B16: Monoclonal Antibodies
Hybridoma production, pregnancy testing, cancer treatment, and locating blood clots
Key Definitions
Monoclonal antibody — An antibody produced from a single clone of identical B-lymphocytes (hybridoma cells); all antibodies are identical and specific to one antigen.
Hybridoma — A cell formed by fusing a B-lymphocyte with a tumour cell; it can divide endlessly (from the tumour cell) and produce one specific antibody (from the B-lymphocyte).
Antigen — A protein on the surface of a cell or pathogen that can trigger an immune response; each type of cell has unique antigens.
Hybridoma — A cell formed by fusing a B-lymphocyte with a tumour cell; it can divide endlessly (from the tumour cell) and produce one specific antibody (from the B-lymphocyte).
Antigen — A protein on the surface of a cell or pathogen that can trigger an immune response; each type of cell has unique antigens.
How Monoclonal Antibodies Are Produced
Step-by-step process:
1. Inject a mouse with the target antigen to stimulate an immune response.
2. The mouse's B-lymphocytes produce specific antibodies against the injected antigen.
3. Extract B-lymphocytes from the mouse's spleen.
4. Fuse the B-lymphocytes with tumour cells (myeloma cells). Tumour cells can divide endlessly but do not produce antibodies; B-lymphocytes produce specific antibodies but cannot divide in culture.
5. The fused cells are called hybridoma cells — they combine the ability to divide endlessly (from the tumour cell) with the ability to produce a specific antibody (from the B-lymphocyte).
6. Clone the hybridoma cells — each clone produces the same (monoclonal) antibody.
7. Screen and select the hybridoma cells producing the desired antibody.
8. Culture the selected hybridoma cells in large quantities to harvest large amounts of the monoclonal antibody.
1. Inject a mouse with the target antigen to stimulate an immune response.
2. The mouse's B-lymphocytes produce specific antibodies against the injected antigen.
3. Extract B-lymphocytes from the mouse's spleen.
4. Fuse the B-lymphocytes with tumour cells (myeloma cells). Tumour cells can divide endlessly but do not produce antibodies; B-lymphocytes produce specific antibodies but cannot divide in culture.
5. The fused cells are called hybridoma cells — they combine the ability to divide endlessly (from the tumour cell) with the ability to produce a specific antibody (from the B-lymphocyte).
6. Clone the hybridoma cells — each clone produces the same (monoclonal) antibody.
7. Screen and select the hybridoma cells producing the desired antibody.
8. Culture the selected hybridoma cells in large quantities to harvest large amounts of the monoclonal antibody.
Example 1: Why Hybridoma Cells Are Needed
B-lymphocytes produce specific antibodies but cannot be cultured in the lab because they do not divide indefinitely outside the body. Tumour cells divide endlessly in culture but do not produce antibodies. By fusing them, hybridoma cells gain both properties: they produce the desired specific antibody AND they can divide endlessly in culture, providing an unlimited supply of identical monoclonal antibodies.
Example 2: The Problem with Mouse Antibodies
Because the original B-lymphocytes come from a mouse, the monoclonal antibodies produced are mouse antibodies. When injected into humans, the immune system may recognise them as foreign and mount an immune response against them, reducing their effectiveness and potentially causing side effects. Modern techniques modify the antibodies to make them more "human" (humanised monoclonal antibodies) to reduce this problem.
Uses of Monoclonal Antibodies
1. Pregnancy Testing
How a pregnancy test works:
— Pregnancy tests detect the hormone hCG (human chorionic gonadotropin), which is present in the urine of pregnant women.
— The test strip contains monoclonal antibodies specific to hCG, attached to coloured dye beads.
— When urine is applied, hCG (if present) binds to the mobile antibodies, forming a complex.
— This complex moves along the strip by capillary action.
— At the test window, immobilised antibodies specific to hCG capture the complex, trapping the coloured beads and producing a visible coloured line = positive result.
— At the control window, immobilised antibodies always capture any antibody complex, producing a second coloured line to confirm the test is working.
— Pregnancy tests detect the hormone hCG (human chorionic gonadotropin), which is present in the urine of pregnant women.
— The test strip contains monoclonal antibodies specific to hCG, attached to coloured dye beads.
— When urine is applied, hCG (if present) binds to the mobile antibodies, forming a complex.
— This complex moves along the strip by capillary action.
— At the test window, immobilised antibodies specific to hCG capture the complex, trapping the coloured beads and producing a visible coloured line = positive result.
— At the control window, immobilised antibodies always capture any antibody complex, producing a second coloured line to confirm the test is working.
Example 3: Why Monoclonal Antibodies Are Ideal for Pregnancy Tests
Monoclonal antibodies are identical and specific to hCG, so they will only bind to hCG and not to other hormones in the urine. This makes the test highly accurate. The antibodies are attached to coloured dye beads, so when they bind to hCG and are captured at the test line, the visible colour change provides an easy-to-read result. The specificity of monoclonal antibodies prevents false positives.
2. Cancer Treatment and Diagnosis
Targeting cancer cells:
— Cancer cells have unique tumour-specific antigens on their surface that normal cells do not have.
— Monoclonal antibodies can be produced that bind specifically to these tumour antigens.
Treatment approaches:
— Direct action — Monoclonal antibodies bind to cancer cell antigens and block the chemical signals that stimulate uncontrolled cell division.
— Drug delivery — A toxic drug (e.g. a chemotherapy drug) or radioactive substance is attached to the monoclonal antibody. The antibody carries the drug specifically to the cancer cells, minimising damage to healthy cells and reducing side effects compared to conventional chemotherapy.
— Immune activation — Antibodies bound to cancer cells flag them for destruction by phagocytes and other immune cells.
Diagnosis: Monoclonal antibodies labelled with a radioactive or fluorescent marker can be injected and will bind to cancer cells, allowing tumours to be located using imaging techniques.
— Cancer cells have unique tumour-specific antigens on their surface that normal cells do not have.
— Monoclonal antibodies can be produced that bind specifically to these tumour antigens.
Treatment approaches:
— Direct action — Monoclonal antibodies bind to cancer cell antigens and block the chemical signals that stimulate uncontrolled cell division.
— Drug delivery — A toxic drug (e.g. a chemotherapy drug) or radioactive substance is attached to the monoclonal antibody. The antibody carries the drug specifically to the cancer cells, minimising damage to healthy cells and reducing side effects compared to conventional chemotherapy.
— Immune activation — Antibodies bound to cancer cells flag them for destruction by phagocytes and other immune cells.
Diagnosis: Monoclonal antibodies labelled with a radioactive or fluorescent marker can be injected and will bind to cancer cells, allowing tumours to be located using imaging techniques.
3. Locating Blood Clots
How monoclonal antibodies detect blood clots:
— When a blood clot forms, proteins in the clot (e.g. fibrin) are exposed.
— Monoclonal antibodies specific to fibrin are labelled with a small amount of radioactive isotope and injected into the blood.
— The antibodies bind to the fibrin in the clot but not to normal blood vessels.
— A radiation detector (gamma camera) is used to locate where the radioactive antibodies have accumulated, pinpointing the blood clot's position.
— When a blood clot forms, proteins in the clot (e.g. fibrin) are exposed.
— Monoclonal antibodies specific to fibrin are labelled with a small amount of radioactive isotope and injected into the blood.
— The antibodies bind to the fibrin in the clot but not to normal blood vessels.
— A radiation detector (gamma camera) is used to locate where the radioactive antibodies have accumulated, pinpointing the blood clot's position.
Example 4: Advantages of Using Monoclonal Antibodies for Cancer Treatment
Conventional chemotherapy drugs circulate throughout the body and kill any rapidly dividing cells, including healthy ones (causing side effects like hair loss, nausea, and immune suppression). Monoclonal antibodies can deliver chemotherapy drugs specifically to cancer cells because they bind only to tumour-specific antigens. This means the drug is concentrated at the tumour site, reducing damage to healthy cells and minimising side effects. The treatment is more targeted and potentially more effective.
Advantages and Disadvantages of Monoclonal Antibodies
| Advantages | Disadvantages |
|---|---|
| Highly specific — bind only to target antigen | Expensive to produce (complex hybridoma technology) |
| Can be used for diagnosis and treatment | Mouse antibodies may trigger immune response in humans |
| Targeted cancer treatment with fewer side effects | Some patients have experienced severe side effects in clinical trials |
| Rapid and accurate pregnancy testing | Not always as effective as hoped — some cancer treatments have shown limited success |
| Can locate blood clots and tumours | Ethical concerns about using mice to produce antibodies |
| Can carry drugs or radioactive markers to specific cells | Production is time-consuming |
Ethical issues:
— Mice are injected with antigens to produce the B-lymphocytes — some people consider this unnecessary animal use and causing suffering to the mice.
— Some monoclonal antibody treatments have caused unexpected serious side effects in clinical trials, raising questions about safety testing.
— The high cost of monoclonal antibody treatments may make them unavailable to patients in poorer countries, raising issues of equality in healthcare access.
— Mice are injected with antigens to produce the B-lymphocytes — some people consider this unnecessary animal use and causing suffering to the mice.
— Some monoclonal antibody treatments have caused unexpected serious side effects in clinical trials, raising questions about safety testing.
— The high cost of monoclonal antibody treatments may make them unavailable to patients in poorer countries, raising issues of equality in healthcare access.
Exam tip: When describing how monoclonal antibodies are produced, use the correct sequence: inject mouse → extract B-lymphocytes → fuse with tumour cells → form hybridoma → clone → harvest antibodies. When discussing uses, explain HOW the antibodies' specificity makes them useful (e.g. they only bind to the target antigen, so they can deliver drugs specifically to cancer cells).
Practice Questions
1. Higher Describe how monoclonal antibodies are produced.
A mouse is injected with the target antigen to stimulate an immune response. B-lymphocytes that produce the specific antibody are extracted from the mouse's spleen. These are fused with tumour cells (myeloma cells) to form hybridoma cells, which can divide endlessly AND produce the specific antibody. The hybridoma cells are cloned and cultured, and the monoclonal antibodies are harvested from the culture medium.
2. Higher Explain how monoclonal antibodies are used in pregnancy testing.
Pregnancy tests detect hCG hormone in urine. The test strip contains monoclonal antibodies specific to hCG, attached to coloured dye beads. When urine containing hCG is applied, the hCG binds to the mobile antibodies. The complex moves along the strip and is captured by immobilised antibodies at the test window, producing a visible coloured line. A second line at the control window confirms the test is working.
3. Higher Explain how monoclonal antibodies can be used to treat cancer and why this is better than conventional chemotherapy.
Monoclonal antibodies are produced that bind specifically to tumour-specific antigens on cancer cells. A chemotherapy drug or radioactive substance is attached to the antibody. When injected, the antibodies carry the drug directly to the cancer cells, concentrating it at the tumour. This is better than conventional chemotherapy because the drug targets cancer cells specifically, minimising damage to healthy cells and reducing side effects (e.g. hair loss, nausea, immune suppression).
4. Higher Discuss the ethical issues associated with the production and use of monoclonal antibodies.
Mice are injected with antigens and their spleen cells harvested, which some consider to be animal exploitation and suffering. Some monoclonal antibody treatments have caused serious side effects in clinical trials, raising safety concerns. The high cost limits access for patients in poorer countries, creating inequality in healthcare. Others argue the medical benefits (cancer treatment, diagnosis, pregnancy testing) justify the use of mice, and that regulations minimise animal suffering.
🔢 Maths Skills
Mathematical Skills
Dilution calculations: calculating concentrations when producing monoclonal antibodies. For example, if a 1 mg/cm³ stock solution is diluted 1:10, the new concentration is 0.1 mg/cm³. Serial dilutions may be used to find the minimum effective concentration in diagnostic tests.
⚠️ Common Misconceptions
Watch Out!
1. Wrong: Monoclonal antibodies are the same as antibiotics Correct: Monoclonal antibodies are identical antibodies produced from a single clone of hybridoma cells that target specific antigens; antibiotics are drugs that kill bacteria
✍️ 6-Mark Question
Extended Answer
6 marks: Describe how monoclonal antibodies are produced and evaluate their uses.
Monoclonal antibodies are produced by injecting a mouse with the target antigen. B-lymphocytes from the mouse's spleen are extracted and fused with tumour cells (myeloma cells) to form hybridoma cells. Hybridoma cells can divide endlessly and produce the specific antibody. The cells are cloned and cultured, and antibodies are harvested. Uses include pregnancy testing (detecting hCG), cancer treatment (delivering drugs specifically to tumour cells), and locating blood clots (using radioactive labels). However, they are expensive to produce, may trigger immune responses in humans, and have had limited success in some clinical trials.
Mark scheme: 1 mark for inject mouse with antigen; 1 mark for fuse B-lymphocytes with tumour cells to form hybridoma; 1 mark for clone and harvest antibodies; 1 mark for two named uses with explanation; 1 mark for evaluation (advantages or disadvantages); 1 mark for QWC
📊 AO3: Analyse & Evaluate
Analysis and Evaluation
Clinical trial data for a monoclonal antibody cancer treatment: 200 patients received the treatment, 200 received conventional chemotherapy. Tumour reduction: monoclonal antibody group 65%, chemotherapy group 52%. Side effects (severe): monoclonal antibody group 8%, chemotherapy group 34%. Cost per patient: monoclonal antibody group £15,000, chemotherapy group £3,000.
1. Calculate the percentage difference in tumour reduction between the two groups. 2. Evaluate whether the monoclonal antibody treatment is better than chemotherapy, considering both effectiveness and cost. 3. Explain why fewer side effects occurred with the monoclonal antibody treatment.
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