Alice Bertaina

Background: Acute graft-versus-host disease (aGVHD) is a leading cause of morbidity and mortality following pediatric hematopoietic stem cell transplantation (HSCT). Approximately half of children achieve complete response (CR) to corticosteroids, whereas steroid-refractory (SR) disease carries a 1–2-year mortality of 41–44%. Mortality risk is 2.6-fold higher in children > 13.9 years, and respiratory failure accounts for 26% of deaths. Existing second-line agents—ruxolitinib, tocilizumab, or extracorporeal photopheresis—have delayed onset or high toxicity. Begelomab (BEGESAND^®), a monoclonal antibody targeting CD26/dipeptidyl peptidase-4 (DPP4), inhibits CD26-mediated T-cell activation and has demonstrated 75% response in adults with minimal toxicity. However, pediatric data are lacking. Methods: We retrospectively reviewed five consecutive pediatric patients (ages 3–20 years) treated with Begelomab (BEGESAND^®) for SR (n = 4) or steroid-dependent (SD; n = 1) aGVHD between 2017–2021 under emergency IND authorization. Begelomab (BEGESAND^®) was administered intravenously at 2.7 mg/m²/day on days 1–5, 10, 14, 17, 21, 24, and 28. GVHD was graded by MAGIC criteria; flow cytometry and immunohistochemistry (IHC) assessed CD26 expression and immune effects. Results: All patients had grade IV disease after ≥2 prior agents. Two with pre-existing sepsis died early, before treatment response could be assessed. Of three evaluable patients, two (67%) achieved CR within 21 days and one achieved durable control by 6 months. All three remain alive; no Begelomab (BEGESAND^®)-related toxicity, cytopenia, or new infections occurred. Flow cytometry showed preserved T-cell subsets, and IHC demonstrated CD26 localization at sites of epithelial injury. Conclusions: Begelomab (BEGESAND^®) showed promising timely and durable responses with excellent safety in pediatric SR/SD-aGVHD, supporting further evaluation in multicenter pediatric trials.

This retrospective registry-based study investigated the role of acute GvHD in the largest reported pediatric population with acute lymphoblastic leukemia (ALL) undergoing allogeneic stem cell transplantation (HSCT). The study included 3328 children. Median age was 9.6 years (IQR 6–13.9 and range 0.4–18). Forty-nine percent were transplanted from an MSD, 37% from MUD, 14% from MMUD; 68% received a TBI-based conditioning. CSA alone or in combination with methotrexate/MMF was administered as GVHD prophylaxis in 94%. The 100-day cumulative incidence of grade II–IV acute GVHD (aGVHD) was 35% (95% CI: 34–37), while that of grade III–IV was 11% (95% CI: 10–12). Two-year cumulative incidence of chronic GVHD (cGVHD) was 17% (95% CI: 15–18)/extensive cGVHD 8% (95% CI: 7–9). With a median follow-up of 3.1 years, OS, leukemia-free survival (LFS), and GVHD-free/relapse-free survival were 74% (95% CI 72–76), 65% (95% CI 64–67) and 51% (95% CI 49–53), respectively. Using multivariable Cox models in 100-day landmark analysis, any degree of aGVHD was associated with reduced risk of relapse; grade III–IV significantly increased NRM and reduced OS; grade II aGVHD offers the best chances of achieving prolonged LFS (HR = 0.78 (0.64–0.94), p = 0.008). Overall, these data confirm that grade II aGvHD prevents the occurrence of leukaemia relapse without causing unacceptable mortality.

Juvenile myelomonocytic leukemia (JMML) is a fatal pediatric cancer characterized by classical features such as splenomegaly, monocytosis, and granulocyte-macrophage colony-stimulating factor (GM-CSF) hypersensitivity, with RAS pathway mutations being the major drivers. Mutations causing loss-of-function of the Neurofibromin 1 gene (NF1LOF) occur in ∼20% of patients with JMML. NF1LOF drives upregulation of RAS/MAPK/PI3K pathways that leads to aggressive proliferation/differentiation of immature myeloid cells. Hematopoietic stem cell transplantation is the only curative option, but relapse occurs in ∼50% of patients, indicating an urgent need for novel and targeted therapeutic strategies. However, low patient sample availability and a lack of reliable disease models have made it difficult to study and treat JMML. Using CRISPR/Cas9, we have generated NF1LOF in human umbilical cord blood-derived hematopoietic stem and progenitor cells (HSPCs). We achieved a high gene knockout rate of ∼89% and concomitant loss of NF1 protein in the modified HSPCs. Importantly, NF1LOF cells displayed marked GM-CSF hypersensitivity in in vitro colony-forming unit assays, mirroring JMML. When transplanted into NSG-SGM3 mice, they caused rapid lethality (median survival of 32 days), myeloid expansion, tissue infiltration (spleen, liver, and lungs), and specific upregulation of RAS/MAPK pathway and STAT5 genes, consistent with patient profiles. This first humanized NF1LOF mouse model recapitulates key JMML features, enabling investigation of disease mechanisms and targeted therapies.

Allogeneic hematopoietic cell transplantation (allo-HCT) is a curative option for patients with high-risk malignancies and nonmalignant disorders. Long-term survival depends on robust immune reconstitution (IR), which governs overall immune homeostasis and risks of infection, graft-versus-host disease, and relapse. However, despite its centrality to posttransplant outcomes, IR is not consistently monitored across transplant centers, limiting ability to generate meaningful, comparable, and translatable data. This review synthesizes current knowledge on numerical and functional IR milestones after allo-HCT, with a primary focus on flow cytometry-based monitoring of key immune cell subsets. Importantly, early CD4+ T-cell recovery (achieving >50 cells per μL by day 100 after transplant), is supported by strong clinical evidence and correlates with improved outcomes. Although emerging data suggest that additional subsets (CD8+ T cells, natural killer cells, B cells, naïve and recent thymic emigrant T cells, and γδ T cells) may also influence clinical trajectories, further harmonized, multicenter studies are needed to validate prognostic relevance across transplant settings. We propose practical, evidence-based guidelines for IR monitoring, including recommended time points, preferred assays, and flow cytometry panel components. Additionally, we highlight modifiable factors (eg, immunosuppressive drug exposures, graft manipulation) offering interventional opportunities for influencing IR. Harmonized monitoring strategies will support robust correlation between IR and clinical outcomes, guide real-time risk stratification, and facilitate the development of targeted, individualized transplant approaches. Standardization efforts led by consortia and registries are essential for advancing knowledge and optimizing care. We provide a roadmap for implementing uniform IR monitoring to improve outcomes and quality of life for allo-HCT recipients.

The interplay between graft-versus-host disease (aGVHD) and the graft-versus-leukemia (GVL) effect in children with acute myeloid leukemia (AML) undergoing allogeneic hematopoietic stem cell transplantation (HSCT) remains complex. This EBMT Pediatric Diseases Working Party (PDWP) retrospective analysis of 2374 pediatric AML patients evaluated the impact of aGVHD on relapse incidence (RI), non-relapse mortality (NRM), overall survival (OS), and leukemia-free survival (LFS). Grade III/IV aGVHD significantly reduced RI (HR: 0.61, p = 0.01) while significantly increasing NRM (HR: 4.51, p < 0.001), offsetting any benefits in OS and LFS. Grade II aGVHD increased NRM (HR: 2.07, p = 0.002) without affecting RI or OS, while grade I aGVHD had no significant impact on these outcomes. Patients with Grade II or higher aGVHD were at greater risk of both chronic (c)GvHD (HR: 1.98 for Grade II; HR: 4.33 for Grade III/IV, p < 0.001) and extensive cGVHD (HR: 2.52 for Grade II; HR: 4.91 for Grade III/IV, p < 0.001). These findings highlight the challenge of mitigating NRM while preserving the GVL effect to optimize disease control and long-term survival in pediatric AML. This study provides critical insights for refining post-transplant strategies in this population.

We hypothesized that the inferior disease-free survival (DFS) seen in older patients who underwent αβ-T-cell/CD19–depleted (AB-TCD) haploidentical hematopoietic cell transplantation (HCT) for hematologic malignancies is caused by excessive exposure to rabbit antithymocyte globulin (rATG; Thymoglobulin). Between 2015 and 2023, 163 patients with a median age of 13 years (range, 0.4-27.4) underwent AB-TCD haploidentical HCT for the treatment of acute lymphoblastic leukemia (n = 98), acute myeloid leukemia/myelodysplastic syndrome (n = 49), or other malignancies (n = 16) at 9 centers in 2 prospective trials. Exposures to rATG before and after HCT were predicted using a validated pharmacokinetic model. Receiver operating characteristic curves were used to identify the optimal target windows for rATG exposure in terms of outcomes. We identified 4 quadrants of rATG exposure, namely quadrant 1 (n = 52) with a high pre-HCT area under curve (AUC; ≥50 arbitrary units [AU] per day per milliliter) and a low post-HCT AUC (<12 AU per day per liter); quadrant 2 (n = 47) with a low pre- and post-HCT AUC; quadrant 3 (n = 13) with a low pre-HCT and a high post-HCT AUC; and quadrant 4 (n = 51) with a high pre- and post-HCT AUC. Quadrant 1 had a 3-year DFS of 86.5%, quadrant 2 had a DFS of 64.6%, quadrant 3 had a DFS of 32.9%, and for quadrant 4 it was 48.2%. An adjusted regression analysis demonstrated additional factors that were associated with an increased hazard for worse DFS, namely minimal residual disease (MRD) positivity and cytomegalovirus (CMV) R+/D− serostatus. Nonoptimal rATG exposure exhibited the strongest effect in unadjusted and adjusted (MRD status or CMV serostatus) analyses. High exposure to rATG after HCT was associated with inferior DFS following AB-TCD haploidentical HCT for pediatric patients with hematologic malignancies. Model-based dosing of rATG to achieve optimal exposure may improve DFS. These trials were registered at www.ClinicalTrials.gov as #NCT02646839 and #NCT04337515.