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Advanced therapy medicinal products — gene therapies, cell therapies, tissue-engineered products — depend on upstream cell culture processes that are robust, GMP-compliant and scalable. At the centre of most ATMP upstream processes is one of two production platforms: CHO cells for therapeutic proteins and viral vectors used in ex vivo modification, or HEK293 cells for viral vector manufacturing.

Serum-free medium is not optional in either context. It is a regulatory expectation and a manufacturing necessity.

Why ATMP Manufacturing Requires Serum-Free Media

The EMA’s Advanced Therapy Classification and the EU ATMP Regulation (1394/2007) set a high bar for raw material characterisation. Animal-derived materials — FBS chief among them — introduce:

• TSE/BSE risk: requires EDQM TSE certificates and sourcing justification per Ph. Eur. 5.2.8
• Lot variability: each lot of FBS is biologically different; GMP processes cannot tolerate undefined variability in critical raw materials
• Downstream contamination risk: residual bovine proteins can appear in the final product and require demonstration of clearance

Serum-free, chemically defined media address all three points. Full component characterisation, no animal-derived raw materials, consistent performance lot to lot.

CHO Cells in ATMP Manufacturing

CHO cells appear in two ATMP-adjacent contexts.

1. Therapeutic protein production for ex vivo cell therapy. Cytokines, growth factors and recombinant proteins used to expand or prime cell therapy products (T cells, NK cells, MSCs) are often produced in CHO. These proteins must be manufactured under GMP with full characterisation — serum-free, chemically defined medium is the standard.

2. Viral vector production. Some AAV manufacturing platforms use CHO or CHO-derived cell lines. More commonly, CHO appears in stable producer cell line strategies for large-scale retroviral or lentiviral vector manufacturing — an area of active development.

For CHO-based ATMP upstream processes, the medium requirements are: chemically defined, protein-free preferred, animal-origin-free documentation, ISO 13485 or GMP certification from the supplier.

→ Serum-Free Media for CHO Cells at SeamlessBio

HEK293 Cells in ATMP Manufacturing

HEK293 is the dominant production platform for viral vectors used in ATMP manufacturing:

• AAV vectors for in vivo gene therapy (retinal dystrophies, haemophilia, neuromuscular disease)
• Lentiviral vectors for ex vivo CAR-T and TCR-T cell modification
• Adenoviral vectors for certain vaccine and gene correction platforms

In each case, the regulatory expectation for GMP clinical manufacturing is serum-free, chemically defined medium with full traceability. For Phase I/II, a research-grade chemically defined medium may be acceptable with appropriate bridging studies. For pivotal trials and commercial manufacturing, GMP-grade medium with ISO 13485 documentation is required.

→ Serum-Free Media for HEK293 Cells at SeamlessBio

CHO vs. HEK293 — Side-by-Side Comparison

Choosing the Right Supplier

For ATMP manufacturing, medium selection is a critical quality decision — not a procurement decision. The supplier must provide:

• Full component list with CAS numbers and sourcing documentation
• Animal-origin-free declaration with traceability to raw material level
• GMP-grade production with ISO 13485 certification
• Batch-specific CoA and CoO
• Regulatory support documentation for IND/IMPD filings

SeamlessBio sources and supplies serum-free, chemically defined media for both CHO and HEK293 platforms, with GMP-grade options and full regulatory documentation support for EU and UK ATMP manufacturers.

→ Contact SeamlessBio to discuss medium requirements for your ATMP manufacturing process.

Der Beitrag Serum-Free Media for ATMP Manufacturing: CHO and HEK293 Side by Side erschien zuerst auf SeamlessBio.

HEK293 is not one cell line. It is a family — and each member has distinct characteristics that affect medium selection. Using a formulation optimised for one sub-line on another is one of the most common sources of suboptimal titre in viral vector manufacturing.

Here is what you need to know about the main HEK293 variants and their serum-free medium requirements.

HEK293 Parental

The original cell line, derived from human embryonic kidney cells transformed with adenovirus 5 DNA in 1973. Adherent, moderate growth rate, well characterised.

Medium requirements: Standard chemically defined formulation supporting adherent culture. Transfection efficiency with PEI is high in properly formulated serum-free conditions. Suitable for early-stage AAV production and recombinant protein expression.

HEK293T

HEK293T contains a stable integration of the SV40 Large T antigen. This allows episomal replication of plasmids containing the SV40 origin of replication — which dramatically increases transient protein expression and is the basis for high-efficiency triple plasmid transfection for AAV and lentiviral vector production.

HEK293T is adherent. It does not adapt well to suspension culture without significant selection and adaptation work.

Medium requirements: Optimised for adherent culture. Low albumin content is important — albumin interferes with PEI-DNA complex formation and uptake. The medium must support very high confluence (70–80% at transfection) without inducing early senescence. Post-transfection viability for 48–72 hours is the critical window.

HEK293F

HEK293F is a suspension-adapted variant of HEK293. It does not contain the SV40 T antigen. It is the preferred cell line for large-scale recombinant protein expression and is increasingly used for suspension AAV production platforms.

Medium requirements: Formulated specifically for suspension culture. High-density growth capability — commercially optimised HEK293F media support viable cell densities above 3–5 × 10⁶ cells/mL routinely. Agitation tolerance is important: the medium must maintain cell viability under the shear conditions of spinner flasks, shake flasks and stirred-tank bioreactors.

HEK293F requires serum-free suspension medium from the outset. Attempting to adapt using stepwise FBS reduction in a medium formulated for adherent culture typically results in poor growth and high cell death.

HEK293FT

HEK293FT combines the SV40 T antigen of HEK293T with selection for fast growth and high transfection efficiency. It is the standard cell line for high-titre lentiviral vector production.

Medium requirements: Similar to HEK293T — adherent format, low albumin, high confluence pre-transfection. The additional selection for fast growth means HEK293FT cultures can be denser at transfection than standard HEK293T, which requires the medium to support slightly higher metabolic demand during the productive phase.

HEK293-EBNA

Contains a stable integration of EBNA-1, enabling episomal replication of plasmids with the EBV origin of replication. Used primarily for transient expression of secreted proteins.

Medium requirements: EBNA-1 expression adds metabolic load. Medium formulations for HEK293-EBNA should support both adherent and early suspension adaptation, as many EBNA protocols involve scale-up in suspension formats.

Summary

→ SeamlessBio supplies serum-free media for HEK293 cells across adherent and suspension formats, with options for AAV production, lentiviral vector manufacturing and recombinant protein expression: Serum-Free Media for HEK293 Cells

Der Beitrag HEK293T vs. HEK293F vs. HEK293FT: Which Serum-Free Medium Does Each Need? erschien zuerst auf SeamlessBio.

The terms are often used interchangeably. They should not be. For manufacturers of therapeutic proteins in CHO cells, confusing chemically defined with protein-free can create serious problems at process validation — and occasionally in regulatory submissions.

Here is a clear breakdown of what each term means and why it matters.

Chemically Defined: Every Component Is Known

A chemically defined (CD) medium contains only components whose chemical identity and concentration are fully specified. No undefined biological extracts, no animal-derived hydrolysates, no serum fractions.

This does not mean the medium is simple. Modern chemically defined CHO media contain 50–80 individual components: amino acids, vitamins, trace elements, lipids, insulin or insulin-like growth factor alternatives, transferrin or recombinant transferrin substitutes, and buffering systems.

The key regulatory benefit: because every component is defined, the medium can be fully documented in a Drug Master File or process description without reference to variable biological sources.

Protein-Free: A Subset of Chemically Defined

A protein-free medium goes further. It eliminates all proteins from the formulation — including recombinant versions of insulin, transferrin and albumin that appear in many chemically defined media.

Why does this matter? Proteins in the medium complicate downstream purification. Any residual protein from the medium becomes a potential impurity in the product stream. For mAb manufacturing where protein A affinity purification is standard, medium-derived proteins that bind to the column or co-purify with the product create additional validation burden.

Protein-free formulations avoid this entirely. They substitute recombinant proteins with small-molecule alternatives: insulin mimetics, iron chelators in place of transferrin, no albumin.

Animal-Origin-Free: The Third Term

A third designation — animal-origin-free (AOF) — is increasingly required in regulatory submissions. An AOF medium contains no components derived from animal sources at any point in the manufacturing chain, including excipients, processing aids and raw material sourcing.

A medium can be chemically defined but not AOF if, for example, it contains recombinant insulin produced in a CHO cell line using animal-derived media components during manufacturing of the insulin itself. Full AOF status requires supplier-level documentation.

The GMP Implications

For Phase I/II clinical manufacturing, a chemically defined medium is typically sufficient. For pivotal trials and commercial manufacturing, protein-free and AOF status become increasingly expected by EMA and FDA reviewers.

What to Ask Your Supplier

Before committing to a CHO medium for GMP manufacturing, request:

1. Full component list with CAS numbers
2. Certificate of compliance for animal-origin-free status
3. Statement on recombinant protein sourcing (how was the rInsulin or rTransferrin manufactured?)
4. GMP-grade batch documentation: CoA, CoO, full traceability
5. ISO 13485 certification for the manufacturing site

→ SeamlessBio supplies chemically defined, protein-free and animal-origin-free CHO media under ISO 13485 with GMP-grade batch documentation: Serum-Free Media for CHO Cells

Der Beitrag Chemically Defined vs. Protein-Free CHO Medium: Why the Difference Matters for GMP erschien zuerst auf SeamlessBio.