Visualization of PD-L1-positive and PD-1-positive immune cell contact in the breast cancer microenvironment

Abstract

Functioning of the PD-1/PD-L1 immune checkpoint in the microenvironment of breast cancer may lead to the tumor escape from the immune response. However, it is unknown how often PD-L1 binds to PD-1 in breast cancer patients, which PD-L1-positive cells are predominantly involved in the interaction, and what prognostic significance it has. The objective of the study was to assess the frequency of co-location of PD-1/PD-L1- positive cells in the microenvironment of breast cancer as well as to determine the population of these cells. Material and Methods. The study included 25 patients with invasive breast carcinoma. Interaction between cells carrying the PD-1 receptor and the PD-L1 ligand in the tumor microenvironment were visualized using multiplex TSA (tyramide signal amplification)-modified immunohistochemistry. Participation of M1 macrophages (CD68+CD163-CD3-CKAE1/3-), M2 macrophages (CD68+/-CD163+CD3-CKAE1/3-), lymphocytes (CD68- CD163-CD3+CKAE1/3-) and other immune cells in these interactions was assessed. Results. Half of the breast cancer patients included in the study had interactions of immune cells of the microenvironment, one of which carried PD-1, and the other carried PD-L1. The contact of cells carrying PD-1 and PD-L1 was associated with the level of TILs and the ratio of PD-1+/ PD-L1+ cells in the tumor microenvironment. The PD-1/PD-L1 interaction was found with similar frequency in PD-L1 positive and negative patients. In the cell contacts, macrophages acted as PD-L1+ cells in the vast majority of cases. Lymphocytes were PD-1-positive cells rather than PD-L1- carrying cells. In addition, it was found that metastasis-free survival was not associated with the presence or absence of co-localized cells carrying PD-1 and PD-L1 in the tumor microenvironment. Conclusion. Co-location of immune cells carrying PD-1 and PD-L1 occurs in breast cancer. M1 and M2 macrophages, CD3+ lymphocytes and other immune cells are involved in these interactions. However, further studies are needed to establish the prognostic significance of these contacts.