Synovial sarcoma X breakpoint 2 peptide–Major histocompatibility complex class I (SSX2-MHC I)

The SSX2 peptide–MHC class I complex is a molecular assembly consisting of an immunodominant peptide fragment derived from the Synovial Sarcoma X Breakpoint 2 (SSX2) protein, typically the SSX2 41-49 epitope (KASEKIFYV), bound within the groove of a Major Histocompatibility Complex (MHC) class I molecule, most frequently HLA-A*02:01 (UniProt P35222; PMID: 11062070). SSX2 is a member of the cancer-testis antigen (CTA) family, which is characterized by restricted expression in the immune-privileged testis and thyroid of healthy adults, but frequent overexpression in various malignancies such as synovial sarcoma and melanoma (PMID: 15150595). This restricted expression pattern makes the SSX2-MHC I complex a highly specific target for cancer immunotherapy, as the complex is presented on the surface of tumor cells but not on most normal somatic cells. Therapeutic interventions targeting this complex include T-cell receptor (TCR) engineered T-cell therapies, such as letetresgene autoleucel (Lete-cel), and multi-antigen vaccines designed to stimulate endogenous CD8+ T-cell responses (ClinicalTrials.gov NCT03391778). Clinical efficacy is dependent on both the patient's HLA haplotype and the quantitative expression of the SSX2 antigen within the tumor microenvironment.

Other names

SSX2-HLA-A*02:01 complexSSX2 peptide-HLA complexSSX2(41-49)-HLA-A2 complexSynovial sarcoma X breakpoint 2-MHC class I complex

T-cell receptor (TCR) binding to the peptide-MHC complex, triggering CD8+ T-cell activation, cytokine release, and targeted lysis of SSX2-expressing tumor cells.