Development and assessment of a general theory of cervical carcinogenesis utilizing a severe combined immunodeficiency murine-human xenograft model

Objective. Currently, we lack a theoretical explanation for why squamous ce ll cervical cancer develops predominantly in specific sites (i.e., along th e squamocolumnar junction). We therefore implanted human cervical tissues c ontaining the transformation zone in severe combined immunodeficiency (SCID ) mice and studied morphology, steroid effects, gene expression, and human papillomavirus (HPV) factors. Methods. Normal and dysplastic human cervical tissues (3 x 2 mm) were place d subcutaneously in SCID-beige mice and later assessed by in situ hybridiza tion for HPV 16/18 DNA and by immunohistochemistry for expression of CD31, keratin, proliferating-cell nuclear antigen, HPV 16 E6, p53, and Notch-1 (a binary cell. fate determination protein). Some normal tissues were implant ed with either a 90-day release 1.7-mg 17 beta-estradiol pellet or a 5-mg t amoxifen pellet; others were infected prior to implantation with human reco mbinant adenovirus 5 vector containing a human cytomegalovirus promoter-dri ven beta-galactosidase gene and later assessed by X-gal staining. Results. Murine and human vessels formed anastomoses by 3 weeks. For at lea st 11 weeks, normal tissue retained the transformation zone and normal cell -type-specific keratin expression and exhibited normal proliferation; Notch -1 was present only in the basal cell layer. Dysplastic tissues exhibited k oilocytosis, increased levels of cellular proliferation, and aberrant kerat in, p53, and Notch-1 expression; HPV 16/18 DNA and HPV 16 E6 protein were d etected for at least 6 weeks. Squamous metaplasia of normal cervical epithe lium resulted from estrogen exposure, and a predominant columnar differenti ation pattern was associated with tamoxifen administration. Through stable adenovirus infection, beta-galactosidase was expressed for at least 6 weeks . Conclusions. This small manipulatable xenograft model maintains normal and dysplastic human cervical epithelium through neovascularization. Neoplastic tissue retains HPV 16/18 DNA and a premalignant phenotype, including eleva ted levels of cellular proliferation and aberrant keratin, p53, and Notch-1 expression. These attributes constitute essential features of a biologic m odel through which one may study HPV-mediated human disease and may be supe rior to cell culture and transgenic murine systems. Furthermore, this may s erve as a model for gene therapy. Finally, we suggest that the normal cervi cal epithelium is maintained through putative interactions between the Notc h locus and cell cycle growth regulators such as p53 and pRb. Neoplastic ce rvical epithelium may arise through disruption of this pathway. This theory may be testable in our animal model. (C) 2000 Academic Press.