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].

Core Viewpoint - The study highlights that intravesical administration of Bacillus Calmette-Guérin (BCG) vaccine can reprogram hematopoietic stem/progenitor cells (HSPC) to enhance anti-tumor immunity, indicating its potential in cancer immunotherapy [1][2][4][6]. Group 1: Mechanism of Action - BCG vaccine can colonize the bone marrow and reprogram HSPC, enhancing myeloid hematopoiesis in both mice and humans [3][4]. - The reprogrammed HSPC can generate neutrophils, monocytes, and dendritic cells, which reshape the tumor microenvironment and drive T cell-dependent anti-tumor responses [3][4]. Group 2: Key Findings - The study confirms that intravesical BCG administration leads to systemic reprogramming of HSPC [4]. - The reprogramming of HSPC is dependent on INFγ and enhances the antigen-presenting function of myeloid cells [4]. - Reprogrammed myeloid cells increase T cell infiltration and work synergistically with PD-1 blockade for anti-cancer effects [4][6]. Group 3: Implications - The findings underscore the broad potential of HSPC reprogramming in enhancing T cell-dependent tumor immunity, suggesting a novel approach in cancer treatment [6].