Purpose of review: Limitations in donor availability for stem cell or organ transplantation require that ABO-incompatible donors be used. Crossing ABO lines can have immune consequences characterized by immediate or delayed hemolysis.
Recent findings: The use of peripheral blood as a stem cell source has essentially eliminated the risk for ABO-mediated hemolysis during infusion. Delayed red cell engraftment is expected after a major ABO-incompatible transplant and may be associated with pure red cell aplasia. The incidence of hemolysis associated with minor ABO incompatibility, the passenger lymphocyte syndrome, is waning because anti-B-cell immunosuppressive therapy is increasingly a component of graft versus host disease prophylaxis. The impact of ABO mismatching on stem cell recipient survival remains an area of active investigation. Although major ABO-incompatible organs are not used routinely for transplantation, minor ABO-incompatible organs are frequently used to meet the demand for organs. Passenger lymphocyte syndrome in this setting is a common complication, and has now been observed with every organ type and increasingly with non-ABO antibodies. Hemolysis can occur, but it is uncommonly severe.
Summary: ABO-mismatched donors are commonly used for transplantation, and immune hemolysis remains the main complication. Clinicians must be vigilant in order to recognize hemolysis and implement appropriate therapy.