Abstract 3978: Assessment of therapeutic responses of disseminated Ewing sarcoma xenografts to adoptive therapy with chimeric receptor gene-modified T cells in mice by whole body magnetic resonance imaging.
Authors: Liebsch Lennart , Kailayangiri Sareetha , Beck Laura , Altvater Bianca , Koch Raphael , Hotfilder Marc , Ring Janine , Faber Cornelius , Vieth Volker , Rossig Claudia 
Published: August 2014

Abstract
Novel treatment strategies in Ewing sarcoma include molecularly targeted drugs and antibodies as well as cellular therapies. Preclinical in vivo models are needed that recapitulate the biology of multifocal disease and reflect the activity of novel therapies against systemic (micro)metastatic disease. Here, we used whole body magnetic resonance imaging techniques to monitor the engraftment and metastatic spread of human Ewing sarcoma xenografts in mice and to address the therapeutic efficacy of adoptive T cell transfer. Of 18 mice receiving intravenous injections of 2x106 VH-64 cells, all developed disseminated tumor growth detectable by whole-body MRI within 31 days. All mice had lung tumors, with a median of 19 tumors (range 1 to 60) per mouse. Sixteen mice had additional tumor manifestations, including bone and/or bone marrow (n=10), soft tissues (n=5), and kidney (n=13). Interobserver agreement was high, with an intraclass correlation of 0.929 for tumor numbers. Dissection and histological analysis confirmed the presence of CD99+ small blue round cell tumors in bones, lungs and kidneys in all examined specimens. Sequential whole body T2 MRI scans at weekly intervals following an initial scan 3 weeks after tumor inoculation revealed in vivo growth of tumors at all sites. To add further tissue information, we performed parallel diffusion weighted whole body imaging with background signal suppression (DWIBS). DWIBS effectively visualized metastatic Ewing sarcoma growth in bones, retroperitoneal organs, and soft tissues, whereas, as expected, susceptibility artifacts in air-filled spaces prevented effective detection of lung tumors. To assess the therapeutic efficacy of adoptive T cell transfer against disseminated Ewing sarcomas in this model, further cohorts of 9 mice each received transfusions of 1x107 14.G2a-28ζ gene-modified human GD2-specific T cells following tumor inoculation. Control mice received non-transduced T cells. The numbers of mice developing tumors and the numbers of tumors at extrapulmonary localizations sites were not noticeably different between treated and control mice. However, animals receiving GD2-targeted gene-modified T cell therapy had lower numbers of pulmonary tumors than controls (p&lt;0.0001). Moreover, the median volumes of soft tissue tumors at first detection were lower in the treatment cohort (p=0.019). Mice treated with GD2-redirected T cells had a growth delay of their lung tumors, with both smaller volumes (p=0.023) and lower numbers of tumors (p=0.024) at 4 weeks after tumor inoculation. Thus, GD2-retargeted T cells cannot prevent disseminated tumor growth in this aggressive systemic disease model, but are active to reduce pulmonary Ewing sarcoma manifestations. Optimized strategies now aim to enhance the efficacy of chimeric T cell receptor therapies.
Citation Format: Lennart Liebsch, Sareetha Kailayangiri, Laura Beck, Bianca Altvater, Raphael Koch, Marc Hotfilder, Janine Ring, Cornelius Faber, Volker Vieth, Claudia Rossig. Assessment of therapeutic responses of disseminated Ewing sarcoma xenografts to adoptive therapy with chimeric receptor gene-modified T cells in mice by whole body magnetic resonance imaging. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3978. doi:10.1158/1538-7445.AM2013-3978