Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive leukemia for which we developed a nationwide network to collect data from new cases diagnosed in France. In a retrospective, observational study of 86 patients (2000-2013), we described clinical and biological data focusing on morphologies and immunophenotype. We found expression of markers associated with plasmacytoid dendritic cell origin (HLA-DRhigh, CD303+, CD304+, and cTCL1+) plus CD4 and CD56 and frequent expression of isolated markers from the myeloid, B-, and T-lymphoid lineages, whereas specific markers (myeloperoxidase, CD14, cCD3, CD19, and cCD22) were not expressed. Fifty-one percent of cytogenetic abnormalities impact chromosomes 13, 12, 9, and 15. Myelemia was associated with an adverse prognosis. We categorized chemotherapeutic regimens into 5 groups: acute myeloid leukemia (AML)–like, acute lymphoid leukemia (ALL)–like, lymphoma (cyclophosphamide, doxorubicin, vincristine, and prednisone [CHOP])–like, high-dose methotrexate with asparaginase (Aspa-MTX) chemotherapies, and not otherwise specified (NOS) treatments. Thirty patients received allogeneic hematopoietic cell transplantation (allo-HCT), and 4 patients received autologous hematopoietic cell transplantation. There was no difference in survival between patients receiving AML-like, ALL-like, or Aspa-MTX regimens; survival was longer in patients who received AML-like, ALL-like, or Aspa-MTX regimens than in those who received CHOP-like regimens or NOS. Eleven patients are in persistent complete remission after allo-HCT with a median survival of 49 months vs 8 for other patients. Our series confirms a high response rate with a lower toxicity profile with the Aspa-MTX regimen, offering the best chance of access to hematopoietic cell transplantation and a possible cure.

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Summary The scarcity of mesenchymal stem cells (MSC) in bone marrow (BM) has justified their ex vivo expansion before therapeutic use, but a method to evaluate the quality of initial mesenchymal content and track the modifications induced by graft processing has not yet been proposed. The aim of this study was to establish such a procedure. Flow cytometric and functional assay methods were modified to count CD45− CD14−/CD73+ subsets containing all MSC and used them to study BM from spongy bone (SB) and iliac crest aspirate (ICA). These methods detected the target subsets in all BM suspensions derived from SB (n = 154) and ICA, (n = 44) with a satisfactory correlation between immuno‐phenotyping and functional tests by low‐density plating. We noted a higher overall MSC frequency in SB cell suspensions but a lower plating efficiency of CD45− CD14−/CD73+ SB cells under standard culture conditions. We propose a cell quality control on un‐manipulated BM cell suspensions to quantify the mesenchymal compartment with regard to varying donor factors, such as age and sampling site, that influence expansion and define a therapeutic threshold value. Furthermore, we were able to confirm differences in plating efficiency and proliferative capacity between two BM origins.

Distinguishing chronic lymphoproliferative disorders of NK cells (CLPD-NK) from reactive NK cell expansions is challenging. We assessed the value of NK receptor phenotyping and targeted high-throughput sequencing in a cohort of 114 consecutive patients with NK cell proliferation, retrospectively assigned to a CLPD-NK group (N=46) and a reactive NK group (N=68). We then developed a NK-clonality score combining flow cytometry and molecular profiling with a positive predictive value of 93%. STAT3 and TET2 mutations were respectively identified in 27% and 34% of the CLPD-NK patients - constituting a new diagnostic hallmark for this disease. TET2-mutated CLPD-NK exhibited preferentially a CD16low phenotype, displayed more frequently a lower platelet count, and were associated with other hematologic malignancies such as myelodysplasia. To explore the mutational clonal hierarchy of CLPD-NK, we performed a whole exome sequencing of sorted, myeloid, T, and NK cells and identified that TET2 mutations were shared by myeloid and NK cells in 3 out of 4 cases. Thus, we hypothesized that TET2 alterations occur early in CLPD-NK disease which could explain a potential link between NK-LGL leukemia and other myeloid malignancies. Finally, we analyzed the transcriptome by RNA-seq of 7 CLPD-NK and evidenced two groups of patients. The first group displayed STAT3 mutations or SOCS3 methylation and overexpressed STAT3 target genes. The second group, including two TET2-mutated cases, significantly under-expressed genes known to be down-regulated in angioimmunoblastic T-cell lymphoma. Our results provide new insights into the pathogenesis of NK cell proliferative disorders and potentially new therapeutic opportunities.

For most therapeutic strategies using MSC, the preliminary amplification is carried out in media containing fetal calf serum (FCS). The theoretical health risk of using a xenogenic serum, a recent practice for which we have limited data, cannot be underestimated, while amplification using human serum (