ALBERT

Description: Background: Cytokine release syndrome (CRS) in the setting of CAR T cell therapy manifests as a wide constellation of symptoms with multi-organ involvement. CRS can vary from a mild, self-limited course to a life-threatening systemic inflammatory response which, in severe cases, may be associated with manifestations similar to those seen in hemophagocytic lymphohistiocytosis (HLH). Tocilizumab, an anti-human IL-6 receptor antibody, has become a widely accepted pharmacologic intervention of first choice in severe CRS based on the observation of elevated levels of inflammatory cytokines, most notably interleukin (IL)-6 and interferon (IFN)-γ. Indeed, following administration of tocilizumab, most patients show rapid signs of improvement. However, in rare circumstances, CRS may be refractory to tocilizumab, and repeat administration or institution of additional immunosuppression is needed. Here we summarize cytokine profiles and CRS seen in patients treated with anti-CD22-CAR T cells and propose tocilizumab-refractory CRS as a potentially distinct pathophysiological entity from typical CRS that may merit alternative immunosuppressive interventions other than tocilizumab. Methods: Children and young adults with relapsed/refractory CD22+ ALL were treated with anti-CD22 CAR T cells. Serial samples for serum cytokine levels (IFN-γ, IL-6, IL-2, IL-10, IL-12p70, IL-1β, IL-15, IL-13, IL-4, IL-8, TNF-α, GM-CSF, MIP1-α) were obtained at pre-specified time points (0, 12, 24, 48, 72 hours, then daily on days 4 - 14 and 28 following CAR T cell infusion). Transduced CAR T cell dosage ranged from 3x10e5 cells/kg (dose level [DL] 1), 1x10e6 cells/kg (DL2), and 3x10e6 cells/kg (DL3). CRS severity was determined according to recently proposed grading system (Lee DW et al., Blood. 2014). Disease burden was assessed using standard morphology and flow cytometry analysis of bone marrow and peripheral blood samples. Results: Cytokine profiles are available on 10 patients treated: first 9 patients enrolled in our phase I trial (NCT02315612), and the tenth patient was treated off-protocol on an emergency investigational new drug protocol given lack of alternative treatment option for rapidly progressing disease. All subjects, median age 20 years (range, 6-22 years), had a diagnosis of multiply relapsed ALL. Seven of 10 subjects developed CRS. Five subjects with CRS were complete responders to CAR therapy (Table). The median time to the onset of CRS was 9 days (range, 7-12 days) post-infusion and resolved within 1 week with supportive care alone except in one patient who received pharmacologic intervention for grade 4 CRS. Rise in C-reactive protein (CRP) tended to correlate with clinical severity of CRS. Chronological changes in the level of IFN-γ, IL-6, IL-1β, IL-8, TNF-α, and MIP1-α generally mirrored the CRP trend, typically preceding CRP change by 1-2 days. In contrast to the CRS (maximum grade 2) seen in the first 9 patients, the 10th patient treated at DL3 developed grade 4 CRS with manifestations characteristic of HLH unresponsive to tocilizumab. Cytokine profile for this patient, compared to those of other CRS patients, was notable for a substantially higher serum IL-2 (35 pg/mL vs median 6.1 (range, 1.2-13.5)) and GM-CSF level (28 pg/mL vs median 1.0 (range, 0-6.1)) at 12 hours post infusion. Subsequent CRP elevation was not initially accompanied by a rise in IL-6 as in other patients, which may have explained the lack of response to tocilizumab (Figure). Evaluation for a genetic cause of HLH did not reveal any mutations (PRF1, MUNC13-4, RAB27A, STX11, STXBP2). Although this patient was a complete responder to therapy, the clinical course was complicated by pre-existing respiratory compromise and bacteremia, which may have contributed to increased CAR toxicity with variability in the cytokine profile. Conclusion: Based on our early experience, we postulate that patients with an early increase in GM-CSF and IL-2 may potentially experience more atypical and severe CRS, which without a concomitant rise in IL-6, may not respond to tocilizumab and thus early intervention with other immunosuppression may be indicated. Analysis of larger numbers of patients is required to better delineate clinical confounders and to develop rational pharmacological approach to CAR-mediated inflammatory responses. Ongoing efforts are underway to further analyze clinical samples for biomarkers. Disclosures Mackall: NCI: Patents & Royalties: B7H3 CAR.

Description: Abstract 2609 Children with relapsed or chemotherapy-refractory ALL have a poor prognosis despite the use of aggressive therapies such as HSCT. Chimeric antigen receptor modified T cells targeting the B-cell antigen CD19 have been reported to be effective in adults with B-cell lymphomas and chronic lymphocytic leukemia. We conducted pre-clinical studies with a CD19-CAR consisting of a CD19-specific scFv and the CD28 and CD3z signaling domains. These cells generated significant levels of IFNg, TNFa, and IL-2 in response to ALL blasts and rapidly eradicated human ALL in murine xenografts. We developed a Phase I clinical trial of CD19-CAR modified autologous T cells for children with CD19+ hematologic malignancies. HSCT-na•ve and post-transplant patients are eligible, and cells are collected directly from patients in both cases. CD19-CAR T cells are manufactured in a semi-closed system over an 11-day period. We report results with the first patient, a 13-year old with chemotherapy-refractory ALL that had relapsed after 2 prior matched related donor HSCTs. Peripheral blood (PB) mononuclear cells were collected from the patient on Day -11 by apheresis. T cells were positively selected and activated by incubation with anti-CD3/anti-CD28 paramagnetic beads in IL-2 for 48 hours then transduced with the CD19-CAR gene via retroviral supernatant for an additional 48 hours. Beads were removed and the expanding CD19-CAR T cells were maintained in culture with IL-2 until harvested for infusion on Day 0. A 59-fold expansion of CAR T cells with 65% transduction efficiency was achieved. The patient was pre-treated with fludarabine (25 mg/m2/day on Days -4, -3, -2) and cyclophosphamide (900 mg/m2 on Day -2) prior to the infusion of 1×106 CAR-transduced T cells/kg. The patient developed signs and symptoms of cytokine release syndrome (CRS) on Day +5 with full resolution by Day +11. Manifestations included fever (maximum 41°C), rigors (Grade 1), and hypotension (Grade 2), the latter of which was responsive to two IV fluid boluses. The patient also developed an erythematous rash (Grade 1) of the extremities from Days +7 to +12 and bilateral scrotal swelling and pain (Grade 1) from Days +8 to +10, which was associated with increased testicular blood flow by ultrasound. Cytokine analysis revealed high levels of IL-6 (53.1 pg/ml; normal

Description: Introduction: Neurocognitive deficits and neurologic toxicity are known complications of ALL therapy, and cumulative therapy may make those with multiply relapsed disease more vulnerable. Novel targeted immunotherapies, such as blinatumomab or anti-CD19 chimeric antigen receptors (CARs), despite promising results, are associated with neurologic toxicity, potentially related to cytokine release syndrome (CRS). Neurologic symptoms may include encephalopathy, seizures, and aphasia, but subtle toxicity is not easily captured by current grading systems. On our anti-CD22 CAR trial (NCT02315612), we prospectively evaluated neurocognitive function, developed a CAR-specific neurological symptom checklist, and incorporated CNS imaging to comprehensively assess for CAR related neurotoxicity. We describe the results in the first 9 consecutively enrolled subjects. Methods: Children and young adults with relapsed/refractory CD22+ ALL enrolled on a phase I dose escalation study of anti-CD22 CAR therapy were evaluated for neurotoxicity pre (baseline) and post-therapy (day 21-28 following infusion). Neurocognitive assessment was performed by psychologists who administered a brief (

Description: Abstract 1497 Background: Vincristine is active in many pediatric cancers, but cumulative neuromuscular toxicity is often dose limiting and requires a maximum dose cap. Liposomal carriers are capable of increasing the therapeutic index of anticancer agents by altering pharmacokinetic behavior. Vincristine sulfate liposomes injection (VSLI, Marqibo®) is a novel preparation of standard vincristine encapsulated in sphingomyelin/cholesterol liposomes. Clinical trials have demonstrated safety, tolerability and activity in adults with leukemias, lymphomas and solid tumors. Pediatric experience with VSLI is limited. Design: This single center Phase I dose-escalation study is designed to determine the maximum tolerated dose (MTD) and to assess safety, pharmacokinetics and activity of VSLI in pediatric patients with relapsed/refractory cancer. Patients with active central nervous system disease or ≥grade 2 sensory or motor neuropathy are excluded. Dose escalation is per a standard 3 + 3 Phase I trial design with enrollment following a rolling 6 strategy. VSLI is administered IV over 60-minutes every 7 days (± 3 days) for 4 consecutive weeks for a 28-day treatment cycle (4 doses/cycle). Cycles may be delayed by up to 1 week for toxicity. Two dose levels have been tested to date: 1.75 mg/m2 and 2.25 mg/m2(adult MTD). No individual dose cap is employed. A validated HPLC tandem mass spectrometry assay was used to quantitate total (liposomal encapsulated and non-encapsulated) vincristine. Results: 9 patients have been treated (Table): 6 with acute lymphoblastic leukemia (ALL) and 3 with solid tumors. All patients were heavily pre-treated and 2 had prior stem cell transplants. 6 of 9 completed at least 1 cycle of therapy, with 1 each removed early for alternative therapy, complications of ALL, or dose-limiting toxicity (DLT). Most treatment-related adverse events were reversible grade 1 and 2 severity including hepatic transaminase elevation, parasthesia, low white blood cell count, neutropenia and fatigue. 2 patients evaluable for hematologic toxicity developed grade 4 neutropenia that spontaneously and rapidly resolved. No DLT occurred on dose level 1. Grade 4 aspartate aminotransferase elevation was observed in one patient at the second dose level and this dose level is being expanded. 1 patient treated at dose level 1 had dose de-escalation starting with Cycle 2 Dose 3 due to neuropathy. No patient was taken off study due to neurotoxicity. 7 of 9 patients received a VSLI dose that exceeded the 2 mg dose limit set for standard vincristine. 6 patients were evaluable for response: 1 had a complete remission (CR) (minimal residual disease negative by flow cytometry); 3 had stable disease (SD); and 2 had progressive disease (PD). First-dose pharmacokinetic analysis revealed wide interpatient variation (Table). The median (range) maximum concentrations (Cmax) of total vincristine (ng/ml) were 1,485 (845-2,120) and 2,450 (1,690-3,690) at dose levels 1 and 2 respectively. The median plasma half-life (T½) was 8.5 and 13.5 hours at dose levels 1 and 2 respectively (range 1.8 to 40.4 hours). Conclusions: VSLI appears to be safe, tolerable and demonstrates preliminary activity in pediatric patients with refractory ALL and solid tumors. The toxicity spectrum appears to be similar in children and adults. Clearance of total vincristine in our study is approximately 100-fold lower in comparison to administration of standard vincristine. VSLI allows for intensification of vincristine therapy in children with cancer. Accrual to the Phase I component at the adult recommended dose is ongoing and an expanded Phase II cohort in pediatric patients with ALL is planned. This study was sponsored by Talon Therapeutics and is supported by the Intramural Research Program of the NIH, National Cancer Institute, Center for Cancer Research. Disclosures: No relevant conflicts of interest to declare.

Description: Background: Adoptive cellular therapy with genetically modified T-cells using viral-based vectors to express chimeric antigen receptors targeting the CD19 molecule have demonstrated dramatic clinical responses in patients ALL. However, not all patients respond and CD19-negative escape has been observed. Thus, additional targets are needed. CD22 is a B-lineage-restricted, transmembrane phosphoglycoprotein of the Ig superfamily that is widely expressed on B-precursor ALL. Therefore, CD22 represents a promising target. This phase I dose-escalation study represents the first in human testing of anti-CD22 CAR adoptive cell therapy. The primary objectives were to determine the feasibility of producing anti-CD22 CAR cells meeting established release criteria and to assess the safety of administering escalating doses of anti-CD22-CAR engineered T cells in children and young adults with relapsed or refractory CD22-expressing B cell malignancies following a cyclophosphamide/fludarabine preparative regimen. Secondary objectives include determination of anti-leukemia effects, measurement of persistence of adoptively transferred anti-CD22 CAR T cells, and evaluation of cytokine profiles. Design: Children and young adults with relapsed/refractory CD22-expressing hematologic malignancies were eligible. Study endpoints included toxicity, feasibility, and antigen-specific immune and clinical responses. All enrolled subjects underwent autologous leukopheresis for peripheral blood mononuclear cells. Cells were then CD3+ enriched and cultured in the presence of anti-CD3/-CD28 beads followed by lentiviral vector supernatant containing the anti-CD22 (M971BBz) CAR, with culture duration of 7-10 days. On Day-4 (cell infusion=Day 0), subjects began induction chemotherapy with fludarabine 25 mg/m2 on Days-4, -3 and -2 and cyclophosphamide 900 mg/m2 on day-2. The first dose level started at 3 x 105 transduced T-cells/recipient weight (kg). Results: 6 subjects, aged 7-22 years, with ALL have been treated to date. All enrolled subjects had previously undergone at least one prior allogeneic hematopoietic stem cell transplant and all had received treatment with CD19 directed CAR-T cell therapy. Five subjects had a CD19 negative antigen escape, and one subject was a non-responder to prior CD19 CAR therapy. All subjects had demonstration of CD22 expression on 〉 99% of their ALL, although the antigen binding capacity had variability from 〈 900 to 〉 13,000 sites/cells. All subjects underwent successful culture, expansion and infusion of anti-CD22 CAR T-cells at the first dose level. The second subject enrolled met criteria for dose-limiting toxicity by virtue of grade 3 diarrhea which led to dose expansion at the first dose-level to treat a total of 6 subjects. Two subjects had grade 1 cytokine release syndrome (CRS), one subject had grade 2 CRS and in two subjects CRS was not seen. Evidence for CAR-T cell expansion was seen in peripheral blood, bone marrow and cerebrospinal fluid (Table). Clinical responses were evaluated at day 28 (+/- 4 days) post-infusion and included two subjects who had disease progression, two with disease stabilization and one subject who attained a minimal residual disease (MRD) negative complete remission. Flow cytometric CAR persistence was detected out to 47 days post-infusion in the responding patient with remission maintained for 3 months post-infusion. One patient is actively undergoing treatment and is too early to evaluate. Conclusions: This first-in-human anti-CD22 CAR T-cell therapy is safe, feasible and clinically active in patients who have undergone previous CAR therapy. Understanding mechanisms which may determine clinical efficacy are being explored. Accrual to the next dose level at 1 x 106 transduced T cells/kg is planned. Table 1.#Age/SexPrior HCTPrior anti-CD19 CARCD19 neg relapse?CD22 site densityPre-HCT disease burden (% leukemia in aspirate)Maximum CD22 CAR expansion (flow)CRSBest ResponsePBMarrowCSF122/MYYY208495-100%00n/aNonePD220/FY (2)YY134525%52.3%19.5%0%1MRD neg CR322/MYYY846〉90%73%36%32%1SD422/MYYN258995%6%1%0%2SD57/FYYY283932%0%1.3%0%NonePD617/FYYY21851%n/an/an/an/an/aSD: stable disease; PD: progressive disease Disclosures Mackall: Juno: Patents & Royalties: CD22-CAR.

Description: CD19 chimeric antigen receptor (CAR) T cells have shown significant promise in multiple early phase trials including our own (Lancet 385:517-28). We manufacture CAR T cells containing CD28 and CD3z domains in 7 days using a retroviral platform. Several challenges remain to its widespread use: 1) reduction in the incidence of grade 4 cytokine release syndrome (CRS) and 2) incorporation with standard salvage regimens. Here, we update our experience with 39 patients. In the first 21 patients we defined the maximally tolerated dose as 1x106 CAR T cells/kg, grade 4 CRS occurred in 16%, and noted that severity of CRS correlated with disease burden. We stratified the current cohort (n=18) by disease burden. Subjects 1-21 and subsequent patients with low burden disease (Arm 1: isolated CNS disease or

Description: Relapsed pre-B acute lymphoblastic leukemia (ALL) portends a poor prognosis even with hematopoietic stem cell transplantation (HSCT). CD19 chimeric antigen receptor (CAR) T cells have shown promise in early studies although morbidity related tohigh gradecytokine release syndrome (CRS) and/or neurotoxicity could limit its wide applicability in patients with high disease burden. The lympho depleting chemotherapy regimen may affect both toxicity and response and has not been well studied. Relapse rates among complete responders to CD19 CAR therapy occur in nearly half of patients in the first year. We report outcomes from our completed clinical trial of 53 children and young adults with relapsed/refractory ALL (n=51) or lymphoma (n=2) with a median follow up (mF/U) of 18.7 months. The first 21 patients received a low dose fludarabine (25 mg/m2/day Days -4 to -2) and cyclophosphamide (900 mg/m2 Day -2) preparative regimen (LDflu/cy) and results are reported in Lancet 385:517-28. The regimen for the subsequent 32 patients, who all received 1x106 CAR+ T cells/kg, was stratified based on disease burden. Subjects with low burden ALL (lowALL; 25% marrow blasts or lymphomatous disease) received an alternative regimen [FLAG (n=6), ifosfamide/etoposide per AALL0031 (n=2) or fludarabine (30mg/m2/day Days -6 to -3) and cyclophosphamide (1200 mg/m2/day Days -4 and -3) (HDflu/cy; n=8)] in an attempt to mitigate severe CRS risk and improve response. Four highALL subjects received LDflu/cy due to comorbidities including Trisomy 21. CRS was graded and anti-cytokine therapy was instituted as per Blood 124:188-95. Date for data cutoff was July 31, 2016. Of the 53 subjects 11 had primary refractory ALL, 5Ph+, 3 with Trisomy 21, 4 with CNS2 and 2 with CNS3 ALL including one with extensive leptomeningeal and parenchymal involvement. Cells were manufactured in 7-11 days and none underwent a test expansion. One patient was not infused due to rapidly progressive fungal pneumonia but was accounted for in all analyses. Of 51 ALL patients, 31 (60.8%) achieved a complete response (CR) with 28/31 (90%) of responders negative for minimal residual disease (MRD-). All 6 subjects with CNS ALL were rendered into CNS1 status with resolution of leptomeningeal enhancement, where appropriate, and CAR cells in CSF. The median leukemia free survival (mLFS) of MRD- CR responders is 18 months with a 49.5% probability of LFS beginning at 18 months (mF/U 22.6 months). Grade 3 (n=5) and 4 (n=2) CRS combined for a severe CRS incidence of 13.5%. Three grade 3 neurotoxicities(1 each: dysphasia, delirium, headache) and 2 seizures (one grade 1, one grade 2) occurred. There were no grade 4 neurotoxicities, even in the subject with extensive CNS disease. Subjects with low ALL had a significantly higher CR rate (18/21; 85.7%) than those with high ALL (13/32; 40.6%) (p=0.0011) and use of a flu/cy regimen correlated with higher response (29/44; 65.9% vs 2/8; 25%; p=0.0301). Overall survival in all subjects receiving a flu/cy regimen was 13.3 months with a 34.7% probability of survival beginning at 38 months (mF/U 18.7 months), which is significantly longer than those who did not receive a flu/cy regimen (5.5 months, no survivors beyond 11 months). The hazard ratio (HR) of not receiving a flu/cy regimen was 6.35 (1.906-21.14; p=0.0026). mLFS of subjects with MRD- CR who received a flu/cy regimen was not reached with a 53.3% probability of LFS beginning at 18 months (mF/U 22.6 months). Of the 28 subjects achieving MRD- CR, 21 had a subsequent HSCT with a median time to HSCT of 54 days from CAR infusion. 8/28 (28.6%) relapsed with CD19+ (n=2), CD19-/dim (n=5), CD19 unknown (n=1) blasts. Relapse was significantly more common in subjects who did not have a HSCT after CAR therapy (6/7; 85.7%) compared to those who did (2/21; 9.5%) (p=0.0001). Even accounting for transplant related mortality, them LFS in the HSCT group was not reached with a 62% probability of LFS beginning at 18 months. This is significantly longer than them LFS of 4.9 months in MRD- CR subjects who did not proceed to HSCT (p=0.0006) with a HR of 16.9 (3.37-85.1) of not having a subsequent HSCT. In all, CD19 CAR T cell therapy was effective and safe with a low incidence of severe CRS and neurotoxicity. In this nonrandomized series, the rate of durable remission was higher when a flu/cy preparative regimen was used and consolidation HSCT was employed. Figure 1 Figure 1. Figure 2 Figure 2. Disclosures Lee: Juno: Honoraria. Kochenderfer:bluebird bio: Patents & Royalties, Research Funding; Kite Pharma: Patents & Royalties, Research Funding. Rosenberg:Kite pharma: Research Funding. Mackall:NCI: Patents & Royalties: B7H3 CAR.

Description: Survival after relapsed and refractory pediatric pre-B ALL and non-Hodgkin lymphoma (NHL) is poor despite intensive chemotherapy and HSCT. CAR T cells combine the specificity and MHC independence of antibodies with the cytotoxic capacity of T cells. By genetically engineering them with a CAR that links an scFv for CD19, present on most NHL and ALL blasts, with the CD3zeta activation domain of the T cell receptor and the CD28 co-stimulatory domain, cytotoxicity can be specifically and fully activated with a single interaction. We undertook a Phase I clinical trial (NCT01593696) of anti-CD19-CD28-zeta CAR T cells in children with relapsed and refractory ALL and NHL with the aim of assessing 1) feasibility of generating adequate numbers of CAR T cells from a high risk population including post-HSCT patients 2) response rate 3) CAR T cell persistence and trafficking to extramedullary sites and 4) toxicities including acute toxicity related to cytokine release syndrome (CRS) and chronic B-cell aplasia related to long-term persistence of CAR T cells. Patients were enrolled on study, then PBMCs were collected by apheresis then immediately enriched for T cells using activating anti-CD3/CD28 beads before retroviral transduction of the CAR gene. After an 11-day manufacturing process, CAR T cells were infused fresh to patients who have received fludarabine (25 mg/m2/day Days -4, -3, -2) and cyclophosphamide (900 mg/m2/day Day -2). We have enrolled and treated 8 patients (7 ALL, 1 NHL; 4 pre-HSCT, 4 post-HSCT) aged 10-23 years. Regarding feasibility, 6 of 8 patients had successful expansion of CAR T cells that met the assigned dose level, with transduction efficiencies of 18-87%. Expansion was insufficient to meet the target dose for 2 patients, but each still received products that were 3% and 14% of the target dose. Response rate The overall complete response (CR) rate is 5 of 8 (62.5%; 95% CI 29-96%) or 5 of 7 ALL patients (71.4%; 95% CI 38-105%) with 3 of these being MRD-negative, including 1 patient who was primarily refractory to chemotherapy, and who proceeded to HSCT following CD19 CAR therapy. Both patients who received cells below the target dose experienced anti-leukemic effects, one with a transient CR and the other with an MRD-negative CR. CAR T cell expansion, persistence and trafficking: CAR T cells have been identified in blood (0.1-38%) and marrow (0.1-5%) in all responding patients. They have also been found in the CSF of 3 patients (0.3-17%), in the pleural fluid (13%) of an NHL patient with pre-existing malignant pleural effusions, and are suspected to have caused Gr 1 scrotal edema in a patient with a remote history of testicular disease. One patient with CNS2 disease at the time of enrollment cleared all CSF blasts as detected by flow cytometry without additional intrathecal chemotherapy after CAR T cells were administered (max 17% CAR T cells in CSF). The mean time to undetectable CAR T cells in any tissue in responding patients was 55 days (± 22.6; 95% CI 35-72). Toxicity Treatment was well tolerated. Two patients had Gr 2 CRS (Gr 3 fever, Gr 2 hypotension) that resolved with IV fluids and correlated with high IL6, GM-CSF, IFNg, TNFa, and C-reactive protein. One DLT (Gr 4 CRS) occurred (3 x 10^6 CAR+ T cells/kg) and required vasopressors for hypotension. After identifying high plasma IL6, the anti-IL6 receptor antibody, tocilizumab, was administered, and quickly reversed most toxicity from CRS. At the time of Day 28 restaging, CD19+ hematogones were detected by flow cytometry in four of five responding patients (mean 81.4% of all CD19+ cells; 95% CI 51-112%), indicating that significant antileukemic effects can be induced by CD19 CAR T cells without chronic depletion of B cell precursors. None of the patients with prior HSCT developed graft versus host (GVH) disease despite administering donor-derived activated T cells harvested from the recipient. Conclusions Anti-CD19-CD28-zeta CAR T cells that mediate potent antileukemic effects can be reliably generated, even from very advanced patients with or without a history of allogeneic HSCT. Using intent-to-treat reporting, CR rates are high (62.5%) in this refractory population. CD19 CAR T cells traffic to extramedullary sites and can mediate anti-tumor effects in CSF. Acute toxicity is manageable and because the anti-CD19-CD28-zeta CAR T cells do not persist at high levels for prolonged periods of time, rapid resumption of B cell lymphopoiesis occurs following therapy. Disclosures: Off Label Use: Anti-CD19 CAR T cells for the treatment of ALL and NHL.

Description: Background: Despite the success of anti-CD19 chimeric antigen receptor (CAR) therapy for relapsed/refractory ALL, not all respond and CD19-negative escape has been observed. To overcome this problem and to test an alternative target, we developed an anti-CD22 CAR. Widely expressed on B-lineage leukemia and lymphomas, CD22 represents an ideal target. The primary objectives of this phase I dose escalation study were to determine the feasibility of producing anti-CD22 CAR cells and to assess the safety of administering escalating doses of anti-CD22-CAR T cells in children and young adults with relapsed or refractory CD22+ B cell malignancies. Secondary objectives include determination of anti-leukemia effects, measurement of persistence of anti-CD22 CAR T cells, and evaluation of cytokine profiles. We report interim results based on the first 9 enrolled subjects in this first-in-human testing of anti-CD22 CAR therapy. Design: Children and young adults with relapsed/refractory CD22+ hematologic malignancies were eligible. Study endpoints included toxicity, feasibility, and clinical responses. All enrolled subjects underwent autologous leukopheresis for peripheral blood mononuclear cells. Cells were then CD3+ enriched and cultured in the presence of anti-CD3/-CD28 beads followed by lentiviral vector supernatant containing the anti-CD22 (M971BBz) CAR, with culture duration of 7-10 days. Subjects began lymphodepleting chemotherapy with fludarabine 25 mg/m2 on Days -4, -3 and -2 and cyclophosphamide 900 mg/m2 on day -2 followed by cell infusion on Day 0. Dose level 1(DL-1) started at 3 x 105 transduced T-cells/recipient weight (kg), with DL- 2 at 1 x 106transduced T cells/kg, respectively. Results: We report on outcomes for the first 9 subjects enrolled and treated. The median age was 20 years (range, 7-22 years), and all had CD22+ ALL. All 9 subjects had previously undergone at least one prior allogeneic hematopoietic stem cell transplant, and 2 patients had received 2 prior transplants. Seven subjects had previously received treatment with anti-CD19 CAR-T cell therapy of whom 6 had a CD19 negative/dim antigen escape. All subjects had CD22 expression on 〉 99% of their malignancy, with a median site density of 2589 molecules per cell (range 846-13452). Dose-escalation was as follows: 6 subjects treated at DL-1 due to expansion at this level following DLT in the second subject with grade 3 diarrhea; 3 subjects treated at DL-2 without DLT. CAR expansion and cytokine release syndrome (CRS) was seen in 6 patients with a maximum CRS grade 2. Anti-CD22 CAR cells were detected in the peripheral blood, CSF and bone marrow of all responders. Clinical responses were evaluated at day 28 (+/- 4 days). Four of 9 (44%) subjects evaluable for response attained a complete marrow remission, all of whom were MRD negative. This included all 3 subjects treated at the second dose level with a sustained remission at 3 months. Conclusions: This first-in-human anti-CD22 CAR T-cell therapy is safe, feasible and clinically active in patients with leukemia who have undergone prior CAR therapy. MRD negative complete remissions were seen in patients who were both CAR-naïve or had previously been treated with anti-CD19 CAR and were CD19 negative. Accrual is ongoing. Disclosures Lee: Juno: Honoraria. Mackall:NCI: Patents & Royalties: B7H3 CAR.