Abstract
Diverse immune cells in the tumor microenvironment form a complex ecosystem, but our knowledge of their heterogeneity and dynamics within hepatocellular carcinoma (HCC) still remains limited. To assess the plasticity and phenotypes of immune cells within HBV/HCV-related HCC microenvironment at single-cell level, we performed single-cell RNA sequencing on 41,698 immune cells from seven pairs of HBV/HCV-related HCC tumors and non-tumor liver tissues. We combined bio-informatic analyses, flow cytometry, and multiplex immunohistochemistry to assess the heterogeneity of different immune cell subsets in functional characteristics, transcriptional regulation, phenotypic switching, and interactions. We identified 29 immune cell subsets of myeloid cells, NK cells, and lymphocytes with unique transcriptomic profiles in HCC. A highly complex immunological network was shaped by diverse immune cell subsets that can transit among different states and mutually interact. Notably, we identified a subset of M2 macrophage with high expression of CCL18 and transcription factor CREM that was enriched in advanced HCC patients, and potentially participated in tumor progression. We also detected a new subset of activated CD8+ T cells highly expressing XCL1 that correlated with better patient survival rates. Meanwhile, distinct transcriptomic signatures, cytotoxic phenotypes, and evolution trajectory of effector CD8+ T cells from early-stage to advanced HCC were also identified. Our study provides insight into the immune microenvironment in HBV/HCV-related HCC and highlights novel macrophage and T-cell subsets that could be further exploited in future immunotherapy.
Highlights
Hepatocellular carcinoma (HCC) is the fourth leading cause of cancer death worldwide, with chronic hepatitis B (HBV) and C (HCV) virus infection as the leading risk factors[1]
We identified two new subsets, including CCL18+ M2 macrophages enriched in advanced HCC, and XCL1+ CD8+ T cells capable of recruiting dendritic cells (DC) to enhance anti-tumor response
CCL18+ macrophages have been linked to various cancers such as breast[40] and gallbladder[41], suggesting the presence of such macrophages is a common feature in cancer and may be a therapeutic target
Summary
Hepatocellular carcinoma (HCC) is the fourth leading cause of cancer death worldwide, with chronic hepatitis B (HBV) and C (HCV) virus infection as the leading risk factors[1]. Tumor microenvironment (TME) is a complex and heterogeneous ecosystem Innate immune cells, such as the classically activated macrophages (M1) can kill and remove tumor cells, while the M2 macrophages, considered as tumor-associated macrophages (TAMs), promote tumor progression[5]. It is currently clear that macrophages play a dual role in tumor immune responses, the heterogeneity, functional characteristics, and relationship between M1 and M2 macrophages still need further characterization. CD8+ cytotoxic T cells play a critical role in tumor control and contribute to a better prognosis for HCC6. These cells could display an exhausted state by persistent antigen stimulation and display a compromised capacity to produce pro-inflammatory cytokines[7]. Comprehensive characterization of diverse immune subsets will bring new clues for developing tumor immunotherapy
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