growth of tumorigenic cells any cells capable of taking up and expressing foreign dna can be employed as the recipient the recipient cells are hereinafter referred to as primary transformants of the dna sequences such as rat f2408 hamster bhk 21 or preferably mouse nih3t3 cells in a preferred embodiment of the present invention the dna sequences encoding the growth factor can be isolated from the primary transformants and transferred to normal nih3t3 cells in a second round of transfection hereinafter referred to as secondary transformants with a selectable genetic marker the selectable genetic marker can be any gene which confers a selective growth advantage to the recipient cell suitable selectable markers include but are not limited to resistance to the antibiotic hygromycin and preferably resistance to the antibiotic neomycin or g418 gibco grand island n y cells which are transfected by both the dna sequence encoding the growth factor of the present invention and for example a gene encoding resistance to g418 can then be selected for their ability to grow in the presence of concentrations of about 250 micrograms per ml of g418 present in the growth medium after the secondary transformants were selected for their ability to grow in the presence of neomycin or g418 and those cells which had been transformed to the neoplastic state isolated the human dna sequences which had been taken up and integrated into the mouse genome were identified molecularly cloned using an appropriate vector.