Alloantibody to a Bw4 Epitope in a Bw4+ B*27: 05 Patient

Next generation sequencing of 11 HLA loci characterises a diverse UK cord blood bank

The introduction of next generation sequencing (NGS) for stem cell donor registry typing has contributed to faster identification of compatible stem cell donors. However, the successful search for a matched unrelated donor for some patient groups is still affected by their ethnicity. In this study, DNA samples from 714 National Health Service (NHS) Cord Blood Bank donors were typed for HLA-A, -B, -C, -DRB1, -DRB345, -DQA1, -DQB1, -DPA1 and -DPB1 by NGS. Analysis of the ethnic diversity showed a high level of diversity, with the cohort comprising of 62.3% European and 37.7% of either multi-ethnic or non-European donors, of which 12.3% were multi-ethnic. The HLA diversity was further confirmed using PyPop analysis, 405 distinct alleles were observed in the overall NHS-CBB cohort, of which 37 alleles are non-CWD, including A*31:14N, B*35:68:02, C*14:23 and DQA1*05:10. Furthermore, HLA-DQA1 and HLA-DPA1 analysis showed 12% and 10%, respectively, of the alleles currently submitted to IMGT, confirming further diversity of the NHS-CBB cohort. The application of 11 HLA loci resolution by NGS revealed a high level of diversity in the NHS-CBB cohort. The incorporation of this data coupled with ethnicity data could lead to improved donor selection, contributing to better clinical outcomes for patients.

Should HLA mismatch acceptability for sensitized transplant candidates be determined at the high-resolution rather than the antigen level?

Defining HLA mismatch acceptability of organ transplant donors for sensitized recipients has traditionally been based on serologically defined HLA antigens. Now, however, it is well accepted that HLA antibodies specifically recognize a wide range of epitopes present on HLA antigens and that molecularly defined high resolution alleles corresponding to the same low resolution antigen can possess different epitope repertoires. Hence, determination of HLA compatibility at the allele level represents a more accurate approach to identify suitable donors for sensitized patients. This approach would offer opportunities for increased transplant rates and improved long term graft survivals.

Human leukocyte antigen Bw4 and Bw6 epitopes recognized by antibodies and natural killer cells

PURPOSE OF REVIEW

To describe the structural basis of human leukocyte antigen (HLA) Bw4 and Bw6 epitopes that are recognized by antibodies and the KIR3DL1 natural killer cell receptor.

RECENT FINDINGS

Molecular modeling and X-ray crystallography have refined our understanding of Bw4 and Bw6. These epitopes had been defined by comparison of HLA allele sequences and by site-directed mutagenesis. Anti-Bw4 and anti-Bw6 antibodies and KIR3DL1 receptors recognize HLA α-1 α-helix residues 77-83 in combination with other HLA regions. The variability of HLA sequences within the 77-83 region and at other sites indicates that the Bw4 epitope is complex. Adding complexity, HLA-bound peptides influence Bw4 and Bw6 epitopes. These structures are recognized by diverse antibodies and KIR3DL1 allotypes. This diversity allowed a Bw4 patient to produce anti-Bw4 antibody without breaking self-tolerance.

SUMMARY

Bw4 and Bw6 epitopes are best regarded as families of related structures that are recognized by a diverse array of antibodies and KIR3DL1 allotypes.