PAX3-FOXO1 fusion-derived peptide–MHC complex (PAX3-FOXO1 pMHC)

The PAX3-FOXO1 fusion-derived peptide–MHC complex is a highly specific tumor neoantigen found in alveolar rhabdomyosarcoma (ARMS) (Sorensen et al., 2002, Journal of Clinical Oncology). It arises from the chromosomal translocation t(2;13)(q35;q14), which creates a unique amino acid sequence at the junction of the PAX3 and FOXO1 proteins. This junctional peptide is processed by the proteasome and presented on the cell surface by Major Histocompatibility Complex (MHC) class I molecules, most commonly HLA-A*02:01 (Gattenloehner et al., 2003, Cancer Research). Because this specific peptide sequence does not exist in normal tissues, the complex serves as an ideal target for immunotherapy, offering high tumor specificity. Current therapeutic approaches focus on developing T-cell receptor (TCR) engineered T-cells and peptide vaccines that can recognize this complex and trigger a cytotoxic immune response (NCI, ClinicalTrials.gov). Targeting this pMHC complex allows for the selective destruction of ARMS cells while sparing healthy cells that lack the fusion protein. However, the effectiveness of these therapies can be limited by low antigen density on the tumor surface or the loss of HLA expression by the cancer cells. Clinical research is ongoing to optimize TCR affinity and overcome the immunosuppressive microenvironment of pediatric soft tissue sarcomas.

Other names

PAX3-FKHR fusion peptide-HLA complexPAX3-FOXO1 neoantigent(2;13) breakpoint peptide-MHCPAX3-FOXO1 junctional peptide-MHC

T-cell receptor (TCR) mediated recognition of the fusion-specific neoepitope presented by MHC, leading to cytotoxic T-lymphocyte activation and selective lysis of translocation-positive tumor cells.