Donor selection in lung transplantation (LTx) is historically based upon clinical urgency, ABO compatibility, and donor size. HLA matching is not routinely considered; however, the presence or later development of anti‐HLA antibodies is associated with poorer outcomes, particularly chronic lung allograft dysfunction (CLAD). Using eplet mismatches, we aimed to determine whether donor/recipient HLA incompatibility was a significant predictor of CLAD. One hundred seventy‐five LTx undertaken at the Alfred Hospital between 2008 and 2012 met criteria. Post‐LTx monitoring was continued for at least 12 months, or until patient death. HLA typing was performed by sequence‐based typing and Luminex sequence‐specific oligonucleotide. Using HLAMatchmaker, eplet mismatches between each donor/recipient pairing were analyzed and correlated against incidences of CLAD. HLA‐DRB1/3/4/5+DQA/B eplet mismatch was a significant predictor of CLAD (hazard ratio [HR] 3.77, 95% confidence interval [CI]: 1.71–8.29 p < 0.001). When bronchiolitis obliterans syndrome (BOS) and restrictive allograft syndrome (RAS) were analyzed independently, HLA‐DRB1/3/4/5 + DQA/B eplet mismatch was shown to significantly predict RAS (HR 8.3, 95% CI: 2.46–27.97 p < 0.001) but not BOS (HR 1.92, 95% CI: 0.64–5.72, p = 0.237). HLA‐A/B eplet mismatch was shown not to be a significant predictor when analyzed independently but did provide additional stratification of results. This study illustrates the importance of epitope immunogenicity in defining donor–recipient immune compatibility in LTx.

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Antibody‐mediated rejection, whereby transplant recipient B cells and/or plasma cells produce alloreactive anti‐human leukocyte antigen (HLA) antibodies, negatively influences transplant outcomes and is a major contributor to graft loss. An early humoral immune response is suggested by the production of anti‐HLA donor‐specific antibodies (DSA) that can be measured using solid phase assays. We report the early posttransplant coexistence of a shared anti‐HLA antibody profile in 5 solid organ transplant recipients who received organs from the same donor. Retrospective analysis of the donor's serum confirmed the presence of the same anti‐HLA profile, suggesting the transfer of donor‐derived anti‐HLA antibodies, or the cells that produce them, to multiple solid organ transplant recipients. The time frame and extent of transfer suggest a novel variant of the passenger lymphocyte syndrome. These findings have important implications for the consideration of all posttransplant antibody measurements, particularly the interpretation of non‐DSAs in the sera of transplant recipients.

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Background. Currently, the assessment of immunological risk in lung transplantation (LTx) does not completely consider HLA compatibility at the molecular level. We have previously demonstrated the association of HLA eplets in predicting chronic lung allograft dysfunction following LTx; however, the associations between HLA eplet mismatch (epMM) loads and overall survival are unknown. Methods. In this retrospective, single-center study, 277 LTx donor-recipient pairs were high resolution HLA typed and analyzed for HLA epMMs using HLAMatchmaker (version 3.1). LTx pairs were also assessed for the presence of the previously described risk epitope mismatches DQ2-DQA1*05 and DQ7-DQA1*05. Results. HLA class I epMMs were not associated with deleterious outcomes; however, lower HLA class II (≤19), DQA1 (≤2), and combined HLA class I and II (≤29) epMM demonstrated an association with increased time to chronic lung allograft dysfunction and improved overall survival. The presence of a risk epitope mismatch was not associated with worse clinical outcomes. Conclusions. HLA epMM can risk-stratify LTx recipients and potentially guide donor-recipient matching and immunosuppression strategies.

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Immune sensitization, defined as the presence of alloreactive donor‐specific antibodies (DSA), is associated with increased wait‐times and inferior transplant outcomes. Identifying pretransplant DSA with a physical cell‐based assay is critical in defining immunological risk. However, improved solid phase antibody detection has provided the potential to forgo this physical assay. Here, we evaluated the association between DSA mean fluorescence intensity (MFI) and the recently introduced Halifaster Flow cytometry crossmatch (FXM) to determine if MFI could predict the outcome of FXM and whether a virtual crossmatch (VXM) would provide an accurate risk assessment. Sera from 134 waitlisted lung patients was retrospectively assessed by Halifaster FXM against lymphocytes preparations from 32 donors, resulting in 265 FXMs. HLA typing was performed to 2‐field allelic level and Luminex single antigen beads (SAB) used to identify DSA. The association between FXM and Luminex MFI was calculated using ROC analysis. MFI threshold accuracy was confirmed using a separate validation cohort (174 recipient sera and 34 donors), whereby both VXM and FXMs were compared. From the 265 FXM performed, 48 (18%) T‐cell (TFXM) and 56 (21%) B‐cell (BFXM) were positive. In the evaluation cohort, MFI thresholds of 2000 for HLA‐A, B, DRB1, and > 4000 for DQB1, were predictive of a positive FXM. The validation cohort of 233 paired FXM and VXM confirmed these MFI thresholds for both TFXM and BFXM with an accuracy of 91.4% and 89.3%, respectively. A positive VXM, defined with HLA‐specific MFI thresholds predicts Halifaster FXM reactivity, and can potentially expedite organ allocation, by minimizing the need for the more time‐consuming FXM.

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