info@mail.ucallm.com
1. Overview
Mammalian cell expression systems are the platform of choice for producing proteins requiring complex post-translational modifications (e.g., glycosylation, phosphorylation, γ-carboxylation) and native three-dimensional structures. Utilizing the transcription and translation machinery of mammalian host cells, these systems enable the production of biologically active recombinant proteins with post-translational modifications and structural features closely resembling those of native human proteins. Depending on the application, expression is categorized into Transient Gene Expression (TGE, for rapid, gram-scale production of research-grade proteins within days) and Stable Cell Line Generation (SCLG, for long-term, high-yield GMP manufacturing of clinical therapeutics).
Regarding host cell selection, Chinese hamster ovary (CHO) cells and human embryonic kidney 293 (HEK293) cells are the two most widely used platforms. CHO cells, with their well-documented regulatory history, robust PTM capabilities, and scalability, remain the industry standard for commercial production of therapeutic antibodies and complex glycoproteins. HEK293 cells, characterized by high transfection efficiency, high protein yields, and rapid workflows, are the top choice for early-stage R&D and transient expression.
2. Core Advantages
(1) Human-like PTMs: Capable of complex N-glycosylation, O-glycosylation, phosphorylation, sulfation, and γ-carboxylation; products exhibit biological activity highly consistent with native target proteins (with HEK293 providing fully humanized glycoforms, and CHO providing highly acceptable mammalian glycoforms).
(2) Proper folding and assembly: Possess chaperones and ER quality control mechanisms ensuring correct assembly of multi-subunit proteins (e.g., antibodies)
(3) High expression levels: Through vector optimization and cell engineering, stable production can achieve gram-per-liter titers under optimized fed-batch conditions; transient expression yields hundreds of milligrams per liter
(4) Product safety: Free of endotoxins, well-characterized cell banks and rigorous viral safety testing support biopharmaceutical manufacturing.
(5) Scalability: Adapted to serum-free suspension culture; can be scaled up to thousands of liters in bioreactors
(6) Wide host selection: Multiple cell lines (CHO, HEK293, etc.) available to meet different protein and production needs
3. System Limitations
(1) High cost: Media, transfection reagents, and consumables are far more expensive than microbial systems.
(2) Long timeline: Stable cell line generation typically takes several months; transient expression is faster but limited in scale
(3) Genetic instability: Long-term passaging may lead to decreased expression or product quality changes.
(4) Viral safety risks: Particularly for human-derived lines (like HEK293), there is a risk of susceptibility to human-pathogenic viruses (e.g., HIV, HBV), requiring strict viral clearance validation in downstream processing.
(5) Scalability challenges: Certain cell lines (especially HEK293) exhibit higher shear sensitivity and faster expression decline during prolonged scaling compared to the highly robust CHO platforms.
(6) Product heterogeneity: PTMs such as glycosylation may vary between batches due to culture condition fluctuations
4. Key Application Areas
(1) Therapeutic monoclonal antibodies: The majority of marketed monoclonal antibodies are produced in CHO cells, e.g., Trastuzumab, Adalimumab.
(2) Fc fusion proteins: Leverages CHO glycosylation to preserve Fc domain function, e.g., Etanercept (TNFR-Fc) for rheumatoid arthritis.
(3) Complex glycoproteins: Including erythropoietin and coagulation factors, e.g., recombinant human erythropoietin for anemia treatment.
(4) Bispecific antibodies: Depends on CHO for correct assembly of complex multi-chain structures, e.g., Emicizumab for hemophilia.
(5) ADC drugs: Production of intact monoclonal antibodies as payload conjugation substrates.
(6) Transient research-grade proteins: Gold standard for research-grade proteins, e.g., EGFR ectodomain for structural studies.
(7) Viral vector production: 293T and derivatives are widely used for high-titer AAV and lentiviral vector production.
(8) Vaccine development: recombinant viral antigens
(9) Receptor signaling and functional studies: Widely used for ion channels and membrane receptors, especially GPCR signaling research.
5. Classification of Expression Vectors
5.1 By expression mode
Type | Features | Vectors |
Transient expression vectors | DNA does not integrate; expression lasts 3–7 days | pcDNA series, pTT5, pHEK293 Ultra |
Stable expression vectors | DNA integrates into genome; long-term expression | pcDNA series (with markers) |
Inducible expression vectors | Gene expression regulated by external inducers | Tet-On/Off, T-REx™ |
5.2 By vector type
Type | Features | Representative Vectors |
Plasmid vectors | Non-viral DNA; high transfection efficiency, easy handling | pcDNA, pTT5, pHEK293 Ultra |
Viral vectors | Enter cells as viral particles; high transduction efficiency | Lentiviral, Adenoviral, AAV vectors |
Episomal vectors | maintained episomally in EBNA1-expressing cells | pTT5 (with oriP) |
5.3 Common mammalian expression vectors
Name | Promoter | Selectable Marker | Features | Suitable Cells |
pcDNA series | CMV | Neo/G418 | Classic constitutive vector; most widely used | HEK293, CHO |
pTT5 | CMV (with oriP) | Ampicillin (bacterial selection) | High expression in HEK293-EBNA1 | HEK293-EBNA1, CHO |
pHEK293 Ultra | CMV with proprietary enhancers | — | Engineered for ultra-high transient expression | HEK293-F/Expi293F |
pCHO 1.0 | CMV/EF1α chimeric | DHFR, Puro | Designed for stable CHO expression; incorporates codon-optimized DHFR selection | CHO-DG44, CHO-S |
pAdVantage | CMV | Neo | Contains adenoviral VA RNA, enhances transient protein expression by increasing translation efficiency | HEK293, CHO |
Transposon Vectors (e.g., PiggyBac) | CAG or EF1α | Puro/Neo | Mediates active, transposition-driven integration; significantly reduces gene silencing and increases high-producer rates | CHO, HEK293 |
6. Common host cells
6.1 CHO cell lines
Cell line | Features | Application |
CHO-K1 | Well-characterized industrial production cell line | Antibody drug production with excellent yield performance |
CHO-S | Suspension-adapted; high proliferation rate | Transient and stable recombinant protein production |
CHO-DG44 | Biallelic DHFR knockout | DHFR selection and gene amplification |
CHO-K1 SV | Glutamine synthetase (GS) selection system | Industrial antibody production |
CHOK1SV GS-KO | Biallelic GS knockout based on CHO-K1 SV | High-expressing stable cell lines |
CHOZN GS | Biallelic GS knockout via ZFN technology | High-expressing stable cell lines |
6.2 HEK293 cell lines
Cell line | Features | Application |
HEK293 | Parental line, immortalized by Ad5 DNA | Routine protein expression, adenovirus amplification |
293T | Stably expresses SV40 large T antigen | Transient protein expression and lentiviral packaging |
293F | Suspension-adapted; fast growth in serum-free media | Transient expression; scalable production |
293E /293-6E | Stably expresses EBNA-1; amplifies oriP plasmids | High-efficiency recombinant protein production |
293FT | 293F background + SV40 large T antigen | High-titer lentiviral production |
293A | Stably integrated E1 gene with good adherence | Adenovirus production and amplification |
AAV-293 | Trans-expressing adenoviral E1 gene | Production of infectious AAV particles |
293S | GnTI-deficient; produces simplified N-glycans | Homogeneous glycoprotein expression |
6.3 Comparative Selection: CHO vs. HEK293
Comparison | CHO | HEK293 |
Primary Application | Stable large-scale production | Transient rapid production |
transfection efficiency | Low | High |
Detailed Glycosylation | Mammalian-like. Lacks α2,6-sialylation (exclusively α2,3-linked). Potential immunogenic glycans (Neu5Gc and α-Gal) may be present. | Fully Humanized. Possesses both α2,3- and α2,6-sialylation. Free of non-human immunogenic glycan epitopes (Neu5Gc/α-Gal-free). |
Timeline | Several months for cell line generation | 1–2 weeks for transient |
Yield | Stable high titers | Moderate transient titers |
Scalability | Excellent | Moderate |
Regulatory acceptance | Highly recognized; mainstream for marketed drugs | Emerging; increasing in gene therapy and vaccines |
Cost | High capital and operational costs | Higher transient costs, but no long-term commitment |
7. Selection Guide
Requirement | Recommended Vector/Hosts | Reason |
Rapid research-grade protein | pcDNA + HEK293F | High transfection efficiency; protein in 1–2 weeks |
Ultra-high transient yield | pHEK293 Ultra + HEK293 | Up to 10× expression of CMV vectors |
Therapeutic antibody/glycoprotein stable production | pCHO 1.0 (DHFR/GS) + CHO-K1 or CHO-S | Stable integration, gene amplification, high yield |
Bispecific antibodies/multi-subunit complexes | Multi-promoter or Multi-plasmid systems (optimized LC:HC ratio)+ CHO | Balanced co-expression, correct assembly |
Viral vector packaging (AAV, lentivirus) | Viral vector systems + 293T or AAV-293 | Efficient transduction and packaging |
Toxic proteins/functional regulation | Tet-On inducible vector + HEK293 | Tight regulation, avoids cytotoxicity |
Long-term stable expression with rapid screening | UCOE-containing vector + CHO | Prevents gene silencing, shortens screening time |
8. Service Highlights
l Cutting-edge expression platforms: ExpiCHO™, Expi293™ systems have achieved gram-per-liter titers for selected proteins
l End-to-end one-stop service: From gene synthesis and vector construction to transient/stable expression and GMP production
l Expertise in challenging targets: Proprietary strategies for membrane proteins, toxic proteins, and multi-subunit complexes
l Strict quality control: All products tested by SDS-PAGE, SEC-HPLC, endotoxin, sterility, etc.; detailed COA provided
l Flexible scales: From micrograms to grams, catering to research and commercial needs.
9. Service Procedure
9.1 Transient Gene Expression Procedure
Service Step | Gene synthesis and plasmid construction | Protein expression and optimisation | Large-scale expression and purification |
Description | l Codon optimization & gene synthesis l Subcloning into high-expression transient vectors l Plasmid validation & preparation
| l Small-scale transfection of high-density HEK293/CHO l Optimization of transfection & Pilot purification l QC analysis (SEC-HPLC, SDS-PAGE, UV, etc) | l Large-scale transient transfection l Protein purification l QC analysis |
Deliverables | l Plasmid sequence l COA report | l Purified protein l COA report | l Purified protein l COA report |
Turnaround Times | 2-3 weeks | 2-3 weeks | 3-4 weeks |
9.2 Stable Cell Line Generation Procedure
Service Step | Gene synthesis and vector construction (Optional) | Transfection & Stable Pool Selection | Single-Clone Isolation & Stability | Cell Banking & Scale-Up |
Description | l lCodon optimization & gene synthesis l lCloning into selection vectors l Cloning into selection vectors | l Transformation into CHO host cells l Metabolic selection l Generate stable cell pools & evaluate pool productivity | l High-throughput single-cell deposition & imaging l Screen top high-producing clones l Long-term stability testing | l Establishment of Research Cell Bank l Bioreactor scale-up run l QC analysis
|
Deliverables | l Plasmid sequence l COA report | l Stable cell pools l COA report | l Monoclonality validation data l COA report | l Frozen RCB vials l Purified protein (from scale-up) l Comprehensive SCLD report (IND-enabling) |
Turnaround Times | 2-3 weeks | 4-6 weeks | 6-12 weeks | 4-6 weeks |
10. Case Studies
11. Frequently Asked Questions (FAQs)
l Q1: How to choose between CHO and HEK293?
A: For large-scale, high-purity, stable production of therapeutic proteins/antibodies, choose CHO stable expression. For rapid research-grade proteins for proof-of-concept or functional studies, choose HEK293 transient expression.
l Q2: How to increase protein yield in mammalian cells?
A: Optimize by: ① Codon optimization; ② Choosing strong promoters and efficient signal peptides; ③ Optimizing transfection conditions (DNA/PEI ratio, cell density); ④ Adding culture additives (e.g., sodium butyrate); ⑤ Optimizing harvest time.
l Q3: Do you offer stable cell line generation services?
A: Yes. We offer stable cell line generation in CHO-K1, CHO-S, HEK293, and other cells, using gene knockout, targeted integration, and transposon-based random integration. We offer animal-component-free, chemically defined media and processes compliant with GMP-compatible.