Persistent expression of recipient-type ABH antigen following ABO-incompatible stem cell transplantation despite complete donor-type chimerism.

Patients undergoing ABO-incompatible hematopoietic stem cell transplantation (ABOi-HSCT) demonstrate a gradual transition from their original blood group to that of the donor in the post-transplantation period. However, ABH antigens present on non-hematopoietic tissues continue to express the recipient's antigens for life. These soluble ABH antigens may adsorb from the plasma onto the donor-derived red blood cells. This phenomenon not only complicates the interpretation of the recipient's blood typing and transfusion decision after transplantation but also impacts the assessment of the patient's clinical conditions, which includes raising concerns about transplant outcomes and the potential for relapse. Herein, we report two cases of persistent weak A antigen expression in recipients following minor ABOi-HSCT, despite achieving complete donor-type chimerism. In Case 1, a 35-year-old male, AB, RhD-positive, with T-cell acute lymphoblastic leukemia (ALL), was transplanted with an HLA-matched sibling carrying the B, RhD-positive blood group. In Case 2, a 4-year-old boy, A, RhD-positive, with B-cell ALL, was transplanted with an HLA-matched related group O, RhD-positive donor. Both patients exhibited persistent antigen A in forward typing more than 18 months post-HSCT, without any sequelae. These two cases underscore the necessity of performing detailed serological investigations to accurately determine blood type following ABOi-HSCT.