Anti-PD-1/PD-L1 Based Combination Immunotherapy to Boost Antigen-Specific CD8+ T Cell Response in Hepatocellular Carcinoma

Abstract

Thirty to fifty percent of hepatocellular carcinomas (HCC) display an immune class genetic signature. In this type of tumor, HCC-specific CD8 T cells carry out a key role in HCC control. Those potential reactive HCC-specific CD8 T cells recognize either HCC immunogenic neoantigens or aberrantly expressed host's antigens, but they become progressively exhausted or deleted. These cells express the negative immunoregulatory checkpoint programmed cell death protein 1 (PD-1) which impairs T cell receptor signaling by blocking the CD28 positive co-stimulatory signal. The pool of CD8 cells sensitive to anti-PD-1/PD-L1 treatment is the PD-1dim memory-like precursor pool that gives rise to the effector subset involved in HCC control. Due to the epigenetic imprints that are transmitted to the next generation, the effect of PD-1 blockade is transient, and repeated treatments lead to tumor resistance. During long-lasting disease, besides the TCR signaling impairment, T cells develop other failures that should be also set-up to increase T cell reactivity. Therefore, several PD-1 blockade-based combinatory therapies are currently under investigation such as adding antiangiogenics, anti-TGFβ1, blockade of other negative immune checkpoints, or increasing HCC antigen presentation. The effect of these combinations on CD8⁺ T cells is discussed in this review.

Keywords: CD8 T cell response; PD-1; PD-L1; combination therapy; hepatocellular carcinoma; immune check-point inhibitor; immunotherapy.

Figure 1

Type of anti-PD-1/PD-L1 based combination therapy, according to immune HCC subtypes. Progressive impairment in the balance between CD8 T cells and M2 TAM is observed in different HCC clusters. Neo-angiogenesis is induced in “Wound healing” and “Inflammatory” types. TGF-b1 genes are up-regulated in “Wound healing” HCC type. Absence of CD8 T cells in the “Lymphocyte depleted” type could be due to the lack of neoantigens or T cell deletion. TGF-β1 dominant and the immunologically quiet clusters are poorly represented in HCC.

Figure 2

Flow-cytometric analysis of peripheral blood and intrahepatic lymphocytes in a patient with a Barcelona Clinic Liver Cancer Stage B hepatocellular carcinoma with hepatitis C cirrhosis, HBV negative, CMV positive. The ex-vivo CD8⁺ T cell response against the HLA-A2 restricted HCC epitopes Glypican-3_144–152 and NY-ESO-1_157–165 was tested by staining with CD8, CD3 and HLA-I pentameric complexes loaded with specific peptides. A tumoral sequestration of HCC-specific CD8 T cells and a PD-1 up-regulation gradient between peripheral blood and tumor was observed. PBL: peripheral blood lymphocytes, IHL: intrahepatic lymphocytes, MFI: mean fluorescence intensity, FMO: fluorescence minus one.

Figure 3

Scheme showing the potential mechanisms involved in HCC-specific CD8 T cell impairment. The graph also highlights the possible PD-1/PD-L1 blockade-based combination therapies to rescue effector and precursor HCC-specific cytotoxic T cell response. PD-1: programmed cell death protein 1, CTLA-4: cytotoxic T lymphocyte antigen-4, Tim-3: T cell immunoglobulin domain and mucin domain, LAG-3: lymphocyte-activation gene 3, T regs: CD4 T regulatory cells, Th: T helper, IL: interleukin, TFG: tumor growth factor, VEGF: vascular endothelial growth factor, 4-1BB: tumor necrosis factor receptor superfamily member 9, OX-40: Tumor necrosis factor receptor superfamily member 4, γc: gamma-chain.