A Method for Distinguishing Human and Mouse Cells in Solid Tumors Using in Situ Hybridization

A common technique used in the study of human malignancies involves the inoculation of nude mice with human neoplastic cells. It is usually assumed that the tumor arising is composed predominantly of human cells with mouse tissue present only to provide minimal stromal support. Several reports, however, have shown evidence of host cell neoplastic transformation. Therefore, in order to effectively study and characterize such xenografts, it is important to establish the relative involvement of human and mouse cells. In the present study, a method for easily distinguishing human and mouse cells is described. The method involves in situ hybridization of formalin-fixed tissues using DIG-labeled oligomer probes which correspond to species-specific portions of Alu sequences. This method can be applied to archival material either as a means of confirming that the tissue taken from nude mice xenografts is predominantly human or as a vehicle for studying the mechanisms of host cell neoplastic transformation and their relevance to human malignant spread. The proposed technique may also serve as a basis for other in situ applications, particularly those involving formalin-fixed tissues and oligomer probes.