ABSTRACT
Effective in vitro maintenance and growth of animal cells requires culture conditions similar to those found in vivo with respect to temperature, oxygen and carbon dioxide concentrations, pH, osmolality, and nutrients. Within normal tissue in vivo, animal cells receive nutrients through blood circulation. For growth in vitro, animal cells require an equivalent supply of a complex combination of nutrients. For this reason, the first attempts in animal cell culture were based on the use of biological fluids such as plasma, lymph and serum, as well as on extracts from embryonic-derived tissue. Medium composition is one of the most important factors in the culture
of animal cells. Its function is to provide appropriate pH and osmolality for cell survival and multiplication, as well as to supply all chemical substances required by the cells that they are unable to synthesize themselves. Some of these substances can be provided by a culture medium consisting of low molecular weight compounds, known as basal media. However, most basal media fail to promote successful cell growth by themselves and require supplementation with more complex and chemically undefined additives such as blood serum. Many attempts have been made to develop culture media that do not
need this type of supplementation, that is, serum-free media formulations. These serum-free media present several practical advantages. However, the formulations that have been developed are specific for certain cell types and a universal culture medium suitable for the culture of all animal cell types seems, so far, unreachable. While some culture media are formulated to promote cell multiplication
(growth media), others only maintain cell structural and metabolic integrity (maintenance media), but do not stimulate cell division. Media prepared with highly purified compounds and with known composition are designated chemically defined media. These are particularly attractive for biopharmaceutical production, because they are less vulnerable to contamination and quality control is easier. Nevertheless, these media can be expensive. A complete medium for the culture of animal cells can be considered to
have two distinct parts. The first supplies basic cell needs of nutrients,
salts, and pH control, while the second comprises a set of supplements that provide other cell needs, allowing cell growth in the basal medium. A nutrient can be defined as a chemical substance that enters into the cell and is used as a structural component, such as a substrate for cell biosynthesis or energy metabolism, or as a catalyst in metabolic processes. Additional compounds required for cell proliferation can be considered as supplements, including all undefined additives such as serum and other biological fluids. Media frequently employed in the culture of continuous mammalian
cell lines include: Eagle’s medium, MEM (Eagle, 1959); Eagle’s medium modified by Dulbecco, DMEM (Dulbecco and Freeman, 1959); RPMI 1640 medium (Moore et al., 1967); CMRLTM 1066 medium (Parker et al., 1957); and Ham’s F12 medium (Ham, 1965). For the cultivation of adherent continuous cell lines the following basal media are suitable: CMRLTM 1066, MCDB 411, DMEM. F12, MCDB 301, and IMDM. For non-transformed cells, the media DMEM, IMDM, MCDB 104, 105, 202, 401, and 501 are suitable (Freshney, 1992). Each of these basal formulations may be supplemented with serum or other specific proteins. For insect cells the following basal media can be used: Grace’s, TC 100,
TNM-FH, D22, Schneider, and M3. These media normally require supplementation with fetal bovine serum. Alternatively, different serum-free media are available for insect cells, such as Sf900II, Ex-Cell
1 400, 405, and
420, Express Five1 SFM, Insect-XPRESSTM, HyQ SFX-InsectTM, and IPL 41. These have the advantage of higher reproducibility and lower cost when compared with serum-supplemented basal media (Ikonomou et al., 2003). For comparison purposes, Table 5.1 shows the composition of DMEM
(one of the most versatile medium formulations, typically employed in the culture of mammalian cells) and Schneider’s medium (used for diptera insect cells, especially Drosophila melanogaster). A total of 34 different components are present in DMEM, although some minor variations in composition may occur between suppliers.
