Engineered E. coli Nissle 1917 strain after accumulation in the tumor tissue converted ammonia to l-arginine recruiting tumor-infiltrating T cells showing a remarkable antitumor effect.129 Gurbatri et al. engineered a probiotic bacteria system to tightly control the release of nanobodies, which targeted PD-L1 and CTLA-4 and activated T cells.130 In another case, engineered Salmonella (△ppGpp) was utilized to secret the development endothelial locus 1 (Del-1) protein promoting the recruitment of M1 macrophage to tumors.131. The gene discussed is CTLA4; the disease is neoplasm.