Preferential Expression of Programmed Death Ligand 1 Protein in Tumor-Associated Macrophages and Its Potential Role in Immunotherapy for Hepatocellular Carcinoma

Abstract

A predictive biomarker of immune checkpoint inhibitor (ICI)-based treatments in hepatocellular carcinoma (HCC) has not been clearly demonstrated. In this study, we focused on the infiltration and programmed death ligand 1 (PD-L1) expression of tumor-associated macrophages (TAMs) in the tumor microenvironment of HCC. Immunohistochemistry demonstrated that PD-L1 was preferentially expressed on CD68+ macrophages in the tumor microenvironment of HCC, suggestive of its expression in TAMs rather than in T cells or tumor cells (P < 0.05). A co-culture experiment using activated T cells and M2 macrophages confirmed a significant increase in T cell functionality after the pretreatment of M2 macrophages with anti-PD-L1. Syngeneic mouse model experiments demonstrated that TAMs expressed PD-L1 and tumors treated with anti-PD-L1 showed smaller diameters than those treated with IgG. In these mice, anti-PD-L1 treatment increased activation markers in intratumoral CD8+ T cells and reduced the size of the TAM population. Regarding nivolumab-treated patients, three of eight patients responded to the anti-PD-1 treatment. The percentage of Ki-67-positive CD4+ and CD8+ T cells was higher in responders than non-responders after nivolumab. Overall, PD-L1 expression on TAMs may be targeted by immune-based HCC treatment, and ICI treatment results in the reinvigoration of exhausted CD8+ T cells in HCC.

Crosstalk between tumor-associated macrophages and neighboring cells in hepatocellular carcinoma

“…The TME of HCC is infiltrated by PD-L1-expressing “activated” monocytes with protumoral features [ 55 , 56 ]. Generally, PD-L1 is expressed at a higher level in macrophages/monocytes with an activated M1 phenotype [ 12 ]. Therefore, TAMs in the TME of HCC cannot be defined as a pure M2 phenotype.…”

“…The expression of PD-L1 was reported to be higher in macrophages compared to that in cancer cells, providing a potential indicator for the response to immunotherapy in HCC. Additionally, PD-L1 + TAMs from the analyzed HCC samples did not exhibit a complete M2 polarization [ 12 ]. Additionally, these TAMs exhibited a high HLA-DR expression, reflecting the potential immunogenic nature of tumor cells and susceptibility to therapy designed to deplete these PD-L1-expressing TAMs [ 57 , 58 ].…”

“…The expression of PD-L1 in macrophages may act as a marker for an anti-PD-1/PD-L1 response in HCC. The enrichment of PD-L1 + macrophages in the TME is associated with an activated immunity in TME with a considerable CD8 + T cell infiltration and immune-related gene expression, indicating that the tumor may be responsive to immune-based therapy [ 12 , 57 , 110 ]. TAM activity in HCC is also regulated by the immune checkpoint molecule TIM-3, which is highly expressed on the surface of macrophages and activated by TGF-β in the TME [ 145 ].…”

“…Especially, they are impeded by the activity of immunosuppressive cells, including regulatory T cells, tumor-associated macrophages (TAMs), myeloid-derived suppressive cells (MDSCs), and neutrophils, which are associated with an unfavorable prognosis [ 11 ]. Also, TAMs have central immune-regulatory roles and may limit the efficacy of immune-based therapy via crosstalk with tumor and killer cells [ 12 ]. Immune subtyping using data from The Cancer Genome Atlas describes HCC as a C4 subtype associated with an M2 macrophage enrichment [ 7 , 13 , 14 ].…”

Tumor-Associated Macrophages: Combination of Therapies, the Approach to Improve Cancer Treatment

“…In addition, DNA methylation, histone modifications, and microRNA application are named as regulatory approaches for TAM alteration at the epigenetic level. It has been thought that the additional studies in TAM alteration at the transcriptional, epigenetic, and metabolic levels may show a promising new horizon in the fight with many cancer types such as breast, colon, colorectal, lung, ovarian, pancreatic, prostate and skin cancers, glioma, myeloma, hepatocellular carcinoma, and many others as well [185,186]. Table 2 summarizes the most promising TAM-based novel therapy approaches and their involvement in specific cancers and their therapies.…”