Rationale: There is a major interest in identifying adjuvants for sublingual allergy vaccines with the aim to enhance allergen-specific tolerance.

Methods: Candidate adjuvants were screened using cocultures of human or murine dendritic cells (DC) with naïve CD4+ T lymphocytes. Patterns of cytokine production and DC maturation were analysed by cytofluorometry. Quantitative PCR analysis of Fox p3/GATA3/TBet/IL4/IFNγ/IL10/TGFß genes was performed to assess Th1/Th2/T Reg lymphocyte polarization within 7 days. Selected adjuvants were tested in vivo, in a therapeutic murine model of sublingual immunotherapy (SLIT) in BALB/c mice sensitized with ovalbumin. Whole body plethysmography, lung histology and a detailed analysis of immune responses in blood, spleen and cervical lymph nodes were used as readouts

Results: Fifty ligands for major Toll like receptors (TLR2, 3, 4, 5, 7/8), as well as biological candidate adjuvants (ie over 15 strains of probiotics) have been tested. Both Lactobacillus plantarum, 1,25-dihydroxy vitamin D3 plus dexamethasone, the TLR2 ligand Pam3 CSK4, as well as a synthetic TLR4 ligand (DL8) were all identified as potent inducers of IL10 (with or without interferon γ) in naïve T lymphocytes. When administered together with OVA, all these Th1/Treg adjuvants enhance SLIT efficacy in mice by reducing both airways hyperresponsiveness (AHR), and established Th2 responses. VitD3/dexamethasone administered sublingually induces Foxp3+ regulatory T cells. L. plantarum elicits a strong proliferation of OVA-specific T cells in cervical lymph nodes, whereas Pam3CSK4 inhibits such a T cell priming.

Conclusions: Several IL10 and IFNγ-inducing adjuvants enhance the efficacy of sublingual vaccines via distinct mechanisms. Such adjuvants should allow to reduce the allergen dose and simplify immunization schemes.