Cardiolipin Induces CXCL9/CXCL10 Expression in Tumor-Infiltrating Lymphocytes

Background: Cardiolipin (CL) is a phospholipid composed of a glycerol linked with two phosphatidate moieties that constitutes an integral part of the human inner mitochondrial membrane under physiological conditions. It is also vital for bacterial membrane transport and key bacterial functions associated with cell division and infection. CL is released in the cytosol or into the extracellular milieu upon cell death and during inflammation. We therefore tested the ability of CL to activate and expand tumor infiltrating lymphocytes (TIL) from patients with epithelial cancer. Methods: TIL were isolated from gastrointestinal tumor tissues and expanded in vitro in the presence of CL. The role of the NLRP3 inflammasome was evaluated using the specific inhibitor MCC950 and siRNA-mediated silencing of NLRP3. Phenotypic changes and T-cell potency were assessed via CXCL9/10 expression levels. To characterize the immune repertoire, deep TCR sequencing was performed to compare the TCR Vα and Vβ CDR3 regions between TIL and the corresponding tumor tissue. Recognition of autologous tumor cells and tumor-specific mutations, including mutations in KRAS and mitochondrial UQCRFS1 (D145V), was assessed using MHC class I and II restriction assays. Results: CL-expanded TIL exhibited increased CXCL9/10 expression, which is associated with increased potency of tissue invasion. CL-TIL exhibited broader recognition of frequently occurring KRAS mutations, and this effect could be blocked with an inhibitor (MCC950) of the NLRP3 pathway, a multiprotein inflammatory complex associated with danger signaling. TIL exhibited an enriched TCR Vα and Vβ CDR3 repertoire compared to tumor tissue, as defined by deep TCR sequencing. TCR αβ+ TIL recognized autologous tumor tissue in an MHC class I- and class II-restricted fashion, including the mutant HLA-DP-restricted mitochondrial protein associated with the electron respiratory chain complex III (UQCRFS1 D145V) presented by autologous tumor cells. Conclusions: CL activates the NLRP3 inflammasome pathway in TIL from patients with GI cancer and increases CXCL9/CXCL10 expression in TIL, resulting in enhanced recognition of mutant cancer-associated target epitopes, including a mitochondrial protein. CL may provide a danger signal: that facilitates TIL expansion via CL-activated pathways.