Influence of anti-thymocyte globulin plasma levels on outcome parameters in stem cell transplanted children

Patients Beyond the Optimal Range of rATG-AUC Still Benefit from the Targeted Dosing Strategy in Unmanipulated Haplo-PBSCT

Rabbit antithymocyte globulin (rATG) is widely used in allogeneic hematopoietic stem cell transplantation to prevent graft failure and severe graft-versus-host disease (GVHD). We developed a rATG-targeted dosing strategy based on the optimal areas under the concentration-time curve (AUC) of active rATG. This study compared the outcomes of the optimal AUC arm with nonoptimal AUC arm to assess the effect of the rATG-targeted dosing strategy. Eighty patients (median age: 32 years) with hematological malignancies who received their first haplo-PBSCT were enrolled successively. With rATG-targeted dosing, the AUC values of 60 patients (75%, optimal AUC arm) fell within the optimal range (100-148.5 UE/mL/day) and 20 fell beyond this range (nonoptimal AUC arm). In the historical control group of 102 haplo-PBSCT patients who received a fixed dose of rATG (10 mg/kg), less patients fell within the optimal range (57.8%, P = .016). Looking at the nonoptimal AUC arms in both groups, lower cumulative incidence of CMV was noted in the targeted dosing group compared with the historical control group(50.0%, 95% CI, 30.8%-72.9% versus 81.4%, 95% CI, 68.6%-91.3%; P = .004). The cumulative incidences of EBV, relapse, overall survival and disease-free survival tended to be superior in the nonoptimal AUC arm in the targeted dosing group compared with the historical control. In the targeted dosing group, the cumulative incidence of cytomegalovirus (CMV) reactivation on day +180 tended to be lower in the optimal AUC arm (30.0%, 95% CI, 20.1%-43.3%) compared with the nonoptimal AUC arm (50.0%, 95% CI, 30.8%-72.9%, P = .199) without statistical difference. There were no significant differences of acute or chronic GVHD, relapse, nonrelapse mortality, overall survival, disease-free survival or lymphocyte reconstitution between the two arms. In conclusion, the rATG-targeted dosing strategy made the exposure of active rATG in more patients with the optimal AUC range. Even patients who fell beyond this range would still benefit from the strategy.

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.

Impact of Treosulfan Exposure on Early and Long-Term Clinical Outcomes in Pediatric Allogeneic Hematopoietic Stem Cell Transplantation Recipients: A Prospective Multicenter Study

Treosulfan-based conditioning has gained popularity in pediatric allogeneic hematopoietic stem cell transplantation (HSCT) because of its presumed favorable efficacy and toxicity profile. Treosulfan is used in standardized dosing regimens based on body surface area. The relationships between systemic treosulfan exposure and early and long-term clinical outcomes in pediatric patients undergoing allogeneic HSCT for nonmalignant diseases remain unclear. In this a multicenter, prospective observational study, we assessed the association between treosulfan exposure and early and, in particular, long-term clinical outcomes. Our study cohort comprised 110 pediatric patients with nonmalignant diseases who underwent HSCT between 2011 and 2019 in Leiden, The Netherlands and Rome, Italy. Blood samples were collected, and treosulfan area under the receiver operating characteristic curve (AUC_0-∞) was estimated as a measure of exposure. Cox proportional hazard survival analyses were performed to assess the relationships between treosulfan exposure and overall survival (OS) and event-free survival (EFS). The predictive value of systemic treosulfan exposure for the occurrence of toxicity within 28 days was evaluated using a multivariable logistic regression analysis. In the overall cohort, OS and EFS at 2 years were 89.0% and 75.3%, respectively, with an excellent OS of 97% in children age <2 years. The occurrence of grade II-IV acute graft-versus-host disease, the level of 1-year whole blood chimerism, and 2-year OS and EFS were not correlated with treosulfan exposure. The occurrence of skin toxicity (odds ratio [OR], 3.97; 95% confidence interval [CI], 1.26-13.68; P = .02) and all-grade mucositis (OR, 4.43; 95% CI, 1.43-15.50; P = .02), but not grade ≥2 mucositis (OR, 1.51; 95% CI, 0.52 to 4.58; P = .46) was related to high treosulfan exposure (>1750 mg*h/L). Our study demonstrates that standardized treosulfan-based conditioning results in a favorable OS and EFS in infants and children with nonmalignant diseases, independent of interindividual variation in treosulfan exposure. These outcomes can be achieved without the need for therapeutic drug monitoring, thereby emphasizing the advantage of treosulfan use in this category of patients. Although higher treosulfan exposure increases the risk of skin toxicity, there is no absolute necessity for therapeutic drug monitoring if proper preventive skin measures are taken. More research is needed to assess whether deescalation of treosulfan doses is possible to minimize early and long-term toxicity without compromising efficacy.