Hepatocellular carcinoma (HCC) is the most common primary liver cancer and a significant global health issue due to its high incidence and mortality rates1. According to the World Health Organization, HCC ranks as the fifth most common cancer and the second leading cause of cancer-related deaths worldwide2. It is particularly prevalent in regions with high rates of chronic hepatitis B and C infections, such as East Asia and sub-Saharan Africa3. Major risk factors include viral hepatitis, cirrhosis, and metabolic syndrome4. HCC requires long-term treatment, imposing substantial physical and financial burdens, underscoring the need for effective prevention, early detection, and innovative treatment strategies5.
The immune system plays a crucial role in the development of HCC. The liver is an immunologically active organ with an abundance of immune cells, including liver-resident macrophages, natural killer (NK) cells, and T cells, which are essential for monitoring and eliminating abnormal cells6. However, HCC can evade immune surveillance by expressing immunosuppressive molecules, recruiting immunosuppressive cells, and altering the tumor microenvironment7,8. This immune escape not only promotes tumor growth and metastasis but also affects the response to immunotherapy9,10.
Systemic and local immune responses in the tumor microenvironment are key factors influencing cancer progression and therapeutic outcomes. Systemic immune responses involve circulating immune cells that can recognize and attack distant tumor cells, such as peripheral T cells, NK cells, and monocytes that can target tumor cells throughout the body. Local immune responses focus on immune cell activity within the tumor microenvironment, including tumor-infiltrating lymphocytes (TILs), tumor-associated macrophages (TAMs), and regulatory T cells (Tregs). While TILs often exert cytotoxic effects against tumor cells, TAMs and Tregs typically contribute to an immunosuppressive environment that supports tumor growth11,12. Tumor cells and stromal cells can reshape the tumor microenvironment to promote immunosuppression and evade immune surveillance. The interaction between systemic and local immune responses determines the overall effectiveness of anti-tumor immunity11. Understanding this interaction can aid in developing more effective immunotherapy strategies.
Traditional flow cytometry and immunohistochemistry, while widely used in immunological studies, exhibit significant limitations when it comes to analyzing complex immune landscapes due to their inability to perform comprehensive, high-dimensional analysis. Flow cytometry is highly effective for detecting surface and functional markers at the single-cell level; however, its capacity for simultaneous multi-marker analysis is restricted, often limited by spectral overlap and practical constraints on the number of fluorescent tags that can be used13,14. Immunohistochemistry, on the other hand, provides valuable insights into the tissue context of specific markers, but it is similarly hampered by the limited number of analyzable markers and the inherent difficulties of achieving robust, quantitative, high-dimensional assessments15.
To effectively characterize complex immune environments, high-dimensional techniques like mass cytometry (cytometry by time-of-flight [CyTOF]) are essential. Mass cytometry is an advanced technology that employs mass spectrometry to analyze multiple protein markers in single cells. It enables multiparametric analysis of individual cells without the spectral overlap issues seen in traditional flow cytometry16. By using metal-tagged antibodies, it can measure dozens of markers simultaneously, offering a comprehensive and unbiased view of cellular phenotypes and functions17. For example, Gadalla et al. developed a CyTOF panel with more than 40 parameters for the analysis of peripheral blood mononuclear cells (PBMC) and tumor tissue, demonstrating its advantage in high-dimensional immunophenotyping18. Traditional flow cytometry, with its limited number of detectable parameters, was unable to identify these rare cell populations exhibiting unique phenotypes. In contrast, mass cytometry enabled a comprehensive evaluation of the functional states of these cells, providing a more detailed and robust characterization. Behbehani et al. utilized mass cytometry to analyze bone marrow samples from patients with myelodysplastic syndromes (MDS), successfully identifying and characterizing rare aberrant hematopoietic progenitor cells18. The ability of mass cytometry to simultaneously detect over 40 surface and intracellular markers significantly enhanced the detection of these low-frequency cell subsets19. These capabilities overcome traditional limitations and provide deeper insights into immune landscapes, driving progress in immunology and therapeutic development. The ability to comprehensively profile cellular phenotypes and functions at the single-cell level greatly advances the understanding of immunological processes and aids in the development of targeted therapies.
Mass cytometry provides comprehensive insights into the systemic and local immune cell populations in HCC by simultaneously detecting multiple protein markers. This technology can distinguish between various types of T cells within the tumor microenvironment, such as effector T cells, regulatory T cells (Tregs), and exhausted T cells, elucidating their specific roles in tumor progression. By utilizing mass cytometry, researchers can identify immune markers associated with HCC prognosis20. For instance, T cell subsets with high Programmed Cell Death Protein 1 (PD-1) expression can serve as predictors of a patient's response to immune checkpoint inhibitors21. Additionally, it facilitates the discovery of new therapeutic targets by identifying specific immunosuppressive molecules, thereby providing a foundation for personalized treatment strategies. Technology's ability to detect multiple markers and its single-cell resolution make it particularly advantageous for uncovering novel therapeutic targets and designing combination immunotherapies. This advanced approach holds significant potential for improving treatment outcomes in HCC patients by offering a detailed understanding of the immune landscape and enabling the development of tailored therapeutic interventions.
This study aims to utilize mass cytometry to analyze the systemic and local immune cell profiles of patients with HCC. The objectives are to characterize the immune cell populations, correlate these characteristics with clinical outcomes and therapeutic responses, and identify specific immune markers and cell subsets associated with HCC prognosis. By elucidating the roles of various immune cells in treatment responses, this study seeks to provide a foundation for personalized treatment strategies. The findings are expected to optimize existing immunotherapies and offer valuable insights for developing new treatments, ultimately aiming to improve overall survival and quality of life for HCC patients.