SS18-SSX fusion-derived peptide–Major Histocompatibility Complex (SS18-SSX pMHC)

The SS18-SSX fusion-derived peptide–Major Histocompatibility Complex (pMHC) is a highly specific neoantigen target found in synovial sarcoma, a rare soft tissue malignancy (Nielsen et al., 2002). This target arises from the t(X;18)(p11;q11) chromosomal translocation, which creates a unique fusion protein (SS18-SSX) that is not present in normal cells (Worley et al., 2001). Intracellular processing of this fusion protein generates a junctional peptide that is presented on the cell surface by MHC class I molecules, most commonly HLA-A*02:01 (Shiga et al., 2021). Because this peptide-MHC complex is entirely tumor-specific, it provides an ideal window for immunotherapy, particularly T-cell receptor (TCR) engineered T-cell therapies. These therapies involve engineering a patient's T cells to express a TCR that specifically recognizes the SS18-SSX neoantigen, leading to targeted destruction of the sarcoma cells (NCT04044768). Clinical trials are currently investigating the safety and efficacy of these TCR-T cells, as well as peptide-based vaccines designed to prime the immune system against the fusion breakpoint. Monitoring for HLA expression and the presence of the specific SS18-SSX fusion transcript is essential for patient selection in these precision medicine approaches.

Other names

SS18-SSX neoantigenSynovial sarcoma fusion peptide-HLA complexSS18-SSX breakpoint peptide-MHCSYT-SSX fusion peptide-MHC

T-cell receptor (TCR) mediated recognition of the fusion-derived neoantigen peptide presented by MHC molecules, leading to cytotoxic T-cell activation and tumor cell apoptosis.