Alternative BCR/ABL splice variants in Philadelphia chromosome-positive leukemias result in novel tumor-specific fusion proteins that may represent potential targets for immunotherapy approaches.
Imatinib currently represents the standard treatment in the early chronic phase of chronic myelogenous leukemia (CML), thanks to the high percentage of cytogenetic complete remission achieved, but it is yet unclear to what extent it can eradicate leukemia. Therefore, different vaccination strategies have been suggested, mainly based on the exploitment of the junctional peptides spanning the fusion region of the Bcr/Abl proteins. To identify new potential immunologic targets, 63 Philadelphia chromosome-positive patients and 6 BCR/ABL-positive cell lines were tested in nested reverse transcriptase PCR to detect the presence of BCR/ABL transcripts arising from the alternative splicing of the main BCR/ABL transcripts. We could detect BCR/ABL transcripts with junctions between BCR exon 1, 13, or 14 and ABL exon 4 in approximately 80% of patients and 84% of cell lines, beside the main fusion transcripts. Translation products of these transcripts were characterized at their COOH terminus by a large amino acid portion derived from the out of frame (OOF) reading of ABL gene. These proteins were detected in BCR/ABL-positive cell lines by immunoprecipitation and immunohistochemistry. Finally, we determined whether OOF-specific CD8+ T cells could be found in the peripheral blood of CML patients and whether they could acquire effector function following in vitro sensitization with OOF-derived peptides predicted to bind to human leucocyte antigen (HLA)-A2 and HLA-A3 molecules. We detected the presence of OOF-specific CD8+ T cells in four of four patients studied, and in one case, these T cells exhibited specific cytotoxic activity against both peptide-pulsed targets and autologous primary CML cells.
Volpe
Gisella
G
Department of Clinical, University of Turin, Turin, Italy. gisella.volpe@unito.it
Cignetti
Alessandro
A
Panuzzo
Cristina
C
Kuka
Mirela
M
Vitaggio
Katiuscia
K
Brancaccio
Mara
M
Perrone
Giuseppe
G
Rinaldi
Monica
M
Prato
Giuseppina
G
Fava
Milena
M
Geuna
Massimo
M
Pautasso
Marisa
M
Casnici
Claudia
C
Signori
Emanuela
E
Tonon
Giancarlo
G
Tarone
Guido
G
Marelli
Ornella
O
Fazio
Vito M
VM
Saglio
Giuseppe
G
D000951:Antigens, Neoplasm / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D018984:Epitopes, T-Lymphocyte / Q000276:immunology; D005091:Exons; D016044:Fusion Proteins, bcr-abl / Q000235:genetics / Q000276:immunology*; D015789:HLA-A2 Antigen / Q000276:immunology; D006801:Humans; D007167:Immunotherapy / Q000379:methods*; D020014:K562 Cells; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000235:genetics / Q000276:immunology* / Q000628:therapy; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics / Q000276:immunology* / Q000628:therapy; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology
D000951:Antigens, Neoplasm; D018984:Epitopes, T-Lymphocyte; D015789:HLA-A2 Antigen; D020033:Protein Isoforms; D012333:RNA, Messenger; D016044:Fusion Proteins, bcr-abl