Associate Director, Histocompatibility Laboratory Mayo Clinic Arizona Cave Creek, AZ
Body:
Background: The accuracy of a virtual crossmatch (VXM) relies on up-to-date human leukocyte antigen (HLA) antibody testing and knowledge of patient sensitizing events. Patients awaiting heart transplant (HT) are often supported with mechanical circulatory support (MCS) devices to improve waitlist survival. Use of intra-aortic balloon pumps (IABPs) as a bridge to HT has increased over 3-fold since the 2018 UNOS policy change which elevated IABP patients to status 2, expanding donor access (Figure 1). While existing literature suggests that durable support devices such as ventricular assist devices are associated with an increase HLA I & II antibodies, similar evidence with temporary devices such as IABPs is lacking. This study aims to raise awareness that IABP placement can lead to a memory antibody response in certain sensitized patients.
Case report: We describe the case of a 56-year-old African American female who had a striking increase in HLA antibodies within two weeks of IABP insertion. Her history included 3 pregnancies but no transfusions. Our lab performs single antigen bead (SAB) testing every other month for active waitlist patients. The patient had an IABP placed 27 days pretransplant. Routine SAB testing on a sample drawn 20 days pretransplant showed results consistent with history. This sample was used for the VXM for a subsequent heart offer. The heart was transplanted based on a negative VXM. Unexpectedly, the retrospective flow cytometry XM was strongly positive for T & B cells with her admission sample. SAB testing on that sample showed a marked increase in HLA antibodies (Figure 2) including donor specific antibodies (DSA) (A23, 32903 MFI; A33, 2504 MFI; B63, 15154 MFI; Cw6, 20949 MFI).
Outcome: The patient developed cardiogenic shock requiring temporary MCS. Thymoglobulin induction immunosuppression was augmented with plasma exchange, Eculizumab and Daratumumab to prevent DSA-mediated graft damage. We closely monitored DSA levels to guide therapy. As levels dropped, graft function improved.
Conclusion:
Conclusion: To our knowledge, this is the first case describing IABP-induced activation of a memory anti-HLA antibody response in a previously sensitized patient. Hence, it is important for HT programs to report IABP placement to the HLA laboratory as a potential sensitizing event.
