Nicholas K. Brown

The rapid advances in HLA genotyping technology and the massive amounts of associated data have created a demand for better and more efficient laboratory data management practices. However, while some standards have been developed, there is a need for comprehensive guidelines that include all laboratory data‐related processes such as messaging, storage and retention, documentation, reporting, validation and quality control. An important consideration in developing these recommendations is the feasibility of application in a laboratory setting without posing a substantial staff and cost burden for implementation and long‐term maintenance and the availability of publicly available tools. This article presents evidence‐based recommendations for multiple laboratory general data practices, focusing on HLA genotyping data and associated meta‐data. These recommendations are compiled by experts in the fields of histocompatibility and immunogenetics (H&I) and representation from multiple H&I worldwide professional society leadership with the long‐term goal of adopting these recommendations in future laboratory accreditation requirements.

Standardised data representation is fundamental to the integrity, interoperability and reproducibility of immunogenetics and histocompatibility testing. While well‐established standards such as the genotype list (GL) String, histoimmunogenetics markup language (HML) and minimum information for reporting next‐generation sequence genotyping exist for encoding HLA genotyping results, no equivalent syntax currently exists for describing phenotype‐ or antigen‐level information that underlies antibody testing and immunological risk assessment. We introduce the phenotype list (PL) String grammar and the phenotype list string code (PLSC) syntax, structured, machine‐readable grammars designed to represent antigen‐ and protein‐level data across three contexts: (1) the HLA phenotype composition of assay reagents, (2) test results derived from those reagents and (3) clinical interpretations of HLA antibody specificities. PL String extends the hierarchical logic of the GL String grammar, while adapting a subset of GL String delimiters and rules to describe ambiguity, heterodimeric relationships and phenotypic composition. PL String incorporates explicit namespace definitions (e.g., World Health Organization HLA Nomenclature Committee for Factors of the HLA System, Organ Procurement and Transplantation Network, Eurotransplant and NMDP) to ensure traceability and compatibility with existing regulatory and operational frameworks. By harmonising how HLA phenotypic and antibody data are encoded, PL Strings enable automated data exchange between laboratories, registries and information systems, reducing transcription errors and improving computational interpretation. This new grammar establishes a foundation for interoperable representation of serologic and functional HLA data, facilitating reproducible research and enhancing clinical decision support in transplantation and immunogenetics. Technical specifications for PL Strings and PLSCs are available at plstring.org .

A comprehensive toolkit for clinical Human Leukocyte Antigen (HLA) informatics, built on 'tidyverse' principles and making use of genotype list string (GL string, Mack et al. (2023) ) for storing and computing HLA genotype data. Specific functionalities include: coercion of HLA data in tabular format to and from GL string; calculation of matching and mismatching in all directions, with multiple output formats; automatic formatting of HLA data for searching within a GL string; truncation of molecular HLA data to a specific number of fields; and reading HLA genotypes in HML files and extracting the GL string.

We describe a unique ABO compatible and 9/10 HLA‐matched case of successful allogeneic hematopoietic cell transplantation (HCT) after effective desensitization of a strong anti‐HLA‐A24 donor‐specific antibody (DSA) with mean fluorescence intensity of approximately 18 000. Due to absence of a suitable matched unrelated donor the patient sibling was considered the best available donor, and it was decided to desensitize patient prior to transplant. The strength of HLA‐A24 DSA slowly decreased over the course of treatment, necessitating a total of 23 sessions of therapeutic plasma exchange in order to bring the DSA strength to undetectable levels, followed by a successful transplant. In summary, the outcome of this case shows effective application of desensitization treatment to remove strong DSA in HCT patients.