TCR sequencing sheds light on tumor immune interactions in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) stands as the dominant form of liver cancer, ranking as the fourth leading cause of cancer-related deaths globally. Often diagnosed at advanced stages, the therapeutic landscape is limited, with transarterial chemoembolization (TACE) serving as a key locoregional treatment. TACE, while effective in inducing tumor necrosis, exerts dual effects on the tumor microenvironment (TME), necessitating integration with systemic therapies like immune checkpoint inhibitors (ICIs). Yet, therapeutic resistance, hypoxia-induced angiogenesis, and immune evasion remain significant barriers. The advent of T-cell receptor (TCR) sequencing offers a transformative lens to unravel these challenges, spotlighting tumor-immune interactions and adaptive immune mechanisms pivotal to advancing precision oncology.

TCR repertoire and its characterization

The TCR repertoire encapsulates the diversity of T-cell responses against antigens. TCRs, primarily αβ heterodimers, undergo somatic V(D)J recombination to achieve remarkable diversity and specificity. Three key complementarity-determining regions (CDRs) drive antigen recognition, with CDR3 exhibiting the highest variability. The repertoire’s diversity is quantified using metrics like Shannon entropy, Simpson index, and clonality indices, providing insights into T-cell dynamics within the TME.

High-throughput sequencing (HTS) has enabled comprehensive profiling of TCR repertoires. Bulk sequencing facilitates large-scale analyses, while single-cell sequencing offers detailed insights into TCR pairing and phenotypic states. However, challenges like amplification bias and limited capture of rare clonotypes persist. Innovations in single-cell platforms and computational tools are progressively addressing these gaps, enhancing the understanding of T-cell-mediated immunity.

Impact of TACE on the immune microenvironment

TACE induces ischemia and chemotherapy-mediated tumor necrosis, releasing tumor neoantigens and triggering immunogenic cell death (ICD). This process activates effector T cells and remodels the TME to a more immunosupportive state initially. However, prolonged hypoxia and ischemic stress shift the TME toward immunosuppression, characterized by regulatory T-cell (Treg) expansion, T-cell exhaustion, and recruitment of tumor-associated macrophages (TAMs). Elevated levels of VEGF and hypoxia-inducible factors (HIF-1α) further facilitate angiogenesis and tumor recurrence.

Chemotherapeutic agents used in TACE, such as doxorubicin, exhibit dual roles: inducing ICD and enhancing adaptive immune responses while minimizing immunosuppressive pathways. Yet, inflammatory responses induced by TACE can paradoxically promote tumor proliferation and immune evasion. Understanding these dynamics is crucial to optimizing TACE’s role in combination therapies.

Combination therapy: TACE with systemic treatments

The integration of TACE with systemic treatments, including ICIs and tyrosine kinase inhibitors (TKIs), represents a paradigm shift in advanced HCC management. ICIs, such as pembrolizumab, target inhibitory checkpoints like PD-1/PD-L1 to sustain T-cell activation, while TKIs modulate VEGF signaling to normalize tumor vasculature and improve immune infiltration. TACE-induced neoantigen release synergizes with these systemic therapies, transforming the TME from “cold” to “hot” and enhancing responsiveness to immunotherapy.

Emerging strategies, such as “Immune Boost TACE,” advocate for partial embolization to amplify immune responses while mitigating the immunosuppressive effects of complete embolization. Early clinical trials indicate promising outcomes, with improved progression-free survival (PFS) and overall survival (OS) rates in patients receiving triple therapy (TACE, ICI, and TKI).

Applications of TCR repertoire in HCC treatment

TCR sequencing holds significant promise in diagnostic, prognostic, and therapeutic domains. The distinct TCR repertoires between tumor and adjacent tissues provide biomarkers for tumor heterogeneity and progression. Monitoring TCR diversity and clonality through liquid biopsies offers non-invasive tools for disease surveillance. Additionally, TCR-T cell therapy, involving engineered TCRs targeting tumor-associated antigens (TAAs), has demonstrated efficacy in preclinical studies and ongoing trials.

TCR repertoire analysis also informs treatment responses, predicting the efficacy of TACE and combination therapies. Alterations in T-cell clonality and diversity post-treatment reflect adaptive immune modulation, aiding in the development of personalized therapeutic strategies. Furthermore, the identification of high-affinity TCRs enables the design of precision TCR-T therapies, enhancing anti-tumor efficacy while minimizing off-target effects.

Future directions

Advancements in TCR sequencing, including spatial transcriptomics and lineage tracing, are poised to refine the understanding of TME remodeling and immune escape mechanisms. Overcoming technical challenges like low capture efficiency and the cost of single-cell sequencing will expand clinical applications. Integration of TCR repertoire analysis with biomarkers such as PD-L1 expression and tumor mutational burden holds potential for improving prognostic models and therapeutic monitoring.

Innovations in antigen-specific TCR identification and combinatory therapies targeting the immunosuppressive TME are essential for enhancing TCR-T therapy outcomes. Strategies to address tumor heterogeneity, including multifocal sequencing and tailored interventions, will further optimize treatment efficacy.

Conclusions

TCR repertoire analysis offers a robust framework for elucidating the interplay between tumor evolution and immune responses in HCC. By leveraging TCR dynamics, clinicians and researchers can refine therapeutic strategies, enhance precision oncology, and ultimately improve outcomes for patients with advanced HCC.