Biomedical Engineering Reference
In-Depth Information
Sear
Protectant
Nutrients
Serum
Virus Design
Virus Quality
(no DIP's)
Timing of
Infection
MOI
Medium Design
Cell Line
Suspension or
immobilization
Infection and Protein
Expression Kinetics
Harvest
Time
Growth Kinetics
Maximum
Cell Density
Growth Rate
Lysis
Protein
Authenticity
Amount of
Protein/cell
Heterogeneity
Protein
modification
Secretion
Reactor Design
O 2 Demand
Recovery and Purification
Volumetric Productivity
No. steps and types
Equipment- type and size
Purity and/or
Heterogeneity
Reactor size
Product Quality
Product Cost
FIGURE 14.14 An overall process consideration for heterologous protein production with the baculovirus
expression system.
even more complex than most other bioprocesses, as the infection process and resulting
protein expression kinetics must be considered. One factor is the ratio of infectious particles
to cells (e.g. multiplicity of infection or MOI), which alters the synchrony of infection and the
resulting protein expression kinetics. Another is the genetic design of the virus (which shares
many of the general features of vector design). Also, the quality of the virus stock is impor-
tant; if the virus stock is maintained incorrectly, mutant virus can form. One example is the
formation of defective interfering particles that reduce protein expression in the culture by 90%
when high MOIs are used.
When designing a bioprocess of cell culture, one should work from the bottom of Fig. 14.14
toward the top. What is the tolerance on the desired product quality? What is the potential of
the product worth? The answers to these questions then guide the selection of bioprocess
strategies to achieve the cost and quality desired. To develop that strategy requires an under-
standing of the basic kinetics and capabilities of the biological system. Understanding these
requirements guides selection of the specific host cell line, the medium, and the molecular
design of the virus. For example, the addition of serum to the medium of some Tini cell lines
results in production of proteins with complex N-linked glycosylation, including a sialic acid
cap, which may be a requirement for product quality. However, the use of serum alters
growth kinetics, expression levels (often less), and the difficulty of purification, which may
alter cost. Such trade-offs need to be considered with respect to alternative approaches
(e.g. development of a genetically engineered host that could perform the same reactions
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