Vox Sanguinis International Forum on application of fetal blood grouping: summary

Equity in blood transfusion precision services

BACKGROUND

Blood collection agencies are integrating precision medicine techniques to improve and individualise blood donor and recipient outcomes. These organisations have a role to play in ensuring equitable application of precision medicine technologies for both donors and transfusion recipients. BODY: Precision medicine techniques, including molecular genetic testing and next generation sequencing, have been integrated in transfusion services to improve blood typing and matching with the aim to reduce a variety of known transfusion complications. Internationally, priorities in transfusion research have aimed to optimise services through the use of precision medicine technologies and consider alternative uses of genomic information to personalise transfusion experiences for both recipients and donors. This has included focusing on the use of genomics when matching blood products for transfusion recipients, to personalise a blood donor's donation type or frequency, and longitudinal donor research utilising blood donor biobanks.

CONCLUSION

Equity in precision services and research must be of highest importance for blood collection agencies to maintain public trust, especially when these organisations rely on volunteer donors to provide transfusion services. The investment in implementing equitable precision medicine services, including development of blood donor biobanks, has the potential to optimise and personalise services for both blood donors and transfusion recipients.

Antenatal RHD screening to guide antenatal anti-D immunoprophylaxis in non-immunized D- pregnant women

In pregnancy, D- pregnant women may be at risk of becoming immunized against D when carrying a D+ fetus, which may eventually lead to hemolytic disease of the fetus and newborn. Administrating antenatal and postnatal anti-D immunoglobulin prophylaxis decreases the risk of immunization substantially. Noninvasive fetal RHD genotyping, based on testing cell-free DNA extracted from maternal plasma, offers a reliable tool to predict the fetal RhD phenotype during pregnancy. Used as a screening program, antenatal RHD screening can guide the administration of antenatal prophylaxis in non-immunized D- pregnant women so that unnecessary prophylaxis is avoided in those women who carry a D- fetus. In Europe, antenatal RHD screening programs have been running since 2009, demonstrating high test accuracies and program feasibility. In this review, an overview is provided of current state-of-the-art antenatal RHD screening, which includes discussions on the rationale for its implementation, methodology, detection strategies, and test performance. The performance of antenatal RHD screening in a routine setting is characterized by high accuracy, with a high diagnostic sensitivity of ≥99.9 percent. The result of using antenatal RHD screening is that 97-99 percent of the women who carry a D- fetus avoid unnecessary prophylaxis. As such, this activity contributes to avoiding unnecessary treatment and saves valuable anti-D immunoglobulin, which has a shortage worldwide. The main challenges for a reliable noninvasive fetal RHD genotyping assay are low cell-free DNA levels, the genetics of the Rh blood group system, and choosing an appropriate detection strategy for an admixed population. In many parts of the world, however, the main challenge is to improve the basic care for D- pregnant women.

Prediction of fetal blood group antigens from maternal plasma using Ion AmpliSeq HD technology

BACKGROUND

Fetal blood group (BG) and platelet (HPA) antigens may trigger maternal immunization, causing a fetal disease. Noninvasive prenatal diagnostics (NIPT) predicts fetal genotype, identifying pregnancies with no risk. All current techniques detect fetal antigen alleles with unspecific background and without estimation of fetal fraction, thus new protocols for detection of fetal BG/HPA alleles with ultrahigh sensitivity still need to be tested to improve NIPT.

AIM

To design NIPT of clinically important antigens using Ion AmpliSeq HD technology.

METHODS

Plasma DNA from 36 pregnant women (9-33 week of gestation, 24 immunized with anti-HPA-1a,-3b,-15a, -K, or -D+C+S), with known BG/HPA genotypes of their neonates/partners, was tested on Ion S5 System using the Ion AmpliSeq HD designer custom gene panel. NGS contained 25 rs-targets encoding relevant BG/HPA antigens and 10 markers.

RESULTS

Using the NGS protocol, 76 out of 85 differences in fetal/maternal BG/HPA genotypes were determined in concentration above 2% fetal paternally inherited allele chimerism. The level of unspecific reads for BG/HPA alleles was below 0.87%. In 24 immunized women NGS revealed feto-maternal incompatibility in 11 cases (from 2.44% to 7.41%) and excluded in 10 (<0.05%), three cases had inconclusive results (1.79%, 0.19%, 0.11%). The presence of fetal DNA was confirmed in each case by detecting markers with at least 2% chimerism.

CONCLUSION

The use of Ion AmpliSeq HD technology improves the prediction of feto-maternal incompatibility, increasing the sensitivity of BG/HPA NIPT and serving confirmation of the fetal DNA at the same workflow.

The role of non-invasive prenatal testing (NIPT) for fetal blood group typing in Australia

Maternal alloimmunisation against red blood cell antigens can cause haemolytic disease of the fetus and newborn (HDFN). Although most frequently caused by anti-D, since the implementation of rhesus D (RhD) immunoglobulin prophylaxis, other alloantibodies have become more prevalent in HDFN. Recent advances in non-invasive prenatal testing (NIPT) have allowed early prediction of HDFN risk in alloimmunised pregnancies and allow clinicians to focus health resources on those pregnancies that require intervention. This article aims to provide updates on the current status of NIPT in Australia as both a diagnostic and screening tool in pregnancy.

Noninvasive fetal RHD genotyping to guide targeted anti-D prophylaxis-an external quality assessment workshop

BACKGROUND AND OBJECTIVES

Fetal RHD genotyping of cell-free fetal DNA from RhD-negative pregnant women can be used to guide targeted antenatal and postnatal anti-D prophylaxis for the prevention of RhD immunization. To assure the quality of clinical testing, we conducted an external quality assessment workshop with the participation of 28 laboratories.

MATERIALS AND METHODS

Aliquots of pooled maternal plasma were sent to each laboratory. One sample was positive, and the second sample was negative for fetal RHD, verified by pre-workshop testing using quantitative real-time PCR (qPCR) analysis of RHD exons 4, 5, 7 and 10. Plasma samples were shipped at room temperature. A reporting scheme was supplied for data collection, including questions regarding the methodological setup, results and clinical recommendations. Different methodological approaches were used, all employing qPCR with a total of eight different combinations of RHD exon targets. The samples were tested blindly.

RESULTS

Fetal RHD genotyping was performed with no false-negative and no false-positive results. One inconclusive result was reported for the RHD-positive sample, and four inconclusive results were reported for the RHD-negative sample. All clinical conclusions were satisfactory.

CONCLUSION

This external quality assessment workshop demonstrates that despite the different approaches taken to perform the clinical assays, fetal RHD genotyping is a reliable laboratory assay to guide targeted use of Rh prophylaxis in a clinical setting.

Blood group genotyping

Genomics is affecting all areas of medicine. In transfusion medicine, DNA-based genotyping is being used as an alternative to serological antibody-based methods to determine blood groups for matching donor to recipient. Most antigenic polymorphisms are due to single nucleotide polymorphism changes in the respective genes, and DNA arrays that target these changes have been validated by comparison with antibody-based typing. Importantly, the ability to test for antigens for which there are no serologic reagents is a major medical advance to identify antibodies and find compatible donor units, and can be life-saving. This review summarizes the evolving use and applications of genotyping for red cell and platelet blood group antigens affecting several areas of medicine. These include prenatal medicine for evaluating risk of fetal or neonatal disease and candidates for Rh-immune globulin; transplantation for bone marrow donor selection and transfusion support for highly alloimmunized patients and for confirmation of A2 status of kidney donors; hematology for comprehensive typing for patients with anemia requiring chronic transfusion; and oncology for patients receiving monoclonal antibody therapies that interfere with pretransfusion testing. A genomics approach allows, for the first time, the ability to routinely select donor units antigen matched to recipients for more than ABO/RhD to reduce complications. Of relevance, the growth of whole-genome sequencing in chronic disease and for general health will provide patients' comprehensive extended blood group profile as part of their medical record to be used to inform selection of the optimal transfusion therapy.

Developments beyond blood group serology in the genomics era

Blood group serology and single nucleotide polymorphism-based genotyping platforms are accurate but do not provide a comprehensive cover for all 36 blood group systems and do not cover the antigen diversity observed among population groups. This review examines the extent to which genomics is shaping blood group serology. Resources for genomics include the Human Reference Genome Sequence assembly; curated blood group tables listing variants; public databases providing information on genetic variants from world-wide studies; and massively parallel sequencing technologies. Blood group genomic studies span the spectrum, from bioinformatic data mining of huge data sets containing whole genome and whole exome information to laboratory investigations utilising targeted sequencing approaches. Blood group predictions based on genome sequencing and genomic studies are proving accurate, and have shown utility in both research and reference settings. Overall, studies confirm the potential for blood group genomics to reshape donor and patient transfusion management strategies to provide more compatible blood transfusions.

Prediction of fetal blood group and platelet antigens from maternal plasma using next-generation sequencing

BACKGROUND

Fetuses whose mothers have produced antibodies to red blood cell (RBC) or platelet antigens are at risk of being affected by hemolytic disease or alloimmune thrombocytopenia, respectively, only if they inherit the incompatible antigen. Noninvasive diagnosis of the fetal antigen is employed for management of immunized pregnancies, but the specific detection of SNPs, encoding the majority of antigens, in maternal plasma is still a challenge. We applied targeted next-generation sequencing (NGS) to predict the fetal antigen based on the detection of fetomaternal chimerism.

METHODS AND MATERIALS

The DNA of 13 pregnant women (with anti-K [3] anti-k [1], anti-Fy^a [1], anti-D + C + Jk^a [1], anti-D + E + K [1], anti-HPA-1a [1], anti-HPA-3b [1], anti-HPA-5b [1], and nonimmunized [3]) was sequenced using primers for regions encoding RhD, RhC, Rhc, RhE/e, K/k, Fya/b, Jka/b, MN, Ss, and HPA-1, 2, 3, 5, 15, 4 X-polymorphisms on the Ion Torrent Personal Genome Machine (PGM) System (Thermo Fisher Scientific, Inc., Waltham, MA, USA).

RESULTS

NGS results were in agreement with the phenotype/genotype of women and their neonates (except for the unsuccessful detection of MN and RhC). NGS determined fetal allele chimerism for K, k, Fya, Fyb, Jka, Jkb, S, RhE (from 0.42% to 6.08%); RhD, Rhc (100%); HPA-1a, -2b, -3a, 3b, -5b, -15a, 15b (from 0.23% to 4.11%). NGS revealed fetal chimerism for incompatible antigens (from 0.7% to 4.8%) in 7 immunized cases, excluded in 3 (with anti-K, anti-Fy^a , anti-HPA-3b).

CONCLUSION

The designed NGS predicts the fetal RBC and platelet antigen status universally in cases with various clinically significant antibodies as well as providing confirmation of the presence of fetal DNA. However, some improvement of the unsuccessful primers is required.