Expression of immune checkpoints (PD-L1 and IDO) and tumour-infiltrating lymphocytes in breast cancer

Abstract

Background: Breast cancer (BC) has become the most common cancer globally in 2020 as well as in the United Arab Emirates. The breast tumor microenvironment is composed of various immune cell types, including lymphocytes. Tumour-infiltrating lymphocytes (TILs) play a crucial role in tumor eradication and progression. Further, immune checkpoint markers such as programmed death receptor ligand 1 (PD-L1) and indoleamine-2,3-dioxygenase (IDO) have been associated with tumor evasion from the immune system. In this study, we aimed to explore the status of TILs, PD-L1 and IDO as well as to investigate their association with the clinicopathological parameters.

Materials and methods: A total of 59 patients diagnosed with primary infiltrating BC were selected, after which tissue sections were stained to identify TILs along with immunohistochemical staining of PD-L1 and IDO. Moreover, in-silico tools were used to assess the expression of PD-L1, IDO and CD3ε in various molecular subtypes of BC.

Results: It was found that the percentage of TILs correlated with estrogen receptor (ER) and progesterone receptor (PR) expression. This was supported by the finding that most of the triple-negative breast cancer (TNBC) cases belonged to the group with a high percentage of TILs (h-TILs). Similarly, the expression of PD-L1 and IDO was correlated with the ER and PR, whereas TNBC cases showed a high expression of PD-L1 and IDO. This goes in line with the in-silico findings where the TNBC group showed the highest expression of PD-L1 and IDO as well as the T cell marker CD3ε.

Conclusion: This study highlighted a possible link between the immunosuppressive markers PD-L1 and IDO with TILs density in the BC microenvironment.

Keywords: Breast cancer; IDO; Immune checkpoints; PD-L1; TILs.

Figure 1

Immunohistochemical staining of PD-L1 and IDO in breast cancer patients. Representative images of (A) PD-L1 and (B) IDO expression in infiltrating mammary carcinoma. The PD-L1 and IDO expression cut-off was > 1%.

Figure 2

PD-L1 and IDO expression in different breast cancer molecular subtypes. The breast cancer patients with triple-negative (TNBC) molecular subtype were compared to the other subtypes according to the expression of (A) PD-L1 and (B) IDO. The comparison was done using the Chi-square test with a p-value <0.05, considered statistically significant.

Figure 3

Association between tumour-infiltrating lymphocytes (TILs) and the expression of PD-L1 and IDO in breast cancer. The breast cancer patients presenting with more than 50% of TILs (high-TILs; h-TILs) were compared to the low-TILs (l-TILs) group according to the expression of (A) PD-L1 and (B) IDO. The comparison was done using the Chi-square test with a p-value <0.05 considered statistically significant.

Figure 4

Association between PD-L1 and IDO in breast cancer patients. Most patients expressing positive IDO showed a significant positive expression of PD-L1. The comparison was done using the Chi-square test with a p-value <0.05 considered statistically significant.

Figure 5

In silico analysis of PD-L1, IDO and CD3ε expression in various molecular subtypes of breast cancer. Differential expression of (A) PD-L1, (B) IDO, (C) CD3ε in 719 BC patients with luminal subtypes (n = 566), HER2 positive (n = 37), and triple-negative (TNBC, n = 116) subtypes. The comparison was done using the Student’s t-test, considering unequal variance with a p-value <0.05 considered statistically significant.