Loss of Interleukin 2 Dependence in Cloned Interleukin 2-dependent Rat T Lymphocyte X BW5147 Hybridomas is Not Associated with Segregation of a Specific Pair of Rat Chromosomes

A fusion between the mouse AKR thymoma BW5147 and a culture of homogeneously OX8+ (CD8) rat T lymphoblasts yield interleukin (IL) 2-dependent T cell hybridomas when selected in HAT medium supplemented with IL 2-containing supernatants of concanvalin A-activated cells and dexamethasone. IL 2-independent variants can be selected from cloned IL2-dependent hybrids in the absence of conditioned medium. Karyotype analysis was used to test a previously proposed hypothesis according to which IL2-independent variants arise through loss of a specific cytotoxic T lymphocyte (rat) chromosome carrying a gene responsible for IL2 dependence. Comparison of karyotypes of several independently derived hybrids with those of their IL 2-independent variants showed that the hybrids contain at least one homologue of all rat chromosomes, and that no pair of rat chromosomes is consistently absent in the IL 2-independent variants.