P051 Low-level antibody against shared epitopes – are they relevant?

Abstract

This case illustrates the importance of considering low-level antibody reactivity against HLA shared epitopes. A 58 year African American female patient with ESDR due to DM type 2 was evaluated for simultaneous kidney-pancreas transplantation. Although the patient had 4 pregnancies, based on the One Lambda Single Antigen (SA) results, the patient had only weak ( ∼ 500 MFI. To investigate this discrepancy, phenotype bead assay (LSPRA) was performed, which clearly detected the presence of weak antibodies against A2, A68, and A69, which are known to share an epitope 144TKH (Figure 1B). Reactivity against A2 was additionally confirmed using surrogate crossmatches. We concluded that due to epitope sharing the single antigen bead assays may not have reflected the true strength of the patient’s antibodies and listed A2, A68, and A69 as unacceptable antigens in UNOS. The patient was successfully transplanted on 9/26/17 avoiding pre-existing DSAs. Interestingly, 10 days after transplant A2, A68, A69 increased to ∼ 20,000 MFI (Figure 1C). Since these specificities were not DSAs, no further action required. However, this case underscores that although low-level antibody against a shared epitope may not be effectively detected by solid-phase platforms, but still may result in positive crossmatch and increase the risk of AMR post-transplant. This case shows that setting positive cut-offs solely based on MFI values may be misleading if a patient has antibody against shared epitopes and that any discrepancy between virtual and cell-based crossmatch needs to be investigated. This case also highlights that use of epitope analysis and multiple assays help to evaluate immunological risk post-transplant more accurately.