A series of hybrid cells containing different ratios of parental chromosomes formed by two steps of artificial fusion.

Double hybridization of Ehrlich ascites tumor cells (ETC) and L cells was performed. In the first step, a hybrid (LE) of ETC and L(AG) (a mutant of L cells, resistant to 10 mug/ml of 8-azaguanine) and a hybrid (LL) of L(AG) and L(BrdU) (a mutant of L cells, resistant to 100 mug/ml of 5-bromodeoxyuridine) were prepared by the use of artificial fusion by UV-irradiated HVJ (Sendai virus). In the second step the LE hybrid and ETC, or the LL hybrid and ETC, were fused again by UV-HVJ. The hybrids (LEE and LLE) were segregated during culture. Thus, the series of hybrids L, LLE, LE, LEE, and ETC was obtained. The morphological feature and karyological characters of these hybrids and the distribution of antigens corresponding to each parent on their cell surfaces supported the above identification of the series of hybrids obtained by double hybridization. All three hybrids acquired new characters, such as the ability to form large colonies in soft agar and large tumors on the chorioallantoic membrane of chicken eggs, unlike either parent. The tumor-forming capacity of the series was ETC > LEE > LE > LLE; L cells formed no tumor in mouse abdomen under the test conditions.