Long-Term Functional Persistence, B Cell Aplasia and Anti-Leukemia Efficacy In Refractory B Cell Malignancies Following T Cell Immunotherapy Using CAR-Redirected T Cells Targeting CD19

Recent advances in T cell engineering have enabled clinical trials to evaluate the potential for adoptive transfer of T cells to target malignancy. A single treatment with engineered gene-modified T cells has the potential to generate potent and long-lasting anti-tumor immunity. We have reported initial clinical data on the use of T cells engineered to express a Chimeric Antigen Receptor (CAR) that targets CD19 (CTL019) in patients with advanced treatment-refractory CLL and pediatric ALL (Porter, et al NEJM 2011; Kalos et al. Sci Trans Med 2011, Grupp et al. NEJM 2013). The initial cohort of patients is now disease free between 1 and 3 years post-infusion. In this report we present data on the functional persistence, trafficking, and bioactivity of CTL019 cells from the initial cohort of CLL patients, a larger and more recently treated cohort of CLL patients, a cohort of pediatric ALL patients, as well as an initial cohort of adult ALL patients.

CAR engineering of patient T cells was accomplished by lentivirus transduction followed by in-vitro expansion using anti-CD3 and anti-CD28 antibody-coated beads. Persistence of gene-modified T cells was assessed by quantitative PCR. CAR19 surface expression was detected by flow. B cell aplasia was evaluated by multiparametric flow cytometry. Multiplex cytokine analyses were performed using Luminex^TMtechnology.

Detailed clinical outcomes for each patient cohort will be reported separately at this meeting (Porter, D.L.et al, Grupp S. et al). In summary, as of July 15, 2013: For CLL: A total of 24 adult patients with advanced relapsed and/or treatment-refractory CLL have been treated under two separate protocols. To date 5 patients have achieved ongoing CR, 7 patients PR and 12 patients were NR at the primary endpoint (within 3 months post infusion). For ALL (pediatric): A total of 14 pediatric patients with treatment refractory ALL have been treated and were evaluable under a single protocol. To date 8 patients have ongoing CR, 4 patients have relapsed including 2 with CD19-negative disease and 2 patients were NR. For ALL (Adult): A total of 3 adult patients with advanced relapsed and/or treatment-refractory ALL have been treated under a single protocol. All 3 patients have ongoing CR; one patient went into an allogeneic transplant while in CTL019-induced CR.

In all patients with CR, robust in vivo expansion of CTL019 cells was observed, as assessed by both molecular and flow cytometric analysis, followed by contraction and in all but one patient ongoing stable persistence of engineered cells, elimination of tumor B cells and ongoing B cell aplasia in blood and marrow at all evaluated time points (minimum 3 months, maximum ongoing at 35 months). In CR patients, peak marking exceeded 5% of total CD3+. Patients with PR demonstrated less robust in-vivo expansion accompanied by transient B cell elimination, while NR patients demonstrated minimal in-vivo expansion.

Clinical MRD analysis in patients was supplemented with Illumina-HiSeq/MiSeq-deep sequencing based molecular MRD analysis. These analyses demonstrate that CRs were accompanied with deep and sustained molecular remissions as assessed by the absence of the tumor specific clonotype defined in the enrollment samples.

All patients in CR experienced on-target cytokine release syndrome (CRS) and macrophage activation syndrome (MAS). Multiplex-cytokine analysis of serum samples from patients in CR demonstrated a broad pro-inflammatory signature with significant elevation in a subset of soluble immune modulators including IFN-g, IL-6, and IL2ra. In contrast, patients with NR did not have elevated serum cytokines. Elevation of cytokines coincided with expansion of CTL019 cells, elimination of B cells, and toxicity suggesting the potential for a cytokine-based diagnostic signature to monitor CTL019 treatment efficacy.

Adoptive transfer of CTL019 cells engineered to express CD137 and TCR-zeta signaling domains can result in in-vivo expansion, homing to marrow, and long-term functional persistence of engineered cells, accompanied by ongoing complete clinical responses and long-term B cell aplasia in a substantial fraction of patients with advanced, refractory and high risk CLL and relapsed refractory pre- B cell ALL. These results highlight the potential of CTL019 therapy to effectively target CD19-positive malignancy.

Kalos:Novartis corporation: CART19 technology, CART19 technology Patents & Royalties; Adaptive biotechnologies: Member scientific advisory board , Member scientific advisory board Other. Zheng:Novartis: Patents & Royalties. Levine:Novartis: cell and gene therapy IP, cell and gene therapy IP Patents & Royalties. Grupp:Novartis: Research Funding. June:Novartis: Patents & Royalties, Research Funding.