The rejuvenation toolkit of the near future must include ways to replace some populations of cells. The ones you might be familiar with are immune cells and some populations of long-lived cells that tend to diminish over time such as the dopamine generating neurons whose loss leads to Parkinson's disease and certain cells in the retina essential to vision. The situation for stem cell research is somewhat different to that of much of the rest of the scientific effort needed to bring degenerative aging under medical control and prevent all age-related disease. There is no real lack of funding for one: it is a very energetic, well-supported field that is making good progress towards the goal of fine control over cell operation and fate. The challenge here is more one of steering at least some of this research in the right direction, which is aided by the existing incentives: most of the conditions that will most benefit from stem cell therapies are age-related, and thus researchers must engage with stem cell aging in order to produce treatments that are effective.
Along the way the research community will probably wind up producing useful transitional technologies, ways to revert the decline in stem cell activity with aging that produce meaningful benefits without addressing the underlying damage of aging. It is most likely the case that stem cell populations become less active as a reaction to damage, but since this largely seems to key from circulating levels of specific proteins it is a reaction that can in principle be overridden. This is not a solution for the long term as it doesn't address the underlying causes. It is a patch, but a better class of patch: I think that it is fairly evident from the state of first generation stem cell therapies today that there are worthwhile gains to be obtained.
Here are a few recent snippets of news from the stem cell research community, illustrative of progress well underway. You'll notice there's a lot of focus on repair after the fact and less on the use of cell treatments in a preventative manner. This is one of the things that must change in today's research community, leading to a growing willingness to build therapies for people who are aging but classed as "healthy" so that they do not become damaged and stricken. Prevention trumps cure.
Neurons derived from human induced pluripotent stem cells (iPSC) and grafted into rats after a spinal cord injury produced cells with tens of thousands of axons extending virtually the entire length of the animals' central nervous system. The iPSCs used were developed from a healthy 86-year-old human male. "These findings indicate that intrinsic neuronal mechanisms readily overcome the barriers created by a spinal cord injury to extend many axons over very long distances, and that these capabilities persist even in neurons reprogrammed from very aged human cells."
While numerous connections were formed between the implanted human cells and rat cells, functional recovery was not found. [The researchers] are attempting to identify the most promising neural stem cell type for repairing spinal cord injuries. They are testing iPSCs, embryonic stem cell-derived cells and other stem cell types. "Ninety-five percent of human clinical trials fail. We are trying to do as much as we possibly can to identify the best way of translating neural stem cell therapies for spinal cord injury to patients. It's easy to forge ahead with incomplete information, but the risk of doing so is greater likelihood of another failed clinical trial. We want to determine as best we can the optimal cell type and best method for human translation so that we can move ahead rationally and, with some luck, successfully."
A stroke therapy using stem cells extracted from patients' bone marrow has shown promising results in the first trial of its kind in humans. Five patients received the treatment in a pilot study. The therapy was found to be safe, and all the patients showed improvements in clinical measures of disability. The therapy uses a type of cell called CD34+ cells, a set of stem cells in the bone marrow that give rise to blood cells and blood vessel lining cells. Previous research has shown that treatment using these cells can significantly improve recovery from stroke in animals. Rather than developing into brain cells themselves, the cells are thought to release chemicals that trigger the growth of new brain tissue and new blood vessels in the area damaged by stroke.
A new stem-cell discovery might one day lead to a more streamlined process for obtaining stem cells, which in turn could be used in the development of replacement tissue for failing body parts. The work builds on a strategy that involves reprogramming adult cells back to an embryonic state in which they again have the potential to become any type of cell. The efficiency of this process may soon increase thanks to the scientists' identification of biochemical pathways that can inhibit the necessary reprogramming of gene activity in adult human cells. Removing these barriers increased the efficiency of stem-cell production, the researchers found.
The researchers discovered that young cells, which at first are part of the neural support cells, or the glial cells, leave the nerves at an early stage of the fetal development. The cells change their identity and become both connective tissues in the tooth pulp and odontoblasts - that is, the cells that produce the hard dentin underneath the enamel. "The fact that stem cells are available inside the nerves is highly significant, and this is in no way unique for the tooth. Our results indicate that peripheral nerves, which are found basically everywhere, may function as important stem cell reserves. From such reserves, multipotent stem cells can depart from the nerves and contribute to the healing and reformation of tissues in different parts of the body."