Accurate quantitation of D+ fetomaternal hemorrhage by flow cytometry using a novel reagent to eliminate granulocytes from analysis

Why do RhD negative pregnant women still become anti-D immunized despite prophylaxis with anti-D immunoglobulin?

Maternal allo-anti-D in RhD negative pregnant women may cause mild to severe hemolytic disease of the fetus and newborn. Although several other antibodies may also destroy red blood cells of the fetus and newborn, preventive measures with anti-D immunoglobulin are only available for D antigen. Targeted antenatal care together with postpartum prophylaxis with anti-D immunoglobulin has significantly reduced the D-alloimmunization risk. Potentially sensitizing events like trauma to the pregnant abdomen, vaginal bleeding, and amniocentesis may lead to fetomaternal hemorrhage and necessitate additional doses. Despite comprehensive programs with these targeted measures, allo-anti-D is still the most common reason for severe hemolytic disease of the fetus and newborn. Where do we fail then? Here, in this review, I would therefore like to discuss the reasons for D-alloimmunizations hoping that the greater focus will pave the way for further reduction in the number of pregnancy-related allo-anti-Ds.

Prenatal diagnosis of fetomaternal hemorrhage by a novel hydrogel fluoroimmunoassay that accurately quantifies fetal haemoglobin

Objective: Fetomaternal hemorrhage (FMH) is an alloimmunization resulting caused by the incompatibility between fetal and maternal blood. For the prevention of newborn haemolytic disease (HDN), it is crucial to quantify the amount of fetomaternal hemorrhage. However, the classical Kleihauer-Betke test (K-B test) for detecting fetomaternal hemorrhage is limited by experimental tools and conditions and is not suitable for routine clinical use. Consequently, the method of prenatal diagnosis of fetomaternal hemorrhage applicable to the clinic is a topic worthy of further study. Therefore, it is worthwhile to further investigation on the clinically applicable prenatal diagnosis method for fetomaternal hemorrhage. Methods: This experiment demonstrates hydrogel's ability to separate sensitized red blood cells from soluble antibodies. Using flow cytometry the fluorescence values of sensitized red blood cells and fluorophore-labeled antibodies were measured, and the testing steps for the detection products of a novel technology were determined. The properties of a hydrogel fluoroimmunoassay were evaluated by distinguishing between the amounts of fetal and adult haemoglobin. The precision of this technology is evaluated using the Kleihauer-Betke test as a comparison. Results: This experiment compared the detection of haemoglobin fluorescence in adults (n = 2) and fetuses (n = 6). At the same time, the fluorescence intensity of different fetal haemoglobin (HbF) in adult haemoglobin (HbA) was calculated. The fluorescence value is 1.6% when the fetal hemoglobin concentration is 0.1%. Conclusion: The novel hydrogel fluoroimmunoassay can accurately determine the fluorescence intensity by flow cytometry to differentiate fetal haemoglobin from adult haemoglobin, quantitatively prenatally diagnose fetal haemoglobin, address the incompatibility between fetal and maternal blood types, and prevent alloimmunization.

A report on a modified protocol for flow cytometry-based assessment of blood group erythrocyte antigens potentially suitable for analysis of weak ABO subgroups

BACKGROUND

Flow cytometry (FC) has proven its utility in scrutinizing AB antigen expression in red blood cells (RBCs), cooperating with serological tests for accurate blood group typing. However, technical difficulties may impair the characterization of weak ABO subtypes when background noises appear at non-negligible levels.

STUDY DESIGN AND METHODS

We sought to establish an FC method that could prevent antibody-induced hemagglutination and an increase in cellular autofluorescence, two major issues inherent to RBC-FC analysis of AB expression. We optimized fixatives, multicolor-staining protocols, and sequential gating strategies. Blood samples from weak ABO subtype cases, B_m and A_el , were analyzed with the established protocol.

RESULTS

The optimized mixture of glutaraldehyde and formaldehyde successfully generated fixed RBCs resistant to agglutination while maintaining low autofluorescence. These features allowed co-staining of leukocyte- and erythrocyte-markers, which enabled sequential gating strategies facilitating the precise AB antigen analysis in purely single RBCs with minimum background noises. By the established FC analysis, we could detect in the B_m sample a small RBC population exhibiting weak B antigen expression. The assay also proved it feasible to identify a small population (0.04%) of RBCs weakly expressing the A antigen in the A_el sample confirmed as harboring a rare c.816dupG ABO variant allele.

CONCLUSION

The RBC-FC analysis described here allows the detection of AB antigens weakly expressed in RBCs while achieving minimum background noise levels in negative control samples. Overall, the modified protocol provides a quick and reliable assay valuable in transfusion medicine and is potentially applicable to the characterization of rare weak ABO variants.

Quantitation of residual D positive red cells in D negative recipients of D positive solid organ transplants

BACKGROUND

Solid organ transplants (SOT) from D positive donors are potentially sensitising events for D negative recipients. For this reason, it is important to quantify the presence of residual D positive red blood cells (RBCs) in the recipient's circulation and calculate the correct dose of prophylactic anti-D (PAD) required to prevent sensitisation. This is especially important in females of child-bearing potential where the presence of allo anti-D can, at worst, cause the death of the fetus in future pregnancies.

OBJECTIVE

This study aimed to identify the patient characteristics of D positive SOT cases referred to Red Cell Immunohaematology, NHSBT for flow cytometry investigation. This information could indicate improvements required in the current testing methodology, as well as to the calculations used to prescribe PAD for this patient group.

METHODS

Samples were investigated using a Beckman Coulter Navios Flow Cytometer using BRAD3-FITC (anti-D), AEVZ5.3-FITC (isotype matched negative control) and BIRMA17C-PE (granulocyte exclusion reagent). Mollison's calculation was used to estimate the dose of PAD required to prevent sensitisation in the D negative recipients. The calculation was adapted to consider the presence of organ donor D positive adult RBCs in the circulation of recipients instead of, larger, fetal RBCs.

RESULTS

Samples from 20 patients, all female, aged 14-53 years (one 2-year-old outlier) were referred from 2016 to September 2020. The transplants were-liver (n = 6), kidney (n = 6) and lung (n = 8). D positive cell populations were identified in 11 cases (0.1-8.0 ml); and required PAD (500-1500 IU). From these 20 patients, 10 sent a follow-up sample, where 8 required PAD top-up due to the detection of residual D positive cells (0.1-2 ml)-liver (n = 1), kidney (n = 1) and lung transplant (n = 6).

CONCLUSION

All patients in the study were D negative females, in which 18 were considered by guidelines to be of childbearing potential (2-42 years old) and 2 were >50 years old. Referrals demonstrate an awareness for the correct calculation of PAD to prevent D sensitisation. The sample size is small, but top up requirement in 8/20 of cases demonstrates accurate quantification is clearly needed to ensure the appropriate dose of PAD is provided.

Anti-D monoclonal antibodies from 23 human and rodent cell lines display diverse IgG Fc-glycosylation profiles that determine their clinical efficacy

Anti-D immunoglobulin (Anti-D Ig) prophylaxis prevents haemolytic disease of the fetus and newborn. Monoclonal IgG anti-Ds (mAb-Ds) would enable unlimited supplies but have differed in efficacy in FcγRIIIa-mediated ADCC assays and clinical trials. Structural variations of the oligosaccharide chains of mAb-Ds are hypothesised to be responsible. Quantitative data on 12 Fc-glycosylation features of 23 mAb-Ds (12 clones, 5 produced from multiple cell lines) and one blood donor-derived anti-D Ig were obtained by HPLC and mass spectrometry using 3 methods. Glycosylation of mAb-Ds from human B-lymphoblastoid cell lines (B) was similar to anti-D Ig although fucosylation varied, affecting ADCC activity. In vivo, two B mAb-Ds with 77–81% fucosylation cleared red cells and prevented D-immunisation but less effectively than anti-D Ig. High fucosylation (>89%) of mouse-human heterohybridoma (HH) and Chinese hamster ovary (CHO) mAb-Ds blocked ADCC and clearance. Rat YB2/0 mAb-Ds with <50% fucosylation mediated more efficient ADCC and clearance than anti-D Ig. Galactosylation of B mAb-Ds was 57–83% but 15–58% for rodent mAb-Ds. HH mAb-Ds had non-human sugars. These data reveal high galactosylation like anti-D Ig (>60%) together with lower fucosylation (<60%) as safe features of mAb-Ds for mediating rapid red cell clearance at low doses, to enable effective, inexpensive prophylaxis.

A Novel Rapid Method of Red Blood Cell and Platelet Permeabilization and Staining for Flow Cytometry Analysis

BACKGROUND

Flow cytometry essentially focuses on surface-expressed proteins, with few protocols being devoted to intracellular components. We evaluated a two-step procedure using new formaldehyde-free permeabilization and staining reagents that allow the staining of platelets and red blood cells (RBCs) from whole blood.

METHODS

Citrated blood was treated with the new staining protocol (NSP) or control reagent (phosphate-buffered solution bovine serum albumin) and stained with antibodies against surface or intracellular markers. The effects of the NSP on cell integrity, morphology, and content were evaluated.

RESULTS

The NSP slightly reduced the cell count (~20%) and changed the RBC morphology with a 42% mean diameter reduction. Conversely, the NSP did not affect platelet discoid morphology and led to a minor size decrease (11%). These morphological changes neither impelled a gating strategy modification nor interfered with the discrimination among populations based on surface markers. The NSP provided intracellular access to all the tested antigens: CD62P, FXIII, and CD63 in platelets and glycated and fetal hemoglobin (HbA1c and HbF) and nucleic acid in RBCs. The NSP gave excellent intra-assay precision with minimal impact on cell morphology and fluorescence labelling over time (up to 24 h).

CONCLUSIONS

With the ability to detect surface and intracellular antigens through a rapid preparation protocol without washing steps or toxic formaldehyde treatment, this NSP designed for research offers a marked improvement in the analysis of platelets and RBCs isolated directly from whole blood. Consequently, the NSP opens new avenues to investigate platelet degranulation and erythrocyte subpopulations. © 2019 International Clinical Cytometry Society.

The prevalence of maternal F cells in a pregnant population and potential overestimation of foeto-maternal haemorrhage as a consequence

BACKGROUND

Acid elution (AE) is used to estimate foeto-maternal haemorrhage (FMH). However AE cannot differentiate between cells containing foetal or adult haemoglobin F (F cells), potentially leading to false positive results or an overestimate of the amount of FMH. The prevalence of F cells in pregnant populations remains poorly characterised. The purpose of this study was to ascertain the incidence of HbF-containing red cells in our pregnant population using anti-HbF-fluorescein isothiocyanate flow cytometry (anti-HbF FC) and to assess whether its presence leads to a significant overestimate of FMH.

MATERIAL AND METHODS

Eighty-eight pregnant patients were assessed for the presence of F cells and foetal red cells by AE and anti-HbF FC. The "FMH equivalent", estimated by AE and anti-HbF FC, was calculated.

RESULTS

Thirty-six percent of the pregnant population had F-cell populations detectable by anti-HbF FC while AE detected F cells in 48% of the population. The mean estimated FMH equivalent determined by AE and anti-HbF FC was 0.59 mL (0-23.93 mL) and 0.41 (0 to 2.19 mL), respectively (p=0.012). In 3% of our population, AE overestimated the FMH by >3 mL due to the presence of an F-cell population of at least 16%.

DISCUSSION

Thirty-six percent of a prospectively evaluated group of consecutive pregnant women were found to have F-cell populations. In some patients, these findings were clinically significant as AE overestimated the degree of FMH as a consequence.