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Current techniques to educate dendritic cells (DCs) ex vivo for immunotherapy are plagued by inefficient protocols and DC modifications are often transient and lost upon transplantation. This study investigated the role of sustained presentation of GM-CSF and PEI condensed pDNA (PEI-DNA) on gene transfer and long-term gene expression. Appropriate GM-CSF signaling during DC transfection promoted PEI-DNA uptake, although high cytokine concentrations induced intercellular DNA degradation, indicating the need for controlled presentation. Poly(lactide-co-glycolide) scaffolds that continuously stimulated DCs with both GM-CSF and PEI-DNA led to a 20-fold increase in gene expression, and high levels of expression persisted for a period of 10 days, in vitro. These results encourage the exploitation of biomaterials and GM-CSF to develop novel delivery vectors for genetically modified DCs or to genetically program host DCs in situ for vaccination and the treatment of autoimmunity.