Tertiary lymphoid structure (TLS)-inducing agents, when distributed non-specifically, may trigger autoimmune diseases. On January 9, 2026, Hu Yong from Nanjing University, Zhao Wei from Nanjing Medical University, and Yang Fei from Xuzhou Medical University co-corresponded a study published online in Science Advances, titled "Self-transforming hydrogel mimicking tertiary lymph nodes to activate cGAS-STING pathway for enhanced antitumor immunotherapy."

This study developed an in situ self-transforming chitosan-based hydrogel that functions as a biomimetic TLS. Upon injection into the peritumoral region of tumor-bearing mice, the chitosan hydrogel solution rapidly undergoes in situ gelation. Following the elimination of tumor cells and intratumoral bacteria using doxorubicin and cefotaxime, the hydrogel efficiently adsorbs pathogen-associated molecular patterns (PAMPs) derived from bacteria, damage-associated molecular patterns (DAMPs) from tumor cells, and tumor-associated antigens. These danger signals significantly enhance the recruitment of immune cells into the hydrogel. The adsorbed DNA then activates the cGAS-STING pathway, fully activating dendritic cells (DCs). Activated DCs convert T cells into cytotoxic T lymphocytes (CTLs), which subsequently migrate through the hydrogel’s pores into the tumor tissue, effectively remodeling the immunosuppressive microenvironment and thereby suppressing tumor growth and metastasis.

This research reveals a previously unknown method for constructing safe, easily controllable, and highly efficient biomimetic TLSs, offering a new strategy to revolutionize combination immunotherapies for various cancers.

Cancer immunotherapy harnesses the immune system to specifically kill tumor cells while establishing long-term immune surveillance to prevent recurrence, thus opening a new paradigm in cancer treatment. However, tumors often exhibit poorly differentiated vasculature, leading to insufficient nutrient and oxygen supply and accumulation of metabolic waste. This harsh environment forces immune cells to compete with tumor cells for nutrients, causing metabolic adaptation in immune cells and impairing their effector functions. Moreover, immune-inhibitory molecules expressed on tumor cell surfaces—such as programmed death-ligand 1 (PD-L1)—interact with T cells, further inducing T cell exhaustion. Increasing evidence indicates that specific intratumoral bacteria can exacerbate the immunosuppressive microenvironment and even accelerate tumor metastasis. Collectively, this immunosuppressive tumor microenvironment severely limits the efficacy of anti-tumor immunity.

Researchers are striving to convert immunologically "cold" tumors into "hot" ones to enhance immunotherapy outcomes. Strategies such as photothermal therapy, radiotherapy, chemotherapy, and delivery of immune checkpoint inhibitors or therapeutic antibodies into tumors can promote this conversion. During these treatments, destroyed tumor cells release tumor-associated antigens. Dendritic cells (DCs) uptake these antigens, migrate to tumor-draining lymph nodes, and activate T cell differentiation into effector T cells, which then infiltrate tumor tissue to exert immune functions. However, insufficient infiltration of immune cells into tumors limits therapeutic efficacy. It is hypothesized that limited exposure to tumor-associated antigens and the complex activation and migration processes required by immune cells are key reasons for this limitation.

Tertiary lymphoid structures (TLSs) are ectopic lymphoid aggregates that form in non-lymphoid organs under pathological conditions, structurally and functionally resembling secondary lymph nodes. TLSs are commonly found in autoimmune diseases, chronic infections, and tumors; their presence in tumors often correlates with better treatment response and prognosis. Mature TLSs provide a favorable microenvironment for the activation of T cells, B cells, and other immune cells, thereby promoting rapid and effective anti-tumor immune responses. However, natural TLS formation is slow—studies show that TLS development in mice without additional intervention takes at least 20 weeks. Furthermore, tumor-associated TLSs are highly heterogeneous, with significant differences in maturity and density across tumor types and stages. Immature TLSs have limited capacity to promote anti-tumor immunity, and the location of TLSs within tumors also affects their efficacy. More importantly, due to tumor immune editing and the immunosuppressive microenvironment, only a small fraction of cancer patients naturally develop detectable TLSs. Thus, the immunosuppressive nature and rapid progression of tumors render naturally formed TLSs insufficient for therapeutic needs.

Currently, chemotherapeutic drugs, cytokines, STING agonists, oncolytic viruses, and lymph node-derived cells have been used to promote TLS formation. Notably, these TLS-inducing strategies pose safety concerns. The delivery efficiency of TLS inducers is limited, making it difficult to induce TLS formation effectively and specifically within tumors; TLSs formed in non-tumor tissues may increase the risk of autoimmune diseases. Additionally, pre-existing vascular systems may enable tumor-associated TLSs to participate in tumor metastasis. Therefore, constructing safe, controllable, rapidly formed, and highly efficient TLSs to improve anti-tumor immunity is of critical importance.

Recent studies found that implanted chitosan hydrogels (COS) in mice can recruit innate immune cells. Moreover, different tumors—including breast, lung, ovarian, pancreatic, melanoma, bone, and brain cancers—harbor unique bacterial compositions. Clinical data show high abundance of Escherichia coli (E. coli) in breast cancer tissues, which diminishes anti-tumor efficacy. Thus, this study constructed a modified COS hydrogel as a biomimetic TLS to treat subcutaneous 4T1 tumors in mice pre-colonized with E. coli. The pre-gelled chitosan solution was injected near the tumor and rapidly underwent in situ gelation. After intratumoral injection of doxorubicin (DOX) and antibiotics to kill tumor cells and intratumoral bacteria, released cellular/bacterial debris and fragmented DNA were adsorbed onto the hydrogel via electrostatic interactions. These adsorbed danger signals facilitated efficient recruitment of diverse immune cells—including DCs, T cells, B cells, macrophages, and neutrophils—into the hydrogel. Notably, activated DCs directly initiated cytotoxic T lymphocyte (CTL) activation via the cyclic GMP-AMP synthase (cGAS)-STING signaling pathway. These activated immune cells efficiently migrated through the hydrogel’s pores into the tumor tissue, triggering a robust anti-tumor immune response that significantly suppressed subcutaneous tumor growth and lung metastasis in tumor-bearing mice.

This hydrogel-based biomimetic TLS closely resembles mature tumor-associated TLSs in terms of location, cellular composition, and immune function. Unlike previous TLS-inducing methods, this biomimetic TLS requires no additional immune stimulants (e.g., STING agonists or CpG) and rapidly forms at specific tumor sites, actively creating multiple favorable conditions for immune cell activation and effectively alleviating the immunosuppressive tumor microenvironment. Moreover, these biomimetic TLSs lack vascular structures such as high endothelial venules and lymphatic vessels, thereby avoiding the risk of vascular-mediated tumor metastasis.

In summary, these biomaterial-inspired biomimetic TLSs hold promise for treating various cancers.

Original Link: https://www.science.org/doi/10.1126/sciadv.adz5078