Squamous metaplasia of normal and carcinoma in situ of HPV 16-immortalized human endocervical cells.

The importance of cervical squamous metaplasia and human papillomavirus 16 (HPV 16) infection for cervical carcinoma has been well established. Nearly 87% of the intraepithelial neoplasia of the cervix occur in the transformation zone, which is composed of squamous metaplastic cells with unclear origin. HPV DNA, mostly HPV 16, has been found in 90% of cervical carcinomas, but only limited experimental data are available to discern the role of HPV 16 in this tissue specific oncogenesis. We have initiated in vivo studies of cultured endocervical cells as an experimental model system for development of cervical neoplasia. Using a modified in vivo implantation system, cultured normal endocervical epithelial cells formed epithelium resembling squamous metaplasia, whereas those immortalized by HPV 16 developed into lesions resembling carcinoma in situ. In contrast, their ectocervical counterparts formed well differentiated stratified squamous epithelium and a lesion with mild dysplastic change, respectively. The HPV 16-immortalized cells showed in vivo cytokeratin expression patterns similar to their respective normal counterparts, confirming their different origins. Thus, this study provides direct experimental evidence for the transformation of simple epithelial cells of endocervical origin into stratified squamous metaplasia and indicates the differential susceptibility of endo- and ectocervical epithelial cells for conversion to cancer by HPV 16.