Liver transplantation, whether from a deceased donor or a living donor, is a life-saving procedure for people with end-stage liver disease. For a standard procedure, the donor and recipient blood types must be compatible to prevent immediate rejection of the new organ. However, significant medical progress, particularly in living donor transplants, now provides exceptions to this traditional rule, allowing successful transplants between incompatible blood types (ABOi) under specific protocols. This advancement has helped expand the pool of available donors.
The Role of ABO Blood Types in Liver Donation
Blood type compatibility is necessary for a conventional liver transplant due to the body’s natural immune defense system. The ABO blood group system is defined by the presence or absence of specific surface markers, called antigens, on red blood cells and other tissues, including the liver’s vascular lining. A recipient’s immune system naturally produces pre-formed antibodies against any foreign ABO antigen they do not possess. If a person with type A blood receives a liver from a type B donor, their pre-existing anti-B antibodies will immediately attack the B antigens on the donor liver’s blood vessels. This rapid and severe reaction is known as hyper-acute rejection, which can destroy the transplanted organ quickly. Standard liver transplantation requires the donor and recipient to be ABO-compatible to avoid this powerful immune response.
Strategies for ABO-Incompatible Liver Transplants
When a compatible donor is unavailable, medical teams can perform ABO-incompatible (ABOi) liver transplants using specialized strategies. The primary goal of these protocols is to significantly reduce the recipient’s pre-formed anti-donor antibodies before the new liver is placed. These procedures are complex and generally reserved for urgent or living donor cases where the timing can be managed.
Desensitization Techniques
One of the main techniques is desensitization, which often begins several weeks before the surgery. This protocol typically includes administering Rituximab, a medication that targets and depletes the B-cells responsible for producing the anti-donor antibodies. Reducing the number of these antibody-producing cells is a proactive measure to prevent the hyper-acute rejection response.
Another procedure frequently used is plasmapheresis, a blood filtration technique that physically removes the circulating anti-donor antibodies from the recipient’s bloodstream. During this process, the recipient’s plasma is separated and replaced with a substitute. This is sometimes paired with immunoadsorption, which selectively filters out the specific anti-ABO antibodies.
Recipients of an ABOi transplant require a higher, more intensive level of post-transplant immunosuppression. While the outcomes for ABOi transplants have significantly improved, they still carry an increased risk of complications, such as arterial thrombosis and biliary issues, requiring meticulous post-operative monitoring.
Essential Non-Blood Type Compatibility Factors
While blood type compatibility is a major hurdle, it is only one of several factors that determine a successful liver transplant. For both deceased and living donor procedures, the physical dimensions of the graft must be precisely matched to the recipient’s body. This is especially true for living donor transplants, where a segment of the donor’s liver is used; the segment must be large enough to function effectively but small enough to fit within the recipient’s abdominal cavity.
Organ Allocation and MELD Score
In the case of deceased donor organs, priority for allocation is determined by the Model for End-Stage Liver Disease (MELD) score. This score, which ranges from 6 to 40, assesses the severity of the recipient’s liver disease based on blood tests for bilirubin, creatinine, and INR. A higher MELD score indicates greater urgency, meaning the sickest patients are prioritized for available organs.
The overall medical condition of both the donor and the recipient is also a major consideration. This includes screening for active infections and ensuring the donor organ is structurally and functionally healthy. Although Human Leukocyte Antigen (HLA) tissue matching is a major factor in kidney or heart transplants, it is generally less critical for the liver, which is more resistant to rejection.