Abstract 3420: Whole cell vaccines prevent primary tumor growth and metastases in murine embryonal rhabdomyosarcoma

Abstract

Abstract Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. Despite therapeutic advances, survival of patients with non-metastatic and metastatic rhabdomyosarcoma approximates 75% and 30% respectively. We developed a murine model of embryonal RMS (ERMS) on the C57BL/6 background as a first step toward developing immune based therapies for this disease. Tumor fragments from C57BL/6 HGF Tg+p53+/− mice that spontaneously developed ERMS were passaged in mice, and a highly metastatic ERMS cell line, M3-9-M, was generated by culturing tumor harvested from metastases. M3-9-M was later transfected with luciferase. Following IM injection of M3-9-M into the gastrocnemius, primary tumor growth was measured or the limb was amputated and metastatic disease was monitored using bioluminescent imaging. Vaccines were administered on days −14 and −7, and tumor was administered on day 0. Whole cell vaccines comprised 5×106 irradiated M3-9-M cells administered IP. The survivin vaccine comprised emulsified ATFKWNPFL peptide ± a hepatitis B viral core peptide (helper epitope) in IFA administered SQ. In some experiments, anti-CD25 moAb (PC61), anti-CD8 and/or anti-CD4 were used to deplete T cell subsets. Microarray analysis and immunohistochemistry demonstrate that M3-9-M expresses characteristic RMS markers. M3-9-M tumors reliably grow in immunocompetent C57BL/6 mice following inocula as low as 1×104 cells/mouse, and reach the maximum allowable diameter (2 cm) within 20 to 52 days depending on dose. Metastases (intra-abdominal and pulmonary) develop in essentially all mice, even with early amputation. Whole cell vaccination prevents primary tumor growth in 100% of mice given 1×104 M3-9-M cells and completely prevents metasases in amputated mice receiving 1×105 M3-9-M. Although mice receiving whole cell vaccine show no evidence for immunoreactivity to survivin, immunization with a survivin peptide delays primary tumor growth (time to amputation extended by 7.6 days), implicating survivin as a tumor antigen for RMS. Depletion of CD4 or CD8 T cells diminishes the effect of both vaccines, and depletion of both CD4 and CD8 T cells completely abrogates the effect of the vaccines, implicating T cell mediated adaptive immunity in the effects observed. Interestingly, treatment with anti-CD25 moAb to deplete Treg cells diminishes tumor growth (PC61 treatment vs. control tumor volume p=0.055 at day 35 post tumor challenge) in the absence of tumor vaccination. M3-9-M is a faithful model of human ERMS as evidenced by phenotype, genotype and metastatic behavior. This murine ERMS is immunogenic as evidenced by potent T cell mediated effects of whole cell tumor vaccines on primary and metastatic tumor growth. Survivin is a relevant tumor antigen tumor in this model, but other tumor antigens exist as well. Future studies are underway to molecularly define RMS tumor antigens using this model. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3420.