Identification and epitope enhancement of a PAX-FKHR fusion protein breakpoint epitope in alveolar rhabdomyosarcoma cells created by a tumorigenic chromosomal translocation inducing CTL capable of lysing human tumors

• Published in: Cancer research (Chicago, Ill.) Ill.), 2006-02, Vol.66 (3), p.1818-1823
• Main Authors: VAN DEN BROEKE, Leon T, PENDLETON, C. David, MACKALL, Crystal, HELMAN, Lee J, BERZOFSKY, Jay A
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Antineoplastic agents; Biological and medical sciences; Cell Line, Tumor; Chromosome aberrations; Dendritic Cells - immunology; Diseases of the osteoarticular system; Epitopes - genetics; Epitopes - immunology; Forkhead Transcription Factors - genetics; Forkhead Transcription Factors - immunology; HLA-B7 Antigen - blood; HLA-B7 Antigen - immunology; Humans; Immunotherapy, Adoptive - methods; Medical genetics; Medical sciences; Molecular Sequence Data; Oncogene Proteins, Fusion - genetics; Oncogene Proteins, Fusion - immunology; Paired Box Transcription Factors - genetics; Paired Box Transcription Factors - immunology; Pharmacology. Drug treatments; Rhabdomyosarcoma, Alveolar - genetics; Rhabdomyosarcoma, Alveolar - immunology; Rhabdomyosarcoma, Alveolar - therapy; T-Lymphocytes, Cytotoxic - immunology; Translocation, Genetic - immunology; Tumors; Tumors of striated muscle and skeleton
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/0008-5472.CAN-05-2549

Fusion proteins created by chromosomal translocations in tumors can create neoantigenic determinants at the breakpoint, which are unique to the tumor cells but shared by the vast majority of tumors of that histologic type. If the fusion protein is responsible for the malignant transformation, its expression cannot be lost by the tumor to escape immune responses against this tumor antigen. Here, we identify such a fusion protein breakpoint epitope in the PAX-FKHR fusion protein created by the t(2;13) translocation present in 80% of cases of alveolar rhabdomyosarcoma, a highly aggressive pediatric soft-tissue sarcoma. We use autologous dendritic cells pulsed with the RS10 breakpoint fusion peptide to raise a human CTL line from a normal healthy HLA-B7+ blood donor specific for this peptide. These CTLs are CD8+ (CD4-CD56-) and restricted by HLA-B7. These human peptide-specific CTL lyse human HLA-B7+ rhabdomyosarcoma tumor cells. Therefore, the fusion protein is endogenously processed to produce this natural epitope presented by HLA-B7 and thus this peptide is a bone fide human tumor antigen. We also define a substitution that increases the affinity for HLA-B7 without loss of antigenicity. This epitope-enhanced peptide may serve as a candidate cancer vaccine for HLA-B7+ patients with alveolar rhabdomyosarcoma.