High-resolution typing of HLA loci in the setting of solid organ transplantation allows for the assessment of the so-called eplet mismatch (EMM) score between donor and recipient. Eplets are key elements of epitopes, consisting of superficially located amino acid residues and represent the actual target structures of HLA antibodies. Our aim was to unravel whether there are high-risk EMM that are more likely to lead to the formation of de novo donorspecific antibodies (dnDSA) than others.

We examined 148 kidney donor-recipient pairs regarding their mismatched eplets leading to the development of dnDSA, transplanted at the Goethe university hospital Frankfurt between 2018 and 2022. HLA high-resolution typing of donor and patient for 11 HLA loci was carried out using NGSgo-MX11-3 kit (GenDx) and MiSeq Sequencer (Illumina). Eplet analysis was performed using HLA Matchmaker algorithm (HLA Fusion v.4.4.0, OneLambda-ThermoFisher). Only confirmed HLA eplets were considered. Monitoring for HLA class I and class II antibodies was performed by single antigen microbead assays (SAB) (OneLambda- Lab Screen and Lifecodes-Immucor) for screening and/or for antibody identification. Graph Pad Prism was used for student´s t-test.

In our cohort, 39 patients developed dnDSA, 4 of them suffered from graft failure. The medium EMM loads for class I and II of patients with dnDSA were higher than in the group without (class I: 9.2±5.9 vs. 12±7.3 (mean±SD), p=0.04/class II: 10±5.7 vs. 15±7.2, p=0.001). The mean MM load for both the DRB1 and the DQB1 locus alone was 6 each (range: 1-13/2-12) for patients with dnDSA, the majority of the values were below thresholds proposed earlier (Wiebe et al., 2017). Regarding the EMM there were some which led more often to the formation of dnDSA than others: 16 of the 146 eplets were involved in dnDSA formation with a probability of ≥ 25% (90th percentile) when they occurred. An accumulation of such EMMs was observed in the DQ locus.

We confirmed that some EMM lead more frequently to the formation of dnDSA. Some of our high-risk eplets (163R, 104A, 57V) were associated with increased risk of DCGF in a large cohort with imputed high-resolution typing (Mohammadhassanzadeh et al., 2021). EMM thresholds allow basic risk-stratification but thorough characterization of individual EMMs enable comprehensive assessment of the immunogenicity of a transplant and might provide improved matching strategies with reduced dnDSA formation.

References:

Mohammadhassanzadeh, H., Oualkacha, K., Zhang, W., Klement, W., Bourdiec, A., Lamsatfi, J., Yi, Y., Foster, B., Keown, P., Gebel, H. M., Claas, F., Sapir-Pichhadze, R., & Genome Canada Transplant, C. (2021). On Path to Informing Hierarchy of Eplet Mismatches as Determinants of Kidney Transplant Loss. Kidney Int Rep, 6(6), 1567-1579. https://doi.org/10.1016/j.ekir.2021.03.877

Wiebe, C., Rush, D. N., Nevins, T. E., Birk, P. E., Blydt-Hansen, T., Gibson, I. W., Goldberg, A., Ho, J., Karpinski, M., Pochinco, D., Sharma, A., Storsley, L., Matas, A. J., & Nickerson, P. W. (2017). Class II Eplet Mismatch Modulates Tacrolimus Trough Levels Required to Prevent Donor-Specific Antibody Development. J Am Soc Nephrol, 28(11), 3353-3362. https://doi.org/10.1681/ASN.2017030287

There are no conflicts of interests.