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

Umbilical Cord Blood Reduced Relapse but Increased Nonrelapse Mortality Compared to Matched Unrelated Donor Transplantation in Pediatric Acute Myeloid Leukemia With Active Disease: A CIBMTR 2008 to 2017 Analysis of Donor Source and Residual Disease

Umbilical cord blood (UCB) and matched unrelated donors (MUD) are common alternative donor options in children with high-risk acute myeloid leukemia (AML). Emerging evidence suggests an augmented graft-versus-leukemia (GVL) effect of UCB, but uncertainties persist due to the heterogeneity of the hematopoietic cell transplantation (HCT) characteristics in the previous studies. We reviewed 1148 patients aged ≤18 years with AML, who underwent the first HCT between 2008 to 2017, using a publicly available dataset from the Center for International Blood and Marrow Transplantation Research (CIBMTR) registry data. Multivariable analyses evaluated predictors of DFS and other clinical outcomes, factoring in graft source, conditioning regimen, patient age, cytogenetic risk, and HCT year (significance at P < .01). Residual disease status was assessed both as a covariate and as a stratifying factor. Additionally, the differential effects of conditioning regimens were analyzed specifically within the UCB cohort. UCB was used most frequently (33.8%) followed by MUD (29.1%), both of which had comparable DFS and overall survival. In patients with minimal residual disease or not in remission prior to HCT, human-leukocyte antigen (HLA) ≤5/8 matched UCB was associated with lower relapse rates than MUD (hazard risk [HR]: 0.25 and 0.29, P = .005 and .006, respectively) but with increased nonrelapse mortality (HR: 32.8 and 7.5, P = .001 and .012, respectively). Conditioning regimens varies by graft type; total body irradiation (TBI)-based regimens, primarily combined with cyclophosphamide and fludarabine, were more common in the UCB cohort (45% in UCB versus 19% in the other grafts, P < .001). Within the 388 patients received UCB, multivariable analysis demonstrated comparable DFS and OS across variable busulfan- and TBI-based regimens, with no trend of superiority for either approach. In conclusion, highly HLA-mismatched UCB reduced relapse in pediatric AML with higher disease burden but increased nonrelapse mortality, resulting in similar DFS to MUD. Improved supportive care and toxicity mitigation may improve the outcomes of UCB transplant. Overall, UCB should be considered a viable alternative graft source with equally favorable outcomes to MUD. Further research is warranted to refine conditioning regimen, including TBI- and busulfan-based strategies, mitigate toxicity, and improve supportive care to optimize UCB HCT outcomes.

Comparison of busulfan pharmacokinetics between four-times-daily and once-daily administration in pediatric patients: a preliminary prospective observational trial

Therapeutic drug monitoring (TDM) of busulfan (BU) is useful for achieving the target area under the curve (AUC) because its effective plasma-concentration range is narrow. This preliminary observational study evaluated the pharmacokinetic (PK) parameters of BU administered four times daily or once daily to pediatric patients. The plasma concentrations were measured at both the test dose and first dose, and the doses on day 1 and days 2-4 were determined based on each TDM. A comparison of PK parameters between four-times-daily and once-daily administration was performed for both the test dose and first dose of BU. Of the 11 patients, five received four-times-daily BU and six received once-daily BU. The Vd for once-daily administration was higher than that for four-times-daily administration for the first dose but not for the test dose. The ratio of actual AUC for the first dose to estimated AUC guided by the test dose was lower with once-daily administration than with four-times-daily administration. These results indicate that the PK parameters of BU administered once daily are challenging to predict based on the TDM of the test dose. TDM should be considered on day 1 to achieve the target AUC, especially with once-daily administration.

Childhood myelodysplastic syndromes: Is cytoreductive therapy useful before allogeneic hematopoietic stem cell transplantation?

For most patients with childhood myelodysplastic syndrome (cMDS), allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains the only curative option. In the case of increased blasts (cMDS-IB), the benefit of pretransplant cytoreductive therapy remains controversial. In this multicenter retrospective study, the outcomes of all French children who underwent allo-HSCT for cMDS reported in the SFGM-TC registry between 2000 and 2020 were analyzed (n = 84). The median age at transplantation was 10.2 years. HSCT was performed from matched sibling donors (MSD) in 29% of the cases, matched unrelated donors (MUD) in 44%, haploidentical in 6%, and cord blood in 21%. Myeloablative conditioning was used in 91% of cases. Forty-eight percent of patients presented with cMDS-IB at diagnosis (median BM blasts: 8%). Among them, 50% received pretransplant cytoreductive therapy. Five-year overall survival (OS), cumulative incidence of nonrelapse mortality (NRM), and relapse were 67%, 26%, and 12%, respectively. Six-month cumulative incidence of grade II-IV acute graft-versus-host disease was 46%. Considering the whole cohort, age under 12, busulfan/cyclophosphamide/melphalan conditioning or MUD were associated with poorer 5-year OS. In the cMDS-IB subgroup, pretransplant cytoreductive therapy was associated with a better OS in univariate analysis. This seems to be mainly due to a decreased NRM since no impact on the incidence of relapse was observed. Overall, those data may argue in favor of cytoreduction for cMDS-IB. They need to be confirmed on a larger scale and prospectively.

Chemotherapy-induced intestinal epithelial damage directly promotes galectin-9-driven modulation of T cell behavior

The intestine is vulnerable to chemotherapy-induced damage due to the high rate of intestinal epithelial cell (IEC) proliferation. We have developed a human intestinal organoid-based 3D model system to study the direct effect of chemotherapy-induced IEC damage on T cell behavior. Exposure of intestinal organoids to busulfan, fludarabine, and clofarabine induced damage-related responses affecting both the capacity to regenerate and transcriptional reprogramming. In ex vivo co-culture assays, prior intestinal organoid damage resulted in increased T cell activation, proliferation, and migration. We identified galectin-9 (Gal-9) as a key molecule released by damaged organoids. The use of anti-Gal-9 blocking antibodies or CRISPR/Cas9-mediated Gal-9 knock-out prevented intestinal organoid damage-induced T cell proliferation, interferon-gamma release, and migration. Increased levels of Gal-9 were found early after HSCT chemotherapeutic conditioning in the plasma of patients who later developed acute GVHD. Taken together, chemotherapy-induced intestinal damage can influence T cell behavior in a Gal-9-dependent manner which may provide novel strategies for therapeutic intervention.

"Prehabilitation" for Pediatric Patients With Cancer Before Undergoing Hematopoietic Stem Cell Transplantation

Hematopoietic stem cell transplantation (HSCT) is associated with significant physical debility. Studies have suggested that physical activity can improve endurance and strength. However, studies have not yet investigated "prehabilitation," exercise before HSCT, to improve functional outcomes. We describe the impact of exercise therapy on physical debility in children undergoing HSCT to inform the implementation of prehabilitation. This review was conducted through a search of the electronic database PubMed. Articles included were those with original research, including randomized control trials, prospective studies, case controls, and retrospective studies. Eleven of the 191 resulting studies met our review criteria. None focused on prehabilitation, but instead on interventions during HSCT. Ten studies showed improvement or maintenance of strength, endurance, stretching, or aerobic fitness. This review shows that exercise therapy can positively affect outcomes in patients undergoing HSCT. Further investigations are needed to determine whether prehabilitation has better results than concurrent exercise.

Chemotherapy-induced intestinal injury promotes Galectin-9-driven modulation of T cell function

The intestine is vulnerable to chemotherapy-induced toxicity due to its high epithelial proliferative rate, making gut toxicity an off-target effect in several cancer treatments, including conditioning regimens for allogeneic hematopoietic cell transplantation (allo-HCT). In allo-HCT, intestinal damage is an important factor in the development of Graft-versus-Host Disease (GVHD), an immune complication in which donor immune cells attack the recipient's tissues. Here, we developed a novel human intestinal organoid-based 3D model system to study the direct effect of chemotherapy-induced intestinal epithelial damage on T cell behavior. Chemotherapy treatment using busulfan, fludarabine, and clofarabine led to damage responses in organoids resulting in increased T cell migration, activation, and proliferation in ex- vivo co-culture assays. We identified galectin-9 (Gal-9), a beta-galactoside-binding lectin released by damaged organoids, as a key molecule mediating T cell responses to damage. Increased levels of Gal-9 were also found in the plasma of allo-HCT patients who later developed acute GVHD, supporting the predictive value of the model system in the clinical setting. This study highlights the potential contribution of chemotherapy-induced epithelial damage to the pathogenesis of intestinal GVHD through direct effects on T cell activation and trafficking promoted by galectin-9.

Therapeutic Drug Monitoring of Conditioning Agents in Pediatric Allogeneic Stem Cell Transplantation; Where do We Stand?

Allogeneic hematopoietic stem cell transplantation (HSCT) is an established curative treatment that has significantly improved clinical outcome of pediatric patients with malignant and non-malignant disorders. This is partly because of the use of safer and more effective combinations of chemo- and serotherapy prior to HSCT. Still, complications due to the toxicity of these conditioning regimens remains a major cause of transplant-related mortality (TRM). One of the most difficult challenges to further improve HSCT outcome is reducing toxicity while maintaining efficacy. The use of personalized dosing of the various components of the conditioning regimen by means of therapeutic drug monitoring (TDM) has been the topic of interest in the last decade. TDM could play an important role, especially in children who tend to show greater pharmacokinetic variability. However, TDM should only be performed when it has clear added value to improve clinical outcome or reduce toxicity. In this review, we provide an overview of the available evidence for the relationship between pharmacokinetic parameters and clinical outcome or toxicities of the most commonly used conditioning agents in pediatric HSCT.

Clofarabine-fludarabine-busulfan in HCT for pediatric leukemia: an effective, low toxicity, TBI-free conditioning regimen

CloFluBu-conditioning results in encouraging EFS for ALL and AML, with low TRM, limited incidence of aGvHD and GF, and no cases of VOD.

Minimal residual disease status prior to transplantation impacted outcome due to increased relapse risk in both AML and ALL patients.

We prospectively studied clofarabine-fludarabine-busulfan (CloFluBu)-conditioning in allogeneic hematopoietic cell therapy (HCT) for lymphoid and myeloid malignancies and hypothesized that CloFluBu provides a less toxic alternative to conventional conditioning regimens, with adequate antileukemic activity. All patients receiving their first HCT, from 2011-2019, were included and received CloFluBu. The primary endpoint was event-free survival (EFS). Secondary endpoints were overall survival (OS), graft-versus-host disease (GvHD)-relapse-free survival (GRFS), treatment-related mortality (TRM), cumulative incidence of relapse (CIR), acute and chronic GvHD (aGvHD and cGvHD), and veno-occlusive disease (VOD). Cox proportional hazard and Fine and Gray competing-risk models were used for data analysis. One hundred fifty-five children were included: 60 acute lymphoid leukemia (ALL), 69 acute myeloid leukemia (AML), and 26 other malignancies (mostly MDS-EB). The median age was 9.7 (0.5 to 18.6) years. Estimated 2-year EFS was 72.0% ± 6.0 in ALL patients, and 62.4% ± 6.0 in AML patients. TRM in the whole cohort was 11.0% ± 2.6, incidence of aGvHD 3 to 4 at 6 months was 12.3% ± 2.7, extensive cGvHD at 2 years was 6.4% ± 2.1. Minimal residual disease-positivity prior to HCT was associated with higher CIR, both in ALL and AML. CloFluBu showed limited toxicity and encouraging EFS. CloFluBu is a potentially less toxic alternative to conventional conditioning regimens. Randomized prospective studies are needed.

The Role of Allogeneic Hematopoietic Stem Cell Transplantation in Pediatric Leukemia

Allogeneic hematopoietic stem cell transplantation (HSCT) offers potentially curative treatment for many children with high-risk or relapsed acute leukemia (AL), thanks to the combination of intense preparative radio/chemotherapy and the graft-versus-leukemia (GvL) effect. Over the years, progress in high-resolution donor typing, choice of conditioning regimen, graft-versus-host disease (GvHD) prophylaxis and supportive care measures have continuously improved overall transplant outcome, and recent successes using alternative donors have extended the potential application of allotransplantation to most patients. In addition, the importance of minimal residual disease (MRD) before and after transplantation is being increasingly clarified and MRD-directed interventions may be employed to further ameliorate leukemia-free survival after allogeneic HSCT. These advances have occurred in parallel with continuous refinements in chemotherapy protocols and the development of targeted therapies, which may redefine the indications for HSCT in the coming years. This review discusses the role of HSCT in childhood AL by analysing transplant indications in both acute lymphoblastic and acute myeloid leukemia, together with current and most promising strategies to further improve transplant outcome, including optimization of conditioning regimen and MRD-directed interventions.

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.