Stem cell research has come a long way in just a few years. Already the potential uses for stem cells seems infinite, but there are basic challenges that must be overcome, or discovered, before stem cell therapy becomes a reality. These challenges must be overcome for stem cells to become a useful treatment in any facet, not just macular degeneration.
Stem cells must be clone-able, or cultured, easily and in great quantities. Stem cells must also be able to differentiate or “turn-into” a desired type of cell or tissue. This is called specialization. Yesterday, I said that I won’t pay too much attention to the two different types of stem cells. I will make a small exception. There are two types of stem cells, embryonic and adult (or non-embryonic). The differences between the two are many, but principally, embryonic cells replicated and grow faster and easier that adult cells. Adult cells, meanwhile, differentiate or specialize easier.
The task is to learn how to culture cells easily and get them to differentiate into the desired cell type or tissue. In other words, how do we grow lots and lots of cells and coax them to turn them into, say RPE cells? Scientists must somehow unlock the secrets of each of these cell types to use their respective attributes to meet this goal.
Once placed into the patient, or target organ, the cells must survive. The principle barrier to a transplanted cell or organ is the host’s immune system. While the organ or transplanted tissue may be in perfect shape, the host’s own immune system may “reject” the organ or tissue. Sometimes, with present day organ transplantation, the immune system may be suppressed with drugs to allow the organ to function and survive, but this is usually associated with a high level of systemic complications. Despite efforts to find proper “matches” for bone marrow or other organs, immunologic tissue rejection remains a huge problem.
Stem cell research must find a way to allow the host to “accept” the new transplanted tissue without immunosuppressing the host. This will allow a healthier host/patient and better viability of the transplanted tissue.
Not only to the cells have to survive, but they must integrate and function as they are intended. In the case of macular degeneration, this means that RPE cells may be created that not only look like RPE cells, but they must function as RPE cells. While much of this may indeed be related to how much we learn about a stem cells ability to specialize, it also means that scientists understand the exact functions that are integral to a specific tissue, i.e. exactly what functions of RPE cells are necessary for vision?
The transplanted tissue must not harm the patient, or cause complications. Self explanatory?
How do we transplant the tissue safely? Once created, how do we insert the new tissue into the recipient? Can we do it safely? New techniques and instrumentation will be needed to insert the tissue without damaging the tissue, without damaging the host and doing so with few complications. In our RPE transplantation example, we must learn how to insert the RPE cells underneath the retina, without damaging the new RPE cells, without damaging the retina and without causing vision loss from complications such as infection or retinal detachment.
There is a lot learn, but the subject is really intriguing. I look forward to hearing from you.
Randall V. Wong, M.D.
Ophthalmologist, Retina Specialist