Abstract 3198: TK-6302, a supercharged PRAME TCR-T cell therapy containing a high affinity TCR, an activating CD8 coreceptor (costimCD8 CoR) and a Fas-based switch receptor, drives sustained anti-tumor responses

Abstract Background: T cell receptor (TCR) T cell therapy targeting PRAME mediates durable responses in melanoma and sarcoma but has shown limited efficacy in other solid tumors. Suboptimal T cell engraftment and fitness and immune suppression by the tumor microenvironment (TME) are main causes of the limited efficacy. We have developed TK-6302, a PRAME targeted TCR-T cell therapy with best-in-class potential, manufactured with a non-viral gene editing process, and incorporating a high-affinity TCR, a chimeric CD8 co-receptor that engages CD4 T cells and provides co-stimulation upon TCR engagement (costim CD8 CoR), and a Fas switch receptor (SwR) that boosts fitness in the periphery and prevents apoptosis in the tumor. Methods: High-affinity PRAME TCRs were identified using T-knife’s MyTTM platform. Transcriptomic analysis of 4,622 stage III/IV tumors using TempusTM database identified consistent expression of FasL in cancer types with high PRAME prevalence. Supercharged PRAME TCR-T cells were generated using a non-viral gene editing process inserting all elements into the TRAC locus, and then compared to benchmark products based on dextramer binding, memory and activation/exhaustion phenotype by flow cytometry, cytokine secretion by LEGENDplexTM, and cytotoxicity upon chronic or repeated antigen stimulation using Incucyte. Results: Supercharged PRAME TCR-T cells incorporate three functional elements: (1) high-affinity TCR with EC50 4.73x10-10 M, (2) costimCD8 CoR, a single-chain CD8 CoR with TRAF-binding costimulatory motifs, and (3) Fas-CD40/OX40 (Fas-TNFR) SwR selected based on inhibitory ligand screening of PRAME expressing indications and designed to provide higher resistance to FasL-induced apoptosis compared to the commonly used Fas-4-1BB SwR. Supercharged PRAME TCR-T demonstrated higher in vitro anti-tumor activity compared to known PRAME TCR-T approaches, including clinical candidates, with a minimum of two additional rounds of serial killing and higher levels of pro-inflammatory cytokines against cancer cells with low PRAME expression. Supercharged PRAME TCR-T maintained early memory phenotype upon serial killing compared to benchmark approaches. When PRAME TCR-T products were tested in a multi-cellular model with TME resembling that of PRAME-expressing indications, Supercharged PRAME TCR-T cells were protected from inhibitory signals, as shown by elevated cell numbers and higher cytotoxicity and cytokine production, while benchmark PRAME TCR-T cells failed to control long term growth of cancer cells. Conclusions: Supercharged PRAME TCR-T therapy demonstrates best-in-class preclinical anti-tumor efficacy and T cell fitness compared to current clinical stage PRAME TCR-T approaches, providing the potential for deep and durable responses in hard-to-treat indications. Citation Format: Paul Najm, Kathrin Skibbe, Lia Walcher, Alvaro Haroun-Izquierdo, Laure Twyffels, Mikhail Steklov, Lorenz Knackstedt, Lucia Poncette, Marleen M. van Loenen, Elisa Kieback, Panagiota A. Sotiropoulou. TK-6302, a supercharged PRAME TCR-T cell therapy containing a high affinity TCR, an activating CD8 coreceptor (costimCD8 CoR) and a Fas-based switch receptor, drives sustained anti-tumor responses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3198.