Tumour‐induced host stromal‐cell transformation: Induction of mouse spindle‐cell fibrosarcoma not mediated by gene transfer

Tumour‐induced host‐cell transformation has been addressed by examining human tumours in situ and following xenograft to nude mice. We have found evidence for the transformation of host stromal fibroblasts both in vivo and following the introduction of the tumours to in vitro culture. The in vitro culture of one such xenograft‐derived from a human prostatic adenocarcinoma‐resulted in the outgrowth of a transformed aneuploid mouse cell line. This transformed line was tumourigenic both in BALB/c nu/nu (nude) mice and in heterozygous nu/+ mice, with the morphology of a spindlecell sarcoma. The cell line did not express human isozymes or human histocompatibility antigens, nor were human chromosomes present. Moreover, human DNA sequences were notdetected by human Alu repeat sequence element probing in the transformed cell line grown either in vitro or in vivo. The line contained retroviral long terminal repeat sequences but there was no evidence of proviral activation. These findings indicate that tumour cells may cause transformation of neighbouring stromal cells; that this transformation may proceed in the absence of DNA transfer or activation of endogenous proviruses; and that the means of this observed transformation may involve humoral factors elaborated by the tumour cells.