Polyphosphazene polyelectrolytes are potent immunostimulants. Their in vivo performance has been demonstrated for various antigens in a number of animal models. To improve understanding of the mechanism of action, we performed a comparative study in a model system: bovine serum albumin, BSA-poly[di(carboxylatophenoxy)phosphazene], PCPP, in vitro and in vivo. Multi-angle laser light scattering (MALLS) and size-exclusion HPLC methods were used to investigate polyphosphazene-protein formulations in an attempt to establish correlations between their physicochemical behavior and immunostimulating activity. These studies revealed the formation of water-soluble noncovalent protein-polymer complexes in the system. It was shown that both the amount of bound protein and the complex conformation could play an important role in the in vivo performance of the polyphosphazene polyelectrolytes.

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Intradermal immunization using microfabricated needles represents a potentially powerful technology, which can enhance immune responses and provide antigen sparing. Solid vaccine formulations, which can be coated onto microneedle patches suitable for simple administration, can also potentially offer improved shelf-life. However the approach is not fully compatible with many vaccine adjuvants including alum, the most common adjuvant used in the vaccine market globally. Here, we introduce a polyphosphazene immunoadjuvant as a biologically potent and synergistic constituent of microneedle-based intradermal immunization technology. Poly[di-(carboxylatophenoxy)phosphazene], PCPP, functions both as a vaccine adjuvant and as a key microfabrication material. When used as part of an intradermal delivery system for hepatitis B surface antigen, PCPP demonstrates superior activity in pigs compared to intramascular administration and significant antigen sparing potential. It also accelerates the microneedle fabrication process and reduces its dependence on the use of surfactants. In this way, PCPP-coated microneedles may enable effective intradermal vaccination from an adjuvanted patch delivery system. polyphosphazenes ͉ vaccine adjuvants

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