THE FUTURE OF NEXT-GENERATION SEQUENCING FOR BLOOD GROUP GENOTYPING AND ITS IMPLICATIONS IN TRANSFUSION MEDICINE
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Alloimmunisation becomes a problem when serological discrepancies occur in matching antigens between donors and patients for blood transfusion. The rate of alloimmunisation has been increased especially in multiply transfused patients. Blood group genotyping (BGG) is a DNA-based assay that aids in reducing this situation. Currently, many platforms of BGG have become available, in which every technique has its own advantages and disadvantages. All these platforms lack the ability to identify novel alleles that might have an unknown clinical significance. The advent of next-generation sequencing (NGS) offers identification of the unprecedented alleles due to its basis of sequence-based typing. Moreover, it provides an extreme high-throughput which may be able to screen many donors and patients in a single run. In this project, two approaches have been developed in generating sequencing libraries followed by sequencing on the Ion Torrent Personal Genome MachineTM platform (Ion PGMTM). The first approach was amplicon-based target selection using Ion AmpliseqTM Custom Panel, designated as Human Erythrocyte Antigens and Human Platelet Antigens Panel (HEA and HPA Panel). This panel assay screens 11 blood group systems, as well as 16 human platelet antigens. The outcome was extraordinary, in particular four novel alleles had been identified out of 28 samples, one in the RHCE gene 208C>T (Arg70Trp) in exon 2 and three in the KEL gene. The first SNP was 331G>A (Ala111Thr) in exon 4. The second SNP was 1907C>T (Ala636Val) in exon 17 and the third SNP was 2165T>C (Leu722Pro) in exon 19. However, some issues occurred regarding co-amplification of homologous genes. The second approach was a long-range polymerase chain reaction (LR-PCR) based approach. This method provided a high resolution assay by amplification of entire genes, including the non-coding area, of the Kell and Rh blood group systems. The Kell blood group was initially utilised as a model in order to apply the same approach on the Rh system. Most alleles encoding the antigens of the Kell blood group, especially the high prevalence ones, were identified. The Rh LR-PCR approach was carried out by amplification of the RHD and RHCE genes with seven amplicons. For five RhD-positive samples no mutations were observed within the coding areas. On the other hand, five serotyped weak D samples were genotyped as; two weak D type 1, two weak D type 2 and one DAR3.1 weak partial D 4.0 (RHD*DAR3.01). Regarding the RHCE, the following antigens (C, c, E, c) were predicted properly from the sequencing data. Moreover, the RHCE*ceVS.02 was identified. 64 and 39 intronic SNPs were identified in RHD and RHCE genes, respectively. The intronic SNPs assisted the genotyping process by identifying the haplotype of interest. Interestingly, the novel allele identified in the RHCE gene by the HEA and HPA Panel was confirmed to belong to the RHCE gene by the LR-PCR approach, indicating the panel misaligned it to the RHD gene. In conclusion, NGS paves the way to be an alternative substitution to the previous molecular techniques. It would supplant the conventional serology for typing blood for transfusion.
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