O001 A novel molecular HLA mismatch algorithm to identify transplant patients at low risk of primary alloimmunity

Abstract

Abstract Introduction There is an unmet need for prognostic biomarkers for alloimmune risk stratification to guide personalised recipient care kidney transplantation. Methods We used three molecular Mismatch (molMM) algorithms - Amino-Acid-Mismatch-Score (AAMS), Electrostatic-Mismatch-Score (EMS3D) and NetMHCIIpan in a dataset of patients receiving standardised donor lymphocyte injections to predict de-novo donor-specific-antibody (dnDSA) at the individual HLA level (n=665). Risk thresholds were derived for HLA-DR/DQ mismatch and algorithms combined. External validation was performed in two extensively-phenotyped kidney transplant cohorts (Manitoba, n=856, Denver n=404) and in the NHSBT kidney transplant registry (2000–2020, n=27,028). Results External validation (Manitoba cohort, 10-year follow-up) showed all algorithms predicted dnDSA development using experimentally derived HLA-DR/DQ molMM risk thresholds (HLA-DQ AUC: 0.78-0.80; HLA-DR AUC:0.76-0.81). AAMS and EMS3D had improved risk stratification (low-medium-high risk groups for HLA-DR+DQ dnDSA) vs NetMHCIIpan (p=NS). A combined AAMS+EMS3D molMM algorithm further improved discrimination and identified a large patient cohort (15.4% patients) at very-low risk of Class-II dnDSA (1.3% at 10 years). Multivariate analysis confirmed correlation with primary alloimmune events (dnDSA p<0.001, TCMR p<0.001, ABMR p=0.0049) and all-cause graft loss (p=0.0038). Further external validation of the combined molMM algorithm in an ethnically diverse cohort (Denver) confirmed the dnDSA risk association (p<0.0001), and in the UK registry cohort confirmed significant association with all-cause graft loss (p<0.001). Conclusion We developed and validated a novel molMM algorithm, incorporating information from HLA amino-acid sequence and tertiary structurebthat may be used as a prognostic biomarker of primary alloimmunity risk and to enrich prospective clinical trials in kidney transplantation.