Therapeutic Drug Monitoring of Anti-Thymocyte Globulin in Allogeneic Stem Cell Transplantation: Proof of Concept.

Anti-thymocyte globulin (ATG), a polyclonal antibody, is used in allogeneic hematopoietic cell transplantation (HCT) to prevent graft-vs.-host-disease (GvHD) and graft failure (GF). Overexposure to ATG leads to poor early T-cell recovery, which is associated with viral infections and poor survival. Patients with severe inflammation are at high risk for GF and GvHD, and may have active infections warranting swift T-cell recovery. As ATG exposure may be critical in these patients, individualized dosing combined with therapeutic drug monitoring (TDM) may improve outcomes. We describe the individualized dosing approach, an optimal sampling scheme, the assay to measure the active fraction of ATG, and the workflow to perform TDM. Using a previously published population pharmacokinetic (PK) model, we determine the dose to reach optimal exposures associated with low GvHD and rejection, and at the same time promote T-cell recovery. Based on an optimal sampling scheme, peak and trough samples are taken during the first 3 days of once-daily dosing. The fraction of ATG able to bind to T-cells (active ATG) is analyzed using a bio-assay in which Jurkat cells are co-cultured with patient's plasma and the binding is quantified using flow cytometry. TDM is performed based on these ATG concentrations on the third day of dosing; subsequent doses can be adjusted based on the expected area under the curve. We show that individualized ATG dosing with TDM is feasible. This approach is unique in the setting of antibody treatment and may result in better immune reconstitution post-HCT and subsequently better survival chances.

B-cell depletion abrogates immune mediated cytopenia and rejection of cord blood transplantation in Hurler syndrome.

Umbilical cord blood is the preferred donor cell source for children with Inherited Metabolic disorders undergoing Hematopoietic Cell Transplant (HCT), and its use has been associated with improved "engrafted survival" and higher donor chimerism compared to other cell sources. However, as in other pediatric cord blood transplants for non-malignant disease, immune-mediated cytopenia and primary graft failure limit its use, and the latter remains the commonest cause of death following cord blood transplant for non-malignant disease. We have previously shown an association between immune-mediated cytopenia and graft failure in inherited metabolic diseases suggesting that both immune-mediated cytopenia and graft failure could be mediated by antibodies from the residual recipient B cells. Since rituximab is effective in depletion of B cells and management of refractory immune-mediated cytopenia following HCT, we have added rituximab to the conditioning regimen. We studied 57 patients in 2 centers who received myeloablative conditioning for cord blood transplant in Hurler syndrome, and report a significant improvement in event-free survival with reduced incidence of graft failure and without any evidence of immune-mediated cytopenia in those patients that had received rituximab.

Association study of candidate DNA-repair gene variants and acute graft versus host disease in pediatric patients receiving allogeneic hematopoietic stem-cell transplantation.

Acute Graft versus Host Disease (aGvHD) grades 2-4 occurs in 15-60% of pediatric patients undergoing allogeneic haematopoietic stem-cell transplantation (allo-HSCT). The collateral damage to normal tissue by conditioning regimens administered prior to allo-HSCT serve as an initial trigger for aGvHD. DNA-repair mechanisms may play an important role in mitigating this initial damage, and so the variants in corresponding DNA-repair protein-coding genes via affecting their quantity and/or function. We explored 51 variants within 17 DNA-repair genes for their association with aGvHD grades 2-4 in 60 pediatric patients. The cumulative incidence of aGvHD 2-4 was 12% (n = 7) in the exploratory cohort. MGMT rs10764881 (G>A) and EXO rs9350 (c.2270C>T) variants were associated with aGvHD 2-4 [Odds ratios = 14.8 (0 events out of 40 in rs10764881 GG group) and 11.5 (95% CI: 2.3-191.8), respectively, multiple testing corrected p ≤ 0.001]. Upon evaluation in an extended cohort (n = 182) with an incidence of aGvHD 2-4 of 22% (n = 40), only MGMT rs10764881 (G>A) remained significant (adjusted HR = 2.05 [95% CI: 1.06-3.94]; p = 0.03) in the presence of other clinical risk factors. Higher MGMT expression was seen in GG carriers for rs10764881 and was associated with higher IC50 of Busulfan in lymphoblastoid cells. MGMT rs10764881 carrier status could predict aGvHD occurrence in pediatric patients undergoing allo-HSCT.

Hematopoietic cell transplant in pediatric acute myeloid leukemia after similar upfront therapy; a comparison of conditioning regimens.

The impact of conditioning regimen prior to hematopoietic cell transplant (HCT) in pediatric AML-patients is not well studied. We retrospectively analyzed the impact of Busulfan-Cyclophosphamide (BuCy), Busulfan-Cyclophosphamide-Melphalan (BuCyMel) and Clofarabine-Fludarabine-Busulfan (CloFluBu) in pediatric AML-patients, with similar upfront leukemia treatment (NOPHO-DBHconsortium), receiving an HCT between 2010 and 2015. Outcomes of interest were LFS, relapse, TRM and GvHD. 103 patients were included; 30 received BuCy, 37 BuCyMel, and 36 CloFluBu. The 5-years LFS was 43.3% (SE ± 9.0) in the BuCy group, 59.2 % (SE ± 8.1) after BuCyMel, and 66.7 % (SE ± 7.9) after CloFluBu. Multivariable Cox regression analysis showed a trend to lower LFS after BuCy compared to CloFluBu (p = 0.07). BuCy was associated with a higher relapse incidence compared to the other regimens (p = 0.06). Younger age was a predictor for relapse (p = 0.02). A strong correlation between Busulfan Therapeutic Drug Monitoring (TDM) and lower incidence of aGvHD (p < 0.001) was found. In conclusion, LFS after BuCyMel and CloFluBu was comparable, lower LFS was found after BuCy, due to higher relapse incidence. CloFluBu was associated with lower incidence of aGvHD, suggesting lower toxicity with this type of conditioning. This finding is also explained by the impact of Busulfan monitoring.

Pharmacotherapy in Pediatric Hematopoietic Cell Transplantation.

Hematopoietic cell transplantation (HCT) is a curative treatment option for both malignant and nonmalignant diseases. Success of the procedure mainly depends on disease control and treatment-related complications. Pharmacotherapy plays a major role in HCT and significantly impacts the outcomes. Main drug use within HCT includes conditioning, GvHD prophylaxis, and prevention/treatment of infections.Increasing evidence suggests individualized dosing in (pediatric) HCT may improve outcome. Dose individualization may result in a better predictable drug treatment in terms of safety and efficacy, including timely immune reconstitution after HCT and optimal tumor or disease control, which may result in improved survival chances.

Fludarabine exposure in the conditioning prior to allogeneic hematopoietic cell transplantation predicts outcomes.

Fludarabine is the most frequently used agent in conditioning regimens for allogeneic hematopoietic cell transplantation (HCT). Body surface area-based dosing leads to highly variable fludarabine exposure. We studied the relation between fludarabine exposure and clinical outcomes. A retrospective, pharmacokinetic-pharmacodynamic analysis was conducted with data from patients undergoing HCT with fludarabine (160 mg/m2) as part of a myeloablative conditioning (busulfan targeted to an area under the plasma-concentration-time curve [AUC] of 90 mg*h/L) and rabbit antithymocyte globulin (6-10 mg/kg; from day -9/-12) between 2010 and 2016. Fludarabine exposure as AUC was calculated for each patient using a previously published population pharmacokinetic model and related to 2-year event-free survival (EFS) by means of (parametric) time-to-event models. Relapse, nonrelapse mortality (NRM), and graft failure were considered events. One hundred ninety-two patients were included (68 benign and 124 malignant disorders). The optimal fludarabine exposure was determined as an AUC of 20 mg*h/L. In the overexposed group, EFS was lower (hazard ratio [HR], 2.0; 95% confidence interval [CI], 1.1-3.5; P = .02), due to higher NRM (HR, 3.4; 95% CI, 1.6-6.9; P <001) associated with impaired immune reconstitution (HR, 0.43; 95% CI, 0.26-0.70; P <001). The risks of NRM and graft failure were increased in the underexposed group (HR, 3.3; 95% CI, 1.2-9.4; P = .02; HR, 4.8; 95% CI, 1.2-19; P = .02, respectively). No relationship with relapse was found. Fludarabine exposure is a strong predictor of survival after HCT, stressing the importance of optimum fludarabine dosing. Individualized dosing, based on weight and "renal function" or "therapeutic drug monitoring," to achieve optimal fludarabine exposure might improve survival.

Individualized conditioning regimes in cord blood transplantation: Towards improved and predictable safety and efficacy.

INTRODUCTION: The conditioning regimen used in cord blood transplantation (CBT) may significantly impact the outcomes. Variable pharmacokinetics (PK) of drugs used may further influence outcome. Individualized dosing takes inter-patient differences in PK into account, tailoring drug dose for each individual patient in order to reach optimal exposure. Dose individualization may result in a better predictable regimen in terms of safety and efficacy, including timely T cell reconstitution, which may result in improved survival chances. AREAS COVERED: Conditioning regimens used in CBT varies significantly between and within centres. For busulfan, individualized dosing with therapeutic drug monitoring has resulted in better outcomes. Anti-thymocyte globulin (ATG), used to prevent rejection and GvHD, significantly hampers early T-cell reconstitution (IR). Timely IR is crucial in preventing viral reactivations and relapse. By individudalizing ATG, IR is better predicted and may prevent morbidity and mortality. EXPERT OPINION: Individualization of agents used in the conditioning regimen in CBT has proven its added value. Further fine-tuning, including new drugs and/or comprehensive models for all drugs, may result in better predictable conditioning regimens. A predictable conditioning regimen is also of interest/importance when studying adjuvant therapies, including immunotherapies (e.g. cellular vaccines or engineered T-cell) in a harmonized clinical trial design setting.

Biomarker profiling of steroid-resistant acute GVHD in patients after infusion of mesenchymal stromal cells.

We performed a prospective phase II study to evaluate clinical safety and outcome in 48 patients with steroid-refractory grade II-IV acute graft-versus-host disease (aGVHD) treated with mesenchymal stromal cells (MSCs). Clinical outcomes were correlated to comprehensive analyses of soluble and cellular biomarkers. Complete resolution (CR) of aGVHD at day 28 (CR-28) occurred in 12 (25%) patients, CR lasting >1 month (CR-B) occurred in 24 (50%) patients. One-year overall survival was significantly improved in CR-28 (75 versus 33%, P=0.020) and CR-B (79 versus 8%, P<0.001) versus non-CR patients. A six soluble biomarker-panel was predictive for mortality (HR 2.924; CI 1.485-5.758) when measured before MSC-administration. Suppression of tumorigenicity 2 (ST2) was only predictive for mortality 2 weeks after but not before MSC-administration (HR 2.389; CI 1.144-4.989). In addition, an increase in immature myeloid dendritic cells associated with decreased mortality (HR 0.554, CI 0.389-0.790). Patients had persisting T-cell responses against defined virus- and leukemia-associated antigens. In conclusion, our data emphasize the need to carefully assess biomarkers in cohorts with homogeneous GVHD treatments. Biomarkers might become an additional valuable component of composite end points for the rapid and efficient testing of novel compounds to decrease lifecycle of clinical testing and improve the success rate of phase II/III trials.

Paediatric reduced intensity conditioning: analysis of centre strategies on regimens and definitions by the EBMT Paediatric Diseases and Complications and Quality of Life WP.

The aim of this analysis was to explore the diversity of reduced intensity conditioning (RIC) in paediatric allo-SCT in daily practice across Europe. Data from the European Group for Blood and Marrow Transplantation (EBMT) Promise database from 1994 to 2008 were supplemented by a survey of EBMT centres performing paediatric allo-SCT on the current policy asking for the underlying diseases and for the drug combinations. Records from 161 centres from 30 countries were analysed and 139 various RIC regimens were reported. More centres applied RIC for malignant rather than for non-malignant diseases. In general, fludarabine (FLU)-based regimens predominated except for BU-based regimens in myeloid malignancies and haemoglobinopathies. Treosulfan (TREO) was mainly applied for unspecified malignant diseases and for haemophagocytic diseases. FLU-based regimens revealed the greatest number of different combinations. Correlating the number of regimens with the number of treating centres revealed the lowest variety in FLU and the highest variety in TBI and TREO. FLU/melphalane and FLU/CY were the most frequent combinations. This extreme heterogeneity in RIC may influence both the efficacy and the safety of the procedures, which requires further investigation. Optimization and standardization of RIC is the final goal to provide a platform for future prospective studies.

Cognate CD4 T-cell licensing of dendritic cells heralds anti-cytomegalovirus CD8 T-cell immunity after human allogeneic umbilical cord blood transplantation.

UNLABELLED: Reactivation of human cytomegalovirus (CMV) is hazardous to patients undergoing allogeneic cord blood transplantation (CBT), lowering survival rates by approximately 25%. While antiviral treatment ameliorates viremia, complete viral control requires CD8+ T-cell-driven immunity. Mouse studies suggest that cognate antigen-specific CD4+ T-cell licensing of dendritic cells (DCs) is required to generate effective CD8+ T-cell responses. For humans, this was not fully understood. We here show that CD4+ T cells are essential for licensing of human DCs to generate effector and memory CD8+ T-cell immunity against CMV in CBT patients. First, we show in CBT recipients that clonal expansion of CMV-pp65-specific CD4+ T cells precedes the rise in CMV-pp65-specific CD8+ T cells. Second, the elicitation of CMV-pp65-specific CD8+ T cells from rare naive precursors in cord blood requires DC licensing by cognate CMV-pp65-specific CD4+ T cells. Finally, also CD8+ T-cell memory responses require CD4+ T-cell-mediated licensing of DCs in our system, by secretion of gamma interferon (IFN-γ) by pp65-specific CD4+ T cells. Together, these data show that human DCs require licensing by cognate antigen-specific CD4+ T cells to elicit effective CD8+ T-cell-mediated immunity and fight off viral reactivation in CBT patients. IMPORTANCE: Survival rates after stem cell transplantation are lowered by 25% when patients undergo reactivation of cytomegalovirus (CMV) that they harbor. Immune protection against CMV is mostly executed by white blood cells called killer T cells. We here show that for generation of optimally protective killer T-cell responses that respond to CMV, the early elicitation of help from a second branch of CMV-directed T cells, called helper T cells, is required.

Predictors of invasive fungal infection in pediatric allogeneic hematopoietic SCT recipients.

This study was aimed at finding predictors of invasive fungal infection (IFI) after pediatric allogeneic hematopoietic SCT (HSCT). All children who received allogeneic HSCT in the Wilhelmina Children's Hospital Utrecht between 2004 and 2012 were included. HSCT data were prospectively collected. Patients were retrospectively classified into high- or low-risk groups for developing IFI using criteria based on available literature. Predictors for the occurrence of IFI were analyzed using Cox regression models. We used logistic regression models to analyze the association between other HSCT-related complications and IFI. Secondary outcomes were overall survival and treatment-related mortality (TRM). Two-hundred nine patients were included in the analysis; median age was 6.6 years. The cumulative incidence of IFI was 12%. In patients classified as 'low risk' (n=75), only 5.3% developed IFI (odds ratio (OR): 0.325; P=0.047). In multivariate analysis, a predictor for the occurrence of IFI was an a priori determined HSCT TRM risk >20% (based on EBMT-risk score). Post-HSCT, the administration of high-dose steroids was associated with IFI (OR: 4.458; P=0.010). Patients who developed IFI showed an increased risk of TRM (OR: 3.773; P=0.004). These results confirm that risk group stratification should guide intensity of monitoring for IFI and use of antifungal prophylaxis.

Human herpes virus 6 reactivation: important predictor for poor outcome after myeloablative, but not non-myeloablative allo-SCT.

Hematopoietic SCT (HSCT) is often complicated by viral reactivations. In this retrospective cohort study (January 2004-August 2008), predictors for human herpes virus 6 (HHV6)-reactivation and associations between HHV6-reactivation and clinical outcomes after allogeneic HSCT were studied. HHV6 DNA load in plasma was monitored weekly by quantitative real-time PCR. Associations between the main end point HHV6-reactivation and other end points, that is, acute GVHD (aGVHD) and NRM were analyzed using Cox proportional hazard models. In total, 108 patients receiving either a myeloablative (MA; n=60) or non-myeloablative (NMA; n=48) conditioning regimen were included. Median age was 40 years (range 17-65); median follow-up was 20 months (range 3-36). In 16/60 (27%) patients with MA conditioning regimen, a HHV6 reactivation was observed (mean viral load 50 323 cp/mL) compared with 2/48 (4%) patients with a NMA conditioning regimen with low viral load (mean 1100 cp/mL). In multivariate analysis, MA conditioning was the only predictor for HHV6 reactivation (P=0.02). In addition, HHV6 reactivation was associated with grades 2-4 aGVHD (P<0.001) and NRM (P=0.03). Regular monitoring of HHV6 reactivation after HSCT might be important in MA HSCT patients to enable early initiation of antiviral treatment or to anticipate aGVHD, all of which may improve clinical outcome.

Increased proportion of perforin-expressing CD8+T-cells indicates control of herpesvirus reactivation in children after stem cell transplantation.

Hematopoietic stem cell transplantation (HSCT) is frequently complicated by viral reactivations. Early diagnosis of viral reactivations and preemptive therapy relies on frequent viralload monitoring. An easy marker of effective cytotoxicity in lymphopenia is lacking and therefore we studied perforin-expression in CD8+T-cells in children following HSCT. Prospectively, we weekly monitored viral loads and perforin-expression of CD8+T-cells in whole blood by FACS, until 4months after HSCT in children. 27 patients were included (median age 4,3, range 0.3-20,1years) of whom 19 developed viral reactivations. These patients showed higher percentages of perforin-expressing CD8+T-cells (17,2%, range 0-63%) than those without (6,8%; range 0-16%) (p=0.001). The increased percentage of perforin-expressing CD8+T-cells coincided with a decrease in viral load with a median interval between maximum viral load and maximum level of perforin-expression of 0,4weeks (range 0.1-7.1). We conclude that perforin-expression in CD8+T-cells may be a marker for effective antiviral T-cell reconstitution early after HSCT in children.

Stem cell source-dependent reconstitution of FOXP3+ T cells after pediatric SCT and the association with allo-reactive disease.

In adult patients, regulatory CD4+FOXP3+ T cells are suggested to have a role in the control of allo-reactive disease after hematopoietic SCT (HSCT). We compared CD4+FOXP3+ T-cell reconstitution after unrelated cord blood (UCB), matched unrelated donor (MUD) and matched sibling donor (MSD) HSCT in children, starting as early as 1 week after transplantation, and analyzed the association with allo-reactive disease. A total of 30 children were included who underwent a myeloablative-conditioning regimen followed by UCB (12/30), MUD (7/30) or MSD (11/30) HSCT. These three patient groups showed significant differences in FOXP3+ T-cell reconstitution pattern. Early after UCB and MSD, but not after MUD, HSCT a peak in FOXP3+ T cells was observed. There were significant differences in activation status and Ki67 expression of the FOXP3+ T cells after UCB and MSD, respectively. FOXP3+ T-cell proportions early after HSCT and in the graft were inversely correlated with allo-reactivity. This study indicates that FOXP3 reconstitution after HSCT is dependent on the type of graft used. Furthermore, in children evaluation of FOXP3+ T-cell numbers early after HSCT and in the graft may be used to judge the risk of developing allo-reactivity after HSCT.

First analysis of human herpesvirus 6T-cell responses: specific boosting after HHV6 reactivation in stem cell transplantation recipients.

Early human herpesvirus 6 (HHV6) reactivation after hematopoietic stem cell transplantation (HSCT) is associated with poor survival. We characterized HHV6 immuneresponses in HSCT patients during lymphopenia. Prospectively, HHV6 DNA-load was measured weekly by realtime-PCR. Numbers of IFNγ-producing HHV6-T-cells were retrospectively determined by enzyme-linked immunospot assay 2 months after HSCT. HHV6-specific T-cell proliferative capacity was analyzed with a newly developed assay using antigen-presenting autologous HHV6-infected PBMC. Fifty-six patients were included (median age 4.6 years; range 0.2-21.2 years). HHV6-reactivation occurred in 29/56 (52%) patients with a median time of 14 (range 1-41) days after HSCT. The median number of IFN-γ producing HHV6-specific T-cells at 2 months and the HHV6-specific CD8+ T-cell proliferative capacity at 6 months after HSCT was increased after HHV6-reactivation compared to non-reactivating patients (P=0.006 and p=0.019). In conclusion, HHV6-specific immuneresponses can be initiated during lymphopenia early after HSCT, which implicates a potential window for development of HHV6-specific (immuno)therapy.

Allogeneic hematopoietic SCT for alpha-mannosidosis: an analysis of 17 patients.

Alpha-mannosidosis is a rare lysosomal storage disease. Hematopoietic SCT (HSCT) is usually recommended as a therapeutic option though reports are anecdotal to date. This retrospective multi institutional analysis describes 17 patients that were diagnosed at a median of 2.5 (1.1-23) years and underwent HSCT at a median of 3.6 (1.3-23.1) years. In all, 15 patients are alive (88%) after a median follow-up of 5.5 (2.1-12.6) years. Two patients died within the first 5 months after HSCT. Of the survivors, two developed severe acute GvHD (>=grade II) and six developed chronic GvHD. Three patients required re-transplantation because of graft failure. All 15 showed stable engraftment. The extent of the patients' developmental delay before HSCT varied over a wide range. After HSCT, patients made developmental progress, although normal development was not achieved. Hearing ability improved in some, but not in all patients. We conclude that HSCT is a feasible therapeutic option that may promote mental development in alpha-mannosidosis.

Familial hemophagocytic lymphohistiocytosis in a pediatric patient diagnosed by brain magnetic resonance imaging.

Familial hemophagocytic lymphohistiocytosis (fHLH) is an autosomal recessive disorder characterized by proliferation and infiltration of several organs by activated lymphocytes and macrophages. Without allogeneic stem cell transplantation, fHLH is fatal. We describe a previously healthy 11-month-old boy with a rapidly progressive encephalopathy. An older brother died at 8 months following a subacute encephalopathy diagnosed as meningoencephalitis. The family history led to the suspicion of a metabolic disease, but metabolic studies were unrevealing. MRI showed multiple inhomogeneous signal abnormalities in the cortex and white matter, most prominent in the cerebral hemispheres and around the dentate nucleus. Gadolinium-enhanced T1-weighted images showed a multitude of enhancing foci, suggestive of perivascular enhancement. Based on MRI pattern with multiple lesions, perivascular enhancement and family history, fHLH was suspected. DNA analysis showed that the patient was compound-heterozygous for the c.445 G>A (p.Gly149Ser) mutation in exon 1 and the c.757 G>A (p.Glu253Lys) mutation in exon 2 of the perforin 1 gene. The patient was treated according to the international HLH-2004 protocol (dexamethasone, etoposide, cyclosporine, intrathecal methotrexate and prednisolone) followed by allogeneic cord blood transplantation. He showed a significant neurological and radiological improvement. The reported case demonstrates that MRI pattern recognition can lead to early diagnosis of fHLH, with subsequent adequate treatment.