Chimeric antigen receptor T cells persist and induce sustained remissions in relapsed refractory chronic lymphocytic leukemia

Abstract

Patients with multiply relapsed or refractory chronic lymphocytic leukemia (CLL) have a poor prognosis. Chimeric antigen receptor (CAR)-modified T cells targeting CD19 have the potential to improve on the low complete response rates with conventional therapies by inducing sustained remissions in patients with refractory B cell malignancies. We previously reported preliminary results on three patients with refractory CLL. We report the mature results from our initial trial using CAR-modified T cells to treat 14 patients with relapsed and refractory CLL. Autologous T cells transduced with a CD19-directed CAR (CTL019) lentiviral vector were infused into patients with relapsed/refractory CLL at doses of 0.14 × 10(8) to 11 × 10(8) CTL019 cells (median, 1.6 × 10(8) cells). Patients were monitored for toxicity, response, expansion, and persistence of circulating CTL019 T cells. The overall response rate in these heavily pretreated CLL patients was 8 of 14 (57%), with 4 complete remissions (CR) and 4 partial remissions (PR). The in vivo expansion of the CAR T cells correlated with clinical responses, and the CAR T cells persisted and remained functional beyond 4 years in the first two patients achieving CR. No patient in CR has relapsed. All responding patients developed B cell aplasia and experienced cytokine release syndrome, coincident with T cell proliferation. Minimal residual disease was not detectable in patients who achieved CR, suggesting that disease eradication may be possible in some patients with advanced CLL.

Fig. 1. Overall survival and PFS

(A and B) Kaplan-Meier curves for overall survival (A) and PFS (B) were estimated for the 14 subjects who received therapy. Shaded region indicates 95% CI. Number of subjects at risk is presented in a 3-month interval. Vertical tick marks indicate time points with censored data. (Source data, table S6).

Fig. 2. CTL019 expansion by qPCR in the first 12 months

Peripheral blood CTL019 expansion was measured as copies per microgram of genomic DNA by qPCR in 14 subjects. Values below the quantitative limit of detection (<25 copies/μg DNA) are shown with open circles. (Source data, table S7).

Fig. 3. Association between peak CTL019 expansion and response

(A and B) Peak CTL019 expansion in the first 3 months measured by flow cytometry (A) in 11 subjects and qPCR (B) in 14 subjects. Flow cytometry detection was not available for subjects 01, 02, and 03 because an antibody to detect CTL019 cells was not available at the time of their treatment. Wilcoxon rank-sum P values are provided. (Source data, table S8).

Fig. 4. Long-term persistence of CTL019 cells and poly-functionality in patients achieving CR

(A) Long-term persistence of CTL019 cells by flow cytometry (solid circle) and qPCR (solid triangle) beyond 12 months from infusion. All observed values were above the limit of detection by flow cytometry (0.1%) and above the limit of quantification by qPCR (<25 copies/μg DNA). (B and C) Purified PBMCs from patient UPCC04409-02 from the indicated postinfusion time points were stimulated for 6 hours with APC-expressing CD19 or control antigen (mesothelin) and examined for de-granulation (CD107a) and cytokine protein expression. (B) Contour plots displaying CD107a versus MIP-1β (top two rows) or IL-2 versus IFN-γ expression (bottom rows) in CD8⁺ CAR⁺ T cells stimulated with K562 cells expressing control antigen (mesothelin) or CD19. (C) Summary graph of functional response of CAR19⁺ CD8 T cells upon stimulation with CD19⁺ target cells over time. Data are plotted from (B) and are depicted as the background-subtracted frequency of this subset. (Source data, tables S9 and S10).

Fig. 5. Peak cytokines values over the first month after infusion

(A to D) Peak values for IL-6 (A), IFN-γ (B), IL-2 receptor antagonist (IL-2RA) (C), and IL-2 (D) by CRS grades are displayed. Gray symbols represent nonresponders; black symbols are those who achieved a complete or partial remission. Individual values are plotted with a symbol that reflects their CRS grade (1 to 4). Wilcoxon rank-sum P values are also provided. Cytokine values were missing for one grade 4 subject who achieved CR (n = 13). (Source data, table S11).