There were over 36,500 organ transplants performed in the United States in 2018 — and nearly 115,000 more patients are currently on waiting lists for a transplant.
While these increasingly common transplants have the potential to save lives, treatment does not stop there. Our bodies tend to attack transplanted organs, often damaging them over time to the point of needing another transplant — a temporary solution meaning more time spent on a waiting list.
What is Tissue Rejection and Why Does it Occur?
Tissue rejection, or transplant rejection, is a process in which a transplant recipient’s immune system attacks the transplanted organ or tissue.
Our bodies’ immune systems are supposed to protect us from agents that may be harmful, like bacteria or viruses. The immune cells in blood identify antigens on the surface of the substance that identify it as foreign, triggering an attack, so when those antigens are found on a new organ, the organ can be in jeopardy. With modern developments in transplant medicine, doctors can better match immune systems to lower the risks of organ transplant rejection.
There are multiple types of rejection:
- Hyperacute rejection – occurs just a few minutes after a transplant when the antigens are completely unmatched. An example would be a person being given the wrong blood type during a blood transfusion. If the tissue is not removed right away, the patient will usually die. This is now uncommon.
- Acute rejection – can quickly damage the transplanted organ, but can also be treated with immunosuppressant drugs. The risk is highest in the first three months but can occur even years later. Most patients have an acute rejection of some sort.
- Chronic rejection – can take place over many years, slowly damaging the transplanted organ. Even with immunosuppressant drugs, chronic rejection can result in eventual organ failure.
Immunosuppressant drugs are not without their own risks. They can increase the risk of cancer or even lead to failure in a different organ. While a necessary treatment to hold off the more severe risks of transplant rejection, they tend to shorten the lifespan of transplant recipients.
Historically, all tissue transplants have come with some level of rejection. However, the risks are not equal across different types of transplants.
- 17% of kidney transplant recipients do not have a functioning organ after three years, and only 54% still work after 10 years.
- 25% of liver transplant recipients do not survive five years, with 8,000 liver transplants performed in the U.S. alone each year.
- 12% of heart transplants fail in the first year, and the five-year survival rate is 75 percent.
- Only about 50% of lung transplant recipients survive five years.
While all of these figures improved, it is clear that there is a great deal of room to improve to preserve higher quality and longevity of life for the thousands of people who need a transplant every year.
Do Stem Cells Contain the Solution?
Although tissue rejection has always seemed like an unavoidable occurrence with transplants, stem cells may offer a solution. A clinical trial under the direction of Dr. Gary Levy and Dr. Harold Atkins of The Ottawa Hospital suggests it may be possible to essentially “trick” a body into accepting transplanted organs, without the dangerous immune response that leads to rejection.
The new study is based on Atkins’ groundbreaking research into treating multiple sclerosis with bone marrow-derived hematopoietic stem cell (HSC) transplants. After the organ transplant, the doctors plan to wipe out the patient’s immune system, then replace it with a new immune system from the patients’ own stored HSCs. This new immune system may then recognize a transplanted organ as belonging in the body since it was there before the immune system itself was formed — eliminating the need for immune-suppressing drugs.
Although the trial is still in a limited phase, there are already promising results. Three patients are no longer taking immune-suppressing drugs. Levy describes them as immune tolerant.
One patient remained healthy for four and a half years, after removing the drugs that used to be necessary to stop her immune system from attacking her transplanted organ.
What Does the Future Hold?
Stem cell transplants may very well contain the solution to the most-pressing transplant issues. Although the promising results are from a very small study, in Levy’s own words, “The data looks exciting. If this continues to evolve, and it looks like it’s working, there will be a large international study. That’s the next step.”
With the great potential to improve the lives of thousands of people in the near future, this has the potential to become one of the most important developments in a long series of breakthroughs in stem cell medicine.
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