Multi-Center Clinical Trial of CAR T Cells in Pediatric/Young Adult Patients with Relapsed B-Cell ALL

T cells can be genetically modified to target tumor antigens through the expression of a chimeric antigen receptor (CAR). CAR T cells targeting the CD19 antigen is a novel therapeutic approach for patients with relapsed B cell acute lymphoblastic leukemia (B-ALL). We have previously demonstrated that CAR T cells have a significant clinical benefit in adult patients with relapsed B-ALL. The primary objective of this study (NCT01860937) is to extend the use and test the safety of CD19 specific CAR T cells in a multicenter trial for children and young adults with relapsed CD19⁺ B-ALL. To date, 24 patients with very high risk (VHR) or relapsed B-ALL have been enrolled on protocol with a median age of 12 years (range 2-20 years) at time of T cell collection. We have treated 9 patients with relapsed B-ALL with a median age 15 years (range 3-22 years) using patient derived T cells expressing a CD19 specific CAR (19-28z). 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 5/9 (55%) patients. Significantly, correlations with response included lower disease burden (as assessed by bone marrow cellularity; p<0.02) and fold expansion following CD3/28 bead activation during the generation of CAR T cells (p<0.02). Specifically, BM cellularity ≤50% and fold expansion (average >150 vs <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=2) and grade III-IV (n=3). Systemic immunosuppressants (corticosteroids or anti-IL6 receptor antibody tocilizumab) abrogated clinical symptoms of CRS. Elevated serum cytokines of IFN-g (>20 fold), fractalkine (>20 fold), Flt-3L (>55 fold), IL-5 (>15 fold), IL-6 (>100 fold), and IL-10 (>15 fold) were demonstrated 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. These early results demonstrate the feasibility and significant clinical impact of this approach in patients with relapsed 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.