| MadSci Network: General Biology |
It all sounds like science fiction to bring back a dead person through organ and tissue transplants or replacement, tissue and organ regeneration, or even utilize a machine to perform biological functions. However, the science fiction behind Frankenstein and some Star-Trek episodes may one day be reality. To simply supply the individual with a new or artificial heart, lung, or other organ or tissue, or even provide them with an infusion of regenerating cells in order to bring them back from the brink of death is one of the driving forces behind many of the research and medical projects today. Science has grown by leaps and bounds in this area, with many areas are still considered in their infancy, but all working to this common goal for simplified organ and tissue replacement and regeneration. Until then, we can only hope for the best with what current technology we have. I believe you may find additional answers through researching the current advances and limitations of organ and tissue transplants and even bionics. BIONICS First, I'd like to cover "bionics." Bionics is seen as an attempt to develop better machines through the understanding of biological design principles or imitation of biology and to connect biological systems to artificial organs, or other systems. There have been amazing advances in the realm of bionics such that a deaf person can hear, pace makers are common place, artificial hearts used to sustain an individual until a transplant is available, various joints are replaced with man-made materials that incorporate bone then dissolve away, an implanted chip which can control artificial limbs, and a blind person that may once again be able to see. There is even talk of nanites or nanodes that would traverse the human body making necessary repairs. It's almost like the science fiction of Star-Trek meets the real 20th century. Even with such fantastic advances such as pace makers, artificial joints, and prosthetic technology, there is still a lot of work yet to do in understanding the processes of the human brain (especially for neuro-related bionics) and how foreign materials interact with the human body (artificial limbs) for extended periods of time. In some aspects we are so close but yet so far away. Even with the most common bionic procedures (e.g. joint replacement and pace makers) there are still obstacles. As mentioned earlier, we are still uncertain about the long term interaction of many of the devices used in the human body. Individuals may not take well to the grafting, be allergic to the materials used, not be physically strong enough for the medical procedure, or complications (namely secondary infections) from the medical procedure arise. However, it is still all about taking a chance that we make in efforts to extend a person's life, or more appropriately for many bionic devices, improve a person's quality of life. So, in considering that may be, just may be, if the stars lined up (an artificial organ device is available, the person is well enough to undergo the medical procedures to get it, and there is no rejection of the artificial organ), one would also need to consider the costs associated in receiving this artificial organ or device. And unfortunately, many of the advanced devices are not economically available to the general public and often insurances will not cover those devices considered "experimental". It's a harsh reality but one that exists. Currently most insurance policies covered various joint replacement procedures but, again, will not cover "experimental" procedures. The current advances seen in bionics today speak of eventually seeing machines doing so much for us or becoming an important organ or tissue to replace a failing one. However, we are not there yet. This is where science fiction is becoming reality - SLOWLY. For further information on bionics please see the following websites: http://www.aleph.se/Trans/Individual/Body/bion_page.html http://online.sfsu.edu/~swilson/emerging/artre332.bionics.html http://www.wired.com/wired/archive/5.02/reality_check.html http://www.cem.msu.edu/~cem181fp/brain/ http://www.pbs.org/wgbh/nova/eheart/ http://biotech.about.com/gi/dynamic/offsite.htm?site=http%3A%2F%2Fwww.pbs.o rg%2Fsaf%2F1107 ORGAN AND TISSUE TRANSPLANTS Now to answer your question concerning replacing old and worn out human parts with other human body parts. This field of human body part replacement also has undergone dramatic advances, but still is considered in its infancy in many areas. Doctors and scientists have been able to successfully reattached individuals' fingers, legs, arms, and hands, and graft skin for severely injured individuals. This is great! Yes, individuals have had their limbs reattached, bone marrow transplants, and skin grafts performed successfully. But many times these organs and tissues were typically from their own body. Much, much more comes into play when organs and tissues do not come from the individuals themselves. And just like for bionic parts, there are draw backs; and for transplants there may be more draw backs and considerations. It is not as easy as it sounds to simply replace a failing or aging organ or tissue with another. There are so many factors to consider. Even organ and tissue donor web sites stress the uncertainty involved with transplants and the likelihood for an individual to pass all the medical and psychological testing, wait (and often times a LONG wait) for a match, and have the transplant procedure be successful. No doubt that some procedures have become commonplace, but many are not and carry much more uncertainty in success. COMPATIBILITY AND TESTING To begin with, most living and viable transplant organs or tissues must be compatible to the recipient. Several tests are performed on the individual and organ or tissue for compatibility factors. The recipient must also be strong enough physically and mentally for the procedure before the individual can receive the transplant. First, organs and tissues are "typed" based on blood type and histocompatibility (immune system or white blood cell compatibility). A blood type test (characterization of the red blood cells) is the first step in determining whether the organ or tissue is a suitable match. This test identifies and characterizes the "ABO" of red blood cells and whether or not it matches the potential donor. The following is a table illustrating which blood types can be received and donated to respective blood types: Blood Type Can Receive from Type Can Donate to Type O O O, A, B, AB A A, O A, AB B B, O B, AB AB O, A, B, AB AB Blood type is an important consideration in finding a suitable match, just as it is in giving blood for a blood transfusion. The next important blood test deals with the immune system or white bloods cells. There are basically two tests performed on a transplant patient's white cells. The first test is to characterize the inherited generic markers on the surface of the white cells. These markers are called Human Leukocyte Antigens (HLA). An individual basically inherits one set of these markers, or antigens, from each parent. Even though there are multiple combinations of these antigens, it is possible to locate a non-related donor that has the same HLA combination. The second test is just as important as any other test and it tests the specific immune response between the patient and donor cells. This second test, "crossmatching", measures and characterizes the antibodies the recipient and even donor cells create in order to defend against invading or foreign materials. The crossmatching results show whether and to what degree the recipient and donor's white blood cells create antibodies which would then destroy the other's cells. More specific information on tissue typing is provided in the websites listed toward the end of this section. Other tests that are run on an individual considered for an organ or tissue transplant include and are not limited to the testing of other organs and systems that would support the transplant, a psychological evaluation to make sure the individual can cope with having the transplant, and test for any other medical problems that would make a transplant dangerous, or that would cause the transplant to fail. Some of the other medical tests include screening for cancer, HIV or AIDS, an incurable infection (such as tuberculosis or Hepatitis C), severe disease in another organ system (such as severe coronary heart disease), and emphysema or cirrhosis of the liver. There are also many other medical and even financial factors that I can not even think of that come into play to receive such transplants. A few that I am aware of are if an individual is overweight or elderly are not considered the best candidates for transplants. Being overweight may place too much strain on the new transplant causing it fail. Being older puts the individual at greater risk for complications during the medical procedure, effects from the medications, and increased risks for cancers to develop. Financially, the individual must have sufficient funds or medical insurance coverage to pay for all the medications, regular blood tests, and check ups an individual will need to have for the rest of their life once they receive their transplant. SELF HARVESTING Today, the harvesting of an individual's own organs and tissues allows them to be safely stored and used at a later date. The most commonly known procedure is for cancer treatment patients to have their own or a matched donor's bone marrow harvested and later transplanted after the cancer treatments. There is also bone tissue preservation for trauma and surgical patients, portions of the parathyroid cryo-preserved for re-implantation, and skin tissue preservation for burn, trauma, and surgical patients. With advances in this area, many more individuals are able to get a new lease on life through the use of their own organs and tissues; however, this may not be an option for the many others in need of a transplant. COMPLICATIONS So now that we have all these tests run in order to find a tissue "match" or have harvested the individual's own tissue or organ, what else is there to consider? Organ and tissue rejection is the single major factor for transplants to fail. Even one's own harvested organs or tissues may be seen as foreign and the body attacks it in order to destroy and remove it from the body. An individual's own blood characteristics can change over time due the immune response of the many different viruses, bacteria, etc. that it encounters. It can change significantly since the tissues or organ was first harvested and any time after the transplant. This is why the tissue typing and blood tests are so important, even for self donated tissues. It is hoped that the immune system is sufficiently characterized before and after the transplant to avoid the host turning on the donor cells (graft or organ/tissue rejection) and even the donor cells from turning on the host (graft-vs-host disease). In efforts to minimize an immune response or rejection to the new organ or tissue, immunosuppressive drugs are administered. Another complication seen when such drugs are taken is that it opens the door to many other infections and risks. When the immune system is lowered or compromised, the risk of cancer and other illnesses increase. However, with careful surveillance and antibiotic drugs, many of these "secondary" infections or complications are reduced. One must also remember that at any time the individual may experience organ rejection - even if they take their medications as required. A transplant patient must have regular blood checks for rejection for the rest of their life - not mention taking their anti-rejection medications. A transplant is a life long commitment to keep the transplant healthy and avoiding rejection. REGENERATION Now for science fiction to meet reality, there is on-going research into the "regeneration" of organs and tissues. This section of science has recently made significant advances and discoveries but is still in early infancy. In one scenario, a tissue engineer injects or places a given molecule, such as a growth factor, into a wound or an organ that requires regeneration. These molecules cause the patient's own cells to migrate into the wound site, turn into the right type of cell and regenerate the tissue. In the second more ambitious procedure, the patient receives cells (either his or her own or those of a donor) that have been harvested previously and incorporated into three-dimensional scaffolds of biodegradable polymers, such as those used to make dissolvable sutures. The entire structure of cells and scaffolding is transplanted into the wound site, where the cells replicate, reorganize and form new tissues. At the same time, the artificial polymers break down, leaving only a completely natural final product in the body: a neo-organ. The creation of neo-organs applies the basic knowledge gained in biology only over the past few decades to the problems of tissue and organ reconstruction. Tissue engineering does not yet rival the fictional portrayals seen in movies or in books in which some on can simply regenerate or grow complete organs and tissues, but a glimpse of the future has arrived. The creation of tissue for medical use is already a fact, to a limited extent, performed in hospitals across the U.S. These groundbreaking applications involve fabricated skin, cartilage, bone, ligament and tendon and make musings of "off-the-shelf" whole organs seem less than far-fetched. Scientists must surmount a few obstacles, however, before drugs that promote tissue and organ formation become commonplace. To date, only the factors responsible for bone and blood vessel growth have been characterized. To regenerate other organs, such as a liver, for example, the specific molecules for their development must be identified and then produced reliably. This specific area of science and medicine is progressing rapidly; but unfortunately benefits a selected few areas and needs. More specifics on tissue engineering can be found at the following website: http://www.sciam.com/1999/0499issue/0499mooney.html AVAILABILITY However, the biggest problem associated with organ and tissue transplants is simply "availability". Many individuals on donor waiting lists die because of the shortage of organs and tissues. Currently, each day about 63 people receive an organ transplant, but another 16 people on the waiting list die because not enough organs are available. It seems so unfair that many individuals die before they get the chance at a donated organ or tissue. However, if the organ and tissue was not compatible, the individual may suffer more from the organ/tissue rejection than not having it at all. The United Network for Organ Sharing (UNOS) has been tracking the number of individuals on transplant waiting lists and the number of available organs and tissues available. As of February 28, 2002, the overall number of individuals listed on the national transplant waiting list was 78,945 and by March 23, 2002, the number increased to 79,165. In addition, UNOS tracks the number of available donor organs and tissues recovered. In 2000, a total of only 11,684 available donor organs and tissues recovered. The numbers for 2001 and 2002 were not yet available. Even so, this is a far cry from the number of individuals listed on the waiting list. UNOS also estimated that the number of individuals who died while waiting for a donor organ/tissue was 5,800 in 2000 and 4,320 in 2001. So simply waiting to find an available and compatible organ or tissue to transplant may be the biggest obstacle of all. Getting and keeping a transplant healthy is not by any means an easy one, but there are numerous survivors out there to attest the trails and obstacles have paid off for them. For additional information on organ and tissue transplants please see the following websites: http://www.ultranet.com/~jkimball/BiologyPages/T/Transplants.html http://www.tppp.net/ http://www.transweb.org/ http://pancreas-kidney.tripod.com/index.htm http://www.med.umich.edu/trans/public/ttbrochure/pg1.html http://www.methodisthealth.com/motc/ http://www.med.umich.edu/trans/public/ http://www.A-S-T.org/pcare/english/intro.htm http://www.medscape.com/transplantationhome http://www.unos.org/frame_default.asp http://www.patients.unos.org/ http://www.organdonor.gov/ With as much wishing and dreaming about one simple procedure to replace or regenerate failing and worn out body parts, we are still working to make dreams and hopes reality and hopefully one day make organ and tissue replacement quite commonplace. But right now and to the extent of bringing a dying person back to life, it is going to depend on what organ and tissue is failing, the availability of the organ or tissue (or even an artificial replacement), the overall health of the individual, the compatibility of the individual and the replacement, and current technology and surgeon skill to save the person's life. There always exists the possibly that the most remote chance or operation will help, but sometimes even the most guaranteed procedures do not end as we hope. Life is still quite unpredictable and uncertain. Often at times no matter how we look at it or how hard try to overcome obstacles, individuals slip away and we can only hope to a much better place.
Try the links in the MadSci Library for more information on General Biology.