Sustained Functional T Cell Persistence and B Cell Aplasia Following CD19-Targeting Adoptive T Cell Immunotherapy for Relapsed, Refractory CD19+ Malignacy
Authors: Kalos Michael , Levine Bruce L. , Macatee Timothy L , Kulikovskaya Irina , Suppa Erica , Jena Bipulendu , Gill Saar I. , Cooper Laurence J N , Grupp Stephan A. , Porter David L , June Carl H. 
Published: October 2019

Abstract
Abstract 756

Background
Advances in ex vivo T cell engineering have facilitated clinical trials to evaluate the potential for adoptive T cell transfer to target malignancy. Gene-modified T cells have the potential to expand, functionally persist and mediate long-term anti-tumor activity. Most clinical studies have shown only limited persistence of infused cells, with modest and often temporary anti-tumor activity. We reported initial clinical data on CAR T cells targeting CD19 expressed on normal and malignant B cells (CART19 cells) (Porter, et al NEJM 2011; Kalos et al Sci Trans Med 2011). The CAR included signaling domains from CD3zeta and CD137 (4-1BB) that mediated effector and proliferation/persistence signals. Here we report functional persistence of CART19 cells from the initial cohort at approximately 2 years post-infusion, and data from a more recently treated cohort of CLL patients and a pediatric patient with advanced, treatment refractory ALL.

Methods
Persistence of gene-modified T cells was assessed by quantitative ABI-Taqman based PCR and a qualified assay that detects the CD137-TcR-zeta junction in the anti-CD19 CAR. CAR19 surface expression was detected by flow cytometry with an anti-CAR-19 idiotype specific antibody. B cell aplasia was evaluated by multiparametric flow cytometry. Multiplex cytokine analyses were performed using Luminex™assays.

Results
10 patients with relapsed, refractory disease have been treated to date: 9 adults w/CLL and one child w/pre- B cell ALL. Each had been extensively pre-treated and had active disease at the time of CART19 infusion. All CLL patients received lymphodepleting chemotherapy 4–6 days before infusions, while the ALL patient did not get further lymphodepletion. Patients were infused with an average total of 1.7–50 × 108 total T cells which corresponded to 0.14–5.9 x108CART-19 cells.
9/10 treated patients were evaluable on 8.14.12. Detailed clinical outcomes will be reported separately at this meeting (Porter, D.L., Grupp S. et al). 4 pts (3 CLL, 1 ALL) had achieved CR at the primary endpoint (30 days post infusion) which is sustained and ongoing in all patients (range 1–24 months). Two CLL patients had a partial response (PR) lasting 3 and 5 months, while 3 patients did not respond (NR). In all patients with CR, robust in vivo expansion of CART19 cells was observed. By molecular analysis, CART19 cells demonstrated in vivo expansion, followed by contraction and an ongoing stable persistence at all evaluated timepoints. Expansion kinetics were unique for each patient; in all cases maximal expansion was observed by day +30 post CART-19 infusion. In patients with CR, observed peak marking for CART-19 ranged from 1 × 102-1 × 103 CART-19 cells/uL blood. Patients with PR demonstrated less robust in vivo expansion, with peak observed marking ∼1 × 101 CART-19 cells/uL blood. In NR patients, peak marking was <1 × 101CART-19 cells/uL blood. Long term peripheral blood persistence of CART19 cells and CAR19 surface expression was observed in all patients with CR in both CD3+/CD8+ and CD3+/CD4+ subsets. In patients with CR, elimination of peripheral B cells was observed at the time of CART19 in vivo expansion. Ongoing B cell aplasia has been documented in each CR patient in both peripheral blood and marrow by flow cytometry. Patients with PR showed transient elimination of malignant and normal B cells.
Multiplex-cytokine analysis of serum samples from CR patients revealed a broad pro-inflammatory signature with significant elevation in a subset of soluble immune modulators including IL-6, IL-8, IFN-g, MIP1b, and IL2ra. In contrast, NR patients did not have elevated serum cytokines. In CR patients, elevation of cytokines tracked with expansion of CART19 cells and elimination of B cells, suggesting the potential for a cytokine-based diagnostic signature to monitor CART19 treatment efficacy.

Conclusions
Adoptive transfer of CART19 cells engineered to express CD137 and TCR-zeta signaling domains can result in in vivo expansion, homing to disease sites, and long-term functional persistence of CART19 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 ALL. A detailed cytokine profile and persistent B cell aplasia has been identified that may correlate with treatment efficacy.

Disclosures:
Kalos: University of Pennsylvania: Patents & Royalties. Levine:TxCell: Consultancy, Membership on an entity's Board of Directors or advisory committees; University of Pennsylvania: financial interest due to intellectual property and patents in the field of cell and gene therapy. Conflict of interest is managed in accordance with University of Pennsylvania policy and oversight, financial interest due to intellectual property and patents in the field of cell and gene therapy. Conflict of interest is managed in accordance with University of Pennsylvania policy and oversight Patents & Royalties. June:Novartis: Research Funding, institution owned patents have been licensed by Novartis, institution owned patents have been licensed by Novartis Patents & Royalties.