Abstract 2894: Novel heteroclitic XBP1 peptides induce antigen-specific memory CD3+CD8+ T cells expressing critical T cell markers and transcription regulators
Authors: Bae Jooeun , Prabhala Rao , Carrasco Ruben , Lee Ann-Hwee , Kimmelman Alec , Anderson Kenneth C. , Munshi Nikhil 
Published: May 2015

Background: XBP1 is a critical transcriptional activator of the unfolded protein response that enables tumors to survive prolonged endoplasmic reticulum stress due to nutrient deprivation, hypoxia or accumulation of unfolded/misfolded proteins. This provided us a rational to evaluate XBP1 as an antigen to develop a potential vaccine based immunotherapy against different types of solid tumors.

Methods: XBP1 gene expression was investigated in a variety of primary tumor cells by searching the canEvlove and Oncomine databases and examined its differential expression level from normal cells. A cocktail of heteroclitic XBP1 unspliced (US)184-192 (YISPWILAV) and heteroclitic XBP1 spliced (SP)367-375 (YLFPQLISV) peptides were used to evoke XBP1 specific cytotoxic T Lymphocytes (XBP1-CTL) ex vivo to target breast, colon, and pancreatic cancer cells. XBP1-CTL were also evaluated for critical T cell markers, transcription regulators, and generation of specific memory CTL subsets.

Results: Significantly higher XBP1 gene expression was detected in primary tumor cells from breast and colon cancer patients compared to the corresponding normal cells from healthy donors. Using a cocktail of immunogenic heteroclitic XBP1 US and SP peptides with improved HLA-A2 binding/stability as compared to their native counterparts, we induced XBP1-specific CTL from normal HLA-A2+ individuals' CD3+ T cells. The XBP1-CTL displayed an increased frequency of CD3+CD8+ T cells with enhanced expression (% positive cells, mean fluorescence intensity) of surface T cell markers including CD38, CD40L, CD69, 41BB (CD137), ICOS (CD278) and TCRαβ. In addition, the XBP1-CTL were enriched for central memory (CM: CD45RO+CCR7+) and effector memory (EM: CD45RO+CCR7-) CD3+CD8+ T cells as compared to baseline (unstimulated) CD3+CD8+ T cells. Functionally, the memory (CD45RO+) XBP1-CTL subsets showed increased levels of cellular proliferation, IFN-γ production, IL-2 production, and CD107a degranulation in response to HLA-A2+ breast (MB231), colon cancer (LS180) or pancreatic cancer (Panc1) cell lines. Finally, memory (CD45RO+) subset of XBP1-CTL expressed higher levels of Tbet and Eomes transcription regulators as compared to non-memory (CD45RO-) XBP1-CTL, with the highest frequencies of IFN-γ producing Tbet+, Eomes+ or Granzyme B+ cells in the CM subset.

Conclusions: These results provide the rational for an immunotherapeutic vaccine comprised of a cocktail of heteroclitic XBP1 US184-192 and XBP1 SP367-375 HLA-A2 peptides to induce XBP1-CTL expressing critical T cell markers and transcription regulators as well as distinct memory CTL subsets with specific anti-tumor activities against breast, colon and pancreatic cancers.

Citation Format: Jooeun Bae, Rao Prabhala, Ruben Carrasco, Ann-Hwee Lee, Alec Kimmelman, Kenneth C. Anderson, Nikhil Munshi. Novel heteroclitic XBP1 peptides induce antigen-specific memory CD3+CD8+ T cells expressing critical T cell markers and transcription regulators. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2894. doi:10.1158/1538-7445.AM2014-2894