Animal/Mammalian Cell Culture — Key Terms, Nutrient Media & Optimum Conditions: 23-Chem-B4 Biochemical Engineering, May 2017, Q2

Question 2: Animal/Mammalian Cell Culture — Key Terms, Nutrient Media & Optimum Conditions (20 marks)

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(a) Key terms

Term	Explanation
(i) Vaccine	A biological preparation (a weakened/inactivated pathogen, a purified pathogen sub-unit/antigen, or more recently an mRNA/vector construct) that is administered to stimulate the immune system to raise a protective, memory-forming immune response against a specific infectious agent without causing the disease itself. Many viral vaccines (e.g. polio, influenza) are manufactured by growing the virus in large-scale animal cell culture, then inactivating/purifying it.
(ii) Hybridoma	An immortalized hybrid cell line formed by fusing (typically with polyethylene glycol or electrofusion) an antibody-producing B-lymphocyte from an immunized animal with an immortal myeloma (cancer) cell. The B-cell contributes the ability to secrete one specific antibody; the myeloma cell contributes unlimited replicative capacity in culture. The fused hybridomas are screened and cloned to isolate a single cell line secreting one desired antibody indefinitely.
(iii) Cell culture	The process of growing cells (microbial, plant, or animal/mammalian) outside their natural organism, in a controlled artificial environment (a defined or serum-supplemented liquid medium, at controlled T, pH, and dissolved O₂/CO₂), typically in a flask, roller bottle, or stirred-tank/ airlift bioreactor for large-scale production.
(iv) Anchorage dependence	A property of most normal (non-transformed) mammalian cells whereby they must physically attach and spread on a solid substrate (a charged/coated culture-vessel surface, a microcarrier bead, or an extracellular matrix) in order to receive the attachment-triggered survival/growth signals needed to divide; suspended in liquid without attachment they fail to proliferate and often undergo apoptosis. Some transformed/tumour-derived lines (including many hybridomas) lose this requirement and grow "anchorage-independent" in free suspension, which is industrially preferred because it scales far more easily than surface culture.
(v) Monoclonal antibodies	Antibodies that are chemically and structurally identical because they are all secreted by clones of a single parent B-lymphocyte (via a hybridoma or, in modern processes, a recombinant CHO/other cell line) and therefore all bind the same single epitope with the same affinity — in contrast to the heterogeneous mixture of antibodies (polyclonal) a whole immunized animal's serum contains.

(b) Nutrient media and optimum culture conditions

Animal/mammalian cells are nutritionally far more demanding than microbes because they have lost many biosynthetic pathways over evolution and cannot be grown on simple defined salts-plus-sugar media. A typical cell culture medium (e.g. the classical formulations DMEM, RPMI-1640, or Ham's F12, often used as blends) must supply:

An energy/carbon source — glucose (and often glutamine, which many mammalian cell lines use as a major energy and nitrogen source, sometimes even more than glucose).
Amino acids — a full complement including the "essential" ones the cells cannot synthesize, plus glutamine (often the fastest-depleted and growth-limiting nutrient in batch mammalian culture).
Vitamins (B-complex, etc.) and inorganic salts/trace elements (Na, K, Ca, Mg, phosphate, trace Fe/Zn/Cu/Se) to maintain osmotic balance, membrane potential, and enzyme cofactor supply.
A pH buffer system — almost always sodium bicarbonate/CO₂ (with phenol red as a visual pH indicator), which requires the culture to be kept in a CO₂-controlled (typically 5–10% CO₂) incubator or bioreactor headspace to hold pH steady; HEPES is added as a supplementary buffer for open-bench manipulations.
Growth factors and hormones — historically supplied by 5–20% foetal bovine serum (FBS), which also carries attachment factors, lipids, and trace binding proteins; increasingly replaced in industrial processes by chemically-defined, serum-free/animal-component-free media (lower cost, no lot-to-lot variability, no risk of adventitious agents, easier downstream purification) supplemented with specific recombinant growth factors (e.g. insulin, transferrin, EGF) instead.
Antibiotics (e.g. penicillin/streptomycin) are commonly included at lab scale to suppress microbial contamination, though large validated GMP processes increasingly avoid them to prevent masking low-level contamination and to simplify regulatory approval.

The optimum conditions for most mammalian cell lines mirror mammalian physiology closely, since the cells evolved to function inside a warm-blooded animal: temperature 36–37°C and pH 7.0–7.4 (a narrower and more sensitive range than most microbial fermentations, which often tolerate pH 4–8). Dissolved oxygen is typically held near 20–50% of air saturation — lower than for many microbial cultures, since animal cells lack a rigid wall and are shear-sensitive, so aggressive sparging/agitation used to drive high oxygen transfer in bacterial/yeast fermenters would damage them; gentler aeration (surface aeration, micro-sparging with shear-protective additives such as Pluronic F-68) is used instead.

Topic: Animal/mammalian cell culture — terminology and media/environmental requirements.

Key relations: No numerical kinetics here; the governing constraint is nutritional/ physiological completeness of the medium (energy source + full amino-acid complement + vitamins + salts + growth factors) matched to mammalian physiological set-points (T≈37°C, pH≈7.2, CO₂-bicarbonate buffering).

Why this works: Mammalian cells have lost the biosynthetic self-sufficiency of microbes over evolutionary time (they rely on the whole organism for many nutrients/signals in vivo), so an in-vitro medium must replace everything the bloodstream/serum would otherwise supply; and because these cells evolved to operate inside a homeostatically regulated 37°C, pH≈7.4 animal body, culture conditions must reproduce that narrow physiological window far more tightly than a microbial fermentation needs to.

Common pitfall: Assuming animal cell culture can tolerate the same aeration/agitation intensity as bacterial/yeast fermentation. Because animal cells have no protective cell wall, they are far more shear-sensitive, so oxygen transfer strategy (gentle sparging, shear-protective surfactants, larger bubble diameters, lower tip speeds) must be redesigned rather than simply scaled down from a microbial process.

Source: Shuler & Kargi, Bioprocess Engineering: Basic Concepts, 2nd ed., Ch. 11 (animal cell culture and its bioreactors, monoclonal antibody production); Madigan et al., Brock Biology of Microorganisms, 13th ed. (immunology/antibody structure background for Q2(a)(v)).

Question 2 of 5: Animal/Mammalian Cell Culture — Key Terms, Nutrient Media & Optimum Conditions

Question 2: Animal/Mammalian Cell Culture — Key Terms, Nutrient Media & Optimum Conditions (20 marks)

(a) Key terms

(b) Nutrient media and optimum culture conditions