T cells with chimeric antigen receptors have potent antitumor effects and can establish memory in patients with advanced leukemia

Abstract

Tumor immunotherapy with T lymphocytes, which can recognize and destroy malignant cells, has been limited by the ability to isolate and expand T cells restricted to tumor-associated antigens. Chimeric antigen receptors (CARs) composed of antibody binding domains connected to domains that activate T cells could overcome tolerance by allowing T cells to respond to cell surface antigens; however, to date, lymphocytes engineered to express CARs have demonstrated minimal in vivo expansion and antitumor effects in clinical trials. We report that CAR T cells that target CD19 and contain a costimulatory domain from CD137 and the T cell receptor ζ chain have potent non-cross-resistant clinical activity after infusion in three of three patients treated with advanced chronic lymphocytic leukemia (CLL). The engineered T cells expanded >1000-fold in vivo, trafficked to bone marrow, and continued to express functional CARs at high levels for at least 6 months. Evidence for on-target toxicity included B cell aplasia as well as decreased numbers of plasma cells and hypogammaglobulinemia. On average, each infused CAR-expressing T cell was calculated to eradicate at least 1000 CLL cells. Furthermore, a CD19-specific immune response was demonstrated in the blood and bone marrow, accompanied by complete remission, in two of three patients. Moreover, a portion of these cells persisted as memory CAR(+) T cells and retained anti-CD19 effector functionality, indicating the potential of this major histocompatibility complex-independent approach for the effective treatment of B cell malignancies.

Fig. 1

Schematic representation of the gene transfer vector and transgene, gene-modified T cell manufacturing, and clinical protocol design. (A) T cell manufacturing. Autologous cells were obtained via leukapheresis, and T cells were enriched by mononuclear cell elutriation, washed, and expanded by addition of anti-CD3/CD28–coated paramagnetic beads for positive selection and activation of T cells. Residual leukemic cells were depleted. The lentiviral vector was added at the time of cell activation and was washed out on day 3 after culture initiation. Cells were expanded on a rocking platform device (WAVE Bioreactor System) for 8 to 12 days. On the final day of culture, the beads were removed by passage over a magnetic field and the CART19 cells were harvested and cryopreserved in infusible medium. mAb, monoclonal antibody. (B) Clinical protocol design. Patients were given lymphodepleting chemotherapy as described, followed by CART19 infusion #1 by intravenous gravity flow drip over a period of 15 to 20 min. The infusion was given using a split-dose approach over 3 days (10, 30, and 60%) beginning 1 to 5 days after completion of chemotherapy. Endpoint assays were conducted on study week 4. At the conclusion of active monitoring, subjects were transferred to a destination protocol for long-term follow-up as per FDA guidance.

Fig. 2

Sustained in vivo expansion and persistence in blood and marrow of CART19 cells. (A to D) qPCR analysis was performed on DNA isolated from whole blood (A to C) or bone marrow (BM) (D) samples obtained from UPN 01, UPN 02, and UPN 03 to detect and quantify CAR19 sequences. The frequency of CART19 cells is shown as average transgene copies (A), total calculated CART19 cells in circulation (B), or as a fraction of circulating white blood cells (WBCs) (C). (A) Copies CAR19/microgram DNA is calculated as described in Materials and Methods. (B) The total number of lymphocytes (total normal and CLL cells) versus total CART19⁺ cells in circulation is plotted for all three subjects using the absolute lymphocyte count from complete blood count values and assuming a 5.0-liter volume of peripheral blood. (C) % WBC is calculated as described in Materials and Methods. (D) Bulk qPCR analysis of marrow to quantify CART19 sequences. The data from patient UPN 03 in (A, C, and D) has been published in (9) and is reprinted here with permission. Each data point represents the average of triplicate measurements on 100 to 200 ng of genomic DNA, with maximal percent coefficient of variation (CV) less than 1.56%. Pass/fail parameters for the assay included preestablished ranges for slope and efficiency of amplification, and amplification of a reference sample. The lower limit of quantification for the assay established by the standard curve range was two copies of transgene per microgram of genomic DNA; sample values below that number are considered estimates and presented if at least two of three replicates generated a C_t value with percent CV for the values 15%. CART19 cells were infused at days 0, 1, and 2 for UPN 01 and 03 and at days 0, 1, 2, and 11 for UPN 02.

Fig. 3

Serum and BM cytokines before and after CART19 cell infusion. (A to C) Longitudinal measurements of changes in serum cytokines, chemokines, and cytokine receptors in UPN 01 (A), UPN 02 (B), and UPN 03 (C) on the indicated day after CART19 cell infusion. (D) Serial assessments of the same analytes in the BM from UPN 03. Analytes with a greater than or equal to threefold change are indicated and plotted as relative change from baseline (A to C) or as absolute values (D). In (C) and (D), a subset of the cytokine data (IFN-γ, CXCL10, CXCL9, IL-2Rα, and IL-6) from UPN 03 have been published in (9) and are reprinted here with permission. Absolute values for each analyte at each time point were derived from a recombinant protein-based standard curve over a threefold eight-point dilution series, with upper and lower limits of quantification determined by the 80 to 120% observed/expected cutoff values for the standard curves. Each sample was evaluated in duplicate with average values calculated and percent CV in most cases less than 10%. To accommodate consolidated data presentation in the context of the wide range for the absolute values, data are presented as fold change over the baseline value for each analyte. In cases where baseline values were not detectable, half of the lowest standard curve value was used as the baseline value. Standard curve ranges for analytes and baseline (day 0) values (listed in parentheses sequentially for UPN 01, 02, and 03), all in pg/ml: IL-1Rα: 35.5 to 29,318 (689, 301, and 287); IL-6: 2.7 to 4572 (7, 10.1, and 8.7); IFN-γ: 11.2 to 23,972 (2.8, not detected, and 4.2); CXCL10: 2.1 to 5319 (481, 115, and 287); MIP-1β: 3.3 to 7233 (99.7, 371, and 174); MCP-1: 4.8 to 3600 (403, 560, and 828); CXCL9: 48.2 to 3700 (1412, 126, and 177); IL-2Rα: 13.4 to 34,210 (4319, 9477, and 610); IL-8: 2.4 to 5278 (15.3, 14.5, and 14.6); IL-10: 6.7 to 13,874 (8.5, 5.4, and 0.7); MIP-1α: 7.1 to 13,778 (57.6, 57.3, and 48.1).

Fig. 4

Prolonged surface CAR19 expression and establishment of functional memory CART19 cells in vivo. (A and B) T cell immuno-phenotyping of CD4⁺ (A) and CD8⁺ (B) T cell subsets. Frozen peripheral blood (PB) samples from UPN 03 obtained at days 56 and 169 after T cell infusion were subjected to multiparametric immunophenotyping for expression of markers of T cell memory, activation, and exhaustion; data are displayed after biexponential transformation for objective visualization of events. (C) Functional competence of persisting CAR cells. Frozen PB samples from UPN 03 obtained at days 56 and 169 after T cell infusion were evaluated directly ex vivo for the ability to recognize CD19-expressing target cells using CD107 degranulation assays. Presented data are for the CD8⁺ gated population. The gating strategies for these figures are presented in fig. S2.

Fig. 5

Evaluation of clinical responses after infusion of CART19 cells. (A) UPN 02 was treated with two cycles of rituximab and bendamustine with minimal response (R/B, arrows). CART19 cells were infused beginning 4 and 14 days after bendamustine only (B, arrow). The rituximab- and bendamustine-resistant leukemia was rapidly cleared from blood, as indicated by a decrease in the absolute lymphocyte count (ALC) from 60,600/μl to 200/μl within 18 days of the infusion. Corticosteroid treatment was started on day 18 after infusion because of malaise and noninfectious febrile syndrome. The reference line (dotted) indicates the upper normal limit for ALC. (B) Sequential BM biopsy or clot specimens from UPN 01 were stained for CD20. Leukemia infiltration was present before treatment was absent after treatment; normalization of cellularity and trilineage hematopoiesis were also observed. (C) Sequential CT imaging indicates rapid resolution of chemotherapy-resistant generalized lymphadenopathy. Bilateral axillary masses in UPN 01 resolved by 83 days after infusion, as indicated by arrows and circle.