Abstract
Background: The prognosis of advanced stage rhabdomyosarcoma (RMS) is still sobering. Therefore, novel therapies such as immunotherapy have to be developed. Methods: Expression of the macrophage activating ligand calreticulin and of the inhibitor CD47 was analyzed on 11 RMS tissue samples using mRNA expression arrays and immunohistochemistry. Results were verified by immunocytochemistry and flow cytometry in 2 RMS cell lines. Cytotoxicity was quantified in co-culture experiments of RMS cells and macrophages using MTT-assays. Results: mRNAs of CD47 and calreticulin were detected in RMS tissues in similar quantities as GAPDH. Extracellular expression of CD47 on RMS cells was confirmed. Calreticulin was exclusively detected in the cytoplasm. Viability of RMS cells dropped to 50–60% after co-culturing with macrophages. Susceptibility of RMS cells was neither influenced by an anti-CD47 antibody, nor by the apoptosis inductor vincristine, nor by epigenetic modulators like SAHA. Conclusion: Despite a high expression of CD47, RMS cells were engulfed by macrophages. A more efficient phagocytosis might promote cellular immunotherapy of childhood RMS.
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