The PTPN11 gene encodes SHP-2 (Src homology 2 domain-containing protein tyrosine Phosphatase), a nonreceptor tyrosine protein tyrosine phosphatase (PTPase) that relays signals from activated growth factor receptors to p21 Ras (Ras) and other signaling molecules. Mutations in PTPN11 cause Noonan syndrome (NS), a developmental disorder characterized by cardiac and skeletal defects. NS is also associated with a spectrum of hematologic disorders, including juvenile myelomonocytic leukemia (JMML). To test the hypothesis that PTPN11 mutations might contribute to myeloid leukemogenesis, we screened the entire coding region for mutations in 51 JMML specimens and in selected exons from 60 patients with other myeloid malignancies. Missense mutations in PTPN11 were detected in 16 of 49 JMML specimens from patients without NS, but they were less common in other myeloid malignancies. RAS, NF1, and PTPN11 mutations are largely mutually exclusive in JMML, which suggests that mutant SHP-2 proteins deregulate myeloid growth through Ras. However, although Ba/F3 cells engineered to express leukemia-associated SHP-2 proteins cells showed enhanced growth factor-independent survival, biochemical analysis failed to demonstrate hyperactivation of the Ras effectors extracellular-regulated kinase (ERK) or Akt. We conclude that SHP-2 is an important cellular PTPase that is mutated in myeloid malignancies. Further investigation is required to clarify how these mutant proteins interact with Ras and other effectors to deregulate myeloid growth. (Blood.

PTPN11 encodes the protein tyrosine phosphatase SHP-2, which relays signals from growth factor receptors to Ras and other effectors. Germline PTPN11 mutations underlie about 50% of Noonan syndrome (NS), a developmental disorder that is associated with an elevated risk of juvenile myelomonocytic leukemia (JMML). Somatic PTPN11 mutations were recently identified in about 35% of patients with JMML; these mutations introduce amino acid substitutions that are largely distinct from those found in NS.We assessed the functional consequences of leukemia-associated PTPN11 mutations in murine hematopoietic cells. Expressing an E76K SHP-2 protein induced a hypersensitive pattern of granulocyte-macrophage colony-forming unit (CFU-GM) colony growth in response to granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 3 (IL-3) that was dependent on SHP-2 catalytic activity. E76K SHP-2 expression also enhanced the growth of immature progenitor cells with high replating potential, perturbed erythroid growth, and impaired normal differentiation in liquid cultures. In addition, leukemia-associated SHP-2 mutations conferred a stronger phenotype than a germline mutation found in patients with NS. Mutant SHP-2 proteins induce aberrant growth in multiple hematopoietic compartments, which supports a primary role of hyperactive Ras in the pathogenesis of JMML. IntroductionThe PTPN11 gene encodes SHP-2, a nonreceptor tyrosine phosphatase (PTPase) that relays signals from activated growth factor receptors to p21 ras (Ras), Src family kinases, and other signaling molecules (for reviews, see Barford and Neel 1 and Neel et al 2 ). SHP-2 contains 2 Src homology 2 (SH2) domains and a catalytic PTPase domain. The SHP-2 crystal structure predicts that binding of the N-SH2 domain to phosphotyrosyl peptides results in a conformational shift that relieves inhibition of the PTPase and activates SHP-2 function. 3 Missense mutations in PTPN11 underlie about 50% of cases of Noonan syndrome (NS), a developmental disorder characterized by cardiac defects, facial dysmorphism, and skeletal malformations. 4 Most of the PTPN11 mutations found in NS introduce amino acid substitutions within the N-SH2 and PTPase domains. 4,5 Molecular modeling and biochemical data infer that exon 3 mutations dominantly activate SHP-2 phosphatase activity by altering critical N-SH2 amino acids that lie on the interface with the PTPase domain. 4,5 Infants with NS show a spectrum of hematologic abnormalities that includes isolated monocytosis as well as myeloid disorders with features of chronic myelomonocytic leukemia that may remit spontaneously. [6][7][8] Patients with NS are also predisposed to juvenile myelomonocytic leukemia (JMML), an aggressive myeloproliferative disorder (MPD) characterized by leukocytosis, tissue infiltration, and hypersensitivity to granulocyte-macrophage colonystimulating factor (GM-CSF). 9,10 Studies of JMML specimens and experiments in mutant strains of mice strongly implicate aberrant Ras signaling in response to GM-CSF and othe...

Hemophilia A (HA) is a common bleeding disorder caused by the deficiency of factor VIII (FVIII) with an incidence of ~1 in 5000 male births. Replacement of FVIII is necessary to prevent and treat bleeding episodes. However, with multiple new drugs in addition to old standards, choosing among the different FVIII treatment options is harder than ever. There are FVIII products that are plasma derived or recombinant, FVIII products designed to extend the half-life of FVIII, and the first single-chain FVIII product, recombinant factor VIII single chain (rFVIII-SC). As development of inhibitors to FVIII continues to be a major problem in the care of HA patients, recent studies showing lower rates of inhibitor development with plasma-derived FVIIII products versus recombinant FVIII products have made choosing among the many options now available even more complex. Although still unproven, extended half-life (EHL) products may provide the hope of decreased immunogenicity but need further testing in previously untreated patients (PUPs). This review highlights some of the differences between FVIII products currently available and hopefully assists the clinician to decide which FVIII product to choose for their patients.

Introduction Immune tolerance induction (ITI) is the gold standard for eradication of factor VIII inhibitors in severe haemophilia A; however, it usually requires treatment for extended periods with associated high burden on patients and healthcare resources. Aim Review outcomes of ITI with recombinant factor VIII Fc fusion protein (rFVIIIFc) in patients with severe haemophilia A and high‐titre inhibitors. Methods Multicentre retrospective chart review of severe haemophilia A patients treated with rFVIIIFc for ITI. Results Of 19 patients, 7 were first‐time ITI and 12 were rescue ITI. Of 7 first‐time patients, 6 had at least 1 high‐risk feature for ITI failure. Four of 7 first‐time patients were tolerized in a median of 7.8 months. The remaining 3 patients continue on rFVIIIFc ITI. Of 12 rescue patients, 7 initially achieved a negative Bethesda titre (≤0.6) in a median of 3.3 months, 1 had a decrease in Bethesda titre and continues on rFVIIIFc ITI and 4 have not demonstrated a decrease in Bethesda titre. Of these 4, 3 continue on rFVIIIFc ITI and 1 switched to bypass therapy alone. Two initially responsive patients transitioned to other factors due to recurrence. Overall, 16 of 19 patients remain on rFVIIIFc (prophylaxis or ITI). For those still undergoing ITI, longer follow‐up is needed to determine final outcomes. No adverse events reported. Conclusions Recombinant factor VIII Fc fusion protein demonstrated rapid time to tolerization in high‐risk first‐time ITI patients. For rescue ITI, rFVIIIFc showed therapeutic benefit in some patients who previously failed ITI with other products. These findings highlight the need to further evaluate the use of rFVIIIFc for ITI.

A B S T R A C T Germline mutations in SAMD9 and SAMD9L genes cause MIRAGE (myelodysplasia, infection, restriction of growth, adrenal hypoplasia, genital phenotypes, and enteropathy) (OMIM: *610456) and ataxia-pancytopenia (OMIM: *611170) syndromes, respectively, and are associated with chromosome 7 deletions, myelodysplastic syndrome (MDS), and bone marrow failure. In this retrospective series, we report outcomes of allogeneic hematopoietic cell transplantation (HCT) in patients with hematologic disorders associated with SAMD9/SAMD9L mutations. Twelve patients underwent allogeneic HCT for MDS (n = 10), congenital amegakaryocytic thrombocytopenia (n = 1), and dyskeratosis congenita (n = 1). Exome sequencing revealed heterozygous mutations in SAMD9 (n = 6) or SAMD9L (n = 6) genes. Four SAMD9 patients had features of MIRAGE syndrome. Median age at HCT was 2.8 years (range, 1.2 to 12.8 years). Conditioning was myeloablative in 9 cases and reduced intensity in 3 cases. Syndrome-related comorbidities (diarrhea, infections, adrenal insufficiency, malnutrition, and electrolyte imbalance) were present in MIRAGE syndrome cases. One patient with a familial SAMD9L mutation, MDS, and morbid obesity failed to engraft and died of refractory acute myeloid leukemia. The other 11 patients achieved neutrophil engraftment. Acute post-transplant course was complicated by syndrome-related comorbidities in MIRAGE cases. A patient with SAMD9L-associated MDS died of diffuse alveolar hemorrhage. The other 10 patients had resolution of hematologic disorder and sustained peripheral blood donor chimerism. Ten of 12 patients were alive with a median follow-up of 3.1 years (range, 0.1 to 14.7 years). More data are needed to refine transplant approaches in SAMD9/ SAMD9L patients with significant comorbidities and to develop guidelines for their long-term follow-up.

The PTPN11 gene encodes SHP-2, a non-receptor protein tyrosine phosphatase (PTPase) that relays signals from activated growth factor receptors to p21ras (Ras), Src family kinases, and other signaling molecules. Germ-line, missense mutations in PTPN11 account for approximately 50% of cases of the human developmental disorder Noonan Syndrome (NS). More recently, PTPN11 mutations have been identified in approximately 35% of children with juvenile myelomonocytic leukemia (JMML) without NS and have also been detected in other lymphoid and myeloid malignancies. Interestingly, almost all of these leukemia-associated mutations introduce amino acid substitutions within the N-SH2 domain of SHP-2 that are largely distinct from those found in NS. We have assessed the functional consequences of leukemia-associated PTPN11 mutations in primary hematopoietic cells. Expression of an E76K mutant SHP-2 in murine fetal liver and bone marrow cells confers a hypersensitive pattern of colony-forming unit granulocyte-macrophage (CFU-GM) colony growth in response to granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 3 (IL-3). Specifically, cells expressing E76K mutant SHP-2 display enhanced colony growth at low concentrations of growth factor compared to cells expressing wild-type (WT) SHP-2 protein. Mutant colonies are significantly larger with an abnormal, spreading morphology. E76K-expressing cells also form CFU-GM colonies in the absence of growth factor. The catalytic activity of the E76K mutant is required for aberrant colony growth as expressing the E76K mutation in the context of defective phosphatase activity (C463S) abolishes hypersensitive CFU-GM growth. Mutant E76K expression also enhances the growth of immature progenitor cells with high repopulating potential (HPP-CFC and LPP-CFC) in response to GM-CSF and IL-3 and perturbs erythroid progenitor colony growth. In addition, expressing the E76K mutation results in more pronounced growth factor hypersensitivity than another leukemia-associated SHP-2 mutation (D61Y), and both of these mutations confer a stronger hematopoietic phenotype than the common N308S substitution found in patients with NS.

6-Mercaptopurine (6-MP) is the mainstay of treatment for acute lymphoblastic leukemia and lymphoblastic lymphoma. It is metabolized into the pharmacologically active, 6-thioguanine nucleotide (6-TGN), and 6-methyl mercaptopurine nucleotides (6-MMPN), which is associated with hepatotoxicity that jeopardizes antileukemic therapy. Allopurinol alters the metabolism of 6-MP to increase 6-TGN levels and decreases 6-methyl mercaptopurine nucleotides levels. We report 2 cases in which combination therapy of allopurinol with 6-MP was used successfully to avoid hepatotoxicity while delivering adequate 6-TGN levels. We suggest that this combination therapy can be used safely to change the metabolite production in patients who develop excessive hepatotoxicity.

Monosomy 7 and del(7q) are associated with adverse features in myeloid malignancies. A 2.5-Mb commonly deleted segment (CDS) of chromosome band 7q22 is implicated as harboring a myeloid tumor suppressor gene (TSG); however, molecular analysis of candidate TSGs has not uncovered loss of function. To determine whether haploinsufficiency for the 7q22 CDS contributes to myeloid leukemogenesis, we performed sequential gene targeting to flank a region of orthologous synteny on mouse chromosome band 5A3 with loxP sites. We then generated Mx1-Cre, 5A3 fl mutant mice and deleted the targeted interval in vivo. Although excision was inefficient, we confirmed somatic deletion of the 5A3 CDS in the hematopoietic stem cell compartment. Mx1-Cre, 5A3 fl mice show normal hematologic parameters and do not spontaneously develop myeloid malignancies. The 5A3 fl deletion does not cooperate with oncogenic Kras G12D expression, Nf1 inactivation, or retroviral mutagenesis to accelerate leukemia development and did not modulate responsiveness to antileukemia drugs. These studies demonstrate that it is feasible to somatically delete a large chromosomal segment implicated in tumor suppression in hematopoietic cell populations in vivo; however, our data do not support the hypothesis that the 7q22/5A3 CDS interval contains a myeloid TSG. IntroductionLoss of chromosome 7 and deletion of a segment of the long arm (monosomy 7 and del(7q)) are recurring cytogenetic abnormalities in de novo and therapy-induced myeloid malignancies that are associated with advanced age, antecedent myelodysplastic syndrome (MDS), and resistance to current treatments. 1 Based on precedents in other cancers, it is likely that loss of one or more 7q tumor suppressor genes (TSGs) contributes to leukemogenesis. To facilitate the identification of candidate myeloid TSGs, Le Beau et al delineated 2 commonly deleted segments (CDSs) in patients with myeloid disorders characterized by a del(7q), a proximal interval within band q22 that accounts for most cases, and a second CDS in bands q32-34. 2 Using an ordered set of yeast artificial chromosome clones as probes, these investigators then performed fluorescence in situ hybridization (FISH) experiments to further characterize leukemias with deletion breakpoints within 7q22 and implicated an approximately 2.5-Mb CDS as harboring a myeloid TSG. We and others have extensively characterized this CDS, identified and cloned multiple genes from the interval, analyzed leukemia samples for mutations in these candidate TSGs, and performed Taqman real-time quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) assays to measure expression levels in normal and leukemic human bone marrows. [3][4][5][6] These studies did not uncover biallelic inactivation or epigenetic silencing of any candidate TSGs located within this CDS. [3][4][5] Thus, it was hypothesized that inactivation of a single allele (haploinsufficiency) of one or more TSGs located within the 2.5-Mb CDS might contribute to leukemogenesis. 4,5 Recent technical ...