ABO Mismatch
ABO-Incompatible heart transplantation (ABOi) was first undertaken in young infants by Lori West’s group in Toronto in 1997 to maximize the chance of an infant being transplanted and minimize refusal of otherwise suitable donor organs. Table 1 demonstrates the various combinations of transplant ABO compatibility. Multicenter collaborations have demonstrated long term outcomes, indistinguishable from ABO compatible transplants. Since then the indications have extended outside the infant age range and to sensitized patients.
The initial transplants were done in infant with negligible antibodies but over time it became clear that transplants could be done with significant levels of antibodies. This was first achieved in Japan in the context of renal transplantation - at the time cadaveric donors were illegal and often the only available living donor was a family member with a different blood group. By depleting the antibodies with plasmapheresis and pre transplant rituximab successful transplants were undertaken and interestingly, although antibodies could reappear post transplant, they were short lived and usually disappeared indicating tolerance. Cardiothoracic transplants do not have the luxury of knowing when a transplant is going to occur but despite this ABO mismatched transplants have proved successful, although the price to pay may be initial antibody mediated rejection, which subsides with appropriate management.