Digestive cryptosporidiosis mimics GVHD after Hematopoietic Stem Cell Transplantation and responds to bi-antibiotic therapy

Abstract P376

Glycoprotein Ibalpha promoter drives megakaryocytic lineage-restricted expression after hematopoietic stem cell transduction using a self-inactivating lentiviral vector.

International audienceMegakaryocytic (MK) lineage is an attractive target for cell/gene therapy approaches, aiming at correcting platelet protein deficiencies. However, MK cells are short-lived cells, and their permanent modification requires modification of hematopoietic stem cells with an integrative vector such as a lentiviral vector. Glycoprotein (Gp) IIb promoter, the most studied among the MK regulatory sequences, is also active in stem cells. To strictly limit transgene expression to the MK lineage after transduction of human CD34(+) hematopoietic cells with a lentiviral vector, we looked for a promoter activated later during MK differentiation. Human cord blood, bone marrow, and peripheral-blood mobilized CD34(+) cells were transduced with a human immunodeficiency virus-derived self-inactivating lentiviral vector encoding the green fluorescent protein (GFP) under the transcriptional control of GpIbalpha, GpIIb, or EF1alpha gene regulatory sequences. Both GpIbalpha and GpIIb promoters restricted GFP expression (analyzed by flow cytometry and immunoelectron microscopy) in MK cells among the maturing progeny of transduced cells. However, only the GpIbalpha promoter was strictly MK-specific, whereas GpIIb promoter was leaky in immature progenitor cells not yet engaged in MK cell lineage differentiation. We thus demonstrate the pertinence of using a 328-base-pair fragment of the human GpIbalpha gene regulatory sequence, in the context of a lentiviral vector, to tightly restrict transgene expression to the MK lineage after transduction of human CD34(+) hematopoietic cells. Disclosure of potential conflicts of interest is found at the end of this article

Clofarabine versus fludarabine-based reduced-intensity conditioning regimen prior to allogeneic transplantation in adults with AML/MDS

International audienceWe have retrospectively compared survivals between acute myeloid leukemia (AML)/myelodysplastic syndrome (MDS) patients who received either a clofarabine/busulfan (CloB2A2) or a fludarabine/busulfan (FB2A2) RIC regimen for allogeneic stem cell transplantation. Between 2009 and 2014, 355 allotransplanted cases were identified from the SFGM-TC registry as having received either the FB2A2 (n = 316, 56% males, median age: 59.2 years, AML 78.5%, first complete remission [CR1] 72%, median follow-up: 20 months) or the CloB2A2 (n = 39, 62% males, median age: 60.8 years, AML 62%, CR1 69%, median follow-up: 22.4 months) RIC regimen. In multivariate analysis, FB2A2 was associated with significant lower overall survival (OS, HR: 2.14; 95%CI: 1.05-4.35, P = 0.04) and higher relapse incidence (RI, HR: 2.17; 95%CI: 1.02-4.61, P = 0.04) and a trend for lower leukemia-free survival (LFS, HR: 1.75; 95%CI: 0.94-3.26, P = 0.08). These results were confirmed using a propensity score-matching strategy. However, when considering AML and MDS patients separately, the benefit of the CLOB2A2 regimen was restricted to AML patients (2-year OS FB2A2: 38% [14.5-61.6] vs. CloB2A2: 79.2% [62.9-95.4], P = 0.01; 2-year LFS FB2A2: 38% [16-59.9] vs. CloB2A2: 70.8% [52.6-89], P = 0.03). The better survivals were due to the lower risk of relapse in this CloB2A2 AML subgroup (2-year RI FB2A2: 41.2% [19-62.4] vs. CloB2A2: 16.7% [5-34.2], P = 0.05). This retrospective comparison suggests that the CloB2A2 RIC regimen can likely provide longer survival than that awarded by a FB2A2 RIC regimen and may become a new standard of care RIC regimen for allotransplanted AML patients. A prospective phase 3 randomized study is warranted