Halvard Bonig

Summary ABO incompatibility affects approximately 40% of allogeneic stem cell transplants in Caucasian patient populations. Because bone marrow (BM), the preferred graft from paediatric sibling donors and for non‐malignant diseases, has a red blood cell (RBC) content similar to blood, anti‐donor isoagglutinins must either be depleted from the recipient or RBCs removed from the graft. To achieve tolerability of unmanipulated BM grafts, we used controlled infusions of donor ABO‐type RBC units to deplete isoagglutinins before the transplant. This retrospective study evaluates the outcomes of 52 ABO major incompatible BM transplants performed at our centre between 2007 and 2019. The use of donor‐type RBC transfusions was well tolerated. They effectively reduced isoagglutinins levels, typically achieving target titres after one (60%) or two (29%) transfusions. The approach allowed for successful and uneventful infusions of unmanipulated BM which provided timely engraftment. The transplant outcomes were not inferior to those of a matched‐pair control group of patients with ABO‐identical donors.