A-Level Biology May/June 2025 Q6(a): Describe how monoclonal antibodies are produced using the hybridoma method.

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  The hybridoma method is used to produce large quantities of a single type of antibody.

  1. A specific, non-self antigen is injected into a small mammal, typically a mouse. (Mark 1)
  2. The mouse is left for a period of several weeks to allow time for an immune response to occur, leading to the production of plasma cells that secrete the desired antibody. (Mark 2)
  3. The mouse's spleen is removed, and B-lymphocytes (splenocytes) are isolated from it. (Mark 3)
  4. These B-lymphocytes are fused with myeloma (tumour) cells. A fusogen, such as polyethylene glycol (PEG), is used to facilitate this fusion. (Mark 4 & 7)
  5. The resulting cells are called hybridoma cells. These cells are cultured in a selective medium, such as HAT medium, which allows only the successfully fused hybridoma cells to survive. Unfused B-cells die naturally after a short time, and unfused myeloma cells cannot survive in the HAT medium.
  6. The surviving hybridoma cells are then screened to identify the specific clone that is producing the desired antibody. (Mark 5)
  7. Once identified, the selected hybridoma cell is cloned to produce a large population of identical cells. (Mark 6)
  8. These cloned cells are cultured on a large scale, where they divide rapidly and secrete large quantities of the specific monoclonal antibody, which can then be harvested and purified.

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  How the marks are awarded

  • B1 — Stating that a specific antigen is injected into a mammal, such as a mouse. This is the first step to trigger the specific immune response.
  • B1 — Mentioning the isolation of B-lymphocytes (or splenocytes) from the spleen of the immunised animal.
  • B1 — Describing the fusion of the B-lymphocytes with myeloma (tumour) cells to create hybridoma cells.
  • B1 — Explaining that the hybridoma cells must be screened and selected to find the one producing the correct antibody.
  • B1 — Stating that the selected hybridoma cell is then cloned to produce a large population of identical cells.

  Common mistakes

  • Failing to use specific terminology, for example writing 'immune cells' and 'cancer cells' instead of the required 'B-lymphocytes/splenocytes' and 'myeloma cells'.
  • Omitting the crucial final steps of screening for the correct antibody and then cloning the selected hybridoma cell.
  • Confusing the order of the process, for instance, suggesting that cloning occurs before the cells are screened and selected.
  • Forgetting to mention the initial step of injecting a specific antigen, which is fundamental to producing a specific monoclonal antibody.

  Examiner tip: For questions describing a process, memorise the key steps in a logical sequence, focusing on the specific biological names for cells and molecules involved at each stage.

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