Core Viewpoint - The article discusses the cellular mechanisms underlying the beneficial and detrimental effects of bacterial antitumor immunotherapy, highlighting the importance of injection timing in maximizing therapeutic efficacy and minimizing tumor promotion risks [3][10]. Group 1: Research Findings - The study utilized a non-tumor antigen expressing attenuated strain of Listeria (ΔactA, Lm) to explore immune responses in tumor-bearing mice after different injection methods [5]. - Intratumoral injection (i.t.) of Lm alone recruits neutrophils that convert to an immunosuppressive phenotype, creating an immune escape microenvironment that promotes tumor growth [6]. - Conversely, intravenous injection (i.v.) induces the production of anti-Lm cytotoxic CD8+ T cells, which infiltrate the tumor upon subsequent intratumoral injection, leading to tumor suppression through apoptosis induction and enhanced antigen presentation [7][8]. Group 2: Implications of Injection Timing - The study emphasizes the significance of injection timing, suggesting that prior intravenous injection activates systemic T cells, establishing an immune foundation for subsequent intratumoral injection, thus avoiding the immunosuppressive effects associated with intratumoral injection alone [10].