CD19 Targeted Allogeneic EBV-Specific T Cells for the Treatment of Relapsed ALL in Pediatric Patients Post HSCT

Abstract 353 T cells can be genetically modified to target tumor antigens through the expression of a chimeric antigen receptor (CAR). CAR modified T cells targeting the CD19 antigen is a novel therapeutic approach for patients with relapse B-ALL following allo-HSCT. We have previously demonstrated donor derived Epstein-Barr virus specific cytotoxic T cells (EBV-CTLs) can be safely infused in patients following allo-HSCT. Following retroviral gene transfer with our CD19-specific CAR (19–28z), EBV-CTLs demonstrate in vitro cytotoxicity against CD19+ targets, retain EBV-specificity without allogeneic reactivity, and in vivo, eradicate systemic Burkitt lymphoma in a SCID/Beige murine model. Based on our preclinical studies we have initiated a phase I dose escalation clinical trial (NCT01430390) in pediatric patients with relapsed CD19+ B-ALL following allo-HSCT utilizing donor 19–28z+ EBV-CTLs. Three patients have received conditioning chemotherapy (fludarabine 25mg/m2 × 5 days) followed by infusion of CAR modified EBV-CTLs without infusion related toxicity. Subsequently, patient 1 and 3 safely received additional T cell infusions without (patient 1) and with (patient 3; cyclophosphamide) conditioning chemotherapy. Total CAR+ T cell dose for each infusion ranged from 1.4 – 4.1×105 cells/kg (1×106 total EBV-CTLs/kg per infusion). Patient 1 developed fever and biopsy proven skin GVHD (grade II) three days following his first infusion which resolved 2 weeks after starting topical steroids. Modified T cells were detected by Q-PCR in the bone marrow and peripheral blood up to 3 and 18 weeks respectively in patient 1 following first infusion, up to 2 weeks in the peripheral blood in patient 2, and have been below the limit of detection in patient 3. Patient 1 died from progressive disease 29 weeks following first infusion and patient 2 died from progressive disease 19 weeks post infusion. Patient 3, initially treated in remission following salvage chemotherapy, has no evidence of disease (NED) 15 months after last extramedullary relapse and 5 months post first infusion of 19–28z+ EBV-CTLs. These early results demonstrate the feasibility of allogeneic 1928z+ EBV-CTL infusions without the development of significant GVHD post allo-HSCT. Subsequent cohorts of patients will receive dose escalation of modified T cells and will be evaluated for safety, persistence of 19–28z+ EBV-CTLs, and for anti-tumor efficacy. Disclosures: No relevant conflicts of interest to declare.