Growth factors for mammalian cells in culture.

Essentially all cultured animal cells require for growth1 animal serum or some other biological preparation. An understanding of the nature of the contributions made by these complex mixtures is of great interest for many reasons. Included are the desirability of better defined media for biochemical and other studies, the elucidation of growth requirements not detectable in experiments with whole animals, and the accumulation of a base line of knowledge for future investigation of comparative biochemistry and nutrition on a cellular level. Previous studies with cultured mammalian cells provided some information about two serum activities. One of the growth factors, a protein (1, 2), seems to play its role on the cell surface. The second, replaceable by catalase (3), functions by preventing the cells from synthesizing toxic levels of peroxide or by aiding them to dispose of it once it has been formed. The exact serum components which perform this task are not known but it is likely that they include a mixture of reducing substances. With two cultures of human origin, Appendix A 1 (4, 5) and HeLa (6), the possibility was tested that the protein factor and catalase could substitute for serum in the growth medium. Although multiplication of even relatively small numbers of cells could be obtained, the rates of growth were quite low. Growth rates comparable to those obtained with serum resulted, however, when additional compounds, particularly insulin and Versene (sodium ethylenediaminetetraacetate) were added to the medium. The purpose of this report is to describe the serum-free medium and to present the evidence for the growth-enhancing activity of some of its components. Justification for the presence in the medium of compounds which elicited a small or inconsistent enhancement of growth (vitamin Blz, triiodo-n-thyronine, and serum albumin) will not be presented.