Fusion of cultured Djungarian hamster tumor cells with the host cells in vivo and the characteristics of the hybrids obtained

: Tumor Djungarian hamster cells resistant to 5-bromodeoxyuridine (5-BrdU) were inoculated to newborn hamsters. Tumors occurred in animals and were seeded into HAT medium in vitro. This procedure permitted to select hybrids between tumor and normal cells established in vivo. Hybrid nature of cell cultures was confirmed by karyological analysis. Hybrid cells were tested for their ability to grow progressively in newborn Djungarian hamsters and to form colonies in soft agar. The hybrid cells were less malignant than 5-BrdU-resistant tumor cells, but they could grow in soft agar with the efficiency of the parental tumor cells. Chromosomal constitution of the hybrid tumors indicate that as a rule, the expression of malignancy correlates with elimination of the morphologically normal chromosome pairs No 1, 4, 6, 8. Our data suggest that at least two genes located on different chromosomes of the normal cell are needed for suppression of malignancy in somatic cell hybrids.