Making Monoclonal Antibodies
Step 1: Immunization: A host animal (typically a mouse) is injected with a specific antigen. This triggers the animal's immune system to produce B-lymphocytes that recognize various epitopes on that antigen.
Step 2: Cell Harvest: After a few days, the animal's spleen is removed. The spleen is a rich source of activated B-lymphocytes (plasma cells) that are currently producing the desired antibodies.
Step 3: Fusion: The harvested B-cells are mixed with myeloma cells in the presence of a fusogen, such as polyethylene glycol (PEG) or an electric pulse. This breaks down cell membranes temporarily, allowing the cells to merge into hybridomas.
Step 4: Selection and Screening: The mixture contains fused and unfused cells. They are placed in a selective growth medium where only hybridomas survive. Surviving cells are then screened to identify which ones are producing the specific antibody of interest.
Step 5: Expansion: The chosen hybridoma is cloned (grown from a single cell) and cultured in large fermenters to mass-produce the monoclonal antibodies.
Specificity: Monoclonal antibodies recognize only one specific epitope, whereas polyclonal antibodies are a mixture that recognizes multiple epitopes on the same antigen.
Consistency: Monoclonal production is highly reproducible because it comes from a single immortal cell line. Polyclonal batches vary significantly between different animals and different bleeds.
| Feature | Monoclonal Antibodies | Polyclonal Antibodies |
|---|---|---|
| Source | Single B-cell clone (Hybridoma) | Multiple B-cell lineages |
| Specificity | Single epitope | Multiple epitopes |
| Production Cost | High (complex process) | Lower (simpler process) |
| Supply | Unlimited (immortal line) | Limited by animal lifespan |
Diagnostic Tools: mAbs are used in pregnancy tests to detect hCG, in ELISA tests to detect pathogens like HIV, and in medical imaging to locate blood clots or tumors by attaching radioactive tracers to the antibodies.
Therapeutic Treatments: They are used to treat cancers (e.g., Herceptin for breast cancer) by flagging cancer cells for destruction by the immune system. They can also neutralize toxins (e.g., rabies) or prevent organ rejection by blocking T-cell activity.
Targeted Delivery: mAbs can be conjugated with drugs or toxins to deliver 'magic bullets' directly to diseased cells, minimizing side effects on healthy tissues.
Identify the 'Why': When asked about the fusion step, always emphasize that B-cells provide the antibody blueprint while myeloma cells provide longevity/mitosis. Mentioning only one is a common way to lose marks.
The Spleen Connection: Remember that B-cells are extracted from the spleen, not the blood or bone marrow, in the standard hybridoma protocol.
Selection Logic: Be prepared to explain why a selective medium is used. It is to eliminate unfused myeloma cells (which would otherwise outgrow everything) and unfused B-cells (which naturally die off).
Terminology Precision: Use the term 'clone' when describing the origin of mAbs. This emphasizes that they are genetically identical and produce identical proteins.
Misconception: mAbs are made by the mouse: The mouse only provides the initial B-cells. The actual 'making' of the large-scale antibodies happens in a lab culture of hybridoma cells, not inside the animal.
Confusing B-cells and T-cells: Monoclonal antibodies are strictly a product of B-lymphocytes (plasma cells). T-cells do not produce antibodies and are not used in the hybridoma process.
Forgetting the Screening Step: Fusion is random. Not every hybridoma will produce the right antibody. Screening is the critical step that filters the 'useful' hybrids from the 'useless' ones.