Tried to get an answer over in the Pit, figured this would be a better place.
Of the “Existing lines” of embryonic stem cells that your organization can perform research on without risking your organization’s federal funding, how many are actually available?
Of those that are available, what’s the scope on the number and amount of experiments that they can support before they “run out”? Who decides which experiments get the limited amount of cells?
What is a “line” anyway? The cells from a single embryo? Are they kept alive and multiplying some way?
A ‘cell line’ is a collection of cells that all come from the same source. Someone isolates cells from tissue and lets them grow and reproduce. They can then take cells from the initial culture and use them to make additional cultures. These first-generation cultures can, of course, be used to make yet more cultures. Eventually, there may be thousands of flasks containing cultures of the same cells used to make the original culture. This is useful scientifically because it allows a certain amount of control over the genetic content of the cells, and allows scientists to reproduce an experiment using the same cells that were used in another’s research.
There may be limitations to what can be learned from a small set of cell lines, though, since each cell line represents only one individual’s genetic makeup. In a way, having only 12 stem cell lines would be like testing a new drug on only 12 patients. It might be possible, for example, that stem cells from certain individuals are more suitable for use in therapy than any of the existing lines.
Over time, some cultures in a cell line might diverge from the original culture by contamination or (less likely) mutation. One research facility might have 100 flasks all grown from a single flask which was purchased from a supplier, and these may not resemble the other cultures in the cell line. The original culture may become extinct, meaning that later generations would have to be used.
In theory, though, stem cell cultures are immortal and do not die with the passage of time. In practice, cell cultures are very fragile and very susceptible to contamination. Simply inserting a glass pipette into a culture flask without carefully sterilizing it first might contaminate a flask. A minor fluctuation in temperature might kill a whole sample. Since cell cultures are living organisms being kept alive artificially, they do change over time, and they show a high degree of variation.
Twelve stem cell lines is not a very large number compared to the lines available from other cell types. A search of one repository (the Coriell Institute for Medical Research) indicates that 11 cell lines are available from individuals with a single form of a single disease, osteogenesis imperfecta. Dozens of samples of healthy fibroblasts are in the same repository.