SS18-SSX fusion protein-derived neoantigen (SS18-SSX neoantigen)

The SS18-SSX fusion protein-derived neoantigen is a highly specific tumor marker resulting from the hallmark chromosomal translocation t(X;18)(p11;q11) found in nearly all cases of synovial sarcoma (Nielsen et al., 2002, Lancet Oncology). This translocation fuses the SS18 gene with SSX1, SSX2, or SSX4, creating a unique amino acid sequence at the fusion junction that does not exist in normal human tissues. When these fusion proteins are processed by the proteasome, the resulting junctional peptides can be presented on the cell surface by Major Histocompatibility Complex (MHC) class I molecules, such as HLA-A*02:01 or HLA-A*24:02 (Kawaguchi et al., 2012, Cancer Science). These peptide-MHC complexes serve as neoantigens that can be recognized by the cellular immune system, specifically by T-cell receptors (TCRs). Therapeutic approaches currently under investigation include peptide vaccines and adoptive cell therapies using TCR-engineered T-cells designed to recognize the SS18-SSX breakpoint sequence (Pollack et al., 2020, JCO). Because the target is entirely tumor-specific, these therapies offer the potential for high efficacy with minimal off-target toxicity to healthy tissues.

Other names

SYT-SSX fusion protein neoantigenSS18-SSX1 neoantigenSS18-SSX2 neoantigenSynovial sarcoma fusion peptideSS18-SSX breakpoint peptide

The SS18-SSX fusion protein-derived neoantigen acts as a target for immunotherapy through its presentation as a peptide on Major Histocompatibility Complex (MHC) molecules. Therapeutic agents, such as TCR-engineered T-cells or peptide vaccines, are designed to recognize the unique amino acid sequence at the fusion breakpoint of the SS18 and SSX proteins. Upon recognition of this peptide-MHC complex, cytotoxic T-lymphocytes are activated to release perforins and granzymes, leading to the selective apoptosis of synovial sarcoma cells (Kawaguchi et al., 2012; Pollack et al., 2020).