Allogeneic hematopoietic stem cell transplantation in pediatric myelodysplastic syndromes: a multicenter experience from Argentina.

BACKGROUND: Allogeneic hematopoietic stem cell transplantation (AHSCT) represents the only curative treatment for the majority of pediatric patients with Myelodysplastic Syndrome (MDS). We aimed to evaluate overall survival (OS), disease-free survival (DFS), non-relapse mortality (NRM) and relapse incidence in children who underwent AHSCT for MDS in six institutions from Argentina. PROCEDURE: A retrospective analysis of 54 AHSCT was carried out in 52 patients (mean age: 9 years; range: 2-19; 35 males). RESULTS: MDS subtypes were refractory cytopenia of childhood (RCC) (n: 26, 50%), refractory anemia with excess blasts (RAEB) (n: 9, 18%), RAEB in transformation (RAEB-T) (n: 8, 15%) and juvenile myelomonocytic leukemia (JMML) (n: 9, 17%). At time of transplant, seven (13%) patients transformed to acute myeloid leukemia (AML) and two patients with RCC to RAEB. Donors were related in 32 cases (59%) and the stem cells source was: bone marrow (63%), peripheral blood (26%), and umbilical cord blood (11%). Five-year DFS and OS were 50% and 55% respectively; and for patients with JMML, 57% and 67% respectively. Cumulative incidence of NRM and relapse were 27% and 21% respectively. In the multivariate analysis, umbilical cord blood (HR 4.07; P = 0.025) and age ≥ 9 years at transplantation (HR 3.28; P = 0.017) were associated with lower OS; age and graft-versus-host disease (GVHD) had a higher NRM. CONCLUSIONS: In our series, more than half of the patients achieved long term OS with AHSCT. Less toxic conditioning regimens or more intensive GVHD prophylaxis could lead to better results in some children.

Overexpression of the autoimmunity-associated phosphatase PTPN22 promotes survival of antigen-stimulated CLL cells by selectively activating AKT.

A polymorphic variant of the phosphatase PTPN22 has been associated with increased risk for multiple autoimmune diseases. The risk allele is thought to function by diminishing antigen-receptor signals responsible for negative selection of autoreactive lymphocytes. We now show that PTPN22 is markedly overexpressed in chronic lymphocytic leukemia (CLL), a common malignancy of autoreactive B lymphocytes. We also show that overexpression of PTPN22 significantly inhibits antigen-induced apoptosis of primary CLL cells by blocking B-cell receptor (BCR) signaling pathways that negatively regulate lymphocyte survival. More importantly, we show that PTPN22 positively regulates the antiapoptotic AKT kinase, which provides a powerful survival signal to antigen-stimulated CLL cells. This selective uncoupling of AKT from other downstream BCR signaling pathways is a result of inhibition of a negative regulatory circuit involving LYN, CD22, and SHIP. Finally, we show that PTPN22 can be effectively down-regulated by the PKC inhibitors ruboxistaurin and sotrastaurin, resulting in enhanced killing of CLL cells exposed to proapoptotic BCR stimuli. Collectively, these data suggest that PTPN22 overexpression represents a protective mechanism that allows autoantigen-activated CLL cells to escape from negative selection and indicate that this mechanism could be exploited for therapeutic purposes by targeting PTPN22 with PKC inhibitors.

The Syk inhibitor fostamatinib disodium (R788) inhibits tumor growth in the Eµ- TCL1 transgenic mouse model of CLL by blocking antigen-dependent B-cell receptor signaling.

Inhibition of antigen-dependent B-cell receptor (BCR) signaling is considered a promising therapeutic approach in chronic lymphocytic leukemia (CLL), but experimental in vivo evidence to support this view is still lacking. We have now investigated whether inhibition of BCR signaling with the selective Syk inhibitor fostamatinib disodium (R788) will affect the growth of the leukemias that develop in the Eµ-TCL1 transgenic mouse model of CLL. Similarly to human CLL, these leukemias express stereotyped BCRs that react with autoantigens exposed on the surface of senescent or apoptotic cells, suggesting that they are antigen driven. We show that R788 effectively inhibits BCR signaling in vivo, resulting in reduced proliferation and survival of the malignant B cells and significantly prolonged survival of the treated animals. The growth-inhibitory effect of R788 occurs despite the relatively modest cytotoxic effect in vitro and is independent of basal Syk activity, suggesting that R788 functions primarily by inhibiting antigen-dependent BCR signals. Importantly, the effect of R788 was found to be selective for the malignant clones, as no disturbance in the production of normal B lymphocytes was observed. Collectively, these data provide further rationale for clinical trials with R788 in CLL and establish the BCR-signaling pathway as an important therapeutic target in this disease.

Children admitted to a pediatric intensive care unit after hematopoietic stem cell transplantation: Analysis of survival and predictors of mortality. / Niños con trasplante de progenitores hematopoyéticos admitidos en una unidad de cuidados intensivos: análisis de la sobrevida y los factores predictivos de mortalidad.

INTRODUCTION: Hematopoietic stem cell transplantation (HSCT) in children is a procedure that is not exempt of severe complications. Admission to the pediatric intensive care unit (PICU) is associated with a high mortality rate. Objectives: To analyze survival and predictors of mortality among children who received a HSCT and were admitted to the PICU, and to develop a mortality prediction model in this population. MATERIALS AND METHODS: Retrospective review of children and adolescents who received a HSCT between January 1st, 2005 and December 31st, 2019 and were admitted to the PICU of a tertiary care teaching hospital. RESULTS: Out of 264 children receiving the transplant, 114 were admitted to the PICU. The overall mortality rate was 29% (n = 34). The type of transplant, underlying disease, febrile neutropenia event, cytomegalovirus infection, respiratory failure, graft versus host disease (GVHD), myeloablative chemotherapy, and previous malnutrition were associated with higher mortality rates. In the multivariate analysis, GVHD (odds ratio [OR]: 2.23; 95% confidence interval [CI]: 1.92-2.98), need for mechanical ventilation (OR: 2.47; 95% CI: 1.39- 5.73), alternative donor transplant (OR: 1.58; 95% CI: 1.14-2.17), and previous malnutrition (OR: 1.78; 95% CI: 1.22-3.89) were associated with a higher mortality rate. CONCLUSION: In the studied population, 2 out of 3 children who received a HSCT and were admitted to the PICU survived. GVHD, mechanical ventilation, alternative donor transplant, and previous malnutrition were predictors of mortality.

Introducción: El trasplante de células progenitoras hematopoyéticas (TPH) en niños es un procedimiento no exento de complicaciones graves. El ingreso de esta población a unidades de cuidados intensivos pediátricos (UCIP) se asocia con elevada mortalidad. Objetivos: Analizar la sobrevida y los factores predictivos de la mortalidad en niños que recibieron TPH e ingresaron a la UCIP y elaborar un modelo predictivo de mortalidad en esta población. Materiales y métodos: Revisión retrospectiva de niños y adolescentes que recibieron un TPH entre el 01/01/2005 y el 31/12/2019 e ingresaron a la UCIP de un hospital universitario de alta complejidad. Resultados: De un total de 264 niños que recibieron el trasplante, 114 ingresaron a la UCIP. La mortalidad general fue del 29% (n = 34). El tipo de trasplante, enfermedad basal, evento de neutropenia febril, infección por citomegalovirus, insuficiencia respiratoria, enfermedad de injerto contra huésped (EICH), quimioterapia mieloablativa y desnutrición previa se asociaron con tasas de mortalidad más elevadas. En el análisis multivariado, la EICH (razón de posibilidades [OR, por su sigla en inglés]: 2,23; intervalo de confianza del 95% [IC 95%]: 1,92-2,98), la necesidad de ventilación mecánica invasiva (OR: 2,47; IC95%: 1,39-5,73), el trasplante de donante alternativo (OR: 1,58; IC 95%: 1,14-2,17) y la desnutrición previa (OR: 1,78; IC 95%: 1,223-3,89) se asociaron con mayor mortalidad. Conclusión: En la población estudiada, dos de cada tres niños que recibieron TPH e ingresaron a la UCIP sobrevivieron. La EICH, ventilación mecánica, trasplante de donante alternativo y desnutrición previa fueron factores predictivos de mortalidad.

Signaling pathways activated by antigen-receptor engagement in chronic lymphocytic leukemia B-cells.

Several features of the B-cell receptor (BCR) have emerged as major prognostic factors in chronic lymphocytic leukemia (CLL). In particular, the absence of somatic mutations in the immunoglobulin variable region genes and expression of the protein tyrosine kinase ZAP-70 are strongly associated with an aggressive clinical course, and both features have been correlated with a greater capacity of the BCR to transmit antigen-induced signals. Additionally, differences in BCR structure and reactivity indicate that CLL B-cells from the two prognostic subsets may recognize different types of antigens. Antigens that are not rapidly internalized induce sustained BCR signaling that can promote the survival of the leukemic B-cells. The BCR signal is initially transmitted by the Syk kinase and modulated by ZAP-70, which shows inefficient or absent tyrosine kinase activation in B-cells. However, both ZAP-70 expression and sustained BCR engagement have been associated with prolonged activation of the Akt and ERK kinases, which is required for the induction of several antiapoptotic proteins, including Mcl-1, Bcl-xL and XIAP. Therefore, targeting components along the BCR signaling pathway may be a promising strategy for the treatment of CLL.

Niños con trasplante de progenitores hematopoyéticos admitidos en una unidad de cuidados intensivos: análisis de la sobrevida y los factores predictivos de mortalidad / Children admitted to a pediatric intensive care unit after hematopoietic stem cell transplantation: Analysis of survival and predictors of mortality

Introducción: El trasplante de células progenitoras hematopoyéticas (TPH) en niños es un procedimiento no exento de complicaciones graves. El ingreso de esta población a unidades de cuidados intensivos pediátricos (UCIP) se asocia con elevada mortalidad. Objetivos: Analizar la sobrevida y los factores predictivos de la mortalidad en niños que recibieron TPH e ingresaron a la UCIP y elaborar un modelo predictivo de mortalidad en esta población. Materiales y métodos: Revisión retrospectiva de niños y adolescentes que recibieron un TPH entre el 01/01/2005 y el 31/12/2019 e ingresaron a la UCIP de un hospital universitario de alta complejidad. Resultados: De un total de 264 niños que recibieron el trasplante, 114 ingresaron a la UCIP. La mortalidad general fue del 29 % (n = 34). El tipo de trasplante, enfermedad basal, evento de neutropenia febril, infección por citomegalovirus, insuficiencia respiratoria, enfermedad de injerto contra huésped (EICH), quimioterapia mieloablativa y desnutrición previa se asociaron con tasas de mortalidad más elevadas. En el análisis multivariado, la EICH (razón de posibilidades [OR, por su sigla en inglés]: 2,23; intervalo de confianza del 95 % [IC 95 %]: 1,92-2,98), la necesidad de ventilación mecánica invasiva (OR: 2,47; IC95 %: 1,39-5,73), el trasplante de donante alternativo (OR: 1,58; IC 95 %: 1,14-2,17) y la desnutrición previa (OR: 1,78; IC 95 %: 1,223-3,89) se asociaron con mayor mortalidad. Conclusión: En la población estudiada, dos de cada tres niños que recibieron TPH e ingresaron a la UCIP sobrevivieron. La EICH, ventilación mecánica, trasplante de donante alternativo y desnutrición previa fueron factores predictivos de mortalidad

Introduction: Hematopoietic stem cell transplantation (HSCT) in children is a procedure that is not exempt of severe complications. Admission to the pediatric intensive care unit (PICU) is associated with a high mortality rate. Objectives: To analyze survival and predictors of mortality among children who received a HSCT and were admitted to the PICU, and to develop a mortality prediction model in this population. Materials and methods: Retrospective review of children and adolescents who received a HSCT between January 1st, 2005 and December 31st, 2019 and were admitted to the PICU of a tertiary care teaching hospital. Results: Out of 264 children receiving the transplant 114 were admitted to the PICU. The overall mortality rate was 29 % (n = 34). The type of transplant, underlying disease, febrile neutropenia event, cytomegalovirus infection, respiratory failure, graft versus host disease (GVHD), myeloablative chemotherapy, and previous malnutrition were associated with higher mortality rates. In the multivariate analysis, GVHD (odds ratio [OR]: 2.23; 95 % confidence interval [CI]: 1.92-2.98), need for mechanical ventilation (OR: 2.47; 95 % CI: 1.39-5.73), alternative donor transplant (OR: 1.58; 95 % CI: 1.14-2.17), and previous malnutrition (OR: 1.78; 95 % CI: 1.22-3.89) were associated with a higher mortality rate. Conclusion: In the studied population, 2 out of 3 children who received a HSCT and were admitted to the PICU survived. GVHD, mechanical ventilation, alternative donor transplant, and previous malnutrition were predictors of mortality

The proliferative response to CpG-ODN stimulation predicts PFS, TTT and OS in patients with chronic lymphocytic leukemia.

We recently reported that leukemic cells from IgVH-unmutated/progressive CLL more frequently proliferate in response to CpG-ODN stimulation than their corresponding counterparts. Here we evaluated the prognostic impact of this proliferative response in 91 CLL patients. The proliferative response was highly predictive of PFS, TTT and OS in the whole series and refined prognosis in patients with M-CLL. BCR stimulation modulated the response to CpG-ODN, suggesting that the proliferative capacity of the leukemic cells is related to antigen-encounter history. These data support the hypothesis that the capacity of the leukemic cells to respond to external stimuli influences disease progression in CLL.

Phosphorylation of the activation loop tyrosines is required for sustained Syk signaling and growth factor-independent B-cell proliferation.

The Syk kinase is regarded as a promising target for the treatment of antigen-driven B-cell malignancies, considering its essential role in propagating antigenic stimuli through the B-cell receptor (BCR). In certain common B-cell malignancies Syk is activated even in the absence of BCR engagement, suggesting a wider role for this kinase in lymphomagenesis. In this paper, we have profiled molecular differences between BCR-induced and constitutive Syk activation in terms of phosphorylation of regulatory tyrosine residues, downstream signaling properties and capacity to sustain B-cell proliferation. Analysis of primary chronic lymphocytic leukemia B-cells and diffuse large B-cell lymphoma cell lines revealed that constitutive and BCR-induced Syk activation differ with respect to the phosphorylation status of the regulatory tyrosines at positions 352 and 525/526, with only the first site being phosphorylated in the case of constitutive and both sites in the case of BCR-induced Syk activation. Syk phosphorylated only on Y352 is capable of downstream signaling, as evidenced by experiments with a phosphomimetic mutant in which the activation loop tyrosines (YY525/526) were replaced with phenylalanines. However, phosphorylation at YY525/526 was shown to significantly increase the enzymatic activity of Syk and to be required for sustained PLCgamma2, Akt and ERK signaling as well as B-cell transformation. These data demonstrate that constitutively active Syk and Syk activated by BCR crosslinking represent separate stages of Syk activation with distinct signaling properties and transforming capacities.

The Akt/Mcl-1 pathway plays a prominent role in mediating antiapoptotic signals downstream of the B-cell receptor in chronic lymphocytic leukemia B cells.

Sustained engagement of the B-cell receptor (BCR) increases apoptosis resistance in chronic lymphocytic leukemia (CLL) B cells, whereas transient stimulation usually has an opposite effect. The antiapoptotic BCR signal has been associated with prolonged activation of the PI3K/Akt and MEK/ERK pathways, which are key regulators of survival and proliferation in various cell types. To further define the relative contribution of the Akt and ERK kinases in regulating CLL B-cell survival, we introduced constitutively active mutants of Akt and MEK in primary CLL B cells and evaluated changes in the expression of relevant pro- and antiapoptotic proteins. Sustained activation of Akt resulted in increased leukemic cell viability and increased expression of the antiapoptotic proteins Mcl-1, Bcl-xL, and X-linked inhibitor of apoptosis protein (XIAP), thus largely recapitulating the effects of sustained BCR stimulation. Constitutively active MEK2 also up-regulated XIAP, but did not show a significant impact on leukemic cell survival. Down-regulation of Mcl-1 by siRNA treatment induced rapid and potent apoptosis in CLL B cells and blocked the antiapoptotic effect of sustained BCR stimulation, whereas down-regulation of Bcl-xL and XIAP did not affect leukemic cell viability. These data demonstrate that Akt and Mcl-1 are major components of a survival pathway that can be activated in CLL B cells by antigen stimulation.

ZAP-70 enhances B-cell-receptor signaling despite absent or inefficient tyrosine kinase activation in chronic lymphocytic leukemia and lymphoma B cells.

Expression of ZAP-70 is an important negative prognostic factor in chronic lymphocytic leukemia (CLL). This protein tyrosine kinase is a key mediator of T-cell receptor (TCR) signaling and is structurally homologous to Syk, which plays an analogous role in B-cell receptor (BCR) signaling. Recent studies indicate that ZAP-70 may participate in BCR signaling as well, but the mechanism of action is not completely understood. We have now compared antigen receptor-induced activation of ZAP-70 in B cells and T cells by analyzing phosphorylation of critical regulatory tyrosine residues. We show that BCR-mediated activation of ZAP-70 is very inefficient in CLL and lymphoma B cells and is negligible when compared to activation of Syk. Despite the inefficient catalytic activation, the ability of ZAP-70 to recruit downstream signaling molecules in response to antigen receptor stimulation appeared relatively preserved. Moreover, ectopic expression of ZAP-70 enhanced and prolonged activation of several key mediators of BCR signaling, such as the Syk, ERK, and Akt kinases, and decreased the rate of ligand-mediated BCR internalization. We conclude that the role of ZAP-70 in BCR signaling is quite distinct from its role in TCR signaling and is likely mediated by inhibition of events that terminate the signaling response.