Tertiary Lymphoid Structures: The Body's Hidden Arsenals in the Fight Against Cancer

Imagine a battlefield within the body, where the immune system stands as the last line of defense against the relentless advance of cancer. For decades, scientists have focused on the well-known lymphoid organs like the spleen and lymph nodes as the primary training grounds for cancer-fighting immune cells. However, a series of groundbreaking discoveries has revealed the existence of hidden immune arsenals, known as tertiary lymphoid structures (TLS), that form directly within tumors. These structures are now emerging as a critical factor in determining a patient's response to immunotherapy, and their manipulation is now considered a next-generation cancer immunotherapy strategy.

Introduction

The fight against cancer has been revolutionized by immunotherapies that unleash the power of the immune system. However, only a subset of patients experience lasting benefits, leaving researchers to question what distinguishes responders from non-responders. Recent evidence points to the presence of tertiary lymphoid structures (TLS) as a key determinant of successful anti-tumor immunity. These ectopic lymphoid aggregates, which resemble miniature lymph nodes, form in chronically inflamed tissues, including tumors, and serve as local hubs for generating potent anti-cancer immune responses. A recent review in Nature Reviews Cancer highlights that TLS are associated with improved clinical outcomes and enhanced responses to immunotherapy across a wide range of cancers, including melanoma, sarcoma, and various carcinomas.

Study Summary

To understand the significance of TLS, researchers have employed cutting-edge techniques like spatial transcriptomics to map the intricate cellular and molecular landscapes within tumors. A pivotal study in Cancer Cell investigated TLS in hepatocellular carcinoma (HCC) and revealed that not all TLS are created equal. The researchers were able to classify TLS into different maturation stages, discovering that only mature TLS contribute to effective immunotherapy responses. This work highlights the importance of the tumor microenvironment in shaping TLS function and provides a roadmap for developing strategies to promote their maturation.

Key Findings

• TLS Maturation is Critical for Anti-Tumor Immunity: The degree of TLS maturation is a key determinant of its effectiveness. Mature TLS, characterized by organized B and T cell zones, are associated with a robust anti-tumor immune response, while immature structures are less effective. This suggests that therapeutic strategies should aim to promote the development of mature TLS.
• The Tumor Microenvironment Shapes TLS Function: The local tumor microenvironment plays a crucial role in regulating TLS formation and maturation. For instance, tryptophan metabolism in the tumor microenvironment can restrict TLS maturation, impairing the anti-tumor immune response. This finding opens new avenues for therapeutic intervention by targeting metabolic pathways that influence TLS development.
• TLS as a Predictive Biomarker: The presence and maturity of TLS are emerging as powerful predictive biomarkers for immunotherapy response. Studies have shown that TLS-related gene signatures correlate with prognosis and response to PD-1 blockade in several cancer types, including nasopharyngeal carcinoma. This could help clinicians identify patients who are most likely to benefit from immunotherapy.

Biological Mechanisms

To understand why these findings matter mechanistically, it is essential to delve into the cellular dynamics within TLS. These structures are not mere collections of immune cells; they are highly organized microenvironments where B cells, T cells, and dendritic cells interact to orchestrate a targeted attack against cancer cells. A recent study in Gastroenterology revealed that TLS-associated B cells are crucial for enhancing the response of tissue-resident memory T cells to PD-1 blockade. This finding underscores the importance of the interplay between different immune cell populations within TLS for successful immunotherapy.

Molecular Pathways

The formation and function of TLS are governed by a complex network of molecular pathways. Chemokines, such as CXCL13, play a pivotal role in recruiting immune cells to the tumor site and initiating TLS development. Furthermore, cytokines like IL-33 have been shown to be potent inducers of TLS. A groundbreaking study in Nature demonstrated that IL-33-activated ILC2s can induce the formation of TLS in pancreatic cancer, a tumor type notoriously resistant to immunotherapy. This discovery opens up new therapeutic possibilities for inducing TLS in "cold" tumors that lack pre-existing immune infiltration.

Relevance to Human Health

Beyond the molecular picture, the implications for human health are substantial. The discovery of TLS is not just an academic curiosity; it has the potential to revolutionize how we treat cancer. By understanding the factors that govern TLS formation and function, we can develop more effective and personalized immunotherapies. For example, a study in Cancer Cell has shown that the activity of TLS in ovarian cancer is governed by the tumor's location and surrounding stroma, suggesting that treatment strategies may need to be tailored to the specific characteristics of each patient's tumor.

Therapeutic Applications

• Inducing TLS in 'Cold' Tumors: One of the most exciting therapeutic avenues is the development of strategies to induce TLS formation in tumors that lack them. As shown in the Nature study, cytokines like IL-33 can be used to trigger TLS development in resistant cancers like pancreatic cancer, potentially turning them into immunotherapy-responsive 'hot' tumors.
• Promoting TLS Maturation: For tumors that have immature or dysfunctional TLS, therapies aimed at promoting their maturation could be highly effective. The discovery that inhibiting tryptophan metabolism can enhance TLS maturation provides a tangible therapeutic target that could be combined with existing immunotherapies to boost their efficacy.
• TLS as a Diagnostic and Prognostic Tool: The presence and quality of TLS can serve as a powerful biomarker to predict patient outcomes and guide treatment decisions. As highlighted in a recent review, the maturation and induction of TLS are key to their function, and assessing this could become a routine part of cancer diagnosis.

Future Directions

Despite these advances, key questions remain. Scientists are now investigating how to best harness the power of TLS for therapeutic benefit. A recent review in Med emphasizes the journey of translating TLS research from the laboratory to clinical practice. Future research will focus on developing novel agents that can safely and effectively induce and mature TLS in patients, as well as refining biomarker strategies to better identify individuals who will benefit from these therapies. The prospect of turning immunologically 'cold' tumors 'hot' by creating new immune battlegrounds within them is a truly exciting frontier in cancer medicine.

Conclusion

The discovery and characterization of tertiary lymphoid structures have fundamentally changed our understanding of anti-tumor immunity. These hidden immune arsenals within tumors are not just passive bystanders but active participants in the fight against cancer. By providing a local site for the generation of targeted immune responses, TLS represent a powerful new weapon in our therapeutic arsenal. As research continues to unravel the complexities of TLS biology, we move closer to a future where we can harness their power to improve the lives of cancer patients and bring the promise of immunotherapy to a wider population.

References

1. Tang Z, et al. (2025). Spatial transcriptomics reveals tryptophan metabolism restricting maturation of intratumoral tertiary lymphoid structures. Cancer Cell. 43(6):1025-1044.e14. PMID: 40185093
2. Teillaud JL, et al. (2024). Tertiary lymphoid structures in anticancer immunity. Nat Rev Cancer. 24(9):629-646. PMID: 39117919
3. Peyraud F, et al. (2025). Tertiary lymphoid structures and cancer immunotherapy: From bench to bedside. Med. 6(1):100546. PMID: 39798544
4. MacFawn IP, et al. (2024). The activity of tertiary lymphoid structures in high grade serous ovarian cancer is governed by site, stroma, and cellular interactions. Cancer Cell. 42(11):1864-1881.e5. PMID: 39393357
5. Liu Y, et al. (2024). Single-cell and spatial transcriptome analyses reveal tertiary lymphoid structures linked to tumour progression and immunotherapy response in nasopharyngeal carcinoma. Nat Commun. 15(1):7713. PMID: 39231979
6. Chen Y, et al. (2024). Tertiary lymphoid structures in cancer: maturation and induction. Front Immunol. 15:1369626. PMID: 38690273
7. Amisaki M, et al. (2025). IL-33-activated ILC2s induce tertiary lymphoid structures in pancreatic cancer. Nature. 638(8052):1076-1084. PMID: 39814891
8. Hu C, et al. (2024). Tertiary Lymphoid Structure-Associated B Cells Enhance CXCL13(+)CD103(+)CD8(+) Tissue-Resident Memory T-Cell Response to Programmed Cell Death Protein 1 Blockade in Cancer Immunotherapy. Gastroenterology. 166(6):1069-1084. PMID: 38445519