Background: Recessive dystrophic epidermolysis bullosa (RDEB) is a hereditary blistering disorder due to a lack of type VII collagen. At present, treatment is mainly supportive.Objectives: To determine whether intravenous allogeneic bone marrowederived mesenchymal stromal/ stem cells (BM-MSCs) are safe in RDEB adults and if the cells improve wound healing and quality of life.Methods: We conducted a prospective, phase I/II, open-label study recruiting 10 RDEB adults to receive 2 intravenous infusions of BM-MSCs (on day 0 and day 14; each dose 2-4 3 10 6 cells/kg).Results: BM-MSCs were well tolerated with no serious adverse events to 12 months. Regarding efficacy, there was a transient reduction in disease activity scores (8/10 subjects) and a significant reduction in itch. One individual showed a transient increase in type VII collagen.Limitations: Open-label trial with no placebo.Conclusions: MSC infusion is safe in RDEB adults and can have clinical benefits for at least 2 months.

Mirasol PRT leads to hyperreactive PLTs, probably caused by continuous basal degranulation through storage time. This results in a reduction in the degranulation capacity upon acute stimulation, which influences PLT spreading, but not overtly microaggregation. The clinical relevance needs to be investigated.

approach that had been described before, 24 enabling us to delineate the effects of MEIS1 on specific stages of lineage commitment. Furthermore, using transcriptional profiling of MEIS1-overexpressing CD34 + hematopoietic stem and progenitor cells, we generated an overview of the transcriptional changes following MEIS1 expression.

Megakaryopoiesis is the process during which megakaryoblasts differentiate to polyploid megakaryocytes that can subsequently shed thousands of platelets in the circulation. Megakaryocytes accumulate mRNA during their maturation, which is required for the correct spatio-temporal production of cytoskeletal proteins, membranes and platelet-specific granules, and for the subsequent shedding of thousands of platelets per cell. Gene expression profiling identified the RNA binding protein ATAXIN2 (ATXN2) as a putative novel regulator of megakaryopoiesis. ATXN2 expression is high in CD34+/CD41+ megakaryoblasts and sharply decreases upon maturation to megakaryocytes. ATXN2 associates with DDX6 suggesting that it may mediate repression of mRNA translation during early megakaryopoiesis. Comparative transcriptome and proteome analysis on megakaryoid cells (MEG-01) with differential ATXN2 expression identified ATXN2 dependent gene expression of mRNA and protein involved in processes linked to hemostasis. Mice deficient for Atxn2 did not display differences in bleeding times, but the expression of key surface receptors on platelets, such as ITGB3 (carries the CD61 antigen) and CD31 (PECAM1), was deregulated and platelet aggregation upon specific triggers was reduced.

2330 The homeobox transcription factor MEIS1 is expressed in hematopoietic stem- and progenitor cells (HSCs & HPCs, respectively) such as human CD34+ cells, whereas its expression in lineage-committed blood cells is restricted to megakaryocytes (MKs). We observed that MEIS1 not only drives megakaryopoiesis but is also indispensable for the differentiation of HPCs towards the erythroid lineage. In cord blood CD34+ cells lentiviral-driven MEIS1 overexpression resulted in a 3-fold increase in BFU-E at the expense of CFU-GM colonies and a 2-fold increase in MK colonies was recorded. Vice versa, silencing MEIS1 led to a reduction in the number of MK-colonies and a near absence of BFU-E, a phenotype strongly reminiscent of the ones observed in knock-out mice and zebrafish. To pinpoint at which stage of hematopoietic commitment MEIS1 expression regulates lineage fate, we sorted CD34+ cells further into the HSC and HSPC subsets. MEIS1 overexpression in HSC and common myeloid progenitors (CMP) induced a 3-fold increase in BFU-E at the expense of CFU-GM consistent with the data obtained in CD34+ cells. Remarkably, MEIS1 overexpression also resulted in erythroid colony formation in the granulocyte-monocyte precursor cells (GMP), a subset that naturally is committed to myeloid differentiation. The results show that MEIS1 drives HPCs and HSCs towards megakaryocyte-erythroid precursor cell (MEP) fating. To unravel the underlying mechanism of this fating we performed chromatin immunoprecipitation with MEIS1 antibodies in the megakaryoblastic cell line CHRF 288–11 and primary MKs combined with massive parallel sequencing (ChIP-seq). 13,842 MEIS1 binding events were detected in CHRF and 18012 events in MK, respectively. The transcription factors GATA1 and FOG1 (ZFPM1) are critical for the commitment of HSCs and HPCs towards the erythroid lineage. Lately, it has also been noted that FOG1 limits stem cells towards MEP fating and that GATA1 transcription is induced by FOG1 (Mancini et al., EMBO, 2012). No MEIS1 binding sites were observed in the GATA1 promoter, but potential binding events were observed in the FOG2 promoter at position 625 and 567. These ChIP-seq results were replicated by RT-qPCR, which confirmed MEIS1 binding to the promoter of FOG1 but not of GATA1 or PU.1. Interestingly overexpression of MEIS1 resulted in a 2-fold increase in FOG1 and GATA1 transcripts but the level of PU.1, a transcription factor essential for the differentiation towards the granulocytic/monocytic lineage, remained unaltered. We are currently performing ChIP-Seq on CD34+ cells to define the differences in MEIS1 occupancy between MKs and HSCs. In conclusion, we show that the transcription factor MEIS1 induces a MEP fate by binding to the FOG1 promoter thus positively regulating FOG1 transcription. As MEIS1 does not bind to the GATA1 promoter, we further hypothesize that in human hematopoiesis increased GATA1 expression is mediated by FOG1 as described earlier in the murine model. Disclosures: No relevant conflicts of interest to declare.