Abstract 3485: T cell receptor (TCR)-Based cellular therapy for Fibrolamellar HCC

Abstract Background: Fibrolamellar carcinoma (FLC) is a rare and often lethal liver cancer that primarily affects children and young adults without cirrhosis. There is no standard systemic treatment for FLC and the median survival for patients with advanced, unresectable FLC is approximately 12 months. The FLC transcriptome is characterized by an in-frame fusion of exon 1 of DNAJB1 with exons 2-10 of PRKACA, the catalytic subunit of protein kinase A (PKA), leading to expression of a chimeric protein, DNAJ-PKAc that has thus far been “undruggable” due to unacceptable on-target toxicity. Our overall goal is to target this “undruggable” oncogenic driver using T Cell Receptor (TCR)-Based cellular therapy. Methods: We are performing a clinical trial of a peptide-based therapeutic vaccine targeting DNAJ-PKAc, in combination with the immune checkpoint inhibitors nivolumab and ipilimumab. We analyzed PBMCs from a subset of patients who demonstrated a clinical response to this immune-based combination therapy to identify TCRs with specificity for DNAJ-PKAc. Results: To identify fusion specific T cell receptors (TCRs) generated in response to the vaccine patient peripheral lymphocytes were expanded and 10x single cell transcriptomic with paired TCR sequencing was performed. Candidate TCRs were reconstructed and expressed in T cells prior to co-culturing with HLA matched antigen presenting cells that were pulsed with DNAJ-PKAc peptides to verify fusion specificity via flow cytometry for T cell activation. We reconstructed and verified fusion specificity for multiple TCRs from several patients, and characterized them functionally by HLA specificity, affinity, and killing capacity in vitro. We identified TCRs recognizing DNAJ-PKAc-derived peptides in the context of class II HLAs, including HLA-DRB1*13:01 and HLA-DRB3*01. The TCRs that were identified recognize distinct DNAJ-PKAc-derived epitopes, with variable HLA specificity, TCR affinity, and cytokine response profiles after DNAJ-PKAc antigen stimulation. In general, TCRs with specificity for DNAJ-PKAc presented in the context of HLA-DRB1*13:01 were higher affinity than those recognizing HLA-DRB3*01, even when obtained from the same original patient. Conclusion: This work identifies and characterizes multiple TCRs with specificity for DNAJ-PKAc. Our data provides evidence that the therapeutic efficacy of a peptide-based therapeutic vaccine may be mediated by a CD4 T cell response, and provides potential candidates for off-the-shelf TCR therapy for FLC. Citation Format: Kayla J. Bendinelli, Allison M. Kirk, Paul G. Thomas, Mark Yarchoan T cell receptor (TCR)-Based cellular therapy for Fibrolamellar HCC [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 3485.