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Soluble Coxsackievirus Adenovirus Receptor Is a Putative Inhibitor of Adenoviral Gene Transfer in the Tumor Milieu¹

Department of Medicine and The University of California at Los Angeles (UCLA)/ Wadsworth Pulmonary Immunology and Gene Medicine Laboratory [R. M. B., S. S., B. K. G., S. M. D., R. K. B.], and Jonsson Comprehensive Cancer Center [S. M. D., R. K. B.], UCLA and Veterans Administration-Greater Los Angeles Health Care System, Los Angeles, California 90073; Division of Human Gene Therapy, Departments of Medicine, Pathology and Surgery and the Gene Therapy Center, University of Alabama at Birmingham, Birmingham, Alabama 35222 [J. T. D.]; and Division of Immunologic and Infectious Diseases, Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania 19104 [J. M. B.]

Purpose: Several barriers that collectively restrict gene delivery by viral vectors in vivo have been described. Previously, we identified soluble chondroitin sulfate-proteoglycans/glycosaminoglycans in malignant pleural effusions (MPEs) as inhibitors of retroviral vector transduction. Soluble components of MPE also inhibited adenoviral (Ad) gene transfer, and the factors were characteristically filterable, titrable, stable at 56° C, and blocked the binding of Ad to target cells. Depleting immunoglobulin from MPE, partially reversed the block to Ad transduction, instigating a search for additional factors that bound Ad in MPE.

Experimental design: Vector-protein interactions were identified after the resolution of MPE-components by SDS-PAGE. Viral overlays and immunoblots delineated significant interactions, and the potential relevance of those interactions was tested in transduction efficiency bioassays.

Results: Immunoglobulin is the predominant factor inhibiting Ad gene transfer in MPE. Albumin also interacted with Ad, although at predicted serum concentrations, it did not effect Ad transduction efficiency in vitro. Soluble coxsackievirus-Ad receptor (sCAR) was then identified in MPE. In a survey of 18 MPE, the mean concentration of sCAR was variable and estimated to be 3.51 ± 5.02 ng/ml by ELISA. The impact of sCAR on transduction efficiency in this milieu was next assessed. Whereas immunodepletion of sCAR from MPE by affinity chromatography resulted in enhanced gene transfer within MPE, the inhibition of adenoviral gene transfer was not evident when the predicted concentrations of recombinant sCAR were added into the transduction medium.

Conclusions: These studies indicate that, in addition to anti-Ad antibodies, other specific and nonspecific factors interact with viral vectors and may impair gene transfer in the tumor milieu. The presence of sCAR in MPE puts forward the notion that in certain contexts (e.g., within the extracellular matrix of solid tumors) the concentrations of secreted (or shed) CAR may be high enough to effectively compete with Ad gene delivery.

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