Highlights d CRISPR/Cas9 domain screen reveals RBP dependencies in AML d RBM39 is required for AML maintenance through missplicing of HOXA9 target genes d Proteomic studies identify an essential RBP splicing network in AML d Pharmacologic RBM39 degradation leads to broad antileukemic effects

Glucocorticoid-induced TNF receptor family related protein (GITR) is present on many different cell types. Previous studies have shown that in vivo administration of an anti-GITR agonist mAb (DTA-1) inhibits regulatory T cells (Treg)-dependent suppression and enhances T cell responses. In this study, we show that administration of DTA-1 induces >85% tumor rejection in mice challenged with B16 melanoma. Rejection requires CD4+, CD8+, and NK1.1+ cells and is dependent on IFN-γ and Fas ligand and independent of perforin. Depletion of Treg via anti-CD25 treatment does not induce B16 rejection, whereas 100% of the mice depleted of CD25+ cells and treated with DTA-1 reject tumors, indicating a predominant role of GITR on effector T cell costimulation rather than on Treg modulation. T cells isolated from DTA-1-treated mice challenged with B16 are specific against B16 and several melanoma differentiation Ags. These mice develop memory against B16, and a small proportion of them develop mild hypopigmentation. Consistent with previous studies showing that GITR stimulation increases Treg proliferation in vitro, we found in our model that GITR stimulation expanded the absolute number of FoxP3+ cells in vivo. Thus, we conclude that overall, GITR stimulation overcomes self-tolerance/ignorance and enhances T cell-mediated antitumor activity with minimal autoimmunity.

Mutations affecting RNA splicing factors are the most common genetic alterations in myelodysplastic syndrome (MDS) patients and occur in a mutually exclusive manner. The basis for the mutual exclusivity of these mutations and how they contribute to MDS is not well understood. Here we report that although different spliceosome gene mutations impart distinct effects on splicing, they are negatively selected for when co-expressed due to aberrant splicing and downregulation of regulators of hematopoietic stem cell survival and quiescence. In addition to this synthetic lethal interaction, mutations in the splicing factors SF3B1 and SRSF2 share convergent effects on aberrant splicing of mRNAs that promote nuclear factor κB signaling. These data identify shared consequences of splicing-factor mutations and the basis for their mutual exclusivity.

Histiocytoses are clonal hematopoietic disorders frequently driven by mutations in BRAF and MEK1/2 kinases. Currently, however, the developmental origins of histiocytoses in patients are not well understood, and clinically meaningful therapeutic targets outside of BRAF and MEK are undefined. Here we uncover activating mutations in CSF-1R, as well as rearrangements in RET and ALK which confer dramatic responses to selective inhibition of RET (selpercatinib) and crizotinib, respectively, in histiocytosis patients.

Keratinocyte growth factor (KGF) is a member of the fibroblast growth factor family that mediates epithelial cell proliferation and differentiation in a variety of tissues, including the thymus. We studied the role of KGF in T-cell development with KGF ؊/؊ mice and demonstrated that thymic cellularity and the distribution of thymocyte subsets among KGF ؊/؊ , wildtype (WT), and KGF ؉/؊ mice were similar. However, KGF ؊/؊ mice are more vulnerable to sublethal irradiation (450 cGy), and a significant decrease was found in thymic cellularity after irradiation. Defective thymopoiesis and peripheral T-cell reconstitution were found in KGF ؊/؊ recipients of syngeneic or allogeneic bone marrow transplant, but using KGF ؊/؊ mice as a donor did not affect T-cell development after transplantation. Despite causing an early developmental block in the thymus, administration of KGF to young and old mice enhanced thymopoiesis. Exogenous KGF also accelerated thymic recovery after irradiation, cyclophosphamide, and dexamethasone treatment. IntroductionKeratinocyte growth factor (KGF) is a 28-kDa fibroblast growth factor family member (FGF-7) that mediates epithelial cell proliferation and differentiation in a variety of tissues, including the gut (gut epithelial cells), skin (keratinocytes), and thymus (thymic epithelial cells). [1][2][3] KGF is produced by mesenchymal cells and has a paracrine effect on epithelial cells 4,5 ; it binds FGFR2IIIb, a splice variant of FGF receptor 2, expressed predominantly on these cell types. FGFR2IIIb is activated by 4 known ligands: FGF-1, FGF3, 7 The heterogeneous stromal cell compartment of the thymus includes both cortical and medullary epithelial cells, as well as mesenchymal cells (including fibroblasts). Mesenchymal cells produce fibroblast growth factors and support thymocyte development, especially in cortical areas (reviewed in Anderson and Jenkinson 8 ). Jenkinson et al 9 reported that mesenchymal cells regulate the proliferation of thymic epithelial cells via the production of KGF (FGF-7) and fibroblast growth factor-10 (FGF-10) during fetal development, but the role of mesenchymal cells in regulating the composition of thymic stroma in the neonatal and postnatal period is unclear.Erikson et al 10 have demonstrated that KGF and FGFR2IIIb signaling can affect the development and function of thymic epithelium (TE). In the adult thymus, mature ␣␤ ϩ thymocytes are capable of producing KGF, which leads to the expansion of thymic medullary epithelial cells. 10 However, KGF expression is not detectable in the triple negative (CD3 Ϫ CD4 Ϫ CD8 Ϫ ) thymocyte precursors. 10 In contrast, peripheral ␣␤ Ϫ T cells do not secrete KGF, even in epithelial tissues that comprise the skin, intestine, and vagina. However, ␥␦ Ϫ T cells in epithelial tissues do produce KGF and may also regulate epithelial cell growth. 11 KGF can function as a growth factor for epithelial protection and repair, is found in a variety of tissues (extensively reviewed by Finch and Rubin 12 ), and is up-regulated after various ...