Single-chain Antibodies as Artificial Surface Receptors for Gene-mediated Detection and Treatment

Abstract

We have developed transgenes to express single-chain antibodies (scFv) on the surface of mammalian cells as transmembrane domain fusion proteins. We will discuss results obtained employing scFv against CD3 and the hapten 4-ethoxymelthylene-2-phenyl-2-oxazoline-5-one (phOx). Anti-CD3 scFv induced the proliferation of naive splenocytes. Expressoin of CD80 or CD86 with surface-bound scFv enhanced T-cell proliferation, reduced the stimulation threshold, increased IL-2 production, prolonged T-cell viability and generated more potent T-cell cytotoxicity compared with scFv alone. The tumorigenicity of B16-FI tumors that expressed antiCD3 scFv and CD86 was suppressed compared to tumors that expressed only CD80 or CD86, suggesting that this strategy may be useful for the gene-mediated therapy of tumors that display defects in antigen processing or presentation. We also examined whether phOx-modified proteins can be targeted to tumor cells that express anti-phOx scFv on their surface. β-glucuronidase modified with phOx specifically bound to tumor cells that expressed anti-phOx scFv. A glucuronide prodrug of p-hydroxyaniline mustard (BHAMG) was selectively activated and preferentially killed cells expressing the scFv. Treatment of C57 mice bearing established B16-FI tumors that expressed phOx scFv with phOx-modified βglucuronidase and BHAMG significantly delayed tumor growth.