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Microparticulate delivery systems are a promising and versatile enhancement to DNA vaccines because they can target large payloads of plasmid and immunomodulating materials to antigen presenting cells (APC). A pH sensitive poly-β amino ester (PBAE) has been recently described which substantially increases adjuvancy and delivery efficiency of such microparticle formulations. This work describes the characterization and formulation considerations specific to these PBAE containing microparticles. PBAE increases the supercoiled content and overall effective loading of plasmid DNA. This polymer also significantly buffers the pH microenvironment created by ester bond degradation, rendering encapsulated plasmid more suitable for transfection. Release of plasmid from microparticles is controllable based on the amount of PBAE in the composition. Transfection is dependant upon phagocytosis, and is optimal for 15% and 25% PBAE microparticle formulations. However, larger quantities of PBAE may be toxic to cells indicating that the 15% PBAE formulation is a suitable candidate for delivery in future studies with disease specific, DNA vaccines.