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Encyclopedia of Physical Science and Technology EN009G-399 July 6, 2001 20:4

32 Mammalian Cell Culture

active fibrinolytic enzyme plasmin and are used for cells (ADC) and free-suspension cells. ADC were grown
dissolving blood clots. in small culture vessels and a production batch consti-
Transgenic animals Animals that have incorporated for- tuted hundreds, even thousands, of replicate cultures (i.e.,
eign DNA heritably. a multiple batch process). The need for a unit batch pro-
cess (one large culture vessel), such as the fermenters used
for suspension cells, saw the development of a wide range
CELL CULTURE refers to the ability to grow cells de- of novel culture reactors, but the significant breakthrough
rived from the whole organism as either discrete cells or came with the microcarrier system. This procedure devel-
as small fragments of tissue in vitro. Cell culture has be- oped in 1967 by van Wezel allowed cells to grow attached
come a very important technology in a wide range of life to small (200-micron) spheres which were stirred in a large
science applications. It allows the study of cell growth tank fermenter analogous to suspension cells. This was the
and control, differentiation, genetics, and many diseases first successful large-scale unit process for ADC.
including cancer. In addition, it is extensively used for the Vaccines were the dominant product until the 1970s,
manufacture of a large number of biological products in- but changes in regulatory and licensing procedures then
cluding vaccines, hormones, immunologicals, and blood allowed cells from sources other than normal tissues to
factors and for tissue engineering and gene therapy. be used for human medicinal products. This came about
during the development of a production process for hu-
man interferon proteins using a cancer cell line, Namalva,
I. INTRODUCTION by the company Wellcome. Their pioneering work estab-
lished the safety criteria, and thus acceptance, for using
The initial aims of cell and tissue culture were to study non-normal (heteroploid, transformed, or tumor-derived)
specialized cell behavior and function in vitro. However, cell lines and the feasibility of scaling-up an industrial
these aims could not be realized because only the ubiqui- cell culture process to 8000 L. Cell culture then entered
tous dedifferentiated cell, or cells transformed by carcino- a new, or modern, phase where a wide variety of cell
gens, survived in culture. Although mammalian cells have products (Table I) is produced from a range of cell types
been grown in vitro since before 1907, the factor that gave (see Section II). Two of these can be highlighted as be-
impetus to their current widespread laboratory and indus- ing significant milestones. First, the production of mon-
trial use was the discovery by Enders in 1949 that human oclonal antibodies from hybridoma cells (the fusion of a
pathogenic viruses could be grown in cell cultures. Prior normal antibody-producing cell and a hemopoitic cancer
to this, viruses could only be grown in living tissue, thus cell) which has given rise to hundreds of new products.
vaccine production used living organisms such as the em- Second, the development of recombinant tPA by Genen-
bryonic chicken. The use of cultured cells to grow viruses tech which gave rise to the first genetically engineered
opened up the possibility of a less expensive, easier, bio- clinical product from cell cultures. Currently, applications
logically safer, more controllable (and reproducible), and are widening to include the cell itself as a product in
larger scale method for vaccine manufacture. Following tissue engineering and organ replacement and for gene
this demonstration by Enders, it took only 5 years before therapy.
the first cell-based vaccine was licensed for clinical use Technological advances have obviously driven the
(the Salk polio vaccine in primary monkey kidney cells development of animal cell biotechnology from 1954 to
in 1954). This opened up 20 years of continuous devel- the present day, but the main influencing factor has been
opment of human and veterinary viral vaccines and cre- thesafetyoftheendproduct.Regulatorybodiessuchasthe
ated the need for industrial-scale cell-culture processes. World Health Organization (WHO), the U.S. Food and
The most effective large-scale process developed during Drug Administration (FDA), and others have set down at
this period was for foot and mouth disease virus (FMDV) all stages of the process acceptable standards for cell prod-
based on suspension culture of BHK cells. Developments ucts, and these have had to safeguard against both known
in processes for human vaccines were less dramatic due and perceived hazards such as transforming viruses, dis-
to the need to use biologically safe cell lines. This meant ease agents, carcinogenic and immunologically damaging
the use of human diploid cell lines, such as WI-38 and molecules, and, more recently, prions.
MRC-5, which unfortunately, due to their normality (i.e., In this chapter, emphasis is placed on scale-up be-
they behave as cells in vivo without tumorgenic trans- cause of the relatively low biomass productivity of nat-
formation), only grow attached to a substrate (anchorage ural products from animal cells compared to bacteria and
dependent) and only reach low cell densities. The wide the need to introduce more efficient and economical in-
range of animal cell reactors available is partly due to dustrial processes to meet the production requirements
the dual development of systems for anchorage-dependent of recombinant proteins. However, of equal importance