Comprehensive Prognostication in Critically Ill Pediatric Hematopoietic Cell Transplant Patients: Results from Merging the Center for International Blood and Marrow Transplant Research (CIBMTR) and Virtual Pediatric Systems (VPS) Registries.

Critically ill pediatric allogeneic hematopoietic cell transplant (HCT) patients may benefit from early and aggressive interventions aimed at reversing the progression of multiorgan dysfunction. Therefore, we evaluated 25 early risk factors for pediatric intensive care unit (PICU) mortality to improve mortality prognostication. We merged the Virtual Pediatric Systems and Center for International Blood and Marrow Transplant Research databases and analyzed 936 critically ill patients ≤21 years of age who had undergone allogeneic HCT and subsequently required PICU admission between January 1, 2009, and December 31, 2014. Of 1532 PICU admissions, the overall PICU mortality rate was 17.4% (95% confidence interval [CI], 15.6% to 19.4%) but was significantly higher for patients requiring mechanical ventilation (44.0%), renal replacement therapy (56.1%), or extracorporeal life support (77.8%). Mortality estimates increased significantly the longer that patients remained in the PICU. Of 25 HCT- and PICU-specific characteristics available at or near the time of PICU admission, moderate/severe pre-HCT renal injury, pre-HCT recipient cytomegalovirus seropositivity, <100-day interval between HCT and PICU admission, HCT for underlying acute myeloid leukemia, and greater admission organ dysfunction as approximated by the Pediatric Risk of Mortality 3 score were each independently associated with PICU mortality. A multivariable model using these components identified that patients in the top quartile of risk had 3 times greater mortality than other patients (35.1% versus 11.5%, P < .001, classification accuracy 75.2%; 95% CI, 73.0% to 77.4%). These data improve our working knowledge of the factors influencing the progression of critical illness in pediatric allogeneic HCT patients. Future investigation aimed at mitigating the effect of these risk factors is warranted.

Taurine alleviates repression of betaine-homocysteine S-methyltransferase and significantly improves the efficacy of long-term betaine treatment in a mouse model of cystathionine ß-synthase-deficient homocystinuria.

Classical cystathionine ß-synthase-deficient homocystinuria (HCU) is a life-threatening inborn error of sulfur metabolism. Treatment for pyridoxine-nonresponsive HCU involves lowering homocysteine (Hcy) with a methionine (Met)-restricted diet and betaine supplementation. Betaine treatment efficacy diminishes significantly over time due to impairment of betaine-Hcy S-methyltransferase (BHMT) function. Little is known regarding the regulation of BHMT in HCU. Using a betaine-responsive preclinical mouse model of HCU, we observed that this condition induces a 75% repression of BHMT mRNA, protein and enzyme activity, and significant depletion of hepatic betaine levels. BHMT repression was proportional to plasma Hcy levels but was not observed in mouse models of homocystinuria due to either methylenetetrahydrofolate reductase or Met synthase deficiency. Both Met supplementation and chemically induced glutathione depletion exacerbated hepatic BHMT repression in HCU mice but not wild-type (WT) controls. Conversely, cysteine treatment normalized hepatic BHMT expression in HCU mice but had no effect in WT control animals. Taurine treatment induced BHMT expression in HCU mice by 5-fold and restored maximal lowering of Hcy levels during long-term betaine treatment with a concomitant normalization of inflammatory cytokine expression and a significantly improved coagulative phenotype. Collectively, our findings indicate that adjuvantial taurine treatment has the potential to significantly improve clinical outcomes in HCU.-Maclean, K. N., Jiang, H, Phinney, W. N., Keating, A. K., Hurt, K. J., Stabler, S. P. Taurine alleviates repression of betaine-homocysteine S-methyltransferase and significantly improves the efficacy of long-term betaine treatment in a mouse model of cystathionine ß-synthase-deficient homocystinuria.

Glycemic variability is associated with poor outcomes in pediatric hematopoietic stem cell transplant patients.

BACKGROUND: Among pediatric hematopoietic stem cell transplant (HSCT) recipients, abnormal glycemic control is shown to be associated with increased risk of transplant-related mortality, death from any cause, risk of infection, increased hospitalized, and intensive care days. Independent effects of higher glycemic variability, a component of glycemic control, have not been described. This study aimed to characterize risk factors for, and consequences of, higher glycemic variability in HSCT patients. PROCEDURE: Medical records for a cohort of 344 patients, age 0-30 years, who underwent first HSCT from 2007 to 2016 at Children's Hospital Colorado were retrospectively reviewed. Glucose coefficients of variation (CV) were analyzed for HSCT days -14 to 0 and 0-30, and patients were assessed for potential risk factors and outcomes. RESULTS: Roughly one-third of patients had pre-HSCT and day 0-30 glucose CV above the reported healthy adult range. Independent of HSCT type, doubling of pre-HSCT glucose CV was associated with a 4.91-fold (95% confidence interval [CI], 1.40-17.24) increased hazard of infection, as well as increased risk for intensive care hospitalization for allogenic HSCT patients. Multivariable analysis demonstrated that allogeneic HSCT patients had a 1.40- and 1.38-fold (95% CI, 0.98-1.99 and 1.00-1.91) increased hazard of death for every doubling of pre-HSCT and day 0-30 glucose CV, respectively. CONCLUSIONS: Just as with higher mean glucose, higher glycemic variability in the pediatric HSCT population is independently associated with significantly increased morbidity. Additional research is required to evaluate the utility of glucose control to mitigate these relationships and improve HSCT outcomes.

Hematopoietic Stem Cell Transplantation Activity in Pediatric Cancer between 2008 and 2014 in the United States: A Center for International Blood and Marrow Transplant Research Report.

This Center for International Blood and Marrow Transplant Research report describes the use of hematopoietic stem cell transplantation (HSCT) in pediatric patients with cancer, 4408 undergoing allogeneic (allo) and3076 undergoing autologous (auto) HSCT in the United States between 2008 and 2014. In both settings, there was a greater proportion of boys (n = 4327; 57%), children < 10 years of age (n = 4412; 59%), whites (n = 5787; 77%), and children with a performance score ≥ 90% at HSCT (n = 6187; 83%). Leukemia was the most common indication for an allo-transplant (n = 4170; 94%), and among these, acute lymphoblastic leukemia in second complete remission (n = 829; 20%) and acute myeloid leukemia in first complete remission (n = 800; 19%) werethe most common. The most frequently used donor relation, stem cell sources, and HLA match were unrelated donor (n = 2933; 67%), bone marrow (n = 2378; 54%), and matched at 8/8 HLA antigens (n = 1098; 37%) respectively. Most allo-transplants used myeloablative conditioning (n = 4070; 92%) and calcineurin inhibitors and methotrexate (n = 2245; 51%) for acute graft-versus-host disease prophylaxis. Neuroblastoma was the most common primary neoplasm for an auto-transplant (n = 1338; 44%). Tandem auto-transplants for neuroblastoma declined after 2012 (40% in 2011, 25% in 2012, and 8% in 2014), whereas tandem auto-transplants increased for brain tumors (57% in 2008 and 77% in 2014). Allo-transplants from relatives other than HLA-identical siblings doubled between 2008 and 2014 (3% in 2008 and 6% in 2014). These trends will be monitored in future reports of transplant practices in the United States.

Mer receptor tyrosine kinase is a therapeutic target in pre-B-cell acute lymphoblastic leukemia.

Acute lymphoblastic leukemia (ALL) is currently treated with an intense regimen of chemotherapy yielding cure rates near 85%. However, alterations to treatment strategies using available drugs are unlikely to provide significant improvement in survival or decrease therapy-associated toxicities. Here, we report ectopic expression of the Mer receptor tyrosine kinase in pre-B-cell ALL (B-ALL) cell lines and pediatric patient samples. Inhibition of Mer in B-ALL cell lines decreased activation of AKT and MAPKs and led to transcriptional changes, including decreased expression of antiapoptotic PRKCB gene and increase in proapoptotic BAX and BBC3 genes. Further, Mer inhibition promoted chemosensitization, decreased colony-forming potential in clonogenic assays, and delayed disease onset in a mouse xenograft model of leukemia. Our results identify Mer as a potential therapeutic target in B-ALL and suggest that inhibitors of Mer may potentiate lymphoblast killing when used in combination with chemotherapy. This strategy could reduce minimal residual disease and/or allow for chemotherapy dose reduction, thereby leading to improved event-free survival and reduced therapy-associated toxicity for patients with B-ALL. Additionally, Mer is aberrantly expressed in numerous other malignancies suggesting that this approach may have broad applications.

Effects of Total Body Irradiation on Hematopoietic Cell Transplantation Outcomes in Pediatric Acute Myeloid Leukemia with Prior Central Nervous System Involvement.

The implications of previous central nervous system (CNS) involvement in children with acute myeloid leukemia (AML) undergoing hematopoietic cell transplantation (HCT) remain inadequately understood. Patients with CNS disease require more upfront CNS-directed intrathecal therapy, but little is known about whether transplant conditioning regimens should be intensified or if previous CNS involvement impacts post-HCT outcomes. While total body irradiation (TBI) remains standard for pediatric acute lymphoblastic leukemia myeloablative conditioning, it has been largely replaced with chemotherapy-only myeloablation in pediatric AML, primarily due to toxicity and late effects associated with TBI. In the setting of previous CNS involvement, it has been suggested that TBI-based myeloablation may have advantages due to superior CNS tissue penetration and thus decreased rates of AML relapse post-HCT. We analyzed a publicly available dataset derived from the Center for International Blood and Marrow Transplantation Research (CIBMTR) registry to characterize the impact of TBI in HCT preparative regimens in pediatric AML patients with a history of CNS involvement. The study dataset was obtained from the CIBMTR data repository. The study cohort included patients aged ≤21 years who underwent initial allogeneic HCT with myeloablative conditioning for de novo AML in the first or second complete remission (CR) between 2008 and 2016, who provided consent for research. Patients with mismatched related donor transplants and noncalcineurin inhibitor graft-versus-host disease (GVHD) prophylaxis were excluded. The dataset was further modified by excluding patients with missing disease site data or those with non-CNS extramedullary disease. Patients were categorized as CNS-positive or -negative AML (AML-CNS(+) and AML-CNS(-), respectively) based on the disease status at diagnosis. The Cox regression model and Fine-Grey methods were employed to delineate the effects of TBI and CNS disease on key HCT outcomes. The study cohort comprised 550 pediatric AML patients, of which 25% (n = 136) were AML-CNS(+). CNS involvement was more prevalent in patients aged 0 to 3 years, patients who were in the second CR, and those with a mismatched unrelated donor or umbilical cord blood. AML-CNS(+) patients demonstrated a lower relapse rate (hazard ratio: 0.50, 95% confidence interval: 0.33 to 0.76) compared to AML-CNS(-) patients, with comparable disease-free survival (DFS) and overall survival (OS) (P = .10 and 0.20, respectively) in the two cohorts. The entire TBI-treated cohort showed an association with increased risks of grade 2 to 4 acute GVHD, bloodstream infections, and endocrine dysfunction. TBI use within the AML-CNS(+) cohort was associated with a lower relapse rate but increased risks of nonrelapse mortality and a trend of higher grade 3 to 4 acute GVHD. In this population-based analysis of pediatric patients with de novo AML undergoing HCT, TBI-based conditioning regimens did not confer an advantage in DFS or OS compared to non-TBI regimens, irrespective of CNS disease status. However, TBI use was associated with increased risks of short- and long-term comorbidities. These findings underscore the need for careful consideration of TBI in pediatric AML.

Antiviral cellular therapy for enhancing T-cell reconstitution before or after hematopoietic stem cell transplantation (ACES): a two-arm, open label phase II interventional trial of pediatric patients with risk factor assessment.

Viral infections remain a major risk in immunocompromised pediatric patients, and virus-specific T cell (VST) therapy has been successful for treatment of refractory viral infections in prior studies. We performed a phase II multicenter study (NCT03475212) for the treatment of pediatric patients with inborn errors of immunity and/or post allogeneic hematopoietic stem cell transplant with refractory viral infections using partially-HLA matched VSTs targeting cytomegalovirus, Epstein-Barr virus, or adenovirus. Primary endpoints were feasibility, safety, and clinical responses (>1 log reduction in viremia at 28 days). Secondary endpoints were reconstitution of antiviral immunity and persistence of the infused VSTs. Suitable VST products were identified for 75 of 77 clinical queries. Clinical responses were achieved in 29 of 47 (62%) of patients post-HSCT including 73% of patients evaluable at 1-month post-infusion, meeting the primary efficacy endpoint (>52%). Secondary graft rejection occurred in one child following VST infusion as described in a companion article. Corticosteroids, graft-versus-host disease, transplant-associated thrombotic microangiopathy, and eculizumab treatment correlated with poor response, while uptrending absolute lymphocyte and CD8 T cell counts correlated with good response. This study highlights key clinical factors that impact response to VSTs and demonstrates the feasibility and efficacy of this therapy in pediatric HSCT.

Pathobiological signatures of dysbiotic lung injury in pediatric patients undergoing stem cell transplantation.

Hematopoietic cell transplantation (HCT) uses cytotoxic chemotherapy and/or radiation followed by intravenous infusion of stem cells to cure malignancies, bone marrow failure and inborn errors of immunity, hemoglobin and metabolism. Lung injury is a known complication of the process, due in part to disruption in the pulmonary microenvironment by insults such as infection, alloreactive inflammation and cellular toxicity. How microorganisms, immunity and the respiratory epithelium interact to contribute to lung injury is uncertain, limiting the development of prevention and treatment strategies. Here we used 278 bronchoalveolar lavage (BAL) fluid samples to study the lung microenvironment in 229 pediatric patients who have undergone HCT treated at 32 children's hospitals between 2014 and 2022. By leveraging paired microbiome and human gene expression data, we identified high-risk BAL compositions associated with in-hospital mortality (P = 0.007). Disadvantageous profiles included bacterial overgrowth with neutrophilic inflammation, microbiome contraction with epithelial fibroproliferation and profound commensal depletion with viral and staphylococcal enrichment, lymphocytic activation and cellular injury, and were replicated in an independent cohort from the Netherlands (P = 0.022). In addition, a broad array of previously occult pathogens was identified, as well as a strong link between antibiotic exposure, commensal bacterial depletion and enrichment of viruses and fungi. Together these lung-immune system-microorganism interactions clarify the important drivers of fatal lung injury in pediatric patients who have undergone HCT. Further investigation is needed to determine how personalized interpretation of heterogeneous pulmonary microenvironments may be used to improve pediatric HCT outcomes.

Late effects of total body irradiation and hematopoietic stem cell transplant in children under 3 years of age.

BACKGROUND: Total body irradiation (TBI) is an important component of hematopoietic stem cell transplant (SCT) for pediatric malignancies. With increasing survival rates, late effects of SCT become more important. Younger children may be at particular risk of late effects of radiation and SCT. METHODS: We retrospectively reviewed outcomes of children less than 3 years of age who received TBI as part of their preparative regimen for SCT at Children's Hospital Colorado. Clinical information including the date of last follow-up, most recent lab values, and physiologic tests were extracted from the medical record. RESULTS: Of 81 patients who underwent SCT, 19 received TBI and of those, 15 were long-term survivors available for review. Late effects occurring in greater than 50% of the children included abnormalities involving endocrine, metabolic, renal, cataracts, and neurocognitive systems. Other organs involved less commonly included liver, skeletal, and cardiac abnormalities. Solid tumors were a rare finding with only one patient developing a benign osteochondroma and no identified secondary malignancies. CONCLUSIONS: TBI has been shown to be an important part of the preparative regimen for patients undergoing SCT. Our results, similar to other studies, suggest TBI in patients less than 3 years of age will likely result in multi-organ dysfunction including endocrine, metabolic, renal, eye, and neurocognitive abnormalities. A longitudinal study with standardized testing of these systems would further clarify the late effects concerns in this patient population.

Access to Chimeric Antigen Receptor T Cell Clinical Trials in Underrepresented Populations: A Multicenter Cohort Study of Pediatric and Young Adult Acute Lymphobastic Leukemia Patients.

Chimeric antigen receptor T cell (CAR-T) therapy is a promising approach to improve survival for children and adults with relapsed/refractory (r/r) B cell acute lymphoblastic leukemia (B-ALL), but these clinical trials might not be equally accessible to patients of low socioeconomic status (SES) or to patients from racial or ethnic minority groups. We sought to describe the sociodemographic characteristics of pediatric and adolescent and young adult (AYA) patients enrolled in CAR-T clinical trials and to compare these characteristics to those of other patients with r/r B-ALL. We conducted a multicenter retrospective cohort study at 5 pediatric consortium sites to compare the sociodemographic characteristics of patients treated and enrolled in CAR-T trials at their home institution, other patients with r/r B-ALL treated at these sites, and patients referred from an external hospital for CAR-T trials. The patients were age 0 to 27 years with r/r B-ALL treated at 1 of the consortium sites between 2012 and 2018. Clinical and demographic data were collected from the electronic health record. We calculated distance from home to treating institution and assigned SES scores based on census tract. Among the 337 patients treated for r/r B-ALL, 112 were referred from an external hospital to a consortium site and enrolled in a CAR-T trial and 225 were treated primarily at a consortium site, with 34% enrolled in a CAR-T trial. Patients treated primarily at a consortium site had similar characteristics regardless of trial enrollment. Lower proportions of Hispanic patients (37% versus 56%; P = .03), patients whose preferred language was Spanish (8% versus 22%; P = .006), and publicly insured patients (38% versus 65%; P = .001) were referred from an external hospital than were treated primarily at a consortium site and enrolled in a CAR-T trial. Patients who are Hispanic, Spanish-speaking, or publicly insured are underrepresented in referrals from external hospitals to CAR-T centers. External provider implicit bias also may influence referral of these patients. Establishing partnerships between CAR-T centers and external hospital sites may improve provider familiarity, patient referral, and patient access to CAR-T clinical trials.

HLH-like toxicities predict poor survival after the use of tisagenlecleucel in children and young adults with B-ALL.

Chimeric antigen receptor-associated hemophagocytic lymphohistiocytosis (HLH)-like toxicities (LTs) involving hyperferritinemia, multiorgan dysfunction, coagulopathy, and/or hemophagocytosis are described as occurring in a subset of patients with cytokine release syndrome (CRS). Case series report poor outcomes for those with B-cell acute lymphoblastic leukemia (B-ALL) who develop HLH-LTs, although larger outcomes analyses of children and young adults (CAYAs) with B-ALL who develop these toxicities after the administration of commercially available tisagenlecleucel are not described. Using a multi-institutional database of 185 CAYAs with B-ALL, we conducted a retrospective cohort study including groups that developed HLH-LTs, high-grade (HG) CRS without HLH-LTs, or no to low-grade (NLG) CRS without HLH-LTs. Primary objectives included characterizing the incidence, outcomes, and preinfusion factors associated with HLH-LTs. Among 185 CAYAs infused with tisagenlecleucel, 26 (14.1%) met the criteria for HLH-LTs. One-year overall survival and relapse-free survival were 25.7% and 4.7%, respectively, in those with HLH-LTs compared with 80.1% and 57.6%, respectively, in those without. In multivariable analysis for death, meeting criteria for HLH-LTs carried a hazard ratio of 4.61 (95% confidence interval, 2.41-8.83), controlling for disease burden, age, and sex. Patients who developed HLH-LTs had higher pretisagenlecleucel disease burden, ferritin, and C-reactive protein levels and lower platelet and absolute neutrophil counts than patients with HG- or NLG-CRS without HLH-LTs. Overall, CAYAs with B-ALL who developed HLH-LTs after tisagenlecleucel experienced high rates of relapse and nonrelapse mortality, indicating the urgent need for further investigations into prevention and optimal management of patients who develop HLH-LTs after tisagenlecleucel.

Multicenter Long-Term Follow-Up of Allogeneic Hematopoietic Cell Transplantation with Omidubicel: A Pooled Analysis of Five Prospective Clinical Trials.

Omidubicel is an umbilical cord blood (UCB)-derived ex vivo-expanded cellular therapy product that has demonstrated faster engraftment and fewer infections compared with unmanipulated UCB in allogeneic hematopoietic cell transplantation. Although the early benefits of omidubicel have been established, long-term outcomes remain unknown. We report on a planned pooled analysis of 5 multicenter clinical trials including 105 patients with hematologic malignancies or sickle cell hemoglobinopathy who underwent omidubicel transplantation at 26 academic transplantation centers worldwide. With a median follow-up of 22 months (range, .3 to 122 months), the 3-year estimated overall survival and disease-free survival were 62.5% and 54.0%, respectively. With up to 10 years of follow-up, omidubicel showed durable trilineage hematopoiesis. Serial quantitative assessments of CD3+, CD4+, CD8+, CD19+, CD116+CD56+, and CD123+ immune subsets revealed median counts remaining within normal ranges through up to 8 years of follow-up. Secondary graft failure occurred in 5 patients (5%) in the first year, with no late cases reported. One case of donor-derived myeloid neoplasm was reported at 40 months post-transplantation. This was also observed in a control arm patient who received only unmanipulated UCB. Overall, omidubicel demonstrated stable trilineage hematopoiesis, immune competence, and graft durability in extended follow-up.

Outcomes After Nonresponse and Relapse Post-Tisagenlecleucel in Children, Adolescents, and Young Adults With B-Cell Acute Lymphoblastic Leukemia.

PURPOSE: Nonresponse and relapse after CD19-chimeric antigen receptor (CAR) T-cell therapy continue to challenge survival outcomes. Phase II landmark data from the ELIANA trial demonstrated nonresponse and relapse rates of 14.5% and 28%, respectively, whereas use in the real-world setting showed nonresponse and relapse rates of 15% and 37%. Outcome analyses describing fate after post-CAR nonresponse and relapse remain limited. Here, we aim to establish survival outcomes after nonresponse and both CD19+ and CD19- relapses and explore treatment variables associated with inferior survival. METHODS: We conducted a retrospective multi-institutional study of 80 children and young adults with B-cell acute lymphoblastic leukemia experiencing nonresponse (n = 23) or relapse (n = 57) after tisagenlecleucel. We analyze associations between baseline characteristics and these outcomes and establish survival rates and salvage approaches. RESULTS: The overall survival (OS) at 12 months was 19% across nonresponders (n = 23; 95% CI, 7 to 50). Ninety-five percent of patients with nonresponse had high preinfusion disease burden. Among 156 morphologic responders, the cumulative incidence of relapse was 37% (95% CI, 30 to 47) at 12 months (CD19+; 21% [15 to 29], CD19-; 16% [11 to 24], median follow-up; 380 days). Across 57 patients experiencing relapse, the OS was 52% (95% CI, 38 to 71) at 12 months after time of relapse. Notably, CD19- relapse was associated with significantly decreased OS as compared with patients who relapsed with conserved CD19 expression (CD19- 12-month OS; 30% [14 to 66], CD19+ 12-month OS; 68% [49 to 92], P = .0068). Inotuzumab, CAR reinfusion, and chemotherapy were used as postrelapse salvage therapy with greatest frequency, yet high variability in treatment sequencing and responses limits efficacy analysis across salvage approaches. CONCLUSION: We describe poor survival across patients experiencing nonresponse to tisagenlecleucel. In the post-tisagenlecleucel relapse setting, patients can be salvaged; however, CD19- relapse is distinctly associated with decreased survival outcomes.

Higher doses of tisagenlecleucel are associated with improved outcomes: a report from the pediatric real-world CAR consortium.

Remarkable complete response rates have been shown with tisagenlecleucel, a chimeric antigen receptor (CAR) T-cell therapy targeting CD19, in patients up to age 26 years with refractory/relapsed B-cell acute lymphoblastic leukemia; it is US Food and Drug Administration approved for this indication. Currently, patients receive a single dose of tisagenlecleucel across a wide dose range of 0.2 to 5.0 × 106 and 0.1 to 2.5 × 108 CAR T cells per kg for patients ≤50 and >50 kg, respectively. The effect of cell dose on survival and remission is not yet well established. Our primary goal was to determine if CAR T-cell dose affects overall survival (OS), event-free survival (EFS), or relapse-free-survival (RFS) in tisagenlecleucel recipients. Retrospective data were collected from Pediatric Real World CAR Consortium member institutions and included 185 patients infused with commercial tisagenlecleucel. The median dose of viable transduced CAR T cells was 1.7 × 106 CAR T cells per kg. To assess the impact of cell dose, we divided responders into dose quartiles: 0.134 to 1.300 × 106 (n = 48 [27%]), 1.301 to 1.700 × 106 (n = 46 [26%]), 1.701 to 2.400 × 106 (n = 43 [24%]), and 2.401 to 5.100 × 106 (n = 43 [24%]). OS, EFS, and RFS were improved in patients who received higher doses of tisagenlecleucel (P = .031, .0079, and .0045, respectively). Higher doses of tisagenlecleucel were not associated with increased toxicity. Because the current tisagenlecleucel package insert dose range remains broad, this work has implications in regard to targeting higher cell doses, within the approved dose range, to optimize patients' potential for long-standing remission.

Pulmonary microbiome and transcriptome signatures reveal distinct pathobiologic states associated with mortality in two cohorts of pediatric stem cell transplant patients.

Lung injury is a major determinant of survival after pediatric hematopoietic cell transplantation (HCT). A deeper understanding of the relationship between pulmonary microbes, immunity, and the lung epithelium is needed to improve outcomes. In this multicenter study, we collected 278 bronchoalveolar lavage (BAL) samples from 229 patients treated at 32 children's hospitals between 2014-2022. Using paired metatranscriptomes and human gene expression data, we identified 4 patient clusters with varying BAL composition. Among those requiring respiratory support prior to sampling, in-hospital mortality varied from 22-60% depending on the cluster (p=0.007). The most common patient subtype, Cluster 1, showed a moderate quantity and high diversity of commensal microbes with robust metabolic activity, low rates of infection, gene expression indicating alveolar macrophage predominance, and low mortality. The second most common cluster showed a very high burden of airway microbes, gene expression enriched for neutrophil signaling, frequent bacterial infections, and moderate mortality. Cluster 3 showed significant depletion of commensal microbes, a loss of biodiversity, gene expression indicative of fibroproliferative pathways, increased viral and fungal pathogens, and high mortality. Finally, Cluster 4 showed profound microbiome depletion with enrichment of Staphylococci and viruses, gene expression driven by lymphocyte activation and cellular injury, and the highest mortality. BAL clusters were modeled with a random forest classifier and reproduced in a geographically distinct validation cohort of 57 patients from The Netherlands, recapitulating similar cluster-based mortality differences (p=0.022). Degree of antibiotic exposure was strongly associated with depletion of BAL microbes and enrichment of fungi. Potential pathogens were parsed from all detected microbes by analyzing each BAL microbe relative to the overall microbiome composition, which yielded increased sensitivity for numerous previously occult pathogens. These findings support personalized interpretation of the pulmonary microenvironment in pediatric HCT, which may facilitate biology-targeted interventions to improve outcomes.

Real-world use of tisagenlecleucel in infant acute lymphoblastic leukemia.

Infants with B-cell acute lymphoblastic leukemia (B-ALL) have poor outcomes because of chemotherapy resistance leading to high relapse rates. Tisagenlecleucel, a CD19-directed chimeric antigen receptor T-cell (CART) therapy, is US Food and Drug Administration approved for relapsed or refractory B-ALL in patients ≤25 years; however, the safety and efficacy of this therapy in young patients is largely unknown because children <3 years of age were excluded from licensing studies. We retrospectively evaluated data from the Pediatric Real-World CAR Consortium to examine outcomes of patients with infant B-ALL who received tisagenlecleucel between 2017 and 2020 (n = 14). Sixty-four percent of patients (n = 9) achieved minimal residual disease-negative remission after CART and 50% of patients remain in remission at last follow-up. All patients with high disease burden at time of CART infusion (>M1 marrow) were refractory to this therapy (n = 5). Overall, tisagenlecleucel was tolerable in this population, with only 3 patients experiencing ≥grade 3 cytokine release syndrome. No neurotoxicity was reported. This is the largest report of tisagenlecleucel use in infant B-ALL and shows that this therapy is safe and can be effective in this population. Incorporating this novel immunotherapy into the treatment of infant B-ALL offers a promising therapy for a highly aggressive leukemia.

Optimal fludarabine lymphodepletion is associated with improved outcomes after CAR T-cell therapy.

Chimeric antigen receptor (CAR) T cells provide a therapeutic option in hematologic malignancies. However, treatment failure after initial response approaches 50%. In allogeneic hematopoietic cell transplantation, optimal fludarabine exposure improves immune reconstitution, resulting in lower nonrelapse mortality and increased survival. We hypothesized that optimal fludarabine exposure in lymphodepleting chemotherapy before CAR T-cell therapy would improve outcomes. In a retrospective analysis of patients with relapsed/refractory B-cell acute lymphoblastic leukemia undergoing CAR T-cell (tisagenlecleucel) infusion after cyclophosphamide/fludarabine lymphodepleting chemotherapy, we estimated fludarabine exposure as area under the curve (AUC; mg × h/L) using a validated population pharmacokinetic (PK) model. Fludarabine exposure was related to overall survival (OS), cumulative incidence of relapse (CIR), and a composite end point (loss of B-cell aplasia [BCA] or relapse). Eligible patients (n = 152) had a median age of 12.5 years (range, <1 to 26), response rate of 86% (n = 131 of 152), 12-month OS of 75.1% (95% confidence interval [CI], 67.6% to 82.6%), and 12-month CIR of 36.4% (95% CI, 27.5% to 45.2%). Optimal fludarabine exposure was determined as AUC ≥13.8 mg × h/L. In multivariable analyses, patients with AUC <13.8 mg × h/L had a 2.5-fold higher CIR (hazard ratio [HR], 2.45; 95% CI, 1.34-4.48; P = .005) and twofold higher risk of relapse or loss of BCA (HR, 1.96; 95% CI, 1.19-3.23; P = .01) compared with those with optimal fludarabine exposure. High preinfusion disease burden was also associated with increased risk of relapse (HR, 2.66; 95% CI, 1.45-4.87; P = .001) and death (HR, 4.77; 95% CI, 2.10-10.9; P < .001). Personalized PK-directed dosing to achieve optimal fludarabine exposure should be tested in prospective trials and, based on this analysis, may reduce disease relapse after CAR T-cell therapy.

Tisagenlecleucel outcomes in relapsed/refractory extramedullary ALL: a Pediatric Real World CAR Consortium Report.

Chimeric antigen receptor (CAR) T cells have transformed the therapeutic options for relapsed/refractory (R/R) B-cell acute lymphoblastic leukemia. Data for CAR therapy in extramedullary (EM) involvement are limited. Retrospective data were abstracted from the Pediatric Real World CAR Consortium (PRWCC) of 184 infused patients from 15 US institutions. Response (complete response) rate, overall survival (OS), relapse-free survival (RFS), and duration of B-cell aplasia (BCA) in patients referred for tisagenlecleucel with EM disease (both central nervous system (CNS)3 and non-CNS EM) were compared with bone marrow (BM) only. Patients with CNS disease were further stratified for comparison. Outcomes are reported on 55 patients with EM disease before CAR therapy (CNS3, n = 40; non-CNS EM, n = 15). The median age at infusion in the CNS cohort was 10 years (range, <1-25 years), and in the non-CNS EM cohort it was 13 years (range, 2-26 years). In patients with CNS disease, 88% (35 of 40) achieved a complete response vs only 66% (10 of 15) with non-CNS EM disease. Patients with CNS disease (both with and without BM involvement) had 24-month OS outcomes comparable to those of non-CNS EM or BM only (P = .41). There was no difference in 12-month RFS between CNS, non-CNS EM, or BM-only patients (P = .92). No increased toxicity was seen with CNS or non-CNS EM disease (P = .3). Active CNS disease at time of infusion did not affect outcomes. Isolated CNS disease trended toward improved OS compared with combined CNS and BM (P = .12). R/R EM disease can be effectively treated with tisagenlecleucel; toxicity, relapse, and survival rates are comparable to those of patients with BM-only disease. Outcomes for isolated CNS relapse are encouraging.