Abstract 2710: Combination CXCR4 and PD-1 blockade increases T cell infiltration and effector function in fibrolamellar carcinoma (FLC)

Abstract Introduction: Fibrolamellar carcinoma (FLC), a rare liver cancer affecting young patients without cirrhosis, has a poor prognosis and few systemic therapy options. Current evidence implicates an immunosuppressive tumor microenvironment (TME), including our preliminary data suggesting preferential localization of T cells in stromal bands. We hypothesized that dual blockade of C-X-C chemokine receptor type 4 (CXCR4) and programmed cell death protein (PD-1) would enhance T cell infiltration and activation, respectively, and thereby increase tumor killing. Methods: Flow cytometry and single-nuclear RNA sequencing (snRNA-seq) were used to analyze immune cells and evaluate gene expression, respectively, in patient-derived FLC and non-tumor liver (NTL). Immunohistochemistry (IHC) was used to assess CD3+ T cell localization in relation to CXCL12, the chemokine ligand of CXCR4. Tumor slice cultures (TSCs) from fresh FLC resection specimens (n=11) were treated with control (IgG1), a small molecule CXCR4 inhibitor (AMD3100), anti-PD-1 blocking antibody (αPD-1), or combination CXCR4 and PD-1 blockade (AMD3100/αPD-1). IHC, RNA expression (Nanostring), and live microscopy were used to evaluate T cell mobilization and function. Results: Flow cytometry analysis demonstrated fewer CD45+ cells (16% vs 54% of live cells, p=0. 01) and heterogenous PD-1 expression on T cells in FLC compared with NTL. SnRNA-seq analysis showed that CXCR4 expression is upregulated in FLC lymphocyte and macrophage populations relative to NTL (15% vs 10% and 20% vs 5% expressed), and CXCL12 is expressed primarily in stellate cells. CD3+ T cells colocalized with CXCL12 in the FLC stroma on IHC. Multiplex IHC of treated TSCs revealed more T cells in the carcinoma (CK7+) than the stromal (SMA+) compartment after AMD3100 compared with IgG1 (63% vs 34% T cells in CK7+ compartment, p=0. 05). Nanostring indicated upregulation of effector pathways (apoptosis, cytotoxicity, lymphocyte activation) after AMD3100/αPD-1 compared with IgG1. Time-lapse live microscopy revealed a greater percentage of apoptotic carcinoma cells (SR-FLICA+CK7+) colocalized with CD3+ T cells (37% vs 18%, p=0. 005) and longer CD3+ T cell track length (27 vs 22 μm, p=0. 03) after AMD3100/αPD-1 than before treatment. Cleaved caspase-3 (CC3) IHC demonstrated significantly increased tumor apoptosis after AMD3100/αPD-1 compared with IgG1 and monotherapy (53% vs 32% (IgG1), 39% (AMD3100), and 42% (αPD-1) CC3+ cells, p=0. 002, p=0. 03, p=0. 04). Conclusion: The CXCR4/CXCL12 axis mediates T cell exclusion in the FLC TME. Combination CXCR4 and PD-1 blockade overcomes immunosuppression in FLC by mobilizing T cells into the carcinoma compartment and activating their effector function, with resultant tumor apoptosis. These findings support consideration of clinical trials testing drugs targeting CXCR4 and PD-1 in FLC. Citation Format: Lindsay K. Dickerson, Renske van den Bijgaart, Xiuyun Jiang, Sara K. Daniel, Jason A. Carter, Alaa Farghli, Kevin M. Sullivan, Yongjun Liu, Heidi L. Kenerson, Raymond S. Yeung, Teresa S. Kim, Ian N. Crispe, Praveen Sethupathy, Kevin C. Barry, Venu G. Pillarisetty. Combination CXCR4 and PD-1 blockade increases T cell infiltration and effector function in fibrolamellar carcinoma (FLC) abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2710.