Lymphodepletion chemotherapy followed by infusion of CD19-targeted chimeric antigen receptor–modified T (CAR-T) cells can be complicated by neurologic adverse events (AE) in patients with refractory B-cell malignancies. In 133 adults treated with CD19 CAR-T cells, we found that acute lymphoblastic leukemia, high CD19⁺ cells in bone marrow, high CAR-T cell dose, cytokine release syndrome, and preexisting neurologic comorbidities were associated with increased risk of neurologic AEs. Patients with severe neurotoxicity demonstrated evidence of endothelial activation, including disseminated intravascular coagulation, capillary leak, and increased blood–brain barrier (BBB) permeability. The permeable BBB failed to protect the cerebrospinal fluid from high concentrations of systemic cytokines, including IFNγ, which induced brain vascular pericyte stress and their secretion of endothelium-activating cytokines. Endothelial activation and multifocal vascular disruption were found in the brain of a patient with fatal neurotoxicity. Biomarkers of endothelial activation were higher before treatment in patients who subsequently developed grade ≥4 neurotoxicity. Significance: We provide a detailed clinical, radiologic, and pathologic characterization of neurotoxicity after CD19 CAR-T cells, and identify risk factors for neurotoxicity. We show endothelial dysfunction and increased BBB permeability in neurotoxicity and find that patients with evidence of endothelial activation before lymphodepletion may be at increased risk of neurotoxicity. Cancer Discov; 7(12); 1404–19. ©2017 AACR. See related commentary by Mackall and Miklos, p. 1371. This article is highlighted in the In This Issue feature, p. 1355

Key Points: Characterization of the kinetics and risk factors for severe CRS after CD19 CAR T cells will facilitate preemptive therapy and management. Severe CRS is characterized by endothelial activation.

Purpose: We evaluated the safety and feasibility of anti-CD19 chimeric antigen receptor–modified T (CAR-T) cell therapy in patients with chronic lymphocytic leukemia (CLL) who had previously received ibrutinib. Methods: Twenty-four patients with CLL received lymphodepleting chemotherapy and anti-CD19 CAR-T cells at one of three dose levels (2 × 10⁵, 2 × 10⁶, or 2 × 10⁷ CAR-T cells/kg). Nineteen patients experienced disease progression while receiving ibrutinib, three were ibrutinib intolerant, and two did not experience progression while receiving ibrutinib. Six patients were venetoclax refractory, and 23 had a complex karyotype and/or 17p deletion. Results: Four weeks after CAR-T cell infusion, the overall response rate (complete response [CR] and/or partial response [PR]) by International Workshop on Chronic Lymphocytic Leukemia (IWCLL) criteria was 71% (17 of 24). Twenty patients (83%) developed cytokine release syndrome, and eight (33%) developed neurotoxicity, which was reversible in all but one patient with a fatal outcome. Twenty of 24 patients received cyclophosphamide and fludarabine lymphodepletion and CD19 CAR-T cells at or below the maximum tolerated dose (≤ 2 × 10⁶ CAR-T cells/kg). In 19 of these patients who were restaged, the overall response rate by IWCLL imaging criteria 4 weeks after infusion was 74% (CR, 4/19, 21%; PR, 10/19, 53%), and 15/17 patients (88%) with marrow disease before CAR-T cells had no disease by flow cytometry after CAR-T cells. Twelve of these patients underwent deep IGH sequencing, and seven (58%) had no malignant IGH sequences detected in marrow. Absence of the malignant IGH clone in marrow of patients with CLL who responded by IWCLL criteria was associated with 100% progression-free survival and overall survival (median 6.6 months follow-up) after CAR-T cell immunotherapy. The progression-free survival was similar in patients with lymph node PR or CR by IWCLL criteria. Conclusion: CD19 CAR-T cells are highly effective in high-risk patients with CLL after they experience treatment failure with ibrutinib therapy.

Lymphodepletion chemotherapy with CD19-targeted chimeric antigen receptor–modified T (CAR-T)-cell immunotherapy is a novel treatment for refractory or relapsed B-cell malignancies. Infectious complications of this approach have not been systematically studied. We evaluated infections occurring between days 0 to 90 in 133 patients treated with CD19 CAR-T cells in a phase 1/2 study. We used Poisson and Cox regression to evaluate pre- and posttreatment risk factors for infection, respectively. The cohort included patients with acute lymphoblastic leukemia (ALL; n = 47), chronic lymphocytic leukemia (n = 24), and non-Hodgkin lymphoma (n = 62). There were 43 infections in 30 of 133 patients (23%) within 28 days after CAR–T-cell infusion with an infection density of 1.19 infections for every 100 days at risk. There was a lower infection density of 0.67 between days 29 and 90 (P = .02). The first infection occurred a median of 6 days after CAR–T-cell infusion. Six patients (5%) developed invasive fungal infections and 5 patients (4%) had life-threatening or fatal infections. Patients with ALL, ≥4 prior antitumor regimens, and receipt of the highest CAR–T-cell dose (2 × 10⁷ cells per kg) had a higher infection density within 28 days in an adjusted model of baseline characteristics. Cytokine release syndrome (CRS) severity was the only factor after CAR–T-cell infusion associated with infection in a multivariable analysis. The incidence of infections was comparable to observations from clinical trials of salvage chemoimmunotherapies in similar patients. This trial was registered at www.clinicaltrials.gov as #NCT01865617. Publisher9s Note: There is a Blood Commentary on this article in this issue. Key Points The incidence of infections after CD19 CAR–T-cell immunotherapy was similar to the incidence after other salvage chemoimmunotherapies. Infections were more frequent in patients who had ALL, more prior antitumor treatment, a higher CAR–T-cell dose, or greater CRS severity.

Autologous T cells engineered to express a CD19-specific chimeric antigen receptor (CAR) have produced impressive minimal residual disease–negative (MRD-negative) complete remission (CR) rates in patients with relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL). However, the factors associated with durable remissions after CAR T-cell therapy have not been fully elucidated. We studied patients with relapsed/refractory B-ALL enrolled in a phase 1/2 clinical trial evaluating lymphodepletion chemotherapy followed by CD19 CAR T-cell therapy at our institution. Forty-five (85%) of 53 patients who received CD19 CAR T-cell therapy and were evaluable for response achieved MRD-negative CR by high-resolution flow cytometry. With a median follow-up of 30.9 months, event-free survival (EFS) and overall survival (OS) were significantly better in the patients who achieved MRD-negative CR compared with those who did not (median EFS, 7.6 vs 0.8 months; P < .0001; median OS, 20.0 vs 5.0 months; P = .014). In patients who achieved MRD-negative CR by flow cytometry, absence of the index malignant clone by IGH deep sequencing was associated with better EFS (P = .034). Stepwise multivariable modeling in patients achieving MRD-negative CR showed that lower prelymphodepletion lactate dehydrogenase concentration (hazard ratio [HR], 1.38 per 100 U/L increment increase), higher prelymphodepletion platelet count (HR, 0.74 per 50 000/μL increment increase), incorporation of fludarabine into the lymphodepletion regimen (HR, 0.25), and allogeneic hematopoietic cell transplantation (HCT) after CAR T-cell therapy (HR, 0.39) were associated with better EFS. These data allow identification of patients at higher risk of relapse after CAR T-cell immunotherapy who might benefit from consolidation strategies such as allogeneic HCT. This trial was registered at www.clinicaltrials.gov as #NCT01865617.

Factors associated with durable remission after CD19 chimeric antigen receptor (CAR)-modified T cell immunotherapy for aggressive B-cell non-Hodgkin lymphoma (NHL) have not been identified. We report multivariable analyses of factors impacting response and progression-free survival (PFS) in aggressive NHL patients treated with cyclophosphamide and fludarabine (Cy/Flu) lymphodepletion followed by 2x10⁶ CD19 CAR-T cells/kg. The best overall response rate (ORR) was 51%, with 40% of patients achieving complete remission (CR). The median PFS of aggressive NHL patients who achieved CR was 20.0 months (median follow-up 26.9 months). Multivariable analysis of clinical and treatment characteristics, serum biomarkers, and CAR-T cell manufacturing and pharmacokinetic data showed that a lower pre-lymphodepletion serum LDH and a favorable cytokine profile, defined as serum day 0 MCP-1 and peak IL-7 concentrations above the median, were associated with better PFS. MCP-1 and IL-7 concentrations increased after lymphodepletion and higher intensity of Cy/Flu lymphodepletion was associated with higher probability of a favorable cytokine profile. PFS was superior in patients who received high-intensity lymphodepletion and achieved a favorable cytokine profile compared to those who received the same intensity of lymphodepletion without achieving a favorable cytokine profile. Even in high-risk patients with pre-lymphodepletion serum LDH above normal, a favorable cytokine profile after lymphodepletion was associated with a low risk of a PFS event. Strategies to augment the cytokine response to lymphodepletion could be tested in future studies of CD19 CAR-T cell immunotherapy for aggressive B-cell NHL. Key points LDH, MCP-1, and IL-7 are independently associated with PFS in aggressive NHL after CD19 CAR-T cell immunotherapy. Higher intensity of Cy/Flu lymphodepletion is associated with higher probability of a favorable cytokine profile.