Abstract
Visceral leishmaniasis (VL) caused by Leishmania donovani and L. infantum is a potentially fatal disease. To date there are no registered vaccines for disease prevention despite the fact that several vaccines are in preclinical development. Thus, new strategies are needed to improve vaccine efficacy based on a better understanding of the mechanisms mediating protective immunity and mechanisms of host immune responses subversion by immunopathogenic components of Leishmania. We found that mice vaccinated with CPA162−189-loaded p8-PLGA nanoparticles, an experimental nanovaccine, induced the differentiation of antigen-specific CD8+ T cells in spleen compared to control mice, characterized by increased dynamics of proliferation and high amounts of IFN-γ production after ex vivo re-stimulation with CPA162−189 antigen. Vaccination with CPA162−189-loaded p8-PLGA nanoparticles resulted in about 80% lower parasite load in spleen and liver at 4 weeks after challenge with L. infantum promastigotes as compared to control mice. However, 16 weeks after infection the parasite load in spleen was comparable in both mouse groups. Decreased protection levels in vaccinated mice were followed by up-regulation of the anti-inflammatory IL-10 production although at lower levels in comparison to control mice. Microarray analysis in spleen tissue at 4 weeks post challenge revealed different immune-related profiles among the two groups. Specifically, vaccinated mice were characterized by similar profile to naïve mice. On the other hand, the transcriptome of the non-vaccinated mice was dominated by increased expression of genes related to interferon type I, granulocyte chemotaxis, and immune cells suppression. This profile was significantly enriched at 16 weeks post challenge, a time-point which is relative to disease establishment, and was common for both groups, further suggesting that type I signaling and granulocyte influx has a significant role in disease establishment, pathogenesis and eventually in decreased vaccine efficacy for stimulating long-term protection. Overall, we put a spotlight on host immune networks during active VL as potential targets to improve and design more effective vaccines against disease.
Highlights
Leishmaniasis is a vector-borne disease caused by parasites of the genus Leishmania and is transmitted by the bite of female sandflies to mammalian hosts
We have recently developed PLGA nanoparticles that were surface modified with an 8-mer TNFα-mimicking peptide for the specific targeting of TNFRII on dendritic cells (DCs)’ surface
In the present study an integrated systems biology approach was applied to investigate the evolving immune response following L. infantum challenge in mice vaccinated with CPA160−189-loaded p8-PLGA nanoparticles, an experimental vaccine considered capable of inducing sterilizing immunity
Summary
Leishmaniasis is a vector-borne disease caused by parasites of the genus Leishmania and is transmitted by the bite of female sandflies to mammalian hosts. It is a poverty-related disease with three main clinical forms, visceral, cutaneous, and mucocutaneous leishmaniasis. Visceral leishmaniasis (VL) is the most severe, systemic form of the disease that is usually fatal if left untreated. Despite the fact that the global incidence of VL has decreased substantially in the past decade as a result of better treatment and vector control, in east Africa the case numbers continue to be sustained [1]. The development of prophylactic vaccines against leishmaniasis is an urgent need for the control of infection. Several candidates that incorporate a range of antigens are in pre-clinical development, but only few of them are in clinical studies [3, 4]
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