| Summary: | The cell surface molecule CD276 (B7‐H3) is an immune checkpoint antigen. The elevated expression of CD276 on tumors contributes to the suppression of anti‐tumor T‐cell responses and correlates with poor prognosis. Methods: The expression of CD276 was explored in vitro on eight urothelial carcinoma cell lines (UM‐UC) in comparison to eight normal urothelial cells (NUCs) by RT‐qPCR, Western blotting, and flow cytometry. Cell proliferation was enumerated over consecutive passages. The expression of cancer stem cell markers CD24 and CD44, cytokeratins, and vimentin was investigated by immunofluorescence. The expression of CD276 in bladder tumor samples and metastases was explored by immunohistochemistry. Results: Expression of CD276 on cell surfaces was elevated on UM‐UCs when compared to NUCs. In UM‐UCs, CD276 transcripts correlated moderately positive with CD276 protein expression (ρ = 0.660) and strongly positive with CD276 surface‐expression (ρ = 0.810). CD276 mRNA expression (ρ = −0.475) and CD276 protein expression (ρ = −0.417) had a significant negative correlation with proliferation, while a significant correlation between proliferation and cell surface expression was not observed in UM‐UCs. Conclusion: The expression of CD276 on UM‐UC bladder tumor cell surfaces is elevated. Slow proliferating UM‐UC cells express more CD276 mRNA and protein than fast proliferating cells. In patients, slow proliferating CD276high tumor (stem) cells may evade immune surveillance. However, cancer therapy targeting CD276 may be effective in the treatment of slow proliferating tumor cells. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
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