Abstract: A method of selecting transfected cell lines for heterologous protein expression from a population of cells some of which include an endogenous sequence for an amplificable marker and some of which do not include the sequence. The method is based on a minimum amplifiability index which, contrary to current practice, focuses cell lines having relatively low productivity prior to amplification. Transfected cell lines selected with the instant invention produce greater amounts of heterologous protein than cells selected according to the prior art. In one embodiment, the amplifiability index is used to select for further amplification a cell line transfected with a vector containing the coding sequence for human Factor VIII.

Abstract: Recombinant Factor VIII production is increased by supplementing the serum-free culture of mammalian host cells containing the gene therefor in a serum-free nutrient media with lipoprotein obtained from a mammalian source, preferably low density human lipoprotein or total bovine lipoprotein.

Abstract: A growth medium suitable for increasing the yield of plasminogen activator obtained from plasminogen activator-producing cells. The growth medium is composed of a 1:1:1 (by weight) mixture of Waymouth's MB752/1, Dulbecco MEM and Ham's F-12. The growth medium is preferably supplemented with growth factors.

Abstract: A method of increasing the yield of plasminogen activator from a plasminogen activator-producing cell line by adapting said cell line to grow in a suitable growth medium essentially free of fetal calf serum is disclosed. Also disclosed are cell lines capable of producing relatively large quantities of plasminogen activator, and a chemically defined growth medium suitable for adapting a plasminogen activator-secreting cell line to growth in the absence of fetal calf serum.