Identification of human papillomavirus type 11 E4 gene products in human tissue implants from athymic mice

A new method has recently been described for the growth of human papillomavirus type 11 (HPV11), an agent associated with genital warts, in human tissue xenografts implanted under the renal capsules of athymic nude mice (J. W. Kreider et al., 1986, J. Viriol. 59, 369–376; 1987, J. Virol. 61, 590–593). With this model it is now possible to study productive HPV11 infection under controlled laboratory conditions. To identify proteins encoded by the HPV11 E4 open reading frame in infected implants, we have cloned an HPV11 E4 genomic DNA fragment representing all of the E4 region thought to be expressed in vivo, as evidenced by cDNA cloning and R loop mapping. The cloned HPV11 fragment was expressed in Escherichia coli as a cro-β-galactosidase E4 fusion protein (Gal-E4 fusion). Rabbit antibodies raised against the Gal-E4 fusion protein were affinity purified using an HPV11 E1∧E4 fusion protein. The E1∧E4 protein was synthesized independently by expressing an HPV11 E1∧E4 cDNA in E. coli using a second expression vector. Affinity-purified anti-E4 antibodies identified putative E4 proteins of 10 and 11 kDa in both the condylomatous cyst walls and in the desquamated cells in the cavities of HPV11-infected human skin implants from athymic mice. Similar proteins were not detected in uninfected controls. Implications for use of the athymic mouse system are discussed.