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Hematopoietic cell transplantation (HCT) is the only readily available cure for many life-threatening pediatric nonmalignant diseases (NMD), but most patients lack a matched related donor and are at higher risk for graft-versus-host disease (GVHD). Use of abatacept (Aba) to target donor T-cell activation has been safe and effective in preventing GVHD after unrelated donor (URD) HCT for malignant diseases (Aba2 trial). Our primary objective was to evaluate the tolerability of Aba added to standard GVHD prophylaxis (cyclosporine and mycophenolate mofetil) in pediatric patients with NMD undergoing URD HCT. In this single-arm, single-center phase 1 trial, 10 patients receiving reduced intensity or nonmyeloablative conditioning underwent URD HCT. Immune reconstitution was assessed longitudinally via flow cytometry and compared to pediatric patients on Aba2. Nine patients successfully engrafted, with 1 primary graft rejection in the setting of inadequate cell dose; secondary graft rejection occurred in 1 patient with concurrent cytomegalovirus viremia. Two deaths occurred, both unrelated to Aba. One patient developed probable posttransplant lymphoproliferative disease, responsive to rituximab and immune suppression withdrawal. No patients developed severe acute or chronic GVHD, and 8 patients were off systemic immunosuppression at 1 year. Immune reconstitution did not appear to be impacted by Aba, and preservation of naïve relative to effector memory CD4+ T cells was seen akin to Aba2. Thus, 4 doses of Aba were deemed tolerable in pediatric patients with NMD following URD HCT, with encouraging preliminary efficacy and supportive immune correlatives in this NMD cohort.

Background aims Umbilical cord blood (UCB) infusion is being investigated as a treatment for a range of neurological conditions, primarily because of its potent immunomodulatory effects mediated via paracrine signaling. Although initial research mainly utilized autologous UCB, allogeneic samples from a sibling or unrelated donor have now become more common. With the use of allogeneic UCB, questions have arisen surrounding the necessity for human leukocyte antigen (HLA) matching, preparative regimens and immunosuppressant drugs. To investigate the safety of allogeneic UCB for the treatment of neurological conditions and the impact of HLA mismatching and immunosuppresion, the authors conducted a systematic review of the safety of allogeneic UCB infusion for neurological conditions. Methods A systematic review of published and gray literature was conducted to investigate the safety of allogeneic UCB infusions for neurological conditions. Results Authors identified 10 studies using allogeneic UCB to treat autism spectrum disorder, cerebral palsy, stroke, traumatic brain injury and various other conditions. A total of 361 participants (with at least 442 UCB infusions) received a range of HLA-matched/untyped allogeneic units and cell doses, with the majority not administered post-infusion immunosuppression. There were no reported serious adverse events definitely or probably related to the allogeneic UCB infusion, nor later potential complications such as graft-versus-host disease or teratoma formation. Conclusions Although variability between studies is high, the available data do not identify safety concerns with allogeneic UCB infusion for the treatment of neurological conditions, even with variable HLA matching or no immunosuppression.

Objectives Little is known about the impact of coronavirus disease 2019 (COVID‐19) on healthcare professional emotional health in pediatric hematology/oncology. Primary objective was to describe anxiety, depression, positive affect, and perceived stress among pediatric hematology/oncology healthcare professionals following a COVID‐19 outbreak. Secondary objectives were to compare these outcomes based on contact with a positive person, and to identify risk factors for worse outcomes. Materials and methods We included 272 healthcare professionals working with pediatric hematology/oncology patients. We determined whether respondents had direct or indirect contact with a COVID‐19‐positive individual and then measured outcomes using the Patient‐Reported Outcomes Measurement Information System (PROMIS) depression, anxiety, and positive affect measures, and the Perceived Stress Scale. Results Among eligible respondents, 205 agreed to participate (response rate 75%). Sixty‐nine (33.7%) had contact with a COVID‐19‐positive person. PROMIS anxiety, depression, and positive affect scores were similar to the general United States population. Those who had contact with a COVID‐19‐positive individual did not have significantly different outcomes. In multiple regression, non‐physicians had significantly increased anxiety (nurses: p = 0.013), depression (nurses: p = 0.002, pharmacists: p = 0.038, and other profession: p = 0.021), and perceived stress (nurses: p = 0.002 and other profession: p = 0.011) when compared to physicians. Conclusions Pediatric hematology/oncology healthcare professionals had similar levels of anxiety, depression, and positive affect as the general population. Contact with a COVID‐19‐positive individual was not significantly associated with outcomes. Non‐physician healthcare professionals had more anxiety, depression, and perceived stress when compared to physicians. These findings may help to develop programs to support healthcare professional resilience., During a COVID‐19 outbreak, pediatric hematology/oncology healthcare professionals had similar levels of anxiety, depression, and positive affect compared to the general population. However, non‐physician healthcare professionals had more anxiety, depression, and perceived stress when compared to physicians.

Isolated neuroinflammatory disease has been described in case reports of familial hemophagocytic lymphohistiocytosis (FHL), but the clinical spectrum of disease manifestations, response to therapy and prognosis remain poorly defined. We combined an international survey with a literature search to identify FHL patients with (i) initial presentation with isolated neurological symptoms; (ii) absence of cytopenia and splenomegaly at presentation; and (iii) systemic HLH features no earlier than 3 months after neurological presentation. Thirty-eight (20 unreported) patients were identified with initial diagnoses including acute demyelinating encephalopathy, leukoencephalopathy, CNS vasculitis, multiple sclerosis, and encephalitis. Median age at presentation was 6.5 years, most commonly with ataxia/gait disturbance (75%) and seizures (53%). Diffuse multifocal white matter changes (79%) and cerebellar involvement (61%) were common MRI findings. CSF cell count and protein were increased in 22/29 and 15/29 patients, respectively. Fourteen patients progressed to systemic inflammatory disease fulfilling HLH-2004 criteria at a mean of 36.9 months after initial neurological presentation. Mutations were detected in PRF1 in 23 patients (61%), RAB27A in 10 (26%), UNC13D in 3 (8%), LYST in 1 (3%), and STXBP2 in 1 (3%) with a mean interval to diagnosis of 28.3 months. Among 19 patients who underwent HSCT, 11 neurologically improved, 4 were stable, one relapsed, and 3 died. Among 14 non-transplanted patients, only 3 improved or had stable disease, one relapsed, and 10 died. Isolated CNS-HLH is a rare and often overlooked cause of inflammatory brain disease. HLH-directed therapy followed by HSCT seems to improve survival and outcome.

Blood stream infections (BSI) are a major source of morbidity and mortality both in allogeneic blood and marrow transplant (BMT) recipients. Various risk factors for BSI in BMT have been identified. The impact of race and cytomegalovirus (CMV) viremia, a common complication after engraftment, however, has not been rigorously assessed. This is important because both CMV infection and ganciclovir, the mainstay of pre-emptive therapy, have myelosuppressive and immunosuppressive effects. We conducted a retrospective analysis to test the hypothesis that race and CMV viremia predispose allogeneic BMT patients to postengraftment BSI. We analyzed 278 allogeneic BMT performed at Children's Healthcare of Atlanta between January 1, 2005 and December 31, 2014 that met eligibility criteria. We performed a multivariate analysis to estimate the effect of CMV viremia on risk for BSI in the postengraftment period (days +30 to 100). Risk for BSI was associated with CMV viremia (hazard ratio [HR], 3.34; 95% confidence interval [CI], 1.51 to 7.36; P = .003); grade III and IV acute graft-versus-host disease (HR, 3.28; 95% CI, 1.55 to 6.92; P = .002), and African American race (HR, 2.22; 95% CI, 1.09 to 4.51; P = .027). The results of our study highlight the importance of a novel risk factor for postengraftment BSI, not previously considered—African American race.

Human antibody-secreting cells (ASC) in peripheral blood are found after vaccination or infection but rapidly apoptose unless they migrate to the bone marrow (BM). Yet, elements of the BM microenvironment required to sustain long-lived plasma cells (LLPC) remain elusive. Here, we identify BM factors that maintain human ASC 50 days in vitro. The critical components of the cell-free in vitro BM mimic consist of products from primary BM mesenchymal stromal cells (MSC), a proliferation-inducing ligand (APRIL), and hypoxic conditions. Comparative analysis of protein-protein interactions between BM-MSC proteomics with differential RNA transcriptomics of blood ASC and BM LLPC identify two major survival factors, fibronectin and YWHAZ. The MSC secretome proteins and hypoxic conditions play a role in LLPC survival utilizing mechanisms that downregulate mTORC1 signaling and upregulate hypoxia signatures. In summary, we identify elements of the BM survival niche critical for maturation of blood ASC to BM LLPC.

Human antibody-secreting cells (ASC) in peripheral blood are found after vaccination or infection but rapidly apoptose unless they migrate to the bone marrow (BM). Yet, elements of the BM microenvironment required to sustain long-lived plasma cells (LLPC) remain elusive. Here, we identify BM factors that maintain human ASC > 50 days in vitro. The critical components of the cell-free in vitro BM mimic consist of products from primary BM mesenchymal stromal cells (MSC), a proliferation-inducing ligand (APRIL), and hypoxic conditions. Comparative analysis of protein–protein interactions between BM-MSC proteomics with differential RNA transcriptomics of blood ASC and BM LLPC identify two major survival factors, fibronectin and YWHAZ. The MSC secretome proteins and hypoxic conditions play a role in LLPC survival utilizing mechanisms that downregulate mTORC1 signaling and upregulate hypoxia signatures. In summary, we identify elements of the BM survival niche critical for maturation of blood ASC to BM LLPC., Antibody-secreting cells (ASC) such as plasma cells must migrate to the bone marrow to survive, but microniche elements that promote survival are unknown. Here the authors define specific factors from the microniche that can maintain ASC in vitro for over 50 days, involving MSC secretome proteins, APRIL, and hypoxic conditions.

Transfusion-related alloimmunization is a potent barrier to the engraftment of allogeneic hematopoietic stem cells in patients with nonmalignant diseases (NMDs). Memory T cells, which drive alloimmunization, are relatively resistant to commonly used conditioning agents. Alefacept, a recombinant leukocyte function antigen-3/IgG1 fusion protein, targets CD2 and selectively depletes memory versus naive T cells. Three multiply transfused pediatric patients with NMD received a short course of high-dose i.v. alefacept (.25 mg/kg/dose on days -40 and -9 and .5 mg/kg/dose on days -33, -26, -19, and -12) before undergoing unrelated allogeneic transplant in the setting of reduced-intensity pretransplant conditioning and calcineurin inhibitor-based post-transplant graft-versus-host disease (GVHD) prophylaxis. Alefacept infusions were well tolerated in all patients. Peripheral blood flow cytometry was performed at baseline and during and after alefacept treatment. As expected, after the 5 weekly alefacept doses, each patient demonstrated selective loss of CD2(hi)/CCR7(-)/CD45RA(-) effector memory (Tem) and CD2(hi)/CCR7(+)/CD45RA(-) central memory (Tcm) CD4(+) and CD8(+) T cells with relative preservation of the CD2(lo) Tem and Tcm subpopulations. In addition, depletion of CD2(+) natural killer (NK) cells also occurred. Neutrophil recovery was rapid, and all 3 patients had 100% sorted (CD3/CD33) peripheral blood donor chimerism by day +100. Immune reconstitution (by absolute neutrophil, monocyte, and lymphocyte counts) was comparable with a cohort of historical control patients. All 3 patients developed GVHD but are all now off immune suppression and2 years post-transplant with stable full-donor engraftment. These results suggest that alefacept at higher dosing can deplete both memory T cells and NK cells and that incorporating CD2-targeted depletion into a reduced-intensity transplant regimen is feasible and safe in heavily transfused patients.

High-dose busulfan, cyclophosphamide, and antithymocyte globulin (BU-CY-ATG) is the most commonly used conditioning regimen in HLA-matched related hematopoietic cell transplantation for children with sickle cell disease. Disease-free survival with this regimen is now approximately 95%; however, it produces significant morbidity. We hypothesized we could create a less toxic regimen by adding fludarabine (FLU) to BU-CY-ATG and reduce the dosages of busulfan and cyclophosphamide. We conducted a multicenter dose de-escalation trial with the objective of decreasing the doses of busulfan and cyclophosphamide by 50% and 55%, respectively. Using day +28 donor-predominant chimerism as a surrogate endpoint for sustained engraftment, we completed the first 2 of 4 planned levels, enrolling 6 patients at each and reducing the total dose of cyclophosphamide from 200 mg/kg to 90 mg/kg. On the third level, which involved a reduction of i.v. busulfan from 12.8 mg/kg to 9.6 mg/kg, the first 2 patients had host-predominant T cell chimerism, which triggered trial-stopping rules. All 14 patients survive disease-free. No patients suffered severe regimen-related toxicity. Our results suggest BU-FLU-CY-ATG using lower dose CY could be a less toxic yet effective regimen. Further evaluation of this regimen in a full-scale clinical trial is warranted.

Busulfan influences engraftment and toxicities during hematopoietic stem cell transplantation (HSCT). We report our single-institution experience of targeted busulfan therapy for myeloablative, matched sibling donor (MSD) HSCT for sickle cell disease (SCD) and assess the relationships of busulfan levels to engraftment and toxicities. Twenty-seven patients with SCD underwent MSD HSCT from 1993 to 2007, 25 with busulfan measurements. The conditioning regimen was busulfan (initial dose 0.875 mg/kg for 16 doses), CY and antithymocyte globulin. Busulfan area under curve (AUC) was determined with the first dose, and dose adjustments were made to target the desired AUC range. Median AUC was 963 μmol min/L (range 780-1305 μmol min/L). Engraftment occurred in all cases: 21 (84%) full donor chimerism (95% donor cells), 4 (16%) partial donor chimerism. Hepatic veno-occlusive disease (VOD) occurred in 8 (32%) patients. Lower AUC was seen with partial donor chimerism (862 ± 73 μmol min/L) versus full donor chimerism (AUC 1018 ± 122 μmol min/L) (P = 0.022). VOD was not associated with busulfan AUC (P = 0.153). Of 25 patients, 24 survived with median follow-up of 4.9 years. Our experience shows that targeting busulfan AUC above the range used in previous multicenter trials appears safe and may contribute to sustained engraftment in SCD.

The lack of healthy HLA-identical sibs limits the use of allogeneic hematopoietic cell transplantation in children with high-risk sickle cell disease (SCD). We evaluated unrelated placental blood cell transplantation (UPBCT) after a preparative regimen of busulfan, cyclophosphamide and antithymocyte globulin in three children with SCD who had cerebrovascular accidents (CVAs) and did not have HLA-matched sib donors. The placental blood cell units were matched with the recipients at four of six HLA-A, HLA-B and HLA-DRB1 antigens. Neutrophil levels above 0.5 x 10(9)/l occurred at 23, 38 and 42 days after UPBCT, and platelet levels above 50 x 10(9)/l without transfusions occurred at 62, 81 and 121 days after UPBCT. All patients developed acute graft-versus-host disease (GVHD; two grade II, one grade III), and one developed extensive chronic GVHD. One patient had graft failure and autologous hematopoietic recovery. Two patients have complete donor hematopoietic chimerism without detectable hemoglobin S or symptoms of SCD at 40 and 61 months, respectively, after UPBCT. These observations demonstrate the feasibility of UPBCT in children with SCD. Further studies of UPBCT for SCD are needed but, because of risks of procedure-related morbidity and graft rejection, should be restricted to pediatric patients with high-risk manifestations of SCD.

Both bone marrow and solid organ transplants (SOTs) can be life saving for a wide variety of diseases. We reviewed the literature and summarized the experiences of dual transplants. In total, 37 patients received a SOT for organ failure after a previous hematopoietic stem cell transplant. In all, 12 subjects received SOTs followed by a bone marrow transplant, while three patients received simultaneous SOTs and bone marrow transplants. Of these 52 patients, 37 were alive at the time of the original report at follow-up times ranging from 3 months to 8 years. A special registry for data collection may prove helpful for obtaining long-term follow-up data and providing outcome information that may improve future patient survival.

Background During major ABO-mismatched bone marrow transplant (BMT), the infusion of incompatible red blood cells (RBCs) that are present in the bone marrow graft can cause adverse events from hemolysis. RBC depletion of the bone marrow graft can decrease this risk, but the optimal method to prevent hemolysis is unclear. Procedure We conducted a retrospective cohort study of patients who underwent major ABO-mismatched BMT at a pediatric center and had RBC depletion with either hydroxyethyl starch (HES) sedimentation or Ficoll density gradient separation. Postinfusion hemoglobinuria and creatinine values were compared. Results Between 2002 and 2016, 37 patients received HES-treated and 16 patients received Ficoll-treated major ABO-mismatched bone marrow grafts. The median residual volume of RBCs was significantly greater with HES-treated grafts (HES 21.0 ml vs. Ficoll 1.4 ml, P

Nilotinib is a selective BCR-ABL tyrosine kinase inhibitor related to imatinib that is more potent than imatinib. Nilotinib is widely used to treat chronic myelogenous leukemia (CML) and Philadelphia-positive (Ph+) acute lymphoblastic leukemia (ALL). The present study identifies Mouse double minute 2 homolog (MDM2) as a target of nilotinib. In studying ALL cell lines, we found that the expression of MDM2 in both Philadelphia positive (Ph+) and Philadelphia negative (Ph-) ALL cells was remarkably inhibited by nilotinib, in a dose- and time-dependent manner. Further studies demonstrated that nilotinib inhibited MDM2 at the post-translational level by inducing MDM2 self-ubiquitination and degradation. Nilotinib-mediated MDM2 downregulation did not result in accumulation and activation of p53. Inhibition of MDM2 in nilotinib-treated ALL cells led to downregulation of the anti-apoptotic protein X-linked inhibitor of apoptosis protein (XIAP), a translational target of MDM2, resulting in activation of caspases. Inhibition of XIAP following nilotinib-mediated downregulation of MDM2 resulted in apoptosis of MDM2-expressing ALL; however, similar nilotinib treatment induced stronger apoptosis in Ph+/MDM2+ ALL than in Ph-/MDM2+ or Ph+/MDM2- ALL. The ALL cells that were Ph-/MDM2- were totally resistant to nilotinib. These results suggested that nilotinib can inhibit MDM2 and induce a p53-independent apoptosis pathway by downregulating XIAP; thus, nilotinib can treat not only Ph+, but also Ph- ALL patients whose cancer cells overexpress MDM2.

Background: Blood stream infections (BSI) are a major source of morbidity and mortality after allogeneic blood and marrow transplantation (BMT). In studies of risk for BSI various factors have been identified. The impact of cytomegalovirus (CMV) viremia, however, on risk has not been assessed. This is important since both CMV infection and ganciclovir (GCV), the mainstay of pre-emptive therapy, have myelosuppressive and immunosuppressive effects. We conducted a retrospective analysis to test the hypothesis that CMV viremia predisposes allogeneic BMT patients to BSI. Methods: We retrospectively analyzed 278 allogeneic BMTs performed at Children's Healthcare of Atlanta between January 1st 2005 and December 31st 2014 that met eligibility criteria. The primary outcome was the first episode of BSI occurring between day +30 and +100 seen in engrafted patients following allogeneic BMT. We compared clinical characteristics between patients with and without BSI. This analysis was based on a time dependent competing risk model. Risk events including acute GVHD and CMV viremia were counted only when they preceded the BSI. We performed a multivariate analysis to estimate the effect of CMV viremia on risk for BSI in the post-engraftment period (days +30-100). Results: The median age was 9 years (range 0-22 years). 44.6% of the patients were Caucasian, while 38.5% were African-American. 59.7% received an unrelated marrow, unrelated cord or the alternative donor transplant. 60.8% were transplanted for a hematologic malignancy. The cumulative incidence of BSI between day +30 and+100 was 21.9% (95% confidence interval (CI), 17.5-27.3%). The median day of BSI development was 54 (range 30-99). The leading cause of BSI was Staphylococcus epidermidis. Gram-positive cocci were responsible for 71.4% of all BSIs. In the multivariate analysis, three factors were significant: grade III/IV aGVHD (hazard ratio (HR)=3.490, 95% CI 1.530-7.980, P=0.003), CMV viremia (HR=3.410, 95% CI 1.410-8.250, P=0.007), and African-American ethnicity (HR=2.520, 95% CI 1.130-5.600, P=0.024). Form of insurance (Medicaid/no insurance vs. other), employed as a surrogate for income level, had no influence on risk. In the 57 patients with CMV viremia, the frequency of neutropenia ( Conclusion: Our analysis of risk for post-engraftment BSI in children yielded three factors. One, aGVHD, is well established. The other two, CMV viremia and African-American ethnicity, have not been previously recognized. That CMV viremia would predispose to subsequent BSI is highly plausible. Our results suggest that the risk of CMV viremia may be mediated in part by neutropenia stemming from CMV or its treatment with ganciclovir. That African-American ethnicity has not previously been recognized as a risk factor may simply reflect the ethnic make up of previous studies. Our findings are consistent with those of studies performed in other settings, showing patients of African descent to be at increased risk for bacteremia and sepsis. An increased risk for BSI among patients of African descent could partly explain the concerning excess risk for transplant related mortality previously observed among these patients. Disclosures No relevant conflicts of interest to declare.

of the cases malignant plasma cell have been detected at residual disease levels or higher in stem cell products. Conclusions: Standardized flow cytometric analysis for minimal residual disease (MRD) should be urgently considered for release testing of stem cell transplants in patients with multiple myeloma, since they can identifying biologically aggressive disease with a high risk of early relapse.

Introduction: Major ABO mismatch occurs when the recipient has preformed isoagglutinins against the donor. Since unmanipulated bone marrow transplant (BMT) grafts contain donor red blood cells (RBCs), major ABO mismatch BMT infusions can cause hemolytic reactions that lead to renal dysfunction. To prevent this complication, RBC depletion of the graft can be performed by various techniques. Strong evidence-based recommendations regarding RBC depletion are lacking. In particular, it is unclear what residual volume of incompatible RBCs in the graft is safe, especially for pediatric patients. Methods: We conducted a retrospective cohort study of pediatric patients who had major ABO mismatch BMT at a single center. No patients had pre-BMT plasmapheresis to reduce isoagglutinin titers. RBC depletion was performed on the BMT grafts with either hydroxyethyl starch (HES) sedimentation or Ficoll density gradient separation. All patients received similar supportive care around the BM infusion that included hyperhydration and premedication with acetaminophen, diphenhydramine, and hydrocortisone. Serum creatinine the day after the BM infusion was compared to creatinine the day of the BM infusion. Since 2006 all patients had urine screened for blood post-BMT. Results: Sixty-three patients were identified who received a major ABO mismatch BMT between 9/2004 and 6/2015 (39 had RBC depletion with HES, 24 with Ficoll). Compared to Ficoll RBC depletion, patients who received BM grafts that had RBC depletion with HES received significantly more incompatible RBCs (Table 1). Hemoglobinuria was significantly more common in HES patients, but evidence of post-BM infusion renal impairment was not (Table 1). All patients had donor engraftment with a similar time to neutrophil engraftment for both groups (Table 1). Considering only the HES patients, 8/8 (100%) patients with >25% rise in creatinine had hemoglobinuria compared to 8/21(38%) patients with ≤25% rise in creatinine (p=0.003). Also among just the HES patients, the median amount of incompatible RBCs infused was not significantly different between patients with (0.74 ml/kg) and without (0.62 ml/kg) hemoglobinuria (p=0.42), or between patients with (0.56 ml/kg) and without (0.62 ml/kg) a >25% rise in creatinine (p=0.86). Table 1: Comparison of patients who had RBC depletion with HES vs. Ficoll Table 1.HES n=39Ficoll n=24p-valueMedian volume of RBCs/patient weight 0.62 ml/kg0.04 ml/kg25% rise in creatinine 8 (21%)5 (21%)1.0Number with >50% rise in creatinine 4 (10%)0 (0%)0.29Median day of neutrophil engraftment 20210.11 *considering only patients transplanted after 2006. Conclusion: Our study is the first to analyze pediatric major ABO mismatch BMT infusion hemolysis after two different RBC depletion techniques: HES and Ficoll. Our results suggest that RBC depletion with Ficoll achieves less residual RBCs in the BM graft and likely less resulting hemoglobinuria. However, after both techniques hemolysis-induced renal impairment is rare. The volume of residual incompatible RBCs in the infused BM graft does not appear to strongly determine if clinical hemolysis occurs. The volume that is safe likely depends on other variables that influence the risk of clinical hemolysis. Disclosures No relevant conflicts of interest to declare.

Insufficient expression of factor VIII (fVIII) is a major hurdle in the development of successful nucleic acid treatments for hemophilia. However, we recently showed that under myeloablative and reduced-intensity total body irradiation (TBI) conditioning, transplantation of hematopoietic stem cells (HSCs) transduced with recombinant retroviruses containing B domain–deleted porcine fVIII (BDDpfVIII) sequences provides curative fVIII levels in a hemophilia A mouse model. In the current study, we tested BDDpfVIII activity after nonmyeloablative conditioning with busulfan, cyclophosphamide, or fludarabine and immunosuppressive agents CTLA4-Ig + anti-CD40L or anti-(murine)thymocyte serum (ATS). ATS is similar in action to anti-(human)thymocyte globulin (ATG), which is used clinically with busulfan in bone marrow transplantations to increase donor cell engraftment. Mice conditioned with busulfan + ATS and that received a transplant of BDDpfVIII-transduced stem-cell antigen 1-positive cells exhibited moderate levels of donor cell chimerism (between 20% and 60%) and achieved sustained fVIII levels more than 1 U/mL. Similar results were observed in mice preimmunized with human fVIII and conditioned with 5 Gy TBI + ATS or busulfan + ATS. These data demonstrate that it is possible to achieve sufficient fVIII expression after transplantation of BDDpfVIII-transduced HSCs following low-toxicity pretransplantation conditioning with targeted immunosuppression, potentially even in the context of preexisting inhibitors.

Allogeneic stem cell transplantation (ASCT) has improved leukemia-free survival (LFS) in many but not all patients with acute leukemia. This is an eight-year follow-up to our previous study showing a survival advantage to patients with an increased gammadelta T cells following ASCT. gammadelta T cell levels were collected prospectively in 153 patients (acute lymphoblastic leukemia (ALL) n = 77; acute myelogenous leukemia (AML) n = 76) undergoing partially mismatched related donor ASCT. Median age was 22 years (1-59), and 62% of the patients were in relapse at transplant. Patient-donor human leukocyte antigen (HLA) disparity of three antigens was 37% in the graft-versus-host disease (GvHD) and 29% in the rejection directions. All patients received a partially T cell-depleted graft using T10B9 (n = 46) or OKT3 (n = 107). Five years LFS and overall survival (OS) of patients with increased gammadelta compared to those with normal/decreased numbers were 54.4 vs 19.1%; P0.0003, and 70.8 vs 19.6% P0.0001, respectively, with no difference in GvHD (P = 0.96). In a Cox multivariate analysis, normal/decreased gammadelta (hazard ratio (HR) 4.26, P = 0.0002) and sex mismatch (HR 1.45 P=0.049) were associated with inferior LFS. In conclusion, gammadelta T cells may facilitate a graft-versus-leukemia (GvL) effect, without causing GvHD. Further evaluations of this effect may lead to specific immunotherapy for patients with refractory leukemia.

Objective Granulocyte macrophage colony-stimulating factor (GM-CSF) has been shown to specifically stimulate proliferation of CD34 + hematopoietic progenitor cells. Although signal transducers and activators of transcription 3 (STAT3) is believed essential for transduction of GM-CSF–induced cell proliferation, the signaling mediated by STAT3 is not completely understood. Because survivin regulates cell proliferation and survival via its antiapoptotic function, we studied the link between STAT3 signaling and survivin expression in CD34 + cells. Methods GM-CSF–induced STAT3 and survivin expression in CD34 + cells was examined by Western blot assay. GM-CSF–activated survivin promoter activity was analyzed by gene transfection and reporter assays. The binding of STAT3 to the survivin promoter was evaluated by chromatin immunoprecipitation and electrophoretic mobility shift assay. Western blotting and flow cytometry were utilized to test the effect of Janus family of tyrosine kinases (JAK) inhibitor and STAT3 small interfering RNA (siRNA) on cell apoptosis. Results We found that GM-CSF stimulates survivin promoter activity in CD34 + KG-1 cells, and STAT3 binds to the core survivin promoter containing a STAT response element TT(N) 5 AA at sites −264 to −256. Mutation or deletion of this STAT response element completely abolished the effects of GM-CSF on survivin promoter activity. Furthermore, addition of either JAK inhibitor or STAT3 siRNA was able to inhibit GM-CSF–induced survivin promoter activity and survivin expression. Inhibition of survivin by STAT3 siRNA or by withdrawal of GM-CSF in a GM-CSF–dependent, CD34 + line TF-1 decreased cell growth and increased apoptosis. Conclusion Altogether, our results suggest that survivin is a transcriptional target of STAT3, and that GM-CSF–stimulated CD34 + cell proliferation is regulated by the JAK/STAT3/survivin signaling pathway.

Allogeneic transplantation is successful in a minority of patients with primary refractory acute leukemia (PRAL). An HLA-matched sibling donor (MSD) is available only in 30-40% of the patients, whereas a partially mismatched related donor (PMRD) is available for most. We compared the outcome of 24 MSD (median age 24 years) and 19 PMRD (median age 34 years; P = 0.04) allograft recipients with PRAL. All MSD patients received non-T cell-depleted marrow whereas all PMRD patients received partially T cell-depleted marrow. All evaluable PMRD patients and 90% of the evaluable MSD patients attained CR. Six patients in each group with recurrent/persistent disease died. Ten PMRD (3-year probability 70%) and 14 MSD (3-year probability 63%) patients died of treatment-related causes. At the last follow-up, three PMRD (18-50 months; 3-year probability 14%) and four MSD (20-166 months; 3-year probability 20%) patients were alive and well. We conclude that allogeneic transplantation is a viable therapeutic option for PRAL. PMRD transplantation is a reasonable alternative in patients with no MSD, and results in similar outcome. In terms of identifying a donor and harvesting cells, a PMRD transplant is significantly quicker than an unrelated donor transplant - a point of great practical importance in the setting of failed induction chemotherapy where time is of the essence.

Epstein–Barr virus (EBV) is closely associated with the progressive and often fatal lymphoproliferative disorders (LPD) in post bone marrow transplantation (BMT) and immunocompromised hosts. The incidence increases significantly when alternative donors or manipulation of marrow graft are used. A total of 318 consecutive BMT from partially mismatched related family donors (PMRD) were performed between February 1993 and June 1998. Known risk factors for the development of EBV-LPD were analyzed which included HLA mismatches, T cell depletion, antithymocyte globulin (ATG), and graft-versus-host disease (GVHD). Eighteen patients (5.7%) developed EBV-LPD at a median of 137 days post BMT (range 48–617). The estimated probability of developing EBV-LPD was 0.13 (95% CI 0.07–0.19) at 5 years. The incidence of grade II to IV GVHD was 19.2%, which translated into an increased trend of EBV-LPD. No correlation with other risk factors was observed. Treatment consisted of supportive antiviral agents, tapering of immunosuppressive regimens, donor leukocyte infusions and radiation. Three patients are alive and disease-free at a median follow-up of 69 months (range 36–71). We observed a lower than expected incidence of EBV-LPD despite existing multiple high-risk factors. We believe prevention and early control of GVHD may contribute to this finding. Bone Marrow Transplantation (2001) 28, 1117–1123.

Abstract 3487 Hematopoietic stem cell transplantation (HSCT) is associated with poor response to platelet (PLT) transfusions. It has been posited that vascular endothelial cell (EC) damage from the effects of high dose chemoradiotherapy is responsible for PLT consumption. To test this hypothesis, we assessed the relationship between serial levels of plasma markers of vascular damage and repair, and PLT transfusion requirement. Plasma samples were obtained on 40 adult and pediatric recipients of allogeneic HSCT with myeolablative conditioning for leukemia, lymphoma, or myelodysplastic syndrome at days -10, +5, +15, and +30. Single donor apheresis PLT transfusions were given prophylactically for PLT count 125% of ideal BW, adjusted BW was calculated as 0.25 × (actual – ideal BW) + ideal BW. The influence of response to PLT transfusions prior to transplant admission was considered. Poor response to PLT transfusion was defined as a PLT count rise of Disclosures: Ofori-Acquah: Emory University: Patents & Royalties.

BACKGROUND: Allogeneic hematopoietic stem cell transplantation (HSCT) for sickle cell disease (SCD) provides curative therapy but carries significant risk of transplant-related morbidity and mortality, graft failure, and disease recurrence. Past trials of myeloablative HSCT with busulfan in SCD patients showed a 10–13% rate of rejection and 8–9% rate of partial chimerism with busulfan steady-state concentration (Css) targeted to 400–600 ng/ml (area under curve (AUC) 575–877 mmol•min/L). In thalassemia and other diseases, total systemic exposure to busulfan is a critical determinant of engraftment yet is limited by risk of toxicity. Therapeutic drug monitoring (TDM) is used to measure variability in individual patient pharmacokinetics and allows dose adjustments to achieve desired level of busulfan exposure. A retrospective analysis of busulfan AUC in SCD patients during HSCT was performed to determine if higher systemic busulfan levels resulted in more effective engraftment or increased toxicities. METHODS: A retrospective review of busulfan pharmacokinetics, engraftment status, and clinical toxicities in a cohort of SCD patients who received MSD bone marrow grafts at a single pediatric institution was performed. All patients received a myeloablative preparative regimen with busulfan (initially dosed for total 14 mg/kg), cyclophosphamide (200 mg/kg), antithymocyte globulin (90 mg/kg), and graft versus host disease prophylaxis with methotrexate and cyclosporine. Anticonvulsant prophylaxis with phenytoin or with levitiracetam plus lorazepam was given during busulfan administration. Busulfan was administered every 6 hours for 16 doses. Busulfan AUC was determined for the first dose and adjustments were made on subsequent doses if needed. Total AUC was calculated as a weighted average of total doses. Target AUC varied widely over the study period; however, for the last 3 years, the intended AUC has been targeted to 900–1100 mmol•min/L (Css 618–753 ng/ ml). Busulfan-associated toxicities recorded were: hepatic veno-occlusive disease (VOD), interstitial pneumonitis (IP), and seizure during or 1 day following busulfan administration. RESULTS: Twenty-seven consecutive hemoglobin SS SCD patients received HSCT with MSD between December 1993 and August 2007. All patients transplanted since May 1996 (n=25) had busulfan TDM performed. Median age was 8.8 years (range 3.3–17.4 years). Event-free survival was 96% with a median follow-up time of 3.9 years. Engraftment occurred in all cases with no subsequent graft rejection. Full donor chimerism (>95% donor leukocytes) was seen in 21 (84%) patients, and high partial donor chimerism (50–95% donor) in 4 (16%) at >12 months post-HSCT. Busulfan was administered orally in 18 (72%) and intravenously in 7 (28%). Dose adjustments were made in 17 patients (8 increased, 9 decreased). Median dose increase was 16.3% (range 9.7–76.5%), and median decrease was 14.3% (range 4.2–57.1%). Five (20%) patients had dose alterations >20% of initial dose (2 increased, 3 decreased). Median total dose received was 13.9 mg/kg (range 10.8–24.0). Median AUC for first dose was 968 mmol•min/L (range 595–1379) and median total AUC was 992 mmol•min/L (range 780–1305). Busulfan-associated toxicities were observed in 9 (36%) patients: 8 with mild-moderate VOD, 1 with IP. No seizures occurred during busulfan administration. Patients with busulfan-associated toxicity had mean total AUC of 1044.7 mmol•min/L (range 821–1305) versus 962.4 mmol•min/L (range 780–1184) in those without toxicity (p=0.185). Patients with partial donor chimerism had lower total AUC (mean 861.5 mmol•min/L, range 780–932) compared to those with full donor chimerism (mean 1017 mmol•min/L, range 885–1305; p=0.0379) (Figure). Since the implementation of a target busulfan AUC range of 900–1100 mmol•min/L, all patients (n=10) achieved full donor chimerism. CONCLUSIONS: We conclude that higher busulfan levels are associated with decreased incidence of partial donor chimerism in SCD patients during myeloablative HSCT with MSD bone marrow grafts. A target AUC range of 900–1100 mmol•min/L, attainable with TDM and dose adjustment, provides effective engraftment without increased risk of busulfan-related toxicity. Figure: Total busulfan AUC in patients with full donor chimerism (mean 1017 mmol•min/L) vs. partial chimerism (mean 861.5 mmol•min/L, p=0.0379). Figure:. Total busulfan AUC in patients with full donor chimerism (mean 1017 mmol•min/L) vs. partial chimerism (mean 861.5 mmol•min/L, p=0.0379).

A major barrier to successful gene therapy for hemophilia A using bone marrow cells is achieving engraftment of a sufficient number of gene-modified cells to result in therapeutic factor VIII (fVIII) levels under conditions of acceptable patient risk. Previously, we demonstrated sustained levels of a high-expression porcine (HEP)-fVIII construct, at greater than 1 unit/mL for over one year, in hemophilia A mice following myeloablative HSC transplantation (HSCT) thus overcoming the barrier of low fVIII expression (Gangadharan et al, Blood, 2006). In the current study, we tested HEP-fVIII expression after several non-myeloablative and reduced-intensity stem cell transplantation (RIST) protocols incorporating a clinically-relevant dose of genetically-modified hematopoietic stem cells transduced at low multiplicity of infections of ≤ 2. Recipient fVIII exon 16-knockout mice received 3 × 105 HEP-fVIII-MSCV transduced, congenic stem cell antigen-1+ cells. Mice were conditioned using one of the following regimens: 5.5 Gy total body irradiation (TBI), 2 Gy TBI, 2 Gy TBI + 200 mg/kg cyclophosphamide (Ctx), 200 mg/kg Ctx, 200 mg/kg Ctx + 90 mg/kg fludarabine (Flu), 35 mg/kg busulfan (Bu), 35 mg/kg Bu + 200 mg/kg Ctx, 35 mg/kg Bu + costimulation blockade (0.5mg/day CTLA4-Ig and α-CD40L on days 0, 2 post-transplantation). Resulting donor cell engraftment, HEP-fVIII activity, and inhibitory anti-fVIII antibody levels were followed. No fVIII activity was seen in the 2 Gy, 2 Gy + Ctx, Ctx only, or Ctx + Flu cohorts. The Bu and Bu/Ctx treated animals expressed therapeutic levels of HEP-fVIII (0.05 ± 0.07 U/mL and 0.81 ± 0.37 U/mL, respectively) at 1 wk post-HSCT, but returned to baseline in all mice by 2 wks with inhibitor formation in 3 of 7 mice in the Bu group and 0 of 4 mice in the Bu/Ctx cohort. In order to suppress inhibitor formation following conditioning with Bu, recipient mice were administered a low dose course of costimulation blockade post-HSCT. Four of 10 mice in this group demonstrated therapeutic levels of HEP-fVIII activity on day 34-post HSCT (0.11 ± .09 U/mL). All animals demonstrated donor cell engraftment in peripheral blood mononuclear cells at day 23 post-HSCT (18.4 ± 12.1%) and at 34 days post-HSCT, none of the animals had detectable levels of fVIII inhibitors in a modified Bethesda assay. Additionally, we were able to identify specific hematopoietic lineages expressing HEP-fVIII in recipient mice using a novel enzyme-linked immunospot (ELISPOT) assay developed in our laboratory. These data demonstrate that it is possible to achieve sufficient fVIII expression under conditions of i) low MOI transduction with an optimized high-expression fVIII transgene, ii) mild pretransplantation conditioning, iii) limited genetically-modified HSC engraftment, and iv) mild post-HSCT immunosuppression. Furthermore, our results show that clinically-significant fVIII activity levels can be maintained without inhibitor formation suggesting that the current protocol may be on the threshold, in terms of the level of immunosuppression, of promoting tolerance to HEP-fVIII.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been shown to specifically stimulate proliferation and differentiation of CD34+ hematopoietic progenitor cells. Although STAT3 was thought to be essential for the transduction of GM-CSF-induced cell proliferation, the downstream signaling mediated by STAT3 to support cell proliferation and growth has not been completely understood. Because the inhibitor of apoptosis protein (IAP) survivin is believed to regulate cell proliferation and survival via its anti-apoptotic function, we chose to study the link between STAT3 signaling and survivin expression in CD34+ cells. We constructed plasmids containing the survivin promoter sequence and performed luciferase reporter assay in CD34+ KG-1 cells stimulated with GM-CSF. These experiments showed that GM-CSF stimulated survivin promoter activity. Chromatin immunoprecipitation (CHIP) and electrophoretic mobility shift assay (EMSA) revealed that STAT3 binds to the core survivin promoter containing a STAT response element (SRE) TT(N)5AA at sites −264 to −256. Mutation or deletion of this SRE completely abolished the effect of GM-CSF on survivin promoter activity. Furthermore, specific JAK inhibitor and STAT3 siRNA inhibited GM-CSF-induced survivin promoter activity and survivin expression. Inhibition of survivin by STAT3 siRNA or by withdrawal of GM-CSF in a GM-CSF-dependent CD34+ line TF-1 resulted in decreased cell growth and induction of apoptosis. These results suggest that the anti-apoptotic protein survivin is a transcriptional target of STAT3, and that GM-CSF stimulated-CD34+ cell proliferation is regulated by the JAK/STAT3/survivin signaling pathway.

Although the cytotoxic effect of vitamin K3 (VK3) on human cancer cells has been repeatedly reported, no clear conclusions from either in vitro or in vivo tests have so far been made for VK3 as an anticancer agent due to marked inter-tumor variability of efficacy in response to VK3 treatment. Here, we report that sensitivity of neoplastic cells to VK3-induced killing depends on IKKα expression/NF-kB activation in the cells. We tested the sensitivity to VK3 of 14 leukemic cell lines established from children with acute lymphoblastic leukemia (ALL). The 14 lines were classified into three groups: IKKα +/NF-kB+, IKKα +/NF-kB−, IKKα−/NF-kB−. IKKα +/NFkB+ cell lines that are generally resistant to doxorubicin are more sensitive to VK3 induced cell death than are the IKKα +/NFkB− lines that are usually sensitive to doxorubicin. The median of IC 50 values of VK3 and doxorubicin as tested by WST analysis for IKKα +/NFkB+ cells were 3.92 mM and 1.58 mM, respectively, compared to IKKα +/NFkB− cells (7.3 mM of VK3 and 0.71 mM of doxorubicin, p

UCBT may be curative in patients (pts) with high-risk SCD. Unrelated cord blood units matched at >4/6 HLA are acceptable for UCBTs and available to most pts. We reviewed UCBTs in 7 children with SCD and cerebrovascular accidents performed in 4 centers (1998 to 2003): 4 pts were conditioned with conventional myeloablative regimens, and 3 pts with reduced-intensity regimens. The former received busulfan (BU), cyclophosphamide (CY) and anti-thymocyte globulin (ATG) (3 pts) or BU/CY/ATG plus fludarabine (FLU) (1 pt). Of 3 pts who received 4/6 HLA-matched UCBTs after BU/CY/ATG and GVHD prophylaxis with methylprednisone (MP) and cyclosporine (CSP) or tacrolimus (TAC), 2 have durable engraftment, 1 had autologous reconstitution (BMT2004; 34:405–11). A 5 yr old (yo) female with transfusion-induced alloimmunization received a 5/6 HLA-matched UCBT (6.2 X 10^7/kg nucleated [NC] cells) after BU/CY/ATG/FLU, followed by CSP and MP post-transplant. PMN engraftment and VNTR > 98% of donor origin were documented 24 and 37 days, respectively, after UCBT. Complications included elevated liver enzymes during conditioning, grade IV GVHD of skin, GI and liver, grade III mucositis, VOD, parainfluenza 3 infection, candidemia and adenovirus viremia. Pt died of severe acute GVHD and multi-organ failure 73 days after UCBT. Two different reduced-intensity regimens were used in the other 3 pts. An 8 yo male received a 4/6 HLA-matched UCBT (3.2 X 10^7/kg NC) after conditioning with alemtuzumab, rituximab, hydroxyurea, thiotepa and TBI (600cGy, with 300 cGy total dose to liver and kidneys) and received TAC and mycophenolate mofetil (MMF) post-transplant. This patient failed UCBT 8 months earlier (FLU/CY/ATG/TLI, 4/6 HLA). PMN engraftment and VNTR > 98% of donor origin was documented within 18 days after UCBT. Complications included grade I skin GVHD, grade 1 mucositis and parainfluenza 1 infection. This pt remains engrafted and fully active 1.6 ys after UCBT. A 4 yo female and a 16 yo male received 4/6 or 5/6 HLA-matched cord units, respectively, after BU or CY, ATG, FLU and total lymphoid irradiation (200 or 500 cGy) and received CSP and MMF post-transplant. Neither had evidence of donor engraftment, and autologous reconstitution was documented within 2 weeks after UCBT. Sustained donor engraftment occurred in 3/4 pts (75%) who underwent UCBT after myeloablative conditioning and 1/3 pts (33%) who underwent UCBT after reduced-intensity conditioning. Two of the 3 pts who engrafted after myeloablative preparative regimens developed acute grade III–IV GVHD, and 1 of these pts developed extensive chronic GVHD. The 1 pt who engrafted after a reduced-intensity preparative regimen developed grade I acute GVHD only. Significant viral infections (CMV 1 pt, adenovirus, parainfluenzavirus 2 pts each) occurred in 4 pts. In this limited experience, following various conditioning regimens, optimal GVHD and infection prevention remains a challenge. Both apparent lesser risk and documented durable engraftment may justify further development of non-myeloablative strategies for UCBT in children with high-risk SCD.

Impairment of gut mucosal immunity by the transplant process could facilitate translocation of commensal bacteria and thereby augment the graft-versus-host response. To begin to assess the influence of gut mucosal immunity on the development of acute graft-versus-host disease (GVHD), we conducted a prospective study in 24 pediatric allogeneic hematopoietic cell transplant recipients, assessing 4 fecal markers of mucosal immunity: calprotectin, soluble CD8 (sCD8), soluble intracellular adhesion molecule 1, and β-defensin-2. Stool samples were collected prospectively on transplant days 0, +5, +10, and +15 and analyzed by ELISA. Lower levels on day +5 (calprotectin and β-defensin-2) and day +10 (calprotectin, β-defensin-2, and sCD8) were associated with subsequent acute GVHD. The most striking difference was with calprotectin on day +10. Patients with levels below 424 mg/kg had an incidence of 77.8%, whereas those with levels above this threshold had a cumulative incidence of 0% (P = .002). Relative defects in gut mucosal immunity may be important in the pathogenesis of acute GVHD.

Abstract 4664 Translocation of commensal bacteria across the damaged gut mucosa is critical in the pathogenesis of acute graft versus host disease (AGVHD), promoting inflammation that primes donor T cells. Pre-clinical research has demonstrated that mitigating the effects of the gut flora prevents AGVHD, but preserves the graft versus leukemia effect of the transplant. Rifaximin is a very broadly acting, minimally absorbed oral antibiotic, which has been shown to be effective in inflammatory bowel disease. We conducted a pilot trial to test the hypothesis that rifaximin would abrogate systemic inflammation and resultant T cell activation in allogeneic transplant recipients. Twenty adult and pediatric (≥12 years) allogeneic (related or unrelated) blood and marrow transplant recipients with hematological malignancies were enrolled between January 2008 and May 2009. All patients received myeloablative conditioning. Rifaximin, 400 mg bid, was started on day -10 and continued through day 30. Enzyme-linked immunosorbent assays were performed on plasma samples obtained pre-transplant (as a baseline), day 0 (pre-transplant) and day 15 to measure changes in the levels of two markers of inflammation, soluble TNF receptor 1 (sTNFR1) and interleukin 6 (IL-6), and one marker of donor T cell activation, soluble IL-2 receptor (sIL-2R). A historical control group was formed from a previously conducted study (2006-2007) to assess the potential of soluble markers of immune activation to predict AGVHD. Of the 61 patients enrolled in that study, 24 met the criteria for the rifaximin trial and, thus, were selected as controls. There were no significant differences between the treatment and historical control groups in terms of conditioning regimen, the proportion of alternative donors or GVHD prophylaxis. The treatment group, however, was significantly younger (median age; 17.3 years vs. 38.8 years) and included significantly more unrelated cord blood transplant recipients (7 (3 single unit and 4 double unit) vs. 0, p=0.01). The mean percentage of doses of rifaximin that were successfully administered was 86.2%. There were no serious adverse events attributed to rifaximin. The cumulative incidences of grade 2-4 AGVHD, grade 3-4 AGVHD and stage 1-4 gastrointestinal AGVHD in the treatment group did not differ significantly from those of the historical control group (grade 2-4, treatment=69%, control=58%, p=0.63; grade 3-4, treatment=34%, control=22%, p=0.50; gastrointestinal, treatment=58%, control=45%, p=0.58). The median increase from baseline in the IL-6 level at day 0 was significantly lower for the treatment group (table 1). Otherwise, there was no other significant difference in measured biomarker levels. Controlling for age by stratified analysis, and excluding the cord blood transplants did not alter our results. The results of this pilot study demonstrate that administering rifaximin to prevent AGVHD is safe and feasible. Its effect on systemic inflammation, though, appears to be modest and insufficient to mitigate activation of donor T cells. It, therefore, may not be suitable for GVHD prophylaxis. Horan Salix Pharmaceuticals: Research Funding, investigator initiated clinical trial . Disclosures: Off Label Use: Rifaximin is an oral non-absorbable antibiotic that is approved for the treatment of travelers' diarrhea. In this study we investigate the use of Rifaximin for prophylaxis of acute graft versus host disease.

Methods: Pediatric patients (