Remember we talked about stem cells in the beginning
of this book? The stem cells are very
powerful ancestors of all cells; normal cells that show specific functions are all
essentially derived (differentiated) from stem cells. Therefore, it makes sense to attempt to
utilize the natural power of stem cells to treat different diseases including cancer. Generally, there are several ways to utilize
stem cells for cancer treatment. They are
briefly described as follows:
Using Stem Cells Directly
On type
of stem-cell therapy is to inject stem cells directly into the blood stream for
them to fight against cancer and other diseases. Stem cell based strategy has been shown to be
very promising. A well know example is
to use stem cell transplantation for leukemia.
Briefly,
stem cells can be collected from the bone marrow, circulating (peripheral)
blood, and umbilical cord blood. In a
stem cell transplant, healthy stem cells are infused into the body. Basically, there are two types of stem cell
transplants. Autologous stem cell
transplant is when stem cells are collected from the patients themselves. When stem cells are taken from a matching
donor, the transplant is called allogenic stem cell transplant. In order to find the right match, a human
leukocyte antigens test needs to be conducted on the patient and the potential
donor.
Although
stem cell therapy has been used successfully in many cases, there are also many
cases of failures. Research and studies
in this area are continuing.
Converting Cancer Cells Back
into Stem Cells or Normal Cells
A number of studies are focusing on converting cancer
cells into stem cells. The origin of
this type of research started from a Japanese scientist, Shinya Yamanaka, who
won Nobel Prize in 2012 year for his discovery showing that mature cell
(differentiated) can be reprogrammed to become pluripotent (similar to stem
cells). He
successfully identified a few critical genes in mice; when these genes were activated,
mice skin cells were re-programmed and became stem cells (now referred to as
iPS cells or induced pluripotent stem cells) by using several key ingredients and
a delicate process. Theoretically, these iPS cells can be
differentiated into all types of cells.
Since
then, many studies indicated that, if the condition is right, it is indeed
possible to artificially convert normal cells back into stem cells. At the present time, a lot of research
activities are ongoing to hopefully convert cancer cells back into stem cells
or normal cells.
Use of Exosomes
Stem cells, normal cells, and cancer cells all produce
a variety of biological molecules and one type of very important vesicles,
exosomes, for inter-cellular communication and other functions. Exosomes are cell-derived vesicles; exosomes
from different types of cells contain a common group of molecules, as well as
cell type-specific components. Once
released from the cells, exosomes act as messengers to carry and transfer their
biomolecules to proximal and also distant cells. Indeed, this general description is
correct. However, there is a very
important point not being well characterized: some contents of exosomes can
also be cellular environment-dependent.
Exosomes are present in all biological fluids (blood,
urine, and even cell culture medium). Their
diameters are from 0.04 to 0.1 µM, much smaller than RBC (diameter 6-8 µM) and
WBC (diameter 12-15 µM). Fig. 6.1 shows
a schematic size comparison of a WBC, a RBC, and exosomes.
Exosomes have been shown to have specialized
functions. For example, exosomes play a
key role in intercellular signaling and waste management. Among other functions, exosomes work like
messengers to carry a variety of RNA, proteins, sugar etc. As mentioned before, stem cells have the
amazing power to grow and differentiate.
It is therefore reasonable to assume that stem cells utilize exosomes to
carry important biomolecules to normal cells and cancer cells to deal with many
different cellular issues.
Exosomes are like micro-packages of important biomolecules
to be shipped from one cell to another. Let’s
use an analogy in our daily lives to explain the roles of exosomes as follows.
In our daily lives, we all use the post office to mail
letters and, sometimes, we use FedEx or UPS to ship packages. The letters or packages all contain useful
information or materials that may be useful to the receiving parties. If you still remember, inter-cellular
communication is very important and normal cells communicate better than cancer
cells. However, cancer cells do release
specific exosomes to be conveyed to other cancer or normal cells. Therefore, it will be very important to
figure out what are in the exosomes that are released by cancer cells. If we know the answers, it will be very
useful in finding a better way to deal with cancer. In short, exosomes are becoming a very
important area for cancer research.
In recent years, uses of exosomes for diagnostics and
for treatment of diseases have become a hot area of research. Because individual exosomes contain different
RNAs and proteins and the fact that exosomes can stay in the circulation for a
long time, it is possible to trace back to the tissues that produce them. As a result, it is possible to develop
certain diagnostics to detect cancers at early stages. On the other hand, there are some real
hurdles making the diagnostics at the present time. For example, because of its small size as
compared to RBC and WBC, it is not easy to fish out exosomes out of blood or
urine. In addition, there are a great
number of exosome exist in plasma. All
these make it a real challenge to develop new diagnostic employing exosomes. As to the use of exosomes in therapeutics,
intense research activities are ongoing in many labs.
In short, let’s use another analogy to make it
easier to understand exosomes. Exosomes released
from normal cells are similar to missionaries in real life; exosomes carries a
lot of important ingredients to deal with cancer cells whereas missionaries
carry a lot of information to carry out missions such as religion, education, and
health care.
© Jiajiu Shaw, 2016
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