Suppression of tumorigenicity in interspecific reconstituted cells and cybrids.

The effect of cytoplasms on the expression of tumorigenicity was examined in interspecific reconstituted cells and cytoplasmic hybrids (cybrids) formed by fusions between karyoplasts (or intact cells) from highly tumorigenic mouse melanoma B16 cells and cytoplasts from non-tumorigenic, hypoxanthine-guanine phosphoribosyl-transferase (HGPRT)-deficient and chloramphenicol (CAP)-resistant rat myoblastic cells, L6TG X CAPr. The reconstituted clones and cybrid clones isolated in the double selection medium, HAT and CAP, acquired CAP-resistance, and each showed unique morphology and cellular arrangement. Tumorigenicity was suppressed in all the reconstituted clones and cybrid clones examined at an early stage after their isolation, but re-appeared in some clones after prolonged cultivation of the cells.