# Subclassification-Specific Tumor Immune Microenvironment in Intrahepatic Cholangiocarcinoma: Implications for Appropriate Pharmacotherapy

## TL;DR

This study explores how the immune environment differs between two types of intrahepatic cholangiocarcinoma, aiming to guide better treatment strategies.

## Contribution

The paper is the first to analyze tumor immune microenvironments specific to subclassifications of intrahepatic cholangiocarcinoma.

## Key findings

- Small-duct-type iCCA shows strong dendritic cell infiltration and potential immunosuppressive tumor microenvironment.
- CD8 expression is higher in large-duct-type iCCA compared to small-duct-type.
- DC-high group in small-duct-type iCCA correlates with elevated immune checkpoint markers.

## Abstract

Intrahepatic cholangiocarcinoma (iCCA) is subclassified into small- and large-duct types, and several clinicopathological differences between subclassifications have been reported. However, there are no reports on tumor immune microenvironment (TIME) analyses based on iCCA subclassifications. This study investigated subclassification-specific TIMEs in iCCAs for the purpose of establishing appropriate pharmacotherapy. The results indicate that there is a group of strongly infiltrated DCs in small duct-type iCCA, and in such patients, iCCAs may establish an immunosuppressive TIME to escape from antitumoral immunity induced by the antigen presentation of DCs. The diversity in background factors and the anatomical origins of iCCAs not only contribute to the formation of distinct subclassifications with different clinicopathological characteristics, but also influence the composition of the TIME. This result may contribute to the establishment of appropriate pharmacotherapy for each subclassification.

Background/Objectives: Intrahepatic cholangiocarcinoma (iCCA) is subclassified into small- and large-duct types. Small-duct-type iCCAs are associated with a better prognosis, and each subclassification requires different surgical strategies. The efficacy of chemotherapy, including immune checkpoint inhibitors, may vary between subclassifications. However, there are no reports on tumor immune microenvironment (TIME) analyses based on iCCA subclassifications. This study investigated subclassification-specific TIMEs in iCCAs for the purpose of establishing appropriate pharmacotherapy. Methods: A total of 131 resected iCCA cases were analyzed, comprising 73 tumors classified as small-duct-type and 58 as large-duct-type based on pathological evaluation. Immunohistochemical analyses targeting CD8, PD-1, PD-L1, CTLA-4, and S100 protein (a dendritic cell [DC] marker) were performed to investigate the immune-cell status in each subclassification. Results: Large-duct-type iCCA had a significantly higher CD8 expression in tumor-infiltrating cells than small-duct-type ICC. However, the expression of other molecules did not significantly differ between the two tumor types. The proportion of tumors with a high level of S100 protein expression (DC-high group) in tumor-infiltrating cells was significantly higher in small-duct-type ICCs than in large-duct-type iCCAs (30% vs. 1.7%). In small-duct-type iCCAs, the expression levels of CD8, PD-1, PD-L1, and CTLA-4 were significantly higher in the DC-high group than in the DC-low group. Conclusions: We revealed subclassification-specific TIMEs in iCCAs. A subset of small-duct-type iCCAs exhibited strong DC infiltration. In these patients, the tumors may establish an immunosuppressive TIME to evade antitumor immunity triggered by DC-mediated antigen presentation. These findings may contribute to the development of tailored pharmacotherapy for each iCCA subclassification.