[Clones of the lymphoblastoid line RPMI-6410t requiring an exogenous growth factor]

It was earlier established that the RPMI-6410t cells, obtained from a patient with acute myeloblastemia, synthesized a growth factor which maintains their proliferation and had a specific receptor for this factor on their surface. The use of a medium conditioned by the 6410t cells made it possible to define conditions in which practically 100% efficiency cloning of these cells is attained by the method of limiting dilutions. In the present work, this method of cloning was applied to obtain from the 6410t strain clones which are characterized by a requirement for an exogenous growth factor. These clones, like the 6410t cells, have on their surface specific receptors but, unlike the parental cells, do not synthesize the growth factor and do not form colonies in soft agar, i. e. lose one of the features of malignancy. These facts agree with the published data according to which the proliferation of normal cells is regulated by exogenous growth factors and confirm a suggestion put forward in our previous work that the endocrine regulation of cell growth is one of the mechanisms of malignancy.