(P 226) EARLY EXPERIENCE ON ENLIGHTEN-01: A PHASE 1 STUDY OF BISPECIFIC ADAPTER MOLECULE- CONTROLLED FOLATE RECEPTOR CAR T-CELL THERAPY FOR RELAPSED/REFRACTORY OSTEOSARCOMA

Objective: Patients with relapsed/refractory osteosarcoma (OS) have dismal outcomes, and there are no systemic therapies that provide a survival benefit. Chimeric antigen receptor (CAR) T-cell immunotherapy involves the adoptive transfer of T-lymphocytes that have been engineered to recognize tumor-specific antigens, resulting in targeted lysis of malignant cells. Folate receptor (FR)-α is highly expressed in OS and FRβ is found on tumor-associated macrophages but limited in normal tissues, making FR an ideal target for CAR T-cell therapy. ENLIGHTen-01 (NCT05312411) evaluates UB-TT170 (Umoja Biopharma), a small molecule bispecific “adapter” consisting of folate conjugated to fluorescein (FL), in combination with a fluorescein (FITC-E2)- directed CAR T-cell product manufactured at Seattle Children’s Therapeutics , the combination collectively mediating CAR T cell cytotoxicity on FR-expressing target cells. We hypothesize that administration of FITC-E2 CAR T cells followed by escalating doses of UB-TT170 will personalize immunotherapy for OS patients by promoting optimal CAR T-cell pharmacokinetics and function

Methods: This Phase 1, open-label trial enrolls young adult (15-30 yr) patients with relapsed/refractory OS. The study examines the safety and feasibility of administering a fixed dose of autologous peripheral blood-derived CD4 and CD8 T cells that have been genetically modified using a third generation self-inactivating (SIN) lentiviral vector to express a FL-specific human scFv second generation (4-1BB: zeta) CAR and EGFRt tag, in combination with intra-subject dose escalation of UB-TT170. Using a 3+3 design, the primary objective is to identify a recommended dose escalation sequence for future clinical development.

Results: The trial opened in July 2022. As of June 2024, 10 subjects enrolled and 4 subjects received protocol therapy and are evaluable for safety assessment. CAR T-cell products have been successfully manufactured for all enrolled subjects (median %CD4 21.1%, range 3.5 - 55.4%; median %CD8 79.3%, range 56.1 – 96.4%). Two patients received dose regimen (DR) 1 (Table 1). Both demonstrated rapid CAR T-cell expansion (Figure 1) and experienced DLTs, including immune effector cell-associated hemophagocytic lymphohistiocytosis-like syndrome (IEC-HS). The trial was modified to de-escalate the CAR T-cell dose and UB-TT170 doses (DR-2), Table 2. Two subjects received in DR-2. No DLTs were observed despite robust UB-TT170-dependent expansion and engraftment of CAR T cells (Figure 1). Serial UB-TT170 administration at DR-2 (4-11 doses) has been associated with recurrent but controllable infusion-associated biological activity, including grade 1-3 cytokine-release syndrome (CRS), grade 1-2 IEC-HS, and grade 1-2 DIC.

Conclusion: Accrual is ongoing to allow further optimization of dose, schedule, and duration of therapy.