Vaccine production and stem cell technology
Recombinant vaccines carry only a pathogen's antigen, made in yeast or bacteria, like the hepatitis B vaccine. Stem cells are unspecialised cells that can divide and become many cell types.
How a vaccine works
A vaccine contains an inactivated or weakened pathogen, or just its antigens (proteins that the immune system recognises). It makes the body produce antibodies and memory B and T cells. When the real pathogen attacks later, the body responds fast and strongly.
Making a recombinant vaccine (hepatitis B example)
Your textbook gives the idea in one line: antigenic polypeptides of a pathogen are made in bacteria or yeast. These steps apply the recombinant DNA process of the last chapter to it.
- 1Find the gene for an antigen of the pathogen, for example a surface protein of the hepatitis B virus.
- 2Join the gene to a suitable vector using restriction enzymes and DNA ligase.
- 3Put the recombinant DNA into a host such as yeast.
- 4Grow the host in bioreactors; it makes large amounts of the antigen.
- 5★Purify the antigen by downstream processing and formulate the vaccine.
- 6Test its safety before use. Your textbook notes that transgenic mice are being used to test the safety of the polio vaccine.
★ key step
Traditional vaccine vs recombinant vaccine
What stem cells are
Most body cells are specialised for one job. Stem cells are unspecialised. Your textbook meets them in the inner cell mass of the blastocyst, where they can give rise to all the tissues and organs. Stem cells can divide to make more stem cells (self-renewal) and can differentiate into specialised cells such as blood, muscle or nerve cells. Stem cell technology means growing and guiding these cells in the lab and using them to repair or replace damaged tissue.
Types and sources of stem cells (extra reading, beyond your textbook)
| Type | Source | Can become |
|---|---|---|
| Embryonic stem cells | Inner cell mass of the blastocyst (early embryo) | Almost any tissue or organ of the body (pluripotent) |
| Adult stem cells | Bone marrow and some other tissues | A limited set of related cells (multipotent); bone marrow stem cells form all blood cells |
| Umbilical cord blood stem cells | Blood in the umbilical cord, collected at birth | Blood and immune cells |
Uses and concerns of stem cell technology (extra reading)
- Bone marrow transplants treat blood cancers such as leukaemia and inherited blood disorders such as thalassaemia.
- Research aims to repair damaged heart muscle, nerves and skin.
- Lab-grown cells can be used to test new drugs.
- Concerns: ethical questions about using embryos, rejection of donor cells, and the risk of uncontrolled growth. Treatment must be given only in approved centres.
Indian babies get the hepatitis B vaccine soon after birth under the national immunisation schedule, and it is a recombinant vaccine made in yeast. Bone marrow transplants for children with thalassaemia are a stem cell therapy.
3 marks: “How is a recombinant vaccine, such as the hepatitis B vaccine, produced? Give two advantages over traditional vaccines.” Gene for the viral surface antigen joined to a vector; put into yeast; yeast grown in bioreactors makes the antigen; antigen purified and formulated. Advantages: cannot cause the disease; large-scale production makes it widely available.
2 marks: “What are stem cells? Where are they found in the early human embryo, and what can they form?” Unspecialised cells that can divide and give rise to specialised cells. The inner cell mass of the blastocyst contains stem cells that can give rise to all the tissues and organs.
2 marks: “How does a vaccine protect the body? How has recombinant DNA technology helped vaccine supply?” Its antigens make the body form antibodies and memory B and T cells, which act fast on later infection. rDNA technology makes antigenic polypeptides in bacteria or yeast on a large scale (hepatitis B vaccine from yeast), so vaccines are more widely available.
Vaccine: gene in, antigen out (from yeast). Stem cell: renew and become.