Tan et al. developed a S. typhimurium strain expressing cytolysin A to treat pancreatic cancer.[21] Bacteria also could be designed to express and release IFN‐γ, CTLA‐4 or PD‐L1 nanobodies, and achieve satisfactory effects on tumor treatment.[22, 23, 24] However, a critical consideration of using such engineered bacteria in vivo is how to keep them enriched and grow only in tumor. This evidence concerns the gene CTLA4 and neoplasm.