Residual Disease-negative Complete Remission Research Articles

Comprehensive analysis of the efficacy and safety of CAR T-cell therapy in patients with relapsed or refractory B-cell acute lymphoblastic leukaemia: a systematic review and meta-analysis

Background Relapse/refractory B-cell acute lymphoblastic leukaemia (r/r B-ALL) represents paediatric cancer with a challenging prognosis. CAR T-cell treatment, considered an advanced treatment, remains controversial due to high relapse rates and adverse events. This study assessed the efficacy and safety of CAR T-cell therapy for r/r B-ALL. Methods The literature search was performed on four databases. Efficacy parameters included minimal residual disease negative complete remission (MRD-CR) and relapse rate (RR). Safety parameters constituted cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS). Results Anti-CD22 showed superior efficacy with the highest MRD-CR event rate and lowest RR, compared to anti-CD19. Combining CAR T-cell therapy with haploidentical stem cell transplantation improved RR. Safety-wise, bispecific anti-CD19/22 had the lowest CRS rate, and anti-CD22 showed the fewest ICANS. Analysis of the costimulatory receptors showed that adding CD28ζ to anti-CD19 CAR T-cell demonstrated superior efficacy in reducing relapses with favorable safety profiles. Conclusion Choosing a more efficacious and safer CAR T-cell treatment is crucial for improving overall survival in acute leukaemia. Beyond the promising anti-CD22 CAR T-cell, exploring costimulatory domains and new CD targets could enhance treatment effectiveness for r/r B-ALL.

A Phase 2 Trial of SCRI-CAR19 Demonstrates Favorable Leukemia-Free Survival (LFS), with a Pilot Study of CD19-Expressing T-Cell Antigen Presenting Cells (CD19t T-APCs) Demonstrating Safety and Tolerability

The value of CD19 directed CAR T cell therapy for relapsed, refractory B-ALL has been well established. Iterative and complementary clinical trials have identified subgroups with improved outcomes, including those with low disease burden at the time of treatment as well as those with prolonged CAR T cell in vivo persistence. PLAT-02 was a phase 1/2 study of SCRI-CAR19, a 2 nd generation murine CAR with 41BB co-stimulation. Phase 1 previously reported 1 year LFS, event-free (EFS) and overall survival (OS) of 55%, 51.2%, and 69.5%. Subjects with low CD19 antigen burden in the bone marrow (<15%) prior to lymphodepletion (LD) and those with a rapid contraction of CAR T cells between Day 10 and 14 (ratio ≥1.5) were at higher risk of early loss of persistence. Phase 2 of PLAT-02 was a multisite trial along with a single site pilot study, PLAT-03, to explore administration of exogenous CD19 antigen designed to boost CAR T cell engraftment in subjects at high risk of early loss of persistence. PLAT-02 (NCT02028455) enrolled subjects 1-26 years of age with relapsed, refractory CD19+ B-ALL. The primary efficacy cohort was defined as those who received fludarabine/cyclophosphamide (flu/cy) LD and were infused with CAR19. PLAT-03 (NCT03186118) was a pilot study of CD19t T-APCs (manufactured T cells with CD19 tag) administered at doses of 10x10 6/kg or flat dosing of 5x10 8 for subjects >25kg every 4 weeks up to 6 total doses. Cohort A included subjects with low CD19 antigen burden, and cohort B included those with rapid early contraction of CAR19. 88 subjects with B-ALL were enrolled on PLAT-02 with plans for treatment at the recommended phase 2 dose (RP2D) of 1x10 6 CAR+ T cells/kg. Eighty-six percent had at least one prior relapse and 42% had undergone prior hematopoietic cell transplant (HCT). The feasibility of manufacturing was 98%. 71 subjects were in the primary efficacy cohort with an 89% minimal residual disease negative complete remission (MRDneg CR) rate. EFS and OS probability estimates with 95% CI at 1 year following CAR19 were 0.65 (0.53, 0.75) and 0.76 (0.64, 0.84). LFS at 1 year from entering MRDneg CR was 0.71 (0.58, 0.81). Cytokine release syndrome (CRS) was grade (Gr) 1 (53%), Gr 2 (26%), Gr 3 (10%), and Gr 4 (3%). Neurotoxicity occurred in 53%: Gr 1 (24%), Gr 2 (13%), Gr 3 (15%), and Gr 5 (1%). 25 subjects were treated on PLAT-03, 10 as cohort A (10 received CAR19 on PLAT-03, 9 received T-APCs), and 11 as cohort B (5 received CAR19 on PLAT-02, 6 received CAR19 on PLAT-03, and 9 total received T-APCs). One was cohort C (retreatment) and 3 were cohort D (no T-APCs). A total of 72 infusions of T-APCs were administered, with no occurrence of CRS or neurotoxicity. Two subjects had grade 3 toxicities related to T-APCs, 1 febrile neutropenia and 1 infusion related reaction. EFS and OS probability estimates at 1 year following CAR19 were 0.67 (0.43, 0.83) and 0.95 (0.71, 0.99). Overall LFS at 1 year was 0.63 (0.38, 0.80); by cohort: cohort A, 0.44 (0.13, 0.72) and cohort B, 0.80 (0.41, 0.95). Median duration of persistence, as determined by cumulative incidence using B cell aplasia (BCA) as a surrogate, among all subjects who received RP2D of CAR19 with flu/cy LD across PLAT-02 and PLAT-03, engrafted and achieved MRDneg CR, was 12.9 months (m). For subjects who did not receive T-APCs, the median persistence was 12.1m. Impact of antigen burden prior to LD was again observed; those with >15% CD19 antigen burden had persistence of >12.1m vs. 3.9m in the low antigen burden group. For subjects treated with T-APCs, the median persistence was 16m; 9.9m in cohort A and >16m in cohort B. The improvement in LFS after SCRI-CAR19 in phase 2 compared to phase 1 is likely multi-factorial, with contributing factors including earlier treatment, uniform use of LD, enhanced persistence, and better allocation of patients who benefit from consolidative HCT. The use of T-APCs was well tolerated without recurrent CAR T cell mediated toxicity. Although not directly comparable, there did appear to be enhancement of CAR T cell persistence with the use of T-APCs in populations predicted to have inferior persistence, including those with low antigen burden. There was not a clear improvement of LFS in those who received T-APCs. However, subjects were not randomized to receive T-APCs and those enrolled on PLAT-03 were more heavily treated and more likely to have received a prior HCT. Further exploration of T-APCs is warranted to define and evaluate their impact on persistence and durable responses.

Rituximab Improves Clinical Outcomes of CAR-T Therapy for r/r B-ALL Via Sensitizing Leukemia Cells to CAR-T-Mediated Cytotoxicity and Reducing CAR-T Exhaustion

Background: Despite chimeric antigen receptor (CAR) T-cell therapy has achieved great advances in recent year, approximately 50% of relapsed/refractory B cell acute lymphoblastic leukemia (r/r B-ALL) patients treated with CAR-T experience relapse 6 months post CAR-T treatment. CD20 express on 30 to 50% of B-ALL, which makes CD20 Monoclonal Antibody as one of the potential therapy strategies to decrease the tumor burden and improve the efficacy of CAR-T therapy. Adding Rituximab to chemotherapy protocol had been demonstrated to improve the outcome for CD20-positive ALL. However, rare study explored the influence of Rituximab combined with CAR-T therapy. Methods: We retrospectively analyzed 20 r/r B-ALL patients who received CAR-T therapy, all of whom had failed multiple lines of therapy. Before CAR-T infusion, we administered Rituximab to 10 patient with high CD20 expression at a dose of 375mg/m2 for 1 day. Meanwhile, we selected 10 patients with the comparable features who underwent CAR-T treatment without Rituximab in the same period as the control group. In vitro, the surface molecule expression and killing of CAR-T post Rituximab-treated B-ALL cells co-incubated with CAR-T cells were detected by flow cytometry. Results The day 28 after CAR-T cells infusion, 8（80%） and 6（60%） of the 10 patients achieved minimal residual disease negative complete remission (MRD-negative CR) in Rituximab group and Control group, respectively. The median follow-up of Rituximab and Control groups were 29.27 and 9.83 months. The 2-year overall survival (OS) and leukemia-free survival (LFS) rates both were longer in the Rituximab group (90% vs 26.7%, p=0.034; 41.7% vs 25%, P=0.14). Particularly, subgroup analysis showed that Rituximab could markedly improve the OS and LFS for relapsed patients (88.9% vs 25%, P=0.0203; 87.5% vs 15%, P=0.0112). In addition, CAR-T combined with Rituximab improved long-term outcome in patients who had failed multiple lines of therapy (>5) (2-year OS 100% vs 16.7%, P=0.0205; 1-year LFS 50% vs 0%, P=0.011). There was no significant difference between the two groups in hematological toxicities as well as in non-hematological toxicities. All adverse events were manageable（Figure1）. In vitro, we observed that Rituximab-treated tumor cells are more sensitive to CAR-T killing and a broad range of cytokines and chemokines were produced when Rituximab-treated Nalm-6 cells co-cultured with 19-22CAR-T cells, such as interferon-γ(IFN-γ), tumor necrosis factor-α (TNF-α) and interleukin-2 (IL-2)(IL-2:272.5 pg/ml vs 84.83 pg/ml, P=0.0243; IFN-γ: 6111 pg/ml vs 796 pg/ml, P=0.0451,TNF-α: 1374 pg/ml vs 629.4 pg/ml, P=0.048)（Figure 2）. To investigate whether Rituximab has an effect on CAR-T persistence, we stimulated CAR-T cells repeatedly in vitro with Rituximab-treated Nalm-6 to evaluate the changes in CAR-T surface exhaustion molecules at different times. We found that the expression of exhaustion molecules (LAG-3, PD-1, TIM-3) on CAR-T cells were significantly lower in the Rituximab group than in the Control group (LAG-3: 57.23% vs 71.8%, P=0.0015; PD-1: 35.57% vs 69.03%, P<0.001; TIM-3:36.53% vs 68.9%, P<0.001). Conclusion: Rituximab combined with CAR-T therapy was effective for improving the long-term outcome of B-ALL patients who have failed multiple lines of therapy. In vitro, we observed that rituximab potentially improved CAR-T efficacy by sensitizing Leukemia Cells to CAR T-mediated cytotoxicity and reducing CAR-T exhaustion.

Anti‑BCMA CAR‑T cell immunotherapy for relapsed or refractory multiple myeloma.

The present study aimed to study the efficacy and adverse effects of anti-B-cell maturation antigen (BCMA) chimeric antigen receptor T (CAR-T) cell therapy in relapsed or refractory multiple myeloma. Patients were divided into three dose groups based on cell therapy concentration. After CAR-T cell therapy for 10 patients with recurrent or refractory multiple myeloma, the patients were monitored and evaluated regularly to observe the efficacy and adverse reactions of CAR-T cell therapy. At a median follow-up of 337 (253-504) days, one patient succumbed 24 days due to rapidly progressing disease. The overall response rate of nine patients was 88.9%, including 77.8% (7/9) with minimal residual disease negative complete remission (CR) and 11.1% (1/9) with partial remission. A total of three patients were maintained in remission state for more than a year and eight were maintained for more than six months. Among the three patients with extramedullary invasion, two extramedullary lesions disappeared and one was stable. The highest copy number of CAR-T cells in seven patients with CR was >1x105 copies/µl gDNA, and the best therapeutic effect can be achieved within 30 (7-30) days after the copy number of CAR-T cells reached 1x105 copies/µl genomic DNA. The median onset time in the nine patients was 43 (22-169) days, and the median progression-free survival was 337 (253-504). Among the 10 patients, nine (90%) had cytokine release syndrome, all of which were below grade II. There were nine (90%) patients with hematological adverse reactions, six (60%) patients with severe anemia, five (50%) patients with grade III and above leukopenia, five (50%) patients with granulocytopenia, four (40%) patients with grade III and above thrombocytopenia, and three (30%) patients with grade III and above pancytopenia. It was concluded that anti-BCMA CAR-T cell therapy is a promising treatment method for relapsed or refractory multiple myeloma and extramedullary invasion, with stable efficacy and controllable adverse effects.

Naturally selected CD7 CAR-T therapy without genetic manipulations for T-ALL/LBL: first-in-human phase 1 clinical trial

AbstractDerivation of CD7-targeted chimeric antigen receptor (7CAR) T cells often requires genetic manipulations to ablate the CD7 gene or block CD7 cell surface expression. Our novel approach deriving naturally selected 7CAR (NS7CAR) T cells from bulk T cells was able to overcome major fratricide by minimizing accessible CD7 epitopes. The CD7 molecules of NS7CAR T cells were masked or sequestered by the CD7-targeting CAR. Compared with sorted CD7-negative 7CAR T cells and CD7 knocked-out 7CAR T cells, NS7CAR exhibited similar or superior therapeutic properties, including a greater percentage of CAR+ cells and a higher proportion of CD8+ central memory T cells. In our first-in-human phase 1 trial (NCT04572308), 20 patients with relapsed/refractory T-cell acute lymphoblastic leukemia (T-ALL) (n = 14) and T-cell lymphoblastic lymphoma (T-LBL) (n = 6) were treated with NS7CAR. Nineteen patients achieved minimal residual disease negative complete remission (CR) in the bone marrow (BM) by day 28, and 5 of 9 patients achieved extramedullary CR. With a median follow-up of 142.5 (32-311) days after infusion, 14 patients subsequently received allogeneic hematopoietic stem cell transplant (10 consolidative, 4 salvage) following NS7CAR infusion with no relapses to date. Of the 6 patients who did not receive a transplant, 4 remained in CR at a median time of 54 (32-180) days. Eighteen patients experienced mild cytokine release syndrome (CRS) (grade ≤2), 1 developed grade 3 CRS, and 2 had grade 1 neurotoxicity. These results indicate that NS7CAR-T therapy is a safe and highly effective treatment for T-ALL/LBL. More patients and longer follow-up are needed for validation.

Fedratinib and Venetoclax Have Synergistic Activity Against B-Cell Acute Lymphoblastic Leukemia in Vitro

Treatment of relapsed/refractory B cell acute lymphoblastic leukemia (B-ALL) remains a challenge particularly in patients who do not respond to chemotherapy or immunotherapy. While a subset of these patients can be cured with allogeneic bone marrow transplant, success of the transplant is contingent upon achieving a minimal residual disease negative complete remission. The objective of this study was to assess the efficacy of fedratinib, a semi selective JAK2 inhibitor and venetoclax, a selective BCL-2 inhibitor, on the B-ALL cell lines RS4;11, NALM-6, and SUP-B15. While select studies have examined the efficacy of these drugs on B-ALL as single agents, data is lacking on whether these drugs work optimally as single agents or in combination. Cell lines were treated with either vehicle (DMSO), single agent fedratinib or venetoclax, or the combination of both inhibitors for 48 and 72 hours. Fedratinib doses were tested from 150 nM to 1 uM and venetoclax doses were tested from 2.5 nM to 500 nM. Live/dead discrimination was performed using flow cytometry and a 72-hour MTS assay to assess proliferation. Drug synergy was calculated using CompuSyn software to generate combination index (CI) scores, with a CI score less than 1 reflecting synergy. RNA was isolated from treated leukemia cells and processed on a Nanostring nCounter platform to assess potential changes in gene expression. Results were then analyzed using Rosalind data processing software. In RS4;11, the combination of 5 nM venetoclax and 525 nM fedratinib significantly increased cell death compared to single agent venetoclax (p=0.0451) and fedratinib (p=0.0077). Furthermore, the combination significantly decreased leukemia cell proliferation compared to single agent fedratinib (p<0.0001). In NALM-6, the combination of 300 nM venetoclax and 300 nM fedratinib significantly increased cell death compared to single agent fedratinib (p=0.0103). Combination therapy also significantly decreased cell proliferation compared to single agent fedratinib (p=0.0157). With SUP-B15, the combination of 5 nM venetoclax and 750 nM fedratinib significantly increased leukemic cell death compared to single agent fedratinib (p=0.0081). Combination therapy also significantly decreased cell proliferation compared to both single agent venetoclax (p=0.0012) and fedratinib (p<0.0001). Synergy between venetoclax and fedratinib was seen among respective dose combinations for all three cell lines RS4;11 (CI=0.57258), NALM-6 (CI=0.67991), and SUP-B15 (CI=0.19162). Analysis of gene expression in RS4;11 cells treated with combination fedratinib and venetoclax identified a 3.53-fold decrease in NR4A1 expression (p=0.0001), an orphan nuclear receptor for hormones, and a 4.29-fold increase in SOCS2 expression (p=0.02), a negative regulator of cytokine signaling. Combination therapy with fedratinib and venetoclax has synergistic activity in multiple B-ALL cell lines, in part through regulation of hormone and cytokine signaling. Future studies will explore this combination therapy in vivo and identify signaling pathways impacted by JAK2 and BCL2 inhibition. DisclosuresCapitini: Novartis: Honoraria; Nektar Therapeutics: Honoraria.

Prognostic value of platelet recovery degree before and after achieving minimal residual disease negative complete remission in acute myeloid leukemia patients

BackgroundRisk stratification and prognosis prediction of acute myeloid leukemia (AML) are largely dependent on pre-treatment information. However, post-treatment data also provides much useful information. In this retrospective study, we explored whether the level of blood count recovery before and after the first minimal residual disease (MRD) negative complete remission (CR) is relevant to clinical outcomes of AML patients.MethodsFor each included patient, peripheral platelet counts were measured on the day before initial treatment (PLTpre), whereas platelet peak values (PLTpeak) were recorded after marrow recovery following the chemotherapy course inducing the first MRD-negative CR. The difference (DPLT) between these two values (DPLT = PLTpeak−PLTpre) was calculated. X-tile software was utilized to establish the optimal cut-point for DPLT, which was expected to distinguish CR patients with different clinical outcomes. A cross validation analysis was conducted to confirm the robustness of the established cut-point. The results were further tested by a Cox multivariate analysis.ResultsThe optimal cut-point of DPLT was determined as 212 × 109/L. Patients in high DPLT group were observed to have a significantly better PFS (p = 0.016) and a better OS (without statistical significance, p = 0.106). Cox multivariate analysis showed that higher DPLT was associated with longer PFS (HR = 2.894, 95% CI: 1.320–6.345, p = 0.008) and longer OS (HR = 3.077, 95% CI: 1.130–8.376, p = 0.028).ConclusionPlatelet recovery degree before and after achieving MRD-negative CR (DPLT) is a potential predictor of clinical outcomes in CR patients. Higher DPLT value is associated with longer PFS and OS. Our findings may help to develop simple methods for AML prognosis evaluation.

Review of therapeutic approaches for B-cell malignancies with immune checkpoint blockade and chimeric antigen receptor t-cell therapies: Development, benefits, and limitations.

e14069 Background: Immune checkpoint inhibitors and Chimeric Antigen Receptor (CAR) T-cell therapies have emerged as approaches to treat B-cell malignancies. Methods: PubMed/NCBI/MEDLINE databases were accessed with keywords "immune checkpoint inhibitors and B-cell malignancies" "CAR T-cell and B-cell malignancies", and various permutations including "clinical data" "toxicities", "reviews", "quality of life", and "adverse effects". Results: The first-in-class approved immune checkpoint inhibitor was ipilimumab, which is a fully humanized mAb that blocks the immunosuppressive signal by cytotoxic T-lymphocyte antigen. Thereafter, nivolumab was also approved for use in the treatment of Hodgkin's lymphoma in 2016. In phase I, open-label, dose-escalation, cohort-expansion study, patients with relapsed or refractory B-cell lymphoma received the anti-PD-1 monoclonal antibody nivolumab. Eighty-one patients were treated and drug-related adverse events occurred in 51 (63%) patients. Objective response rates were 40%, 36%, 15%, and 40% among patients with follicular lymphoma and other hematologic malignancies. Clinical trial results describing CD19-targeted CAR T-cell therapy of patients with relapsed B-ALL were published in 2015. In this study, all five patients treated with CAR T cells achieved minimal residual disease negative complete remission. Updated results describing the treatment of 16 patients with relapsed or refractory B-ALL treated with CAR T cells were published: the overall CR rate in this trial was 88% and 12 of 14 patients were classified as minimal residual disease negative. 44% of these patients went on to standard-of- care allogeneic hematopoietic stem cell transplant. Initial studies also reported potent anti-leukemic effects of CD19 CAR T cell therapy in three patients with refractory chronic lymphocytic leukemia where two of the three patients achieved MRD-CR. Infused CAR T cells proliferated up to 10,000-fold and persisted in recipients for at least 6 months and shown to retain antitumor activity after six months. Costs for CAR T-cell therapies remain exorbitant, reaching over $1M (USD) per patient. Conclusions: Clinical data reveal safety and efficacy, and also associated toxicities for both approaches.

Implications of Minimal Residual Disease Negative Complete Remission (MRD-CR) and Allogeneic Stem Cell Transplant on Safety and Clinical Outcome of CD19-Targeted 19-28z CAR Modified T Cells in Adult Patients with Relapsed, Refractory B-Cell ALL

Background: We have previously reported high anti-tumor activity of autologous T cells genetically modified to express 19-28z chimeric antigen receptor (CAR) targeting CD19 in adult patients with relapsed or refractory (R/R) ALL (Park et al. ASH 2014). Herein, we further report the long-term outcome of a larger cohort from our phase 1 clinical trial in adults with R/R ALL (NCT01044069) with a focused analysis on the role of post-treatment minimal residual disease (MRD) negativity as a predictive marker of survival as well as the effect of allogeneic hematopoietic stem cell transplant (allo-HSCT) prior to or after CAR T cell infusion on safety and clinical outcome. Patients and Methods: Adult patients with R/R B-cell ALL (B-ALL) were enrolled. Eligible patients underwent leukapheresis, and T cells were transduced with a retroviral vector encoding a CAR comprising a CD19-specific scFv and CD28 and CD3ζ signaling domains (19-28z). All patients received lymphodepleting chemotherapy followed 2 days later by 1x106 - 3x106 19-28z CAR T cells/kg. The primary objective of the study was to evaluate the safety and anti-tumor activity of 19-28z CAR T cells. Post-treatment MRD was assessed at day 14-28 by multiparameter flow cytometry in bone marrow (BM) samples. Results: 44 patients have been treated to date. The median age was 45 years (range, 22-74). 14 patients (32%) had Philadelphia chromosome positive (Ph+) ALL (T315I mutation in 5 patients), 17 patients (39%) had prior allo-HSCT, and 24 patients (55%) had ≥ 3 prior lines of ALL therapy. Of the 44 patients, 43 patients were evaluable for response. At the time of 19-28z CAR T cell infusion, 22 of the 43 patients (51%) had morphologic disease (≥5% blasts in BM or measurable extramedullary disease) and the remaining 21 patients had minimal disease (&lt;5% blasts in BM). 36 patients (84%) were in complete remission (CR) after 19-28z CAR T-cell infusion. MRD analysis was performed in 35 of 36 CR patients, and 29 of these 35 patients (83%) achieved an MRD-negative CR (MRD-CR). As of July 13, 2015, the median follow-up was 4.2 months (range 1-45), with 16 patients having at least 6 months of follow-up. Responses appear durable with 7 patients remaining disease-free beyond 1 year up to 45 months. A median overall survival (OS) of all patients and patients who achieved MRD-CR is 8.5 months and 10.8 months, respectively. Post-treatment MRD status emerged as a strong predictive marker of OS: OS at 6 months was 76% (95% CI: 51-89) in the MRD-CR cohort vs. 14% (95% CI: 8-45) in the MRD+CR cohort. In contrast, allo-HSCT after achieving CR with CAR T cell infusion did not affect the survival rate. Of the 36 patients in CR following the T cell infusion, 12 patients underwent allo-HSCT. OS at 6 months was 70% (95% CI: 33-89) in patients who underwent post-CAR allo-HSCT vs. 64% (95% CI: 36-82) in patients who did not get allo-HSCT after CAR T cells. Comparing baseline disease characteristics of patients who had prior allo-HSCT before the CAR T cell treatment vs. no prior allo-HSCT, patients who had prior allo-HSCT (n=17) were similar in age (median age 45 vs. 46), but had higher disease burden (65% with morphologic disease vs. 44%), were more heavily pretreated (59% of patients with ≥4 lines of therapy vs. 15%), and included more high-risk disease (41% with Ph+ ALL vs. 26%). However, there was no statistically significant difference in CR rates (75%, CI: 48-93 vs. 89%, CI: 71-98), incidences of severe cytokine release syndrome (24% vs. 22%), and OS at 6 months (57% vs. 60%) between these two cohorts. Fewer patients who had prior allo-HSCT underwent another allo-HSCT following CAR T cell infusion: 2 patients vs. 10 patients with no prior all-HSCT. Although no obvious case of graft-versus-host disease (GvHD) was noted, one patient experienced a grade 3 gastrointestinal toxicity that may have been related to GvHD. Conclusions: These data confirm the potent anti-tumor efficacy of 19-28z CAR T cells (JCAR015) in adult patients with R/R ALL. MRD negativity following the 19-28z CAR T cell treatment is highly predictive of survival, and allo-HSCT post-CAR T cell infusion had no significant impact on survival. Furthermore, 19-28z CAR T cells appear to be safe in patients who had prior allo-HSCT, and may represent an attractive alternative option to second allo-HSCT. These findings are being confirmed in an ongoing multi-center, pivotal phase 2 trial evaluating JCAR015 in adult patients with R/R ALL. Disclosures Park: Amgen: Consultancy; Genentech: Research Funding; Juno Therapeutics: Other: Advisory Board, Research Funding. Riviere:Juno Therapeutics: Other: Co-founder, stockholder and consultant. Curran:Juno Therapeutics: Consultancy. Sadelain:Juno Therapeutics: Consultancy, Equity Ownership, Other: Co-Founder, stockholder, Patents &amp; Royalties: Licensed patents on CARs. Brentjens:Juno Therapeutics: Other: Co-founder, stockholder and consultant.