Dysfunctional Immune System Reconstitution After Rituximab Exposure In Utero.

Rituximab is an antibody that binds to B-lymphocytes and is increasingly used during pregnancy. As an immunoglobulin G, it will transfer across the placenta. Previous case reports describe a diversity of clinical presentations in neonates born following rituximab exposure in utero. Our case is the first to offer the long-term experience in the care of an infant with severe neutropenia and prolonged profound hypogammaglobulinemia and class-switching B cell defect after in utero rituximab exposure.

A Novel Use of Romiplostim for SARS-CoV-2-induced Thrombocytopenia.

The literature regarding coronavirus disease of 2019 (COVID-19) infection in pediatrics indicates that children have less severe clinical presentations and lower mortality rates. There remains limited data regarding hematologic sequelae in pediatric patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Romiplostim has shown a platelet response in pediatric patients with chronic immune thrombocytopenic purpura, and eltrombopag is proven to increase platelet counts in patients with inherited thrombocytopenia. We review SARS-CoV-2-associated thrombocytopenia and present a pediatric patient with acute on chronic thrombocytopenia in the setting of COVID-19 with subsequent platelet recovery using romiplostim.

A Retrospective Review of Mercaptopurine Metabolism Reveals High Rate of Patients With Suboptimal Metabolites Successfully Corrected With Allopurinol.

Skewed drug metabolism of 6-mercaptopurine (6-MP) can jeopardize antileukemic effects and result in toxicities during the treatment of acute lymphoblastic leukemia and lymphoblastic lymphoma. Allopurinol can alter 6-MP metabolism to maximize therapeutic effects while reducing toxicities. Over 75% of our patients with acute lymphoblastic leukemia or lymphoblastic lymphoma experienced a 6-MP-related toxicity. Review of metabolite date a showed 6-methylmercaptopurine nucleotide levels were >10,000 in 55% of the cohort, suggesting 6-MP shunting. Allopurinol was initiated in 12 of 23 shunters with resolution of toxicities. We propose an algorithm to incorporate allopurinol into chemotherapy regimens for patients with inappropriate 6-MP metabolism.

Outcomes of Hematopoietic Cell Transplantation in Patients with Germline SAMD9/SAMD9L Mutations.

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.

Reduction of Factor VIII Inhibitor Titers During Immune Tolerance Induction With Recombinant Factor VIII-Fc Fusion Protein.

The development of inhibitors toward factor VIII (FVIII) is a common and serious complication of hemophilia A (HA) therapy. Patients with hemophilia who develop inhibitors often undergo time- and resource-intensive immune tolerance induction (ITI) protocols. We report a 15-month-old male with severe HA and a high-titer inhibitor that occurred while receiving prophylactic treatment with recombinant FVIII (rFVIII), in whom significant inhibitor titer reduction was achieved with thrice weekly infusions of a new, prolonged half-life rFVIII-Fc fusion protein product (trade name Eloctate). Further studies are warranted to explore the potential of Eloctate in ITI protocols.

Allopurinol Use During Maintenance Therapy for Acute Lymphoblastic Leukemia Avoids Mercaptopurine-related Hepatotoxicity.

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.

Lack of factor VIII detection in humans and dogs with an intron 22 inversion challenges hypothesis regarding inhibitor risk.

BACKGROUND: Almost half of severe hemophilia A (HA) cases are caused by an intron 22 inversion (Int22Inv) mutation, which truncates the 26-exon F8 messenger RNA (mRNA) after exon 22. Another F8 transcript, F8B, is initiated from within F8-intron-22. F8B mRNA consists of a short exon spliced to exons 23 to 26 and is expressed in multiple human cell types. It has been hypothesized that Int22Inv patients have self-tolerance to partial factor (F)VIII proteins expressed from these 2 transcripts. FVIII is expressed in endothelial cells, primarily in the liver and lungs. Several studies have reported FVIII expression in other cell types, although this has been controversial. OBJECTIVES: To determine if partial FVIII proteins are expressed from intron 22-inverted and/or F8B mRNA and if FVIII is expressed in nonendothelial cells. METHODS: A panel of FVIII-specific antibodies was validated and employed to label FVIII in cells and tissues and for immunoprecipitation followed by western blots and mass spectrometry proteomics analysis. RESULTS: Immunofluorescent staining localized FVIII to endothelial cells in liver sections from non-HA but not HA-Int22Inv dogs. Neither FVIII nor FVIIIB was detected in human peripheral blood mononuclear cells, B cell or T cell lines, or cell lines expanded from peripheral blood mononuclear cells, whereas FVIII antigen and activity were readily detected in primary nonhemophilic liver sinusoidal endothelial cells. CONCLUSION: If FVIII is expressed in nonendothelial cells or if partial FVIII proteins are expressed in HA-Int22Inv, the concentrations are below the detection limits of these sensitive assays. Our results argue against promotion of immune tolerance through expression of partial FVIII proteins in Int-22Inv patients.

Hodgkin lymphoma associated vanishing bile duct syndrome treated successfully with a brentuximab based regimen.

We report a combination therapy to successfully treat a patient with Hodgkin's lymphoma complicated by vanishing bile duct syndrome. Our patient was in his 20s and presented with jaundice, emesis, B symptoms and diffuse lymphadenopathy along with cholestatic liver injury prompting a liver biopsy, which revealed this diagnosis, after the exclusion of other aetiologies. Our treatment regimen incorporated brentuximab along with other more conventional agents which attempted to maximise therapeutic efficacy while minimising the consequences of hepatotoxicity on the treatment protocol. Although this patient's treatment course was complicated because of neutropenic infections, the patient achieved a complete metabolic response and is now more than 1 year off therapy.

Use of chromosome engineering to model a segmental deletion of chromosome band 7q22 found in myeloid malignancies.

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.

Retinal hemorrhages as a presenting sign in an adolescent patient with hepatosplenic gamma-delta T-cell lymphoma.

Hepatosplenic gamma-delta T-cell lymphoma is a very rare, aggressive form of peripheral lymphoma first recognized in 1990. Patients often present with organomegaly, anemia, adenopathy, and B symptoms. Rarely in the literature is a pediatric patient described with this subtype of peripheral T-cell lymphoma. Also, retinal hemorrhages have never been described as a presenting symptom of hepatosplenic gamma-delta T-cell lymphoma. We describe an adolescent patient with hepatosplenic gamma-delta T-cell lymphoma who presented with retinal hemorrhages, massive splenomegaly, bone marrow involvement, and B symptoms.

Many factor VIII products available in the treatment of hemophilia A: an embarrassment of riches?

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.

Functional analysis of leukemia-associated PTPN11 mutations in primary hematopoietic cells.

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.

Mutations in PTPN11 implicate the SHP-2 phosphatase in leukemogenesis.

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 p21Ras (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.