New immunodeficient (nude-scid, beige-scid) mice as excellent recipients of human skin grafts containing intraepidermal neoplasms.

Engraftment of normal or lesional human skin onto nude or SCID (severe combined immunodeficiency) mice has been used as an in vivo experimental model. However, this model has some limitations, such as shrinkage and loss of the grafted skin over time. To improve the experimental model, we have produced two new SCID-lineage mouse strains, BALB/cA-nude-scid (nu/nu, scid/scid) and BALB/cA-beige-scid (bg/bg, scid/scid) mice, by the method of cross intercross. Intraepidermal neoplastic lesions such as Bowen's disease were grafted onto the back of the mice of these strains. The rate of reduction in the size of the grafts was lower on nude-scid and beige-scid mice than on SCID mice. Rates of survival of neoplastic cells in the grafts were higher in nude-scid mice than in SCID and beige-scid mice (SCID mice 38%, nude-scid mice 55%, beige-scid mice 38%). Neoplastic cells of Bowen's disease grafted onto a beige-scid mouse proliferated and invaded the dermis during 233 days of observation, confirming the progression to invasive squamous cell carcinoma from carcinoma in situ. The present study revealed that nude-scid and beige-scide mice newly produced by us provide a very useful in vivo experimental model for the investigation of carcinogenesis and tumor progression in human skin.