We know that organ transplant is possible today, but it is not as easy as you are thinking. Several tests need to be done before the transplant is done. Otherwise transplanted organ may be rejected by patient’s body. Now the problem is that why does body reject transplanted organ? There are three main types of rejections called hyperacute, acute and chronic that may occur in case of organ transplant.
Hyperacute rejection occurs immediately after surgery or may take few hours while acute rejection takes months to a year from surgery and chronic rejection may take some years. But why these rejections occur in human body? These rejections happen due to immune system which attack on foreign elements that enter human body intending to harm it. Our immune system identifies the cells of foreign element with the help of the Major histocompatibility complex (MHC) which is capable to identify foreign invader’s cells. A protein called glycoproteins stayed on the walls of our cells constitutes the MHC. They actually inform the white blood cells about foreign invaders. Once a white blood cell comes to know about foreign invaders they start producing T-cells which target foreign cells and destroy them.
There's over 20 genes that code for the MHC and over 50 variations per gene, so there's a lot of different combinations, which is one of the reasons why it can be so hard to match a donor to a recipient.
This is the main reason that causes the failure in transplanting organ. But there are several medicines that suppress immune system so that transplanted organ could be saved. But sometimes patients have to take 12 different medicines and in some cases for entire life.
Latest research says that the use of these medicines could be reduced in futures. To handle these rejections a two-tiered treatment conducted on mice by the scientists from UCSF. First the scientists injected cyclophosphamide to mice, which had undergone surgery for organ transplantation, to destory T-cells produced by white blood cells. Most of their T-cells were successfully eradicated by the injected medicine. Then cell therapy was provided to the mice to increase the number of certain TREG cells to control T-cells. These cells effectively prevented the immune system from attacking the transplanted organ or limb. The study shows that nearly 80 percent of the mice which had transplanted organ didn’t need any drugs to suppress their immune system.
Source: https://www.seeker.com/why-do-organ-transplants-fail-so-often-1792644743.html