A₂/A₂B to B renal transplantation: Past, present, and future directions

One component of the new national kidney allocation system (KAS) in the United States that was implemented on December 4, 2014, was the allocation of kidneys from A₂ and A₂B (A, non-A₁ and AB, non-A₁B) deceased donors into blood group B candidates (A₂/A₂B → B). In so far as this is an important component of the new KAS that has the potential to further increase the access to transplantation for blood group B candidates on the waiting list, most of whom are minority candidates, we will review the body of evidence and historical perspectives that led to its inclusion in the new KAS. This review will also describe prospects for more widespread use of A₂/A₂B → B transplantation and a novel mechanism of humoral immunosuppression in B patients before and after transplantation with an A₂ or A₂B kidney. In this review, the authors summarize and discuss the experience that led to the inclusion of the A₂/A₂B → B component into the United States' new kidney allocation system in 2015, describe future directions to further expand A₂'A₂B → B renal and simultaneous liver-kidney transplantation, and emphasize that in order for this allocation component to improve access of blood group B candidates, more B candidates must be made eligible in the UNOS system.