Recombinant antibodies are the essential tools used in both advanced therapeutics and high-quality research. The consistency and high specificity of these antibodies are essential for accurate data interpretation and robust scientific conclusions.
Antibody gene acquisition is the very first step in recombinant antibody production. In this step, the exact DNA sequences that code for the genetic blueprint (heavy (VH) and light (VL) binding chains) of the antibody are identified.
The success of the final product depends on accurately securing this code. This article covers the two main approaches to acquiring this blueprint:
- Cloning from existing immune cells
- In vitro library screening
Cloning from Existing Immune Cells
This gene acquisition method uses a proven immune response to isolate the required antibody sequences. The goal is to acquire the genetic code from cells that already produce that specific antibody.
Hybridoma cDNA Cloning
In this classic approach, an animal, typically a mouse, is immunized with the target antigen to create a hybridoma, an immortal cell line. The antibody-producing B cells of the animal are then fused with myeloma (tumor) cells. The hybridoma is a stable “factory” that indefinitely produces a specific monoclonal antibody. Researchers isolate the genetic message to acquire the gene.
mRNA Isolation
The messenger RNA extracted from the hybridoma cell is the temporary template for the antibody protein.
RT-PCR (Reverse Transcriptase-Polymerase Chain Reaction)
RT-PCR converts the mRNA into a stable cDNA copy. Specific primers are essential as they target the conserved regions flanking the variable domain. RT-PCR then exponentially amplifies the heavy (VH) and light (VL) chain variable region genes.
The amplified DNA pieces of the antibody genes are then cloned into a basic expression vector.
As sequences originate from an already validated producer cell line, this method yields sequences with confirmed specificity and affinity.
Single B-Cell Isolation and Sequencing
It is a modern, high-throughput method that bypasses the slow hybridoma process.
Isolation
This method uses Fluorescence-Activated Cell Sorting (FACS) or microfluidics to physically identify and isolate individual B cells from an immunized animal. Single B-cell isolation and sequencing ensure that the correct heavy and light chains are paired within the same cell.
Sequencing
RT-PCR and subsequent sequencing are performed directly on the mRNA and subsequently the cDNA of the single isolated cell.
In Vitro Library Screening
This approach uses massive, pre-made collections (libraries) of antibody gene sequences, bypassing animal immunization. The sequences can be either synthetic or semi-synthetic. However, linking the expressed antibody protein to its underlying DNA code can be technically challenging.
Phage Display
In vitro selection technology uses phage display, a genetic technique that uses bacteriophages to display foreign proteins on bacteriophages’ surfaces.
The antibody binding fragments (single-chain variable fragments (scFv) or Fab fragments) are genetically fused to a surface coat protein of a bacteriophage. The genetic fusion causes the phage to display the antibody fragment on its exterior. DNA that codes for that fragment remains safely encased inside the phage head.
Panning and Selection
Panning is the process in which the entire library of billions of unique phages is exposed to the target antigen. Panning acts as a high-stringency selection.
- Phages that display an antibody that binds to the target antigen will “stick.”
- Non-binders are washed away.
- The remaining binders are chemically eluted and amplified by infecting E. coli bacteria.
Gene Acquisition and Benefit
After several rounds of enrichment, the remaining phages are predominantly strong binders. The DNA inside the selected phages is sequenced to acquire the genetic blueprint of the antibody.
This approach generates fully human antibodies from the very first step of recombinant antibody production. This minimizes immunogenicity issues and provides precise control of the selection conditions, allowing researchers to tailor the properties of the antibody.
Gene Engineering and Verification
The heavy (VH) and light (VL) gene sequences go through an engineering phase to transition the raw sequences into a stable, robust tool.
Reformatting the Gene
The VH and VL sequences must be combined with the constant regions of a therapeutic antibody. The complete VH-Constant and VL-Constant gene sequences are then cloned into a specialized, high-yield mammalian expression vector, which contains promoters and necessary regulatory elements to drive high expression in host cells.
Optimization and Verification
The DNA sequence is modified so that the host cell can read the code more efficiently, improving production and reducing costs. The cloned vector is used for small-scale, transient expression to confirm that the final, full-length antibody protein is produced correctly.
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