PD-L1 Expression in Colorectal Carcinoma Correlates with the Immune Microenvironment

Colorectal carcinoma (CRC) is a common malignancy, with its diverse clinical, pathological, and molecular features. The immune microenvironment of a tumor comprises of interplay between various cells and molecules, and has a significant role in deciding the tumor behavior and overall prognosis. PD-L1 (programmed cell death ligand-1) has been implicated in the regulation of the tumor immune microenvironment (TIME). There is limited data regarding the correlation of PD-L1 expression with immune cell profile in CRCs, especially in the Indian setting. The study aimed to assess the PD-L1 expression in CRC tumor cells and its association with TIME, mismatch repair (MMR), and various other clinicopathological parameters.

This is a hospital-based, cross-sectional observational study. PD-L1 expression was assessed at the protein level by immunohistochemistry and mRNA level by qRT-PCR. Immune cell markers (CD4, CD8, CD20, FOXP3, and CD163) were interpreted using the ImageJ Fiji platform.

Of the 104 cases, 21% were PD-L1 positive and were more common in right-sided CRCs. PD-L1 positive cases showed significantly higher concentrations of all T-cell subsets (CD4+ , CD8+ , and FOXP3+), CD20+ B-cells, and CD163+ macrophages were noted. No statistical significance was seen between PD-L1 expression with clinical profile, pathological subtype, grade or stage, mismatch repair status (proficient vs deficient), and survival.

The present study showed a relatively lower frequency of PD-L1 in CRC from the Eastern Indian cohort. The immune cell concentration in the present study was calculated using image analysis-based objectivised methods. Significant correlation of PD-L1 expression in tumor cells with the tumor-infiltrating immune cells indicated its crucial role in the pathobiology of CRC especially by regulating the TIME. Considering the therapeutic implication of PD-L1 in various malignancies, it may be one of the crucial therapeutic targets in a proportion of cases.