Intrahepatic landscape of regulatory T-cell subsets in chronically HCV-infected patients with cirrhosis and HCC
Authors: Xiao-Fan Wang, Firouzeh Korangy
Journal: Hepatology (2014)

The liver microenvironment has long been known to play an important role in the pathogenesis and prognosis of liver diseases such as viral hepatitis, autoimmune disease, cirrhosis, and hepatocellular carcinoma (HCC).1 Regulatory T cells (Tregs) have been shown to be critical in multiple settings in moderating these processes.2 However, a systematic study examining the role of these cells in different environments and differentiating these functions by phenotypic subsets is yet to be performed. In this issue, Piconese et al.3 show the importance of performing systemic studies, illuminating local differences in Tregs that have drastic functional consequences. This opens the door for more research to continue evaluating cell populations (with their different functional subsets) in this and other contexts in a similarly systematic fashion, focusing on mechanistic insight and therapeutic intervention. This study rigorously examines the phenotype and localization of different subsets of Tregs in patients with chronic hepatitis C virus (HCV) infection using a substantial population of patient samples, and elegantly demonstrates a preferential accumulation of a classical suppressive (T-helper 1 [Th1]-suppressing) subset of Tregs in cirrhotic and tumor tissue as opposed to the predominance of a more inflammatory (interferon-gamma [IFN-γ]-producing) Th1-like subset of Tregs in noncirrhotic HCV-positive liver tissue. Preferential expression of several markers was detected on each of these Treg populations, which differentiated the classic Th1-suppressing Tregs from the Th1-like Tregs. Interaction between M2-polarized monocytes/macrophages and OX40+ Tregs was also demonstrated, with OX40L expressed on the monocytes aiding in the induction of Treg proliferation. One finding here is of particular importance in light of other studies as well as data presented here demonstrating a correlation between HCV viral load and OX40L expression. Further in vitro studies provided evidence that OX40 engagement promoted proliferation of OX40+ Tregs. As M2 monocytes/macrophages were present in both noncirrhotic tissue as well as in cirrhotic and tumor tissue, the authors explored the factors that drive the preferential Th1-like phenotype of Tregs in noncirrhotic tissue. They found out that while multiple cytokines were spontaneously released from tissue samples, IL-12 expression was significantly reduced in those areas where more OX40+ Tregs were found (i.e., nontumor cirrhotic liver tissue and HCC) and interleukin (IL)−12 had the ability to aid in the polarization of Tregs to a Th1-like phenotype. The authors correlated these ex vivo data with the abundance of the Treg phenotypes in vivo, and showed that OX40 expression and IL-12 receptor expression are antagonistic processes, concluding that OX40 engagement blocks the deprogramming of Th1-suppressing Tregs to Th1-like IFN-γ-producing Tregs, while IFN-γ in turn reduces the expression of OX40, leading to an environment more skewed to produce Th1-like Tregs (Fig. 1). IL-12 concentration in the environment and the presence of OX40L, which can be found in monocytes in liver samples from HCV-infected patients prime Tregs into an OX40+ subset. This study is of particular importance because the experiments performed using lymphocytes isolated from primary human tissue derived from patients with different degrees of chronic liver diseases. The importance of Tregs for the prognosis of patients with HCC4, 5 has been shown previously; however, Piconese et al. have not only acquired an impressive number of patient samples, but they also carefully dissected tumor from nontumor tissue, allowing for a better understanding of the intrahepatic landscape of the immune microenvironment. This study clearly demonstrates the functional consequences of different microenvironments on immune infiltration and functionality, and vice versa, in the context of Tregs and chronic HCV infection and carcinogenesis. Several intriguing questions are raised by this work. 1) Inhibition of the OX40-OX40L axis slightly but not completely ablates the proliferation of OX40+ Tregs, indicating the presence of other factors contributing to this phenotype. 2) Since OX40/OX40L does not seem to be the sole factor controlling Treg proliferation, do M2 monocytes/macrophages control the proliferation of OX40-Tregs? 3) What other factors are influencing the differentiation and function of these cell types? Also, the data correlating viral load with OX40L expression on M2 monocytes/macrophages raises important questions about whether that is a direct or indirect relationship, as well as if other etiological factors would result in a similar phenotype. In addition, the data showing the differential release of several cytokines other than IL-12 questions their role in this setting as well as the role of other factors influencing both Tregs and other microenvironment cells. The authors briefly (data not shown) mention a cirrhosis-related expansion of OX40+ Tregs which was not observed in patients with other forms of chronic liver diseases such as HBV infection or alcoholic fatty liver disease, pointing towards a pivotal role for OX40L expression in HCV. Finally, and perhaps most important, these experiments raise questions concerning the entire carcinogenic process. How closely can comparisons between cirrhotic and noncirrhotic patient specimens in this experiment describe the pathogenesis of cirrhosis and tumorigenesis? Is a noncirrhotic sample here, which has already developed a tumor, similar to a precirrhotic liver? In addition, it is important to study and compare the same process in cirrhosis and liver cancer from a different etiology. This report provides a clear description of Treg biology in the context of chronic HCV and liver cancer, and also demonstrates both the potential and the necessity of future studies exploring further other microenvironmental factors. Xiao-Fan Wang, Ph.D.1 Firouzeh Korangy, Ph.D.2 1Duke University Medical Center, Durham, NC 2Gastrointestinal Malignancy Section, Thoracic and GI Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD