In Focus
Advancement of new molecular tools for discovery of blood groups
36% of all known systems have been identified in the last 12 years of the 124-year blood group history
Since their discovery over a century ago, blood group antigens have been studied with the help of the most progressive contemporary methods available. This reflects their importance not only in transfusion, maternal-fetal and transplantation medicine, but also in our understanding of inheritance, erythropoiesis, and erythrocyte membrane structures and functions.
Initially, the pace of discovery was slow and confined by the limits of technology, essentially restricted to basic observations of direct agglutination, resulting in only four systems being identified in the 45 years following the discovery of ABO. The pace was significantly accelerated after the development of the indirect antiglobulin test in 1945. A series of major technological advancements in biochemistry and molecular biology resulted in the characterisation of 25 new systems over the next 65-year period.
During this period, antigen and system characterisation was a stepwise, cumbersome, time-consuming process requiring a wide range of skills and equipment. The most important link between an antigen and its encoding gene and carrier molecule was often difficult to establish. The process would usually involve techniques such as immunoprecipitation, cDNA library screening, cloning and Sanger sequencing of individual candidate genes.
Today, much of this evidence can be acquired using relatively few, but highly sophisticated molecular tools, e.g., next generation sequencing (NGS), proteomics and genome-wide association studies (GWAS). The capability of NGS to analyse the whole human exome or genome in a single test, compared to the limited analysis of individual genes by Sanger sequencing, has been transformative. Consequently, identification of the genetic and protein background is today regarded as routine, and there is growing emphasis on expression studies to verify candidate genes and/or proteins identified through these powerful methods.
Enabled by these technological advancements, there has been a dramatic increase in the characterisation of new blood group systems; 36% of all known systems have been identified in the last 12 years of the 124-year blood group history. The 18 new systems ratified in this period were all characterised using either NGS, GWAS, proteomics, in silico analysis or combined approaches. However, it should be noted that despite the sophisticated technology, the starting point for characterisation of any novel antigen is still the serological investigation.
The latest two systems ratified by the ISBT Working Party on Red Cell Immunogenetics and Blood Group Terminology in 2024 are case examples of the creative use of new molecular technologies. The genetic basis of ATP11C (046) and MAL (047) were deduced through whole exome sequencing, with both studies including ex vivo expression work and extensive genetic, biological, and structural characterisation; MAL resolved the molecular basis of the known high-prevalence antigen AnWj, whilst ATP11C represented a de novo system.
Although only a handful of blood group antigens now remain unresolved, this momentum in the blood group characterisation will not end with the currently recognised 47 systems. The advent of technologies such as third generation sequencing, and the integration of artificial intelligence and machine learning will ensure the continued development of our understanding of blood groups within biomedicine and personalised patient care.
