Abstract 3721: Anti-tumor function and long-term persistence of KSQ-001EX, a SOCS1-edited eTIL® therapy, independent of IL-2 co-administration

Abstract Tumor Infiltrating Lymphocyte (TIL) therapy is an autologous adoptive cell therapy for cancer involving the isolation, ex vivo expansion, and infusion of polyclonal T cells from a patient’s own tumor. Seeking to improve clinical efficacy and durability of TIL therapy, we developed KSQ-001EX, a CRISPR/Cas9 engineered TIL (eTIL®) therapy with inactivation of the SOCS1 gene to enhance T cell persistence and anti-tumor functionality. KSQ-001EX is being investigated in a phase 1/2 clinical study (NCT06237881) in patients with advanced solid tumors. Metastatic melanoma patients received lymphodepleting chemotherapy followed by KSQ-001EX without IL-2 in Cohort 1 (n=4) or with high-dose IL-2 in Cohort 2 (n=8), at a dose range of 0.5-10e9 cells (median 5.25e9). KSQ-001EX was directly monitored in blood and tissue samples via indel tracking of the SOCS1 gene locus. Correlative analyses were performed by integrating patient baseline characteristics, drug product (DP) manufacturing data, multi-modal and single-cell characterization of tumor starting material, KSQ-001EX DP, post-infusion PBMCs and on-treatment tumor tissue biopsies. All 12 KSQ-001EX DPs were enriched in CD8+ T cells, exhibiting a “Young TIL” phenotype with a median of 39% CD27+ cells and low expression of exhaustion markers. All DPs showed strong polyfunctionality and cytotoxicity against redirected lysis targetcell lines. Infused cell dose, particularly absolute dose of CD27+ KSQ-001EX cells, predicted post-infusion engraftment, expansion, persistence, and infiltration of KSQ-001EX in tumor tissue at day 28, and was the strongest factor associated with clinical activity. Clonal tracking of T cells in post-infusion blood revealed similar expansion of KSQ-001EX clones before day 9 and after day 21 across most patients and between cohorts, with top infiltrating clones in tumor correlating with clonal expansion in blood at day 28. To further understand the contribution of IL-2 to KSQ-001EX engraftment, persistence and function, cytokines and phenotypic characteristics of peripheral blood CD8+ T cells post-infusion were compared between Cohort 1 and Cohort 2. While no differences were observed in the frequency or activation state of CD8+ T cells between Cohorts, elevated expression of TOX in CD8+ T cells and increased frequencies of Treg were observed in Cohort 2 (with IL-2) between day 9-28 post infusion. In conclusion, higher infused CD27+ KSQ-001EX dose is associated with favorable expansion kinetics and persistence. KSQ-001EX engraftment, function and long-term persistence in absence of IL-2 at lower doses than traditionally used with unmodified TIL suggest the beneficial effects of SOCS1 inactivation. Based on these collective data, we confirm the functional enhancement introduced by SOCS1 deletion. Further investigation of eTIL in the absence of IL-2 and higher DP doses is warranted. Citation Format: Dipen Sangurdekar, Erica Tobin, Karrie Wong, Ashish Yeri, Alex Smashnov, Kelly Bowen, Giorgio Sarkis, Violetta Medik, Hsinyi Lu, Sevinj Isgandarova, Michelle Carrasco, Patricia Harris, Cara L. Haymaker, Micah Benson, Anna Truppel-Hartmann, Rodabe N. Amaria. Anti-tumor function and long-term persistence of KSQ-001EX, a SOCS1-edited eTIL® therapy, independent of IL-2 co-administration [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3721.