Abstract: Tisagenlecleucel, an anti-CD19 chimeric antigen receptor T cell therapy, has demonstrated efficacy in children and young adults with relapsed/refractory B cell acute lymphoblastic leukemia (B-ALL) in two multicenter phase 2 trials (ClinicalTrials.gov, NCT02435849 (ELIANA) and NCT02228096 (ENSIGN)), leading to commercialization of tisagenlecleucel for the treatment of patients up to age 25 years with B-ALL that is refractory or in second or greater relapse. Methods A pooled analysis of 137 patients from these trials (ELIANA: n=79; ENSIGN: n=58) was performed to provide a comprehensive safety profile for tisagenlecleucel. Results Grade 3/4 tisagenlecleucel-related adverse events (AEs) were reported in 77% of patients. Specific AEs of interest that occurred ≤8 weeks postinfusion included cytokine-release syndrome (CRS; 79% (grade 4: 22%)), infections (42%; grade 3/4: 19%), prolonged (not resolved by day 28) cytopenias (40%; grade 3/4: 34%), neurologic events (36%; grade 3: 10%; no grade 4 events), and tumor lysis syndrome (4%; all grade 3). Treatment for CRS included tocilizumab (40%) and corticosteroids (23%). The frequency of neurologic events increased with CRS severity (p 〈 0.001). Median time to resolution of grade 3/4 cytopenias to grade ≤2 was 2.0 (95% CI 1.87 to 2.23) months for neutropenia, 2.4 (95% CI 1.97 to 3.68) months for lymphopenia, 2.0 (95% CI 1.87 to 2.27) months for leukopenia, 1.9 (95% CI 1.74 to 2.10) months for thrombocytopenia, and 1.0 (95% CI 0.95 to 1.87) month for anemia. All patients who achieved complete remission (CR)/CR with incomplete hematologic recovery experienced B cell aplasia; however, as nearly all responders also received immunoglobulin replacement, few grade 3/4 infections occurred 〉 1 year postinfusion. Conclusions This pooled analysis provides a detailed safety profile for tisagenlecleucel during the course of clinical trials, and AE management guidance, with a longer follow-up duration compared with previous reports.

Abstract: Relapse following chimeric antigen receptor (CAR) T-cell therapy directed against CD19 for relapsed/refractory B-acute lymphoblastic leukemia (r/r B-ALL) remains a significant challenge. Three main patterns of relapse predominate: CD19 positive (CD19pos) relapse, CD19 negative (CD19neg) relapse, and lineage switch (LS). Development and validation of risk factors that predict relapse phenotype could help define potential pre- or post-CAR T-cell infusion interventions aimed at decreasing relapse. Our group sought to extensively characterize preinfusion risk factors associated with the development of each relapse pattern via a multicenter, retrospective review of children and young adults with r/r B-ALL treated with a murine-based CD19-CAR construct. Of 420 patients treated with CAR, 166 (39.5%) relapsed, including 83 (50%) CD19pos, 68 (41%) CD19neg, and 12 (7.2%) LS relapses. A greater cumulative number of prior complete remissions was associated with CD19pos relapses, whereas high preinfusion disease burden, prior blinatumomab nonresponse, older age, and 4-1BB CAR construct were associated with CD19neg relapses. The presence of a KMT2A rearrangement was the only preinfusion risk factor associated with LS. The median overall survival following a post-CAR relapse was 11.9 months (95% CI, 9-17) and was particularly dismal in patients experiencing an LS, with no long-term survivors following this pattern of relapse. Given the poor outcomes for those with post-CAR relapse, study of relapse prevention strategies, such as consolidative hematopoietic stem cell transplantation, is critical and warrants further investigation on prospective clinical trials.

Abstract: A single-center trial of CD19 directed, lentiviral transduced chimeric antigen receptor (CAR) T cells (CTL019) for relapsed and refractory (r/r) B-ALL pediatric patients showed rates of CR 〉 90% with prolonged CAR T cell persistence/CR without further therapy in the majority of patients infused (Maude NEJM 2014). We report here the feasibility, safety and efficacy of the first multicenter global pivotal registration CAR T cell trial. Features of this trial include: i) the first trial in which industry-manufactured cells were provided to all patients; ii) enrollment across 25 centers in the US, EU, Canada, Australia, and Japan; iii) successful transfer and manufacturing of cells in a global supply chain; and iv) successful implementation of cytokine release syndrome (CRS) management across a global trial. All patients had CD19 positive B-ALL with morphologic marrow tumor involvement at registration ( 〉 5% blasts), and were either primary refractory; chemo-refractory after first relapse, relapsed after second line therapy; or ineligible for allogeneic SCT. CTL019 was manufactured from patient PBMC under GMP conditions in the US, at a centralized "sponsor-owned" manufacturing facility, and supplied to all sites. The primary endpoint of overall remission rate (CR+CRi) within 3 months and secondary endpoints (EFS, DOR, OS and safety) were assessed by an independent review committee. Based on preliminary data as of March 2016, 57 patients were enrolled. There were 3 manufacturing failures (5%), 5 patients were not infused due to death or adverse events (9%), and 15 patients were pending infusion at the data cut off. Following fludarabine/cyclophosphamide lymphodepleting chemotherapy in the majority of the patients, 34 patients (median age 11 [3-23], 50% with prior HSCT) were infused with a single dose of CTL019 at a median dose of 2.9 x106 transduced CTL019 cells/kg (0.2 to 4). Among 29 patients reaching D28 prior to the data cutoff, 83% (24/29) achieved CR or CRi by local investigator assessment, all of which were MRD-negative. Two early deaths occurred prior to initial disease assessment, one due to disease progression and one due to intracranial hemorrhage. Two patients did not respond. One patient was in CR by BM at D28, but CSF was not assessed, therefore this patient was classified as "incomplete" assessment. Safety was managed by a protocol-specified CRS algorithm with no cases of refractory CRS. Using the Penn CRS grading scale, 82% of patients experienced CRS, with 7 grade 3 (21%) and 8 grade 4 (24%) events. 44% patients with CRS required anti-cytokine therapy; all received tocilizumab with or without other anti-cytokine therapy, with complete resolution of CRS. Besides CRS, the most common grade 3 and 4 non-hematologic AEs were febrile neutropenia (29%), increased bilirubin (21%), increased AST (21%), and hypotension (21%). 21% of patients experienced grade 3 or 4 neuropsychiatric events including confusion, delirium, encephalopathy, agitation and seizure; no cerebral edema was reported. CTL019 in vivo cellular kinetics by qPCR demonstrated transgene persistence in blood in responding patients at and beyond 6 months. Overall exposure (AUC 0-28d) and maximal expansion (Cmax) of CTL019 DNA measured by qPCR was higher in responding compared with non-responding patients. In summary, this pivotal global study in pediatric and young adult patients with r/r B-ALL receiving CTL019, confirms a high level of efficacy and a similar safety profile to that shown in the prior single center experience. Safety was effectively and reproducibly managed by appropriately trained investigators. The study has completed accrual. At the meeting, updated data from a planned formal interim analysis including safety, efficacy (primary and selected secondary endpoints), cellular kinetics, and impact of anti-cytokine therapy will be presented for more than 50 patients infused at 25 global sites. Disclosures Grupp: Jazz Pharmaceuticals: Consultancy; Novartis: Consultancy, Research Funding; Pfizer: Consultancy. Laetsch:Novartis: Consultancy; Loxo Oncology: Consultancy. Bittencourt:Seattle Genetics: Consultancy; Jazz Pharmaceuticals: Consultancy, Other: Educational Grant. Maude:Novartis: Consultancy. Myers:Novartis Pharmaceuticals: Consultancy. Rives:Novartis: Consultancy; Jazz Pharma: Consultancy. Nemecek:Medac, GmbH: Research Funding; Novartis: Consultancy; National Marrow Donor Program: Membership on an entity's Board of Directors or advisory committees. Schlis:Novartis: Honoraria. Martin:Jazz Pharmaceuticals: Other: One time discussion panel; Novartis: Other: Support of clinical trials. Bader:Medac: Consultancy, Research Funding; Riemser: Research Funding; Neovii Biotech: Research Funding; Servier: Consultancy, Honoraria; Novartis: Consultancy, Honoraria. Peters:Novartis: Consultancy; Jazz: Speakers Bureau; Amgen: Consultancy; Pfizer: Consultancy; Medac: Consultancy. Biondi:Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Cellgene: Other: Advisory Board; BMS: Membership on an entity's Board of Directors or advisory committees. Baruchel:Servier: Consultancy; Novartis: Consultancy; Celgene: Consultancy; Jazz: Consultancy; Baxalta: Research Funding. June:University of Pennsylvania: Patents & Royalties; Johnson & Johnson: Research Funding; Celldex: Consultancy, Equity Ownership; Pfizer: Honoraria; Immune Design: Consultancy, Equity Ownership; Novartis: Honoraria, Patents & Royalties: Immunology, Research Funding; Tmunity: Equity Ownership, Other: Founder, stockholder . Sen:Novartis: Employment. Zhang:Novartis: Employment. Thudium:Novartis: Employment. Wood:Novartis Pharmaceuticals: Employment, Other: Stock. Taran:Novartis: Employment. Pulsipher:Chimerix: Consultancy; Jazz Pharmaceutical: Consultancy; Novartis: Consultancy, Other: Study Steering Committee; Medac: Other: Housing support for conference.

Abstract: Background: CTL019 is an investigational therapy derived from autologous T-cells expressing a CD19-specific chimeric antigen receptor (CAR). A single center, phase I/IIa trial of CTL019 showed complete and durable remissions in pediatric/young adult patients (pts) with relapsed/refractory (R/R) B-cell acute lymphoblastic leukemia (B-ALL) (Maude et al NEJM 2014); these results have yet to be reproduced in a multicenter setting. Here, we report results from a 6-month interim analysis of the first multicenter phase II trial of an engineered cell therapy in leukemia. Methods: 9 US sites participated in this single-arm phase II study in pediatric/young adult pts with R/R B-ALL. Leukapheresis products were shipped for centralized manufacturing according to the University of Pennsylvania (Penn) process in an academic-industry collaboration. T cells were transduced with a lentiviral vector encoding a CAR composed of anti-CD19 scFv, CD3ζ and 4-1BB domains. Following lymphodepletion with fludarabine and cyclophosphamide, a single dose of CTL019 cells was administered (target dose 2.0-5.0×106 cells/kg for ≤50 kg and 1.0-2.5×108 cells for 〉 50 kg). The primary endpoint was overall remission rate (ORR = CR + CRi [CRi, complete remission with incomplete blood count recovery] maintained at 2 evaluations ≥28 days apart) as determined by an Independent Review Committee. Secondary objectives included minimal residual disease (MRD), relapse-free survival (RFS), overall survival (OS) and safety. All analyses were performed on infused patient set. Results: 29/35 pts enrolled (82.9%) were infused with CTL019; 6 withdrew prior to infusion (2 manufacturing failures [1 lack of growth, 1 contamination]; 4 deaths [median, 48 days from enrollment; 2 progressive disease, 1 multi-organ failure, 1 pneumonia] ). Mean bone marrow involvement at enrollment was 68.2% (SD, 27.3%; Table 1). 2 pts did not receive lymphodepleting chemotherapy due to leukopenia. Collection, manufacturing and infusion were feasible in a multicenter setting with a median time from enrollment to infusion of 37 days. Target cell dose was met in 24/33 (72.7%) manufactured products. ORR in all infused pts was 69.0% (20/29 pts; 98.95% CI 43.6, 88.1). Of the 5 pts who received CTL019 below the target dose, 2 achieved CR/CRi. Of note, deep remission with no evidence of MRD ( 〈 0.01%) was achieved in 18/29 pts (62.1%; 95% CI 42.3, 79.3) within 6 months. Median RFS and median survival have not yet been reached. Median duration of follow-up was 6.4 months (range 0.4-14.0). CR/CRi was not achieved in 9 pts: 2 pts died before Day 28 (1 ALL; 1 embolic stroke not attributed to CTL019 at Day 25 after infusion), 6 did not respond and 1 pt achieved CRi at Day 28 but relapsed 17 days later. Of the 20 pts who achieved a CR/CRi, 8 pts relapsed 1.7-7.6 months after onset of remission; 2 were CD19 negative. RFS and OS at 6 months (Figures 1, 2) were 66.4% and 75.7%, respectively. Serious adverse events occurred in 79.3% of pts within 8 weeks of infusion. Overall 10 deaths occurred at 0.4-8.8 months (9 ALL; 1 embolic stroke); no deaths attributable to CTL019. The most common adverse event was cytokine release syndrome (CRS), which was graded on the Penn scale and managed according to a standardized algorithm. All 26 (89.7%) cases of CRS were reversible; 11 pts (37.9%) had grade 3 or 4 CRS, of which 7 (26.9%) required systemic anti-cytokine therapy, 9 (34.6%) required high dose vasopressors for hypotension, 6 (23.1%) required mechanical ventilation, 4 (15.4%) underwent dialysis. Reversible neuropsychiatric events occurred in 9 (31%) pts (1 grade 3; no grade 4), including seizures in 2 pts but no cases of cerebral edema. Conclusions: In this first multicenter trial of CAR-modified T cell therapy, CTL019 therapy was feasible and efficacious, showing a high ORR with durable remissions in pediatric/young adult pts with R/R B-ALL. Despite the high rate of toxicity with CTL019 in the R/R setting, the rate of grade 3 or 4 CRS was comparable to the single center study, and standardized management of CRS was successful in a multicenter trial with no deaths attributable to CRS. In this highly refractory population, a vast majority of eligible pts can be successfully infused in a timely fashion and outcomes appear reproducible in a multicenter setting despite a more heterogeneous population than the single center study. The trial is continuing under Novartis manufacturing. Disclosures Maude: Novartis: Consultancy. Pulsipher:Medac: Other: Travel support for a study group; Chimerix: Consultancy, Other: Advisory Board ; Jazz Pharmaceutical: Consultancy, Other: Advisory Board; Novartis: Consultancy, Other: Advisory Board, Steering Committee for Phase II Study. Grupp:Pfizer: Consultancy; Novartis: Consultancy, Research Funding. Davies:Novartis: Honoraria. Verneris:Bimogen: Other: Advisory Board. Schlis:Novartis: Honoraria. Driscoll:Novartis: Consultancy. June:Immune Design: Consultancy, Equity Ownership; Pfizer: Honoraria; Celldex: Consultancy, Equity Ownership; Novartis: Honoraria, Patents & Royalties, Research Funding; Johnson & Johnson: Honoraria; Novartis: Honoraria, Patents & Royalties, Research Funding; Tmunity Therapeutics: Equity Ownership. Levine:GE Healthcare Bio-Sciences: Consultancy; Novartis: Patents & Royalties, Research Funding. Wood:Novartis Pharmaceuticals: Employment, Other: Stock. Yi:Novartis: Employment.

Abstract: Introduction: Chimeric antigen receptor (CAR) T-cells redirected against CD19 have demonstrated remarkable clinical activity in children and adults with relapsed/refractory (r/r) B-cell malignancies. The risk of lineage switch (LS) following CD19-directed therapies has been well documented but has been primarily limited to case reports. Additionally, the risk of subsequent malignant neoplasms (SMN) following CAR T-cells has not yet been described. Distinguishing LS (B-ALL to myeloid malignancy) from a therapy-related myeloid neoplasm is both clinically and biologically relevant. The former emerges from a highly refractory leukemic clone, likely resistant to salvage therapy, whereas the latter represents a new malignancy that can be associated with long-term survival. Methods: We conducted a multicenter, retrospective review of children and young adults with r/r B-acute lymphoblastic leukemia (B-ALL) who received either commercial tisagenlecleucel or 1 of 3 investigational murine-based CD19-CAR constructs on clinical trials at 7 US centers between 2012-2019. Patients diagnosed with B-ALL before age 25 years were included and patients who had received any prior CAR product were excluded. Results: Of 420 CAR-treated patients, with a median follow-up of 30.1 months, 12 (2.9%) experienced LS and 6 (1.4%) developed a SMN (Table). The median time to diagnosis of LS following CAR T-cell infusion was significantly shorter compared to diagnosis of SMN (65.5 days vs. 883.5 days; p=0.005). Eleven of 12 patients (91.7%) with LS converted to acute myeloid leukemia (AML). One patient converted to mixed phenotype acute leukemia, B/myeloid type. The leukemia of 10 of 12 patients with LS harbored cytogenetics similar to those at initial diagnosis. For the remaining 2 patients with LS, cytogenetics were unavailable, but the leukemias were considered LS by the treating institution. KMT2Ar rearrangement (KMT2Ar) was a predominant cytogenetic abnormality seen in patients with LS. Overall, 38 of 420 patients (9%) had a KMT2Ar. KMT2Ar was present in 9 of 12 (75%) patients with LS compared to 20 of 408 (7.1%) non-LS patients (p & lt;0.001). Patients with LS were younger at initial diagnosis compared to the remaining cohort (median age, 1.6 years vs. 7.7 years; p=0.001), reflecting the inherent association between KMT2Ar and infant ALL. Otherwise, there were no significant differences in gender, prior hematopoietic stem cell transplant (HSCT), prior blinatumomab exposure, or CAR response. Within the KMT2Ar cohort, 31 (81.6%) patients achieved a complete remission post-CAR. Eight of these patients received a consolidative HSCT (representing 4 first and 4 second HSCTs). No KMT2Ar patient experienced a post-HSCT LS and 3 are alive with a median follow-up of 1164 days post-CAR. In contrast, of the 23 KTM2Ar patients who did not receive HSCT post-CAR, 7 developed LS and 14 are alive with a median follow-up of 864 days post-CAR. Relative contraindications to post-CAR HSCT included a prior HSCT (n=11) or early LS (n=5). Of the 7 CAR non-responding patients with KMT2Ar, 2 (28.6%) had rapid emergence of LS by the first restaging timepoint. There are no long-term survivors following LS, regardless of KMT2A status, dying a median of 123 days (range, 36-594 days) after diagnosis of LS. The 6 SMNs were cholangiocarcinoma, synovial sarcoma, malignant melanoma and 3 therapy-related myeloid neoplasms (MDS/AML), distinguished from LS based on loss of original cytogenetics. Notably, 4/6 (67%) patients that developed a SMN had received an allogeneic HSCT prior to development of SMN. Four patients (67%) remain alive and in remission with a median follow-up of 304 days after diagnosis of SMN, including 2 patients with MDS/AML. Conclusions: In the largest series of pediatric patients treated with CAR T-cell therapy, we show that LS occurs in 2.9% of children. The presence of a KMT2Ar was the biggest risk factor, with 23.7% of these patients experiencing LS. We found that LS can occur very early in a patient's post CAR T-cell course, and despite a variety of treatment approaches, the outcomes for these patients are dismal. Given the predisposition to LS, the role for consolidative HSCT in KMT2Ar patients warrants further study. Limited by a short follow-up period, we saw SMNs in only 1.4% of our patients. Causality is unknown and likely unrelated to CAR-T, but this further supports the long-term safety of CAR T-cells in children with B-ALL. Figure 1 Figure 1. Disclosures Borowitz: Amgen, Blueprint Medicines: Honoraria. Lee: Harpoon Therapeutics: Consultancy; Amgen: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Kite Pharma: Other: trial funding; Gilead: Other: trial funding. Grupp: Novartis, Adaptimmune, TCR2, Cellectis, Juno, Vertex, Allogene and Cabaletta: Other: Study steering committees or scientific advisory boards; Novartis, Roche, GSK, Humanigen, CBMG, Eureka, and Janssen/JnJ: Consultancy; Novartis, Kite, Vertex, and Servier: Research Funding; Jazz Pharmaceuticals: Consultancy, Other: Steering committee, Research Funding. Verneris: jazz: Other: advisory board; Novartis: Other: advisory board; Fate Therapeutics: Consultancy. Gore: Mirati: Current equity holder in publicly-traded company; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Current equity holder in publicly-traded company, Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche/Genentech: Consultancy, Honoraria; Clovis: Current equity holder in publicly-traded company; Celgene: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Sanofi Paris: Current equity holder in publicly-traded company; Anchiano: Current equity holder in publicly-traded company; Blueprint Medicines: Current equity holder in publicly-traded company. Brown: Novartis: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Kura: Membership on an entity's Board of Directors or advisory committees; KIte: Membership on an entity's Board of Directors or advisory committees. Pulsipher: Equillium: Membership on an entity's Board of Directors or advisory committees; Adaptive: Research Funding; Jasper Therapeutics: Honoraria. Rheingold: Pfizer: Research Funding; Optinose: Other: Spouse's current employment. Gardner: BMS: Patents & Royalties; Novartis: Consultancy.

Abstract: We previously reported strong power to predict relapse and lower event free survival (EFS) associated with the presence of minimal residual disease (MRD) 〉 0.1% detected in bone marrow (BM) both pre- and post-transplant by standardized multi-channel flowcytometry in children with ALL enrolled on a randomized phase III Children's Oncology Group/Pediatric Blood and Marrow Transplant Consortium trial, ASCT 0431. We performed further analysis of this cohort to test whether the high level of sensitivity of MRD detection offered by deep-sequencing methods increases predictive power for relapse and event free-survival (EFS). Patients in the trial were children aged 1-21yrs who underwent TBI-based myeloablative HCT for high risk ALL in CR1 or CR2. BM samples were taken within 2 weeks of initiation of the preparative regimen (pre-HCT sample) and at 1,3, and 9-12 months after HCT. These samples were sent for central flow cytometry and banked. DNA was prepared from marrow specimens at each time point in a patient, and used as template in preparing IGH VDJ sequencing reactions. 20,000 B cell genomes were used as input for index specimen libraries, used to define IGH sequences greater than 5% frequency in the sample. For a large majority of patients the index sample was taken at diagnosis, prior to transplant, but in five patients this specimen was unavailable, so a specimen taken at relapse was used to define the tumor tagging sequences. 130 bp reads starting at the WGXG motif in the J segment and extending back across the CDR3 region into the V segment were collected in each library, to a coverage of at least 5X for the input genomes. Tumor tagging sequences were confidently identified in 64 patients. To assess MRD, we then prepared libraries from the equivalent of 100,000 B cell genomes at each time point during or after transplant, and screened the resulting data for the frequency of each tumor tracking sequence in the individual. The Kaplan-Meier estimate of EFS and the Gray estimate of cumulative incidence of relapse were calculated. Evidence of tumor in the pre-transplant sample had significantly increased 36-month cumulative incidence (CI) of relapse when compared with no evidence tumor (57% v. 4.4%; p=0.008). Similarly, evidence of tumor was associated with a significant increase in 36-month CI of relapse or death when compared with no evidence of tumor (70% v. 17%, p=0.0014; and 54% v. 17%, p=0.012). Evidence of tumor in the post-transplant sample (within 90 days of transplant) had significantly increased 36-month cumulative incidence (CI) of relapse when compared with no evidence tumor (75% v. 26%; p 〈 0.001). Similarly, evidence of tumor was associated with a significant increase in 36-month CI of relapse or death when compared with no evidence of tumor (83% v. 33%, p=0.0014; and 59% v. 27%, p=0.012). Conclusions Patients with no detectable leukemia by deep sequencing pre-HCT relapsed less that 5% of the time, a striking improvement compared to our previous ability to predict relapse with flow MRD (No detectable MRD by flow, 25% risk of relapse in the previous analysis). Detection of any tumor in the first 90 days after HCT by this method is also highly predictive of relapse and survival. Patients identified as high risk for relapse by this method may be candidates for interventions aimed at preventing relapse. Analysis including a direct comparison with flow MRD and post transplant chimerism, as well as definition of specific cut points for levels of disease detected by deep sequencing will be presented with this data. Disclosures: Carlson: Adaptive Biotechnologies: Consultancy, Equity Ownership, Patents & Royalties. Kalos:Novartis corporation: CART19 technology, CART19 technology Patents & Royalties; Adaptive biotechnologies: Member scientific advisory board , Member scientific advisory board Other. Cindy:Adaptive Biotechnologies: Employment. Williamson:Adaptive Biotechnologies: Employment. Grupp:Novatis: Research Funding.