Synthetic peptide analogs derived from bcr/abl fusion proteins and the induction of heteroclitic human T-cell responses.
OBJECTIVE
Chronic myelogenous leukemia (CML) presents a unique opportunity to develop therapeutic strategies using vaccination against a truly tumor-specific antigen that is also the oncogenic protein required for neoplasia. We have shown in phase I and II trials that a tumor-specific, bcr-abl-derived peptide vaccine can be safely administered to patients with chronic phase CML and can elicit a reliable specific CD4 immune response. However, variable CD8 responses and no HLA A0201-restricted responses were found. One strategy to circumvent this poor immunogenicity is to design synthetic immunogenic analog peptides that cross-react with the native peptides (a heteroclitic response). The aim of this study was to design such peptides.


METHODS
By using computer prediction analysis. We designed a number of synthetic peptides derived from the junctional sequences of CML (p210/b3a2 or p210/b2a2) in which single and double amino acid substitutions were introduced at key HLA A0201 binding positions. The binding of these peptides was tested by a thermostabilization assay using a T2 cell line.


RESULTS
We found three peptides that predicted good binding to HLA A0201 molecules and stabilized MHC class I A0201 molecules on the surface of T2 cell lines. These peptides were screened for eliciting HLA restricted, peptide-specific cytotoxic T lymphocyte responses using CD3+ T cells from several A0201 donors and CML patients. The CD8+ cytotoxic T lymphocytes lines were assessed by either interferon-g ELISPOT or a chromium release assay using pulsed, HLA-matched leukemic cell lines. The analog peptides generated larger immune responses (increased CD8 T-cell precursor frequency) than did the native peptides. Importantly, CD8+ T cells stimulated with the new synthetic peptides cross-reacted with the native bcr-abl peptides.


CONCLUSIONS
In conclusion, analog CML fusion peptides with increased immunogenicity and heteroclitic properties can be synthesized and may be useful in vaccination strategies.
Pinilla-Ibarz
Javier
J
Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, NY 10021, USA.
Korontsvit
Tatyana
T
Zakhaleva
Victoriya
V
Roberts
Wendy
W
Scheinberg
David A
DA
D045744:Cell Line, Tumor; D020650:Combinatorial Chemistry Techniques / Q000379:methods; D016044:Fusion Proteins, bcr-abl / Q000737:chemistry* / Q000502:physiology*; D015234:HLA-A Antigens / Q000276:immunology / Q000378:metabolism; D006801:Humans; D010446:Peptide Fragments / Q000138:chemical synthesis* / Q000276:immunology* / Q000378:metabolism; D011485:Protein Binding / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism
D015234:HLA-A Antigens; D010446:Peptide Fragments; D016044:Fusion Proteins, bcr-abl