Mouse-human somatic cell hybrids: loss of mouse and human chromosomes.

Testicular germ cell tumors are unusual because they can be cured in over 80% of patients with combination chemotherapy. In order to identify chromosomes carrying genes controlling drug sensitivity, fusions were made between a mouse embryonal carcinoma (EC) cell line, F9, and a human bladder cancer cell line, MGH-UI. In contrast to some previous reports, interspecies hybrids of mouse EC cells with human cells were easy to produce. Six independent hybrids were cloned and grown for 10 further passages and karyotyped. Surprisingly, all the independent hybrids retained approximately 80% of the 40 mouse chromosomes and approximately 80% of the 83 human chromosomes. Despite the positive selection for mouse chromosomes and the absence of selection for human chromosomes, it appears that some of both sets of chromosomes are essential for these hybrids.