HLA-B leader genotypes in a clinical population

Influence of HLA-B Leader (-21M/T) Dimorphism With Bw4/Bw6 Epitopes on Graft Versus Host Disease After Allogenic Haematopoietic Stem Cell Transplantation in North Indians

High degree of variability in human leukocyte antigens (HLAs) system restricts availability of histocompatible HLA-matched-related donors, thus increasing reliance on worldwide bone marrow registries network. Nevertheless, due to limited coverage/accessibility/affordability of some ethnicities in these registries, haploidentical haematopoietic stem cell transplantation (HSCT) emerged as an alternative option, though with allorecognition-mediated graft versus host disease (GvHD) (>40% cases). A dimorphism [-21 methionine (M) or threonine (T)] in HLA-B leader peptide (exon 1) which differentially influences its HLA-E binding, plausibly regulates natural killer cell functionality, affecting GvHD vulnerability and clinically in practice for donor selection. Here, we analysed population-specific influence of this functionally relevant dimorphism on post HSCT GvHD occurrence and clinical utility (if any) towards defining donor permissibility. High resolution HLA-B genotyping data were analysed in 178 study participants, including 89 HSCT patient-donor pairs, for the frequency distribution of -21 leader dimorphism. Distribution of HLA-Bw4/Bw6 was deduced with killer cell immunoglobulin receptor ligand calculator tool in IPD-IMGT/HLA database. Though -21T (∼85%) was over represented in the study participants, no significant influence is observed for this variant between HLA-identical v/s haplo HSCT either with or without GvHD, at allelic and genotypic levels as well as in BLEAT (HLA-B Leader Assessment Tool)-based donor-recipient matching. Stratified analysis of -21 M/T into Bw4/Bw6 groups revealed a higher frequency of -21T + Bw4 in GvHD (+) group compared to GvHD (-) (p < 0.05), plausibly linking this haplotype with occurrence of GvHD post HSCT and importance of HLA class I-mediated NK cell functionality in GvHD.

The Novel HLA-B*38:123 Allele With A Unique M-Leader Sequence

HLA-B*38:123 differs from HLA-B*38:01:01:01 by a single nucleotide substitution in codon -14 in exon 1.

The novel HLA-B*44:387 allele shows a -21 methionine residue in the signal peptide

Characterization of the novel HLA‐B*44:387 allele.

The genotype list string code syntax for exchanging nomenclature-level genotyping results in clinical and research data management and analysis systems

The nomenclatures used to describe HLA and killer-cell immunoglobulin-like receptor (KIR) alleles distinguish unique nucleotide and peptide sequences, and patterns of expression, but are insufficient for describing genotyping results, as description of ambiguities and relations across loci require terminology beyond allele names. The genotype list (GL) String grammar describes genotyping results for genetic systems with defined nomenclatures, like HLA and KIR, documenting what is known and unknown about a given genotyping result. However, the accuracy of a GL String is dependent on the reference database version under which it was generated. Here, we describe the GL string code (GLSC) system, which associates each GL String with meta-data describing the specific reference context in which the GL String was created, and in which it should be interpreted. GLSC is a defined syntax for exchanging GL Strings in the context of a specific gene-family namespace, allele-name code-system, and pertinent reference database version. GLSC allows HLA and KIR genotyping data to be transmitted, parsed and interpreted in the appropriate context, in an unambiguous manner, on modern data-systems, including Health Level 7 Fast Healthcare Interoperability Resource systems. Technical specification for GLSC can be found at https://glstring.org.