Development of an interleukin 2 receptor targeted gene therapy vehicle
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The effectiveness of most chemotherapeutic regimens is limited by the toxicity of the therapy to normal healthy cells. Therapies to selectively modulate abnormal T cells bearing the interleukin 2 receptor (IL-2R) have been developed to treat diseases associated with aberrant immune response. This study describes the development and optimization of a targeted gene or oligonucleotide therapy vehicle to IL-2R bearing T cells for selective elimination of these cells. In this work, a monoclonal antibody to the IL-2R was used to target the oligonucleotide delivery vehicle which consisted of a polyamidoamine dendrimer. Optimization of the delivery vehicle involves understanding the factors that govern its association with oligonucleotide, the pathway of IL-2R endocytic trafficking, and the stability of the oligonucleotide in the biological milieu. Oligonucleotide stability in a cellular environment was examined intra- and extracellularly. Results showed that the rate of intracellular degradation of oligonucleotides was much greater than extracellular degradation. Binding of oligonucleotides to dendrimers was demonstrated as a function of dendrimer generation. The total binding capacities for dendrimers differed depending upon dendrimer size and surface group, whereas equilibrium binding affinity was comparable for all dendrimers tested. Binding of oligonucleotide delivery vehicle to the cell surface and subsequent internalization was inversely related to dendrimer size, and in all cases, significantly less than binding and internalization of the natural ligand for the IL-2R. Based on experimental results, a kinetic model of the delivery vehicle was derived which includedthe dependence of binding and internalization on dendrimer size and surface charge and intracellular degradation of oligonucleotide. Based on model predictions, we show that larger dendrimers carry more oligonucleotide than the smaller dendrimer vehicles, and delivery is more effective with larger vehicles. This work establishes our ability to predict the effects of different delivery vehicle properties on oligonucleotide delivery and aids in the development of design criteria for new vehicles for delivery of antisense, siRNA, or genes to IL-2R bearing cells.