A high ratio of IC31(®) adjuvant to antigen is necessary for H4 TB vaccine immunomodulation.

A tuberculosis (TB) vaccine consisting of a recombinant fusion protein (H4) and a novel TLR9 adjuvant (IC31) is in clinical development. To better understand the H4-IC31 ratio, we measured the binding capacity of IC31 for H4 protein and immunized mice with formulations that contained limiting to excess ratios of IC31 to H4. An immunomodulated H4-specific IFNγ response was only observed when IC31 was present in excess of H4. Since TLR expression is species-specific and the vaccine is intended to boost BCG-primed immunity, we questioned whether data in mice would translate to humans. To address this question, we used the fresh human Whole Blood (hWB) recovered from BCG-vaccinated subjects to screen H4-IC31 formulations. We found IC31 modulation in hWB to be quite distinct from the TLR4-Adjuvant. Unlike TLR4-Adjuvant, IC31 formulations did not induce the pro-inflammatory cytokine TNFα, but modulated a robust H4-specific IFNγ response after 12 d of culture. We then re-stimulated the fresh hWB of 5 BCG-primed subjects with formulations that had excess or limiting IC31 binding for H4 protein and again found that an immunomodulated H4-specific IFNγ response needed an excess of IC31. Finally, we monitored the zeta (ζ) potential of H4-IC31 formulations and found that the overall charge of H4-IC31 particles changes from negative to positive once IC31 is in greater than 9-fold excess. Using two diverse yet mutually supportive approaches, we confirm the need for an excess of IC31 adjuvant in H4 TB vaccine formulations and suggest surface potential may be an important factor.

Formulation, stability and immunogenicity of a trivalent pneumococcal protein vaccine formulated with aluminum salt adjuvants.

We investigated the immunogenicity, stability and adsorption properties of an experimental pneumococcal vaccine composed of three protein vaccine antigens; Pneumococcal histidine triad protein D, (PhtD), Pneumococcal choline-binding protein A (PcpA) and genetically detoxified pneumolysin D1 (PlyD1) formulated with aluminum salt adjuvants. Immunogenicity studies conducted in BALB/c mice showed that antibody responses to each antigen adjuvanted with aluminum hydroxide (AH) were significantly higher than when adjuvanted with aluminum phosphate (AP) or formulated without adjuvant. Lower microenvironment pH and decreased strength of antigen adsorption significantly improved the stability of antigens. The stability of PcpA and PlyD1 assessed by RP-HPLC correlated well with the immunogenicity of these antigens in mice and showed that pretreatment of the aluminum hydroxide adjuvant with phosphate ions improved their stability. Adjuvant dose-ranging studies showed that 28 µg Al/dose to be the concentration of adjuvant resulting in optimal immunogenicity of the trivalent vaccine formulation. Taken together, the results of theses studies suggest that the type of aluminum salt, strength of adsorption and microenvironment pH have a significant impact on the immunogenicity and chemical stability of an experimental vaccine composed of the three pneumococcal protein antigens, PhtD, PcpA, and PlyD1.