Molecular basis for the high-incidence antigens of the Kell blood group system

Extended Donor Typing by Pooled Capillary Electrophoresis: Impact in a Routine Setting

Background

PCR with sequence-specific priming using allele-specific fluorescent primers and analysis on a capillary sequencer is a standard technique for DNA typing. We aimed to adapt this method for donor typing in a medium-throughput setting.

Methods

Using the Extract-N-Amp PCR system, we devised a set of eight multiplex allele-specific PCR with fluorescent primers for Fy^a/Fy^b, Jk^a/Jk^b, M/N, and S/s. The alleles of a gene were discriminated by the fluorescent color; donor and polymorphism investigated were encoded by product length. Time, cost, and routine performance were collated. Discrepant samples were investigated by sequencing. The association of new alleles with the phenotype was evaluated by a step-wise statistical analysis.

Results

On validation using 312 samples, for 1.1% of antigens (in 5.4% of samples) no prediction was obtained. 99.96% of predictions were correct. Consumable cost per donor were below EUR 2.00. In routine use, 92.2% of samples were successfully predicted. Discrepancies were most frequently due to technical reasons. A total of 11 previously unknown alleles were detected in the Kell, Lutheran, and Colton blood group systems. In 2017, more than 20% of the RBC units prepared by our institution were from donors with predicted antigen status. A steady supply of Yt(a-), Co(a-) and Lu(b-) RBC units was ensured.

Conclusions

Pooled capillary electrophoresis offers a suitable alternative to other methods for extended donor DNA typing. Establishing a large cohort of typed donors improved transfusion support for patients.

An innovative test for non-invasive Kell genotyping on circulating fetal DNA by means of the allelic discrimination of K1 and K2 antigens

OBJECTIVE

The aim of this study was to present a new method for fetal Kell genotyping by means of the allelic discrimination of K1 and K2 in real-time polymerase chain reaction (PCR).

METHODS

Real-time quantitative polymerase chain reaction incorporating an allele-specific primer was developed for detecting the K allele of KEL.

RESULTS

By means of this method, the K1/K2 genotype was able to be determined in all blood samples analyzed. Results using cell-free fetal DNA (cffDNA) from two Kell-negative pregnant women confirmed the Kell-positive genotype of fetuses. The real-time PCR analysis also allowed the determination of the fetal fraction using the quantification of Kell-positive DNA.

CONCLUSION

An efficient and reliable strategy for Kell genotyping is herein presented. The method was optimized on cffDNA to create a non-invasive prenatal test which could be routinely used for the prevention of hemolytic disease of the fetus and the newborn (HDFN).

KEL*02 alleles with alterations in and around exon 8 in individuals with apparent KEL:1,-2 phenotypes

BACKGROUND AND OBJECTIVES

Antibodies to antigens in the Kell blood group system, especially anti-KEL1, are involved in both haemolytic disease of the newborn and foetus and haemolytic transfusion reactions. Correct typing results are important and discrepancies between serologic and genetic typing must be resolved. Here, we describe the investigation of three healthy individuals who were initially phenotyped as KEL:1,-2.

MATERIALS AND METHODS

Antigen typing was performed by standard serological techniques and by flow cytometric analysis. The KEL*01/02 polymorphism was tested by an allele-discrimination TaqMan assay as well as by PCR with allele-specific primers and PCR-RFLP. DNA sequencing of the KEL coding region was also performed.

RESULTS

Two KEL*02N alleles with mutated splice sites around exon 8 were identified: intron 7 -1g>c (novel) and intron 8 +1g>t (previously reported in one case of K(0)). In the third sample, a missense mutation in exon 8, 787G>A (novel) predicting Gly263Arg, was detected on a KEL*02 allele and associated with dramatically weakened KEL2 antigen expression.

CONCLUSION

Resolution of discrepant phenotype/genotype results identified silencing mutations in or around exon 8. A combination of molecular and serologic methods has the potential to improve the quality of test results and was required to ensure both the accurate KEL2 antigen status and KEL*01 zygosity of these individuals.

Molecular genetic blood group typing by the use of PCR-SSP technique

BACKGROUND

DNA-based methods are useful for enhancing immunohematology typings. Ready-to-use Conformité Européenne (CE)-marked test kits based on polymerase chain reaction with sequence-specific priming (PCR-SSP) have been developed, which enable the examination of weak, unexpected, or unclear serologic findings. DEVELOPMENT AND VALIDATION: Primers were designed according to established mutation databases. Proficiency testing for CE marking was performed in accordance with Directive 98/79EC of the European Parliament and of the Council of October 27, 1998 on in vitro diagnostic medical devices using pretyped in-house and external samples. INTENDED USE: BAGene PCR-SSP kits are in vitro diagnostic devices. Genotyping of ABO and RHD/RHCE as well as HPA and KEL, JK, and FY specificities has to be performed after the conclusion of the serologic determination.

APPLICATION

Ready-to-use PCR-SSP typing kits allow the determination of common, rare, or weak alleles of the ABO blood group, Rhesus, and Kell/Kidd/Duffy systems as well as alleles of the human platelet antigens.

RESULTS

The investigations showed clear-cut results in accordance with serology or molecular genetic pretyping.

CONCLUSION

PCR-SSP is a helpful supplementary technique for resolving most of the common problems caused by discrepant or doubtful serologic results, and it is an easy-to-handle robust method. Questionable cases in donor, recipient, and patient typing can be examined with acceptable cost.

Genetic basis of the K0phenotype in the Swedish population

BACKGROUND

The absence of all Kell blood group antigens (K(0) phenotype) is very rare. K(0) persons, however, can produce clinically significant anti-Ku (K5) after transfusion and/or pregnancy and require K(0) blood for transfusion. Ten alleles giving rise to the K(0) phenotype have been reported: different populations were studied although none from Scandinavia.

STUDY DESIGN AND METHODS

Three K(0) samples were identified by blood banks in Sweden (Uppsala, Umeå, and Linköping) during a 20-year period. Kell antigen typing was performed with standard serologic techniques by the respective blood banks and K(0) status was confirmed by the International Blood Group Reference Laboratory in Bristol, England. Polymerase chain reaction and DNA sequencing of the KEL coding region (exons 1-19) was performed on genomic DNA.

RESULTS

The Uppsala K(0) was homozygous for a 1540C>T substitution in exon 13, leading to an immediate stop codon. The Umeå K(0) was homozygous for 1023delG in exon 8 that results in a frameshift and a premature stop codon in exon 9. In the Linköping K(0), a previously reported mutation g>a at +1 of intron 3 was found.

CONCLUSION

Two novel and one previously reported null alleles at the KEL locus are described. The identified nonsense mutations abolish expression of the Kell glycoprotein and are thus responsible for the K(0) phenotype in these Swedish families.

Heterozygosity for two novel null alleles of the KEL gene causes the Kell-null phenotype in a Japanese woman

The Kell-null (Ko) phenotype is rare and it does not express the Kell antigens on erythrocyte membranes. Recently, several distinct missense and nonsense base substitutions in the coding region and the donor splice site of intron 3 were identified in the KEL gene in individuals with the Ko phenotype. We analysed both genomic DNA and cDNA sequences of the KEL gene in a Japanese woman with the Ko phenotype. She was found to be heterozygous for two novel null KEL alleles. One allele contained an A to G substitution in intron 5 that changes the 3'-splice site of intron 5 from AAG to AGG, resulting in a reading frameshift by a single guanine insertion in KEL mRNA, and the other allele contained a single G to A substitution in exon 12 (codon 459) creating a termination codon. Neither mutation was found in 114 randomly selected Japanese individuals. The results suggested that the Ko blood group phenotype might be owing to several distinct non-functional alleles without any prevalent allele.

Point mutations in KEL exon 8 determine a high-incidence (RAZ) and a low-incidence (KEL25, VLAN) antigen of the Kell blood group system

BACKGROUND AND OBJECTIVES

The molecular basis of two Kell blood group antigens, RAZ (provisionally KEL27) and VLAN (KEL25), were determined.

MATERIALS AND METHODS

The DNA sequences of the open reading frames and the flanking intron regions of the 19 KEL exons from RAZ and VLAN probands were compared with that of common KEL. Genotyping assays were designed to confirm and detect RAZ and VLAN phenotypes.

RESULTS

A homozygous G865A mutation, encoding lysine instead of glutamic acid at amino acid position 249 of Kell protein, defines the RAZ phenotype, while a heterozygous G863A mutation in KEL, encoding an arginine to glutamine substitution at amino acid 248, characterizes the VLAN phenotype.

CONCLUSION

Point mutations G865A and G863A, in adjacent codons of KEL exon 8, which cause amino acid substitutions, characterize the RAZ and VLAN Kell blood group phenotypes.

Molecular defects underlying the Kell null phenotype

Expression of the Kell blood group system is dependent on two proteins, Kell and XK, that are linked by a single disulfide bond. Kell, a type II membrane glycoprotein, is a zinc endopeptidase, while XK, which has 10 transmembrane domains, is a putative membrane transporter. A rare phenotype termed Kell null (Ko) is characterized by the absence of Kell protein and Kell antigens from the red cell membrane and diminished amounts of XK protein. We determined the molecular basis of eight unrelated persons with Ko phenotypes by sequencing the coding and the intron-exon splice regions of KEL and, in some cases, analysis of mRNA transcripts and expression of mutants on the cell surface of transfected cells. Six subjects were homozygous: four with premature stop codons, one with a 5' splice site mutation, G to A, in intron 3, and one with an amino acid substitution (S676N) in exon 18. Two Ko persons with premature stop codons had identical mutations in exon 4 (R128Stop), another had a different mutation in exon 4 (C83Stop), and the fourth had a stop codon in exon 9 (Q348Stop). Two Ko persons were heterozygous for two mutations. One had a 5' splice site mutation (G to A) in intron 3 of one allele that caused aberrant splicing and exon skipping, and the other allele had an amino acid substitution in exon 10 (S363N). The other heterozygote had the same amino acid substitution in exon 10 (S363N) in one allele and a premature stop codon in exon 6 (R192Stop) in the other allele. The S363N and S676N mutants, expressed in 293T cells, were retained in a pre-Golgi compartment and were not transported to the cell surface, indicating that these mutations inhibit trafficking. We conclude that several different molecular defects cause the Kell null phenotype.

Molecular basis of the Kell-null phenotype: a mutation at the splice site of human KEL gene abolishes the expression of Kell blood group antigens

The Kell blood group system is polymorphic, and 23 antigens have been defined to date. The Kell antigens are located on a single red cell transmembrane glycoprotein, encoded by the 19 exons of the KEL gene. The different Kell phenotypes result from point mutations leading to amino acid changes in the Kell glycoprotein. An unusual phenotype, which is defined as the complete lack of all of the Kell antigens, has been identified and designated as the Kell-null or Ko phenotype. The coding region of the KEL gene of the Ko individual showed a normal KEL2/KEL4/KEL7 gene sequence; nevertheless, a G to C mutation at the splice donor site (5' splice site) of intron 3 was found to be present as a homozygote in the individual. The mutation destroys the conserved GT sequence of the splice donor site. Reverse transcription-polymerase chain reaction analysis showed the absence of the complete KEL mRNA. Instead, a major transcript with the exon 3 region skipped was found. The exon 3 of the KEL gene encodes the transmembrane domain of the Kell glycoprotein, and a transcript without exon 3 is predicted to have a premature stop codon that abolishes the translation of C-terminal segment. The segment contains all of the known positions responsible for characterizing different Kell antigens, and this explains the lack of all Kell antigens in Ko red cells.

Differentiation of autologous ABO, RHD, RHCE, KEL, JK, and FY blood group genotypes by analysis of peripheral blood samples of patients who have recently received multiple transfusions

BACKGROUND

After multiple transfusions, the serologic typing of autologous blood group phenotypes is difficult, because of mixed RBC populations. The genotyping of ABO, Rh, Kell, Kidd, and Duffy systems could be used to determine autologous blood group antigen status.

STUDY DESIGN AND METHODS

Blood samples from patients and donors were analyzed before and after 26 multiple-transfusion events. An average of 6.9 non-WBC-reduced RBC units with an average age of 5.9 days were administered per transfusion event. The average period of blood sampling after transfusions was 5.3 days. All samples were serologically phenotyped for ABO, Rh, Kell, Kidd, and Duffy. Pretransfusion, posttransfusion, and buccal samples from patients were genotyped for the corresponding alleles by a uniform PCR sequence-specific primer protocol that allowed their simultaneous determination within 3 hours.

RESULTS

All posttransfusion samples exhibited mixed-cell populations of various blood group systems on serologic testing. Genotyping from peripheral blood produced results identical to the autologous blood group phenotypes, regardless of the amount of blood transfused or of the length of the sampling period after transfusion.

CONCLUSION

A fast and reliable PCR-sequence-specific primer DNA genotyping assay for simultaneous determination of autologous ABO, Rh, Kell, Kidd, and Duffy blood groups can be performed on peripheral blood samples, even though the patients have recently received multiple transfusions.

The Kell blood group system: Kell and XK membrane proteins

Two membrane proteins express the antigens that comprise the Kell blood group system. A single antigen, Kx, is carried on XK, a 440-amino acid protein that spans the membrane 10 times, and more than 20 antigens reside on Kell, a 93-kd, type II glycoprotein. XK and Kell are linked, close to the membrane surface, by a single disulfide bond between Kell cysteine 72 and XK cysteine 347. Although primarily expressed in erythroid tissues, Kell and XK are also present in many other tissues. The polymorphic forms of Kell are due to single base mutations that encode different amino acids. Some Kell antigens are highly immunogenic and may cause strong reactions if mismatched blood is transfused and severe fetal anemia in sensitized mothers. Antibodies to KEL1 may suppress erythropoiesis at the progenitor level, leading to fetal anemia. The cellular functions of Kell/XK are complex. Absence of XK, the McLeod phenotype, is associated with acanthocytic red blood cells (RBCs), and with late-onset forms of muscular dystrophy and nerve abnormalities. Kell, by homology, is a member of the neprilysin (M13) family of membrane zinc endopeptidases and it preferentially activates endothelin-3 by specific cleavage of the Trp21-Ile22 bond of big endothelin-3.

Intracellular assembly of Kell and XK blood group proteins

Kell, a 93 kDa type II membrane glycoprotein, and XK, a 444 amino acid multi-pass membrane protein, are blood group proteins that exist as a disulfide-bonded complex on human red cells. The mechanism of Kell/XK assembly was studied in transfected COS cells co-expressing Kell and XK proteins. Time course studies combined with endonuclease-H treatment and cell fractionation showed that Kell and XK are assembled in the endoplasmic reticulum. At later times the Kell component of the complex was not cleaved by endonuclease-H, indicating N-linked oligosaccharide processing and transport of the complex to a Golgi and/or a post-Golgi cell fraction. Surface-labeling of transfected COS cells, expressing both Kell and XK, demonstrated that the Kell/XK complex travels to the plasma membrane. XK expressed in the absence of Kell was also transported to the cell surface indicating that linkage of Kell and XK is not obligatory for cell surface expression.

Molecular genetic methods: principles and feasibility in transfusion medicine

The scale of the application of molecular biological techniques to modern medicine and research in the biological sciences is vast, and in many instances has captured widespread public appeal. The intention of this review is to summarise the impact of molecular techniques on Transfusion Medicine ranging from diagnostic testing (platelet, granulocyte and red cell genotyping; microbiological testing), stable gene integration into haematopoeitic stem cells (gene therapy), production of blood products in transgenic animals and cell lines, and the inhibition of gene expression using synthetic antisense oligodeoxynucleotides. All of these techniques involve the manipulation of genes, be it from the relatively simple examination of different alleles to the technically demanding ability to express mammalian genes in culture and other animals.