02:01C ES cells in vitro and in vivo in a highly restricted manner. As STEAP1 is overexpressed in a wide variety of cancers, we anticipate these STEAP1-specific TCRs to be potentially useful for immunotherapy of other STEAP1-expressing tumors.

The endochondral bone protein Chondromodulin-I (CHM1) provides oncogene addiction in Ewing sarcoma (ES). We pre-clinically tested the targetability of CHM1 by TCR transgenic, allo-restricted, peptide specific T cells to treat ES. We previously generated allo-restricted wildtype CD8+ T cells directed against the ES specific antigen CHM1319 causing specific responses against ES. However, utilization of these cells in current therapy protocols is hampered due to high complexity in production, relatively low cell numbers, and rapid T cell exhaustion.In order to provide off-the-shelf products in the future, we successfully generated HLA-A*02:01-restricted T cell receptor (TCR) transgenic T cells directed against CHM1319 by retroviral transduction.After short-term expansion a 100% purified CHM1319-TCR-transgenic T cell population expressed a CD62L+/CD45RO and CD62L+/CD45RA+ phenotype. These cells displayed specific in vitro IFNg and granzyme B release in co-culture with HLA-A*02:01+ ES cell lines expressing CHM1. When co-injected with ES cells in Rag2−/−ɣc−/− mice, CHM1-specific TCR-transgenic T cells significantly inhibited the formation of lung and liver metastases in contrast to control mice. Lungs and livers of representative mice displayed CD8+ T cell infiltration in the presence (control group treated with unspecific T cells) and in the absence (study group) of metastatic disease, respectively. Furthermore, mice receiving unspecific T cells showed signs of graft-versus-host-disease in contrast to all mice, receiving CHM1319-TCR-transgenic T cells.CHM1319 specific TCR-transgenic T cells were successfully generated causing anti-ES responses in vitro and in vivo. In the future, CHM1319-TCR-transgenic T cells may control minimal residual disease rendering donor lymphocyte infusions more efficacious and less toxic.

Ewing sarcomas (ES) are highly malignant, osteolytic bone or soft tissue tumors, which are characterized by EWS–ETS translocations and early metastasis to lung and bone. In this study, we investigated the role of the BRICHOS chaperone domain‐containing endochondral bone protein chondromodulin I (CHM1) in ES pathogenesis. CHM1 is significantly overexpressed in ES, and chromosome immunoprecipitation (ChIP) data demonstrate CHM1 to be directly bound by an EWS–ETS translocation, EWS‐FLI1. Using RNA interference, we observed that CHM1 promoted chondrogenic differentiation capacity of ES cells but decreased the expression of osteolytic genes such as HIF1A,IL6,JAG1, and VEGF. This was in line with the induction of the number of tartrate‐resistant acid phosphatase (TRAP +)‐stained osteoclasts in an orthotopic model of local tumor growth after CHM1 knockdown, indicating that CHM1‐mediated inhibition of osteomimicry might play a role in homing, colonization, and invasion into bone tissues. We further demonstrate that CHM1 enhanced the invasive potential of ES cells in vitro. This invasiveness was in part mediated via CHM1‐regulated matrix metallopeptidase 9 expression and correlated with the observation that, in an xenograft mouse model, CHM1 was essential for the establishment of lung metastases. This finding is in line with the observed increase in CHM1 expression in patient specimens with ES lung metastases. Our results suggest that CHM1 seems to have pleiotropic functions in ES, which need to be further investigated, but appears to be essential for the invasive and metastatic capacities of ES.

In this study we report the functional comparison of T cell receptor (TCR)-engineered major histocompatibility complex (MHC) class I-restricted CD4+ versus CD8+ T cells targeting a peptide from six transmembrane epithelial antigen of the prostate 1 (STEAP1) in the context of HLA-A*02:01. STEAP1 is a tumor-associated antigen, which is overexpressed in many cancers, including Ewing sarcoma (EwS). Based on previous observations, we postulated strong antitumor potential of tumor-redirected CD4+ T cells transduced with an HLA class I-restricted TCR against a STEAP1-derived peptide. We compared CD4+ T cell populations to their CD8+ counterparts in vitro using impedance-based xCELLigence and cytokine/granzyme release assays. We further compared antitumor activity of STEAP130-TCR transgenic (tg) CD4+ versus CD8+ T cells in tumor-bearing xenografted Rag2−/−γc−/− mice. TCR tgCD4+ T cells showed increased cytotoxic features over time with similar functional avidity compared to tgCD8+ cells after 5–6 weeks of culture. In vivo, local tumor control was equal. Assessing metastatic organotropism of intraveniously (i.v.) injected tumors, only tgCD8+ cells were associated with reduced metastases. In this analysis, EwS-redirected tgCD4+ T cells contribute to local tumor control, but fail to control metastatic outgrowth in a model of xenografted EwS.