STRIvE-01: Phase I Study of EGFR806 CAR T-cell Immunotherapy for Recurrent/refractory Solid Tumors in Children and Young Adults.

2541 Background: The epidermal growth factor receptor (EGFR) is a cell surface tyrosine kinase receptor associated with cell proliferation and differentiation. EGFR expression and activating mutations are associated with aggressive neoplastic disease, chemotherapy resistance, and increased metastatic potential. Published data and EGFR immunohistochemistry (IHC) performed on tissue microarrays indicate that 15-40% of pediatric solid tumors (ST) express EGFR. The unique EGFR monoclonal antibody (mAb) 806 selectively binds to an epitope that is conformationally hidden when EGFR is tethered but revealed when tethering is perturbed as occurs with EGFR overexpression, truncation, or through extra-cellular domain missense mutations. Methods: Children and young adults (CYA) with EGFR-expressing recurrent/refractory (R/R) ST were enrolled on a Phase 1 trial to examine the safety and feasibility of administering autologous chimeric antigen receptor (CAR) T cells derived from autologous T cells genetically modified to express a second generation EGFR806-specific scFV-IgG4hinge-CD28tm/cyto-4-1-BB-zeta and EGFRt tracking/suicide contract. All subjects received lymphodepleting chemotherapy with fludarabine and cyclophosphamide prior to the administration of cryopreserved CAR T cells a the prescribed dose level. The biologically effective dose (BED) or maximum tolerated dose was determined based upon observed toxicity through day 28 from initial CAR-T infusion and using a 3+3 statistical design. Results: Eleven subjects (n=10 evaluable, age range 9-25, median 18) were enrolled and received either dose level (DL) 1 (0.5 x 106 CAR-T/kg, n=4) or DL2 (1 x 106 CAR-T cells/kg, n=7). CAR T were manufactured successfully in all subjects. Most common toxicities were fatigue, tumor-related pain and cytokine release syndrome (n=2, maximum CTCAE grade 1). Dose limiting toxicity of CTCAE grade 4 transaminase level and hyperbilirubinemia occurred at DL2 (n=1). Maximum circulating CAR-T expansion was 29.66 cells/uL (range 0.05-29.66 cells/uL) with median persistence of 28 days (range 0-90). Two subjects on DL1 and one subject on DL2 demonstrated mixed response on day 28 and tolerated additional CAR T infusion without dose limiting toxicity. Conclusions: EGFR806 directed CAR-T cells have an acceptable toxicity profile in CYA with R/RST and demonstrate anti-tumor activity in some patients. Additional analyses are ongoing to identify biomarkers of response and toxicity. Clinical trial information: NCT03618381.