ABSTRACT
For immunotherapy of residual disease in patients with Philadelphia-positive leukemias, the BCR-ABL fusion regions are attractive disease-specific T-cell targets. We analyzed these regions for the prevalence of cytotoxic T lymphocyte (CTL) epitopes by an advanced reverse immunology procedure. Seventeen novel BCR-ABL fusion peptides were identified to bind efficiently to the human lymphocyte antigen (HLA)-A68, HLA-B51, HLA-B61 or HLA-Cw4 HLA class I molecules. Comprehensive enzymatic digestion analysis showed that 10 out of the 28 HLA class I binding fusion peptides were efficiently excised after their C-terminus by the proteasome, which is an essential requirement for efficient cell surface expression. Therefore, these peptides are prime vaccine candidates. The other peptides either completely lacked C-terminal liberation or were only inefficiently excised by the proteasome, rendering them inappropriate or less suitable for inclusion in a vaccine. CTL raised against the properly processed HLA-B61 epitope AEALQRPVA from the BCR-ABL e1a2 fusion region, expressed in acute lymphoblastic leukemia (ALL), specifically recognized ALL tumor cells, proving cell surface presentation of this epitope, its applicability for immunotherapy and underlining the accuracy of our epitope identification strategy. Our study provides a reliable basis for the selection of optimal peptides to be included in immunotherapeutic BCR-ABL vaccines against leukemia.
Subject(s)
CD8-Positive T-Lymphocytes/immunology , Cancer Vaccines/immunology , Epitopes, T-Lymphocyte/immunology , Fusion Proteins, bcr-abl/immunology , Leukemia, Myelogenous, Chronic, BCR-ABL Positive/immunology , Amino Acid Sequence , Cell Line, Tumor , Epitope Mapping/methods , Fusion Proteins, bcr-abl/genetics , Fusion Proteins, bcr-abl/metabolism , HLA-A Antigens/immunology , HLA-A Antigens/metabolism , HLA-A2 Antigen , HLA-B Antigens/immunology , HLA-B Antigens/metabolism , HLA-B51 Antigen , HLA-C Antigens/immunology , HLA-C Antigens/metabolism , Humans , Immunotherapy/methods , Leukemia, Myelogenous, Chronic, BCR-ABL Positive/therapy , Molecular Sequence Data , Peptide Fragments/genetics , Peptide Fragments/immunology , Peptide Fragments/metabolism , Protein Binding/immunologyABSTRACT
Nearly ten years of research on the feasibility of specific immunotherapy targeting the junctional regions of BCR-ABL has considerably increased our knowledge of which MHC alleles might present BCR-ABL peptides, yet has failed to provide us with definite proof of appropriate processing of the hybrid oncoprotein into such antigenic peptides. This paper intends to provide an overview of the current state of affairs as well as to delineate limitations and future directions of this line of research.
