P143 Determining the serologic equivalent of a relatively rare common allele DRB1∗11:17

Aim Many common and well-documented (CWD) alleles have not been assigned official World Health Organization (WHO) approved serologic equivalents, which often makes the reporting of time-sensitive deceased donor typing and virtual crossmatch very challenging. Here we report the characterization of the serologic reactivity of a relatively rare CWD allele, DRB1 ∗ 11:17. Methods A 31 year-old African American female deceased donor was presented for HLA typing using the real-time (RT) PCR and PCR-SSP methods at the low-intermediate resolution. High resolution typing was retrospectively performed by SBT. Serologic specificity was investigated by way of surrogate flow cytometric crossmatch (FCXM) using donor lymphocytes and selected patient sera with well characterized antibody specificities as defined by single antigen solid-phase assays. Results Donor DR typing was confirmed by all assays as DRB1 ∗ 11:01, DRB1 ∗ 11:17. According to the NMDP database, DRB1 ∗ 11:17 has an overall frequency 0.04% in African Americans, where most commonly found, and accounts for 0.27% of all DR11 alleles reported. While there is no official WHO assigned serologic specificity for DRB1 ∗ 11:17, the artificial Neural Network (NN) analysis predicted it to react as DR14. Of the 9 surrogate FCXMs performed using selected sera containing antibody reactivity to DR14 (5 to DRB1 ∗ 14:01 only; 2 to DRB1 ∗ 14:02 only; 2 to both DRB1 ∗ 14:01/14:02) at various strengths (2000–14000 MFI), 8 resulted in positive B-cell crossmatches. No noticeable difference was observed between the reactivity to DRB1 ∗ 14:01 vs 14:02. The one negative crossmatch could be attributed to a rather weak DR14 reactivity ( ∗ 11:17 could not be determined, as the other donor haplotype also contained a DRB1 ∗ 11 allele. Protein sequence analysis indicated that, while DRB1 ∗ 11:17 was assigned to the DRB1 ∗ 11 allele group, it contained 7 amino acid (aa) substitutions compared to DRB1 ∗ 11:01/11:02, whereas it contained ⩽ 4 aa substitutions as compared to DRB1 ∗ 14:01G, indicating a higher sequence homology to DRB1 ∗ 14 than to DRB1 ∗ 11 alleles. Conclusion In this study, the serologic specificity of DRB1 ∗ 11:17 has been confirmed as DR14, which is consistent to that predicted by the NN analysis.