Abstract
Each year millions of neonates die due to vaccine preventable infectious diseases. Our study seeks to develop novel neonatal vaccines and improve immunogenicity of early childhood vaccines by incorporating TLR agonist-adjuvant combinations that overcome the inherent neonatal Th2 bias and stimulate Th1 polarizing response from neonatal APCs. We systematically stimulated cord blood mononuclear cells with single and multiple combinations of TLR agonists and measured levels of IL-12p70, IFN-γ, IFN-α, IL-10, IL-13, TNF-α, IL-6 and IL-1β from cell culture supernatants. APC-specific surface expression levels of costimulatory markers CD40, CD83 and PD-L1 were assessed by flow cytometry. Whole blood assays were included to account for the effect of plasma inhibitory factors and APC intracellular TNF-α and IL-12p40 secretions were measured. We found robust Th1 polarizing IL-12p70, IFN-γ and IFN-α responses when cord blood APCs were stimulated with TLR agonist combinations that contained Poly I:C, Monophosphoryl Lipid A (MPLA) or R848. Addition of class A CpG oligonucleotide (ODN) to Th1 polarizing TLR agonist combinations significantly reduced cord blood IL-12p70 and IFN-γ levels and addition of a TLR2 agonist induced significantly high Th2 polarizing IL-13. Multi-TLR agonist combinations that included R848 induced lower inhibitory PD-L1 expression on cord blood classical dendritic cells than CpG ODN-containing combinations. Incorporation of combination adjuvants containing TLR3, TLR4 and TLR7/8 agonists to neonatal vaccines may be an effective strategy to overcome neonatal Th2 bias.