Page 262 - Advances in Textile Biotechnology

Developments in recombinant silk and other elastic protein fi bers 243

levels in mammalian cells (Griffiths and Page, 1997). Insect cell cultures
provide an environment in which the process parameters can be carefully
controlled and monitored allowing the use of a single cell line with more

uniform post-translational modifications. The main drawbacks are that the
process requires a significant set-up and running cost for the sterile growth

facilities. The employment of larvae is more advantageous because the cost
is lower than insect cell culture and some post-translational processing

events such as glycosylation and secretion may be more efficient in larvae,

with final protein yield approximately equal to 1 L of cultured cells
(Mahmoud, 2007).

10.4.5 Mammalian cells

There are two approaches for mammalian host transformation, i.e. by using
mammalian cell lines or by producing transgenic animals delivering the
genetic material to embryonic cells. Cultivated mammalian cells have
become the dominant system for the production of recombinant proteins
for clinical applications because of their capacity for proper folding, assem-
bly and post-translational modifications (today about 60–70% of all phar-

maceuticals based on recombinant proteins are produced in mammalian
cells). Many of these proteins are expressed in immortalized Chinese
hamster ovary (CHO cells), but other cell lines, such as those derived from
mouse myeloma (NS0), baby hamster kidney (BHK), human embryo
kidney (HEK-293) and human retinal cells have gained regulatory approval
for recombinant protein production. All mammalian recombinant thera-
peutics are naturally secreted proteins or have been developed from gene
constructs that mediate protein secretion. On the other hand, transgenic
animal technology has enabled targeting of recombinant proteins to specifi c
animal tissues or secretions allowing their production in living whole
animals (Wurm, 2004).
Mammalian expression techniques, however, have several drawbacks.
They are time-consuming and technically difficult, with complex nutrient

requirement and low product concentration, and are much more diffi cult
to perform on a large scale, all of which means that the end product is
extremely expensive. For transgenic animal technology, the process requires
thousands of fertilized oocyte microinjections to generate a single trans-
genic animal and there are also ethical issues to consider (Rai and Padh,
2001, Wurm, 2004).

10.4.6 In vitro systems

Cell-free protein synthesis systems are based on extracts from prokaryotic
or eukaryotic organisms known for their good protein synthesis capabilities.

© Woodhead Publishing Limited, 2010