Cell expansion is one of the most critical steps in the biopharmaceutical manufacturing process. It involves growing cells in large quantities through multiple passages until the desired cell numbers are achieved. This is necessary because biomanufacturing requires billions of cells to produce sufficient amounts of therapeutic proteins. The three main types of cells used in it are mammalian cells, microbial cells, and stem cells. Each cell type has unique requirements for growth parameters like culture conditions, nutrients, and growth factors.

Mammalian Cell Expansion

Chinese hamster ovary (CHO) cells are the most commonly used mammalian cells for biomanufacturing due to their ability to grow in suspension and produce complex therapeutic proteins. The expansion of CHO cells usually starts with a seed train consisting of multiple small-scale bioreactors or shakes flasks. Cells grown in the seed train are then transferred to progressively larger bioreactors until final production bioreactors with volumes of 2000L or more are reached. Key parameters that must be tightly controlled during CHO Cell Expansion  include temperature, pH, dissolved oxygen levels, nutrient concentrations, and agitation. CHO cells can undergo around 25-30 population doublings before reaching senescence, so the overall expansion process takes 2-3 weeks.

Microbial Cell Expansion

Bacteria and yeast are the predominant microbial cell types used for large-scale bioproduction. Escherichia coli is widely employed for expressing therapeutic proteins due to its fast growth rate, high protein yields, and well-characterized genetics. E. coli cells are first grown in shake flasks and then transferred to bioreactors as the cell densities increase. Dissolved oxygen levels and agitation need careful monitoring to ensure aerobic growth conditions. E. coli cultures can reach maximum cell densities over 100 billion cells/mL within 3-4 days. Yeast species like Pichia pastoris are also commonly used and require similar culture parameters to E. coli during expansion. Overall, microbial it is a relatively rapid and high yield process.

Stem Cell Expansion

Adult stem cells offer potential applications in regenerative medicine but are present in very small quantities in adult tissues, requiring extensive expansion before clinical use. Mesenchymal stem cells (MSCs) are one of the most widely studied adult stem cell types. MSC expansion employs culture methods similar to CHO cells, using serum-supplemented media and substrates like microcarriers or multi-well plates. MSCs double roughly every 24-36 hours but have a limited lifespan, restricting expansion to 10-15 passages. Specialized growth factors are often added to promote self-renewal while preventing differentiation. Proper control of culture parameters and aseptic conditions are critical for producing clinical-grade stem cells.

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