Viability, advantages and uses

Viability tests show whether cells are alive. They are used, for example, to see how a drug, toxin or pesticide affects cells.

• Dye exclusion: a healthy cell membrane keeps dyes out. Add a dye such as trypan blue, propidium iodide, 7-AAD or acridine orange: dead cells take it in and stain, while live cells stay clear.
• Metabolic assays measure a reaction that only live cells carry out. In the MTT assay, enzymes in the mitochondria of living cells turn yellow MTT into purple formazan, which is dissolved in DMSO. The depth of colour is proportional to the number of living cells.

Advantages of cell culture: conditions can be controlled; the cell populations are uniform; there are enough cells to study; and medicines (biopharmaceuticals) can be made easily. Limits: cultured cells are very sensitive to small changes, and may not fully behave like cells in the body.

Uses: as models of disease and of how drugs act; for virus research; to make vaccines; and to make medicinal proteins, many of them in CHO (Chinese hamster ovary) cells:

• Erythropoietin (EPO), which boosts red blood cell production, for anaemia, without needing blood donors.
• Clotting factors VIII and IX, for haemophilia A and B.
• tPA (tissue plasminogen activator), which dissolves clots after a heart attack or stroke: the first medicine made in mammalian cell culture.
• FSH (a fertility hormone) and human growth hormone.

Monoclonal antibodies are made in culture too:

• OKT3 (muromonab-CD3) blocks T cells, reversing the sudden rejection of a transplanted organ. It was the first approved monoclonal antibody medicine.
• Trastuzumab binds the HER2 protein, slowing HER2-positive breast cancer.