Validation of a single tube 3-colour immature red blood cell screening assay for the detection and enumeration of small, medium and large paroxysmal nocturnal haemoglobinuria clones by flow cytometry

INTRODUCTION

The reliable diagnosis of paroxysmal nocturnal haemoglobinuria (PNH) by flow cytometry is based on mandatory analysis of the erythroid, neutrophilic and monocytic lineages. In this study, we have evaluated the performance characteristics of a recently published immature red blood cell (iRBC) assay as a potential screening test for PNH by flow cytometry.

METHODS

Intra- and inter-assay imprecision were determined in five replicates of small, medium and large PNH iRBC clones. Analytical and functional sensitivity was assessed by performing spiking tests for five replicates. Thirty healthy donors and 441 PNH patients were tested for evaluation of clinical specificity, sensitivity, positive and negative predictive values.

RESULTS

Coefficients of variation (CV) for intra-/inter-assay imprecision analyses were 1.31/1.50, 3.19/2.61 and 3.99/1.58 for the big, medium and small clone sizes, respectively. Absolute values (100%) were found for both clinical specificity and sensitivity as well as for both positive and negative predictive values. The CV from 5 replicate results for 10 clustered events was 15.7%. The coefficient of determination (r² ), Pearson's correlation coefficient (r) and Bland-Altman mean bias were 0.9436/0.9234/1.7 for PNH iRBC compared to PNH neutrophils and 0.9553/0.9387/2.1 for PNH iRBCs compared to PNH monocytes.

CONCLUSION

Our results confirm very good performance characteristics, high analytical and functional sensitivity, absolute clinical specificity and sensitivity as well as favourable correlation between PNH iRBCs and both PNH neutrophils and monocytes, suggesting that this cost-effective 3-colour iRBC assay can be used as a reliable screening test for evaluation of small, medium and large PNH clones by flow cytometry.

Inflammatory Biomarkers, Hematopoietic Stem Cells, and Symptoms in Breast Cancer Patients Undergoing Adjuvant Radiation Therapy

Background

Fatigue and insomnia are common symptoms experienced by breast cancer patients undergoing adjuvant radiation therapy (RT), yet the underlying mechanisms of these symptoms are unclear. In particular, the roles of hematopoietic stem cells (HSCs) and inflammatory cytokines remain to be elucidated.

Methods

Breast cancer patients (n = 147) completed questionnaires to longitudinally assess symptoms before, during, and after adjuvant RT. Phlebotomies were performed prior to RT, at the second and fifth treatment fractions, end of treatment (EOT), and 1 month after completing RT, assessing for CD34⁺, CD45⁺, full hematology, and 17 inflammatory cytokines. The associations between symptoms and all biomarkers were evaluated. All statistical tests were 2-sided.

Results

General fatigue and insomnia worsened with RT, with peak levels observed at EOT, which remained statistically significant even after controlling for anxiety and depression (P < .05 for all). CD34⁺, CD45⁺, white blood cell, and lymphocyte counts decreased, with the lowest levels also observed at EOT (P < .001). Fatigue and insomnia were associated with changes in both interferon γ-induced protein 10 (IP-10) - (P = .03 and P = .01, respectively) and tumor necrosis factor receptor II (TNF-RII) (P = .02 and P = .006, respectively), while mental fatigue was associated with increased matrix metalloproteinases-2 (MMP-2) levels (P = .03). Patients who received prior chemotherapy demonstrated statistically significantly greater severity in all symptoms, with lower baseline HSC levels.

Conclusions

This is the first longitudinal study to examine linkages between symptoms, HSCs, and cytokines, demonstrating that fatigue and insomnia shared associations with increasing serum levels of IP-10 and TNF-RII, and mental fatigue was associated with increasing serum levels of MMP-2. Our findings highlight opportunities for further research into mechanisms and potential interventions for these symptoms.

Multi-laboratory assay for harmonization of enumeration of viable CD34+ and CD45+ cells in frozen cord blood units

BACKGROUND AIMS

In 2016, specifications for both pre-cryopreserved and post-thawed cord blood were defined in the sixth edition of NetCord Foundation for the Accreditation of Cellular Therapy (FACT) Standards for Cord Blood Banks. However, for several experts, harmonization regarding flow cytometry analysis performed on post-thawed samples is still a concern. A multicenter study led by Héma-Québec aimed to provide scientific data to support the cord blood accreditation bodies such as NetCord FACT in the revision of standards.

METHODS

Twelve cord blood units were processed for plasma and red cell reduction following standard operating procedures. Cord blood unit aliquots were shipped to eight participating centers under cryogenic conditions for analysis before and after standardization of protocol. Repeatability of stem cell count, measured pre- and post-intervention with the centers, was estimated using multilevel linear regression models with a heterogeneous compound symmetry correlation structure among repeated measures.

RESULTS

Excellent inter-center repeatability was reported by each participant regarding the viable CD34+ cells concentration, and a successful improvement effect of protocol standardization was also observed. However, we observed that better control over the critical parameters of the protocol did not have a significant effect on improving homogeneity in the enumeration of CD45+ cells.

CONCLUSIONS

The current practice in cord blood selection should now also consider relying on post-thaw CD34+ concentration, providing that all cord blood banks or outsourcing laboratories in charge of the analysis of post-thaw CB samples take into account the consensual recommendations provided in this work and adhere to a good-quality management system.

CD71 improves delineation of PNH type III, PNH type II, and normal immature RBCS in patients with paroxysmal nocturnal hemoglobinuria

BACKGROUND

The diagnosis of paroxysmal nocturnal hemoglobinuria (PNH) relies on flow cytometric demonstration of loss of glycosyl-phosphatidyl inositol (GPI)-anchored proteins from red blood cells (RBC) and white blood cells (WBC). High-sensitivity multiparameter assays have been developed to detect loss of GPI-linked structures on PNH neutrophils and monocytes. High-sensitivity assays to detect PNH phenotypes in RBCs have also been developed that rely on the loss of GPI-linked CD59 on CD235a-gated mature RBCs. The latter is used to delineate PNH Type III (total loss of CD59) and PNH Type II RBCs (partial loss of CD59) from normal (Type I) RBCs. However, it is often very difficult to delineate these subsets, especially in patients with large PNH clones who continue to receive RBC transfusions, even while on eculizumab therapy.

METHODS

We have added allophycocyanin (APC)-conjugated CD71 to the existing CD235aFITC/CD59PE RBC assay allowing simultaneous delineation and quantification of PNH Type III and Type II immature RBCs (iRBCs).

RESULTS

We analyzed 24 medium to large-clone PNH samples (>10% PNH WBC clone size) for PNH Neutrophil, PNH Monocyte, Type III and Type II PNH iRBCs, and where possible, Type III and Type II PNH RBCs. The ability to delineate PNH Type III, Type II, and Type I iRBCs was more objective compared to that in mature RBCs. Additionally, total PNH iRBC clone sizes were very similar to PNH WBC clone sizes.

CONCLUSIONS

Addition of CD71 significantly improves the ability to analyze PNH clone sizes in the RBC lineage, regardless of patient hemolytic and/or transfusion status.

ICCS/ESCCA consensus guidelines to detect GPI-deficient cells in paroxysmal nocturnal hemoglobinuria (PNH) and related disorders part 3 - data analysis, reporting and case studies

Over the past several years, a diverse group of physicians and other laboratory scientists have developed various recommendations and guidelines regarding best practices for PNH testing. This manuscript is based on these previous recommendations as well as various other relevant publications of experts in the area of PNH testing. The goal is to provide flow cytometry laboratories with an updated consensus approach to analysis and reporting of PNH results and to address the most common analytical challenges for accurate reporting of this rare disease. A comprehensive case library is included in this section. © 2017 International Clinical Cytometry Society.

How we treat paroxysmal nocturnal hemoglobinuria: A consensus statement of the Canadian PNH Network and review of the national registry

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematologic disease characterized by intravascular hemolysis, thrombophilia, and marrow failure. Its phenotype is due to absent or reduced expression of GPI-linked complement regulators and subsequent sensitivity of hematopoietic cells to complement-mediated damage and lysis. Introduction of the terminal complement inhibitor eculizumab drastically improved outcomes in PNH patients; however, despite this improvement, there remain several challenges faced by PNH patients and physicians who care for them. One of the most important is increasing awareness of the heterogeneity with which patients can present, which can lead to significant delays in recognition. Data from the Canadian PNH Registry are presented to demonstrate the variety of presenting symptoms. In Canada, geography precludes consolidation of care to just a few centers, so management is distributed across academic hospitals, linked together as the Canadian PNH Network. The Network over the last several years has developed educational programs and clinical checklists and has worked to standardize access to diagnostics across the country. Herein, we address some of the common diagnostic and therapeutic challenges faced by PNH physicians and give our recommendations. Gaps in knowledge are also addressed, and where appropriate, consensus opinion is provided.

Dual gold and photoredox catalysed C-H activation of arenes for aryl-aryl cross couplings

A mild and fully catalytic aryl-aryl cross coupling via gold-catalysed C-H activation has been achieved by merging gold and photoredox catalysis. The procedure is free of stoichiometric oxidants and additives, which were previously required in gold-catalysed C-H activation reactions. Exploiting dual gold and photoredox catalysis confers regioselectivity via the crucial gold-catalysed C-H activation step, which is not present in the unselective photocatalysis-only counterpart.

Standardizing leucocyte PNH clone detection: an international study

BACKGROUND

Consensus and Practical Guidelines for robust high-sensitivity detection of glycophosphatidylinostitol-deficient structures on red blood cells and white blood cells in paroxysmal nocturnal hemoglobinuria (PNH) were recently published.

METHODS

UK NEQAS LI issued three stabilized samples manufactured to contain no PNH cells (normal), approximately 0.1% and 8% PNH leucocyte populations, together with instrument-specific Standard Operating Procedures (SOPs) and pretitered antibody cocktails to 19 international laboratories experienced in PNH testing. Samples were tested using both standardized protocol/reagents and in-house protocols. Additionally, samples were issued to all participants in the full PNH External Quality Assessment (EQA) programs.

RESULTS

Expert laboratory results showed no difference in PNH clone detection rates when using standardized and their "in-house" methods, though lower variation around the median was found for the standardized approach compared to in-house methods. Neutrophil analysis of the sample containing an 8% PNH population, for example, showed an interquartile range of 0.48% with the standardized approach compared with 1.29% for in-house methods. Results from the full EQA group showed the greatest variation with an interquartile range of 1.7% and this was demonstrated to be significantly different (P<0.001) to the standardized cohort.

CONCLUSIONS

The results not only demonstrate that stabilized whole PNH blood samples are suitable for use with currently recommended high-sensitivity reagent cocktails/protocols but also highlight the importance of using carefully selected conjugates alongside the standardized protocols. While much more variation was seen among the full UK NEQAS LI EQA group, the standardized approach lead to reduced variation around the median even for the experienced laboratories.

Standardizing Leucocyte PNH clone detection: An international study

Background: Consensus and Practical Guidelines for robust high-sensitivity detection of glycophosphatidylinostitol (GPI)-deficient structures on Red Blood Cells (RBCs) and White Blood Cells (WBCs) in Paroxysmal Nocturnal Hemoglobinuria (PNH) were recently published. Methods: UK NEQAS LI issued 3 stabilized samples manufactured to contain no PNH cells (normal), approximately 0.1% and 8% PNH leucocyte populations, together with instrument-specific SOPs and pre-titered antibody cocktails to 19 international laboratories experienced in PNH testing. Samples were tested using both standardized protocol/reagents and in-house protocols. Additionally, samples were issued to all participants in the full PNH EQA programmes. Results: Expert laboratory results showed no difference in PNH clone detection rates when using standardized and their 'in-house' methods though lower variation around the median was found for the standardized approach compared to in-house methods. Neutrophil analysis of the sample containing an 8% PNH population, for example, showed an interquartile range of 0.48% with the standardized approach compared with 1.29% for in-house methods. Results from the full EQA group showed the greatest variation with an inter-quartile range of 1.70 and this was demonstrated to be significantly different (P<0.001) to the standardized cohort. Conclusions: The results not only demonstrate that stabilized whole PNH blood samples are suitable for use with currently recommended high-sensitivity reagent cocktails/protocols but also highlight the importance of using carefully selected conjugates alongside the standardized protocols. While much more variation was seen amongst the full UK NEQAS LI EQA group, the standardized approach lead to reduced variation around the median even for the experienced laboratories. © 2014 Clinical Cytometry Society.

Use of CD157 in FLAER-based assays for high-sensitivity PNH granulocyte and PNH monocyte detection

Background: Recent Flow Cytometric guidelines to detect Paroxysmal Nocturnal Hemoglobinuria (PNH) in white blood cells recommend using FLAER-based assays to detect granulocytes and monocytes lacking expression of GPI-linked structures. However national proficiency testing results continue to suggest a need for improved testing algorithms, including the need to optimize diagnostic analytes in PNH. Methods: CD157 is another GPI-linked structure expressed on both granulocytes and monocytes and here we assess its ability to replace CD24 and CD14 in predicate 4-color granulocyte and monocyte assays respectively. We also assess a single tube, 5-color combination of FLAER, CD157, CD64, CD15 and CD45 to simultaneously detect PNH clones in granulocyte and monocyte lineages. Results: Delineation of PNH from normal phenotypes with 4- or 5-color CD157-based assays compared favorably with 4-color predicate methods and PNH clone size data were similar and highly correlated (R2 >0.99) with predicate values over a range (0.06% - 99.8%) of samples. Both CD157-based assays exhibited similar high levels of sensitivity and low background levels in normal samples. Conclusion: While CD157-based 4- and 5-color assays generated closely similar results to the predicate assays on a range of PNH and normal samples, the 5-color assay has significant advantages. Only a single 5-color WBC reagent cocktail is required to detect both PNH granulocytes and monocytes. Additionally, sample preparation and analysis time is reduced yielding significant efficiencies in technical resources and reagent costs. All 4- and 5-color reagent sets stained stabilized whole blood PNH preparations, used in external quality assurance programs. © 2013 Clinical Cytometry Society.

ISHAGE protocol: are we doing it correctly?

BACKGROUND

Flow cytometric CD34(+) stem cell enumeration is routinely performed to optimize timing of peripheral blood stem cell collections and assess engraftment capability of the apheresis product. While a number of different flow methodologies have been described, the highly standardized ISHAGE protocol is currently the most widely employed, with 204/255 (81%) international participants in the UK NEQAS CD34(+) stem cell enumeration program indicating their use of this method. Recently, two laboratories were identified as persistent poor performers, a fact attributed to incorrect ISHAGE protocol usage/setup. This prompted UK NEQAS to question whether other laboratories were making similar errors and, if so, how this might affect individual EQA performance.

METHODS AND RESULTS

In send out 0801, where two stabilized samples were issued, the EQA center surveyed 255 participants with flow analysis data and subsequent results collected. One hundred and ninety-six laboratories returned results with 103 returning dot plots. Eighty-three out of one hundred and three stated that they used the ISHAGE protocol gating strategy but 43% (36/83) were incorrectly set-up. Analysis of the data showed those incorrectly using single platform ISHAGE gating strategy were twice as likely to fail an EQA exercise compared to those using the protocol correctly. This failure rate increased two fold when incorrect ISHAGE protocol was used in a dual platform setting.

CONCLUSION

This study suggests a widespread fundamental lack of understanding of the ISHAGE protocol and the need to deploy it correctly, potentially having significant clinical implications and highlights the need to monitor participants rigorously in their deployment of the ISHAGE protocol. It is hoped that once these findings have been disseminated, performance can be improved.

Guidelines for the diagnosis and monitoring of paroxysmal nocturnal hemoglobinuria and related disorders by flow cytometry

BACKGROUND

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematopoietic stem cell disorder characterized by a somatic mutation in the PIGA gene, leading to a deficiency of proteins linked to the cell membrane via glycophosphatidylinositol (GPI) anchors. While flow cytometry is the method of choice for identifying cells deficient in GPI-linked proteins and is, therefore, necessary for the diagnosis of PNH, to date there has not been an attempt to standardize the methodology used to identify these cells.

METHODS

In this document, we present a consensus effort that describes flow cytometric procedures for detecting PNH cells.

RESULTS

We discuss clinical indications and offer recommendations on data interpretation and reporting but mostly focus on analytical procedures important for analysis. We distinguish between routine analysis (defined as identifying an abnormal population of 1% or more) and high-sensitivity analysis (in which as few as 0.01% PNH cells are detected). Antibody panels and gating strategies necessary for both procedures are presented in detail. We discuss methods for assessing PNH populations in both white blood cells and red blood cells and the relative advantages of measuring each. We present steps needed to validate the more elaborate high-sensitivity techniques, including the need for careful titration of reagents and determination of background rates in normal populations, and discuss technical pitfalls that might affect interpretation.

CONCLUSIONS

This document should both enable laboratories interested in beginning PNH testing to establish a valid procedure and allow experienced laboratories to improve their techniques.

Use of a FLAER-based WBC assay in the primary screening of PNH clones

Diagnosis of paroxysmal nocturnal hemoglobinuria (PNH) with flow cytometry traditionally involves the analysis of CD55 and CD59 on RBCs and neutrophils. However, the ability to accurately detect PNH RBCs is compromised by prior hemolysis and/or transfused RBCs. Patients with aplastic anemia (AA) and myelodysplastic syndrome (MDS) can also produce PNH clones. We recently described a multiparameter fluorescent aerolysin (FLAER)-based flow assay using CD45, CD33, and CD14 that accurately identified PNH monocyte and neutrophil clones in PNH, AA, and MDS. Here, we compared the efficiency of this WBC assay with a CD59-based assay on RBCs during a 3-year period. PNH clones were detected with the FLAER assay in 63 (11.8%) of 536 samples tested, whereas PNH RBCs were detected in only 33 (6.2%), and always with a smaller clone size. The FLAER assay on WBCs is a more sensitive and robust primary screening assay for detecting PNH clones in clinical samples.

Methods for accurate measures of total ventricular activation time

The purpose of this study was to determine improved measures of total ventricular activation time for the diagnosis and treatment of patients undergoing cardiac resynchronization therapy (CRT). This work investigates the accuracy of a root mean square (RMS) based QRS width computed from unipolar electrograms (EGs) measured in heart for representing true total ventricular activation time (TVAT). The study also investigated the use subsets of EGs obtained from the endocardial and epicardial surfaces as indicators of TVAT. Transmural needle electrodes (96) were used to obtain 960 EGs from six normal isolated canine hearts. RMS-based QRS-widths from the endocardial and epicardial surfaces and volume were compared to the TVAT measured from all 960 EGs. No statistically significant differences were found in RMS-based QRS-widths obtained from all three sets of electrograms when compared with true TVAT. Activation times obtained from endocardial and epicardial surfaces were found to be poor indicators of true TVAT. The results support the use of RMS techniques for providing more accurate measures of TVAT.

Diagnosing PNH with FLAER and multiparameter flow cytometry

BACKGROUND

PNH is an acquired hematopoietic stem cell disorder leading to a partial or absolute deficiency of all glycophosphatidyl-inositol (GPI)-linked proteins. The classical approach to diagnosis of PNH by cytometry involves the loss of at least two GPI-linked antigens on RBCs and neutrophils. While flow assays are more sensitive and specific than complement-mediated lysis or the Hams test, they suffer from several drawbacks. Bacterial aerolysin binds to the GPI moiety of cell surface GPI-linked molecules and causes lysis of normal but not GPI-deficient PNH cells. FLAER is an Alexa488-labeled inactive variant of aerolysin that does not cause lysis of cells. Our goals were to develop a FLAER-based assay to diagnose and monitor patients with PNH and to improve detection of minor populations of PNH clones in other hematologic disorders.

METHODS

In a single tube assay, we combined FLAER with CD45, CD33, and CD14 allowing the simultaneous analysis of FLAER and the GPI-linked CD14 structure on neutrophil and monocyte lineages.

RESULTS

Comparison to standard CD55 and CD59 analysis showed excellent agreement. Because of the higher signal to noise ratio, the method shows increased sensitivity in our hands over single (CD55 or CD59) parameter analysis. Using this assay, we were able to detect as few as 1% PNH monocytes and neutrophils in aplastic anemia, that were otherwise undetectable using CD55 and CD59 on RBC's. We also observed abnormal FLAER staining of blast populations in acute leukemia. In these cases, the neutrophils stained normally with FLAER, while the gated CD33bright cells failed to express normal levels of CD14 and additionally showed aberrant CD45 staining and bound lower levels of FLAER.

CONCLUSION

FLAER combined with multiparameter flow cytometry offers an improved assay for diagnosis and monitoring of PNH clones and may have utility in detection of unsuspected myeloproliferative disorders.

Clonality analysis of cell lineages in acute myeloid leukemia with inversion 16

Bone marrow from 5 patients with acute myeloid leukemia with inversion 16, inv(16), was studied by a combination of fluorescence activated cell sorting (FACS) and fluorescence in situ hybridization (FISH) to establish the extent of cell-lineage involvement of inv(16). In all cases, interphase FISH demonstrated the inv(16) in 80-92% of blasts, monocytes, granulocytes, and a proportion of B-cells (21-41%). In contrast, inv(16) was not detectable above threshold levels in mature T-cells. The current study provides a direct evidence for the clonal involvement of myeloid lineage cells and B-lymphocytes and suggests that T-cells are not part of the malignant clone in this disease.

Identification of cell lineages involved by t(15;17) in acute promyelocytic leukemia by combined fluorescence activated cell sorting and FISH

Bone marrow cells from five patients with acute promyelocytic leukemia (APL) with t(15;17) were studied by a combination of fluorescence activated cell sorting and fluorescence in situ hybridization (FISH) to establish the cell lineage involvement of t(15;17). Interphase FISH demonstrated that the fusion gene (PML/RARA) was present in almost all abnormal promyelocytes. In one case, the translocation was demonstrated in both CD34+ and CD34- APL cells. The t(15;17) abnormality was not detectable in erythroblasts nor in T- or B-lymphoid cells. These results suggest that lymphocytes and erythroblasts are not clonally involved in APL, and that malignant transformation in some cases of APL may occur at the level of CD34+ cells.

Interphase cytogenetic analysis of clonality in peripheral blood cells from a patient with Down syndrome and acute megakaryoblastic leukemia

A combination of fluorescence-activated cell sorting and interphase fluorescence in situ hybridization (FISH) techniques was used to detect a clonal chromosomal marker in blasts, granulocytes, and T and B lymphocytes of the peripheral blood from a patient with Down syndrome and acute megakaryoblastic leukemia (AMKL) associated with trisomy 8 as a karyotypic abnormality. Immunophenotypic studies with flow cytometry showed two populations of leukemic blasts distinguished by their expression of the CD34 antigen. Interphase FISH studies revealed clonal trisomy 8 FISH signals in almost all blast cells, regardless of CD34 expression, as well as in a small subpopulation of granulocytes. Normal chromosome 8 signal patterns were detected in T and B cells and in a great majority of granulocytes. The present study provides evidence for the clonal involvement of leukemic blasts in AMKL of Down syndrome, indicating that a trisomy 8 abnormality may be a primary event in leukemogenesis. The transformation occurs in progenitor cells with limited myeloid differentiation and without involvement of lymphoid lineage cells.

Validation of the single-platform ISHAGE method for CD34(+) hematopoietic stem and progenitor cell enumeration in an international multicenter study

BACKGROUND

Flow cytometric enumeration of CD34+ hematopoietic sterm and progenitor cells (HPC) is the reference point for undertaking apheresis and evaluation of adequacy for PBSC engraftment. An external quality assurance (EQA) scheme for CD34+ HPC enumeration has been operational in Belgium, Netherlands and Luxemburg (Benelux) since 1995. Within this group, a multicenter survey was held to validate the state-of-the-art methodology, i.e., multiparametric definition of HPC based on light scatter, expression of CD34 and CD45, and counting beads (i.e., 'single platform ISHAGE' method).

METHODS

'Real-time' EQA was used to monitor the application of the single-platform ISHAGE method by 36 participants. Three send-outs of stabilized blood with CD34+ cell counts 35-60 cells/microl were distributed to 36 participants, who were required to assay the samples on three occasions using the standard assay and their local techniques. These results were compared with thosed obtained by 111-116 UK NEQAS participants testing the same specimens.

RESULTS

Using the single platform ISHAGE methods, between-laboratory coefficients of variations (CVs) as low as 10% were achieved. Intra-laboratory CVs were < 5% for approximately 50% of the participants. Local single-platform techniques yielded between-laboratory CVs as low as 9% in both Benelux and UK NEQAS cohorts. In contrast, the lowest between-laboratory CVs using dual-platform techniques were 17% (Benelux) and 21% (UK NEQAS), respectively.

CONCLUSION

The single-platform ISHAGE method for CD34+ cell enumeration has been validated by an international group of 36 laboratories. The observed varation between laboratories allows a meaningful comparison of CD34+ cell enumeration.

Antibody W7C5 defines a CD109 epitope expressed on CD34+ and CD34- hematopoietic and mesenchymal stem cell subsets

The cell surface antigen recognized by monoclonal antibody W7C5 is expressed at low levels on human CD34(+) and CD34(-) bone marrow stem cell populations but at high levels on fetal liver CD34(+) cells. To identify the recognized antigen, we performed partial amino acid sequence and MALDI analysis of purified W7C5 antigens. The analyses revealed that MoAb W7C5 detects CD109, a recently cloned glycophosphatidylinositol-linked glycoprotein. The specificity of MoAb W7C5 was further confirmed by the selective recognition of CHO cells transfected with human CD109 cDNA.

Number of viable CD34(+) cells reinfused predicts engraftment in autologous hematopoietic stem cell transplantation

Reduced CD34(+) cell viability due to cryopreservation has unknown effects on subsequent hematopoietic engraftment in autologous transplantation. Thirty-six consecutive autologous peripheral stem cell collections were analyzed for absolute viable CD34(+) cell numbers at the time of stem cell collection and prior to re-infusion. Viable CD34(+) cells were enumerated using single platform flow cytometry and the molecular exclusion dye 7-amino actinomycin D. The median number of viable CD34(+) cells was 3.6 x 10(6)/kg at the time of harvest and 2.0 x 10(6)/kg after thawing. When viable CD34(+)cells enumerated after thawing were <2.0, 2.0-5.0, or >5.0 x 10(6)/kg, the median time to platelet engraftment was 17, 12 and 10 days, respectively (P < 0.05 for comparison of the group with <2.0 x 10(6)/kg and the other two groups), and the median time to neutrophil engraftment was 13, 14 and 12 days, respectively (P = NS). A minimum of 2.0 x 10(6) CD34(+) cells/kg was harvested in 33 of 36 patients (92%) but only 19 of 36 (52%) patients met this threshold at the time of reinfusion. The reduced numbers of viable CD34(+) cells measured prior to re-infusion is associated with time to platelet engraftment and may be useful in monitoring stem cell loss during processing and identifying patients at risk of graft failure.

A tyrosine703serine polymorphism of CD109 defines the Gov platelet alloantigens

The biallelic platelet-specific Gov antigen system-implicated in refractoriness to platelet transfusion, neonatal alloimmune thrombocytopenia, and posttransfusion purpura-is carried by the glycosylphosphatidylinositol (GPI)-linked protein CD109. The recent identification of the human CD109 complementary DNA (cDNA) has allowed the molecular nature of the Gov alleles to be elucidated. By using reverse transcriptase-polymerase chain reaction (RT-PCR) to amplify CD109 cDNAs from 6 phenotypically homozygous Gov(aa) and Gov(bb) individuals, we have determined that the Gov alleles differ by an A to C single nucleotide polymorphism (SNP) at position 2108 of the coding region, resulting in a Tyr/Ser substitution at CD109 amino acid 703. Allele-specific PCR sequence-specific primers (SSP), PCR-restriction fragment length polymorphism, and real-time PCR studies of 15 additional donors (5 Gov(aa), 5 Gov(bb), and 5 Gov(ab)) confirmed that this SNP correlates with the Gov phenotype. In addition, Chinese hamster ovary cells transiently expressing nucleotide 2108 A>C CD109 cDNA variants were recognized specifically by allele-specific Gov antisera, indicating that this polymorphism defines the Gov alloantigenic determinants. Real-time PCR was then used to genotype 85 additional Gov phenotyped donors. In all but 3 cases, genomic testing concurred with the Gov phenotype. Repeat testing corrected 2 of these discrepancies in favor of the genotyping result. The third discrepancy could not be resolved, likely reflecting low-level CD109 expression below the sensitivity of the phenotyping assay. We conclude that the Gov alleles are defined by a 2108 A>C SNP that results in a Tyr703Ser substitution of CD109 and that genotyping studies are more accurate for Gov alloantigen determination than are conventional serologic methods.

Cell surface antigen CD109 is a novel member of the alpha(2) macroglobulin/C3, C4, C5 family of thioester-containing proteins

Cell surface antigen CD109 is a glycosylphosphatidylinositol (GPI)-linked glycoprotein of approximately 170 kd found on a subset of hematopoietic stem and progenitor cells and on activated platelets and T cells. Although it has been suggested that T-cell CD109 may play a role in antibody-inducing T-helper function and it is known that platelet CD109 carries the Gov alloantigen system, the role of CD109 in hematopoietic cells remains largely unknown. As a first step toward elucidating the function of CD109, we have isolated and characterized a human CD109 cDNA from KG1a and endothelial cells. The isolated cDNA comprises a 4335 bp open-reading frame encoding a 1445 amino acid (aa) protein of approximately 162 kd that contains a 21 aa N-terminal leader peptide, 17 potential N-linked glycosylation sites, and a C-terminal GPI anchor cleavage-addition site. We report that CD109 is a novel member of the alpha 2 macroglobulin (alpha 2M)/C3, C4, C5 family of thioester-containing proteins, and we demonstrate that native CD109 does indeed contain an intact thioester. Analysis of the CD109 aa sequence suggests that CD109 is likely activated by proteolytic cleavage and thereby becomes capable of thioester-mediated covalent binding to adjacent molecules or cells. In addition, the predicted chemical reactivity of the activated CD109 thioester is complement-like rather than resembling that of alpha 2M proteins. Thus, not only is CD109 potentially capable of covalent binding to carbohydrate and protein targets, but the t(1/2) of its activated thioester is likely extremely short, indicating that CD109 action is highly restricted spatially to the site of its activation.

Differences in cell cycle kinetics of candidate engrafting cells in human bone marrow and mobilized peripheral blood

Patients undergoing hematopoietic stem cell transplantation (HSCT) with mobilized peripheral blood (MPB) engraft quicker than those receiving bone marrow (BM). Our objective was to determine whether candidate engrafting cells--primitive hematopoietic progenitors (PHPs)--from MPB and BM exhibit different responses to cytokines that could explain this observation. We compared the cell cycle kinetics and ex vivo expansion of PHP-enriched cells obtained from MPB (n = 12) and BM (n = 10) by fluorescence-activated sorting of CD90+, AC133+ or CD38(dull) subsets of pre-selected CD34(+) cells. Cell cycle status, before and after 40 hours of serum-free culture with a cytokine cocktail, was assessed by multiparameter flow cytometry following incubation with Hoechst 33342 and pyronin Y. We found that 0.2% +/- 0.3% of MPB CD34(+)CD90(+) cells were in S/G(2)/M phases at hour 0, compared with 5% +/- 2.5% of those from BM (p = 0.0001), and 86.3% +/- 9.7% were in G(0), compared with 65.3% +/- 10% of those in BM (p = 0.0001). After 40 hours of culture, CD34(+)CD90(+) cells from MPB were more mitotically active than those from BM, with 29% +/- 4.9% in S/G(2)/M and 20% +/- 11.4% in G(0), compared to 19% +/- 6.5% (p = 0.001) and 39.2% +/- 22% (p = 0.027) of cells from BM. There was greater expansion of both total CD34(+) cells and the CD90(+) subset from MPB samples (p = 0.001 and 0.0001, respectively). Results from PHPs defined on the basis of AC133 expression correlated well with results obtained in CD90(+) subsets (r(2) = 0.81; p = 0.014).MPB PHPs appear to be primed for a greater acceleration in mitotic activity upon cytokine exposure. This qualitative difference may contribute to the earlier engraftment seen after HSCT using MPB grafts.

Flow cytometric enumeration and immunophenotyping of hematopoietic stem and progenitor cells

Flow cytometric enumeration of CD34(+) hematopoietic stem and progenitor cells (HPC) is widely used to evaluate the adequacy of peripheral blood stem cell grafts and is also useful for planning the apheresis sessions needed to obtain these grafts. A state-of-the-art method to enumerate CD34(+) cells has been developed that makes use of a multiparameter definition of HPC, based on their light scatter characteristics and dim expression of CD45, utilizing fluorescent counting beads. This approach allows the absolute CD34(+) cell count to be determined directly from a flow cytometer. The method can be extended with a viability stain and additional markers for further immunologic characterization of CD34(+) cells, and has been successfully implemented in multicenter trials. Using such a standardized assay, it should be possible to define more accurately the lower threshold for a safe HPC graft in terms of short- and long-term hematopoietic reconstitution. Semin Hematol 38:139-147.

Replicative stress after allogeneic bone marrow transplantation: changes in cycling of CD34+CD90+ and CD34+CD90- hematopoietic progenitors

To further characterize hematopoietic "replicative stress" induced by bone marrow transplantation (BMT), the cell-cycle status of CD90+/- subsets of marrow CD34+ cells obtained 2 to 6 months after transplantation from 11 fully chimeric recipients was examined. Cycling profiles, derived by flow cytometry after staining with Hoechst 33342 and pyronin Y, were compared with those of 14 healthy marrow donors. Primitive CD34+CD90+ cells represented a smaller proportion of CD34+ cells in recipients (10% +/- 4% versus 19.6% +/- 5.3% in donors; P <.0001) and were more mitotically active, with the proportion of cells in S/G2/M nearly 4-fold higher than in donors (15.6% +/- 3% and 4.4% +/- 1.6%, respectively; P <.0001). By comparison, there was a modest increase in the proportion of CD34+CD90- progenitors in S/G2/M after BMT (10.9% +/- 1% vs 9.6% +/- 2% in donors; P =.04). Replicative stress after BMT is borne predominantly by cells in a diminished CD34+CD90+ population.

Structural and functional features of the CD34 antigen: an update

CD34 is a heavily glycosylated type I transmembrane molecule, that can be phoshorylated by a variety of kinases including Protein kinase C and Tyrosine kinases. The classification of epitopes detected by different CD34 MAbs has aided the selection of appropriate antibodies for use in specific clinical and research laboratory settings. Detailed structural analyses and cloning studies have confirmed that CD34 is a sialomucin, and have suggested that the fine composition of the carbohydrate moieties contained in its extended N-terminal region is important in determining its interactions with a variety of different ligands. For high endothelial venules (HEV) CD34 to serve as a ligand for L-selectin, the O-linked glycans of HEV CD34 are modified in an exquisitely specific manner with a variety of sialyl- and sulfo-transferases. In contrast, CD34 is not the ligand for L-selectin in hematopoietic stem/progenitor cells (HSPCs) and despite much endeavour, ligands for hematopoietic CD34 remain to be identified.

Flow cytometric enumeration and immunophenotyping of hematopoietic stem and progenitor cells

Flow cytometric enumeration of CD34+ hematopoietic stem and progenitor cells (HPC) is widely used for evaluation of graft adequacy of peripheral blood stem cell grafts, and is also useful in planning the apheresis sessions necessary to obtain these grafts. The state-of-the-art method to enumerate CD34+ cells makes use of a multiparameter definition of HPC based on their light scatter characteristics and dim expression of CD45, and the use of counting beads to derive the concentration of CD34+ cells directly from the flow cytometric assessment. This method can be extended with a viability stain and additional markers for further immunological characterization of CD34+ cells, and has been successfully implemented in multicenter trials. Thus, the lower threshold of a safe HPC graft in terms of short- and long-term hematopoiesis may be more accurately defined.