Significance of PD-L1 clones and C-MET expression in hepatocellular carcinoma

Abstract

Programmed cell death ligand 1 (PD-L1) is an essential immune checkpoint protein implicated in immune evasion by malignant tumors. Overexpression of programmed cell death protein 1 (PD-1) and its ligand PD-L1 is associated with poor prognosis in various types of cancer. Recently, multiple advances have occurred in the area of cancer immunotherapy. Inhibiting the ligation of PD-1 by PD-L1 has been the major focus of anti-tumor immunotherapy. In diagnostic pathology, it has become crucial to detect PD-L1⁺ tumor cases using a validated immunohistochemistry (IHC) approach. Preliminary data demonstrate that C-MET promotes survival of some (e.g., renal) cancer types through regulation of PD-L1. However, C-MET expression, and its association with PD-L1, has not been well-characterized in the context of hepatocellular carcinoma (HCC), and no anti-HCC immunotherapy is currently available in Korea. Therefore, it is crucial to investigate the expression of C-MET and PD-L1, and their association with clinicopathologic factors, to facilitate the development of targeted treatments for HCC. PD-L1 expression was examined in tumor cells (TC) and immune cells (IC) of 70 patient-derived HCC specimens using IHC. Two anti-PD-L1 monoclonal antibodies (MAbs), SP263 and SP142, were utilized. Additionally, TC C-MET expression was assessed. Correlations between PD-L1 expression (as identified by both MAbs), C-MET expression and clinicopathologic factors were assessed. More PD-L1⁺ cases were identified via SP263 than via SP142 when assessing both TC and IC; in the former group, SP236 identified 14/70 positive cases, while SP142 identified only 2/70. In the latter group, SP236 identified 49/70 positive cases, while SP142 identified 30/70. Both MAbs demonstrated a higher frequency of PD-L1 expression by IC than TC. The Edmondson-Steiner grade statistically correlated with a higher frequency of SP236-detected TC PD-L1 expression. C-MET was significantly associated with advanced tumor size and was positively correlated with SP263-detected PD-L1 expression in TC. These results suggest that C-MET may serve a role in regulating PD-L1 expression in HCC. Furthermore, while SP263 generally exhibited a higher sensitivity for PD-L1 detection, concordance in PD-L1⁺ case detection between the two different MAbs was generally good. These background data may be helpful in the development of targeted anti-HCC immunotherapy focused on PD-L1 or C-MET, and in evaluating selection criteria for target populations best suited to such treatments.

Keywords: C-MET; hepatocellular carcinoma; immunohistochemistry; immunotherapy; programmed cell death ligand 1.

Figure 1.

Immunostaining pattern using 3 antibodies (magnification, ×20). (A-D) SP263 (anti-PD-L1 MAb); (A and B) positive staining in TC, (C) staining in <5% of TC and (D) expression in peritumoral IC. (E-H) SP142 (anti-PD-L1 MAb); (E and F) positive staining in TC and (G and H) positive staining in peri- and intratumoral IC. (I-L) Anti-C-MET MAb; (I) 3+ staining, (J) 2+ staining, (K) 1+ staining and (L) negative staining. PD-L1, Programmed cell death-ligand 1; MAb, monoclonal antibody; TCs, tumor cells; ICs, immune cells.

Figure 2.

Immunostaining scores of each antibodies in representative cases. (A) [N,N,N,N,3+], (B) [N,N,P,N,2+], (C) [P,N,P,P,1+], (D) [N,P,P,P,N]. 1, expression of PD-L1 (SP142) in TCs; 2, expression of PD-L1 (SP142) in ICs; 3, expression of PD-L1 (SP263) in TCs; 4, expression of PD-L1 (SP263) in ICs; and 5, expression of C-MET in TCs. N, negative; P, positive; TCs, tumor cells; ICs, immune cells; PD-L1, Programmed cell death-ligand 1.