vaccine antigen L111f in combination with TLR agonists significantly recovered CD4+ T cell IFN-γ intracellular production in T cells from asymptomatic VL dogs. Vaccine antigen NS with TLR agonists significantly recovered CD4+ T cell production in both endemic control and VL dogs. Combinations of TLR agonists and vaccine antigens overcame L. infantum induced cellular exhaustion, allowing robust Th1 CD4+ T cell responses from symptomatic dogs that previously had dampened responses to antigen alone. Antigen-agonist adjuvants can be utilized to promote more robust vaccine responses from infected hosts in endemic areas where vaccination of asymptomatic, L. infantum-infected animals is likely.

Allopurinol therapy provides long term clinical improvement, but additional immunotherapy is required for sustained parasite clearance, in L. infantum-infected dogs

“…This immune exhaustion is characterized by anti-inflammatory responses, lack of proliferation in response to Leishmania antigens, and lymphocyte apoptosis [27]. Ex vivo incubation with combinations of TLR agonists indicate the potential to overcome L. infantum -induced cellular exhaustion, allowing robust Th1 responses in cells from symptomatic dogs that exhibit dampened responses to antigen alone [28]. The initial use of chemotherapy to transiently reduce parasite burden may permit immune responsiveness that can be manipulated by immunization to generate sustained parasite control.…”

Immunoprophylactic Potential of a New Recombinant Leishmania infantum Antigen for Canine Visceral Leishmaniasis: An In Vitro Finding

“…Lci13 induced a significant higher expression of the pro-inflammatory cytokine IFN-γ in relation to LSA in the NInD group, and this gene expression was also significantly higher in relation to the levels obtained in the InD group. Studies indicate that resistance to L. infantum infection in dogs is owed to a strong Th1 response, mainly due to IFN-γ, responsible for stimulating cell proliferation and, together with TNF, for activating macrophages and other cells of the immune system, leading to parasite destruction by increasing intracellular NO levels ( 4 , 40 , 43 , 44 ). The expression for TNF, IL-10 and TGF-β was very similar between groups, but gene expression for the regulatory cytokine TGF-β in both groups presented a negative mean in relation to sample without stimulus.…”

“…It is considered endemic in more than 70 countries, and approximately 2.5 million dogs are infected just in south-western Europe ( 1 , 2 ). As a result of a balance between host and parasite interaction, a great proportion of animals remain asymptomatic, but a significative number may develop severe signals and symptoms, such as hepatosplenomegaly and renal failure ( 3 , 4 ). An effective diagnostic strategy, as well as prevention and treatment approaches for CanL are extremely important for controlling human visceral leishmaniasis (VL), since infected dogs are reservoirs of major epidemiological importance ( 5 , 6 ).…”

Safety Analysis of Leishmania Vaccine Used in a Randomized Canine Vaccine/Immunotherapy Trial

“…[16][17][18] Because of vaccination practices in endemic countries, in both Europe and South America, asymptomatic, seronegative, infected dogs are frequently vaccinated. Based on our previous studies, 8,12,19,20 asymptomatically infected dogs may have altered vaccine responsiveness, leading to increased inflammation after vaccination. Assessing the safety of vaccine use within asymptomatic dogs is necessary to assure that vaccination is safe within a population including infected animals.…”