Why the clone matters
A production cell line is the factory behind a biologic. If it makes too little, drifts over time or produces a slightly different molecule from one batch to the next, every downstream step pays for it. Clone development is the work of choosing, from thousands of possible cells, the one that is productive, stable and makes the right product.
1. Design the construct
The process starts on paper. The gene is optimised for the chosen host, paired with a promoter and regulatory elements that drive strong, steady expression, and given a signal sequence if the product is to be secreted. A selection marker is built in so that only cells carrying the construct survive later steps.
2. Choose the host and introduce the gene
Chinese hamster ovary (CHO) cells are the workhorse for monoclonal antibodies and many other proteins because they grow well in suspension culture, fold and modify human-type proteins, and have a long regulatory track record. Other hosts, including microbial systems, suit different molecules. The construct is then delivered into the cells, either transiently for quick test material or stably for a lasting line.
3. Select and build pools
Selective pressure kills cells that did not take up the gene, leaving a mixed pool of survivors that differ widely in how much product they make and where the gene landed in the genome. Pools are evaluated early to check that the construct works and to rank options.
4. Isolate single cells
To make a clonal line, individual cells are separated and allowed to grow into colonies, using limiting dilution, cell sorting or imaging-assisted methods. Regulators expect evidence that the final line came from a single cell, so the process is documented, often with images from the day the cell was seeded.
5. Screen for the clone you actually want
- Titre: how much product the clone makes in a small-scale fed culture.
- Growth and viability under conditions that mimic the planned process.
- Product quality: aggregation, charge and size variants, and for glycoproteins the sugar profile.
- Stability: whether productivity and quality hold over dozens of generations of growth.
The highest-titre clone is not always the best one. A clone with slightly lower titre but better quality attributes and stable growth is usually the safer choice.
6. Bank the cells
The chosen clone is expanded and frozen as a master cell bank, from which working banks are made for production. Banks are tested for identity, sterility, mycoplasma and adventitious agents, and stored under monitored conditions with documented chain of custody.
What to ask a development partner
- Which host and expression system, and why that one for your molecule?
- How is clonality demonstrated and documented?
- What product-quality attributes are used to rank clones, not just titre?
- What stability data will be generated before the bank is released?
- Who owns the cell line and the associated licences?
Theertha Biopharma offers clone development as the first step of an integrated route through process development, analytical development, formulation and technology transfer. See our services or talk to our team.
Frequently asked questions
How long does clone development take?
It varies with the molecule and the host, and usually takes a number of months from gene design to a banked, characterised clone. Difficult-to-express proteins take longer.
Why are CHO cells so widely used?
They grow well in suspension, produce human-compatible protein folding and modifications, and have a long regulatory history for biologics.
What is a master cell bank?
A large set of identical vials made from the chosen clone and stored as the reference stock. Working banks are made from it for day-to-day production.
General information for readers in biopharmaceutical development; not regulatory or medical advice.