Epstein Barr virus-directed T-cell therapy for refractory EBV-PTLD in a toddler post Orthotopic heart transplantation.

Epstein-Barr Virus (EBV) is a ubiquitous herpes type virus that is associated with post-transplant lymphoproliferative disorder (PTLD). Usual management includes reduction or cessation of immunosuppression and in some cases chemotherapy including rituximab. However, limited therapies are available if PTLD is refractory to rituximab. Several clinical trials have investigated the use of EBV-directed T cells in rituximab-refractory patients; however, data regarding response is scarce and inconclusive. Herein, we describe a patient with EBV-PTLD refractory to rituximab after orthotopic heart transplantation (OHT) requiring EBV-directed T-cell therapy. This article aims to highlight the unique and aggressive clinical presentation and progression of PTLD with utilization of EBV-directed T-cell therapy for management and associated pitfalls.

Dasatinib with intensive chemotherapy in de novo paediatric Philadelphia chromosome-positive acute lymphoblastic leukaemia (CA180-372/COG AALL1122): a single-arm, multicentre, phase 2 trial.

BACKGROUND: The outcome of children with Philadelphia chromosome-positive (Ph-positive) acute lymphoblastic leukaemia significantly improved with the combination of imatinib and intensive chemotherapy. We aimed to investigate the efficacy of dasatinib, a second-generation ABL-class inhibitor, with intensive chemotherapy in children with newly diagnosed Ph-positive acute lymphoblastic leukaemia. METHODS: CA180-372/COG AALL1122 was a joint Children's Oncology Group (COG) and European intergroup study of post-induction treatment of Ph-positive acute lymphoblastic leukaemia (EsPhALL) open-label, single-arm, phase 2 study. Eligible patients (aged >1 year to <18 years) with newly diagnosed Ph-positive acute lymphoblastic leukaemia and performance status of at least 60% received EsPhALL chemotherapy plus dasatinib 60 mg/m2 orally once daily from day 15 of induction. Patients with minimal residual disease of at least 0·05% after induction 1B or who were positive for minimal residual disease after the three consolidation blocks were classified as high risk and allocated to receive haematopoietic stem-cell transplantation (HSCT) in first complete remission. The remaining patients were considered standard risk and received chemotherapy plus dasatinib for 2 years. The primary endpoint was the 3-year event-free survival of dasatinib plus chemotherapy compared with external historical controls. The trial was considered positive if one of the following conditions was met: superiority over chemotherapy alone in the AIEOP-BFM 2000 high-risk group; or non-inferiority (with a margin of -5%) or superiority to imatinib plus chemotherapy in the EsPhALL 2010 cohort. All participants who received at least one dose of dasatinib were included in the safety and efficacy analyses. This trial was registered with ClinicalTrials.gov, NCT01460160, and recruitment is closed. FINDINGS: Between March 13, 2012, and May 27, 2014, 109 patients were enrolled at 69 sites (including 51 COG sites in the USA, Canada, and Australia, and 18 EsPhALL sites in Italy and the UK). Three patients were ineligible and did not receive dasatinib. 106 patients were treated and included in analyses (49 [46%] female and 57 [54%] male; 85 [80%] White, 13 [12%] Black or African American, five [5%] Asian, and three [3%] other races; 24 [23%] Hispanic or Latino ethnicity). All 106 treated patients reached complete remission; 87 (82%) were classified as standard risk and 19 (18%) met HSCT criteria and were classified as high risk, but only 15 (14%) received HSCT in first complete remission. The 3-year event-free survival of dasatinib plus chemotherapy was superior to chemotherapy alone (65·5% [90% Clopper-Pearson CI 57·7 to 73·7] vs 49·2% [38·0 to 60·4]; p=0·032), and was non-inferior to imatinib plus chemotherapy (59·1% [51·8 to 66·2], 90% CI of the treatment difference: -3·3 to 17·2), but not superior to imatinib plus chemotherapy (65·5% vs 59·1%; p=0·27). The most frequent grade 3-5 adverse events were febrile neutropenia (n=93) and bacteraemia (n=21). Nine remission deaths occurred, which were due to infections (n=5), transplantation-related (n=2), due to cardiac arrest (n=1), or had an unknown cause (n=1). No dasatinib-related deaths occurred. INTERPRETATION: Dasatinib plus EsPhALL chemotherapy is safe and active in paediatric Ph-positive acute lymphoblastic leukaemia. 3-year event-free survival was similar to that of previous Ph-positive acute lymphoblastic leukaemia trials despite the limited use of HSCT in first complete remission. FUNDING: Bristol Myers Squibb.

Trends in Pediatric Cancer Care in Florida From 1981-2020: Changing Patterns in a Growing and Increasingly Diverse Population.

Background The Florida Association of Pediatric Tumor Programs (FAPTP) has used the Statewide Patient Information Reporting System (SPIRS) since 1981 to track all new cases of pediatric cancer. We reviewed the last 40 years of data to see how pediatric cancer care has evolved. Methods We retrospectively analyzed SPIRS data from 1981 through 2020 in five-year increments, looking at numbers of new diagnoses, care delivery sites, and trial enrollment in Children's Oncology Group (COG) studies. Results From 1981-2020 Florida's population increased almost 88% while the pediatric population only grew 61%. New pediatric cancer diagnoses increased 326% to over 1,000 new cases/year. The percentage of patients treated at FAPTP centers grew from 30% to 57% with an annual percentage change (APC) of 10.3% (95% Confidence Interval [CI] of 0.6 to 20.9%). The rate of COG clinical trial enrollment decreased from 32% in 1981-1985 to 20% in 2016-2020, for an APC of 8.91% (95% CI of -13.3 to -4.3%). Conclusions The striking increase in pediatric cancer cases in Florida over the last 40 years was out of proportion to the population growth. More patients received care at FAPTP centers, but a lower percentage were enrolled on COG trials.

Establishing Cost-Effective Allocation of Proton Therapy for Patients With Mediastinal Hodgkin Lymphoma.

PURPOSE: For curative treatment of Hodgkin lymphoma, radiation therapy benefit must be weighed against toxicity. Although more costly, proton radiation therapy reduces dose to healthy tissue, potentially improving the therapeutic ratio compared with photons. We sought to determine the cost-effectiveness of proton versus photon therapy for mediastinal Hodgkin lymphoma (MHL) based on reduced heart disease. METHODS AND MATERIALS: Our model approach was 2-fold: (1) Use patient-level dosimetric information for a cost-effectiveness analysis using a Markov cohort model. (2) Use population-based data to develop guidelines for policymakers to determine thresholds of proton therapy favorability for a given photon dose. The HD14 trial informed relapse risk; coronary heart disease risk was informed by the Framingham risk calculator modified by the mean heart dose (MHD) from radiation. Sensitivity analyses assessed model robustness and identified the most influential model assumptions. A 30-year-old adult with MHL was the base case using 30.6-Gy proton therapy versus photon intensity modulated radiation therapy. RESULTS: Proton therapy was not cost-effective in the base case for male ($129,000/ quality-adjusted life years [QALYs]) or female patients ($196,000/QALY). A 5-Gy MHD decrease was associated with proton therapy incremental cost-effectiveness ratio <$100,000/QALY in 40% of scenarios. The hazard ratio associating MHD and heart disease was the most influential clinical parameter. CONCLUSIONS: Proton therapy may be cost-effective a select minority of patients with MHL based on age, sex, and MHD reduction. We present guidance for clinicians using MHD to aid decision-making for radiation therapy modality.

Eating behaviors and dietary quality in childhood acute lymphoblastic leukemia survivors.

BACKGROUND: Childhood acute lymphoblastic leukemia (ALL) survivors' increased risk for adverse health outcomes could be mitigated through consuming a balanced diet. Nonetheless, >70% of adult survivors do not meet survivorship dietary recommendations. ALL treatment may amplify risk for restricted dietary preferences (picky eating) and poor self-regulation of food intake that could contribute to suboptimal diets in survivorship. This study aims to: (a) characterize differences in picky eating and self-regulation of food intake between survivors and peer controls; and (b) examine the associations between these eating behaviors and dietary quality in ALL survivors relative to peer controls. METHODS: Participants were children (5-13 years) with (n = 32) and without (n = 32) a history of ALL and their caregivers. Children's dietary quality (Healthy Eating Index-2015) was calculated from 24-h dietary recalls. Caregivers completed the Child Eating Behavior Questionnaire-Food Fussiness subscale and the Child Self-Regulation in Eating Questionnaire. RESULTS: Independent samples t-tests revealed survivors exhibited greater picky eating than peer controls but comparable self-regulation of food intake. Bootstrapped grouped multivariate regression results showed that for ALL survivors, greater picky eating was associated with worse dietary quality (controlling for age and self-regulation of food intake). For peer controls, worse self-regulation of food intake was associated with poorer dietary quality (controlling for picky eating and age). CONCLUSIONS: Results provide preliminary support that different eating behaviors contribute to poor dietary quality in children with and without an ALL history. These findings suggest that interventions to improve ALL survivors' dietary quality may benefit targeting picky eating.

Incidence and Risk Factors for 30-Day Readmission after Inpatient Chemotherapy among Acute Lymphoblastic Leukemia Patients.

Chemotherapy for acute lymphoblastic leukemia (ALL) patients is complex and intense, resulting in a high readmission rate. We aimed to identify the incidence, causes, and risk factors of readmission following inpatient chemotherapy among ALL patients, using 2016 National Readmission Database. We applied three different definitions of 30-day readmission: (1) nonelective readmission based on readmission type, (2) unplanned readmission defined by CMS, and (3) unintentional readmission, combining (1) and (2). We used unweighted multivariable Poisson regression with robust variance estimates for risk factors analysis, including patient-, hospital-, and admission-related characteristics. Percentage for nonelective, unplanned, and unintentional readmission were 33.3%, 22.4%, and 18.5%, respectively. The top three causes for unplanned readmissions were neutropenia/agranulocytosis (27.8%), septicemia (15.3%), and pancytopenia (11.5%). Risk ratios for unintentional readmission were 1.21 (1.08-1.36) for nonelective vs. elective admission, 1.19 (1.06-1.33) for public vs. private insurance enrollees, 0.96 (0.95-0.98) for each day of hospital stay, 0.77 (0.62-0.95) for large teaching and 0.87 (0.70-1.08) for small teaching vs. nonteaching hospitals. Possible strategies to reduce readmission among ALL patients could be shortening the gap in quality of care among teaching vs. non-teaching hospitals, understanding the difference between privately vs. publicly insured patients, and avoiding aggressive discharge after chemotherapy.

How we approach Philadelphia chromosome-positive acute lymphoblastic leukemia in children and young adults.

Treatment for children with Philadelphia chromosome-positive acute lymphoblastic leukemia has changed radically over the past 20 years. This type of leukemia used to have dismal prognosis, but today cure rates have improved with combination of cytotoxic chemotherapy and a tyrosine kinase inhibitor such as imatinib or dasatinib, with hematopoietic stem cell transplant reserved for patients who are at high risk based on slow response to therapy or who relapse. Treating these patients can be challenging particularly if they are not enrolled on a clinical trial. Here, we describe our approach to these patients.

Irradiating Residual Disease to 30 Gy with Proton Therapy in Pediatric Mediastinal Hodgkin Lymphoma.

BACKGROUND: Local relapse is a predominant form of recurrence among pediatric patients with Hodgkin lymphoma (PHL). Although PHL radiotherapy doses have been approximately 20 Gy, adults with Hodgkin lymphoma receiving 30 to 36 Gy experience fewer in-field relapses. We investigated the dosimetric effect of such a dose escalation to the organs at risk (OARs). MATERIALS AND METHODS: Ten patients with PHL treated with proton therapy to 21 Gy involved-site radiation therapy (ISRT21Gy) were replanned to deliver 30 Gy by treating the ISRT to 30 Gy (ISRT30Gy), delivering 21 Gy to the ISRT plus a 9-Gy boost to postchemotherapy residual volume (rISRTboost), and delivering 30 Gy to the residual ISRT target only (rISRT30Gy). Radiation doses to the OARs were compared. RESULTS: The ISRT30Gy escalated the dose to the target by 42% but also to the OARs. The rISRTboost escalated the residual target dose by 42%, and the OAR dose by only 17% to 26%. The rISRT30Gy escalated the residual target dose by 42% but reduced the OAR dose by 25% to 46%. CONCLUSION: Boosting the postchemotherapy residual target dose to 30Gy can allow for dose escalation with a slight OAR dose increase. Treating the residual disease for the full 30Gy, however, would reduce the OAR dose significantly compared with ISRT21Gy. Studies should evaluate these strategies to improve outcomes and minimize the late effects.

Post Transplant Lymphoproliferative Disorder risk factors in children: Analysis of a 23-year single-institutional experience.

INTRODUCTION: PTLD is the most frequent malignancy following SOT in children and the second most common SOT complication in adults. However, factors determining outcomes in children are poorly understood due to its relative rarity. METHODS: This study was performed at the University of Florida. Univariate and multivariate analyses were used to identify prognostic factors in pediatric patients diagnosed with PTLD. RESULTS: We reviewed records of 54 pediatric (younger than 18 years old at diagnosis) patients diagnosed with PTLD from 1994 to 2017. The median follow-up was 28.8 months. The estimated 5-year survival rate was 87.6% (95% CI 74.3-94.2%). Univariate analysis showed that organ transplanted (specifically heart transplant), poor response to initial treatment, allograft rejection, and low Karnofsky score were statistically significant for negative prognostic factors in determining survival. Multivariate analysis determined progression in response to initial treatment and presence of allograft rejection as statistically significant prognostic factors affecting overall survival. We found no statistically significant impact of EBV serological status on PTLD prognosis. CONCLUSIONS: Disease progression and allograft rejection were strong negative prognostic indicators in our study cohort. Close attention to graft status and development of therapies that protect the graft from rejection while bolstering anti-EBV immunity will be essential to further improving PTLD outcomes in children.

Primary pulmonary artery sarcoma in the pediatric patient: Review of literature and a case report.

Primary pulmonary artery sarcoma (PAS) is extremely rare in children. Nevertheless, distinguishing primary PAS from pulmonary embolism is critical to a child's survival. Primary PAS is commonly misdiagnosed as a pulmonary embolism due to similar presenting symptoms and radiographic findings. However, compared to adults, pulmonary embolism is rare in children, especially in patients who do not have predisposing factors or hypercoagulable state. We present a child with primary PAS which mimicked pulmonary embolism on presentation but eventually was resected and is doing well 5 years after resection. In the absence of predisposing factors or hypercoagulable state, solid tumors such as primary PAS should be considered when assessing a pediatric patient with presumed pulmonary embolism.

A genomics-informed computational biology platform prospectively predicts treatment responses in AML and MDS patients.

Patients with myelodysplastic syndromes (MDS) or acute myeloid leukemia (AML) are generally older and have more comorbidities. Therefore, identifying personalized treatment options for each patient early and accurately is essential. To address this, we developed a computational biology modeling (CBM) and digital drug simulation platform that relies on somatic gene mutations and gene CNVs found in malignant cells of individual patients. Drug treatment simulations based on unique patient-specific disease networks were used to generate treatment predictions. To evaluate the accuracy of the genomics-informed computational platform, we conducted a pilot prospective clinical study (NCT02435550) enrolling confirmed MDS and AML patients. Blinded to the empirically prescribed treatment regimen for each patient, genomic data from 50 evaluable patients were analyzed by CBM to predict patient-specific treatment responses. CBM accurately predicted treatment responses in 55 of 61 (90%) simulations, with 33 of 61 true positives, 22 of 61 true negatives, 3 of 61 false positives, and 3 of 61 false negatives, resulting in a sensitivity of 94%, a specificity of 88%, and an accuracy of 90%. Laboratory validation further confirmed the accuracy of CBM-predicted activated protein networks in 17 of 19 (89%) samples from 11 patients. Somatic mutations in the TET2, IDH1/2, ASXL1, and EZH2 genes were discovered to be highly informative of MDS response to hypomethylating agents. In sum, analyses of patient cancer genomics using the CBM platform can be used to predict precision treatment responses in MDS and AML patients.

Functional Improvement of Chimeric Antigen Receptor Through Intrinsic Interleukin-15Rα Signaling.

INTRODUCTION: Recent studies on CD19-specific chimeric antigen receptor (CAR)-modified T cells (CARTs) have demonstrated unprecedented successes in treating refractory and relapsed B cell malignancies. The key to the latest CART therapy advances can be attributed to the improved costimulatory signals in the CAR design. METHODS: Here, we established several novel CARs by incorporating T cell signaling domains of CD28 in conjunction with intracellular signaling motif of 4-1BB, CD27, OX40, ICOS, and IL-15Rα. These novel CARs were functionally assessed based on a simple target cell killing assay. RESULTS: The results showed that the CD28/IL-15Rα co-signaling (153z) CAR demonstrated the fastest T cell expansion potential and cytotoxic activities. IL-15 is a key cytokine that mediates immune effector activities. The 153z CARTs maintained prolonged killing activities after repetitive rounds of target cell engagement. Consistent with the enhanced target killing function, the 153z CARTs produced increased amount of effector cytokines including IFN-γ, TNFα and IL-2 upon interaction with the target cells. CONCLUSION: In a follow-up clinical study, an acute lymphoblastic leukemia (ALL) patient, who experienced multiple relapses of central nervous system leukemia (CNSL) and failed all conventional therapies, was enrolled to receive the CD19-specific 153z CART treatment. The patient achieved complete remission after the 153z CART cell infusion. The translational outcome supports further investigation into the safety and enhanced therapeutic efficacy of the IL-15Rα-modified CART cells in cancer patients.

Dasatinib Plus Intensive Chemotherapy in Children, Adolescents, and Young Adults With Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia: Results of Children's Oncology Group Trial AALL0622.

Purpose Addition of imatinib to intensive chemotherapy improved survival for children and young adults with Philadelphia chromosome-positive acute lymphoblastic leukemia. Compared with imatinib, dasatinib has increased potency, CNS penetration, and activity against imatinib-resistant clones. Patients and Methods Children's Oncology Group (COG) trial AALL0622 (Bristol Myers Squibb trial CA180-204) tested safety and feasibility of adding dasatinib to intensive chemotherapy starting at induction day 15 in patients with newly diagnosed Philadelphia chromosome-positive acute lymphoblastic leukemia age 1 to 30 years. Allogeneic hematopoietic stem-cell transplantation (HSCT) was recommended for patients at high risk based on slow response and for those with a matched family donor regardless of response after at least 11 weeks of therapy. Patients at standard risk based on rapid response received chemotherapy plus dasatinib for an additional 120 weeks. Patients with overt CNS leukemia received cranial irradiation. Results Sixty eligible patients were enrolled. Five-year overall (OS) and event-free survival rates (± standard deviations [SD]) were 86% ± 5% and 60% ± 7% overall, 87% ± 5% and 61% ± 7% for standard-risk patients (n = 48; 19% underwent HSCT), and 89% ± 13% and 67% ± 19% for high-risk patients (n = 9; 89% underwent HSCT), respectively. Five-year cumulative incidence (± SD) of CNS relapse was 15% ± 6%. Outcomes (± SDs) were similar to those in COG AALL0031, which used the same chemotherapy with continuous imatinib: 5-year OS of 81% ± 6% versus 86% ± 5% ( P = .63) and 5-year disease-free survival of 68% ± 7% versus 60% ± 7% ( P = 0.31) for AALL0031 versus AALL0622, respectively. IKZF1 deletions, present in 56% of tested patients, were associated with significantly inferior OS and event-free survival overall and in standard-risk patients. Conclusion Dasatinib was well tolerated with chemotherapy and provided outcomes similar to those with imatinib in COG AALL0031, where all patients received cranial irradiation. Our results support limiting HSCT to slow responders and suggest a potential role for transplantation in rapid responders with IKZF1 deletions.

Developmental Stage-Specific Manifestations of Absent TPO/c-MPL Signalling in Newborn Mice.

Congenital amegakaryocytic thrombocytopaenia (CAMT) is a disorder caused by c-MPL mutations that impair thrombopoietin (TPO) signalling, resulting in a near absence of megakaryocytes (MKs). While this phenotype is consistent in adults, neonates with CAMT can present with severe thrombocytopaenia despite normal MK numbers. To investigate this, we characterized MKs and platelets in newborn c-MPL ­/­ mice. Liver MKs in c-MPL ­/­ neonates were reduced in number and size compared with wild-type (WT) age-matched MKs, and exhibited ultrastructural abnormalities not found in adult c-MPL ­/­ MKs. Platelet counts were lower in c-MPL ­/­ compared with WT mice at birth and did not increase over the first 2 weeks of life. In vivo biotinylation revealed a significant reduction in the platelet half-life of c-MPL ­/­ newborn mice (P2) compared with age-matched WT pups, which was not associated with ultrastructural abnormalities. Genetic deletion of the pro-apoptotic Bak did not rescue the severely reduced platelet half-life of c-MPL ­/­ newborn mice, suggesting that it was due to factors other than platelets entering apoptosis early. Indeed, adult GFP+ (green fluorescent protein transgenic) platelets transfused into thrombocytopenic c-MPL ­/­ P2 pups also had a shortened lifespan, indicating the importance of cell-extrinsic factors. In addition, neonatal platelets from WT and c-MPL ­/­ mice exhibited reduced P-selectin surface expression following stimulation compared with adult platelets of either genotype, and platelets from c-MPL ­/­ neonates exhibited reduced glycoprotein IIb/IIIa (GPIIb/IIIa) activation in response to thrombin compared with age-matched WT platelets. Taken together, our findings indicate that c-MPL deficiency is associated with abnormal maturation of neonatal MKs and developmental stage-specific defects in platelet function.

Two novel RUNX1 mutations in a patient with congenital thrombocytopenia that evolved into a high grade myelodysplastic syndrome.

Here we report two new RUNX1 mutations in one patient with congenital thrombocytopenia that transformed into a high grade myelodysplastic syndrome with myelomonocytic features. The first mutation was a nucleotide base substitution from guanine to adenine within exon 8, resulting in a nonsense mutation in the DNA-binding inhibitory domain of the Runx1 protein. This nonsense mutation is suspected a de novo germline mutation since both parents are negative for the mutation. The second mutation identified was an in-frame six nucleotide base pair insertion in exon 5 of the RUNX1 gene, which is predicted to result in an insertion in the DNA-binding runt homology domain (RHD). This mutation is believed to be a somatic mutation as it was mosaic before allogeneic hematopoietic cell transplantation and disappeared after transplant. As no other genetic mutation was found using genetic screening, it is speculated that the combined effect of these two RUNX1 mutations may have exerted a stronger dominant negative effect than either RUNX1 mutation alone, thus leading to a myeloid malignancy.

Integrin VLA-5 and FAK are Good Targets to Improve Treatment Response in the Philadelphia Chromosome Positive Acute Lymphoblastic Leukemia.

Acute lymphoblastic leukemia bearing the Philadelphia chromosome is among the most difficult types of ALL to cure. However, the advent of targeted tyrosine kinase inhibitor (TKI) imatinib has ushered in a new era of treatments that have the potential to be less toxic to patients. Integrins and tyrosine kinases play important roles in mediating and transducing signals for cell survival and suppressing apoptosis. Focal adhesion kinase (FAK) is a non-receptor type tyrosine kinase that is constitutively activated in Ph+ ALL. We sought to investigate the specificity of integrin α5ß1 (VLA-5) on Ph+ leukemia by its expression and function. We found VLA-5 expression increases after serum starvation. Integrin α5 inhibitory antibody inhibited adhesion of Ph+ leukemia to human fibronectin and acted synergistically with imatinib to induce Ph+ leukemia cell apoptosis. We used different strategies to block integrin signaling and knocked down the expression of integrin VLA-5 to observe the effect on proliferation and engraftment of Ph+ leukemia cells in immunodeficient mice. We found that blocking integrin activity by incubating Ph+ leukemia cells with disintegrin, a peptide inhibitor of integrins, or α5 inhibitory antibody, or knocking down the α5 integrin subunit impaired and delayed the engraftment of Ph+ leukemia in immunodeficient mice. We then treated mice xenografted with Ph+ leukemia cells with the FAK inhibitor TAE226 in combination with a BCR-ABL TKI nilotinib. While 2 weeks of treatment with TAE226 alone did not significantly inhibit leukemia growth in mice, TAE226 in combination with nilotinib provided the most optimum growth inhibition at 4-6 weeks. We conclude that blocking VLA-5 signaling or combining FAK inhibitors with TKI targeting BCL/ABL might be good strategies to improve treatments in patients with Ph+ ALL. By altering Ph+ leukemia cell interactions with the microenvironment, we may increase their susceptibility to therapy targeting BCR/ABL.

Conditional deletion of Jak2 reveals an essential role in hematopoiesis throughout mouse ontogeny: implications for Jak2 inhibition in humans.

Germline deletion of Jak2 in mice results in embryonic lethality at E12.5 due to impaired hematopoiesis. However, the role that Jak2 might play in late gestation and postnatal life is unknown. To understand this, we utilized a conditional knockout approach that allowed for the deletion of Jak2 at various stages of prenatal and postnatal life. Specifically, Jak2 was deleted beginning at either mid/late gestation (E12.5), at postnatal day 4 (PN4), or at ∼2 months of age. Deletion of Jak2 beginning at E12.5 resulted in embryonic death characterized by a lack of hematopoiesis. Deletion beginning at PN4 was also lethal due to a lack of erythropoiesis. Deletion of Jak2 in young adults was characterized by blood cytopenias, abnormal erythrocyte morphology, decreased marrow hematopoietic potential, and splenic atrophy. However, death was observed in only 20% of the mutants. Further analysis of these mice suggested that the increased survivability was due to an incomplete deletion of Jak2 and subsequent re-population of Jak2 expressing cells, as conditional deletion in mice having one floxed Jak2 allele and one null allele resulted in a more severe phenotype and subsequent death of all animals. We found that the deletion of Jak2 in the young adults had a differential effect on hematopoietic lineages; specifically, conditional Jak2 deletion in young adults severely impaired erythropoiesis and thrombopoiesis, modestly affected granulopoiesis and monocytopoiesis, and had no effect on lymphopoiesis. Interestingly, while the hematopoietic organs of these mutant animals were severely affected by the deletion of Jak2, we found that the hearts, kidneys, lungs, and brains of these same mice were histologically normal. From this, we conclude that Jak2 plays an essential and non-redundant role in hematopoiesis during both prenatal and postnatal life and this has direct implications regarding the inhibition of Jak2 in humans.

Molecular mechanisms of platelet and stem cell rebound after 5-fluorouracil treatment.

Sublethal irradiation and 5-fluorouracil (5-FU) treatment are two commonly used myelosuppressive methods used in the study of hematopoiesis. These methods have been considered interchangeable by some researchers because the morphological changes in the bone marrow to these treatments are similar. Here, we sought to compare the responses of hematopoietic cells, stem and progenitor cells and the bone marrow microenvironment to these treatments. Although bone marrow cellularity decreased after both treatments, the underlying mechanism of the bone marrow cell regression and recovery were very different between the two models. We found: 1. Myeloid cells and lymphoid cells had different sensitivity to the different treatments. 2. Following an initial decrease in stem cell number, 5-FU treated mice had profound thrombopoietin (Tpo) dependent stem cell rebound above baseline levels. 3. Platelet rebound in 5-FU treated animals was not the result of stem cell rebound. 4. Stem cell and platelet rebound did not occur in sub-lethally irradiated mice. 5. Platelet rebound resulted from an indirect effect of 5-FU on the microenvironment cells, but not a direct effect on the stem cells. 6. Microarray studies demonstrated that up-regulation of the angiopoietin-1/Tie2 signaling pathway coincided with platelet rebound. 7. Suppression of genes involved in chromosomal organization coincided with stem cell and platelet rebound.

Post-transplant lymphoproliferative disorder in children: recent outcomes and response to dual rituximab/low-dose chemotherapy combination.

PTLD is a major complication after transplantation. Treatment options for PTLD are not standardized, usually sequential, starting with reduction in immunosuppression. Recently, we have used a dual combination of rituximab and reduced dose chemotherapy (R/C) directly after failed RI. We retrospectively identified 30 pediatric PTLD cases across four organ systems at our center from 1995 to 2008. We assessed recent outcomes of PTLD in children, comparing the responses to different regimens. Two-yr failure-free survival was best in renal and heart recipients (80-88%), followed by liver (57%) and lung (0%). Of note, two patients were Epstein-Barr peripheral blood viral load low positive but tumor EBER negative. Three patients had no detectable viral load but were EBER positive. The R/C regimen (n = 8) had the highest CR rate (100%), low recurrence (12%) and lowest mortality (12%). Interferon (n = 4) had 75% CR, 33% recurrence and 25% mortality. Rituximab/prednisone (n = 5) had 80% CR, 50% recurrence and 20% mortality. Other chemotherapy (n = 7, including all 4 T-cell PTLDs) had 57% CR, 0% recurrence and 14% mortality. Direct dual R/C combination therapy after failed RI is effective and offers another treatment option for B-cell PTLD.

Differences between newborn and adult mice in their response to immune thrombocytopenia.

BACKGROUND: Sick neonates frequently develop severe thrombocytopenia. OBJECTIVE AND METHODS: In order to test the ability of fetal mice to increase their megakaryocyte size and ploidy in response to thrombocytopenia, we injected an antiplatelet antibody (MWReg30) into pregnant mice daily for 7 days, and into nonpregnant adult mice to serve as controls. After that time, platelet counts were obtained and megakaryocytes in the bone marrow, liver, and spleen were stained with anti-von Willebrand factor antibody, individually measured, and quantified. RESULTS: Our study demonstrated that megakaryocytopoiesis in newborn mice shares many features of human fetal/neonatal megakaryocytopoiesis, including the small size of megakaryocytes. In response to thrombocytopenia, adult mice increased megakaryocyte volume and concentration, primarily in the spleen. Newborn mice, in contrast, increased the megakaryocyte concentration in the spleen, but exhibited no increase in megakaryocyte volume in any of the organs studied. In fact, the megakaryocyte mass was significantly lower in the bone marrow of thrombocytopenic neonates than in age-matched controls. CONCLUSIONS: We concluded that fetuses have a limited ability to increase their megakaryocyte mass in response to consumptive thrombocytopenia, compared to adult mice. These observations provide further evidence for the existence of biological differences between fetal/neonatal and adult megakaryocytopoiesis.