Abstract 3420: Whole cell vaccines prevent primary tumor growth and metastases in murine embryonal rhabdomyosarcoma
Authors: Meadors Joanna L. , Cui Yongzhi , Poon Rita , Zhang Hua , Fewkes Natasha M. , Orentas Rimas J. , Merlino Glenn , Khan Javed , Chen Qing-Rong , Song Young K. , Mackall Crystal L. 
Published: February 2011

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.