High fludarabine exposure and relationship with treatment-related mortality after nonmyeloablative hematopoietic cell transplantation

Upfront Umbilical Cord Blood Transplantation Versus Immunosuppressive Therapy for Pediatric Patients With Idiopathic Severe Aplastic Anemia

Umbilical cord blood transplantation (UCBT) has been rarely reported as a first-line treatment for idiopathic severe aplastic anemia (SAA) patients lacking HLA-matched sibling donors (MSD). Our study aimed to compare the clinical outcomes of pediatric SAA patients who received UCBT and immunosuppressive therapy (IST) upfront. A retrospective analysis was performed on 43 consecutive patients who received frontline IST (n = 17) or UCBT (n = 26) between July 2017 and April 2022. The 3-year overall survival (OS) was comparable between the UCBT and IST groups (96.2% versus 100%, P = .419), while the 3-year event-free survival (EFS) was significantly better in the former than in the latter (88.5% versus 58.8%, P = .048). In the UCBT group, 24 patients achieved successful engraftment, 2 patients developed severe acute graft-versus-host disease (aGVHD), no extensive chronic GVHD (cGVHD), and a high GVHD-free, failure-free survival (GFFS) of 84.6% at 3 years. After 1 year of treatment, 12 patients in the IST group responded, while 5 patients did not achieve remission and 2 patients had disease relapse. At both 3 and 6 months after treatment, the proportion of transfusion-independent patients was higher in the UCBT group than in the IST group. Faster immune recovery and earlier transfusion independence further reduced the risk of infection and bleeding, thereby improving health-related quality of life in the UCBT-treated group. Our results suggested that UCBT as upfront therapy may be an effective and safe option for pediatric SAA patients, with favorable outcomes in experienced centers.

Autologous engineered T cell receptor therapy in advanced cancer

To overcome challenges associated with adoptive cell therapy (ACT), we developed a personalized autologous T-cell therapy program. Patients with advanced cancer with HLA-A *02:01 allele and tumor expression of PRAME, MAGEA1, MAGEA4, MAGEA8, NY-ESO-1, COL6A3 exon 6, MXRA5, and/or MMP1 underwent leukapheresis and T-cell product manufacturing. Patients received lymphodepletion, IMA101 infusion and interleukin 2 for 14 days. Of 214 screened patients, 14 were treated (6, IMA101; 8, IMA101 and atezolizumab). The most common adverse events were cytokine release syndrome (G1, n = 6; G2, n = 4) and cytopenia. At 6 weeks, 12 (85.7%) patients had stable disease. Three patients had prolonged disease stabilization for 12.9, 7.3, and 13.7 months, respectively. The median progression-free survival and overall survival were 3.4 months and 9.4 months, respectively. Target-specific T cells expanded to constitute up to 78.7% of CD8+ cells. In conclusion, IMA101 was feasible and well tolerated, leveraging the potential of multi-targeted ACT that warrants further investigation.

Feasibility and Safety of Personalized, Multi-Target, Adoptive Cell Therapy (IMA101): First-in-Human Clinical Trial in Patients with Advanced Metastatic Cancer

IMA101 is an actively personalized, multi-targeted adoptive cell therapy (ACT), whereby autologous T cells are directed against multiple novel defined peptide-HLA (pHLA) cancer targets. HLA-A*02:01-positive patients with relapsed/refractory solid tumors expressing ≥1 of 8 predefined targets underwent leukapheresis. Endogenous T cells specific for up to 4 targets were primed and expanded in vitro. Patients received lymphodepletion (fludarabine, cyclophosphamide), followed by T-cell infusion and low-dose IL2 (Cohort 1). Patients in Cohort 2 received atezolizumab for up to 1 year (NCT02876510). Overall, 214 patients were screened, 15 received lymphodepletion (13 women, 2 men; median age, 44 years), and 14 were treated with T-cell products. IMA101 treatment was feasible and well tolerated. The most common adverse events were cytokine release syndrome (Grade 1, n = 6; Grade 2, n = 4) and expected cytopenias. No patient died during the first 100 days after T-cell therapy. No neurotoxicity was observed. No objective responses were noted. Prolonged disease stabilization was noted in three patients lasting for 13.7, 12.9, and 7.3 months. High frequencies of target-specific T cells (up to 78.7% of CD8+ cells) were detected in the blood of treated patients, persisted for >1 year, and were detectable in posttreatment tumor tissue. Individual T-cell receptors (TCR) contained in T-cell products exhibited broad variation in TCR avidity, with the majority being low avidity. High-avidity TCRs were identified in some patients' products. This study demonstrates the feasibility and tolerability of an actively personalized ACT directed to multiple defined pHLA cancer targets. Results warrant further evaluation of multi-target ACT approaches using potent high-avidity TCRs. See related Spotlight by Uslu and June, p. 865.

Prospective Validation and Refinement of a Population Pharmacokinetic Model of Fludarabine in Children and Young Adults Undergoing Hematopoietic Cell Transplantation

Fludarabine is a nucleoside analog with antileukemic and immunosuppressive activity commonly used in allogeneic hematopoietic cell transplantation (HCT). Several fludarabine population pharmacokinetic (popPK) and pharmacodynamic models have been published enabling the movement towards precision dosing of fludarabine in pediatric HCT; however, developed models have not been validated in a prospective cohort of patients. In this multicenter pharmacokinetic study, fludarabine plasma concentrations were collected via a sparse-sampling strategy. A fludarabine popPK model was evaluated and refined using standard nonlinear mixed effects modelling techniques. The previously described fludarabine popPK model well-predicted the prospective fludarabine plasma concentrations. Individuals who received model-based dosing (MBD) of fludarabine achieved significantly more precise overall exposure of fludarabine. The fludarabine popPK model was further improved by both the inclusion of fat-free mass instead of total body weight and a maturation function on fludarabine clearance. The refined popPK model is expected to improve dosing recommendations for children younger than 2 years and patients with higher body mass index. Given the consistency of fludarabine clearance and exposure across its multiple days of administration, therapeutic drug monitoring is not likely to improve targeted exposure attainment.

Is Monitoring of the Intracellular Active Metabolite Levels of Nucleobase and Nucleoside Analogs Ready for Precision Medicine Applications?

Nucleobase and nucleoside analogs (NAs) play important roles in cancer therapy. Although there are obvious individual differences in NA treatments, most NAs lack direct relationships between their plasma concentration and efficacy or adverse effects. Accumulating evidence suggests that the intracellular active metabolite levels of NAs predict patient outcomes. This article reviewed the relationships between NA intracellular active metabolite levels and their efficacy or adverse effects. The factors affecting the formation of intracellular active metabolites and combination regimens that elevate intracellular active metabolite levels were also reviewed. Given the mechanism of NA cytotoxicity, NA intracellular active metabolite levels may be predictive of clinical outcomes. Many clinical studies support this hypothesis. Therefore, the monitoring of intracellular active metabolite levels is beneficial for individualized NA treatment. However, to perform clinical monitoring in practice, well-designed studies are needed to explore the optimal threshold or range and the appropriate regimen adjustment strategies based on these parameters.

A randomized phase III study of pretransplant conditioning for AML/MDS with fludarabine and once daily IV busulfan ± clofarabine in allogeneic stem cell transplantation

Pretransplant conditioning with Fludarabine (Flu)-Busulfan (Bu) is safe, but clofarabine (Clo) has improved antileukemic activity. Hypothesis: Flu+Clo-Bu (FCB) yields superior progression-free survival (PFS) after allogeneic transplantation. We randomized 250 AML/MDS patients aged 3–70, Karnofsky Score ≥80, with matched donors, to FCB (n = 120) or Flu-Bu (n = 130), stratifying complete remission (CR) vs. No CR, (NCR). HCT-CI scores varied, from 0 to 10. All evaluable patients engrafted. Median follow-up was 66 months (interquartile range: 58–80). Three-year relapse incidence (RI), 25% with FCB, vs. 39% with Flu-Bu (p = 0.018), offset by higher non-relapse mortality, 22.6% (95%CI: 16–30.2%) vs. 12.3% (95%CI: 6.5–19%). Three-year PFS was 52% (95%CI: 44–62%) (FCB), vs. 48% (95%CI: 41–58%) (Flu-Bu). FCB benefited CR patients less, NCR patients age ≤ 60 had 3-year 34% RI (95%CI: 19–49%) (FCB) vs. 56% (95%CI: 38–70%) after Flu-Bu (p = 0.037). NCR patients >60 years had 3-year RI 10.0% (FCB), vs. 56.0%, after Flu-Bu (p = 0.003). Bayesian regression analysis including treatment-covariate interactions showed FCB superiority in NCR patients with low HCT-CI (0–2). Serious adverse event profiles were similar for the regimens. Conditioning with FCB did not improve PFS overall, but improved disease control in NCR patients, mandating confirmatory trials. Remission status and HCT-CI should be considered when using FCB.

Relationship of iothalamate clearance and NRM in patients receiving fludarabine and melphalan reduced-intensity conditioning

The reduced-intensity conditioning regimen, fludarabine and melphalan, is frequently used in allogeneic hematopoietic stem cell transplantation (HSCT). Melphalan and the active metabolite of fludarabine, F-ara-A, are excreted via the kidneys. Existing methods to assess clearance in this setting are based on serum creatinine, which has known limitations for glomerular filtration rate (GFR) estimation in patients with malignancy. Measured GFR (mGFR) may better predict drug dosing to mitigate toxicity and increase the chances of successful engraftment. The primary objective of this study was to assess the association between mGFR and risk for non-relapse mortality (NRM) in allogeneic HSCT patients receiving conditioning with fludarabine and melphalan. In the 109 included patients, mGFR < 65 ml/min/1.73m2 predicted a significantly higher rate of overall NRM (HR 2.13, 95% CI, 1.03-4.35, P = 0.04) and 1-year incidence of infection (HR 2.63, 95% CI, 1.54-4.55, P < 0.001) in addition to a significantly lower 2-year survival (P = 0.019). Kidney function estimated via eGFR and eCrCl did not correlate with post-transplant outcomes. These results suggest that mGFR is a promising approach for assessing clearance in allogeneic HSCT patients and may be preferred to standard creatinine-based eGFR strategies.

Advances in the management of α-thalassemia major: reasons to be optimistic

α-Thalassemia major (ATM) is a severe disease resulting from deletions in all 4 copies of the α-globin gene. Although it is usually fatal before birth, the advent of in utero transfusions has enabled survival of a growing number of children. Postnatal therapy consists of chronic transfusions or stem cell transplantation, similar to patients with β-thalassemia major. In this review, we discuss the experience with postnatal stem cell transplantation in patients with ATM, as well as the ongoing phase 1 clinical trial of in utero stem cell transplantation for this condition.

Feasibility and Efficacy of a Pharmacokinetics-Guided Busulfan Conditioning Regimen for Allogeneic Stem Cell Transplantation with Post-Transplantation Cyclophosphamide as Graft-versus-Host Disease Prophylaxis in Adult Patients with Hematologic Malignancies

Busulfan (Bu) is an alkylating agent routinely used for conditioning regimens before allogeneic stem cell transplantation (allo-SCT). Bu shows wide pharmacokinetic (PK) variability among patients. Patients can have a higher systemic exposure (expressed as area under the curve [AUC]) with an increased risk of toxicity or a lower AUC with a higher probability of graft rejection and/or disease relapse. After i.v. administration, an optimal Bu therapeutic window (AUC target of 16,000 to 24,000 μM·minute) has been identified. The use of PK-guided Bu dosing leads to improved overall survival (OS) and progression-free survival (PFS) compared with fixed-dose administration in a variety of hematologic diseases. The aim of this study was to evaluate the outcomes and feasibility of a reduced-toxicity conditioning (RTC) regimen comprising thiotepa, Bu, and fludarabine (TBF) with therapeutic drug monitoring of Bu in patients with hematologic disorders. We report on 41 adult patients with myeloid or lymphoid malignancies who underwent an allo-SCT with a PK-guided Bu-based RTC regimen between January 2019 and October 2020. Patients received a total Bu dose to achieve a target AUC of 16,000 μM·minute in combination with Flu and thiotepa. The median time to absolute neutrophil count recovery and transfusion-independent platelet count recovery was 23 days (range, 15 to 42 days) and 29 days (range, 14 to 97 days), respectively. The cumulative incidence (CI) of nonrelapse mortality was 7% at 100 days and 13% at 1 year. Grade 3 liver toxicity was observed in 6 patients. One patient developed sinusoidal obstruction syndrome at day +27. Grade 3 mucositis occurred in 18 patients. Looking at grade ≥3 infections, the CI was 29% at 30 days, 34% at 60 days, 44% at 100 days, and 56% at 1 year. The 180-day CI of grade II-IV acute graft-versus-host disease (GVHD) was 15%, and the 1-year CI of overall chronic GVHD was 20%. With a median follow-up of alive patients of 14.4 months (range, 3.2 to 24 months), the CI of relapse at 1 year was 6%. The 1-year PFS was 81%, and 1-year OS was 84%. In conclusion, these data support the efficacy of PK-guided Bu dose in the context of a TBF conditioning regimen and the feasibility of therapeutic dosage monitoring of i.v. Bu for patients with hematologic diseases. © 2021 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

T-cell receptor-based therapy: an innovative therapeutic approach for solid tumors

T-cell receptor (TCR)-based adoptive therapy employs genetically modified lymphocytes that are directed against specific tumor markers. This therapeutic modality requires a structured and integrated process that involves patient screening (e.g., for HLA-A*02:01 and specific tumor targets), leukapheresis, generation of transduced TCR product, lymphodepletion, and infusion of the TCR-based adoptive therapy. In this review, we summarize the current technology and early clinical development of TCR-based therapy in patients with solid tumors. The challenges of TCR-based therapy include those associated with TCR product manufacturing, patient selection, and preparation with lymphodepletion. Overcoming these challenges, and those posed by the immunosuppressive microenvironment, as well as developing next-generation strategies is essential to improving the efficacy and safety of TCR-based therapies. Optimization of technology to generate TCR product, treatment administration, and patient monitoring for adverse events is needed. The implementation of novel TCR strategies will require expansion of the TCR approach to patients with HLA haplotypes beyond HLA-A*02:01 and the discovery of novel tumor markers that are expressed in more patients and tumor types. Ongoing clinical trials will determine the ultimate role of TCR-based therapy in patients with solid tumors.

Higher Fludarabine and Cyclophosphamide Exposures Lead to Worse Outcomes in Reduced-Intensity Conditioning Hematopoietic Cell Transplantation for Adult Hematologic Malignancy

Reduced-intensity conditioning regimens using fludarabine (Flu) and cyclophosphamide (Cy) have been widely used in hematopoietic cell transplantation (HCT) recipients. The optimal exposure of these agents remains to be determined. We aimed to delineate the exposure-outcome associations of Flu and Cy separately and then both combined on HCT outcomes. This is a single-center, observational, pharmacokinetic (PK)-pharmacodynamic (PD) study of Flu and Cy in HCT recipients age ≥18 years who received Cy (50 mg/kg in a single dose), Flu (150 to 200 mg/m² given as 5 daily doses), and total body irradiation (TBI; 200 cGy). We measured trough concentrations of 9-β-D-arabinosyl-2-fluoradenine (F-ara-A), an active metabolite of Flu, on days -5 and -4 (F-ara-A_Day-5 and F-ara-A_Day-4, respectively), and measured phosphoramide mustard (PM), the final active metabolite of Cy, and estimated the area under the curve (AUC). The 89 enrolled patients had a nonrelapse mortality (NRM) of 9% (95% confidence interval [CI], 3% to 15%) at day +100 and 15% (95% CI, 7% to 22%) at day +180, and an overall survival (OS) of 73% (95% CI, 63% to 81%) at day +180. In multivariate analysis, higher PM area under the curve (AUC) for 0 to 8 hours (PM AUC_{0-8 hr}) was an independent predictor of worse NRM (P < .01 at both day +100 and day +180) and worse day +180 OS (P < .01), but no associations were identified for F-ara-A trough levels. We observed lower day +100 NRM in those with both high F-ara-A_Day-4 trough levels (≥40 ng/mL; >25th percentile) and low PM AUC_{0-8 hr} (<34,235 hr ng/mL; <75th percentile), compared with high exposures to both agents (hazard ratio, 0.06; 95% CI, 0.01 to 0.48). No patients with low F-ara-A_Day-4 (<40 ng/mL; <25th percentile) had NRM by day +100, regardless of PM AUC. The interpatient PK variability was large in F-ara-A_Day-4 trough and PM AUC_{0-8 hr} (29-fold and 5.0-fold, respectively). Flu exposure alone was not strongly associated with NRM or OS in this reduced Flu dose regimen; however, high exposure to both Flu and Cy was associated with a >16-fold higher NRM. These results warrant further investigation to optimize reduced-intensity regimens based on better PK-PD understanding and possible adaptation to predictable factors influencing drug clearance.

Kidney injury and disease in patients with haematological malignancies

Acute kidney injury (AKI) is common in patients with cancer, especially in those with haematological malignancies. Kidney injury might be a direct consequence of the underlying haematological condition. For example, in the case of lymphoma infiltration or extramedullary haematopoiesis, it might be caused by a tumour product; in the case of cast nephropathy it might be due to the presence of monoclonal immunoglobulin; or it might result from tumour complications, such as hypercalcaemia. Kidney injury might also be caused by cancer treatment, as many chemotherapeutic agents are nephrotoxic. High-intensity treatments, such as high-dose chemotherapy followed by haematopoietic stem cell transplantation, not only increase the risk of infection but can also cause AKI through various mechanisms, including viral nephropathies, engraftment syndrome and sinusoidal obstruction syndrome. Some conditions, such as thrombotic microangiopathy, might also result directly from the haematological condition or the treatment. Novel immunotherapies, such as immune checkpoint inhibitors and chimeric antigen receptor T cell therapy, can also be nephrotoxic. As new therapies for haematological malignancies with increased anti-tumour efficacy and reduced toxicity are developed, the number of patients receiving these treatments will increase. Clinicians must gain a good understanding of the different mechanisms of kidney injury associated with cancer to better care for these patients.

Total Body Irradiation Forever? Optimising Chemotherapeutic Options for Irradiation-Free Conditioning for Paediatric Acute Lymphoblastic Leukaemia

Total-body irradiation (TBI) based conditioning prior to allogeneic hematopoietic stem cell transplantation (HSCT) is generally regarded as the gold-standard for children >4 years of age with acute lymphoblastic leukaemia (ALL). Retrospective studies in the 1990's suggested better survival with irradiation, confirmed in a small randomised, prospective study in the early 2000's. Most recently, this was reconfirmed by the early results of the large, randomised, international, phase III FORUM study published in 2020. But we know survivors will suffer a multitude of long-term sequelae after TBI, including second malignancies, neurocognitive, endocrine and cardiometabolic effects. The drive to avoid TBI directs us to continue optimising irradiation-free, myeloablative conditioning. In chemotherapy-based conditioning, the dominant myeloablative effect is provided by the alkylating agents, most commonly busulfan or treosulfan. Busulfan with cyclophosphamide is a long-established alternative to TBI-based conditioning in ALL patients. Substituting fludarabine for cyclophosphamide reduces toxicity, but may not be as effective, prompting the addition of a third agent, such as thiotepa, melphalan, and now clofarabine. For busulfan, it's wide pharmacokinetic (PK) variability and narrow therapeutic window is well-known, with widespread use of therapeutic drug monitoring (TDM) to individualise dosing and control the cumulative busulfan exposure. The development of first-dose selection algorithms has helped achieve early, accurate busulfan levels within the targeted therapeutic window. In the future, predictive genetic variants, associated with differing busulfan exposures and toxicities, could be employed to further tailor individualised busulfan-based conditioning for ALL patients. Treosulfan-based conditioning leads to comparable outcomes to busulfan-based conditioning in paediatric ALL, without the need for TDM to date. Future PK evaluation and modelling may optimise therapy and improve outcome. More recently, the addition of clofarabine to busulfan/fludarabine has shown encouraging results when compared to TBI-based regimens. The combination shows activity in ALL as well as AML and deserves further evaluation. Like busulfan, optimization of chemotherapy conditioning may be enhanced by understanding not just the PK of clofarabine, fludarabine, treosulfan and other agents, but also the pharmacodynamics and pharmacogenetics, ideally in the context of a single disease such as ALL.

Population Pharmacokinetics of Fludarabine in Children and Adults during Conditioning Prior to Allogeneic Hematopoietic Cell Transplantation

Background

Fludarabine is often used as an important drug in reduced toxicity conditioning regimens prior to hematopoietic cell transplantation (HCT). As no definitive pharmacokinetic (PK) basis for HCT dosing for the wide age and weight range in HCT is available, linear body surface area (BSA)-based dosing is still used.

Objective

We sought to describe the population PK of fludarabine in HCT recipients of all ages.

Methods

From 258 HCT recipients aged 0.3–74 years, 2605 samples were acquired on days 1 (42%), 2 (17%), 3 (4%) and 4 (37%) of conditioning. Herein, the circulating metabolite of fludarabine was quantified, and derived concentration-time data were used to build a population PK model using non-linear mixed-effects modelling.

Results

Variability was extensive where area under the curve ranged from 10 to 66 mg h/L. A three-compartment model with first-order kinetics best described the data. Actual body weight (BW) with standard allometric scaling was found to be the best body-size descriptor for all PK parameters. Estimated glomerular filtration rate (eGFR) was included as a descriptor of renal function. Thus, clearance was differentiated into a non-renal (3.24 ± 20% L/h/70 kg) and renal (eGFR × 0.782 ± 11% L/h/70 kg) component. The typical volumes of distribution of the central (V1), peripheral (V2), and second peripheral (V3) compartments were 39 ± 8%, 20 ± 11%, and 50 ± 9% L/70 kg respectively. Intercompartmental clearances between V1 and V2, and V1 and V3, were 8.6 ± 8% and 3.8 ± 13% L/h/70 kg, respectively.

Conclusion

BW and eGFR are important predictors of fludarabine PK. Therefore, current linear BSA-based dosing leads to highly variable exposure, which may lead to variable treatment outcome.

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.

Clinical Trial Simulation To Optimize Trial Design for Fludarabine Dosing Strategies in Allogeneic Hematopoietic Cell Transplantation

Optimal fludarabine exposure has been associated with improved treatment outcome in allogeneic hematopoietic cell transplantation, suggesting potential benefit of individualized dosing. A randomized controlled trial (RCT) comparing alternative fludarabine dosing strategies to current practice may be warranted, but should be sufficiently powered for a relevant end point, while still feasible to enroll. To find the optimal design, we simulated RCTs comparing current practice (160 mg/m² ) to either covariate-based or therapeutic drug monitoring (TDM)-guided dosing with potential outcomes being nonrelapse mortality (NRM), graft failure, or relapse, and ultimately overall survival (covering all three aforementioned outcomes). The inclusion in each treatment arm (n) required to achieve 80% power was calculated for all combinations of end points and dosing comparisons. The trial requiring the lowest n for sufficient power compared TDM-guided dosing to current practice with NRM as primary outcome (n = 70, NRM decreasing from 21% to 5.7%). We conclude that a superiority trial is feasible.

Transplant-Associated Thrombotic Microangiopathy in Pediatric Hematopoietic Cell Transplant Recipients: A Practical Approach to Diagnosis and Management

Transplant-associated thrombotic microangiopathy (TA-TMA) is an endothelial damage syndrome that is increasingly identified as a complication of both autologous and allogeneic hematopoietic cell transplantation (HCT) in children. If not promptly diagnosed and treated, TA-TMA can lead to significant morbidity (e.g., permanent renal injury) or mortality. However, as the recognition of the early stages of TA-TMA may be difficult, we propose a TA-TMA "triad" of hypertension, thrombocytopenia (or platelet transfusion refractoriness), and elevated lactate dehydrogenase (LDH). While not diagnostic, this triad should prompt further evaluation for TA-TMA. There is increased understanding of the risk factors for the development of TA-TMA, including those which are inherent (e.g., race, genetics), transplant approach-related (e.g., second HCT, use of HLA-mismatched donors), and related to post-transplant events (e.g., receipt of calcineurin inhibitors, development of graft-vs. -host-disease, or certain infections). This understanding should lead to enhanced screening for TA-TMA signs and symptoms in high-risk patients. The pathophysiology of TA-TMA is complex, resulting from a cycle of activation of endothelial cells to produce a pro-coagulant state, along with activation of antigen-presenting cells and lymphocytes, as well as activation of the complement cascade and microthrombi formation. This has led to the formulation of a "Three-Hit Hypothesis" in which patients with either an underlying predisposition to complement activation or pre-existing endothelial injury (Hit 1) undergo a toxic conditioning regimen causing endothelial injury (Hit 2), and then additional insults are triggered by medications, alloreactivity, infections, and/or antibodies (Hit 3). Understanding this cycle of injury permits the development of a specific TA-TMA treatment algorithm designed to treat both the triggers and the drivers of the endothelial injury. Finally, several intriguing approaches to TA-TMA prophylaxis have been identified. Future work on the development of a single diagnostic test with high specificity and sensitivity, and the development of a robust risk-scoring system, will further improve the management of this serious post-transplant complication.

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.

Reduced-Intensity Conditioning Followed by Related and Unrelated Allografts for Hematologic Malignancies: Expanded Analysis and Long-Term Follow-Up

Reduced-intensity conditioning (RIC) extends the curative potential of allogeneic hematopoietic cell transplantation (HCT) to patients with hematologic malignancies unable to withstand myeloablative conditioning. We prospectively analyzed the outcomes of 292 consecutive patients, median age 58 years (range, 19 to 75) with hematologic malignancies treated with a uniform RIC regimen of cyclophosphamide, fludarabine, and total body irradiation (200 cGy) with or without antithymocyte globulin and cyclosporine and mycophenolate mofetil graft-versus-host disease (GVHD) prophylaxis followed by allogeneic HCT at the University of Minnesota from 2002 to 6. Probability of 5-year overall survival was 78% for patients with indolent non-Hodgkin lymphoma, 53% for chronic myelogenous leukemia, 55% for Hodgkin lymphoma, 40% for acute myelogenous leukemia, 37% for myelodysplastic syndrome, 29% for myeloma, and 14% for myeloproliferative neoplasms. Corresponding outcomes for relapse were 0%, 13%, 53%, 37%, 39%, 75%, and 29%, respectively. Disease risk index (DRI) predicted both survival and relapse with superior survival (64%) and lowest relapse (16%) in those with low risk score compared with 24% survival and 57% relapse in those with high/very-high risk scores. Recipient cytomegalovirus (CMV)-positive serostatus was protective from relapse with the lowest rates in those also receiving a CMV-positive donor graft (29%). The cumulative incidence of 2-year nonrelapse mortality was 26% and was lowest in those receiving a matched sibling graft at 21%, with low (21%) or intermediate (18%) HCT-specific comorbidity index, and was similar across age groups. The incidence of grades II to IV acute GVHD was 43% and grades III to IV 27%; the highest rates were found in those receiving an unrelated donor (URD) peripheral blood stem cell (PBSC) graft, at 50%. Chronic GVHD at 1 year was 36%. Future approaches incorporating alternative GVHD prophylaxis, particularly for URD PBSC grafts, and targeted post-transplant antineoplastic therapies for those with high DRI are indicated to improve these outcomes.

Pharmacokinetics and Model-Based Dosing to Optimize Fludarabine Therapy in Pediatric Hematopoietic Cell Transplant Recipients

A prospective multicenter study was conducted to characterize the pharmacokinetics (PK) and pharmacodynamics (PD) of fludarabine plasma (f-ara-a) and intracellular triphosphate (f-ara-ATP) in children undergoing hematopoietic cell transplantation (HCT) and receiving fludarabine with conditioning. Plasma and peripheral blood mononuclear cells (PBMCs) were collected over the course of therapy for quantitation of f-ara-a and f-ara-ATP. Nonlinear mixed-effects modeling was used to develop the PK model, including identification of covariates impacting drug disposition. Data from a total of 133 children (median age, 5 years; range, .2 to 17.9) undergoing HCT for a variety of malignant and nonmalignant disorders were available for PK-PD modeling. The implementation of allometric scaling of PK parameters alone was insufficient to describe drug clearance, particularly in very young children. Renal impairment was predicted to increase drug exposure across all ages. The rate of f-ara-a entry into PBMCs (expressed in pmoles per million cells) decreased over the course of therapy, resulting in 78% lower f-ara-ATP after the fourth dose (1.7 pmoles/million cells [range, .2 to 7.2]) compared with first dose (7.9 pmoles/million cells [range, .7 to 18.2]). The overall incidence of treatment-related mortality (TRM) was low at 3% and 8% at days 60 and 360, respectively, and no association with f-ara-a exposure and TRM was found. In the setting of malignancy, disease-free survival was highest at 1 year after HCT in subjects achieving a systemic f-ara-a cumulative area under the curve (cAUC) greater than 15 mg*hour/L compared to patients with a cAUC less than 15 mg*hour/L (82.6% versus 52.8% P = .04). These results suggest that individualized model-based dosing of fludarabine in infants and young children may reduce morbidity and mortality through improved rates of disease-free survival and limiting drug-related toxicity. ClinicalTrials.gov Identifier: NCT01316549.

Population pharmacokinetics of fludarabine in patients with aplastic anemia and Fanconi anemia undergoing allogeneic hematopoietic stem cell transplantation

Although hematopoietic stem cell transplantation (HSCT) with a conditioning regimen consisting of fludarabine (F-araA) and cyclophosphamide (Cy) is associated with improved outcome in young patients with aplastic anemia (AA) and Fanconi anemia (FA), several factors limit the success of the procedure. We evaluated the population pharmacokinetics (POPPK) of F-araA and its influence on HSCT outcome in patients (n=53) with AA and FA undergoing HSCT. Patients carrying a 5′-UTR polymorphism in NT5E gene (rs2295890 G>C) exhibited significantly lower plasma F-araA clearance compared to those with wild-type genotype (7.12 vs 5.03 L/h/m² (29%) P<0.05). F-araA clearance was significantly higher in patients with AA compared to FA (2.46 ×, P<1e−6). Of all the outcome parameters evaluated (engraftment, rejection/graft failure, GvHD, TRM, OS), high F-araA AUC (>29.4 μm*h) was the only significant factor associated with the development of aGvHD by both univariate and multivariate analysis (P=0.02). The influence of plasma F-araA levels need to be evaluated in a larger cohort of patients to propose the need for therapeutic drug monitoring.

Personalized fludarabine dosing to reduce nonrelapse mortality in hematopoietic stem-cell transplant recipients receiving reduced intensity conditioning

Patients undergoing hematopoietic cell transplantation (HCT) with reduced intensity conditioning (RIC) commonly receive fludarabine. Higher exposure of F-ara-A, the active component of fludarabine, has been associated with a greater risk of nonrelapse mortality (NRM). We sought to develop a model for fludarabine dosing in adult HCT recipients that would allow for precise dose targeting and predict adverse clinical outcomes. We developed a pharmacokinetic model from 87 adults undergoing allogeneic RIC HCT that predicts F-ara-A population clearance (Clpop) accounting for ideal body weight and renal function. We then applied the developed model to an independent cohort of 240 patients to identify whether model predictions were associated with NRM and acute graft versus host disease (GVHD). Renal mechanisms accounted for 35.6% of total F-ara-A Clpop. In the independent cohort, the hazard ratio of NRM at day 100 was significantly higher in patients with predicted F-ara-A clearance (Clpred) <8.50 L/h (P < 0.01) and area under the curve (AUCpred) >6.00 μg × h/mL (P = 0.01). A lower Clpred was also associated with more NRM at month 6 (P = 0.01) and trended toward significance at 12 months (P = 0.05). In multivariate analysis, low fludarabine clearance trended toward higher risk of acute GVHD (P = 0.05). We developed a model that predicts an individual's systemic F-ara-A exposure accounting for kidney function and weight. This model may provide guidance in dosing especially in overweight individuals and those with altered kidney function.

A Multidrug-resistant Engineered CAR T Cell for Allogeneic Combination Immunotherapy

The adoptive transfer of chimeric antigen receptor (CAR) T cell represents a highly promising strategy to fight against multiple cancers. The clinical outcome of such therapies is intimately linked to the ability of effector cells to engraft, proliferate, and specifically kill tumor cells within patients. When allogeneic CAR T-cell infusion is considered, host versus graft and graft versus host reactions must be avoided to prevent rejection of adoptively transferred cells, host tissue damages and to elicit significant antitumoral outcome. This work proposes to address these three requirements through the development of multidrug-resistant T cell receptor αβ-deficient CAR T cells. We demonstrate that these engineered T cells displayed efficient antitumor activity and proliferated in the presence of purine and pyrimidine nucleoside analogues, currently used in clinic as preconditioning lymphodepleting regimens. The absence of TCRαβ at their cell surface along with their purine nucleotide analogues-resistance properties could prevent their alloreactivity and enable them to resist to lymphodepleting regimens that may be required to avoid their ablation via HvG reaction. By providing a basic framework to develop a universal T cell compatible with allogeneic adoptive transfer, this work is laying the foundation stone of the large-scale utilization of CAR T-cell immunotherapies.

Association of fludarabine pharmacokinetic/dynamic biomarkers with donor chimerism in nonmyeloablative HCT recipients

PURPOSE

Fludarabine monophosphate (fludarabine) is an integral component of many reduced-intensity conditioning regimens for hematopoietic cell transplantation (HCT). Fludarabine's metabolite, 9-β-D-arabinofuranosyl-2-fluoroadenine (F-ara-A), undergoes cellular uptake and activation to form the active cytotoxic metabolite fludarabine triphosphate (F-ara-ATP), which inhibits cellular DNA synthesis in CD4(+) and CD8(+) cells. In this study, we evaluated whether fludarabine-based pharmacologic biomarkers were associated with clinical outcomes in HCT recipients.

METHODS

Participants with hematologic diseases were conditioned with fludarabine and low-dose total body irradiation (TBI) followed by allogeneic HCT and post-grafting immunosuppression. After fludarabine administration, we evaluated pharmacological biomarkers for fludarabine-F-ara-A area under the curve (AUC) and the ratio of circulating CD4(+) and CD8(+) cells (CD4(+)/CD8(+) ratio) after fludarabine administration-in 102 patients; F-ara-ATP accumulation rate in enriched CD4(+) and CD8(+) cells was evaluated in 36 and 34 patients, respectively.

RESULTS

Interpatient variability in the pharmacological biomarkers was high, ranging from 3.7-fold (F-ara-A AUC) to 39-fold (F-ara-ATP in CD8(+) cells). Circulating CD8(+) cells were more sensitive to fludarabine administration. A population pharmacokinetic-based sampling schedule successfully allowed for estimation of F-ara-A AUC in this outpatient population. There was a poor correlation between the F-ara-AUC and the F-ara-ATP accumulation rate in CD4(+) (R (2) = 0.01) and CD8(+) cells (R (2) = 0.00). No associations were seen between the four biomarkers and clinical outcomes (day +28 donor T cell chimerism, acute graft-versus-host disease (GVHD), neutrophil nadirs, cytomegalovirus reactivation, chronic GVHD, relapse, non-relapse mortality, or overall mortality).

CONCLUSIONS

Considerable interpatient variability exists in pharmacokinetic and fludarabine-based biomarkers, but these biomarkers are not associated with clinical outcomes in fludarabine/TBI-conditioned patients.

Hematopoietic Stem Cell Transplantation for Severe Combined Immunodeficiency

Hematopoietic stem cell transplantation (HSCT) is an effective approach for the treatment of severe combined immunodeficiency (SCID). However, SCID is not a homogeneous disease, and the treatment required for successful transplantation varies significantly between SCID subtypes and the degree of HLA mismatch between the best available donor and the patient. Recent studies are beginning to more clearly define this heterogeneity and how outcomes may vary. With a more detailed understanding of SCID, new approaches can be developed to maximize immune reconstitution, while minimizing acute and long-term toxicities associated with chemotherapy conditioning.

Population pharmacokinetic/dynamic model of lymphosuppression after fludarabine administration

PURPOSE

Quantitative relationships between 9-β-D-arabinofuranosyl-2-fluoroadenine (F-ara-A) concentrations and lymphosuppression have not been reported, but would be useful for regimen design. A population pharmacokinetic/pharmacodynamic model was constructed in this study using data from 41 hematopoietic cell transplant (HCT) recipients conditioned with busulfan in combination with fludarabine (total dose 120 mg/m², Protocol 1519) or with fludarabine (total dose 250 mg/m²) with rabbit antithymocyte globulin (rATG, Protocol 2041).

METHODS

Individual pharmacokinetic parameters were fixed to post hoc Bayesian estimates, and circulating absolute lymphocyte counts (ALC) were obtained during the 3 weeks prior to graft infusion. A semi-physiological cell-kill model with three lymphocyte transit compartments was applied and aptly characterized the time course of suppression of circulating ALC by fludarabine administration. Drug- and system-specific parameters were estimated using a maximum likelihood expectation maximization algorithm, and the final model was qualified using an internal visual predictive check.

RESULTS

The final model successfully characterized the time course and variability in ALC. Pharmacodynamic parameters exhibited considerable between subject variability (38.9-211 %). The HCT protocol was the only covariate associated with the pharmacodynamic parameters, specifically the lymphocyte kill rate, the transit rate between lymphocyte compartments, and the baseline ALC.

CONCLUSIONS

This model can be used to simulate the degree of lymphosuppression for design of future fludarabine-based conditioning regimens.

Simultaneous determination of fludarabine and clofarabine in human plasma by LC-MS/MS

A method for quantification of fludarabine (FDB) and clofarabine (CFB) in human plasma was developed with an API5000 LC-MS/MS system. FDB and CFB were extracted from EDTA plasma samples by protein precipitation with trichloroacetic acid. Briefly, 50 μL plasma sample was mixed with 25 μL internal standard (50 ng/mL aqueous 2-Cl-adensosine) and 25 μL 20% trichloroacetic acid, centrifuged at 25,000 × g (20,000 rpm) for 3 min, and then transfered to an autosampler vial. The extracted sample was injected onto an Eclipse extend C18 column (2.1 mm×150 mm, 5 μm) and eluted with 1mM NH4OH (pH 9.6) - acetonitrile in a gradient mode. Electrospray ionization in positive mode (ESI(+)) and multiple reaction monitoring (MRM) were used, and ion pairs 286/134 for FDB, 304/170 for CFB and 302/134 for the internal standard were selected for quantification. The retention times were typically 3.72 min for FDB, 4.34 min for the internal standard, 4.79 min for CFB. Total run time was 10 min per sample. Calibration range was 0.5-80 ng/mL for CFB and 2-800 ng/mL for FDB. The method was applied to a clinical pharmacokinetic study in pediatric patients.

Fludarabine and exposure-targeted busulfan compares favorably with busulfan/cyclophosphamide-based regimens in pediatric hematopoietic cell transplantation: maintaining efficacy with less toxicity

Busulfan (Bu) is used as a myeloablative agent in conditioning regimens before allogeneic hematopoietic cell transplantation (allo-HCT). In line with strategies explored in adults, patient outcomes may be optimized by replacing cyclophosphamide (Cy) with or without melphalan (Mel) with fludarabine (Flu). We compared outcomes in 2 consecutive cohorts of HCT recipients with a nonmalignant HCT indication, a myeloid malignancy, or a lymphoid malignancy with a contraindication for total body irradiation (TBI). Between 2009 and 2012, 64 children received Flu + Bu at a target dose of 80-95 mg·h/L, and between 2005 and 2008, 50 children received Bu targeted to 74-80 mg·h/L + Cy. In the latter group, Mel was added for patients with myeloid malignancy (n = 12). Possible confounding effects of calendar time were studied in 69 patients receiving a myeloablative dose of TBI between 2005 and 2012. Estimated 2-year survival and event-free survival were 82% and 78%, respectively, in the FluBu arm and 78% and 72%, respectively, in the BuCy (Mel) arm (P = not significant). Compared with the BuCy (Mel) arm, less toxicity was noted in the FluBu arm, with lower rates of acute (noninfectious) lung injury (16% versus 36%; P = .007), veno-occlusive disease (3% versus 28%; P = .003), chronic graft-versus-host disease (9% versus 26%; P = .047), adenovirus infection (3% versus 32%; P = .001), and human herpesvirus 6 infection reactivation (21% versus 44%; P = .005). Furthermore, the median duration of neutropenia was shorter in the FluBu arm (11 days versus 22 days; P < .001), and the patients in this arm required fewer transfusions. Our data indicate that Flu (160 mg/m(2)) with targeted myeloablative Bu (90 mg·h/L) is less toxic than and equally effective as BuCy (Mel) in patients with similar indications for allo-HCT.

A pilot pharmacologic biomarker study in HLA-haploidentical hematopoietic cell transplant recipients

PURPOSE

Eleven patients diagnosed with various hematologic malignancies receiving an HLA-haploidentical hematopoietic cell transplant (HCT) participated in an ancillary biomarker trial. The goal of the trial was to evaluate potential pharmacologic biomarkers pertinent to the conditioning regimen [fludarabine monophosphate (fludarabine) and cyclophosphamide (CY)] or postgrafting immunosuppression [CY and mycophenolate mofetil (MMF)] in these patients.

METHODS

We characterized the interpatient variability of nine pharmacologic biomarkers. The biomarkers evaluated were relevant to fludarabine (i.e., area under the curve (AUC) of 2-fluoro-ara-A or F-ara-A), CY (i.e., AUCs of CY and four of its metabolites), and MMF (i.e., total mycophenolic acid (MPA) AUC, unbound MPA AUC, and inosine monophosphate dehydrogenase (IMPDH) activity).

RESULTS

Interpatient variability in the pharmacologic biomarkers was high. Among those related to HCT conditioning, the interpatient variability ranged from 1.5-fold (CY AUC) to 4.0-fold (AUC of carboxyethylphosphoramide mustard, a metabolite of CY). Among biomarkers evaluated as part of postgrafting immunosuppression, the interpatient variability ranged from 1.7-fold (CY AUC) to 4.9-fold (IMPDH area under the effect curve). There was a moderate correlation (R (2) = 0.441) of within-patient 4-hydroxycyclophosphamide formation clearance.

CONCLUSIONS

Considerable interpatient variability exists in the pharmacokinetic and drug-specific biomarkers potentially relevant to clinical outcomes in HLA-haploidentical HCT recipients. Pharmacodynamic studies are warranted to optimize the conditioning regimen and postgrafting immunosuppression administered to HLA-haploidentical HCT recipients.

Improved quantitative method for fludarabine in human plasma by liquid chromatography and tandem mass spectrometry

An improved quantitative assay was developed and validated for fludarabine in human plasma. Fludarabine and its internal standard, cladribine, were separated on a C18 analytical column after sample purification by strong anion-exchange solid-phase extraction. Quantitation was performed by electrospray triple-quadrupole mass spectrometry in positive ionization mode using multiple-reaction monitoring. This assay had excellent inter- and intra-assay precisions within 8%, and accuracies ranging from 100 to 116%. The method was linear within the concentration range of 0.2-250ng/mL using 100μL of plasma with mean R(2)=0.9999. The extraction recoveries were 85% for fludarabine and 95% for the internal standard, which represent a significant improvement over the previously published methods. We utilized this method for pharmacokinetic (PK) investigations in 215 patients. Interference peaks constantly observed in each blank plasma sample were well resolved from fludarabine using our optimized LC-MS/MS conditions, demonstrating the reliability of this improved assay. The validated method will be further applied to PK studies within our bone marrow transplant program, which will allow for optimal dose and scheduling of fludarabine in these patients.

Nonmyeloablative conditioning regimen to increase engraftment of gene-modified hematopoietic stem cells in young rhesus monkeys

Immune responses to transgene products may lead to rejection of transduced cells, limiting successful gene therapy for genetic diseases. While moderate dosages of chemotherapeutic agents such as busulfan may increase hematopoietic stem cells (HSC) engraftment, they are not immune suppressive and do not abrogate immune responses to transgene products. Studies focused on nonmyeloablative conditioning with busulfan ± fludarabine in a clinically relevant monkey model to induce immune suppression to allow cells expressing a foreign transgene product to persist. Bone marrow CD34(+) HSC were transduced in two equal fractions using simian immunodeficiency virus (SIV)-based lentiviral vectors carrying a nonexpressed DNA sequence tag (NoN) and the green fluorescent protein (GFP) reporter gene. Post-transplant there was no evidence of elimination of cells containing the potentially immunogenic GFP gene; several recipients had stable persistence of cells, and no differences were detected with fludarabine, which was rapidly cleared. Antibodies and cellular immune responses to GFP developed in recipients with the highest levels of GFP-marked cells, although these cells were not eliminated. These studies establish a clinically relevant pediatric primate model to assess the effects of conditioning regimens on the engraftment of transduced HSC and the immune responses to cells expressing a foreign gene product.

Cytotoxic purine nucleoside analogues bind to A1, A2A, and A3 adenosine receptors

Fludarabine, clofarabine, and cladribine are anticancer agents which are analogues of the purine nucleoside adenosine. These agents have been associated with cardiac and neurological toxicities. Because these agents are analogues of adenosine, they may act through adenosine receptors to elicit their toxic effects. The objective of this study was to evaluate the ability of cytotoxic nucleoside analogues to bind and activate adenosine receptor subtypes (A(1), A(2A), A(2B), and A(3)). Radioligand binding studies utilizing Chinese hamster ovary cells, stably transfected with adenosine A(1), A(2A), or A(3) receptor subtype, were used to assess the binding affinities of these compounds, whereas adenylyl cyclase activity was used to assess the binding to A(2B) receptors. Clofarabine and cladribine both bound to the A(2A) receptor with a K (i) of 17 and 15 μM, respectively. Clofarabine was the only adenosine analogue to bind to the A(3) receptor with a K (i) of 10 μM, and none of these compounds bound to the A(2B) receptor. Results show that clofarabine, cladribine, and fludarabine bind to the A(1) receptor. In addition, clofarabine, cladribine, and fludarabine were A(1) agonists (IC(50) 3.1, 30, and 30 μM, respectively). Neither pyrimidine nucleoside analogues gemcitabine nor cytarabine associated with any of the adenosine receptor subtypes (K (i) > 100μM). This is the first report of an interaction between all adenosine receptor subtypes and chemotherapeutic nucleoside analogues commonly used in the treatment of cancer. Therefore, activation of these receptors may be at least one mechanism through which fludarabine-associated toxicity occurs.