Abstract IA07: Chimeric antigen receptor T cells for cancer immunotherapy
Authors: Curran Kevin J. , Silverman Lewis B. , Kobos Rachel , Kernan Nancy A. , Margossian Steven P. , Park Jae H. , Sauter Craig S. , Szenes Victoria , Wang Xiuyan , O'Reilly Richard J. , Sadelain Michel , Riviere Isabelle , Brentjens Reiner J. 
Published: May 2016

Background: T cells can be genetically modified to target tumor antigens through the expression of a chimeric antigen receptor (CAR). CAR structure consists of two fundamental domains – the antigen binding portion (most commonly single chain variable fragment (scFv) derived from a monoclonal antibody) joined to one or more intracellular T cell signaling domains. To be effective CAR T cells must expand, persist, exhibit enduring anti-tumor cytotoxicity, withstand and/or counteract an immunosuppressive tumor microenvironment, and overcome targeted tumor antigen escape following infusion. T cells targeting the CD19 antigen is a novel therapeutic approach for patients with hematologic malignancies. To this end, we have previously demonstrated that CAR T cells have a significant clinical benefit in adult patients with relapsed or refractory (R/R) B-cell acute lymphoblastic leukemia (B-ALL). We now extend this novel treatment approach by testing of our CD19-specific CAR in a multicenter trial for children and young adults with relapsed CD19+ B-ALL.

Patients and Methods: Pediatric and young-adult patients with very high risk (VHR) or R/R CD19+ B-ALL were eligible for enrollment and leukapheresis. Patients with R/R B-ALL were eligible for infusion if they demonstrated residual disease following salvage chemotherapy. Once eligibility was determined isolation and transduction of T cells was performed using a retroviral vector encoding a CD19-specific CAR comprised of a CD19-specific scFv and the CD28 and CD3ζ signaling domains (termed 19-28z). All patients received conditioning chemotherapy followed 2 days later by 1x106 3x106 19-28z CAR T cells/kg. The primary objective of the study was to evaluate the safety and anti-tumor activity of 19-28z CAR T cells. Post-treatment response was assessed at day 14-28 bone marrow aspirate including multiparameter flow cytometry for minimal residual disease (MRD).

Results: To date, 28 patients with have been enrolled on protocol with a median age of 11.5 years (range 9 months to 20 years) at time of T cell collection. We have treated 11 patients with 19-28z CAR T cells with a median age 14.9 years (range 3-22 years). Patients received a dose of 1-3 x 10^6 CAR T cells/kg and complete response (complete remission or complete remission with incomplete count recovery) occurred in 7/11 (64%) patients. Significantly, correlations with response included lower disease burden (as assessed by bone marrow cellularity; p&lt;0.004) and fold expansion following CD3/28 bead activation during the generation of CAR T cells (p&lt;0.03). Specifically, BM cellularity ≤50% and fold expansion (average &gt;135 vs &lt;40 fold expansion) was seen in responders compared to non-responders. Pre-collection peripheral blood absolute lymphocyte count, lymphocyte proliferative response (phytohemagglutinin proliferation assay), and CD3 absolute count did not correlate with response in this small sample size. Development of fever and cytokine release syndrome (CRS) occurred in responders including grade I-II (n=3) and grade III-IV (n=4). Systemic immunosuppressants (corticosteroids or anti-IL6 receptor antibody tocilizumab) abrogated clinical symptoms of CRS. Elevated serum cytokines (notably IFN-γ and IL-6) was noted in patients with CRS. Monitoring of bone marrow demonstrated peak 19-28z CAR T cell detection within 1-2 weeks following infusion with gradual contracture over 1-2 months.

Conclusions: These early results demonstrate the feasibility and significant clinical impact of CAR T cells in patients with R/R B-ALL. In an effort to more rapidly generate statistically relevant data, demonstrate the exportability of this technology between academic institutions, and offer this therapeutic option to a broader number of pediatric patients with chemo-refractory B-ALL we have expanded this trial to include a collaborating institution. The objective of our trial is not to provide an intent-to-treat cohort, but rather demonstrate the tolerability of this technology in patients with relapsed B-ALL. Furthermore, patients meeting disease eligibility were not pre-screened for lymphocyte function prior to collection and/or treatment. Subsequent cohorts of patients will receive 19-28z CAR T cells and will be evaluated for toxicity, persistence of CAR T cells, and for anti-leukemic efficacy.

Citation Format: Kevin J. Curran, Lewis B. Silverman, Rachel Kobos, Nancy A. Kernan, Steven P. Margossian, Jae H. Park, Craig S. Sauter, Victoria Szenes, Xiuyan Wang, Richard J. O'Reilly, Michel Sadelain, Isabelle Riviere, Reiner J. Brentjens. Chimeric antigen receptor T cells for cancer immunotherapy. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Pediatric Cancer Research: From Mechanisms and Models to Treatment and Survivorship; 2015 Nov 9-12; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(5 Suppl):Abstract nr IA07.