Optimization of ligand presentation for immunoadsorption using star-configured polyethylene glycols

Medical, pharmaceutical, and industrial applications of immunoadsorption are frequently limited by the technologic problems of low affinity, inadequate capacity, hydrophobicity, and bioincompatibility. To overcome these difficulties we studied the use of star-burst configured polyethylene glycols (star-PEGs) with immunoreactive molecules covalently bound to the end of each of the multiple flexible arms. The optimum pH ranges were determined to maintain stability of the tresyl chloride modified star reagents, and the chemistry was designed for their subsequent linkage to the immunoadsorbent moiety. We then devised the chemical reactions using nitration or hydrazine activation to tether these 64-arm structures to polymer supports made of polysulfone or polymethylmethacrylate, respectively. Transmission, scanning, and atomic force microscopy confirmed the preservation of the star configuration, even after linkage to the luminal surface of hollow fiber devices. To establish that these modified devices also maintained immunoadsorption reactivity, we used a model having relevance for human autoimmune disease and demonstrated the clearance of antihistone antibodies by tethered histones. This novel approach to increasing the capacity of immunoadsorption benefits from the star configuration which provides a high density of ligand, improved hydrophilicity of the surface, spacing of reactive molecules away from the support structure, and possible optimization of epitope immunoreactivity by arm-to-arm interaction of the bound molecules.