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Frequently Asked Questions

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How can you harvest living cells from someone who is dead? Doesn't the fact that they are dead mean that their cells are dead?

It is quite clear that clinically defined death, which in most states is simply the cessation of cardiac and respiratory activity, does not mean that all of the cells of the body have died. It simply means that the cells required to maintain/sustain life, namely, cardiac muscle cells and diaphragmatic muscle cells no longer function adequately. Those cells may still be alive, just not functioning.

In addition, the point you raised about brain death illustrates the dichotomy from yet another angle. Brain death, cessation of brain function as defined by flat-line EEG and lack of cerebral blood flow, is a legal definition (which varies slightly state to state), not a clinical one.

In brain death cases, there may be adequate cardiorespiratory activity but a complete lack of cerebral activity. Under these circumstances, removal of organs for transplant is legally allowed, including heart and lungs. Clearly in this case the organs responsible for maintaining life (as clinically defined) are adequately functioning, otherwise they would be of no use to a transplant recipient. In addition, clearly, once the heart and lungs have been removed the patient would be considered clinically, as well as legally, dead.

Even after the criteria for legal and clinical definitions of death have been satisfied, many, if not most, cells of the body remain viable (alive) for quite some time. For example, it is well known that skin fibroblasts may be harvested and grown from a cadaver as long as three days after death.

However, other cells do not last nearly as long. The capacity of cells to remain viable after death of an organism is relatively linearly related to their lack of functional and/or respiratory complexity as a cell. That is, cells that have elaborated, through expression of specific genes, a biochemical repertoire that relies heavily on energy production tend to be the cells that lose viability the earliest.

For example, in the brain neurons, with their much higher metabolic rates, die sooner than glia. From a whole body point-of-view, organs with a higher metabolic rate are much more susceptible to a loss of energetic potential -- brain and muscle "die" sooner that skin or bone.

To extend this whole scenario to stem cells, therefore, is quite simple. Stem cells, by definition, have not elaborated complex biochemical machinery; they are awaiting instructions to do so. These cells should logically be more resistant to a cessation of nutrient input. They should remain viable much longer than highly metabolic cells after the delivery of glucose and oxygen has ceased. And this is, in fact, what we have shown in our Nature paper.

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