High-throughput strategy for molecular identification of Vel- blood donors employing nucleic acids extracted from plasma pools used for viral nucleic acid test screening

CRISPR/Cas9-Editing K562 Cell Line as a Potential Tool in Transfusion Applications: Knockout of Vel Antigen Gene

Introduction

The Vel- phenotype is a rare blood group, and it is challenging for identifying this phenotype due to limited available reagents. Moreover, there are relatively few studies on genomic editing of erythroid antigens and generation of knockout (KO) cell lines at present.

Methods

To identify the high-efficiency small-guiding RNA (sgRNA) sequence, candidate sgRNAs were transfected into HEK 293T cells and analyzed using Sanger sequencing. Following this, the high-efficiency sgRNA was transfected into K562 cells using lentivirus transduction to generate KO Vel blood group gene cells. The expression of the Vel protein was detected using Western blot on single-cell clones. Additionally, flow cytometry was used to detect the erythroid markers CD235a and CD71. Hemoglobin quantification and Giemsa staining were also performed to evaluate the erythroid differentiation of KO clones induced by hemin.

Results

The high-efficiency sgRNA was successfully obtained and used for CRISPR-Cas9 editing in K562 cells. After limiting dilution and screening, two KO clones had either deleted 2 or 4 bases and showed no expression of the Vel protein. In the hemin-induced KO clone, there was a significant difference in erythroid marker and hemoglobin quantification compared to untreated cells. The morphological changes were also observed for the hemin-induced KO clone.

Conclusion

In this study, a highly efficient sgRNA was screened out and used to generate Vel erythroid antigen KO single-cell clones in K562 cells. The edited cells could then be induced to undergo erythroid differentiation with the use of hemin.

Using droplet digital PCR to screen for rare blood donors: Proof of principle

BACKGROUND

Digital droplet PCR (ddPCR) is a very sensitive high throughput genotyping methodology. To date, the use of ddPCR in immunohematology is restricted to fetal genotyping of red blood cell antigens. Our hypothesis is that this technology could be applied to screen for rare red blood cell genotypes, such as Di(b-).

METHODS

Nucleic acid of 3168 donors was extracted for viral screening routine in pools of 6, which were converted into three types of 48-donor pools: control pools (only DI*B/*B samples), pools with varying amount of DI*A/*B samples (n = 1-5) and a pool with one rare DI*A/*A sample. Pools were genotyped using ddPCR to detect and quantify DI*A and DI*B alleles.

RESULTS

DI*A allele was accurately detected in all pools containing Di(a + b+) samples and in the pool containing one Di(a + b-) sample. No copies were detected in the control pools (n = 60). The ratio between the number of DI*A and DI*B copies varied significantly between the pools and the triplicates.

CONCLUSION

The proposed ddPCR assay was accurate in identifying the rare DI*A allele in large pools of donors and can be applied to screen for Di(b-) phenotype. The strategy can potentially be extended to search for other rare RBC phenotypes.

The screening of rare blood donors in a highly admixed population: A new approach for Holley and Diego genotyping and impact of genomic and self-reported ancestry

OBJECTIVES

The present study aimed to develop strategies for genotyping DO*HY (Dombrock system) and DI*A/DI*B (Diego system) alleles and to evaluate the impact of genomic and self-declared ancestry on rare donor screening in admixed populations.

BACKGROUND

The antigens Hy and Di^b demonstrate clinical importance. The lack of antisera for the serological evaluation of these antigens makes it necessary to develop molecular methods. In addition, considering that some rare red blood cell phenotypes present differences in frequency between ethnic groups, it is important to assess the applicability of self-declared ancestry in the search for rare donors in admixed populations.

METHODS

DO*HY and DI*A/DI*B genotyping based on real-time polymerase chain reaction (PCR) was standardised. A total of 457 blood donors clustered by self-defined skin colour/race categories were genotyped. Furthermore, individual genomic ancestry was used in the analyses.

RESULTS

The assays developed are reproducible and provide satisfactory results even at low concentrations of DNA, which make them useful in situations where the DNA is scarce, such as dried blood spots on filter paper, or when screening for pooled samples. No significant difference was observed in the frequencies of the DI*A, DI*B and DO*HY, comparing the self-declared White (branco) donors with those who are Black (preto) and Brown (pardo).

CONCLUSION

Real-time PCR, especially using pooled samples, is a promising strategy to screen rare blood donors. Although both self-reported race/colour and some blood group phenotypes are associated with ancestry, the results point to a greater complexity in the application of self-declared race/colour in the screening of rare donors in admixed populations.

SMIM1 at a glance; discovery, genetic basis, recent progress and perspectives

Recent elucidation of the genetic basis of the Vel blood group system has offered the field of blood transfusion medicine an additional consideration in determining the causes of hemolytic reactions after a patient is transfused. The identification of the SMIM1 gene to be responsible for the Vel blood group allows molecular based tools to be developed to further dissect the function of this antigen. Genetic signatures such as the homozygous 17 bp deletion and the heterozygous 17 bp deletion in combination with other single nucleotide polymorphisms (SNPs) and insertion sequences regulate the expression level of the gene. With this knowledge, it is now possible to study this antigen in-depth.

SMIM1 intron 2 gene variations leading to variability in Vel antigen expression among Brazilian blood donors

BACKGROUND

There is a significant inter-individual heterogeneity of Vel antigen expression which can lead to inaccuracies on Vel phenotyping of blood donors and, potentially, to hemolytic post-transfusion reactions. Our aim was to evaluate the impact of genetic variants in the SMIM1 intron 2 on the expression of Vel antigen among Brazilian blood donors harboring the c.64_80del17 deletion in heterozygosity.

METHODS

Donors presenting the SMIM1 c.64_80del17 in heterozygosity were included in the study and subjected to SMIM1 intron 2 direct sequencing aiming to genotype the following polymorphisms: rs143702418, rs1181893, rs191041962, rs6673829, rs1175550 and rs9424296.

RESULTS

SMIM1 intron 2 sequencing was performed on two hundred donors presenting one c.64_80del17 allele. The rs1175550 polymorphism significantly impacted on Vel antigen expression. Variations in the strength of agglutination on Vel phenotyping were also observed according to the rs6673829 genotype, but this difference did not persist with statistical relevance after multivariate analysis.

CONCLUSION

The presence of the rs1175550A allele of SMIM1 is significantly and independently associated with a decrease in Vel antigen expression. Even though the population in Brazil is intensely mixed, the allele frequencies obtained in the current study were very similar to that reported for Europeans.

The Polymorphism of SMIM1 Gene in Chinese Dividuals

The SMIM1 gene, which encodes the high-frequency blood group antigen Vel, has not been systematically analyzed at the molecular level in Chinese individuals. To better understand the SMIM1 genetic polymorphism, we assessed mutations among healthy Chinese individuals, patients with red blood cell autoantibodies and hematological disease. A total of 130 patients with hematological disease (case I group), 50 patients with red blood cell autoantibodies (case II group), and 500 healthy controls (control group) were enrolled. Exons 3 and 4 in the SMIM1 gene were sequenced to identify genetic variants or mutations. A polyclonal anti-Vel antibody was used to evaluate the expression of the Vel antigenon red blood cells in patients with novel alleles. The novel alleles of the SMIM1 gene were intron 3 position 193 (TT, CT, CC), 194 (GG, AG), 3' untranslated region positions 81 (CC, CA) and 87 (AA, CA). The single nucleotide polymorphism (SNP) frequencies of intron 3 position 193 TT, CT, CC were 13.1, 39.2, 47.7% in case group I, 6.7, 33.3, 60.0% in case group II and 8.5, 35.6, 56.2% in the control group, respectively. Other minor allele frequencies were all greater than 10% and all SNPs in Chinese showed Vel antigen expression on RBC membranes. The allele at intron 3 position 193 was the most frequent mutant allele found in the Chinese population and Vel antigen deficiency may not cause problems in Chinese patients with hematological diseases and RBC autoantibodies.

Screening for the SMIM1*64_80 del Allele in blood donors in a population from Southern Brazil

BACKGROUND AND OBJECTIVES

Serological screening for the Vel- phenotype is complex given the large individual variation in the levels of expression of the Vel antigen, and the polyclonal anti-human sera of immunised persons, when available, show heterogeneous reactivity levels. Studies of the SMIM1 gene have enabled the development of several molecular methodologies that will be crucially important for the screening of different populations, including Brazilians. To evaluate the deletion of 17 bp in the SMIM1 gene in a population from the south of Brazil, 448 unrelated blood donors from 7 regions comprising the haemotherapy network in the state of Santa Catarina were evaluated between August 2011 and March 2014.

MATERIALS AND METHODS

DNA samples from these donors were analysed employing a 5' nuclease real-time polymerase chain reaction (PCR) assay targeting the 17 bp deletion in the SMIM1 gene.

RESULTS

Among the 448 samples analysed, 10 (2·23%) harboured the 17 bp deletion of the gene SMIM1, and all were heterozygote for the SMIM1*64_80 del allele.

CONCLUSION

The allelic frequency found differed from those observed in other Caucasian populations. This difference can be explained by the ethnic make-up of each Caucasian population. The data obtained are important to characterise the correct phenotype of the donor as the serological assay results are not reliable due to variations in the expression intensity of the Vel antigen in heterozygote donors for the SMIM1*64_80 del allele. Moreover, the tool used in this study is of great value for identifying a donor Vel- phenotype and supplying a possible need for transfusion.