Neutrophils activated by micropatches hold promising prospects in tumor immunotherapy

This study used polymer micropatches as a platform for sustained and targeted activation of neutrophils. The micropatches can promote the rapid conversion of neutrophils to the N1 type while also enhancing the activation of other immune cells in vivo. The activated neutrophils are recruited to the tumor site, where they exert effective antitumor effects. A recent study published in Nature Biomedical Engineering designs a cyto-adhesive micropatches (CAMPs) to activate neutrophils for achieving tumor immunotherapy.1 This study offered an innovative strategy for adoptive activated neutrophil therapy in solid tumors (Figure 1). Neutrophils are the predominant immune cells in peripheral blood. In recent years, the role of neutrophils in tumor progression has become increasingly valued. Neutrophils can be recruited in solid tumors. The recruited neutrophils have high plasticity in the tumor environment and polarize into two phenotypes.2 The protumorigenic N2 phenotype promotes tumor growth by generating vascular endothelial growth factors and matrix-degrading enzymes, mediating antitumor resistance as well as inhibits antitumor immune responses. In contrast, the anti-tumorigenic N1 phenotype exerts antitumor effects by upregulating the production of TNF, intercellular adhesion molecule (ICAM)-1, reactive oxygen species (ROS), and Fas (CD95) while downregulating arginase expression. This characteristic enables direct cytotoxicity toward tumor cells and facilitates interactions with dendritic cells (DCs) to coordinate adaptive immune responses, thereby leading to the acquisition of antitumor capabilities.2 However, current research indicates that neutrophils predominantly express the tumor-promoting N2 phenotype in most environments. Therefore, current research on neutrophil-based tumor cell therapy predominantly focuses on preventing neutrophils from being recruited into tumor cells or inhibiting the function of N2 phenotype neutrophils. Little effort has been made to harness neutrophils as antitumor effector cells. Previous studies have shown that neutrophils can activate potent cytotoxic effects in inflammatory environments to exert tumor-suppressive effects. Moreover, this immunotherapeutic mechanism not only relies solely on adaptive immunity but also activates T-cell immunity through the activation of DC populations.3 This suggests that activated neutrophils may acquire an N1 phenotype to exert antitumor effects. However, the significance of neutrophils and their functions within the tumor microenvironment may profoundly vary depending on the tumor background. However, the significance of neutrophils and their functions in the tumor microenvironment can be profoundly influenced by the tumor context.2 The specific induction of neutrophils to differentiate into the N1 phenotype is crucial for harnessing their antitumor effects. This process involves manipulating various molecular signals and pathways, including the modulation of specific cytokines, chemokines, and signaling molecules that promote the N1 phenotype over the immunosuppressive N2 phenotype. Currently, cell therapies for cancer primarily rely on CAR-T cell therapy, but this approach results in poor infiltration into solid tumors and is limited by complex manufacturing processes. However, neutrophils are characterized by easy accessibility and efficient tumor homing. These findings indicated that N1-phenotype neutrophils may hold great promise for use in tumor cell therapy. The use of micropatches technology to alter cell phenotypes for immunotherapeutic effects represents an attractive platform to improve the efficacy of cell therapy. The micropatches have been applied to antitumor treatment in areas such as immune cell activation and regulation, drug delivery, vaccine development, and microenvironment modulation. Mitragotri et al. have already utilized micropatches to activate NK cells or monocytes for immunotherapy.4, 5 Based on this perspective, Ninad and colleagues employed CAMPs to activate neutrophils and mediate antitumor effects. CAMPs composed of a mixture of PLGA and PLGA-polyethylene glycol (PEG)-maleimide possess a high aspect ratio, enabling them to adhere to neutrophils via anti-CD11b Fab modification without being internalized.1 CAMPs remain on the cell surface, parallel to the cell membrane, without internalization. The authors also verified that the attachment of the patch is an activity process requiring actin recombination. Furthermore, attachment can withstand physiologically relevant shear forces, ensuring the sustained activation of neutrophils via CAMP membrane adhesion under dynamic physiological conditions in vivo. The major limitation of the use of neutrophils in tumor cell therapy is their short lifespan. The half-life of circulating neutrophils in the human body is approximately 7 h, while in mice, it ranges from 8 to 10 h. In this case, prolonging the lifespan of neutrophils and rapid activation are crucial. The authors verified that neutrophils that adhered to CAMPs did not have a shortened lifespan in both in vivo and in vitro experiments. However, their ability to release MPO and express the degranulation marker CD63 was activated at 4 h, far exceeding that of conventional potent neutrophil activators such as GM-CSF. Furthermore, actively adherent neutrophils with CAMPs can also serve as antigen presenters for adaptive immune cells. The MHC-II on neutrophils exposed to CAMPs exhibited a 1.2-fold increase within 4 h. and a 1.7-fold increase at 24 h. These findings demonstrated that CAMPs can rapidly activate neutrophils and function as antigen-presenting cells. Subsequently, researchers investigated the mechanism of neutrophil activation by CAMPs. They found that increased binding of CAMPs led to increased neutrophil activation. The binding of antigens to antibodies activates neutrophils, and this adhesion behavior plays a decisive role in neutrophil activation.1 To validate the mechanism by which activated neutrophils exert antitumor effects in vivo, researchers performed RNA-seq. They found that in the CAMP-treated population, the tumor necrosis factor-alpha (TNF-α) signal through the nuclear factor-kappa B (NF-κB) pathway was markedly upregulated in neutrophils attached to at least one CAMP. This upregulation was accompanied by an overexpression of pathways related to cell apoptosis, IL-2/STAT5 signal transduction, and inflammatory responses. Interestingly, neutrophils without CAMPs attachment also showed an increase in T TNF-α in the CAMP-treated population,1 indicating that activated neutrophils can initiate a cascade reaction by directly contacting and secreting signals to activate adjacent neutrophils. Attachment to CAMPs promotes a shift towards an antitumor phenotype in neutrophils, as revealed by single-cell sequencing, where the total expression of N1-related genes in CAMP-treated neutrophils was significantly higher compared to untreated neutrophils. Furthermore, this study also found that activation of neutrophils leads to activation of CD8+ T cells, NK cells, dendritic cells, and macrophages.1 This confirms that neutrophils attached to CAMPs have the ability to polarize surrounding immune cells towards a pro-inflammatory phenotype. However, the extent of this capability depends on the proximity between CAMP-treated neutrophils and the target immune cells. In in vivo experiments, researchers have also verified the enhancement of the overall antitumor immune environment by CAMPs. Neutrophils tend to accumulate near tumors because activated neutrophils are recruited to solid tumors. This biological behavior has been validated in both melanoma and breast cancer models. Activated neutrophils in the 4T1 model exhibit greater accumulation effects compared to the B16F10 model, potentially due to the higher immunogenicity and inflammatory microenvironment of 4T1-Luc tumors. This results in superior direct tumor cytotoxicity. The study also identified a synergistic effect between this cellular therapy and anti-cytotoxic T-lymphocyte antigen 4 (anti-CTLA4) checkpoint inhibitors. This effect is attributed to the high accumulation of activated neutrophils in lymph nodes, where these neutrophils not only exert tumor-killing effects but also recruit dendritic cells. The increased expression of MHC-II and costimulatory molecules on neutrophils induced by CAMPs promotes antigen presentation. Combined therapy with anti-CTLA4 enhances CD28-B7 costimulation between T cells, thereby eliciting effective and sustained antitumor immune responses.1 CAR therapy often leads to immune overactivation, causing life-threatening cytokine storms. While activated neutrophils in vivo can lead to slight upregulation of the expression of some cytokines, the expression of IL-6 remains unchanged.1 The safety and tolerability of this therapy underscore its clinical relevance and significance. In conclusion, Ninad and colleagues presented a novel cell therapy approach. By adhering of micropatches, neutrophils can be rapidly activated ex vivo, polarizing them toward the N1 phenotype. After intravenous injection into the body, activated neutrophils can be quickly recruited to tumor sites, where they exert cytotoxic effects and mediate systemic immune responses, thereby achieving antitumor effects. The recruitment and survival of neutrophils within tumor tissues involve upstream regulation of myelopoiesis and a complex network of chemokines, cytokines, G-CSF, and complement components.2 This study represents an innovative exploration into neutrophil therapy, addressing the issue of neutrophil activation hindered by their short lifespan. It provides insights into improving the tumor immune microenvironment. However, how to optimize the antitumor effects of neutrophil therapy within the complex tumor microenvironment remains to be explored. Mengran Chen wrote the manuscripts. Bingyang Chu and Yu Wu reviewed and modified the manuscript. All authors have read and approved the final manuscript. We would like to thank FigDraw 2.0 for providing the image materials used in Figure 1. This study was supported by the National Natural Science Foundation of China (82272147 and 32271450); and the Science and Technology Project of Sichuan Province (2023YFS0118). The authors declare no conflict of interest. No ethical approval was necessary for this study. No data were used for the research described in this study.