Vaccination With Pancreatic Cancer Cells Expressing Alpha-Gal Epitopes Effectively Induced Immune Responses Against Not Only Differentiated Cancer Cells But Also Cancer Stem Cells

Abstract Cancer stem cells (CSCs) are generally dormant or slowly cycling tumor cells that have the ability to reconstitute tumors. It is necessary to develop an effective therapy for CSCs to eradicate cancer cells. But, they are thought to be involved in highly tumor resistance to chemo/radiation therapy and tumor relapse and progression. Recently, pancreatic cancer cells expressing the cell surface markers CD44, CD24, and epithelial-specific antigen (ESA) were identified as pancreatic CSCs. Human natural Ab, anti-Gal is an IgG known to be present in large amounts in normal subjects and patients with malignancies, comprising ∼1% of serum circulating IgG. Anti-Gal specifically interacts with α-gal epitopes (Galα1, 3Galβ1, 4GlcNAc-R), synthesized by α1, 3 galactosyltransferase (α1,3GT) on cell surface glycolipids and glycoproteins. We hypothesized that biosynthesis of α-gal epitopes on the carbohydrate of CSC markers, including CD44, CD24, expressed on pancreatic CSCs could effectively induce Ab production against these CSCs. To address this strategy, a human pancreatic cancer cell line, PANC1, which expresses MUC1 was employed and transfected with α1,3GT gene (α-gal PANC1). High anti-Gal α1,3GT KO mice, which displayed anti-Gal titers similar to those found in humans were generated by immunization of pig tissue. These mice were vaccinated with either 1 × 106 irradiated parental PANC1 (control group) or α-gal PANC1 (α-gal group). We investigated that α-gal PANC1 vaccination elicited both the production of anti-MUC1 Abs [number of anit-MUC1 spots at 1 × 106 splenocytes by ELISPOT: α-gal vs. control: 553.6 ± 66.7 vs. 319.5 ± 18.9 (p<0.0001)] and the expansion of systemic T-cell response to MUC1 [number of IFNγ spots at 1 × 106 splenocytes by ELISPOT: α-gal vs. control: 1237.5±283.1 vs. 211± 33.4 (p<0.0001)]. We confirmed that the subpopulation of pancreatic CSCs, which expressed CD44, CD24, and ESA in parental PANC1 cells. Flow cytometric quantification showed that 70.4 % of PANC1 cells were CD44+CD24+ and 82.4 % were CD44+ESA+. We isolated PANC1 cells with CD44+CD24+ phenotype by magnetic beads and assessed Ab production against both pancreatic CSCs (binding cells with beads) and differentiated cancer cells (nonbinding cells with beads). A strong Ab production against both CSCs and differentiated cancer cells was effectively elicited by α-gal PANC1 vaccination as judged by the mean fluorescence intensity (MFI) [MFI of pancreatic CSCs: α-gal vs. control: 181.9 vs. 10.3, MFI of differentiated cancer cells: α-gal vs. control: 261.2 vs. 11.5]. We conclude that the buildup of α-gal epitopes on carbohydrates of CSC markers to be internalized by APC, is a novel strategy for treatment of cancer cells, including differentiated/pancreatic CSCs and may cure pancreatic cancer by destruction of micro-metastasis and minimal residual disease. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 759. doi:10.1158/1538-7445.AM2011-759