Abstract 991: Platelets inhibit hepatocellular carcinoma growth in the context of nonalcoholic fatty liver disease
Authors: McVey John C. , Ma Chi , Diggs Laurence , Fu Qiong , Greten Tim F. 
Published: September 2020

Abstract
Purpose: Non-alcoholic fatty liver disease (NAFLD) is a major risk factor for hepatocellular carcinoma (HCC) in the US and globally. Platelets have been recognized as an important element of immune system and recently, platelets have been shown to be activated and aggerate in the livers of mice and humans with NAFLD. However, the role of platelets in HCC disease progression in NAFLD is still unknown.
Methods: In this study, mice underwent an intrahepatic injection of an HCC cell line and were fed a methionine choline deficient (MCD) diet to generate an HCC NAFLD mouse model. The mouse model was then used to interrogate the interplay between platelets, immune responses and HCC growth within a liver with NAFLD. Anti-GP1bα or clopidogrel were used to deplete or inhibit platelet function and effects on tumor growth and immune cell activation were studied. Platelets express leukotriene receptors, and the possible involvement of leukotrienes was tested with zileuton, a leukotriene inhibitor. Finally, antibody dependent T cell depletion was used to identify the effector cells controlling HCC tumor development.
Results: NAFLD mice with HCC treated with clopidogrel showed a close to 3-fold increase in tumor weight compared to vehicle control (50.6g vs 147.8g P&lt;0.05) as well as tumor-to-liver weight ratio (0.05 vs 0.13 P&lt;0.05). CD4+ and CD8+ T-cells from the livers of NAFLD mice showed a 2- to 3-fold increase in CD69+ T-cells compared to non-NAFLD mice (24.2% vs 9.1% P&lt;0.05 in CD4+ and 23.7% vs 8.9% P&lt;0.05 in CD8+, respectively). Interestingly, in NAFLD mice treated with clopidogrel, there was a decrease in CD69+ compared to NAFLD mice treated with control in both CD4+ (18.3% vs 24.2% P&lt;0.05, respectively) and CD8+ (15.32% vs 23.7% P&lt;0.05, respectively) T-cells. Consistently, when NAFLD mice were depleted of platelets with anti-GP1bα, there was a significant decreased in T cell activation compared to IgG control. Similarly, when NAFLD mice were treated with zileuton, there was a decrease in IFN-gamma production in liver isolated CD4+ (5.4% vs 3.1% P=0.12) and CD8+ (23.7% vs 16.7% P&lt;0.05) T-cells compared to vehicle control treated mice. Finally, the clopidogrel treatment increased HCC tumor-to-liver weight ratio was abolished in mice treated with anti-CD8 (0.29 vs 0.23 P&gt;0.05) but not in mice treated with anti-CD4 (0.11 vs 0.16 P&lt;0.05).
Conclusion: The results of this study show that in NAFLD livers, platelets increase immune cell activation and inhibit HCC in a CD8+ T-cell dependent manner. The results also suggest that leukotrienes may play a key role in modulating this response, but further studies are required to better characterize this observation.
Citation Format: John C. McVey, Chi Ma, Laurence Diggs, Qiong Fu, Tim F. Greten. Platelets inhibit hepatocellular carcinoma growth in the context of nonalcoholic fatty liver disease [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 991.