*Purpose: In general, preformed donor-specific antibodies (pDSAs) can lead to an increased risk of antibody-mediated rejection (AMR); however, their prevalence, risk factors, and the efficacy of rituximab desensitization in liver transplantation (LT) remain unclear.

*Methods: We retrospectively reviewed consecutive 370 adult (≥18 years) LT in our institute (2009-2019). We have routinely determined anti-HLA antibodies perioperatively using Luminex technology from 2009. Mean fluorescence intensity (MFI) ≥500 by single antigen beads was considered positive. Clinicopathological factors studied were recipient/donor age and gender, liver etiologies, MELD scores, number of pDSA+ loci, sum of MFI (if several DSAs were found), rituximab desensitization or not, and with or without splenectomy, etc.

*Results: Fifty recipients had at least one pDSA (13.5%). Of these, 10 ABO-incompatible cases were excluded to eliminate the influence from anti-ABO antibodies. Thus, 40 recipients (male/female: 6/34 [nulli-/uni-/multiparous: 9/3/22]; median age: 53 years [IQR, 42-61]) were enrolled in the analyses. Primary diseases included PBC (12), HCV-related (10), biliary atresia (6). The median MELD score was 20 (IQR, 13-29). Living-donor- and deceased-donor-LT were 30 and 10, respectively, in which 14 underwent splenectomy. The number of HLA loci with pDSAs ranges from 1 to 7 (median: 1; IQR: 1-2), and the median of sum-MFI was 7124 (IQR, 3904-17995). Rituximab was administered in 7 cases preoperatively. AMR was diagnosed in 5 cases based on the Banff criteria. Univariate analysis identified sum-MFI ≥10000 (P =0.003) and pDSAs for multiple loci (P =0.004) as the risk factor for AMR. All the 5 cases with AMR fulfilled the both criteria, which was a significant risk factor for AMR occurrence (P =0.0002). Pre-transplant rituximab desensitization efficiently reduced post-transplant DSAs in 3 cases (Fig.1-A); however, the other 2 cases with persistent high-titers even after LT developed refractory AMR (Fig.1-B).

*Conclusions: Preformed DSA was found in 13.5% of LT recipients, in which multiparous women and PBC were the most populations. High-titer (sum-MFI ≥10000) and multi-loci pDSAs were identified as the risk factors for AMR after LT. Persistent high pDSAs after LT despite pre-transplant rituximab desensitization should be carefully observed with the possibility of AMR occurrence in mind.

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