*Purpose: A donor-reactive alloimmune memory response can arise from prior exposure to foreign human leukocyte antigen by sensitization history in transplant recipients. Assessing risk levels in the memory alloimmune response or producing de novo DSA is important. We evaluated the incidence of antibody mediated rejection (ABMR) in kidney recipients with sensitizing history.

*Methods: A total of 690 living kidney graft were performed from 2007 to 2016 in the Department of Urology, Tokyo Women’s Medical University. We excluded recipients who had a transplant history, more than two sensitization histories, and an unknown sensitization history, and divided 547 recipients into three groups as follows: control group (n = 350) without a history of sensitization, transfusion group (n = 114) with a history of transfusion only, and pregnancy group (n = 83) with a history of pregnancy only. We investigated the incidence of alloimmunization before transplantation, incidence of ABMR, and clinical outcomes among the three groups.

*Results: The proportion of the recipients positive for complement dependent cytotoxicity crossmatch (CDC-XM) or flowcytometry crossmatch (FCXM) was 0.6% in the control group, 2.7% in the transfusion group, and 9.2% in the pregnancy group. The proportion of recipients with preformed DSA was 13.8% in the control group, 16.2% in the transfusion group, and 30.3% in the pregnancy group. When we evaluated the rejection incidence in recipients who had negative CDC-XM and FCXM, the incidence of acute ABMR was higher in the pregnancy group (22.4%) than in the transfusion group (10.8%) and control group (6.0%) (p < 0.001). There was no significant difference in the incidence of chronic ABMR among the three groups, but the pregnancy group had a higher incidence of chronic ABMR (6.6%, 9.0%, and 14.5%, respectively, p = 0.073). After excluding recipients with positive preformed DSA, the acute ABMR incidence was also highest in the pregnancy group, followed by the transfusion group and control group (16.9%, 11.6%, and 5.3%, respectively, p = 0.004). There was also no significant difference in the incidence of chronic ABMR among the three groups, but the pregnancy and transfusion groups had a higher incidence of chronic ABMR (6.6%, 9.5%, and 11.9%, respectively, p = 0.325). There was no significant difference in patient survival, graft survival, and graft function among the three groups.

*Conclusions: We concluded that recipients with a sensitizing history have a higher risk of acute ABMR even when they do not have preformed DSA. We must pay careful attention to recipients with a sensitizing history, particularly even without positive XM or DSA.

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