Long-Term Follow-Up of Anti-CD19 Chimeric Antigen Receptor T-Cell Therapy

Abstract

Purpose: Anti-CD19 chimeric antigen receptors (CARs) are artificial fusion proteins that cause CD19-specific T-cell activation. Durability of remissions and incidence of long-term adverse events are critical factors determining the utility of anti-CD19 CAR T-cell therapy, but long-term follow-up of patients treated with anti-CD19 CAR T cells is limited. This work provides the longest follow-up of patients in remission after anti-CD19 CAR T-cell therapy.

Methods: Between 2009 and 2015, we administered 46 CAR T-cell treatments to 43 patients (ClinicalTrials.gov identifier: NCT00924326). Patients had relapsed B-cell malignancies of the following types: diffuse large B-cell lymphoma or primary mediastinal B-cell lymphoma (DLBCL/PMBCL; n = 28), low-grade B-cell lymphoma (n = 8), or chronic lymphocytic leukemia (CLL; n = 7). This report focuses on long-term outcomes of these patients. The CAR used was FMC63-28Z; axicabtagene ciloleucel uses the same CAR. Cyclophosphamide plus fludarabine conditioning chemotherapy was administered before CAR T cells.

Results: The percentages of CAR T-cell treatments resulting in a > 3-year duration of response (DOR) were 51% (95% CI, 35% to 67%) for all evaluable treatments, 48% (95% CI, 28% to 69%) for DLBCL/PMBCL, 63% (95% CI, 25% to 92%) for low-grade lymphoma, and 50% (95% CI, 16% to 84%) for CLL. The median event-free survival of all 45 evaluable treatments was 55 months. Long-term adverse effects were rare, except for B-cell depletion and hypogammaglobulinemia. Median peak blood CAR-positive cell levels were higher among patients with a DOR of > 3 years (98/µL; range, 9-1,217/µL) than among patients with a DOR of < 3 years (18/µL; range, 0-308/μL, P = .0051).

Conclusion: Complete remissions of a variety of B-cell malignancies lasting ≥ 3 years occurred after 51% of evaluable anti-CD19 CAR T-cell treatments. Remissions of up to 9 years are ongoing. Late adverse events were rare.

Figures

FIG 1.

Trial design and responses. (A) Schematics of clinical treatment protocols are shown. Patients in cohort 1 received cyclophosphamide (Cy) 60 mg/kg on days −7 and −6, fludarabine (Flu) 25 mg/m2 on days −5 to day −1, and chimeric antigen receptors (CAR) T-cell infusion on day 0. High-dose intravenous interleukin-2 (IL-2) administration started on day 0. IL-2 administration continued until either patient toxicity required cessation or 6 days of IL-2 administration were completed. Patients in cohort 2 received Cy doses of 30 or 60 mg/kg on days −7 and −6, Flu 25 mg/m2 on days −5 to −1, and CAR T-cell infusion on day 0. IL-2 was not administered. Patients in cohort 3 received daily doses of Cy 300 or 500 mg/m2 + Flu 30 mg/m2 on days −5 to −3. CAR T-cell infusion was on day 0 with no IL-2 administration. (B) Best responses of each patient and durations of responses are shown. Each bar represents one patient. Three patients were retreated with CAR T-cells; patient 1 (follicular lymphoma), patient 3 (CLL), and patient 4 (splenic marginal zone lymphoma) were each treated twice. These retreatments are shown. Patients 2 and 11 were not evaluable for response because of early death and are not shown. Patient 18 was omitted because this patient was not evaluable for response due to patient noncompliance. Patients who were no longer evaluable due to development of a second malignancy, loss to follow-up, or treatment with allogeneic stem-cell transplantation while in ongoing response are indicated on the figure. Ongoing responses are indicated by black arrows. CAR+, Chimeric antigen receptor positive; CLL, chronic lymphocytic leukemia; DLBCL, diffuse large B-cell lymphoma; PMBCL, primary mediastinal B-cell lymphoma.

FIG 2.

Anti-CD19 chimeric antigen receptor (CAR) T cells generated long-term complete remissions (CRs). (A) Event-free survival (EFS) curves of all 45 evaluable CAR T-cell treatments. For the three patients who received two CAR T-cell treatments, both treatments are included separately on this plot. The median EFS was 55 months. (B) Overall survival (OS) of all 42 evaluable patients. For patients who received second CAR T-cell treatments, the OS from the time of the second CAR T-cell infusion is shown. Median OS was not reached. (C) EFS curves of each CAR T-cell treatment divided by malignancy type. The median EFS for patients with diffuse large B-cell lymphoma (DLBCL) or primary mediastinal B-cell lymphoma (PMBCL) was 15 months. The median EFS for patients with low-grade lymphoma was 55 months, and the median EFS for patients with chronic lymphocytic leukemia (CLL) was 40.5 months. No statistically significant differences were found when the EFS curves of each malignancy type were compared. For patients 1, 3, and 4 who received two CAR T-cell treatments, both the first and second treatments are included. (D) OS curves divided by malignancy type are shown. The median OS was not reached for any of the malignancy types. For patients who received two CAR T-cell treatments, OS was calculated starting from the time of the second treatment. No statistically significant differences were found when the OS curves of each malignancy type were compared. (E) EFS curves of each treatment cohort are shown. (continued on following page)(Continued). The median EFS of cohorts 1, 2, and 3 were 12, 66, and 20 months, respectively. For patients who received retreatments, both treatments are included on the plot. No statistically significant differences were found when the EFS curves of each cohort were compared. (F) The plot shows EFS of treatments that resulted in CRs. Patient 3 received two treatments that both resulted in CR, and both treatments are included on this graph. The median EFS was not reached. All plots were prepared using the Kaplan-Meier method, and all curve comparisons were made using the log-rank test. Patients who were no longer evaluable for response due to diagnosis of non–skin cancer second malignancies or loss to follow-up were censored and are indicated with a red mark. Red marks are also present for patients in ongoing remission at the time of final data analysis. Patient 18 was not included in the analysis for EFS or OS due to patient noncompliance with follow-up.

FIG 3.

Association of higher peak chimeric antigen receptor–positive (CAR+) cell levels with anti-lymphoma responses. (A) The peak numbers of blood CAR+ cells for CAR T-cell treatments that resulted in best responses of complete remission (CR) are compared with peak numbers of blood CAR+ cells for CAR T-cell treatments that resulted in responses of partial remission (PR), stable disease (SD), or progressive disease (PD; n = 41 of 46 total administered treatments). Two treatments were not evaluable due to lack of cell samples for polymerase chain reaction (PCR) analysis, and three treatments were not evaluable due to lack of response assessment data. (B) The levels of blood CAR+ cells at 28-56 days after CAR T-cell infusion are compared for treatments resulting in best responses of CR versus PR, SD, or PD (n = 38 of 46 total treatments). Three patients were not evaluable due to lack of response assessment data, and five patients were not evaluable due to lack of samples for PCR. (C) The peak levels of blood CAR+ cells are compared for CAR T-cell treatments that resulted in durations of response (DORs) > 3 years versus DORs < 3 years (n = 39 of 46 total treatments). Five treatments lacked lymphoma response follow-up for this analysis, and two lacked PCR data due to lack of blood samples. (D) The levels of blood CAR+ cells at 28-56 days after CAR T-cell infusion are compared for treatments resulting in DORs > 3 years versus DORs < 3 years (n = 36 of 46 total treatments). Five treatments lacked lymphoma response follow-up for this analysis, and five lacked PCR data due to lack of blood samples. All CAR+ cell values were determined using quantitative PCR with an assay specific for the CAR. Data are presented as CAR+ cells per microliter, and all values are rounded to the nearest whole number. Median values are indicated by the black horizontal bars. Each dot indicates an individual patient. All statistical comparisons were done using two-tailed Mann-Whitney U tests. Statistically significant P values are shown on the graph. P < .05 was considered statistically significant. NS, not statistically significant.

FIG 4.

Time to recovery of B cells and immunoglobulins after chimeric antigen receptor (CAR) T-cell infusion. (A) The number of blood CD19+ cells was determined by flow cytometry before conditioning chemotherapy and at the indicated time points after CAR T-cell infusion (normal range, 61-321 cells/µL). (B) Serum immunoglobulin (Ig) G levels (normal range, 700-1,600 mg/dL) were determined before treatment and at the indicated time points after CAR T-cell infusion. (C) Serum IgA levels (normal range, 70-400 mg/dL) were determined before treatment and at the indicated time points after CAR T-cell infusion. (D) Serum IgM levels (normal range, 40-230 mg/dL) were determined before treatment and at the indicated time points after CAR T-cell infusion. Median values are indicated by the black horizontal bars; the blue boxes include the 25th to 75th percentiles; each dot indicates an individual patient; and the whiskers extend from the minimum to the maximum values. The dashed line on each plot indicates the lower limit of normal for each measured parameter. A total of 24 treatments are presented because there were 24 treatments that resulted in complete remission and had blood samples available for long-term immunoglobulin and B-cell monitoring. The treatments were all for unique patients, except both the first and second treatments for patient 3 are included.