Demi-Lee Brennan had O-negative blood type before receiving a replacement liver six years ago.
However, she is now O-positive after her body adopted to the immune system of the organ's donor, with an estimated odds one in six billion.
It means that Brennan no longer needs immunosuppressant drugs, which are used so that the body would accept the new organ.
Only a small number of patients were able to come off the drugs although it was usually advised to take the drugs for life.
Brennan's doctors said they cannot fully explain her recovery and have no precedent for what happened. They plan to go over everything that happened to find out if they can understand why it happened and to see if it can be replicated.
