Patients

Figure 1. Figure 1. Screening, Enrollment, Treatment, and Follow-up. The first patient’s first visit occurred on April 8, 2015. The median time from tisagenlecleucel infusion to data cutoff was 13.1 months. The reasons for patients not enrolling in the study after screening included not meeting the inclusion criteria or meeting the exclusion criteria (11 patients, including <5% blasts in the bone marrow in 8 patients), death before acceptance of the apheresis sample at the manufacturing facility (2 patients; 1 who died from pulmonary hemorrhage and 1 who died from multiorgan failure), physician decision (1), and apheresis-related issue (1). All patients who completed screening and whose apheresis product was received and accepted by the manufacturing facility were enrolled in the study. Of the 75 patients who received an infusion, 65 (87%) received bridging chemotherapy between enrollment and infusion, and 72 (96%) received lymphodepleting chemotherapy (fludarabine–cyclophosphamide [71 patients] or cytarabine–etoposide [1]). Seventeen enrolled patients did not receive a tisagenlecleucel infusion because of product-related issues (7 patients), death (7 patients; 4 from disease progression and 1 each from sepsis, respiratory failure, and fungemia), and adverse events (3 patients; 1 each from graft-versus-host disease, systemic mycosis, and fungal pneumonia). Tisagenlecleucel product-related issues included an inability to manufacture as a result of poor cell growth for 6 patients and a technical issue unrelated to cell growth for 1 patient. Patients who received the infusion but discontinued follow-up were followed for survival. At the time of data cutoff, 27 patients had discontinued follow-up owing to death (11 patients; 7 from disease progression and 1 each from encephalitis, cerebral hemorrhage, systemic mycosis, and hepatobiliary disorders related to allogeneic hematopoietic stem-cell transplantation), lack of efficacy (9 patients; nonresponse or relapse), new therapy while in complete remission (5), and patient or guardian decision (2); 48 patients remained in follow-up. ALL denotes acute lymphoblastic leukemia.

Between April 8, 2015, and the data cutoff on April 25, 2017, a total of 107 patients were screened, and 92 were enrolled (Figure 1). A total of 75 patients received an infusion of tisagenlecleucel, with a median time from enrollment to infusion of 45 days (range, 30 to 105). The median duration of follow-up among patients who received a tisagenlecleucel infusion was 13.1 months. At enrollment, patients who received tisagenlecleucel had a median age of 11 years (range, 3 to 23), a median of 3 previous therapies (range, 1 to 8), and a median marrow blast percentage of 74% (range, 5 to 99); 46 patients (61%) had undergone previous allogeneic hematopoietic stem-cell transplantation (Table S1 in the Supplementary Appendix).

Before tisagenlecleucel infusion, 72 of 75 patients (96%) received lymphodepleting chemotherapy, which was not given at investigator discretion if a patient had leukopenia. Patients received a median weight-adjusted dose of 3.1×106 transduced viable T cells per kilogram of body weight (range, 0.2×106 to 5.4×106 cells per kilogram); the median total dose of transduced viable T cells was 1.0×108 (range, 0.03×108 to 2.6×108 cells) (Table S2 in the Supplementary Appendix).

Efficacy

In the interim analysis, which included 50 patients, the primary end point was met, with an overall remission rate of 82% (95% confidence interval [CI], 69 to 91; P<0.001); the results with regard to all key secondary end points were also significant.4 In this updated analysis involving 75 patients who received a tisagenlecleucel infusion and had at least 3 months of follow-up, the overall remission rate was 81% (95% CI, 71 to 89); 45 patients (60%) had complete remission, and 16 (21%) had complete remission with incomplete hematologic recovery. All patients who had a best overall response of complete remission with or without complete hematologic recovery were negative for minimal residual disease; 95% (58 of 61) of these patients were negative by day 28. In an intention-to-treat analysis of the full enrolled population (92 patients), which included patients who discontinued participation in the study before tisagenlecleucel infusion, the overall remission rate was 66% (95% CI, 56 to 76) (Table S3 in the Supplementary Appendix). In subgroup analyses that included patients with or without previous transplantation, with high-risk genomic lesions, or with Down’s syndrome, the overall remission rate ranged from 79% to 83% (Fig. S1 in the Supplementary Appendix).

Figure 2. Figure 2. Duration of Remission, Event-free Survival, and Overall Survival. Panel A shows the duration of remission, defined as the time to relapse after the onset of remission, in the 61 patients who had a best overall response of either complete remission or complete remission with incomplete hematologic recovery. Panel B shows event-free survival among the 75 patients who received an infusion, defined as the time from tisagenlecleucel infusion to the earliest of the following events: no response (8 patients), relapse before response was maintained for at least 28 days (2), or relapse after having complete remission or complete remission with incomplete hematologic recovery (17). A total of 32 patients had still not had an event at the time of data cutoff. Data for 16 more patients were censored for event-free survival — 8 patients for allogeneic stem-cell transplantation during remission, 7 patients for new cancer therapy other than stem-cell transplantation during remission (4 received humanized anti-CD19 CAR T cells, 1 received ponatinib, 1 received vincristine sulfate and blinatumomab, and 1 received antithymocyte globulin), and 1 patient for lack of adequate assessment. Ten patients were followed for relapse after new therapy, 4 of whom had a relapse or died. Panel B also shows overall survival among the 75 patients who received an infusion from the date of tisagenlecleucel infusion to the date of death from any cause. Nineteen patients died after tisagenlecleucel infusion, and 56 patients had their data censored at the time of the last follow-up. Tick marks indicate the time of censoring.

Among the 61 patients with complete remission with or without complete hematologic recovery, the median response duration was not reached (Figure 2A). The rate of relapse-free survival among patients with a response to treatment was 80% (95% CI, 65 to 89) at 6 months and 59% (95% CI, 41 to 73) at 12 months. Among patients with complete remission, 17 had a relapse before receiving additional anticancer therapy. Relapse also occurred in 3 patients who proceeded to receive new cancer therapy for the emergence of minimal residual disease or loss of tisagenlecleucel persistence and in 2 patients who had already been classified as not having a response to treatment because remission was not maintained for at least 28 days. No patients were found to have relapses in the central nervous system (CNS) during primary follow-up; 1 CNS relapse was reported after new anticancer therapy. Characterization of CD19 status at the time of relapse showed that 1 patient had a CD19+ recurrence and 15 patients had CD19− (3 with concomitant CD19+ blasts); 6 patients had unknown CD19 status.

The rate of event-free survival was 73% (95% CI, 60 to 82) at 6 months and 50% (95% CI, 35 to 64) at 12 months (Figure 2B); median event-free survival was not reached. Eight patients underwent allogeneic hematopoietic stem-cell transplantation while in remission, including 2 patients with minimal residual disease–positive bone marrow and 2 with B-cell recovery within 6 months after infusion. All 8 patients were alive at the time of manuscript submission — 4 with no relapse and 4 with unknown disease status. The rate of overall survival among the 75 patients who received tisagenlecleucel was 90% (95% CI, 81 to 95) at 6 months after infusion and 76% (95% CI, 63 to 86) at 12 months after infusion (Figure 2B, and Fig. S2 in the Supplementary Appendix).

Tisagenlecleucel Expansion and Persistence

Tisagenlecleucel transgene was detected in peripheral blood by means of qualitative polymerase chain reaction.5 Among the 60 patients with a response at day 28 who could be evaluated for cellular kinetics, the median time to maximum expansion (T max ) was 10 days (range, 5.7 to 28), whereas 6 patients with no response had a T max of 20 days (range, 13 to 63) (Table S4 in the Supplementary Appendix). Nine patients who could not be evaluated for response were not included in the analysis. Expansion, measured as the geometric mean of the area under the concentration–time curve in peripheral blood from time 0 to day 28 (expressed as copies per microgram of DNA times days), was 315,000 in patients with a response and 301,000 in patients without a response (Table S4 in the Supplementary Appendix). The median duration of persistence of tisagenlecleucel in blood was 168 days (range, 20 to 617 days; 60 patients) at data cutoff. Across the wide range of doses infused, no relationship between dose and expansion was observed (r2<0.001) (Fig. S3 in the Supplementary Appendix), and clinical responses were observed across the entire dose range.

B-Cell Aplasia

All patients with a response to treatment had B-cell aplasia, and most patients in the study received immunoglobulin replacement in accordance with local practice. The median time to B-cell recovery was not reached (Fig. S4 in the Supplementary Appendix). The probability of maintenance of B-cell aplasia at 6 months after infusion was 83% (95% CI, 69 to 91).

Cytokine Response

Among the 75 patients who received tisagenlecleucel, transient increases in serum interleukin-6, interferon gamma, and ferritin levels occurred during the cytokine release syndrome after infusion; these increases tended to be more pronounced in patients with grade 4 cytokine release syndrome than in patients with lower grades (Fig. S5 in the Supplementary Appendix). Similar trends were observed in the levels of other cytokines, including interleukin-10, interleukin-12p70, interleukin-1β, interleukin-2, interleukin-4, interleukin-8, and tumor necrosis factor α. A transient increase in the C-reactive protein level was observed in most patients, but with large variability.

Safety

Table 1. Table 1. Overall Safety of Tisagenlecleucel.

The safety analysis set included all 75 patients who received an infusion of tisagenlecleucel; the median time from infusion to data cutoff was 13.1 months (range, 2.1 to 23.5). Eighteen patients (24%) received their infusions in an outpatient setting. All patients had at least one adverse event during the study; 71 of 75 patients (95%) had an adverse event that was suspected by the investigators to be related to tisagenlecleucel (Table 1). The most common nonhematologic adverse events of any grade at any time after infusion were the cytokine release syndrome (77%), pyrexia (40%), decreased appetite (39%), febrile neutropenia (36%), and headache (36%) (Tables S6 and S7 in the Supplementary Appendix). Within 8 weeks after infusion, febrile neutropenia occurred in 35% of the patients, and grade 3 or 4 neutropenia with a body temperature higher than 38.3°C occurred in 46 of 75 patients (61%). Fever, neutropenia, and the cytokine release syndrome often occurred concurrently after lymphodepleting chemotherapy and tisagenlecleucel infusion; differences in reporting may reflect differential attribution of fever to the cytokine release syndrome rather than to neutropenia.

Table 2. Table 2. Grade 3 or 4 Adverse Events Suspected to Be Related to Tisagenlecleucel That Occurred in at Least 5% of Patients.

Table 3. Table 3. Adverse Events of Special Interest within 8 Weeks after Infusion, Regardless of Relationship to Tisagenlecleucel.

A total of 66 of 75 patients (88%) had a grade 3 or 4 adverse event; 55 of 75 patients (73%) had a grade 3 or 4 tisagenlecleucel-related adverse event (Table 1). Within 8 weeks after infusion, 52 of 75 patients (69%) had a grade 3 or 4 tisagenlecleucel-related adverse event; during the period from 8 weeks to 1 year after infusion, the incidence decreased to 12 of the 70 patients for whom follow-up data were available (17%) (Table 2). Adverse events of special interest included the cytokine release syndrome, cytopenias not resolved by day 28, infections, neurologic events, and the tumor lysis syndrome; 67 of 75 patients (89%) had an adverse event of special interest within 8 weeks after infusion (Table 3). The cytokine release syndrome occurred in 58 of 75 patients (77%); the median time to onset was 3 days (range, 1 to 22), and the median duration was 8 days (range, 1 to 36). A total of 35 of 75 patients (47%) were admitted to the intensive care unit (ICU) for management of the cytokine release syndrome, with a median stay of 7 days (range, 1 to 34). Nineteen patients (25%) were treated with high-dose vasopressors, 33 (44%) received oxygen supplementation, 10 (13%) received mechanical ventilation, 7 (9%) underwent dialysis, and 28 (37%) received tocilizumab for management of the cytokine release syndrome.6

Neurologic events occurred in 30 of 75 patients (40%) within 8 weeks after infusion. Ten patients (13%) had grade 3 neurologic events; no grade 4 events or cerebral edema were reported. The most common neurologic events of any grade were encephalopathy (11%), confusional state (9%), delirium (9%), tremor (8%), agitation (7%), and somnolence (7%); 1 patient had a seizure (grade 3). The majority of neurologic events occurred during the cytokine release syndrome or shortly after its resolution. Severe neurologic events occurred more frequently in patients with higher-grade cytokine release syndrome (Table S7 in the Supplementary Appendix); grade 3 neurologic events occurred more frequently in patients with grade 4 cytokine release syndrome than among those with grade 0 through 3 (32% [6 of 19] vs. 7% [4 of 56]; 95% CI for the difference, −1 to 50 percentage points). Among grade 3 neurologic episodes that resolved, 50% resolved within 10 days, and 75% resolved within 18 days. Four grade 3 neurologic episodes were unresolved in 3 patients at the time of discontinuation for no response (1 patient) or at the time of death (1 death due to leukemia progression and 1 due to encephalitis), 2 of which were thought to be related to tisagenlecleucel (1 each of encephalopathy and delirium). Neurologic events were managed with supportive care after ruling out other potential causes of the symptoms.

A total of 31 of 75 patients (41%) had grade 3 or 4 decreased platelet counts that had not resolved by day 28. Of those 31 patients, 22 had resolution to grade 2 or lower by the last assessment, and 9 did not. By month 3, the Kaplan–Meier estimate of the percentage of patients with resolution to grade 2 or lower was 73%. A grade 3 or 4 decreased neutrophil count that had not resolved by day 28 was reported in 40 of 75 patients (53%). Of those 40 patients, 32 had resolution to grade 2 or lower by the last assessment, and 8 did not; the Kaplan–Meier estimate of the percentage of patients who had resolution to grade 2 or lower by month 3 was 66%. Eighteen of these 40 patients (45%) had grade 3 or 4 infections. In rare cases, prolonged grade 3 or 4 neutropenia before and after tisagenlecleucel infusion was associated with infections that were severe (grade 3 human herpesvirus 6 [HHV-6] encephalitis) or fatal (encephalitis and systemic mycosis).

Nineteen deaths occurred after tisagenlecleucel infusion. Within 30 days after infusion, 1 patient died from cerebral hemorrhage in the context of coagulopathy and resolving cytokine release syndrome (15 days after infusion), and 1 patient died from progressive B-cell ALL. More than 30 days after infusion, 17 patients died; the causes of death were B-cell ALL relapse or progression (12 patients), HHV-6–positive encephalitis in association with prolonged neutropenia and lymphopenia (1), systemic mycosis in association with prolonged neutropenia (1), and unknown causes (1); in 2 patients, death occurred after new therapies for B-cell ALL (1 from pneumonia and 1 from hepatobiliary disease).