{"doi":"10.64898/2025.12.08.693072","title":"Armoring STEAP1 CAR T cells with IL-18 potentiates antitumor activity in Ewing sarcoma","abstract":"ABSTRACT Background Ewing sarcoma (EwS) is a highly aggressive cancer driven by the EWS::FLI1 fusion oncoprotein affecting children, adolescents, and young adults. Six transmembrane epithelial antigen 1 (STEAP1) is a cell surface antigen transcriptionally controlled by EWS::FLI1 that is broadly expressed in EwS, positioning it as a rational immunotherapy target. However, translating CAR T therapy to solid tumors requires overcoming barriers to potency while maintaining safety. Methods Analyses of transcriptome and proteome data were performed to evaluate the effects of EWS::FLI1 perturbation on STEAP1 expression at the transcript and protein levels in EwS models. STEAP1 expression was validated in EwS patient tissues by immunohistochemistry. Second-generation STEAP1-BBζ CAR T cells were tested in orthotopic and disseminated EwS xenograft models. To enhance antitumor activity, an IL-18-armored STEAP1 CAR was engineered. Dose-dependent therapeutic efficacy and safety were evaluated through measurement of tumor burden, survival, and observation for gross toxicities. Results STEAP1 was expressed in ∼97% of primary EwS tumors and directly associated with EWS::FLI1 fusion protein expression in EwS cell lines. In orthotopic EwS models, STEAP1 CAR T cells induced complete tumor regression at 5 x 10 6 cells. In disseminated disease models, responses were dose-dependent with no evidence of antigen loss. Notably, IL-18 armored STEAP1 CAR T cells achieved complete responses in ∼80% of mice at a reduced dose of 10 6 cells without overt toxicity. Conclusions These data establish STEAP1 as a clinically relevant and highly expressed target in EwS and demonstrate that IL-18 armoring significantly improves CAR T cell efficacy by enhancing potency evident through antitumor activity at reduced cell dose. STEAP1 CAR T cells are currently under evaluation in a first-in-human phase 1/2 dose-escalation clinical trial for metastatic castration-resistant prostate cancer ( NCT06236139 ) and these studies support future clinical translation of STEAP1 CAR T cell therapy for relapsed/refractory EwS.","journal":"bioRxiv (Cold Spring Harbor Laboratory)","year":2025,"id":584948,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":0,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9569,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2025-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":1018266,"name":"Annabelle Tsao","orcid":"0000-0002-7879-7529","position":1,"is_corresponding":false},{"id":1498386,"name":"Truman Chong","orcid":null,"position":2,"is_corresponding":false},{"id":1362453,"name":"Peter P. Challita","orcid":null,"position":3,"is_corresponding":false},{"id":724662,"name":"Keke Liang","orcid":"0000-0002-0007-6326","position":4,"is_corresponding":false},{"id":869932,"name":"Erolcan Sayar","orcid":"0000-0002-3922-5683","position":5,"is_corresponding":false},{"id":290797,"name":"Jiaoti Huang","orcid":"0000-0003-1195-1998","position":6,"is_corresponding":false},{"id":735028,"name":"Elizabeth R. Lawlor","orcid":"0000-0002-2350-1540","position":7,"is_corresponding":false},{"id":291422,"name":"Michael C. Haffner","orcid":"0000-0003-0809-6425","position":8,"is_corresponding":false},{"id":292453,"name":"Behnam Nabet","orcid":"0000-0002-6738-4200","position":9,"is_corresponding":false},{"id":686741,"name":"Vipul Bhatia","orcid":"0000-0002-4091-8866","position":0,"is_corresponding":true}],"reference_count":53,"raw_metadata":{"citation_network_status":"fetched"},"created_at":"2026-07-19T02:59:16.166424Z","pmid":"41415362","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}