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.

STRIVE-02: A first-in-human phase 1 trial of systemic B7H3 CAR T cells for children and young adults with relapsed/refractory solid tumors

10011

Background: B7H3 (CD276) has limited expression in normal tissues and high cell-surface expression in pediatric solid malignancies providing rationale for immunologic therapeutic targeting. We present a first-in-human experience of B7H3 chimeric antigen receptor T cells (CAR-T) for children and young adults (CYA) with relapsed or refractory solid tumors (R/RST). Methods: CYA patients with R/RST were enrolled onto a Phase 1 trial (NCT04483778) to examine the safety of autologous T cells genetically modified to express scFV-IgG4hinge-CD28tm-4-1BB-zeta B7H3-specific CAR with the methotrexate resistance/selection cassette DHFRdm and the tracking/suicide construct EGFRt. All patients received lymphodepleting fludarabine and cyclophosphamide prior to infusion of cryopreserved CAR-T at the prescribed dose level. The maximal tolerated dose or biologically effective dose (BED) was determined based upon observed toxicity through day 28 from initial CAR-T infusion and using a 3+3 statistical design. Results: Sixteen subjects (age 11-24, median 17 years) enrolled and received dose level (DL) 1 (0.5 x 106 CAR-T/kg, n = 3) or DL2 (1 x 106 CAR-T cells/kg, n = 6). No dose limiting toxicity was observed following first infusion, most common toxicities were fatigue and cytokine release syndrome (CRS) (n = 2, maximum CTCAE grade 2). Maximum circulating CAR-T expansion on first infusion was 4.98 cells/uL (range 0.23-4.98 cells/uL) with median persistence of 28 days (range 14-90). Best overall response of Stable Disease was observed in 3 of the 9 subjects infused. Given observed expansion and persistence, DL2 was determined to be the BED. A second infusion at DL2 in one subject demonstrated CAR T expansion to 1590 cells/uL (86% of circulating CD3 cells) with CTCAE grade 2 CRS and transient dose limiting CTCAE grade 4 liver enzyme elevation. A partial metabolic response on FDG-PET by PERCIST criteria was observed in this subject at Day 28. Conclusions: B7H3 CAR T cells are safe and demonstrate anti-tumor activity in CYA with R/RST. CAR-T cell expansion and persistence may be necessary to achieve objective responses. STRIvE-02 Arm B will explore dual expression of CD19 CAR with B7H3 CAR, using lymphocytic CD19 expression to drive CAR expansion and persistence. Clinical trial information: NCT04483778.