Blood donor genotyping for prediction of blood group antigens: Results from 5 years' experience (2017-2022)

BACKGROUND AND OBJECTIVES

For 5 years, routine genotyping has been performed for selected blood groups of blood donors in the Copenhagen Capital Region, Denmark. The result is summarized in the following.

MATERIALS AND METHODS

Genotyping was carried out by an external service provider using the competitive allele specific PCR (KASP) technology. The genotypes were returned to the blood bank and translated into phenotypes by a proprietary IT application.

RESULTS

In total, 65 alleles from 16 blood group systems (ABO, MNS, Rh, Lutheran, Kell, Duffy, Kidd, Diego, Yt, Dombrock, Colton, Landsteiner-Wiener, Cromer, Knops, Vel, secretor status) and the HPA1, HPA5 and HPA15 antigens were interrogated. After translation, phenotypes were imported into the laboratory information management system of the blood bank. The results from 31,538 genotyped blood donors were used to calculate the allele frequencies for a Danish blood donor population. ABO genotyping was done for sample ID purposes. Determination of the 1061delC single nucleotide polymorphism (SNP) (NM_020469.2), most frequently characteristic of ABO*A2, was validated against a series of 1287 samples with Dolichos biflorus lectin determination of the A1 phenotype.

CONCLUSION

We report allele frequencies and phenotype frequencies for 16 blood groups from a total of 31,538 genotyped blood donors. Blood products were supplied from a total of 64,312 active blood donors, and of these active blood donors 25,396 (39.5%) were genotyped. These donors represent a valuable resource for patient treatment. This genotyping has enabled the provision of rare genotyped donor blood for patients with alloantibodies and rare reagent cells for serology.

Reduced susceptibility to COVID-19 associated with ABO blood group and pre-existing anti-A and anti-B antibodies

BACKGROUND

Susceptibility to severe acute respiratory syndrome coronavirus 2 shows individual variability in un-vaccinated and previously un-exposed individuals. We investigated the impact of ABO blood group, titers of anti-A and anti-B, other blood group antigens, and the extracellular deposition of ABH antigens as controlled by secretor fucosyltransferase 2 (FUT2) status.

STUDY DESIGN AND METHODS

We studied incidents in three different hospitals between April to September 2020, where un-diagnosed coronavirus disease 2019 (COVID-19) patients were cared for by health care workers without use of personal protection and with close contact while delivering therapy. We recruited 108 exposed staff, of whom 34 were diagnosed with COVID-19. ABO blood type, titer of anti-A and -B, blood group specific alleles, and secretor status were determined.

RESULTS

Blood group O was associated with lower risk of COVID-19 (OR 0.39, 95 %CI (0.16-0.92), p = 0.03) compared to non-O, i.e., blood groups A, B and AB. High titer anti-A immunoglobulin G (IgG) compared to low titer was associated with lower risk of COVID-19 (OR 0.24 95 %CI (0.07-0.78), p = 0.017). High titer of anti-B immunoglobulin M (IgM) compared to no anti-B (IgM) was associated with lower risk of COVID-19 (OR 0.16, 95 %CI (0.039-0.608), p = 0.006) and the same applies to low titer anti-B (IgM) compared to no titer (OR 0.23, 95 %CI (0.07-0.72), p = 0.012). The 33Pro variant in Integrin beta-3, that is part of human platelet antigen 1b (HPA-1b), was associated with lower risk of COVID-19 (OR 0.23, 95 %CI (0.034-0.86), p = 0.028).

CONCLUSION

Our data showed that blood group O, anti-A (IgG) titer, anti-B (IgM) titer as well as HPA-1b are associated with lower risk for COVID-19.

Secretor status of blood group O mothers is associated with development of ABO haemolytic disease in the newborn

BACKGROUND AND OBJECTIVES

Identification of antibody characteristics and genetics underlying the development of maternal anti-A/B linked to inducing haemolytic disease of the foetus and newborn could contribute to the development of screening methods predicting pregnancies at risk with high diagnostic accuracy.

MATERIALS AND METHODS

We examined 73 samples from mothers to 37 newborns with haemolysis (cases) and 36 without (controls). The secretor status was determined by genotyping a single nucleotide polymorphism in FUT2, rs601338 (c.428G>A).

RESULTS

We found a significant association between secretor mothers and newborns developing haemolysis (p = 0.028). However, stratifying by the newborn's blood group, the association was found only in secretor mothers to blood group B newborns (p = 0.032). In fact, only secretor mothers were found in this group. By including antibody data from a previous study, we found higher median semi-quantitative levels of IgG1 and IgG3 among secretor mothers than non-secretor mothers to newborns with and without haemolysis.

CONCLUSION

We found that the maternal secretor status is associated with the production of anti-A/B, pathogenic to ABO-incompatible newborns. We suggest that secretors experience hyper-immunizing events more frequently than non-secretors, leading to the production of pathogenic ABO antibodies, especially anti-B.

Droplet digital PCR-based testing for donor-derived cell-free DNA in transplanted patients as noninvasive marker of allograft health: Methodological aspects

In solid organ transplantation, donor-derived cell-free DNA (dd-cfDNA) is a promising universal noninvasive biomarker for allograft health, where high levels of dd-cfDNA indicate organ damage. Using Droplet Digital PCR (ddPCR), we aimed to develop an assay setup for monitoring organ health. We aimed to identify the least distinguishable percentage-point increase in the fraction of minute amounts of cfDNA in a large cfDNA background by using assays targeting single nucleotide polymorphisms (SNPs). We mimicked a clinical sample from a recipient in a number of spike-in experiments, where cfDNA from healthy volunteers were mixed. A total of 40 assays were tested and approved by qPCR and ddPCR. Limit of detection (LOD) was demonstrated to be approximately 3 copies per reaction, observed at a fraction of 0.002%, and which would equal 6 copies per mL plasma. Limit of quantification (LOQ) was 35 copies per reaction, estimated to 0.038%. The lowest detectable increase in percentage point of dd-cfDNA was approximately 0.04%. Our results demonstrated that ddPCR has great sensitivity, high precision, and exceptional ability to quantify low levels of cfDNA. The ability to distinguish small differences in mimicking dd-cfDNA was far beyond the desired capability. While these methodological data are promising, further prospective studies are needed to determine the clinical utility of the proposed method.

Laboratory Monitoring of Mother, Fetus, and Newborn in Hemolytic Disease of Fetus and Newborn

Background

Laboratory monitoring of mother, fetus, and newborn in hemolytic disease of fetus and newborn (HDFN) aims to guide clinicians and the immunized women to focus on the most serious problems of alloimmunization and thus minimize the consequences of HDFN in general and of anti-D in particular. Here, we present the current approach of laboratory screening and testing for prevention and monitoring of HDFN at the Copenhagen University Hospital in Denmark.

Summary

All pregnant women are typed and screened in the 1st trimester. This serves to identify the RhD-negative pregnant women who at gestational age (GA) of 25 weeks are offered a second screen test and a non-invasive fetal RhD prediction. At GA 29 weeks, and again after delivery, non-immunized RhD-negative women carrying an RhD-positive fetus are offered Rh immunoglobulin. If the 1st trimester screen reveals an alloantibody, antenatal investigation is initiated. This also includes RhD-positive women with alloantibodies. Specificity and titer are determined, the fetal phenotype is predicted by non-invasive genotyping based on cell-free DNA (RhD, K, Rhc, RhC, RhE, ABO), and serial monitoring of titer commences. Based on titers and specificity, monitoring with serial peak systolic velocity measurements in the fetal middle cerebral artery to detect anemia will take place. Intrauterine transfusion is given when fetal anemia is suspected. Monitoring of the newborn by titer and survival of fetal red blood cells by flow cytometry will help predict the length of the recovery of the newborn.

ABO haemolytic disease of the newborn: Improved prediction by novel integration of causative and protective factors in newborn and mother

BACKGROUND AND OBJECTIVES

Prediction of haemolytic disease of the foetus and newborn (HDFN) caused by maternal anti-A/-B enables timely therapy, thereby preventing the development of kernicterus spectrum disorder. However, previous efforts to establish accurate prediction methods have been only modestly successful.

MATERIALS AND METHODS

In a case-control study, we examined 76 samples from mothers and 76 samples from their newborns; 38 with and 38 without haemolysis. The IgG subclass profile of maternal anti-A and anti-B was determined by flow cytometry. Samples from newborns were genetically analysed for the A² subgroup, secretor and FcγRIIa receptor alleles.

RESULTS

Surprisingly, we found a correlation between the newborn secretor allele and haemolysis (p = 0.034). No correlation was found for FcγRIIa alleles. The A² subgroup was found only in newborns without haemolysis. Unexpectedly, different reaction patterns were found for maternal anti-A and anti-B; consequently, the results were treated separately. For the prediction of haemolysis in A-newborns, the maternal IgG1 subclass determination resulted in an accuracy of 83% at birth. For B-newborns, an accuracy of 91% was achieved by the maternal IgG2 subclass determination.

CONCLUSION

We improved the prediction of ABO-HDFN by characterizing maternal anti-A and anti-B by flow cytometry and we presented genetic traits in newborns with correlation to haemolysis. We propose a new understanding of A- and B-substances as immunogens that enhance the maternal immune response and protect the newborn, and we suggest that the development of ABO-HDFN is different when caused by maternal anti-A compared to maternal anti-B.

Early and Accurate Sex Determination by qPCR of Y Chromosome Repetitive Sequence (YRS) In Cell-Free Fetal DNA from Maternal Plasma

BACKGROUND

Circulating cell-free fetal DNA (cffDNA) provides the opportunity for noninvasive prenatal diagnosis. Early knowledge of the fetal sex is essential in cases with a risk of a sex-linked genetic disease. A reliable and highly sensitive sex determination test is required for first trimester testing because of the low amounts of cffDNA.

METHODS

First trimester blood samples from 326 pregnant women were analyzed by real-time quantitative polymerase chain reaction (qPCR) for the presence of Y chromosome repetitive sequence (YRS). Blood samples were collected from gestational weeks 4-12. Fetal sex was predicted on the basis of results from the YRS assay of cffDNA extracted from maternal plasma. The predicted sex was compared with the phenotypic sex of the newborn baby (n = 294).

RESULTS

There was high concordance between the test results from the YRS assay and the actual sex at birth. There were no false-positive results, indicating agreement between male YRS results and male sex at birth. Two results were false negative (from gestational weeks 4 and 6) predicting female fetuses, when the actual sex at birth was male. Overall, the sensitivity of the YRS assay was 98.6% (95% CI, 95.1%-99.8%), specificity was 100% (95% CI, 97.5%-100%), and accuracy was 99.3% (95% CI, 97.5%-99.9%). From 7 weeks of gestation, sensitivity, specificity, and accuracy were 100%.

CONCLUSIONS

This study shows that qPCR can be used to detect and quantify repetitive DNA sequences from 0.3 genome equivalents per milliliter of plasma. Prenatal sex determination by qPCR of YRS in cffDNA from maternal plasma was reliable and robust with cffDNA extracted from 1 mL of nonhemolyzed plasma, with a plasma equivalent per PCR of 167 μL. The YRS assay can be used for early noninvasive prenatal sex determination from a gestational age of 7 weeks.

Noninvasive Antenatal Screening for Fetal RHD in RhD Negative Women to Guide Targeted Anti-D Prophylaxis

RhD negative pregnant women who carry an RhD positive fetus are at risk of immunization against the D antigen, which may result in hemolytic disease of the fetus and the newborn. Predicting the fetal RhD status by noninvasive antenatal screening for the fetal RhD gene (RHD) can guide targeted use of antenatal anti-D prophylaxis.Cell-free fetal DNA is extracted from maternal plasma from RhD negative pregnant women at a gestational age of 25 weeks. A real-time PCR-based detection of two RHD exons enables reliable prediction of the fetal RhD status to determine the administration of antenatal prophylaxis, as well as postnatal prophylaxis.

How to evaluate PCR assays for the detection of low-level DNA

High sensitivity of PCR-based detection of very low copy number DNA targets is crucial. Much focus has been on design of PCR primers and optimization of the amplification conditions. Very important are also the criteria used for determining the outcome of a PCR assay, e.g. how many replicates are needed and how many of these should be positive or what amount of template should be used? We developed a mathematical model to obtain a simple tool for quick PCR assay evaluation before laboratory optimization and validation procedures. The model was based on the Poisson distribution and the Binomial distribution describing parameters for singleplex real-time PCR-based detection of low-level DNA. The model was tested against experimental data of diluted cell-free foetal DNA. Also, the model was compared with a simplified formula to enable easy predictions. The model predicted outcomes that were not significantly different from experimental data generated by testing of cell-free foetal DNA. Also, the simplified formula was applicable for fast and accurate assay evaluation. In conclusion, the model can be applied for evaluation of sensitivity of real-time PCR-based detection of low-level DNA, and may also assist in design of new assays before standard laboratory optimization and validation is initiated.

Next-generation sequencing: proof of concept for antenatal prediction of the fetal Kell blood group phenotype from cell-free fetal DNA in maternal plasma

BACKGROUND

Maternal immunization against KEL1 of the Kell blood group system can have serious adverse consequences for the fetus as well as the newborn baby. Therefore, it is important to determine the phenotype of the fetus to predict whether it is at risk. We present data that show the feasibility of predicting the fetal KEL1 phenotype using next-generation sequencing (NGS) technology.

STUDY DESIGN AND METHODS

The KEL1/2 single-nucleotide polymorphism was polymerase chain reaction (PCR) amplified with one adjoining base, and the PCR product was sequenced using a genome analyzer (GAIIx, Illumina); several millions of PCR sequences were analyzed.

RESULTS

The results demonstrated the feasibility of diagnosing the fetal KEL1 or KEL2 blood group from cell-free DNA purified from maternal plasma.

CONCLUSION

This method requires only one primer pair, and the large amount of sequence information obtained allows well for statistical analysis of the data. This general approach can be integrated into current laboratory practice and has numerous applications. Besides DNA-based predictions of blood group phenotypes, platelet phenotypes, or sickle cell anemia, and the determination of zygosity, various conditions of chimerism could also be examined using this approach. To our knowledge, this is the first report focused on antenatal blood group determination using NGS.

Is current serologic RhD typing of blood donors sufficient for avoiding immunization of recipients?

BACKGROUND

Avoiding immunization with clinically important antibodies is a primary objective in transfusion medicine. Therefore, it is central to identify the extent of D antigens that escape routine RhD typing of blood donors and to improve methodology if necessary.

STUDY DESIGN AND METHODS

We screened 5058 D- donors for the presence of the RHD gene, targeting Exons 5, 7, and 10 with real-time polymerase chain reaction. Samples that were positive in the screen test were investigated further by adsorption-elution, antibody consumption, flow cytometry, and sequencing of all RHD exons with intron-specific primers. Lookback was performed on all recipients of RBCs from RHD+ donors.

RESULTS

We found 13 RHD+ samples (0.26%). No variants or chimeras were found. Characterization of DNA revealed a novel DEL type (IVS2-2 A>G). In the lookback of the 136 transfusions with subsequent antibody follow-up, of which 13 were from DEL donors, one recipient developed anti-D. However, in this case, a competing and more likely cause of immunization was the concurrent transfusion of D+ platelets. Eleven recipients were immunized with 13 antibodies different from anti-D, of which five were anti-K.

CONCLUSION

In our laboratory, serologic RhD typing was safe. We detected all D variants and only missed DEL types. In assessing the immunization risk we included a DEL donor, found previous to this study, that did immunize a recipient with anti-D. We conclude that inadvertent immunization with D antigens in our setting was rare and in the order of 1.4 in 100,000 D- transfusions.

Improvement in fetal DNA extraction from maternal plasma. Evaluation of the NucliSens Magnetic Extraction system and the QIAamp DSP Virus Kit in comparison with the QIAamp DNA Blood Mini Kit

OBJECTIVE

Prenatal diagnostic assays have been developed using free fetal DNA circulating in the maternal blood of pregnant women. Efficient DNA extraction is crucial for a robust analysis. To improve fetal DNA yield, we tested two manual extraction methods--the NucliSens Magnetic Extraction (NMAG) system and the QIAamp DSP Virus Kit (QDSP)--against our current standard method, the widely used QIAamp DNA Blood Mini Kit (QDNA).

METHODS

The fetal DNA yield of the two extraction systems was evaluated using the RHD exon 7 as target in DNA extracts of 75 plasma samples from pregnant RhD-negative women, known to have given birth to RhD-positive infanto. The total DNA yield was evaluated in 23 samples, targeting GAPDH.

RESULTS

The fetal DNA yield was improved by a mean factor of 1.7 using the NMAG system, and improved by a mean factor of 1.5 using the QDSP. The total DNA yield was improved by a mean factor of 2.3 using the NMAG system, and by a mean factor of 1.3 using the QDSP.

CONCLUSION

Both extraction systems tested were superior to our standard with regard to DNA yield. This improvement may have a great impact on the success of genotyping in early pregnancy.

Quantitation of RHD by real-time polymerase chain reaction for determination of RHD zygosity and RHD mosaicism/chimerism: an evaluation of four quantitative methods

BACKGROUND

Determination of RHD zygosity of the spouse is crucial in preconception counseling of families with history of hemolytic disease of the fetus and newborn caused by anti-D. RHD zygosity can be determined by quantitative real-time polymerase chain reaction (PCR) basically by determining RHD dosage, and this feature is relevant in investigating RHD mosaicism and chimerism.

STUDY DESIGN AND METHODS

Monoplex and duplex real-time PCRs, uncalibrated and calibrated, were tested. RHD zygosity was determined for 72 samples and compared with serology-based prediction of RHD zygosity. Additionally, a range of constructed RHD dosages were compared with determined RHD dosages. Finally three samples, Days 1, 90, and 120, from a patient with loss of D were included.

RESULTS

All setups enabled differentiation between hemi- and homozygous samples. Results from calibrated methods had the smallest variation and enabled differentiation at the mean +/- 3SD. Incongruity between determined and predicted RHD zygosity was found in three samples. PCR-sequence-specific priming specific for the hybrid downstream Rhesus box was performed on those samples confirming the real-time PCR results. Determined RHD dosage equaled constructed RHD dosage in both calibrated real-time PCRs. Patient samples showed RHD with a mean of 1, 5, and 8 percent relative to GAPDH in all samples.

CONCLUSION

Duplex calibrated real-time PCR was a robust and exact method for determination of RHD zygosity and applicable in evaluation of RHD mosaicism and chimerism. This was illustrated with patient samples, where this assay revealed for the first time signs of mosaicism in both expression of D antigens and in RHD dosage.

[Antenatal determination of fetal RhD-blood type based on fetal DNA in plasma from the RhD-negative mother--secondary publication]

We present a reliable test for prenatal prediction of fetal RhD type using maternal plasma from RhD-women. This test is needed for a future antenatal RH prophylaxis. A new real time PCR based assay targeting RHD exon 7 and a published assay for RHD exon 10 were used to determine the fetal RHD status in DNA extracted from plasma from 56 pregnant women in 15th-36th week of gestation. Prediction of fetal RhD type was compared with the phenotype determined after birth, and showed 100% concordance. This setup will be of value in antenatal RH prophylaxis and in the management of immunised women.

Reliable test for prenatal prediction of fetal RhD type using maternal plasma from RhD negative women

OBJECTIVES

The objective of this study was to establish a reliable test for prenatal prediction of fetal RhD type using maternal plasma from RhD negative women. This test is needed for future prenatal Rh prophylaxis.

METHODS

A novel real-time PCR-based assay targeting RHD exon 7 combined with a published assay for RHD exon 10 were used to determine the fetal RHD status in DNA extracted from plasma, sampled from 56 pregnant RhD negative women in 15th-36th week of gestation. Thirty-eight samples were from ongoing pregnancies of Danish women and 21 samples from 18 pregnant women were stored anonymized samples from the International Blood Group Reference Laboratory, Bristol, United Kingdom. Prediction of fetal RhD type was compared with the serological result obtained after birth.

RESULTS

The prediction of the fetal RhD type was in 100% concordance with the serological RhD type from the 16th week of gestation. One sample from the 15th week of gestation was inconclusive. The number of copies of fetal RHD DNA was found to increase with gestational age. Low levels of DNA were found to follow the Poisson distribution (p = 1.0000).

CONCLUSION

Our set-up was very reliable for determination of fetal RhD genotype, and thus will be of value in prenatal Rh prophylaxis and in the management of immunized women.