Black race and Hispanic ethnicity are associated with higher mortality in severe combined immunodeficiency (SCID) following hematopoietic cell transplantation (HCT), though mechanisms remain unclear. We evaluated 796 children with SCID who received nonsibling HCT between 1982 and 2020 using data from the Primary Immune Deficiency Treatment Consortium. Overall survival for Black (aHR 2.47, 95%CI 1.64, 3.71) and Asian/Pacific Islander patients (aHR 1.82, 95%CI 1.00, 3.30) was significantly lower compared with non-Hispanic White patients, while Hispanic patients had lower event-free survival (aHR 1.83, 95%CI 1.27, 2.63) compared with non-Hispanic White patients. Even after adjusting for age and infection, Black patients with SCID had more than twofold hazard of death compared with non-Hispanic White patients. NBS was associated with earlier diagnosis, reduced infection at HCT, and elimination of survival disparities between Black and non-Hispanic White patients. These findings suggest that universal, system-level interventions such as NBS can mitigate disparities in outcomes for children with SCID.

Abstract: In utero hematopoietic cell transplantation (IUHCT) has the potential to treat patients who have hemoglobinopathies by harnessing the unique period of fetal tolerance to maternal cells, thereby enabling semiallogeneic transplantation without conditioning or immunosuppression. We conducted a phase 1 clinical trial of IUHCT in fetuses with α-thalassemia major (ATM), a diagnosis that requires serial in utero transfusions (IUT) for survival. We also analyzed outcomes in fetuses with ATM treated with IUT alone in the same time period. Six fetuses underwent transplantation with maternal CD34+ cells (1.33 × 108 ± 2.67 × 107 cells per kg + 1% T cells) at 23.1 ± 1.1 weeks’ gestation. All received serial IUT and were delivered at, or near, term. Perinatal outcomes were broadly similar to those undergoing IUT alone. Two mothers received prophylactic antibiotics because of late positive cultures of harvested cells (without fetal adverse events). Low-level maternal microchimerism was detected in all recipients; T-cell hyporeactivity to maternal antigens was detected in 2 of 6 offspring but persisted in only 1 child. Cord blood from ATM-affected pregnancies demonstrated marked expansion of host hematopoietic stem and progenitor cells compared with healthy controls, suggesting a competitive disadvantage for donor cells in this disease context. Neurodevelopmental assessments were largely reassuring, with high quality-of-life scores. Overall, this protocol was safe and feasible but demonstrates the limitations of IUHCT for ATM without concurrent bone marrow conditioning. The favorable perinatal and neurologic outcomes in most offspring underscore the benefits of prenatal transfusions and the unmet medical need for developing definitive therapies for ATM. This trial was registered at www.clinicaltrials.gov as NCT02986698.

BACKGROUND:Transplant-associated thrombotic microangiopathy (TA-TMA) is a serious complication of hematopoietic cell transplantation (HCT) associated with high morbidity and mortality. The disease is driven by endothelial injury and complement dysregulation. Eculizumab, a complement C5 inhibitor, has been used off-label for TA-TMA, but reported outcomes are variable. Real-world response rates and predictors of treatment failure remain incompletely defined, particularly in children. Additionally, the optimal time point to assess treatment response has been identified as a key gap in the field. OBJECTIVE:To evaluate real-world response rates, predictors of nonresponse, and clinical outcomes among children treated with eculizumab for TA-TMA, and to identify an optimal time point for response assessment. METHODS:This retrospective study serially enrolled all patients treated with eculizumab for TA-TMA across 7 centers from 2015 to 2023. Organ, hematologic, and overall responses were defined using Consensus criteria as complete response (CR), clinically meaningful partial response (PR), or no response (NR). Clinical characteristics, treatment patterns, and outcomes were analyzed. Multivariable models were used to identify predictors of NR and mortality. RESULTS:Among 176 patients, 74% were allogeneic HCT recipients, 42% of whom had grade 3 to 4 acute graft-versus-host disease (GVHD). The cohort was enriched for severe disease, with 96% experiencing ≥1 organ dysfunction and 61.4% requiring intensive care. TA-TMA was diagnosed at a median of 49 days post-HCT. Patients received a median of 12 doses of eculizumab over a median duration of 10 weeks. Six months from treatment initiation, 24% achieved an overall CR, 19% achieved PR, and 57% had NR. Response rates were similar across high-risk subgroups defined by the Jodele criteria, Consensus criteria, and among allogeneic recipients with ≥1 organ dysfunction. Six-month nonrelapse mortality (NRM) was significantly lower among responders (CR/PR) compared with nonresponders (2.3% vs. 24.2%). Allogeneic HCT recipients were more likely to have NR than autologous recipients (HR, 1.84). Multiorgan dysfunction at TA-TMA diagnosis was independently associated with NR across transplant types. Patients who did not achieve at least a PR by day 45 had ≤25% likelihood of subsequent response and a 3.74-fold higher mortality risk compared with those with PR/CR at day 45. CONCLUSIONS:In this large pediatric cohort, approximately half of children with TA-TMA demonstrated clinical improvement after treatment with eculizumab, whereas the remaining half had no response and substantially worse survival. Multiorgan dysfunction was an adjusted risk factor for poor response across transplant types. Failure to achieve at least a partial response by day 45 strongly predicts poor response and is associated with an increased mortality risk, supporting this as a clinically meaningful time point to reassess therapy and consider alternative treatment strategies. © 2026 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

Introduction Chronic granulomatous disease (CGD) is an inborn error of immunity characterized by life-threatening infections and inflammatory complications. Allogeneic hematopoietic cell transplantation (HCT) is a curative therapy with event-free survival approaching 80% with human leukocyte antigen (HLA)-matched donors. Objectives In patients without HLA-matched donors, mismatched related or unrelated donors (MMRD or MMUD) have been used, but detailed comparisons of HCT outcomes for these two options are limited. Methods This study investigated 46 patients with CGD who underwent MMRD (n=24) or MMUD (n=22) HCT at 21 Primary Immunodeficiency Treatment Consortium (PIDTC) centers between 1996 and 2023. HLA match was classified based on typing for 8 alleles. Results Most (n=42, 91%) were male, most (n=38, 83%) had X-linked CGD. Patients with MMRD were significantly older at HCT [median 5.6 (range 0.5-23.6) vs. median 2.2 (range 0.7-19) years, p=0.010] and had a higher incidence of pre-HCT inflammatory disease (63% vs. 19%, p=0.009) than patients with MMUD. Because of this, a significantly higher percentage of MMRD patients received systemic corticosteroids in the year prior to HCT (46% vs. 14%, p=0.018). Severe inflammation was the primary indication for MMRD HCT (42%); in contrast, severe infection (45%) or a diagnosis of CGD (45%) were the primary indications for MMUD HCT. MMRD HCTs were more likely to be T cell depleted, 7 (29%) with TCRαβ/CD19+ depletion and 11 (46%) with post-HCT cyclophosphamide (PTCy). Conversely, 11 (50%) MMUD grafts underwent ex vivo T cell depletion, and no patients received PTCy. Most (n=34, 74%) patients received busulfan-based conditioning and most (n=38, 83%) received serotherapy. Graft-versus-host disease (GVHD) prophylaxis regimens were different between the two groups. MMRD patients received primarily PTCy-based regimens (46%) or no prophylaxis with TCRαβ/CD19+ depletion (29%) whereas patients with MMUD received primarily calcineurin inhibitor-based (73%) regimens. Estimated 5-year overall (MMRD 70%, MMUD 77%, p=0.645) and event-free survival (MMRD 58%, MMUD 58%, p=0.88) (Figure 1), cumulative incidence of graft failure (MMRD 21%, MMUD 11%, p=0.242), and rates of Grade II-IV acute (MMRD 31%, MMUD 21%, p=0.314), Grade III-IV acute (MMRD15%, MMUD 11%, p=0.XXX) and chronic (MMRD 29%, MMUD 12%, p=0.576) GVHD (Figure 2) were similar between the two groups. Pre-existing infections and inflammatory disease resolved post-HCT in both groups with no new CGD-related infections or inflammatory disease for up to 10 years of follow up. Conclusion MMRD and MMUD HCT are associated with higher rates of GVHD and lower event-free survival than HLA-matched HCT but are feasible options for CGD patients without an HLA-matched donor, offering long-term survival and resolution of disease. Future efforts should be focused on the reduction of graft failure and GVHD.

PURPOSE:Pediatric supportive care trials frequently rely on analyses of multiple clinically relevant outcomes, posing challenges for overall trial interpretation. Hierarchical composite endpoints (HCEs) rank relevant outcomes by prespecified clinical importance and offer potential advantages such as harmonizing trial conclusions. METHODS:We reanalyzed two randomized supportive care trials utilizing post-hoc HCE, each conducted through the Children's Oncology Group. ACCL0934 evaluated levofloxacin for prevention of bloodstream infection (BSI) in patients with acute leukemia (AL) or undergoing hematopoietic cell transplant (HCT) and was chosen because of observed multidimensional benefits of levofloxacin. ACCL0431 evaluated sodium thiosulfate (STS) for prevention of cisplatin-induced hearing loss. ACCL0431 analyses were performed for overall and localized disease subgroups, chosen due to conflicting effect directionality on hearing vs survival by cohort. We estimated treatment effects on HCEs using win-odds ratios (WO). For ACCL0934, the primary HCE included death, severe infection, BSI, and neutropenic fever. For ACCL0431, the HCE included death, relapse/progression, and hearing loss. RESULTS:In ACCL0934, levofloxacin reduced BSI incidence, but only with corresponding p-value <0.05 in the AL cohort (22% vs 43% on control; P =0.003; HCT: 11% versus 17% on control; P= 0.06). Using HCE reanalysis, the estimated win-odds achieved statistical significance in both cohorts (AL: WO=1.74, P= 0.002; HCT: WO=1.28, P= 0.031). In ACCL0431, HCE analyses resulted in an estimated null effect (WO=1) in the overall cohort but resulted in beneficial effects (WO>1) for analyses of the localized cohort. CONCLUSION:HCEs can provide a harmonized framework for interpreting complex supportive care trials by integrating outcomes of varying clinical importance. These post-hoc analyses should not be used to reinterpret either trial but motivate consideration of prospective use of HCE going forward.

Background Patients following Allogeneic Hematopoietic Stem Cell Transplantation (AlloHSCT), Solid Organ Transplantation (SOT) and with Primary Immunodeficiency (PID) are at high risk of developing refractory ADV and CMV infections. Viral-specific (VS) T-cell immune reconstitution is essential to control ADV and CMV infections in these immunocompromised hosts. We developed a methodology of related donor-derived ADV and CMV CTLs by utilizing the IFN-γ cytokine capture system (CCS®) on the CliniMACS Prodigy® device by direct selection of VS-CTLs. Objective To evaluate genomic and immunomic characteristics, safety and efficacy of related donor-derived VS-CTLs in immunocompromised hosts with refractory viral infection. (IND 17449, NCT03266627, NCT03266640). Methods Patients following HSCT, SOT or with PID with refractory CMV or ADV infection and/or intolerant to anti-viral therapy were eligible. Related donors (HLA ≥ 3/6 matches) who screened positive for memory VS-CTLs underwent non mobilized apheresis collection and donor-derived VS-CTLs were enriched as we previously described by direct selection using the ADV or CMV PepTivator® generously provided by Miltenyi. 0.5 × 104 CD3 cells/kg were infused into recipients every two weeks with a maximum of 5 doses until CR or DLT. CTL characterization was performed utilizing scRNAseq, mass cytometry, NanoString® Immunoprofiling and multidimensional flow cytometry. Results Among the ADV and CMV CTLs recipients (N=20, N=19), median age and gender were (10.1 [0.11-19.1] and 8.0 [0.7-19.0] yrs), M/F (8/12, 13/6), haploidentical vs HLA-matched original AlloHSCT donor (68% vs 32%, and 74% vs 26%), AlloHSCT/SOT/PID (100%, 0, 0) (90%, 5%, 5%), respectively. ADV and CMV CTL post enrichment CD4+/IFN-γ+ and CD8+/ IFN-γ+ (mean ± SEM) percentages are 45 ± 10.1% and 39 ± 8.7%, 42 ± 9.6% and 67.1 ± 15.4%, respectively. Viral CMV CTL demonstrated significant increase in CD8+ TEM, TEMRA and CD4TH, CD4TFH1 subtypes (p < 0.05, 0.05, 0.001, 0.01, Fig 1), distinct gene expression profile highly enriched for IFN-γ and IL-2 (Fig 2A), CD4+ and CD8+ memory T cells CD27-CD45RO+ (Fig 2B) and significantly increased central memory and effector memory T-cells (p<0.01, 0.001), respectively. Both ADV and CMV CTLs were well tolerated. One Grade I and 3 Grade II transient aGVHD, no CRS, IRR, ICANS, GF nor neurotoxicity were reported and resulted in 85% and 84% CR median of 34 (6-112) and 30 (6-82) days, 1 yr OS of 70% and 74%, and 1yr viral associated mortality of 5% and 0%, respectively (Fig 3). Conclusions Related ADV and CMV CTLs enrichment by direct selection using the CliniMACS Prodigy® CCS (IFN-γ) is feasible, well tolerated and are characterized by central & effector memory T-cells secreting IFN-γ and IL-2 and associated with a high CR rate and low 1 yr viral associated mortality.

The landscape of pediatric hematopoietic cell transplantation for nonmalignant disorders has evolved through disease-adapted conditioning, pharmacokinetic-guided dosing, expanded donor options, and gene therapy (GT). These advances have transformed curative strategies for children with select inborn errors of immunity, hemophagocytic lymphohistiocytosis, hemoglobinopathies, bone marrow failure syndromes, and select metabolic disorders. Early diagnosis, especially newborn screening for severe combined immunodeficiency, enables timely intervention, with contemporary series reporting more than 90% survival in select early-treated infants. Similarly, modern matched related donor transplantation for pediatric severe aplastic anemia approaches 98% 3-year survival. Fludarabine-based platforms combined with busulfan, melphalan, or treosulfan support durable engraftment with reduced toxicity, while matched unrelated, haploidentical, and cord blood donors expand access. GT now offers a parallel curative platform for select sickle cell disease, transfusion-dependent beta-thalassemia, and immunodeficiencies. For pediatricians, early referral before irreversible complications is critical. This review proposes a five-axis framework to guide referral, treatment selection, and survivorship planning.

Background: Hematopoietic stem cell transplantation–associated thrombotic microangiopathy (HSCT-TMA) is a rare, life-threatening complication that can result in multiorgan failure and death. Historically, severe HSCT-TMA has a 6-month survival rate as low as 18% in pediatric populations. Terminal complement activation is a key driver of disease. There are no approved therapies for HSCT-TMA.Ravulizumab (rav), a monoclonal antibody against C5, is being evaluated as a treatment for HSCT-TMA in adult and pediatric populations. Objective: To evaluate protocol-defined complete and partial TMA responses, hematologic response, survival, and nonrelapse mortality (NRM) after treatment with rav in children with HSCT-TMA. Methods: A phase 3, open-label, single-arm trial (NCT04557735) of rav was conducted in children aged ≥28 days to <18 years who: 1) received HSCT within 12 months; 2) had HSCT-TMA persisting ≥72 hours despite initial management; and 3) weighed ≥5 kg. The study aimed to enroll patients presenting with early HSCT-TMA, which was diagnosed with 4 inclusion criteria: 1) de novo thrombocytopenia or transfusion refractoriness; 2) lactate dehydrogenase (LDH) above the upper limit of normal for age or presence of schistocytes; 3) proteinuria ≥1 mg/mg; and 4) de novo anemia or hypertension. Participants received weight-based loading doses on days 1, 5, and 10, and maintenance doses every 4 weeks (weight <20 kg) or 8 weeks (weight ≥20 kg) from day 15 through week 26. The primary endpoint was complete TMA (cTMA) response during the 26-week treatment period. Protocol-defined cTMA response criteria were platelet count >50,000/mm3(baseline platelets ≤50,000/mm3) or ≥50% increase in platelet count (baseline platelets >50,000/mm3) without platelet transfusion support in the previous 7 days, normalization of LDH with absence of schistocytes (≤1% or “none”), and ≥50% reduction in urine protein/creatinine ratio from baseline. Each response criterion must have been met at 2 separate assessments ≥24 hours apart and any measurement in between. Protocol-defined partial TMA response was meeting ≥1 but not all of the cTMA response criteria. Secondary endpoints included hematologic response (criteria included platelet count and LDH), overall survival (OS), and NRM. Results: Of 41 participants enrolled and treated, 28 (68.3%) completed the 26-week treatment period, and 13 discontinued study treatment. The median (range) age of participants was 6.0 (<1 to 17) years, and approximately half were female (51.2%) and White (53.7%). The most frequent transplant indication for HSCT was malignancy in 27 (65.9%) participants; 38 (92.7%) participants received allogeneic HSCT. By week 26, cTMA response was observed in 7 (17.1%) participants. Hematologic response occurred in 10 (24.4%) participants. As individual components of hematologic response, 24 (58.5%) and 15 (36.6%) participants met the platelet (including transfusion independence) and LDH response criteria, respectively. Hemoglobin response of ≥10 g/dL, including absence of red blood cell transfusions, was observed in 17 (41.5%) participants. The presence or absence of schistocytes varied throughout the study with no clear trends. Protocol-defined complete or partial TMA response occurred in 29 of 41 participants (70.7%) meeting ≥1 criterion. The Kaplan-Meier estimate of OS was 92.6% (95% CI, 78.8-97.6) at 100 days and 87.2% (95% CI, 71.8-94.5) at 26 weeks. All deaths during the treatment period were due to NRM (n=5); causes of death were multiorgan failure (n=2), hypoxic respiratory failure (n=1), heart failure (n=1), and septic shock (n=1). Conclusions: In this single-arm study, children diagnosed with HSCT-TMA and treated with rav for 26 weeks were observed to have complete and partial TMA responses alongside a clinically meaningful OS of 87.2%. Further posthoc analyses will be performed in subgroups of participants.

Pediatric supportive care clinical trials often involve multiple clinically important outcomes, complicating trial interpretation. Hierarchical composite endpoints (HCEs) provide a framework to integrate key outcomes according to clinical importance. We performed post hoc analyses using HCE in two randomized trials conducted by the Children's Oncology Group. We found that HCE can be more sensitive overall endpoints for detecting treatment benefit as well as found that HCE can support harmonized trial conclusions in the presence of intervention benefits and harms. These analyses illustrate the potential of HCE to improve the interpretability of complex pediatric supportive care trials and support consideration of their prospective use.

Background Thiotepa (TT) is an alkylating agent with immunosuppressive properties often included in high-dose chemotherapy prior to hematopoietic cell transplantation (HCT) to support stem cell engraftment. However, the pharmacokinetics (PK) of TT and its active metabolite, TEPA, remain largely uncharacterized in children and young adults undergoing HCT. Using prospective multicenter data, this study aimed to characterize TT and TEPA PK, and to identify key patient covariate-PK relationships to inform future model-informed precision dosing (MIPD) approaches. Methods TT PK data were collected from 2017 to 2023 across 5 pediatric bone marrow transplant sites as a part of a prospective study (NCT03609827). TT was administered intravenously and all patients underwent PK sampling during a single dosing interval. Samples were analyzed using a previously validated LC/MS/MS assay. Covariates evaluated included age, weight, height, sex, ancestry (patient identify ethnicity and race), liver function tests, and renal function. A nonlinear mixed effects modeling approach was used to characterize TT and TEPA PK in which R (v4.3) was utilized for data visualization, NONMEM (v7.6) for model estimation. Results The dataset included a total of 210 and 235 quantifiable concentrations for TT and TEPA from 91 patients. Among the study subjects, the median age of patients was 4.5 years (0.23-22.5) years with a median body weight of 16.7 kg (4.6-110). Final model parameters are shown in Table 1. The best fit model for these data was a 2-compartment structure for TT, a nonlinear conversion from TT to TEPA, and a 1-compartment structure for TEPA. Covariate relationships included in the final model included age and allometrically-scaled fat-free mass (FFM). For age, separate maturation function terms were estimated for PK parameters of clearance (CLTT, CLTEPA, Vmax), and Vc,TT. For FFM allometric scaling, exponents 0.75 for CLTT and CLTEPA, and 1.0 for Vc,TT and Vp,TT were used. Given the nature of modeling parent and metabolite data, the VTEPA term is unidentifiable and fixed to 1. The visual predictive checks (VPC) shows the distribution of the data is well-captured by the model across the majority of the PK-time curve, with slight misspecification at TT peak concentrations, likely driven by the limited information on peak data due to the sampling strategy for this study (Figure 1). Conclusions The developed population PK model characterizes TT and TEPA in children and young adults undergoing HCT and identifies FFM and age as impactful covariates and supports future MIPD efforts of thiotepa. Given limited existing PK data for TT and TEPA, internal and external validations were not available; future prospective trials with expanded data will be vital to improve the model for personalized dosing.

RATIONALE:Lung injury after hematopoietic stem cell transplantation (HCT) occurs due to infection, chemotherapy toxicity, and alloreactive inflammation. Analyses of bronchoalveolar lavage (BAL) fluid have revealed dominant pathobiologic signatures, but minimally-invasive diagnostics are needed. OBJECTIVES:To determine whether microbiome and gene expression perturbations are shared along the respiratory tract or isolated to the alveoli in pediatric HCT patients with lung injury. METHODS:We performed bulk RNA sequencing on 206 paired nasal and BAL samples from 160 HCT patients and 17 healthy controls enrolled at 28 children's hospitals (2016-2025). Microbial and human transcripts were compared using multivariable models accounting for age, sex, and paired sampling. MEASUREMENTS AND MAIN RESULTS:HCT BAL and nasal transcriptomes differed across 13,698 genes, 48 cellular components, and network interactions linking inflammation, reactive oxygen species, and immunometabolism. Minimal BAL-nasal correlation was observed in gene expression levels (median ρ = 0.03, IQR -0.03 to 0.08) or fractional abundance of key cells such as neutrophils and CD8 + T-cells. BAL microbiomes harbored fewer commensal bacteria and more fungi and DNA viruses. BAL bacterial RNA was associated with diminished immune signaling whereas nasal bacterial RNA aligned with inflammatory gene expression. Further, only BAL microbial RNA was linked to transcriptional shifts in epithelial injury response, keratinization, and collagen deposition. Finally, BAL commensal microbiome depletion, epithelial injury, and immune dysregulation signatures were associated with death or prolonged mechanical ventilation, whereas nasal samples provided minimal prognostic information. CONCLUSIONS:These data support alveolar compartmentalization in pediatric HCT and emphasize the ongoing need for minimally-invasive but informative diagnostics.

Objectives Ravulizumab (Rav), an anti-complement C5 monoclonal antibody, demonstrated efficacy and safety over a 26-week (wk) treatment period in pediatric hematopoietic stem cell transplantation-associated thrombotic microangiopathy (HSCT-TMA).1 Here, data up to 52 wks are reported. Methods ALXN1210-TMA-314 (NCT04557735) is a phase 3, open-label, single-arm, multicenter study. Eligible patients (pts) were aged 28 days to <18 years, weighed ≥5 kg, received HSCT within the prior 12 months, and had HSCT-TMA persisting for ≥72 hours despite trigger management. Protocol inclusion criteria included proteinuria of ≥1 mg/mg. Pts received body weight-based Rav plus best supportive care for 26 wks, followed by a 26-wk follow-up period of only best supportive care. The primary endpoint was protocol-defined complete TMA response (≥50% reduction in urine protein/creatinine ratio [UPCR], ≥50% improvement in platelets, and lactate dehydrogenase [LDH] normalization with absence of schistocytes) during the 26-wk treatment period. Key secondary endpoints included individual TMA response components, overall survival (OS; at day 100, wk 26 and 52), and safety (incidence of treatment-emergent adverse events [TEAEs] and serious TEAEs). Results Of 41 enrolled pts (mean age 7.6 years, 51% female, 54% White), 28 (68.3%) completed 26 wks, and 24 (45.5%) completed 52 wks.At wk 26, protocol-defined TMA response occurred in 29 (70.7%) participants meeting ≥1 criterion, of which 7 (17.1%) met protocol-defined complete TMA response and 22 (53.7%) met protocol-defined partial TMA response. Mean UPCR improved from 5.5 mg/mg at baseline (n=41) to 0.93 mg/mg at wk 26 (n=21), and 0.27 mg/mg at wk 52 (n=21, Fig. 1). Mean platelets were 46976/mm3 at baseline (n=41) (reference range lower limit of normal = 163000), 169000/mm3 at wk 26 (n=25), and progressively improved to 216000/mm3 at wk 52 (n=18). Age-normalized LDH decreased from 1.6 x upper limit of normal (ULN) at baseline (n=37) to <1.0 x ULN at wk 26 (n=28), which was maintained through wk 52 (n=24). At wk 52 79% of pts had normal LDH.Estimated OS was 92.6% at day 100, 87.2% at wk 26, and 73.4% at wk 52 (Fig. 2). During the 26 wk treatment period, 41/41 pts experienced ≥1 TEAE (n=860), 30/41 (73.2%) reported 94 serious TEAEs, and 3 pts (7.3%) had serious TEAEs assessed as related to Rav. During the 26 wk follow-up period (wks 26 through 52), 24/29 pts (82.8%) experienced ≥1 TEAE (n=178),15/29 (51.7%) reported 27 serious TEAEs, and 2 pts (6.9%) had serious TEAEs assessed as related to Rav. No meningococcal infections were reported, and no unexpected or new safety signals were identified. Conclusion In this global Phase 3 trial in pediatric pts with HSCT-TMA, Rav treatment resulted in clinically meaningful OS of 73.4% at 52 wks and normalization of early laboratory markers of TMA beyond 26 wks.

Introduction Thiotepa (TT) is given in combination with other agents to prevent rejection and relapse following HLA-mismatched HCT. Standard dosing of 5 mg/kg x 2 was developed in an adult population. Objectives We hypothesized that outlier TT exposure would be associated with inferior event-free- (EFS) and overall- (OS) survival due to increased rejection and transplant-associated thrombotic microangiopathy (TA-TMA) in pediatric patients undergoing alpha-beta-T-cell/CD19-depleted (AB-TCD) haploidentical HCT. Methods Utilizing a validated PK model, we retrospectively predicted exposure of the combination of TT and its active metabolite TEPA as a cumulative area under the curve (cAUC) in 203 patients with hematologic malignancy undergoing AB-TCD haploidentical HCT at 9 centers on 2 prospective trials between 2015 and 2025. Events were rejection, non-relapse mortality (NRM), and relapse. Results The median TT dose was 5.0 mg/kg (range, 3.4-5.3) for 2 doses; the median predicted cAUC was 50.3 mg/L*hr (range, 36.8-64.7). We modeled time-to-event or death (EFS) as a function of TT cAUC using fitted “b-splines” under Cox regression with complexity limited to control over-fitting. We identified the cAUC level that maximized the 2-year EFS probability as 46 mg/L*hr (95% CI, 42-50), classifying patients as having low (<42; n=21), optimal (42-50; n=78), or high (>50; n=104) exposure. Low TT exposure was significantly associated with 1-yr rejection (p=0.002; Figure 1A) and high TT exposure with 3-yr NRM (p=0.012; Figure 1B). No statistical associations were found with 3-yr relapse (Figure 1C) or EFS (Figure 1D). Three-yr OS was significantly lower in those with high TT exposure (p=0.019; Figure 1E). Higher TT exposure (> median) led to a NRM HR of 3.92 (95% CI, 1.46-10.51). To assess the extent this measure of association was explained by potential confounders (patient / donor age, antithymocyte globulin exposure, etc.), propensity scores were used to reweight the dataset to balance the distributions of confounders across TT exposure-defined groups; the re-estimated HR after adjustment was 3.67 (95% CI, 1.00-12.96). The Youden's J-statistic of an ROC analysis suggested a TT cAUC cutoff of ≥53 mg/L*hr was associated with TA-TMA; the 1-yr cumulative incidence was significantly higher in those with TT exposure ≥53 mg/L*hr (n=60) compared to <53 mg/L*hr (p<0.001; n=143; Figure 1F). Conclusion In pediatric patients undergoing AB-TCD haploidentical HCT for hematologic malignancies a PK-model predicted cAUC of TT is associated with risk of rejection, TA-TMA, NRM, and OS. The identified optimal cAUC of 46 mg/L*hr was below the median of 50.3, suggesting that the conventional dose of 5 mg/kg x 2 may be supra-therapeutic for many patients. Model-based dosing of TT to achieve optimal exposure may lower toxicity and improve outcomes and should be tested in prospective trials.

BACKGROUND:Mucopolysaccharidosis IV A (MPS IVA) or Morquio A syndrome is a lysosomal storage disorder that results from a deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS), causing deposition of glycosaminoglycans, keratan sulfate, and chondroitin-6-sulfate in multiple organs. The main clinical manifestations include severe short stature, severe cervical spine stenosis, and progressive skeletal dysplasia, which leads to severe mobility limitation resulting in patients becoming wheelchair-bound in their second decade of life, and overall shortened life span. The current standard of care for Morquio A is weekly enzyme replacement therapy (ERT). However, ERT is expensive, not widely available worldwide, and offers limited long-term benefits. Allogeneic hematopoietic cell transplantation (HCT) is a way to provide a life-long endogenous enzyme and has the potential to improve outcomes. OBJECTIVE:The main objectives of this study were to investigate the safety and assess the benefits of allogeneic HCT in the treatment of patients with Morquio A. STUDY DESIGN:We performed a retrospective study of 41 patients who underwent allogeneic HCT at 9 international centers. RESULTS:Forty-one patients with Morquio A received allogeneic HCT. Three patients experienced graft failure and underwent second transplants. Most (77%) of the transplants were performed using either matched or mismatched unrelated donors, and 71% of the transplants utilized peripheral blood stem cells as the graft source. The overall 3-year survival rate was 90.5%. Graft-versus-host disease (GVHD) was a direct or indirect contributor to mortality in 3 out of 4 patients. The median myeloid engraftment was 100% at the last follow-up, with a median follow-up of 3 years; the median times for neutrophil and platelet engraftment were 12 and 13 days, respectively. The incidence of grade II to IV acute GVHD was 35.5%. Interestingly, in patients who had received pretransplant ERT, the incidence of acute grade II to IV GVHD was 14.9%, compared to 45% in those who had not received pretransplant ERT (P = .075). The incidence of grades III to IV acute and chronic GVHD was 14.2% and 12.7%, respectively. When available, disease-specific outcomes showed complete to near normalization of metabolic biomarkers, as well as improvement in movement scores, stability of heart function, eyes, and cervical spine stenosis. Notably, in patients transplanted below the age of 3 years, growth continued in 6 out of 8 patients, while this effect was less notable in the older cohort. CONCLUSION:Allogeneic HCT for patients with Morquio A is safe and feasible. This treatment can potentially lead to significantly improved biochemical markers of the disease, preservation of organs, and better clinical manifestations. Additionally, when performed at a young age, ideally before the age of 3 years, allogeneic HCT may result in improved growth. The use of bone marrow as a stem cell source whenever possible, combined with effective GVHD prophylaxis, may enhance transplant success and disease-related outcomes. Long-term benefits and risks require further investigation.

For CAYA with very high-risk/relapsed B-ALL HCT, outcomes have been correlated with MFC or PCR-based MRD status pre- and post-HCT. NGS has emerged as a methodology that detects MRD 3-4 logs lower than MFC. Literature comparing NGS with MFC MRD is minimal in CAYA, although it is increasingly used for therapeutic decisions. To address this gap, we performed a prospective correlative study as part of the NCI-funded PTCTC ONC1401 trial. Samples from 9 US centers with CAYA transplanted from 2015 to 2021 were obtained for MRD testing at 6 specified time points listed in Table 2. We hypothesized that BM NGS would be highly predictive of relapse, relapse-free survival (RFS), and non-relapse mortality (NRM), superior to BM MFC. A secondary hypothesis was that PB NGS would outperform BM MFC.Our cohort included 120 CAYA with B-ALL at a median age of 11.5 (range <1-27.0) years. Most patients were in CR1 (34.2%) or CR2 (45.8%). Over half (59.5%) were male and over half were Hispanic/Latino. The majority received haplo (46.7%) or unrelated donor grafts (40.0%). NGS MRD values were centrally performed using the Clonoseq® assay; NGS results were not available to clinicians.Penalized multivariable Cox proportional hazards (PH) models were used to assess RFS, and penalized Fine-Gray models evaluated relapse and NRM. Predictive performance was assessed using the C-index. Landmark analyses generated conditional event predictions, and time-dependent Cox PH models examined how MRD at different time points influenced event risks.Pre-HCT, 8.3% had positive BM MFC while 30.8% and 13.3% were positive by NGS BM and PB, respectively, showing higher sensitivity for both BM and PB NGS compared to BM MFC. Post-HCT, BM NGS was 3-6x more sensitive than BM MFC and 2-3x more sensitive than PB NGS.Pre-HCT, MRD by BM MFC and BM and PB NGS were all predictive of relapse with the highest C-index for PB NGS, likely because PB NGS detected higher levels of disease than BM NGS (Table 1). Post-HCT, landmark analysis showed PB NGS-MRD to be the most predictive for relapse at Day +28, though it did not reach statistical significance (Table 2). Later post-HCT, the predictive power of MRD became significant for relapse, RFS, and NRM (Table 2). At TP04 and TP05, where only PB NGS was collected, positive NGS MRD was highly predictive of relapse and RFS, suggesting that PB NGS may be reasonable for post-HCT relapse monitoring. Notably, time-dependent analysis showed patients receiving MSD transplants were more likely to experience relapse and had lower RFS compared to haplo and unrelated donor sources (Table 3). Ongoing analyses to be presented at the meeting include an assessment of the effect of GVHD on outcomes.In summary, BM NGS-MRD is highly sensitive and predictive pre- and post-HCT and superior to other monitoring methods. PB NGS-MRD is more sensitive than MFC-MRD and is a reasonable choice for monitoring when BM testing is not practical.

Wiskott-Aldrich syndrome (WAS), an X-linked disorder characterized by immunodeficiency, thrombocytopenia, autoimmunity, and malignancy, can be effectively treated with allogeneic hematopoietic cell transplantation (HCT). Older age at HCT and mismatched donors are known to impact overall survival (OS). The influence of specific clinical manifestations or WAS variant class on OS and factors associated with event-free survival (EFS) remain incompletely defined. We analyzed outcomes of 308 patients with WAS who underwent HCT at 37 institutions of the Primary Immune Deficiency Treatment Consortium (PIDTC) from 1990-2018. With a median follow-up of 5.3 years, the 5-year OS and EFS were 87.2% and 79.7%, respectively. Age ≥5 years, donor type, and a pre-HCT history of severe infection had a negative impact on OS and EFS, whereas pre-HCT autoimmunity had no impact. Reduced intensity regimens were associated with lower T cell and myeloid donor chimerism, particularly when non-busulfan-based regimens were used. Low myeloid donor chimerism was associated with lower platelet counts. Mixed chimerism was not consistently associated with post-HCT autoimmunity. Patients with class I (exon 1-2 missense and intron 5 hotspot variants) and class II variants (all others) had similar pre-HCT clinical symptom severity and no difference in OS, EFS or platelet recovery post-HCT. In conclusion, our study showed excellent long-term OS and EFS following HCT for WAS, highlighting the importance of early HCT, before the development of severe infections. We confirmed that HCT using busulfan-based conditioning was associated with improved donor chimerism and platelet recovery. This study was registered at www.clinicaltrials.gov as #NCT02064933.

Thiotepa is commonly included in combination with other agents to prevent rejection and relapse following alpha-beta-T-cell/CD19-depleted (AB-TCD) haploidentical hematopoietic cell transplant (HCT) for pediatric patients with hematologic malignancies. A standard regimen of 5 mg/kg for two doses was developed in adults and has been extrapolated to the pediatric population. We hypothesized that outlier (low or high) thiotepa exposures would be associated with inferior event-free- (EFS) and overall- (OS) survival due to increased rejection and non-relapse mortality (NRM) in pediatric patients undergoing AB-TCD haploidentical HCT. We also hypothesized that there would be an increased incidence of transplant-associated thrombotic microangiopathy (TA-TMA) in patients with high thiotepa exposure. Utilizing a validated pharmacokinetic (PK) model, we retrospectively predicted total exposure of thiotepa and its active metabolite TEPA combined as a cumulative area under the curve (cAUCtotal) in 203 patients with hematologic malignancy undergoing AB-TCD haploidentical HCT at nine centers on two prospective trials between 2015 and 2025. No actual PK samples were available. The median thiotepa dose was 5.0 mg/kg (range, 3.4 to 5.3) administered in two doses 12 h apart, resulting in a median predicted cAUCtotal of 50.3 mg·h/L (range, 36.8 to 64.7). We first modeled time-to-event (rejection, relapse, or death) as a function of thiotepa cAUCtotal using fitted "b-splines" under Cox regression, with complexity limited to control over-fitting. We identified the cAUCtotal level that maximized the 3-yr EFS probability as approximately 45 mg·h/L (95% confidence interval [CI], 43 to 52). We next established conservative cut-points to identify an optimal range of exposure to account for residual variability in the PK model, classifying patients as having low (<42 mg·h/L; n = 21), medium (42 to 50 mg·h/L; n = 78), or high (>50 mg·h/L; n = 104) exposure. Low thiotepa exposure was significantly associated with a higher 1-yr cumulative incidence of rejection (23.8% versus 4.5% for ≥42 mg·h/L; P < .001), and high thiotepa exposure was significantly associated with a higher 3-yr NRM (20% versus 6.8% for <50 mg·h/L; P = .007). Furthermore, a thiotepa cAUCtotal of ≥53 mg·h/L was associated with development of TA-TMA; the 1-yr cumulative incidence was significantly higher in those with thiotepa exposure ≥53 mg·h/L (25.6% versus 7.5% for <53 mg·h/L; P < .001). No statistically significant associations were found between thiotepa exposure and Day 100 sinusoidal obstruction syndrome (P = .337), 3-yr relapse (P = .449), or 3-yr EFS (P = .212). However, 3-yr OS was significantly lower in those with high thiotepa exposure (68.9% versus 85.8% for <50 mg·h/L; P = .007). We then sought to evaluate whether key thiotepa exposure-outcome associations were explained by potential confounders (patient/donor age, antithymocyte globulin exposure, etc.). To contrast outcomes across groups defined by high relative to medium/low exposure, propensity scores (PSs) were used to re-weight the dataset to balance confounders across groups. The PS-weighted hazard ratio (HR) for NRM was 3.19 (high relative to medium/low exposure; 95% CI, 1.14 to 19.89). The data did not support PS reweighting to contrast low relative to medium/high thiotepa exposure, and we instead used adjusted Cox regression. The adjusted HR for rejection was 6.81 (low relative to medium/high exposure; 95% CI, 1.55 to 29.83). The associations between thiotepa exposure and key outcomes such as NRM and rejection did not appear to be explained by measured confounders. For pediatric patients undergoing AB-TCD haploidentical HCT for treatment of hematologic malignancies, we found predicted cAUCtotal of thiotepa was associated with increased risk of rejection (low exposure), TA-TMA and NRM (high exposure), as well as overall mortality (high exposure). The identified optimal cAUCtotal of 45 mg·h/L was well below the median of 50.3, suggesting that the conventional regimen of 5 mg/kg × 2 doses may be supra-therapeutic for many patients. Model-based dosing of thiotepa to achieve optimal exposure may lower toxicity and improve outcomes and should be tested in prospective trials.