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Allogeneic bone marrow transplantation (BMT) is the only curative treatment available for sickle cell disease (SCD). The effectiveness of the treatment is primarily assessed by the chimerism rate, which is the fraction of cells derived from the donor's hematopoietic stem cells (HSCs) relative to the recipient's cells. New less toxic conditioning agents, described as reduced, nonmyeloablative (as opposed to myeloablative conditioning agents) are now used for BMT with sibling donors. Moreover, most sibling donors are sickle cell trait carriers (heterozygous A/S genotype). In the absence of a test performed on erythroid cells, the rate of chimerism is currently assessed either on different subpopulations of myeloid cells by molecular biology techniques or on hemoglobin measurement by chromatography (HPLC). However, the percentage of myeloid chimerism is rarely representative of the percentage of erythroid chimerism in these patients and HPLC cannot allow analysis at the single cell level. An easy-to-implement method for accurate measurement of fetal hemoglobin (HbF) content in individualized red blood cells (RBCs) has recently been developed (Hebert, et. al, AJH 2020). This method relies on flow cytometry for cell individualization and intracellular labeling of HbF with a fluorescent monoclonal antibody for quantification. Based on the same approach, we propose the use of monoclonal antibodies directed against adult hemoglobins (HbA0 and HbA2) or hemoglobin S (HbS). This strategy allows to discriminate, from a blood sample, the different RBC subpopulations coming from either the recipient or the donor, or from the transfusion associated with this procedure, thus allowing us to precisely determine the rates of erythroid chimerism in patients. As a proof of concept, we show here the evaluation of the percentage of erythroid chimerism during a longitudinal follow-up performed on 3 patients with SCD (P1 - 18 months, P2 - 4 months, and P3 - 4 months). The 3 patients received allogeneic BMT from a sibling A/S donor following nonmyeloablative conditioning consisting of the administration of an anti-CD52 antibody associated with radiotherapy (300 cGy TBI - total-body irradiation). We observed for P1 and P2 donor erythroid chimerism >90% and >95%, 1 and 2 months after BMT, respectively (measured after exclusion of transfused RBCs). These results are in accordance with the presence of most RBCs HbA- and HbS-positive, as determined by flow cytometry. In addition, the analysis of the reticulocyte (retic) subpopulations (CD71-positive cells) of these patients provides precise information on the RBC production of the bone marrow following transplantation. Retic donor chimerism levels were >99% for both P1 and P2, 1 month after BMT procedure. P1 and P2 showed stable donor reticulocyte and donor erythroid chimerism levels during the follow-up. On the contrary, P3 presented a different response with 43%, 41% and 5% donor erythroid chimerism 1, 2 and 3 months after BMT, respectively. Retrospectively, this bad response in P3 would have been predicted by low donor reticulocyte chimerism levels (5%, 6% and 0.5% at 1, 2 and 3 months after BMT, respectively). Our erythroid specific chimerism results were also compared to the assessment of chimerism performed on either total white blood cells (WBCs) or lineage specific subpopulations after sorting. Over 18 months after BMT in P1, the correlation between retic chimerism and total WBCs or T lymphocytes (CD3-positive cells) chimerism were not statistically significant (P = 1 and P = 0.833, respectively - Spearman test) (Figure 1). This new tool to monitor BMT outcome to treat SCD shows great precision and potentially a stronger predictive capability than total WBCs or lineage specific chimerism assessed by molecular biology. Our results highlight the importance of analyzing reticulocyte population to better assess BMT efficacy and predict the outcome a few days after the transplant. Its use could also be considered in the context of the various gene therapy strategies currently under development using modified β-globin gene addition or direct mutation correction through CRISPR/Cas9 and homologous recombination system. Figure 1 Figure 1. Disclosures Bencheikh: Innovhem: Current Employment. Bartolucci: Innovhem: Current holder of individual stocks in a privately-held company.

Chronic myelomonocytic leukemia (CMML) is a myelodysplastic syndrome/ myeloproliferative neoplasm whose diagnosis is currently based on the elevation of peripheral blood monocytes to1 × 10(9)/L, measured for ≥3 months. Diagnosis can be ambiguous; for example, with prefibrotic myelofibrosis or reactive monocytosis. We set up a multiparameter flow cytometry assay to distinguish CD14(+)/CD16(-) classical from CD14(+)/CD16(+) intermediate and CD14(low)/CD16(+) nonclassical monocyte subsets in peripheral blood mononucleated cells and in total blood samples. Compared with healthy donors and patients with reactive monocytosis or another hematologic malignancy, CMML patients demonstrate a characteristic increase in the fraction of CD14(+)/CD16(-) cells (cutoff value, 94.0%). The associated specificity and sensitivity values were 95.1% and 90.6% in the learning cohort (175 samples) and 94.1% and 91.9% in the validation cohort (307 samples), respectively. The accumulation of classical monocytes, which demonstrate a distinct gene expression pattern, is independent of the mutational background. Importantly, this increase disappears in patients who respond to hypomethylating agents. We conclude that an increase in the fraction of classical monocytes to94.0% of total monocytes is a highly sensitive and specific diagnostic marker that rapidly and accurately distinguishes CMML from confounding diagnoses.

Introduction: Hemolytic anemia combines 3 components to various extents: extravascular hemolysis, intravascular hemolysis and dyserythropoiesis. Global hemolysis in excess to defense lines induces oxidative and inflammatory syndromes and vascular damages in various organs. Therefore, accurate hemolysis biomarkers are required for a better evaluation of hemolytic disorders, such as sickle cell disease (SCD) or thalassemia syndromes and to evaluate the efficacy of various therapies. Accordingly, we have developed a new spectrophotometric method to measure and calculate several hemolysis biomarkers in plasma or serum including Hemoglobin in various forms (HbO2, HbCO, MetHb), Heme or Hemin bound to albumin or to hemopexin, total bilirubin and total hemopexin. Patients and Method : Blood samples were collected at steady-state for 77 SCD adults (mean age 39.8 ± 10.2 yrs, M/F ratio 0.64) and 23 beta thalassemia patients (mean age 42.7 ± 16 yrs, M/F ratio 0.91); SCD patients (SS or Sb0-Thalassemia) were either treated with Hydroxycarbamide (HU: 27) or not (NT: 50). For comparison, plasma samples from healthy volunteers (HV) were also analyzed. Continuous variables were expressed as means ± SD or medians [interquartile range], depending on their normal or asymmetric distributions. Categorical variables were expressed as numbers (%). Univariate analyses were done using Student's t-test or Mann-Whitney non-parametric test, depending on the distribution. Correlation were analyzed using a spearman test. The dosage methodology is based on the light absorption spectrophotometry of plasma samples using an appropriate mathematical conversion of the signal, reference spectra of the different species and some chemical modifications of the iron redox and ligation states. Results: The levels of plasma Hb were statistically higher in homozygous SCD patients compared to beta-thalassemia patients (p=0.001) and healthy volunteers, with median of 6.3 [3.4-11], 2.6 [1-5.4] and 1.7 [0.5-3] µM respectively (Table 1). Interestingly levels of plasma heme were higher in beta thalassemia patient compared to SCD patients (p=0.0001) and HV, with a mean of 1.05 [0.05-3], 10.5 [3.5-24] and ≤ 0.2 µM level of detection respectively (Table 1). A significant negative correlation was found between heme and hemopexin levels in both diseases (p Discussion and Conclusions: plasma Hb is a more accurate dosage for intra vascular hemolysis than other biomarkers which are not specific of intra vascular hemolysis and could be biased by other pathological conditions: LDH or ASAT can be increased in hepatic or muscular cytolysis, bilirubin is dependent on the heme oxygenase and glycuronyl transferase activities, and reticulocytes are dependent on erythropoiesis. Our results showed that the intra-vascular hemolysis is more pronounced in SCD compared to beta-thalassemia based on the plasma Hb levels. The elevated plasma heme concentration in beta thalassemia is a new finding that should be investigated in more details. It could reflect the ineffective erythropoiesis or heme export from erythroblasts or macrophages involving hemopexin scavenging. Disclosures Bencheikh: Hemanext: Research Funding. Bartolucci:HEMANEXT: Membership on an entity's Board of Directors or advisory committees; AddMedica: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees.

La drepanocytose est une maladie genetique due a une mutation de l’hemoglobine (Hb), entrainant la falciformation des globules rouges (GR), une hemolyse chronique ainsi que des crises vaso-occlusives tres douloureuses. L’echange transfusionnel est une des strategies therapeutiques utilisees pour remplacer les GR malades et diminuer les crises. La qualite des GR transfuses est primordiale, a la fois pour ameliorer le rendement transfusionnel mais aussi pour limiter les interactions pathologiques entre les GR et les cellules endotheliales, endommagees par l’hemolyse. Or, au cours de leur conservation, la qualite des GR diminue, principalement a cause de dommages oxidatifs. La technologie Hemanext permet de conserver les GR en hypoxie, ameliorant la concentration en ATP, 2-3DPG, l’hemolyse et la deformabilite des GR. Notre etude avait pour but de comparer la qualite des GR conserves de facon conventionnelle a ceux conserves avec la technologie Hemanext. Nous avons demontre une non-inferiorite d’Hemanext en termes d’adherence des GR en flux sur des cellules endotheliales. De plus, nous avons mis en evidence une reduction de la concentration en Hb libre (produite par la lyse des GR) dans les poches Hemanext, une baisse de la senescence des GR et de leur adherence sur la thrombospondine, dont la concentration est augmentee pendant la crise drepanocytaire. Ces resultats suggerent que la technologie Hemanext repond aux criteres de securite pour la transfusion des patients drepanocytaires, et pourrait meme leur apporter un benefice clinique.