Abstract 638: Lenalidomide treatment enhances the anti-tumor activities of XBP1 specific cytotoxic T lymphocytes by increasing the frequency and tumor-specific response of central memory CD3+CD8+ T cells

Introduction: Lenalidomide is an agent with immunomodulatory properties with demonstrated direct effects on the immune system and tumor microenvironment. The unfolded protein response (UPR) is a primary cellular adaptive mechanism that allows tumor cell survival under endoplasmic reticulum stress conditions by increasing its protein folding capacity. Thus, targeting the UPR is a rational approach for selective cancer cell killing. Here, we provide the basis for a novel immunotherapeutic approach by combining the antigen specific CTL against XBP1, an important transcriptional activator of the UPR, in combination with Lenalidomide, to boost the immune targeting against a variety of solid tumor cancer cells that over-express XBP1. Methods: XBP1 peptides-specific CTL (XBP1-CTL) were generated ex vivo from HLA-A2+ normal donors’ CD3+ T cells by repeated stimulation using a cocktail of heteroclitic XBP1 unspliced (US)184-192 (YISPWILAV) and XBP1 spliced (SP)367-375 (YLFPQLISV) peptides. XBP1-CTL were then incubated with or without Lenalidomide (5 µm), and evaluated for their immune responses and anti-tumor activities against breast, colon or pancreatic cancer cells. In addition, we characterized the XBP1-CTL, following lenalidamide treatment, for their enhanced expression of key T cell markers and transcriptional regulators, which are critical for immune function of effector and memory T cells. Results: An increased number of CD45RO+ memory CD3+CD8+ T cells, but not CD45RO- non-memory CD3+CD8+ T cells nor total CD3+CD8+ T cells, was observed within XBP1-CTL by Lenalidomide treatment. The combination of XBP1-CTL with Lenalidomide consistently enhanced the frequency and anti-tumor activity of the central memory CTL subset (CM: CD45RO+CCR7+/CD3+CD8+ T cells) as compared to the effector memory CTL subset (EM: CD45RO+CCR7-/CD3+CD8). In addition, Lenalidomide increased the expression of critical T cell surface markers including CD28, CD38, CD40L, CD69 and 41BB, but not ICOS nor TCRαβ. Lenalidomide treatment also enhanced anti-tumor activities of XBP1-CTL by increasing the frequencies of T-bet+/IFN-γ+, Eomes+/IFN-γ+, and Akt+ CD3+CD8+ T cells within both CM and EM subsets in response to HLA-A2+ breast (MB231), colon (LS180) or pancreatic (Panc1) cancer cell lines. Finally, the memory CD3+CD8+ T cells of XBP1-CTL displayed increased cytotoxicity (Granzyme B+) and IFN-γ production against the respective solid tumor cells when the XBP1-CTL were treated with Lenalidomide. Conclusions: This study provides the framework for using heteroclitic XBP1 US184-192 and XBP1 SP367-375 peptides as a vaccine to generate XBP1-CTL targeting a variety of solid tumors. Finally, it provides support for combination of the XBP1-based peptides vaccine with immunomodularoty drug Lenalidomide to improve patient outcome. Citation Format: Jooeun Bae, Rao Prabhala, Ruben Carrasco, Paul Richardson, Glen Dranoff, Kenneth C. Anderson, Nikhil C. Munshi. Lenalidomide treatment enhances the anti-tumor activities of XBP1 specific cytotoxic T lymphocytes by increasing the frequency and tumor-specific response of central memory CD3+CD8+ T cells. [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 638. doi:10.1158/1538-7445.AM2014-638