Author(s): McDonald D, Stockwin L, Matzow T, Blair Zajdel ME, Blair GE
The role of two receptors, previously proposed to mediate the entry of adenoviruses into human cells, the coxsackie and adenovirus receptor (CAR) and the major histocompatibility complex (MHC) class I heavy chain has been investigated. The expression of MHC class I in many tumours is reduced or absent, therefore if this were a means by which adenoviruses gained entry into cells, it would have important implications for their application in cancer treatment. In order to determine if MHC class I heavy chain is involved in adenovirus type 5 (Ad5) uptake, the binding of recombinant Ad5 fibre knob domain (which mediates viral attachment) to human cell lines that had greatly different levels of surface MHC class I was studied. We also created derivatives of a non-permissive Chinese hamster ovary (CHO) cell line that expressed human class I (HLA-A2) and found that these cells did not bind fibre or take up virus. In addition, the extracellular domain of CAR was expressed in E. coli and used to generate a polyclonal anti-CAR antibody. This antibody blocked both 125I labelled fibre knob binding and virus uptake. Thus CAR, and not MHC class I, is a receptor for human adenoviruses in cultured tumour cells. Tissue CAR levels may therefore be an important factor in the efficiency of adenovirus-mediated gene therapy.