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In this study, we aimed at disclosing the main features of paroxysmal nocturnal hemoglobinuria (PNH) clones, their association with presentation syndromes, and their changes during follow-up. A large-scale, cooperative collection (583 clones from 529 patients) of flow cytometric and clinical data was entered into a national repository. Reason for testing guidelines were provided to the 41 participating laboratories, which followed the 2010 technical recommendations for PNH testing by Borowitz. Subsequently, the 30 second-level laboratories adopted the 2012 guidelines for high-resolution PNH testing, both upon order by the local clinicians and as an independent laboratory initiative in selected cases. Type3 and Type2 PNH clones (total and partial absence of glycosyl-phosphatidyl-inositol-anchor, respectively) were simultaneously present in 54 patients. In these patients, Type3 component was sevenfold larger than Type2 (p 0.001). Frequency distribution analysis of solitary Type3 clone size (N = 442) evidenced two discrete patterns: small (20% of peripheral neutrophils) and large ( 70%) clones. The first pattern was significantly associated with bone marrow failure and myelodysplastic syndromes, the second one with hemolysis, hemoglobinuria, and thrombosis. Pediatric patients (N = 34) showed significant preponderance of small clones and bone marrow failure. The majority of PNH clones involved neutrophils, monocytes, and erythrocytes. Nevertheless, we found clones made exclusively by white cells (N = 13) or erythrocytes (N = 3). Rare cases showed clonal white cells restricted only to monocytes (6 cases) or neutrophils (3 cases). Retesting over 1-year follow-up in 151 cases showed a marked clone size increase in 4 cases and a decrease in 13, demonstrating that early breaking-down of PNH clones is not a rare event (8.6% of cases). This collaborative nationwide study demonstrates a clear-cut difference in size between Type2 and Type3 clones, emphasizes the existence of just two classes of PNH presentations based on Type3 clone size, depicts an asymmetric cellular composition of PNH clones, and documents the possible occurrence of changes in clone size during the follow-up.

A 75-year-old patient diagnosed as having acute myeloid leukaemia with t(8;21) received G-CSF alone as induction therapy. Complete remission was achieved following 2 weeks of treatment. Flow cytometric analysis, performed by CD45 technique modified by the introduction of preliminary gating with LDS-751, confirmed the disappearance of blast cells along with myeloid maturation. Finally, in vitro studies demonstrated that G-CSF, as compared to other differentiation inducers, was able to induce a striking effect toward neutrophilic differentiation.

Background Aldehyde dehydrogenase (ALDH) is a cytosolic enzyme highly expressed in hematopoietic precursors from cord blood and granulocyte-colony stimulating factor mobilized peripheral blood, as well as in bone marrow from patients with acute myeloblastic leukemia. As regards human normal bone marrow, detailed characterization of ALDH+ cells has been addressed by one single study (Gentry et al, 2007). The goal of our work was to provide new information about the dissection of normal bone marrow progenitor cells based upon the simultaneous detection by flow cytometry of ALDH and early hematopoietic antigens, with particular attention to the expression of ALDH on erythroid precursors. To this aim, we used three kinds of approach: i) multidimensional analytical flow cytometry, detecting ALDH and early hematopoietic antigens in normal bone marrow; ii) fluorescence activated cell sorting of distinct subpopulations of progenitor cells, followed by in vitro induction of erythroid differentiation; iii) detection of ALDH+ cellular subsets in bone marrow from pure red cell aplasia patients. Results In normal bone marrow, we identified three populations of cells, namely ALDH+CD34+, ALDH-CD34+ and ALDH+CD34- (median percentages were 0.52, 0.53 and 0.57, respectively). As compared to ALDH-CD34+ cells, ALDH+CD34+ cells expressed the phenotypic profile of primitive hematopoietic progenitor cells, with brighter expression of CD117 and CD133, accompanied by lower display of CD38 and CD45RA. Of interest, ALDH+CD34- population disclosed a straightforward erythroid commitment, on the basis of three orders of evidences. First of all, ALDH+CD34- cells showed a CD71bright, CD105+, CD45- phenotype. Secondly, induction of differentiation experiments evidenced a clear-cut expression of glycophorin A (CD235a). Finally, ALDH+CD34- precursors were not detectable in patients with pure red cell aplasia (PRCA). Conclusion Our study, comparing surface antigen expression of ALDH+/CD34+, ALDH-/CD34+ and ALDH+/CD34- progenitor cell subsets in human bone marrow, clearly indicated that ALDH+CD34- cells are mainly committed towards erythropoiesis. To the best of our knowledge this finding is new and could be useful for basic studies about normal erythropoietic differentiation as well as for enabling the employment of ALDH as a red cell marker in polychromatic flow cytometry characterization of bone marrow from patients with aplastic anemia and myelodysplasia.

Fetal liver tyrosine kinase 3 (FLT3) mutations represent a powerful prognostic indicator in acute myeloid leukemia (AML). Further, interaction between FLT3 and its ligand plays a role in normal hematopoiesis. Accordingly, FLT3 mutations may affect mobilization of peripheral blood stem cells (PBSCs) and feasibility of autologous stem cell transplantation (ASCT) in AML. We analyzed the effect of FLT3 mutations on mobilization of CD34(+) cells and on PBASCT feasibility from 111 patients with AML, with a median age of 58 years and normal karyotype. Overall, 23 patients (21%) had FLT3 mutations. The complete remission rate was 74% and was not influenced by FLT3 mutations (73% for patients with FLT3(-) and 78% for those with FLT3(+); P = .78). The successful mobilization rate was 79% and was comparable for patients with FLT3(-) and with FLT3(+) (P = .42). Median numbers of CD34(+) cells collected were 7.6 x 10(6)/kg and 7.1 x 10(6)/kg for patients with FLT3(-) and those with FLT3(+), respectively (P = .64). Among 73 patients evaluated for mobilization, feasibility of ASCT was 71%, and there was no difference between patients with FLT3(-) (74%) and those with FLT3(+) (61%), P = .43. We conclude that the FLT3 mutations have no influence on mobilization of CD34(+) cells or on feasibility of PBASCT in patients with AML and normal karyotype. (C) 2006 American Society for Blood and Marrow Transplantation.

The membrane expression of CD45RA and CD45RO on fresh leukaemic cells taken from 529 cases of acute haemopoietic malignancies, including 117 B-origin acute lymphoblastic leukaemia (B-origin ALL), 37 T-origin acute lymphoblastic leukaemia (T-origin ALL0, 297 de novo acute myeloid leukaemia (AML), 42 refractory anaemia with excess of blasts in transformation (RAEB-T) and 36 myeloid blastic phase of chronic myelogenous leukaemia (CML-BP-my), was analysed. B-origin ALLs were characterized by the lack of the RO isoform along with the consistent presence of RA. Conversely, a differential expression of the two isoforms was detected in different subsets of T-origin ALL, in that T-stem cell leukaemias (T-SCL: CD7+, CD4-, CD8-, CD1-) preferentially expressed CD45RA whereas conventional T-acute lymphoblastic leukaemias (T-ALL: CD7+, CD4+ and/or CD8+ and/or CD1+) were consistently marked by CD45RO. Within myeloid malignancies, most of AMLs displayed CD45RA, while a substantial group of CML-BP-my preferentially exhibited CD45RO. As a general rule, a reciprocal exclusion of the two isoforms was observed in AML as well as in ALL. Nevertheless, a frequent coexpression of CD45RA and CD45RO was observed in CD14+ AML. In vitro treatment with all-trans retinoic acid (ATRA) was able to promote a switch from CD45RA to CD45RO expression in 27 de novo AML, independently from morphological subtyping. To our knowledge, this is the first report on CD45 isoform expression in a large series of patients with acute leukaemia. The knowledge of the differential expression of CD45RA and CD45RO can ameliorate our classificative approach to haematological malignancies, as well as disclose new multiple overlap points between normal and leukaemic cell differentiation.

Abstract 3482 Three different types of PNH have been described so far, based upon the presence of hemolysis and bone marrow failure (BMF): a) florid PNH (hemolysis+/BMF-), b) PNH in the context of a BMF syndrome (hemolysis+/BMF+), c) subclinical PNH (hemolysis-/BMF+). In any case, the presence of a PNH clone is a prerequisite and Flow Cytometry (FCM) plays a crucial role in detecting and monitoring it with high sensitivity and specificity. In 2010, an Italian archive of FCM-detected PNH clones (http://int.clonepnh.com/) was created on a multi-laboratory basis. Eighty-one laboratories participated in the project. The aim was twofold: a) to provide a large dictionary of Italian PNH clones; b) based upon stringent rules regarding the compilation of records, to obtain an auto-educational effect on participating laboratories. Here, we describe the cellular composition and the clonal evolution of 295 type III (complete defect of GPI-linked proteins) PNH clones identified during the study. Forty-nine of these clones (16.6%) were accompanied by a PNH-II clone (partial defect of GPI-linked proteins). Hemoglobinuria was the most frequent (27%) reason for testing (RFT), followed by aplastic anemia (AA, 13%), MDS (13%), hemolytic anemia (12%), unexplained cytopenia (UC, 10%), BMF (5%), atypical venous thrombosis (5%), other (15%). Fluorescent Aerolysin (FLAER) was used since 2007, with an increasing % of utilization, from 4% to 60% of cases. CD24 utilization also progressively increased. CD59 was the most used antigen for RBC typing. The most used gating strategies were based upon physical parameters for RBC, CD45 and/or CD33 vs side scatter for granulocytes and monocytes. The 295 clones were categorized into 3 classes according to their size, determined as the percent of PNH cells in peripheral granulocytes: 0–10% (112 clones, or 38%, defined as “small”), 10.1%–70% (69 clones, or 23%, defined as “intermediate”), 70.1%–100% (115 clones, or 39%, defined as “large”). This distribution was significantly different from that expected on the basis of a random distribution within the three classes (i.e. 10%, 60% and 30%): chi square was 51 with a p value Type of change N of cases Median of months to change (range) Increase of 1 category 9 8 (4–74) Decrease of 1 category 7 18 (3–23) Increase of 2 categories (from “small” to “large”) 1 7 (N.A.) Decrease of 2 categories (from “large” to “small”) 3 22 (4–55) The vast majority of clones (287, or 97.3%), typed by analyzing neutrophils, monocytes and red cells, proved trilinear, while 8 clones were composed just by white cells, with red cells completely normal. This is the first multi-laboratory relational database of FCM-detected PNH clones described so far. An auto-educational goal was reached, since general sensitivity increased progressively and reagent choice significantly changed, leading to a stable FCM protocol, consisting of FLAER and CD24 for granulocytes, FLAER and CD14 for monocytes, CD59 for erythrocytes. As regards clonal evolution, the rarity of migration between extreme categories suggests that the belonging to these ones could be sustained by different backgrounds and pressures. Disclosures: No relevant conflicts of interest to declare.

The nature of the blast cells in 163 cases of acute leukemia was investigated by immunophenotyping, with particular emphasis on the expression of "ectopic" surface membrane structures. Although no antigen included in our panel except CD3 revealed absolute lineage restriction, immunological typing allowed a definite characterization of blast cells in more than 90% of cases. Four groups of patients were identified (A, B, C, D) with different degrees of antigen ectopic expression. We classified as group A leukemias (74%) those expressing conventional antigenic patterns, in absence of cross-lineage markers. Samples classified as group B (18%) showed a single ectopic membrane specificity, apparently discordant with the overall composite phenotype; such a "low-grade deviation" did not prevent a definite immunodiagnosis. Pattern C specimens (5%) revealed a promiscuous coexpression of markers related to different lineages (biphenotypic leukemias), whereas group D included unclassifiable phenotypes, characterized by no antigen or DR-only expression. Our findings suggest the possibility of interpreting complex phenotypic constellations of membrane markers in a consistent and logical manner.

The immunological detection of T surface antigens has been successfully applied to the study of molecules that regulate T cell physiology. In particular, investigations of activation antigens led to the recognition of growth factor receptors, such as those for interleukin-2 (1,2) and transfer-rin (3,4), thus providing critical information for biochemical and functional studies of membrane molecules regulating T cell proliferation.

Isolated familial pseudohyperkalemia is a dominant red cell trait characterized by cold-induced ‘passive leak’ of red cell potassium ions into plasma. The causative gene of this condition is ABCB6, which encodes an erythrocyte membrane ABC transporter protein bearing the Langereis blood group antigen system. In this study analyzing three new families, we report the first functional characterization of ABCB6 mutants, including the homozygous mutation V454A, heterozygous mutation R276W, and compound heterozygous mutations R276W and R723Q (in trans). All these mutations are annotated in public databases, suggesting that familial pseudohyperkalemia could be common in the general population. Indeed, we identified variant R276W in one of 327 random blood donors (0.3%). Four weeks’ storage of heterozygous R276W blood cells resulted in massive loss of potassium compared to that from healthy control red blood cells. Moreover, measurement of cation flux demonstrated greater loss of potassium or rubidium ions from HEK-293 cells expressing ABCB6 mutants than from cells expressing wild-type ABCB6. The R276W/R723Q mutations elicited greater cellular potassium ion efflux than did the other mutants tested. In conclusion, ABCB6 missense mutations in red blood cells from subjects with familial pseudohyperkalemia show elevated potassium ion efflux. The prevalence of such individuals in the blood donor population is moderate. The fact that storage of blood from these subjects leads to significantly increased levels of potassium in the plasma could have serious clinical implications for neonates and infants receiving large-volume transfusions of whole blood. Genetic tests for familial pseudohyperkalemia could be added to blood donor pre-screening. Further study of ABCB6 function and trafficking could be informative for the study of other pathologies of red blood cell hydration.