Anti-Jk-b Antibodies and Hemolytic Disease of the Fetus and Newborn: Case-Based Learning.

The Kidd blood group is clinically significant as Kidd antibodies have the potential to trigger both acute and delayed transfusion reactions, along with hemolytic disease of the fetus and newborn (HDFN). Here, we have reported a case of HDFN due to Jk-b antibodies. A 31-year-old pregnant female was found to have Jk-b antibodies on screening with the Bio­Rad ID Dia 11-cell panel (Bio-Rad Laboratories, Inc., CA) after her cross-matching results were incompatible. Emergency lower segment caesarian section was done; the baby was non-hydropic at birth with an increase in bilirubin that required high-intensity phototherapy. HDFN resulting from anti-Jk-b incompatibility is rare and tends to present with mild clinical symptoms and a favorable prognosis. However, monitoring of antibody titers is essential to prevent potentially fatal complications. Additionally, antenatal antibody screening should be mandatory for all pregnant women, regardless of their Rh-(D) antigen status, to detect red cell alloimmunization to other clinically significant blood group antigens.

[Serological Characteristics and Clinical Significance of Irregular Antibodies in Pregnant Women].

OBJECTIVE: To understand the serological characteristics of irregular antibodies in pregnant women and explore their clinical significance. METHODS: From January 2017 to March 2022, 151 471 pregnant women in Women and Children's Hospital of Chongqing Medical University were enrolled in this study, microcolumn gel card test was used for irregular antibody screening, and antibody specificity identification was further performed in some antibody-positive subjects. RESULTS: The positive rate of irregular antibody screening in the enrolled pregnant women was 0.91% (1 375/151 471), 0.23% (355/151 471) was detected in the first trimester, 0.05% (71/151 471) in the second trimester, and 0.63% (949/151 471) in the third trimester. The positive rate of irregular antibody screening in the third trimester was significantly higher than that in the first and second trimester, and a significant increase in the number of positive cases was found in the third trimester than that in the second trimester. The analysis of agglutination intensity of 1 375 irregular antibody screening positive results showed that the weakly positive agglutination intensity accounted for 50.11% (689/ 1 375), which was the highest, the suspicious positive was 18.69% (257/1 375), and the positive was 31.20% (429/1 375). The significant difference in distribution of agglutination intensity was not observed between the first trimester group and the second trimester group, however, in the third trimester, the proportion of suspicious positive and weakly positive was lower than the first trimester, while, the proportion of positive was higher than the first trimester, and the difference was statistically significant (P < 0.001). Among the irregular antibody screening positive pregnant women, the proportion of pregnant women with pregnancy number ≥ 2 was significantly higher than that with pregnancy ≤ 1. Among 60 pregnant women who underwent antibody identification, the distributions of the antibodies were as follows: Rh blood group system accounted for 23.33% (14/60), Lewis system 43.33% (26/60), Kidd system 3.33% (2/60), MNS system 16.67% (10/60), P1PK system 1.67% (1/60), autoantibodies 1.67% (1/60), and 4 cases was unable to identify (6.67%, 4/60). Among specific antibodies, the anti-Lea was the most common (30.00%), followed by anti-E (16.67%) and anti-M (16.67%). CONCLUSION: The differences of irregular antibody serological characteristics exist in pregnant women from different regions with different genetic backgrounds, understanding the characteristics of irregular antibody in local pregnant women is of great significance for ensuring transfusion safety in pregnant women and preventing hemolytic disease of newborn.

Evaluating the TaqMan Jra-Genotyping Method for Rapidly Predicting the Presence of Anti-Jra Antibodies.

Background: The Jra antigen is a high-prevalence red blood cell (RBC) antigen. Reports on cases of fatal hemolytic disease of the fetus and newborn and acute hemolytic transfusion reactions suggest that antibodies against Jra (anti-Jra) have potential clinical significance. Identifying anti-Jra is challenging owing to a lack of commercially available antisera. We developed an alternative approach to rapidly predict the presence of anti-Jra using the TaqMan single-nucleotide polymorphism (SNP)-genotyping method. Methods: Residual peripheral blood samples from 10 patients suspected of having the anti-Jra were collected. Two samples with confirmed Jr(a-) RBCs and anti-Jra were used to validate the TaqMan genotyping assay by comparing the genotyping results with direct sequencing. The accuracy of the assay in predicting the presence of anti-Jra was verified through crossmatching with in-house Jr(a-) O+ RBCs. Results: The TaqMan-genotyping method was validated with two Jr(a-) RBC- and anti-Jra-confirmed samples that showed concordant Jra genotyping and direct sequencing results. Jra genotyping for the remaining samples and crossmatching the serum samples with inhouse Jr(a-) O+ RBCs showed consistent results. Conclusions: We validated a rapid, simple, accurate, and cost-effective method for predicting the presence of anti-Jra using a TaqMan-based SNP-genotyping assay. Implementing this method in routine practice in clinical laboratories will assist in solving difficult problems regarding alloantibodies to high-prevalence RBC antigens and ultimately aid in providing safe and timely transfusions and proper patient care.

Development of multiplexed flow cytometry-based red blood cell antibody screen and identification assays.

BACKGROUND AND OBJECTIVES: The purpose of this study was to develop a high-throughput method of performing red blood cell antibody screens and identification by utilizing flow cytometry and intracellular dyes to allow a multiplexed assay where three-cell screens can be performed in a single test well and 11-cell panels in three test wells. MATERIALS AND METHODS: Reagent red blood cells were labelled using Violet Proliferation Dye 450 (V450) and Oregon Green fluorescent dyes, which bind intracellular proteins to allow up to four cells to be interrogated in a single test well. Sixteen 3-cell screen panels and ten 11-cell identification panels were tested using sera with known antibody specificity. Antibody binding was detected using secondary anti-immunoglobulin G and anti-immunoglobulin M fluorescently labelled antibodies. RESULTS: Intracellular dyes allowed clear separation of the different screen and identification panel test cells. Three distinct populations of V450+, Oregon Green+ and negative for both stains were demonstrated in the screening panel and an additional double positive for V450 and Oregon Green was utilized to include a fourth cell in the identification panel testing to increase throughput. A total of 158 screen or identification panel RBC/serum combinations were tested against different known antibodies, and expected results were obtained with 100% concordance. CONCLUSION: This study demonstrates the successful development of a high-throughput multiplexed flow cytometry-based red cell antibody screen and identification panel assays. This method could be implemented in clinical laboratories to complement existing antibody detection methods. The multiplexing enabled via intracellular staining could be utilized to further augment other flow cytometry-based transfusion assays.

[Identification of Complex and Combined Antibody Consisted of Anti-c, Anti-E, Anti-Jka and Anti-Fya].

OBJECTIVE: To investigate the role of multiple serological methods in the identification of complex antibodies. METHODS: The blood group antigens were detected by saline and microcolumn agglutination methods. The saline method was used to screen and identify IgM-type antibodies in the patient's serum, while the polybrene, anti-globulin, microcolumn agglutination, enzymic and absorption-elution methods were used to screen and identify IgG-type antibodies. RESULTS: The patient was B/CCDee/Jk(a-b+)/Fy(a-b+) blood type. The serum reacted with panel cells, and the reaction presented anti-E pattern in the saline medium. It was fully positive in the microcolumn agglutination card, except 2 negative ones after using papain to treat the panel cells. Referring to the pattern table, it was concluded that there existed anti-c, anti-E, and anti-Jka antibodies, and one antibody corresponding to an antigen that was easily destroyed by papain. The red blood cells with specific phenotype were selected for absorption-elution to identify IgG-type anti-c, anti-E, anti-Jka and anti-Fya antibodies. CONCLUSION: It is confirmed that IgM-type anti-E, and IgG-type anti-c, anti-E, anti-Jka and anti-Fya antibodies exist in the patient's serum by multiple serological methods.

The exclusion of anti-D alloantibody in a suspected anti-G antibody in a pregnant 28-year-old Odiya Indian woman.

The Rh-D negative pregnancy is commonly associated with alloimmunization against D-antigen. It can be prevented by anti-D prophylaxis in pregnant patients with negative results on antibody screening. Hence, it is essential to exclude alloantibody-D in the presence of multiple alloantibodies. Anti-G antibody is formed after exposure to G antigen in neonate RBCs. Blood-group discrepancy was noted in reverse grouping, and antibody-screening results were positive in our case individual, a 28-year old Odiya Indian woman. We performed antibody identification on serum specimens from this patient, which revealed the pattern of anti-D + anti-C antibody specificity. Blood-group discrepancy was solved using rr (ce/ce)-phenotype pooled cells for reverse grouping. We identified anti-G antibodies by themselves without anti-D and anti-C after performing sequential adsorption of serum with r'r' (Ce/Ce) and R2R2 (DcE/DcE) group-O RBCs in the mother, who had rr phenotype and primigravida designation. After completing antibody screening at the first antenatal check-up, we recommended prophylactic anti-D for the mother in any future pregnancies she may have.

Situation analysis and blood transfusion strategy of Lewis antibodies in Hunan Province.

BACKGROUND: Detection rate, serological characteristics, and clinical data of patients with Lewis blood group antibodies in Hunan Province were analyzed through retrospective analysis. This was undertaken in order to optimize the detection methods and blood transfusion strategies of these patients. METHODS: Blood typing, antibody screening, and cross-matching were performed by microcolumn gel, and Lewis antigen was detected by immediate spin test, antibody identification of positive and negative ABO samples, positive antibody screening, and cross-blood mismatch samples. Antibodies were identified by immediate spin test and microcolumn gel antiglobulin method, and the clinical data of the patients with Lewis antibody characteristics were analyzed. RESULTS: A total of 74 samples (15.91%) with Lewis antibodies were detected from 465 positive samples; cases were distributed in different cities of Hunan Province, with Changsha city being the most frequent (28%) one, with mostly non-O (66), anti-Lea (31; 41.89%), anti-Lea+anti-Leb (23; 31.08%), anti-Leb (5; 6.76%), anti-LebH and anti-Lea+anti-LebH (1+4; 6.76%), and antibody types immunoglobulin M (IgM) (51; 68.92%), immunoglobulin G (8; 10.81%), and IgG+IgM (4; 5.41%) cases. Patients included more females (67.57%) than males. The detection rate of gynecological diseases and patients with solid tumors was highest (44.59%). In all cases, the Lewis blood group was Le (a-b-); none of the 15 transfusion patients had hemolytic transfusion reaction. CONCLUSION: A variety of experimental methods must be adopted simultaneously to determine specificity and prevent the leakage of Lewis antibodies. The infusion of red blood cells matching with antiglobulin media at 37°C was recommended to ensure safe transfusion for recipients with Lewis antibodies.

Situation analysis and blood transfusion strategy of Lewis antibodies in Hunan Province

Background: Detection rate, serological characteristics, and clinical data of patients with Lewis blood group antibodies in Hunan Province were analyzed through retrospective analysis. This was undertaken in order to optimize the detection methods and blood transfusion strategies of these patients. Methods: Blood typing, antibody screening, and cross-matching were performed by microcolumn gel, and Lewis antigen was detected by immediate spin test, antibody identification of positive and negative ABO samples, positive antibody screening, and cross-blood mismatch samples. Antibodies were identified by immediate spin test and microcolumn gel antiglobulin method, and the clinical data of the patients with Lewis antibody characteristics were analyzed. Results: A total of 74 samples (15.91%) with Lewis antibodies were detected from 465 positive samples; cases were distributed in different cities of Hunan Province, with Changsha city being the most frequent (28%) one, with mostly non-O (66), anti-Lea (31; 41.89%), anti-Lea+anti-Leb (23; 31.08%), anti-Leb (5; 6.76%), anti-LebH and anti-Lea+anti-LebH (1+4; 6.76%), and antibody types immunoglobulin M (IgM) (51; 68.92%), immunoglobulin G (8; 10.81%), and IgG+IgM (4; 5.41%) cases. Patients included more females (67.57%) than males. The detection rate of gynecological diseases and patients with solid tumors was highest (44.59%). In all cases, the Lewis blood group was Le (a-b-); none of the 15 transfusion patients had hemolytic transfusion reaction. Conclusion: A variety of experimental methods must be adopted simultaneously to determine specificity and prevent the leakage of Lewis antibodies. The infusion of red blood cells matching with antiglobulin media at 37°C was recommended to ensure safe transfusion for recipients with Lewis antibodies (AU)

An epitope-directed selection strategy facilitating the identification of Frizzled receptor selective antibodies.

The lack of incorporating epitope information into the selection process makes the conventional antibody screening method less effective in identifying antibodies with desired functions. Here, we developed an epitope-directed antibody selection method by designing a directed library favoring the target epitope and a precise "counter" antigen for clearing irrelevant binders in the library. With this method, we successfully isolated an antibody, pF7_A5, that targets the less conserved region on the FZD2/7 CRD as designed. Guided by the structure of pF7_A5-FZD2CRD, a further round of evolution was conducted together with the "counter" antigen selection strategy, and ultimately, an FZD2-specific antibody and an FZD7-preferred antibody were obtained. Because of targeting the predefined functional site, all these antibodies exhibited the expected modulatory activity on the Wnt pathway. Together, the method developed here will be useful in antibody drug discovery, and the identified FZD antibodies will have clinical potential in FZD-related cancer therapy.

Identification of antibody against highly prevalent antigen through serological test and molecular biology technology / 中国输血杂志

【Objective】 To identify a case of antibody against highly prevalent antigen through molecular biology technology. 【Methods】 Blood group typing, unexpected antibody identification and cross matching were performed by serological test, and genetic testing of Diego blood group was performed by molecular biology technology. 【Results】 Serological test showed that there was a high prevalence of anti-Dib in the serum of the patient. Gene sequencing showed that the genotype of the patient was Di(a+b-) . Two cases with Di(a+b-) matched with the patient were screened from 856 blood donors. 【Conclusion】 The combined detection method based on serological test supplemented by molecular biology technology is beneficial to the detection of antibody against highly prevalent antigens, and is of great significance for ensuring the safety of clinical blood transfusion.

Unexpected antibody distribution among tumor patients: analysis of 111 483 cases / 中国输血杂志

【Objective】 To analyze the distribution of unexpected antibodies in tumor patients retrospectively and explore the clinical significance. 【Methods】 Unexpected antibody screening was performed on inpatients with blood preparation and blood transfusion in our hospital from January 2004 to December 2022, with 1 176 cases tested positive, and the types of unexpected antibodies and distribution characteristics were statistically analyzed. 【Results】 Unexpected antibodies were screened in 1 176 cases, with the positive rate at 1.05% (1 176/111 483). The unexpected antibodies were mainly anti-E 16.33%(192/1 176), anti-M 7.99% (94/1 176), anti-Mur 5.70% (67/1 176) and anti-Lea 4.76% (56/1 176). Among the 1 176 cases, gastrointestinal tumors accounted for 27.99% (329/1 176), gynecological tumors accounted for 24.84% (292/1 176), respiratory tumors accounted for 16.67% (196/1 176) . 【Conclusion】 The influencing factors of unexpected antibodies in tumor patients were disease type, blood transfusion history and blood type. Therefore, it is necessary for clinical departments to carry out unexpected antibody screening and perform Rh blood type matched transfusion for tumor patients to avoid alloantibody production.

Identification of Complex and Combined Antibody Consisted of Anti-c, Anti-E, Anti-Jka and Anti-Fya / 中国实验血液学杂志

OBJECTIVE@#To investigate the role of multiple serological methods in the identification of complex antibodies.@*METHODS@#The blood group antigens were detected by saline and microcolumn agglutination methods. The saline method was used to screen and identify IgM-type antibodies in the patient's serum, while the polybrene, anti-globulin, microcolumn agglutination, enzymic and absorption-elution methods were used to screen and identify IgG-type antibodies.@*RESULTS@#The patient was B/CCDee/Jk(a-b+)/Fy(a-b+) blood type. The serum reacted with panel cells, and the reaction presented anti-E pattern in the saline medium. It was fully positive in the microcolumn agglutination card, except 2 negative ones after using papain to treat the panel cells. Referring to the pattern table, it was concluded that there existed anti-c, anti-E, and anti-Jka antibodies, and one antibody corresponding to an antigen that was easily destroyed by papain. The red blood cells with specific phenotype were selected for absorption-elution to identify IgG-type anti-c, anti-E, anti-Jka and anti-Fya antibodies.@*CONCLUSION@#It is confirmed that IgM-type anti-E, and IgG-type anti-c, anti-E, anti-Jka and anti-Fya antibodies exist in the patient's serum by multiple serological methods.

Comparison of solid-phase red cell adherence and microcolumn agglutination technology using untreated and enzyme-treated red blood cells.

Screening for clinically significant antibodies is crucial in transfusion medicine and is a routine part of pre-transfusion testing. The indirect antiglobulin test (IAT) is the most reliable and effective test for detecting clinically significant alloantibodies reacting at the antihuman globulin phase. Two of the main methods used for antibody detection and identification are solid-phase red cell adherence (SPRCA) and microcolumn agglutination technology (CAT), with or without enzyme-treated red blood cells (RBCs). This study was undertaken to detect and identify alloantibodies by performing antibody screen (ABS) and antibody identification (ABID) testing using SPRCA and CAT, with and without ficin-treated RBCs. Residual patient samples collected between 1 December 2020 and 19 May 2021 were saved, de-identified, and frozen at ≤-30°C before testing for alloantibodies. Seventy antibodies were detected in 53 samples among the 203 samples that underwent an ABS. Of those samples, 150 (73.0%) were nonreactive, 47 (23.1%) yielded positive results with both CAT and SPRCA, and six (3.0%) yielded positive ABS results with SPRCA only. Fifty-three samples that underwent ABID by both methods yielded eight samples with antibodies identified by SPRCA only. Additional enhancement of the CAT method by the use of ficin-treated RBCs was required to detect seven of the eight SPRCA-only antibodies; one sample remained nonreactive regardless. SPRCA testing detected clinically significant antibodies without the addition of enzyme-treated RBCs that was necessary in the CAT testing.

Prevalence of irregular red cell antibody in transfusion recipients vis-a-vis healthy blood donors attending a tertiary care hospital in North India.

CONTEXT: Alloimmunization by foreign red cell antigens is a matter of concern as it may lead to hemolysis in transfused patients as well as fetus of pregnant females. AIMS: This study aimed to perform a comparative analysis of prevalence and type of irregular antibodies in healthy donors, vis-a-vis blood transfusion recipients. SETTINGS AND DESIGN: Blood samples of 4000 individuals comprising healthy donors, exposed patients, and nonexposed patients were collected and were analyzed for irregular antibodies. MATERIALS AND METHODS: Commercially available three-cell antigen panel was used for the antibody screening. The samples positive in antibody screen were further subjected to an extended 11-cell panel for antibody identification in low-ionic strength saline with and without enzyme. STATISTICAL ANALYSIS: Statistical analysis was done using SPSS for Windows 15.0 program. Chi-square test was used for detecting statistical significance of exposure to red blood cell antigens in the formation of alloantibodies. RESULTS: Of the 4000 samples, antibodies were identified in 105 (2.6%) samples. Overall, nonexposed group showed a seropositivity of 0.36%, while the exposed group showed a seropositivity of 9.4%. Anti-D was the most common antibody found in 38 patients (33.3%). Anti-E was the most common antibody in males, while anti-D was the most common antibody in females. CONCLUSIONS: Since the risk of alloimmunization is more common in multitransfused patients, it is advisable to screen at least those cases for irregular antibodies.

Enzyme treatment of red blood cells: use of ficin and papain.

Proteolytic enzymes are used to treat red blood cells (RBCs) to aid in complex antibody identification. Although there are many enzymes that can be used, for the purpose of this method review, enzyme-treated RBCs refers only to RBCs treated with ficin or papain. Ficin and papain can increase the sensitivity of antibody detection by modifying the RBC membrane. Enzyme treatment and test methods can be performed using one-stage or two-stage procedures. Enzyme treatment is especially useful for the differentiation of multiple antibodies, enhancement of detection of weak antibodies, and adsorption methods. In all cases, quality control is required to ensure adequate treatment of RBCs before additional testing. Ficin and papain are useful tools for both immunohematology reference laboratories and transfusion services.

Red Blood Cell Immunization and Contributing Factors in 685 Thalassemia Patients.

Background: An analysis of red blood cell alloimmunization in patients with thalassemia can help to devise specific strategies to decrease the alloimmunization rate. This study explored the frequency and specificity of alloantibodies and autoantibodies against red blood cell (RBC) antigens in patients with thalassemia referring to the Iranian Blood Transfusion Organization (IBTO) Immunohematology Reference Laboratory (IRL) in Tehran. Materials and Methods: This study first examined the laboratory records of 23,113 patients suffering from different diseases referring to IBTO's IRL for pretransfusion testing in the 2008-2015 period. ABO and Rh(D) typing and antibody screening tests were performed for all 23,113 patient records and 685 (2.97%) beta-thalassemia patients with positive pre-transfusion test results (antibody screening and/or DAT) were selected for further investigation. Results: The antibody screening test was positive in 640 out of 685 thalassemic patients (93.4%). DAT was performed for 529 patients, 226 (33%) of which showed positive results. Meanwhile, 161 out of 685 beta-thalassemia patients (23.5%) had positive auto control test results, reflecting the possible presence of allo- and/or autoantibodies. The most common antigen-specific alloantibodies were directed against K and E RBC antigens with a frequency of 25% (Anti-K) and 11.91% (Anti-E), respectively. The development of two antibodies (double antibodies) in one patient was observed in 80 individuals (11.46%). Conclusion: Age, gender, history of pregnancy, and splenectomy were not contributing factors to the antibody presence in the patient population under study. Extended red blood cell phenotyping should be considered as an essential procedure for expected multi-transfused thalassemia patients before blood transfusion. Considering the high frequency of anti-K and anti-E observed in this study, it is recommended that thalassemia patients in Iran are tested through phenotyping of RBC units for K and E antigens before transfusion.

MALDI-TOF-MS-Based Identification of Monoclonal Murine Anti-SARS-CoV-2 Antibodies within One Hour.

During the SARS-CoV-2 pandemic, many virus-binding monoclonal antibodies have been developed for clinical and diagnostic purposes. This underlines the importance of antibodies as universal bioanalytical reagents. However, little attention is given to the reproducibility crisis that scientific studies are still facing to date. In a recent study, not even half of all research antibodies mentioned in publications could be identified at all. This should spark more efforts in the search for practical solutions for the traceability of antibodies. For this purpose, we used 35 monoclonal antibodies against SARS-CoV-2 to demonstrate how sequence-independent antibody identification can be achieved by simple means applied to the protein. First, we examined the intact and light chain masses of the antibodies relative to the reference material NIST-mAb 8671. Already half of the antibodies could be identified based solely on these two parameters. In addition, we developed two complementary peptide mass fingerprinting methods with MALDI-TOF-MS that can be performed in 60 min and had a combined sequence coverage of over 80%. One method is based on the partial acidic hydrolysis of the protein by 5 mM of sulfuric acid at 99 °C. Furthermore, we established a fast way for a tryptic digest without an alkylation step. We were able to show that the distinction of clones is possible simply by a brief visual comparison of the mass spectra. In this work, two clones originating from the same immunization gave the same fingerprints. Later, a hybridoma sequencing confirmed the sequence identity of these sister clones. In order to automate the spectral comparison for larger libraries of antibodies, we developed the online software ABID 2.0. This open-source software determines the number of matching peptides in the fingerprint spectra. We propose that publications and other documents critically relying on monoclonal antibodies with unknown amino acid sequences should include at least one antibody fingerprint. By fingerprinting an antibody in question, its identity can be confirmed by comparison with a library spectrum at any time and context.

Simultaneous Use of Two Recombinant Blood Group Antigens for Identification of Rare Complex Antibody Mixtures.

Background: Antibodies to high-frequency antigens in red blood cells make antibody identification difficult for immunohaematology laboratories to conduct using conventional methods, especially when the sample contains multiple co-existing allo-antibodies. This study presents the successful application of an antibody inhibition method based on recombinant blood group antigens (rBGAs) to identify mixtures of allo-antibodies as well as an antibody to a high-frequency antigen observed in two patients. Methods: rBGAs were utilised in detecting antibodies in two samples where more than one antibody was inhibited simultaneously from polyreactive plasma. The inhibition step was followed using conventional column agglutination techniques. Results: In the sample of Patient A, anti-f and the previously missed anti-Jkb were identified after simultaneous inhibition of anti-Yta and anti-Fya. The results of the sample of Patient B show anti-C and anti-M identified after simultaneous inhibition of anti-Ch1 and anti-Fya. Conclusions: The presented technique is an excellent supporting aid in antibody identification used with conventional column agglutination techniques. Antibody inhibition using mixed rBGAs allows reference and routine laboratories to identify rare antibody mixtures in a fast and efficient manner. Routine laboratories may be able to conduct difficult antibody identifications independently without referring these samples to a reference laboratory, resulting in faster identification results and elimination of delay in patient care. Simultaneous rBGA inhibition is an off-label technique not instructed in the user manual of rBGA and should be used with caution.

What is the optimal pretransfusion testing interval for multi-transfused patients? The University Hospital of Brest experience.

The red cell allo-antibodies research is mandatory before transfusion. In France, pretransfusion testing intervals that are prescribed by regulatory and accrediting agencies are commonly 72hours. In the University hospital of Brest, the interval for multi-transfused patients has been 24hours. In this study we aim to analyse these practice and argue the delay. METHODS: This is a retrospective study of post-transfusional allo-immunizations from 2015 to 2020. For each patient, the time interval between the last negative research and the allo-immunization was investigated. RESULTS: 189 patients developed allo-antibodies. In 16 patients (8,5%), the interval for allo-immunization was 24hours, 48hours and 72hours in 4, 8 and 4 patients respectively. 12 patients were transfused after the discovery of the allo-antibodies. That means if we have chosen a delay of validity of 72hours, then 9 patients would have been transfused with a negative result. CONCLUSION: Checking for allo-antibodies before RBC transfusion with an interval of 24hours (and not 72hours) is pertinent in order to assure an optimal transfusion safety and to limit the risk of hemolytic transfusion reactions. A pretransfusion testing interval of 24hours for multi-transfused patients should be considered.

Generation of 'designer erythroblasts' lacking one or more blood group systems from CRISPR/Cas9 gene-edited human-induced pluripotent stem cells.

Despite the recent advancements in transfusion medicine, red blood cell (RBC) alloimmunization remains a challenge for multiparous women and chronically transfused patients. At times, diagnostic laboratories depend on difficult-to-procure rare reagent RBCs for the identification of different alloantibodies in such subjects. We have addressed this issue by developing erythroblasts with custom phenotypes (Rh null, GPB null and Kx null/Kell low) using CRISPR/Cas9 gene-editing of a human induced pluripotent stem cell (hiPSC) parent line (OT1-1) for the blood group system genes: RHAG, GYPB and XK. Guide RNAs were cloned into Cas9-puromycin expression vector and transfected into OT1-1. Genotyping was performed to select puromycin-resistant hiPSC KOs. CRISPR/Cas9 gene-editing resulted in the successful generation of three KO lines, RHAG KO, GYPB KO and XK KO. The OT1-1 cell line, as well as the three KO hiPSC lines, were differentiated into CD34+ CD41+ CD235ab+ hematopoietic progenitor cells (HPCs) and subsequently to erythroblasts. Native OT1-1 erythroblasts were positive for the expression of Rh, MNS, Kell and H blood group systems. Differentiation of RHAG KO, GYPB KO and XK KO resulted in the formation of Rh null, GPB null and Kx null/Kell low erythroblasts, respectively. OT1-1 as well as the three KO erythroblasts remained positive for RBC markers-CD71 and BAND3. Erythroblasts were mostly at the polychromatic/ orthochromatic stage of differentiation. Up to ~400-fold increase in erythroblasts derived from HPCs was observed. The availability of custom erythroblasts generated from CRISPR/Cas9 gene-edited hiPSC should be a useful addition to the tools currently used for the detection of clinically important red cell alloantibodies.