Understanding recombinant protein production: from discovery to developability

Recombinant protein production has become a cornerstone of biotechnology and will stay a major growth driver for the biotech market in the present decade^​1​. One major reason is the growing demand for recombinant antibodies as innovative biopharmaceuticals, since they are expected to demonstrate higher therapeutic efficacies along with reduced side-effects compared to traditional therapeutics.

With this article, we want to take our readers on a tour through the basics of recombinant protein productions and highlight some noteworthy details of the involved processes.

Executive summary: key takeaways for recombinant protein production

• The Developability Standard: Recombinant protein production, specifically through transient CHO expression, is the critical path for transitioning biotherapeutics from discovery to clinical viability.
• Solving R&D Bottlenecks: Modern recombinant workflows must address “runway risk” for early-stage biotechs and capacity limitations for mid-sized pharma by utilizing High-Throughput (HTP) screening.
• Validating AI Designs: The rise of in silico AI-designed antibody libraries requires rapid, scalable recombinant expression to generate actionable, real-world developability data.

What are recombinant proteins?

Recombinant proteins are proteins that are made in the laboratory by living cells that follow the instructions encoded in recombinant DNA sequences. Recombinant proteins might be completely artificial by using DNAs that have no counterpart in natural sources, although they might be indistinguishable from natural proteins if the sequence is identical to a natural genetic blueprint and gene expression is done in a suitable host organism.^​2​

Protein production: Introduction

Protein production is the process of creating protein matter from simple substrates, usually by employing biotechnological means, i. e. suitable hosts. The host cells are mostly prokaryotic single cellular organisms such as bacteria (E. coli), yeasts or eukaryotic mammalian cell lines which are genetically engineered using expression vectors to produce the protein of interest in high yields. The target proteins are then removed from the culture medium and purified into biopharmaceuticals or reagents.^​3​

Why recombinant protein production is critical for modern biotherapeutics

The demand for high-quality recombinant protein production is accelerating, driven largely by the shift towards complex biologics, such as bispecific antibodies and customized fusion proteins. For mid-sized and large pharma, the primary challenge is translation risk—ensuring that a candidate behaves the same in early R&D as it will in clinical scale-up.

By prioritizing mammalian-derived recombinant proteins from the earliest screening phases, researchers mitigate the risk of late-stage failure due to incorrect folding or aberrant post-translational modifications. Today, rapid recombinant protein production is not just about yielding diagnostic reagents; it is the fundamental engine for validating in silico sequences, accelerating runway timelines for startups, and producing highly potent biopharmaceuticals.

Recombinant protein production: the process

Now we want to take a closer look into recombinant protein production and subsequent downstream processes that involve recombinant protein purification:

1. Construct generation and transfection

At the beginning of recombinant protein production stands the preparation of the gene of interest from the genome of the species that produces a related peptide or protein. Since the expression host would not naturally express these proteins, they’re called heterologous proteins.

Modern recombinant methods allow the joining of DNA molecules stemming from different species (resulting in fusion proteins), using RNA from in vivo samples by reverse transcription and PCR to generate cDNA.

The gene undergoes several rounds of optimization and is then equipped with the necessary regulatory elements (e.g. promoters that can be activated by the addition of IPTG in Escherichia Coli) or labeling with affinity tags to allow for efficient protein overexpression and purification. After embedding the sequence into plasmids and subsequent amplification, the constructs are inserted into bacterial cells or mammalian cells.

2. Cell culture

The host cells are then kept in flasks for small scales such as high-throughput experiments for screening for variants or mutations, or alternatively in bioreactors for large-scale manufacture. The cells are grown under tightly controlled culture conditions to facilitate optimal metabolic states for maximal cell growth and protein synthesis during the fermentation phase. When the cell culture reaches optimal cell densities, the proteins will be harvested.

3. Harvest

While some soluble proteins undergo secretion to the culture media, aggregation occurs at high protein yield and many proteins, especially membrane proteins, are concentrated in inclusion bodies. Therefore, cells are preferably lysed by chemical means (enzymes or detergents such as SDS) to gain access to the target proteins. Since biomacromolecules are susceptible to degradation by shear forces, physical lysis methods are to be used cautiously.

4. Purification

At this stage, the crude lysate contains all contents of the host cells along with the recombinant protein of interest. Problematic is the presence of proteases which begin to degrade the target protein immediately after lysis. Therefore, the crude solution is cooled and quickly subjected to a cascade of separation and purification steps to remove unwanted substances and enrich the target protein in high-quality. If affinity tags were used in the design of the recombinant protein, the target protein can be fished from the preprocessed solution by affinity chromatography.

However, for therapeutic candidates, purification must go beyond basic affinity capture. To combat the reproducibility crisis in preclinical research, rigorous polishing steps must be employed to guarantee exceptionally low endotoxin burdens. At evitria, our baseline for recombinant protein production demands >95% purity and endotoxin levels of <1 EU/mg, ensuring that downstream functional assays reflect the true biology of the molecule, unclouded by manufacturing artifacts.

Read more: Recombinant antibody purification

5. Storage and Analytics

Finally, the pure recombinant protein is put into storage in the frozen state.

A small sample of the product is then put through all the analytical tools of proteomics to obtain a complete characterization of its chemical identity, amino acid residue sequence, purity, impurity profiles, absence of microbial contaminants and for antibodies or receptors as well as perhaps their specificity towards antigens or ligands.

Common expression hosts for recombinant protein production

A successful recombinant protein production campaign depends on the correct choice of expression hosts. While the highest quality of compatibility to the human physiology is generally achieved by using mammalian cells, this is not always necessary.
Now, we want to highlight several popular expression hosts.

Further readings: Recombinant antibody expression

Recombinant protein production in bacterial hosts

The method of recombinant protein production was first developed using bacteria (E. coli strains) as host organisms. Due to their simple cell biology, scientists first understood connections between DNA and RNA as templates for polymerases. The ribosome reads the codons on mRNA strands and assembles amino acids to produce peptides and proteins.

While bacteria are very cost-efficient due to their ease in handling and high recombinant protein yields, for complex proteins stemming from eukaryotic sources, they are often non-functional due to incorrect folding or absent post-translational modifications. Such proteins should be expressed in eukaryotic host organisms.

Recombinant protein production in insect cells

The use of insect cells for recombinant protein production was a relatively early addition to the toolbox and offers advantageous post-translational modifications (similar to mammalian systems) at high expression levels.

Popular protocols employ recombinant viral particles that can be loaded with the genetic material coding for the protein of interest, which then infect the cultured insect cells and reprogram them to express the desired protein in very high yields.

Recombinant protein expression in mammalian cells

While recombinant protein expression in mammalian cells requires highly controlled environments, the biological advantages are categorical. The industry gold standard is the Chinese Hamster Ovary cell line. CHO cells provide evolutionary, highly advanced mammalian cell biology that yields proteins with intact, human-like post-translational modifications – facilitating correct 3D folding via chaperones, precise disulfide bond formation, and crucial glycosylation profiles.

Transient vs. Stable Expression

Historically, developers relied on stable cell lines, which are time-consuming and rigid. Today, transient CHO expression offers absolute scientific flexibility. It allows early-stage biotechs and researchers to produce milligram to gram quantities of complex recombinant proteins—including challenging bispecifics—in a matter of weeks rather than months. By keeping discovery and early developability testing within the CHO platform, sponsors eliminate the translational risk of switching hosts between R&D and clinical manufacturing.

Other expression systems for recombinant proteins

Alternatively, cell-free methods for recombinant protein production are available. In vitro translation (IVT) relies on translation-competent cell extracts that contain all cell constituents necessary for protein synthesis, thus avoiding the need for actual cell culture. This method is not suitable for scale up.

Choosing the right expression system

In this section, we want to give our readers a succinct overview over the pros and cons of different protein expression systems and how they compare to each other:

Recent achievements in recombinant protein expression

Recombinant protein expression has become a multi-billion dollar market and novel ways to improve the process key performance indicators are major achievements, economically speaking.

Synthetic biology approaches are applied on expression hosts to alleviate the metabolic impact of reprogramming them to express unnaturally large amounts of proteins^​5​. These advancements aim to make recombinant protein expression more efficient.

Another example targets inclusion bodies (IBs), where cells tend to deposit protein of low solubility. Significant amounts of protein are lost in IBs. Researchers developed methods employing freeze-thaw cycles to increase recovery rates from inclusion bodies.^​6​

Validating AI-Designed Libraries with HTP Expression

Recombinant protein expression has evolved beyond simple yield optimization. The most significant recent achievement is the integration of High-Throughput recombinant protein production to bridge the gap between computational biology and physical validation.

As early-stage biotechs increasingly rely on AI to design novel antibody sequences, they face a critical bottleneck: computationally derived constructs must be biologically validated. Advanced transient CHO platforms now allow for the simultaneous transfection, expression, and purification of thousands of unique variants. This rapid HTP execution turns in silico predictions into empirical developability data, drastically reducing “runway risk” and accelerating the path to lead candidate selection.

Recombinant antibody production service

Recombinant protein production serivice, particularly the engineering of complex, afucosylated, or bispecific antibodies, requires more than just a service provider; it requires a specialized extension of your lab.

Leveraging 15 years of singular expertise, >140,000 transfections, and our proprietary CHO-based transient expression platform, we help startups and large pharma alike clear internal bottlenecks. From validating AI-designed libraries at high throughput to fine-tuning the developability of novel bispecifics, we deliver the data, speed, and uncompromising quality required to move your pipeline forward.