Transarterial Embolization Enhances Programmed Cell Death Ligand 1 Expression and Influences CD8 + T Lymphocytes Cytotoxicity in an Orthotopic Hepatocellular Carcinoma Rat Model.

Purpose: To investigate the influence of transarterial embolization (TAE) on programmed cell death-ligand 1(PD-L1) expression and CD8 ⁺ T tumour infiltrative lymphocyte cytotoxicity in the Sprague-Dawley (SD) rat model of hepatocellular carcinoma (HCC).
Materials and Methods: An orthotopic HCC model was established in twenty SD rats treated with TAE (lipiodol, n = 10) or sham (normal saline, n = 10) using homologous N1S1 hepatoma cells. Rats were euthanized 1 week after embolization. Flow cytometry was used to assess the proportion of CD4 ⁺ T, CD8 ⁺ T and programmed cell death-1 ⁺ (PD-1 ⁺ ) CD8 ⁺ T lymphocytes in the spleens and tumours. Distribution of CD8 ⁺ T, granzyme-B ⁺ CD8 ⁺ T lymphocytes and PD-L1 ⁺ cells was assessed by immunohistochemistry (IHC) or multiplex IHC. p value < 0.05 was considered statistically significant.
Results: The CD4/CD8 ratio and PD-1 ⁺ CD8 ⁺ T lymphocytes exhibited higher values in TAE-treated tumours compared to sham-treated tumours (p = 0.021 and p = 0.071, respectively). Conversely, the number of CD8 ⁺ T lymphocytes was decreased in TAE-treated tumours (p = 0.043), especially in the central region (p = 0.045). However, more CD8 ⁺ T lymphocytes were found infiltrating the marginal region than central region in TAE-treated tumours (p = 0.046). The proportion of granzyme-B ⁺ CD8 ⁺ T lymphocytes and the PD-L1 positive areas was elevated in tumours that treated with TAE (p all < 0.05). There was a negative correlation between PD-L1 expression and the number of infiltration of CD8 ⁺ T lymphocytes (p = 0.036).
Conclusions: Immune cells are distributed unevenly in the tumours after TAE. The intrinsic induction state of the tumour after embolization may be insufficient to elicit a maximal response to PD-1/PD-L1 inhibitors.
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