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Novel heteroclitic XBP1 peptides evoking antigen-specific cytotoxic T lymphocytes targeting various solid tumors.
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Background: Activation of the unfolded protein response (UPR) allows for tumor cells to survive prolonged endoplasmic reticulum stress and hypoxic conditions. XBP1 is an upstream element and a critical transcriptional activator of the UPR, and its up-regulation in a variety of human solid tumor cancers makes it as a promising immunotherapeutic target. The purpose of these studies was to evaluate immunogenic HLA-A2 XBP1-specific peptides for their ability to elicit cytotoxic T lymphocytes (CTL) against a variety of solid tumor cell lines. Methods: Upon the validation of XBP1 peptides for their strong HLA-A2 bindings and stabilities, peptide-specific CTL were generated ex vivo by repeated stimulation of CD3+ T lymphocytes obtained from HLA-A2+normal donors with XBP1 peptides-pulsed antigen-presenting cells, either dendritic cells or T2 cells. Results: A cocktail of heteroclitic XBP1 US184-192 (YISPWILAV) and heteroclitic XBP1 SP367-375 (YLFPQLISV) peptides with significantly improved HLA-A2 affinity and stability from their native counterparts were used to evoke XBP1 antigen-specific CTL. The CTL were predominantly CD3+CD8+ T cells (>80%) containing a high percentage of Effector Memory (EM; CCR7-CD45RO+) cells, which were distinctively evoked by repeated stimulation with the XBP1 peptides. In addition, the XBP1-CTL displayed a high level of cellular activation (CD69+/CD3+CD8+). The XBP1-CTL demonstrated effective anti-tumor responses including cell proliferation and IFN-g production, as well as degranulation (cytotoxic activity) against HLA-A2+breast cancer (MB231, MCF7), colon cancer (LS180, SW480) and pancreatic cancer (8902, Panc1, PL45) cell lines, which over-express both unspliced and spliced XBP1 antigens. Importantly, the specific anti-tumor activities were detected primarily in the EM CTL subset. Conclusions: These results suggest the immunotherapeutic potential of a cocktail of heteroclitic XBP1 US184-192 and XBP1 SP367-375 peptides to elicit effective anti-tumor responses against various solid tumors, and provide the framework for clinical development of vaccine trials to improve patient outcome.
Abstracts by J. Bae:
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