Introduction Obe-cel, an autologous, fast off-rate 4-1BB-ζ CD19-directed CAR T, demonstrated long-term efficacy and low severe immunotoxicity in adult R/R B-ALL (Roddie C, et al. NEJM 2024). In the Phase I CARPALL study (NCT02443831), obe-cel showed promising efficacy and safety in pediatric R/R B-ALL (Ghorashian S, et al. Nat Med 2019). Objective To evaluate the preliminary safety/efficacy of obe-cel in the R/R B-ALL cohort of the Phase Ib/II CATULUS study (NCT06173518). Methods CATULUS is a single-arm, open-label, international multi-center study. Eligible pts (<18 years, with primary refractory R/R B-ALL/high-risk first relapse/≥2 relapses) underwent lymphodepletion (fludarabine 4 × 30 mg/m2; cyclophosphamide 2 × 500 mg/m2), followed by a single obe-cel infusion (target dose: 1.0 × 106/kg CAR T-cells). The Phase Ib primary endpoints include frequency/severity of treatment-emergent adverse events. Secondary endpoints include overall remission rate (ORR; complete remission [CR]/CR with incomplete hematologic recovery [CRi]), CAR T-cell expansion, CAR T-cell persistence, and B-cell aplasia. Results As of April 30, 2025, 20/21 (95.2%) enrolled pts with R/R B-ALL received obe-cel at the target dose; all products were in specification. Baseline characteristics are shown in Table 1. Post infusion, Grade ≥3 cytokine release syndrome (CRS)/immune effector cell-associated neurotoxicity syndrome (ICANS) each occurred in two pts; five pts had Grade ≥3 infection (Table 2). One pt died from progressive disease. At data cut-off (median follow-up: 6.7 months [range: 0.9–15.2 months]), the ORR (CR/CRi) was 95.0% (n=19; 95% confidence interval: 75.1–99.9). Following obe-cel infusion, the geometric mean for Cmax was 92,773 copies/µg DNA (coefficient of variation [CV%]: 156.7) and 860,815 copies/µg DNA × days (CV%: 169.6) for AUC0–28d. The median Tmax was 14 days (range: 9–21 days). All responders (n=19) achieved measurable residual disease (MRD)-negative remission (<10–4 leukemic cells). Of the responders, 17/19 (89.5%) were still in ongoing remission at data cut-off. While in remission, 3/19 (15.8%) pts received stem cell transplant (SCT); 14/16 (87.5%) pts who did not receive SCT post obe-cel were in ongoing B-cell aplasia at data cut-off. Pts with morphological relapse (n=1)/emergence of MRD (n=1) received further anti-leukemic therapy. Conclusions Manufacture of obe-cel was successful for all pts. Obe-cel effectively expanded after a single infusion of 1.0 × 106/kg CAR T-cells. The pediatric safety profile of obe-cel was consistent with that previously reported for adults, with low rates of high-grade CRS/ICANS. ORR was high at 95%; nearly 90% of responders had ongoing remission at data cut-off. While longer follow-up is needed, obe-cel holds potential as treatment in pediatric R/R B-ALL. Additional Phase Ib data will be presented and the Phase II expansion trial is being planned.

Introduction Despite therapeutic advances, pediatric acute myeloid leukemia (AML) remains associated with substantial relapse risk and poor survival. High-risk patients are commonly consolidated with allogeneic hematopoietic stem cell transplant (HSCT) in first complete remission (CR1) to improve long-term outcomes. Historically, three chemotherapy (chemo) cycles have been administered prior to HSCT; however, many centers now proceed more rapidly after fewer cycles once CR1 is achieved. The optimal number of cycles prior to HSCT and its impact on outcomes remain unclear, particularly in the era of measurable residual disease (MRD)-based risk stratification. To address this knowledge gap, we compared outcomes among pediatric and young adult AML patients in CR1 who underwent HSCT after ≤2 versus ≥3 cycles of chemo. Methods We conducted a multicenter retrospective cohort study of patients ≤25 with AML diagnosed between 2012-2022 who underwent HSCT in CR1. Patients were grouped by number of pre-HSCT chemo cycles (≤2 vs. ≥3). Outcomes included relapse, leukemia-free survival (LFS), overall survival (OS), treatment-related mortality (TRM), and relapse mortality (RM). Kaplan-Meier and regression models (Cox for OS/LFS, Fine-Gray for relapse/RM, and logistic for TRM) were used, adjusting for age, sex, race, performance status (PS), cytogenetic risk, MRD pre-HSCT, extramedullary disease (EMD) at diagnosis, and cycles of chemo required to achieve CR1. Results The study included 479 patients from 14 institutions. Median age was 12 years (range 0-24); 53.4% were male. Overall, 127 patients (26.5%) received ≤2 cycles and 352 (73.5%) received ≥3 cycles of chemo pre-HSCT. Groups differed significantly (p<0.05) by number of cycles required to achieve CR1, race, and EMD at diagnosis, while age, sex, PS, cytogenetic features, and MRD pre-HSCT were similar (Figure 1).Four-year LFS and OS were significantly higher in the ≤2 cycle group: 67% vs. 56% (p=0.025; adjusted hazard ratio [aHR]=1.48, 95% Confidence Interval (CI) 1.02-2.14, p=0.039) and 75% vs. 63% (p=0.025; aHR=1.60, 95% CI 1.05-2.44, p=0.028; both adjusted for age, PS, pre-HSCT MRD and cycles to CR1), respectively (Figure 2). Relapse incidence was 26% in the ≤2 vs. 34% in the ≥3 cycle group, but the difference was not statistically significant (p=0.071; aHR=1.40, 95% CI 0.95-2.08, p=0.091). TRM (Odds Ratio=3.37, 95% CI 0.77-14.73, p=0.107) and RM (aHR=1.35, 95% CI 0.82-2.22, p=0.238) did not differ significantly between groups. Conclusion We illustrated that HSCT after ≤2 chemo cycles was associated with superior OS and LFS compared to ≥3 cycles. These findings support consideration of earlier transplantation in pediatric and young adult AML patients once CR1 is achieved. Ongoing analyses are underway to delineate the impact of additional disease and treatment-related factors that may influence these findings.

BACKGROUND:Inborn errors of immunity (IEI) are characterized by impaired lymphoid or myeloid immune cell function, resulting in recurrent infections, end-organ damage, and increased premature mortality. Allogeneic hematopoietic cell transplantation (allo-HCT) constitutes a curative treatment option for many IEI. Allo-HCT in this patient population poses unique challenges that necessitate the utilization of a conditioning regimen that affords rapid and stable engraftment, reduced organ toxicity, and low rates of graft-versus-host disease (GVHD). OBJECTIVE:Evaluate survival, engraftment, and toxicity after reduced intensity conditioning (RIC) allo-HCT in patients with IEI. STUDY DESIGN:This IRB-approved, multicenter phase 2 clinical trial aimed to estimate the overall (OS) and characterize longitudinal engraftment of patients with IEI undergoing allo-HCT using an optimized reduced-intensity conditioning (RIC) regimen. The regimen consisted of alemtuzumab on days -14 through -12 (cumulative dose 45 mg in patients weighing ≥ 10 kg, 30 mg if < 10 kg), fludarabine on days -8 through -4 (150 mg/m² or 5 mg/kg in patients weighing <10 kg), thiotepa on day -4 (8 mg/kg total) and melphalan on day -3 (140 mg/m² or 4.7 mg/kg in patients weighing <10 kg). Graft sources included bone marrow (BM), peripheral blood stem cells (PBSCs), or umbilical cord blood (UCB). RESULTS:Twenty-eight pediatric and young adult patients with IEI received study treatment. The 1-year and 3-year overall survival (OS) for the entire cohort was 96.3% (95% CI: 76.5 to 99.5) and 87.5% (95% CI: 66.0 to 95.8), respectively. Event-free survival (EFS) was significantly lower in infants [1-year EFS 57.1% (95% CI: 17.2 to 83.7) and 3-year EFS 38.1% (95% CI: 6.1 to 71.6)] compared to older children [1-year EFS 90.5% (95% CI: 67.0 to 97.5) and 3-year EFS 84.4% (95% CI: 58.7 to 94.8)] (P = .0007) owing to higher rates of treatment failure (TF, loss of donor chimerism or recurrence of IEI). The cumulative incidence of TF in infants was 42.9% (95% CI: 7.6% to 75.7%) at 1 year and 61.9% (95% CI: 10.4% to 90.3%) at 3 years compared to 9.5% (95% CI: 1.5% to 26.6%) at 1 and 3 years in older children (P = .004). Most infants (4/5,80%) with TF were successfully salvaged with second allo-HCT. The cumulative incidence of Grade II-IV acute and chronic GVHD was 10.7% (95% CI: 2.6 to 25.4) and 12.9% (95% CI: 3.0 to 30.2), respectively. Immune reconstitution was robust in most patients, with timely lymphocyte subset recovery, restored thymopoiesis, and independence of immunoglobulin administration. CONCLUSION:This RIC allo-HCT regimen for treatment of IEI had excellent OS with resolution of underlying immune abnormality, reconstitution of normal immune function, and low rates of GVHD. Future efforts will focus on optimizing engraftment in infants.

Pneumocystis jirovecii pneumonia (PJP) in hematopoietic cell transplant (HCT) recipients can be prevented by efficient prophylaxis. We surveyed HCT centers in North America to assess their PJP prophylaxis practices. Most institutions used intravenous (IV) pentamidine (29.6%) or inhaled pentamidine (14.8%); 37% institutions changed from trimethoprim/sulfamethoxazole (TMP-SMX) to another medication after conditioning; and 44% administered no PJP prophylaxis during the pre-engraftment period. Most institutions avoided using TMP-SMX during the pre-engraftment period, mainly because of concerns about myelotoxicity, despite this being the preferred PJP prophylaxis agent. There is a need to evaluate the effects of TMP-SMX on engraftment.

Background We are conducting a Phase 1 clinical study to evaluate the safety and efficacy of escalating doses of autologous CD123-CAR T cells for pediatric patients with r/r CD123-positive AML or ALL. We previously reported (Naik et al, Blood 2022, 140 (Supplement 1): 4584-5) that infusion of CD123-CAR T cells after lymphodepleting chemotherapy with fludarabine and cyclophosphamide was well tolerated, with transient fevers representing grade 1 cytokine release syndrome (CRS) and without dose limiting toxicities. We observed anti-AML activity as evidenced by responses in two out of six infused patients albeit with limited CAR T-cell expansion. Mechanistic studies revealed that CD123-CAR T cells were predominantly effector memory and expressed markers associated with T cell exhaustion (TIM3, PD1 or CD39). This phenotype was completely reversed by generating CD123-CAR T cells in the presence of dasatinib (CD123-CAR.dasa T cells), a multikinase inhibitor known to transiently inhibit CAR signaling. Based on these findings, we modified the CD123-CAR T cell production for our protocol and now report on an extended comparison of CD123-CAR and CD123-CAR.dasa T cells and on the clinical course of patients who were infused with CD123-CAR.dasa T cells. Methods and Results Single cell RNA seq analysis revealed that CD123-CAR.dasa T cells had upregulated IFNa signaling pathways in comparison to CD123-CAR T cells. In addition, they were in a less differentiated state as judged by a methylation-based multipotency index, exhibited preferential oxphos metabolism, and had increased apoptosis after initial antigen exposure as evidenced by caspase 3/7 activity. Six patients (5 AML, 1 ALL) were infused with CD123-CAR.dasa T cells on dose level (DL) 3 (3x106/kg) or 4 (1x107/kg). All patients developed high-grade fevers within 3 hours of infusion. All 3 patients on DL3 developed grade 2 CRS that responded to a single dose of tocilizumab. On DL4, all 3 patients presented with grade 4-5 CRS with evidence of immune effector cell-associated hemophagocytic lymphohistiocytosis-like syndrome (IEC-HS). All DL4 patients required multiple doses of immune modulatory agents including tocilizumab, steroids and emapalumab. One patient also received ruxolitinib, anakinra and etanercept without benefit, and died of cardiorespiratory failure. Autopsy results were consistent with CRS and no evidence of on target/off cancer toxicity. Patients post CD123-CAR.dasa T-cell infusion had significantly higher levels of circulating chemokines and cytokines, including IFNg, GMCSF, IL10, IL6 and TNFa, in comparison to patients who had received CD123-CAR T cells. Peak expansion of CD123-CAR.dasa T cells, as judged by qPCR analysis, was higher in comparison to CD123-CAR T cells. However, this did not translate into improved anti-leukemia activity as no patients had a response. Conclusions CD123-CAR T cells generated in the presence of dasatinib induced high grade CRS and/or IEC-HS without improved anti-leukemia activity. Our findings are in contrast with CAR.dasa T-cell products that target other antigens. While additional mechanistic studies are in progress, our results highlight that dasatinib cannot be considered a universal agent to improve the effector function of CAR T cells for hematological malignancies.

OBJECTIVES/GOALS: Patients who require a hematopoietic cell transplant (HCT) and dont have an HLA-matched related or unrelated donor may rely on a haploidentical donor. The optimal haploidentical donor and guidance for selection is limited. We aim to determine how donor characteristics affect outcomes following haploidentical-HCT for pediatric patients. METHODS/STUDY POPULATION: This is a retrospective cohort study evaluating the effect of donor age and relationship on post-HCT outcomes in children (0-18y) from 2008-2018. Multivariable logistic regression analysis will identify if donor age or donor relationship affect the development of graft-versus-host-disease (GVHD), while adjusting for other patient, donor, and transplant related variables. Two-year overall survival & event-free survival will be determined using Kaplan-Meier curves, stratified by donor age group and donor relationship, and compared by log-rank testing. Sub-analyses will be performed for myeloablative transplants and reduced intensity conditioning, as well as for malignant and non-malignant diseases. RESULTS/ANTICIPATED RESULTS: Our primary aim to is determine the effect of donor age and the effect of donor relationship to patient on the development of GVHD. We hypothesize that utilization of a younger donor will decrease the incidence of GVHD. Further, we hypothesize that utilizing a sibling haploidentical donor will result in less GVHD than a parental donor. Secondary aims include evaluating the effect of donor age and donor relationship on overall survival, event-free survival, non-relapse mortality, relapse, graft failure and time to engraftment. The results of this study will help us to develop criteria for optimal haploidentical donor selection. If donor selection is optimized, this could result in improved outcomes following haploidentical transplants. DISCUSSION/SIGNIFICANCE: Haploidentical donors are increasingly used as many patients, especially ethnic minorities, do not have an HLA-matched donor. This will be the largest study of haploidentical HCT in children. The data gathered will allow us to identify important donor characteristics to help guide physician decision-making when choosing a haploidentical donor.

Delayed management of nonconvulsive status epilepticus (NCSE) can lead to an increased morbidity and mortality. We previously established that inefficient treatment of NCSE at our institution stemmed from delayed initiation of emergent anti-seizure medications (ASM). In the present study, we assessed the trajectories of these time parameters and determined patient outcomes following the specific quality improvement (QI) interventions.The QI interventions, including the revision of the educational content for trainees and pharmacy workflow optimization were implemented between January 2019 and September 2021 by a dedicated multidisciplinary task force. The times needed to initiate and administer the ASMs for patients with NCSE as well as patient mortality were assessed in comatose and noncomatose patients and compared with the corresponding values prior to the interventions.There were 79 occurrences of NCSE in 74 patients. The median time from seizure detection on EEG to the order of the first and second ASM for NCSE was reduced by 4 (p = 0.83) and 8 min (p = 0.52), respectively compared to the times prior to the initiation of interventions. The median times from the order to administration of the first and third ASM for all NCSE occurrences were reduced by 8 and 10 min, respectively (p = 0.28 and p = 0.10). In the present cohort of comatose patients, the median time spent to order the first ASM was reduced by 16.5 min and the time to administer it reduced by 35 min compared to that in our previous study. The overall patient mortality was decreased by 11.1%.More efficient delivery of rescue ASMs in patients with NCSE and improvement in their mortality can be achieved with multidisciplinary team efforts aimed at streamlining the functioning of pharmacy and strengthening the education of trainees and nurses.

Hematological toxicity (hematotoxicity) leading to peripheral cytopenias is a common long-term adverse effect following the use of CD19-chimeric antigen receptor (CD19-CAR) T-cell therapies. However, management remains unclear for patients whose cytopenias persist beyond 1 month after CAR T-cell infusion. We present the case of a 21-year old who received CD19-CAR T-cell therapy for relapse following a haploidentical transplant. He developed hematotoxicity and consequently multiple life-threatening infections. We administered a CD34(+) hematopoietic stem cell boost (HSCB) from his transplant donor, which led to hematopoietic recovery and resolution of his infections without any effect on the activity of CD19-CAR T cells. CD34(+) HSCB can be a safe and effective option to treat hematotoxicity following CD19-CAR T-cell therapy.

In embryonal rhabdomyosarcoma (ERMS) and generally in sarcomas, the role of wild-type and loss- or gain-of-function TP53 mutations remains largely undefined. Eliminating mutant or restoring wild-type p53 is challenging; nevertheless, understanding p53 variant effects on tumorigenesis remains central to realizing better treatment outcomes. In ERMS, >70% of patients retain wild-type TP53, yet mutations when present are associated with worse prognosis. Employing a kRASG12D-driven ERMS tumor model and tp53 null (tp53-/-) zebrafish, we define wild-type and patient-specific TP53 mutant effects on tumorigenesis. We demonstrate that tp53 is a major suppressor of tumorigenesis, where tp53 loss expands tumor initiation from <35% to >97% of animals. Characterizing three patient-specific alleles reveals that TP53C176F partially retains wild-type p53 apoptotic activity that can be exploited, whereas TP53P153Δ and TP53Y220C encode two structurally related proteins with gain-of-function effects that predispose to head musculature ERMS. TP53P153Δ unexpectedly also predisposes to hedgehog-expressing medulloblastomas in the kRASG12D-driven ERMS-model.

A fetus with features of hydrops was given intra-uterine transfusion at 27 weeks and 31 weeks of gestation. Mother had been alloimmunized with anti-D and anti-C antibodies. At birth, laboratory investigations revealed bone marrow suppression along with features of hemolytic anemia. The neonate was started on a combination of phototherapy and intravenous immunoglobulin. During the course, the neonate was transfused with one unit of packed red cells (top-up transfusion). Neonatal hyperbilirubinemia responded to phototherapy and the bone marrow activity spontaneously resumed after 3 weeks of life. In neonates with anemia at birth who have history of multiple intra-uterine transfusions, early-onset hypoproliferative anemia should be considered.

Pediatric and adolescent and young adult (AYA) patients who receive many blood product transfusions, such as individuals with sickle cell disease (SCD), severe aplastic anemia (SAA) or indolent hematologic malignancies, are at high risk for developing donor-specific antibodies (DSA). DSAs with mean fluorescence intensity (MFI) greater than 5000 have been associated with significant graft failure, but lower MFI values between 2000 and 5000 may result in poor graft function after hematopoietic cell transplant (HCT). Desensitization strategies have been developed to reduce the DSA burden in HCT recipients before graft infusion, but the experience with these strategies in the pediatric and AYA populations is not well described in the literature. Here, we describe our experience with successful desensitization by using a combination of treatment strategies in five pediatric and AYA patients, including a novel use of daratumumab in a young adult patient who had refractory DSAs and had suffered serious side effects from conventional desensitization strategies. The presence of elevated DSAs in pediatric and AYA recipients of a human leukocyte antigen (HLA)-mismatched haploidentical HCT can be overcome by a multipronged treatment strategy.

Background The prognosis of pediatric patients with relapsed or refractory (r/r) Acute Myeloid Leukemia (AML) remains dismal. Evaluation of novel therapies such as chimeric antigen receptor (CAR) T cells is therefore urgently needed. CD123 is overexpressed on AML blasts and leukemic stem cells (LSC), making it an attractive target for CAR T-cell directed therapy. Methods and Results We designed a 'bridge to allogeneic hematopoietic cell transplant (HCT)’ Phase 1 study to evaluate the safety and feasibility of treating pediatric patients with r/r AML with CD123-CAR T-cell on four dose levels (DL): DL1: 3x105/kg, DL2: 1x106/kg, DL3: 3x106/kg, DL4: 1x107/kg (NCT04318678). CD123-CAR T-cells were generated from CD4/CD8-selected autologous leukapheresis products using a lentiviral vector, which encoded a CD123-CAR with CD28.z signaling domain and a CD20 safety switch. Patients received lymphodepleting chemotherapy with Fludarabine and Cyclophosphamide followed by a single CAR T cell infusion. To date we have enrolled 12 patients. The median age of treated patients was 17 years (range 12-21years). Except for the first patient who had primary refractory disease, all other patients had relapsed following HCT (n=1-4 previous HCTs). Despite patients being heavily pre-treated, we successfully manufactured products on all patients. The infused products had a predominantly CD4+ effector memory immunophenotype, with a median CD123-CAR+/CD20+ expression of 60.2% (range 46.1-79.4%, N=6). All infused CAR T cell products exhibited potent antitumor activity in vitro when cultured against CD123+ targets (including autologous blasts for 2 patients). We infused 2 patients on DL1 and 3 patients on DL2. Two patients were infused on single patient protocols. All infusions were well tolerated, without any adverse infusion events. Post infusion, we observed isolated fevers that resolved within 24 hours (possible Grade 1 Cytokine Release Syndrome (CRS)). No Grade 2 ≥ CRS or neurotoxicity was seen. Multiplex cytokine analysis showed statistically significant increase of IL15 after lymphodepletion without significant increase in Th1 cytokines or IL6 after T cell infusion. While transient cytopenias were observed, patients did not develop persistent marrow aplasia. No dose limiting toxicities were noted. Disease evaluation was performed at 4-6 weeks following CAR T cell infusion. The 2 patients on DL1 showed no response. In the 3 patients on DL2, we observed: reduction in blast percentage without complete remission (CR) in 1 patient, no response in 1 patient and CR in 1 patient. The patient with CR had isolated extramedullary disease, showing complete resolution of all lesions by week 4 by PET imaging (Figure 1). She recurred 2 months following infusion, coinciding with loss of CAR T-cell detection by qPCR. She received a second infusion off study and again achieved a short-lived CR. One additional patient was infused on dose level 2 off protocol. She achieved morphological CR at day 28 with low level minimal residual disease (0.19%). Correlative studies revealed CD123-CAR T cell expansion in patients on DL2 (Figure 2), but not on DL1. However, peak expansion on DL2 was low in comparison to published reports on CAR T cells for Acute Lymphoblastic Leukemia. Detailed phenotypic analysis revealed that CD123-CAR T cell products were predominantly effector memory (CD45RO+CCR7-) with <2% naïve-like (CD45RO-CCR7+ or CD45RO-CD62L+) T cells. In addition, PD1, TIM3 and CD39 were expressed at a median of 43, 81 and 16% in CD4+ and 3, 72 and 45% in CD8+ T cells. This phenotype could be completely reversed by inhibiting CAR signaling with dasatinib during the manufacturing process, resulting in a CAR T cell product dominated by naïve-like T cells that did not express TIM3, PD1 or CD39, leading to enhanced T-cell effector function. Mechanistic analysis revealed that the observed phenotype could be explained by the transient, increased cell surface expression of CD123 on T cells upon activation during manufacturing, and not by tonic CAR signaling. Conclusions Our initial clinical experience with CD123-CAR T cells for pediatric patients with r/r AML demonstrates feasibility, safety, and evidence of anti-leukemic activity. Upcoming CD123-CAR T cell products will be manufactured in the presence of dasatinib to limit T-cell differentiation and exhaustion as we continue to explore our CD123-CAR T cell therapy approach for pediatric r/r AML. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Background Extranodal NK/T cell lymphoma (ENKTL) is an aggressive form of Epstein-Barr virus (EBV)-associated non-Hodgkin's lymphoma which historically has a poor prognosis. When relapse occurs, particularly in the cerebral nervous system (CNS), survival is rare. The immune checkpoint pathway family of proteins is highly expressed in many human tumors, especially in EBV-related malignancies. To the best of our knowledge, there are no reports of immune checkpoint inhibitors used either alone or in combination for the treatment of ENTKL CNS relapse, yet there are promising results in metastatic CNS involvement of other malignancies. Case presentation This is the case of a 29-year-old Hispanic male with ENKTL who was treated at first relapse with 24 doses of the programmed death-ligand 1 (PD-L1) immune checkpoint inhibitor, atezolizumab, over a 17-month period. He remained in remission for 18 months until he experienced an isolated CNS relapse and on-going evidence of chronic EBV infection. Salvage therapy was provided as a combination of triple intrathecal (TIT) chemotherapy, radiation, and atezolizumab. He continues on maintenance atezolizumab and remains alive 1-year post CNS relapse. Conclusions The results from this case suggest that atezolizumab should be considered as part of the treatment regimen for relapsed ENKTL. They also demonstrate the benefit of using atezolizumab in combination with TIT chemotherapy and radiation as a viable treatment option for ENKTL CNS relapse and indicate that atezolizumab is an option for long-term maintenance therapy for patients with ENKTL.

ABSTRACT IMPACT: By assessing function of mutant (patient-specific) tp53 in zebrafish embryonal rhabdomyosarcoma will inform clinicians of the severity of mutant tp53 alleles. OBJECTIVES/GOALS: This study aims to define loss- and gain-of-function TP53 mutations by comparing effects in tp53-null and wild-type tumors. In addition, it aims to generate a rapid in vivo analysis platform to assign function to patient specific TP53 mutations in the clinic METHODS/STUDY POPULATION: To define tp53 function in ERMS pathogenesis, we previously generated a new tp53-null mutant (tp53-/-) in zebrafish by deleting the entire tp53 genomic locus using TALEN mutagenesis. tp53-/- zebrafish spontaneously develop a spectrum of tumors including sarcomas, leukemia and germ cell tumors (Ignatius…Baxi et. al., eLife) reminiscent of tumors observed in Trp53-null mice. Using the tp53-/- mutants to generate kRASG12D-induced ERMS, we discovered that tp53 is a potent repressor of metastases but rather surprisingly had no effect on self-renewal (Ignatius…Baxi et. al., eLife). Here, using tp53-/- zebrafish, we assessed effects of wild-type and mutant (patient specific) tp53 on tumor initiation, proliferation and apoptosis. RESULTS/ANTICIPATED RESULTS: ERMS tumor initiation in the tp53-/- background is observed in > 97% of animals whereas only <40% of wild-type animals develop ERMS. Additionally, tp53 is a potent suppressor of ERMS proliferation and its effect on apoptosis is minor. Next, we expressed either WT zebrafish or human TP53 in tp53-/- animals along with kRASG12D and both genes suppressed tumor initiation and growth. We co-expressed TP53C176F (found in two ERMS patients) and TP53P153del (identified in a patient with osteosarcoma in our clinic) in zebrafish ERMS, and find that the TP53C176F allele significantly suppressed tumor initiation with effects predominantly on enhanced apoptosis. However, the TP53P153del allele initiated tumors at similar frequency compared to tp53-/- animals but increased the initiation of tumors in the head musculature. DISCUSSION/SIGNIFICANCE OF FINDINGS: Different TP53 alleles identified in patient tumors have very different effects on tumorigenesis in vivo and can respond differently to potentially therapeutic compounds. Thus, the type of precision modeling demonstrated here promises to help further define patient-specific TP53 biology and improve clinical strategies in the future.

Angiosarcoma is a clinically aggressive tumor with a high rate of mortality. It can arise in vascular or lymphatic tissues, involve any part of the body, and aggressively spread locally or metastasize. Angiosarcomas spontaneously develop in the tp53 deleted (tp53del/del) zebrafish mutant. However, established protocols for tumor dissection and transplantation of single cell suspensions of angiosarcoma tumors result in inferior implantation rates. To resolve these complications, we developed a new tumor grafting technique for engraftment of angiosarcoma and similar tumors in zebrafish, which maintains the tumor microenvironment and has superior rates of engraftment.

Journal of Palliative MedicineVol. 24, No. 10 Personal ReflectionWhen a Tumor Becomes a Legacy: A Collection of PerspectivesAmanda E. Lipsitt, Patricia K. DeForest, Andrea J. Canon, Andrea R. Gilbert, and Gail E. TomlinsonAmanda E. LipsittAddress correspondence to: Amanda E. Lipsitt, MD, Division of Pediatric Hematology Oncology, University of Texas Health San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA. E-mail Address: lipsitta@uthscsa.eduhttps://orcid.org/0000-0002-3757-8493Division of Pediatric Hematology Oncology, University of Texas Health San Antonio, San Antonio, Texas, USA.Greehey Children's Cancer Research Institute, University of Texas Health San Antonio, San Antonio, Texas, USA.Search for more papers by this author, Patricia K. DeForestDivision of Pediatric Palliative Care, University of Texas Health San Antonio, San Antonio, Texas, USA.VITAS Hospice and Palliative Care, San Antonio, Texas, USA.Search for more papers by this author, Andrea J. CanonVITAS Hospice and Palliative Care, San Antonio, Texas, USA.Search for more papers by this author, Andrea R. GilbertDepartment of Pathology, University of Texas Health San Antonio, San Antonio, Texas, USA.Search for more papers by this author, and Gail E. TomlinsonDivision of Pediatric Hematology Oncology, University of Texas Health San Antonio, San Antonio, Texas, USA.Greehey Children's Cancer Research Institute, University of Texas Health San Antonio, San Antonio, Texas, USA.Search for more papers by this authorPublished Online:20 Sep 2021https://doi.org/10.1089/jpm.2021.0138AboutSectionsView articleView Full TextPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail View articleFiguresReferencesRelatedDetails Volume 24Issue 10Sep 2021 InformationCopyright 2021, Mary Ann Liebert, Inc., publishersTo cite this article:Amanda E. Lipsitt, Patricia K. DeForest, Andrea J. Canon, Andrea R. Gilbert, and Gail E. Tomlinson.When a Tumor Becomes a Legacy: A Collection of Perspectives.Journal of Palliative Medicine.Sep 2021.1572-1574.http://doi.org/10.1089/jpm.2021.0138Published in Volume: 24 Issue 10: September 20, 2021PDF download