Abstract 1559: A new immunotherapy for pancreatic cancer stem cells by tumor lysate vaccine, expressing α-gal epitopes

Abstract

Abstract Pancreatic cancer (PC) cells, expressing the markers CD44, CD24, and epithelial-specific antigen (ESA) were identified as PC stem cells (CSCs). Treatments targeting the CSCs may be more effective in resulting in PC cure, but traditional treatments, including chemo/radiation therapy can easily miss CSCs, because they are highly resistant to these therapies. Human natural Ab, anti-Gal is an IgG known to be present in large amounts in normal subjects and cancer patients, comprising ∼1% of serum circulating IgG. Anti-Gal specifically interacts with α-gal epitopes (Galα1, 3Galα1, 4GlcNAc-R), synthesized by α1, 3 galactosyltransferase (≥1,3GT) on cell surface glycolipids and glycoproteins. We hypothesized that biosynthesis of α-gal epitopes on the carbohydrate of CSC markers, including CD44, CD24 could effectively induce Ab production against CSCs and immune-mediate eradication of PC CSCs. To address this strategy, a human PC cell line, PANC1, which expresses MUC1 was employed and transfected with α1,3GT gene (α-gal PANC1). To generate tumor lysate, 2 X 106 of either parental or α-gal PANC1 were injected S.C. into NOD/SCID mice, and the grown tumors were enucleated and homogenized. 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 intraperitoneally (ip) by 10mg of either parental (parental group) or α-gal PANC1 tumor lysate (α-gal group). We isolated PANC1 cells with CD44+CD24+ phenotype by magnetic beads and assessed Ab production toward both CSCs (binding PANC1 with beads) and differentiated cancer cells (unbinding PANC1 with beads). In FACS analysis, a marked Ab production against both CSCs and differentiated cancer cells were observed in α-gal group. To demonstrate in vivo tumor destruction, an animal model was performed. Splenocytes from vaccinated KO mice were prepared, then these cells were transferred ip (30X106 cells/ip X 3 times) into NOD/SCID mice. Transferred mice were challenged with S.C. injection with either 1 X 107 of live PANC1 or 5 X 106 of CD44+CD24+ PANC1. PANC1 tumors in mice transferred from parental group reached the size of 150 mm2 at 45 days after injection. For tumors in mice transferred from α-gal group, regrowth of tumor was completely prevented. Survival of α-gal transferred mice was significantly prolonged [α-gal vs. parental: 82.5±21.9 vs. 48.0±6.7 days, p<0.0001]. CSC tumors in mice transferred from parental group reached the size of 100 mm2 at 49 days after injection. For CSC tumors in mice from α-gal group, no tumor formation was observed. Survival was significantly prolonged [α-gal vs. parental: 85.0±20.8 vs. 49.3±14.3 days, p=0.0002]. We conclude that immunotherapy with tumor lysate vaccine, expressing α-gal epitopes effectively targets both differentiated and PC CSCs and may provide PC cure by destruction of micro-metastasis and minimal residual cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1559. doi:1538-7445.AM2012-1559