High mass clearance of autoantibodies from a murine model of lupus nephritis by immunoadsorption using star-configured polyethylene glycols

The extracorporeal immunoadsorption of antibodies as part of the therapy fo r human autoimmune diseases has been limited by technology with inadequate and nonselective mass clearance or problems with bioincompatibility. To ove rcome these shortcomings, we designed a method utilizing star-configured po lyethylene glycols (star-PEGs) having up to 63 free arms with immunoreactiv e (tresylate ester) end-groups for each arm immobilized to a polymer suppor t substrate. The flexibility and length of the arms are thought to allow op timization of epitope presentation and to permit interaction with immunolig ands on adjacent arms. To demonstrate efficacy we used an in vitro murine a ntibody model of human lupus nephritis, wherein we could study the kinetics and mass clearance of hybridoma derived antihistone antibodies from human plasma. Histones were covalently bound to the star-PEG end-groups and the k inetics of antibody adsorption were assessed using a surface plasmon resona nce technique. The equilibrium constants of antihistone antibody binding to histone-star-PEGs that were linked to a support grid demonstrated high aff inity with a K-A of 3.56E + 07 and a K-D of 2.81E - 08. The optimum reactio n conditions were determined to accomplish the hydrophilization of polysulf one (PS; by an aqueous nitration method) and polymethylmethacrylate substra tes (PMMA; by hydrazine), using sheet casts of both polymer substances. Hol low fiber devices of these polymers (commercial hemodialyzers) were modifie d so that histone-bound star-PEGs were linked to their intracapillary lumin al surfaces, using a process which we have shown retains their immunoadsorp tion properties for antihistone antibodies. A dosed loop recirculating mode l was constructed to measure mass clearance of antibodies from a reservoir. After optimizing conditions using extraction from saline solutions, the re moval of antibody from human plasma by control and surface-modified devices was assessed over 4 h. There was no measurable antibody clearance by the c ontrol fibers over this time interval. The 2.1 m(2) luminal surface area PM MA devices removed 5.0 +/- 3.3 mg, with a maximum of 7.0 mg. The 1.8 m(2) P S device cleared 11.3 +/- 6.2 mg with a maximum of 17.5 mg. In summary, sta r-PEG immunoadsorption is a promising technique for the treatment of human autoimmune disease because it can achieve very high-mass clearance of autoa ntibodies using modified biocompatable hollow-fiber polymer devices. (C) 20 01 John Wiley & Sons, Inc.