The effects of RTKIs vary from immunosuppression to immune-activation, depending on the pathways inhibited by the specific agent. In 2008 the RTKI sorafenib was approved by the Food and Drug Administration (FDA) to treat advanced HCC, increasing the median overall survival from 7.9 to 10.7 months.5

However, sorafenib did not delay time to symptomatic progression and the cost of treatment remains prohibitive. Furthermore, sorafenib caused reduced proliferation of T cells (CD4 and CD8) and impaired maturation and function of dendritic cells (DCs) leading to an immune-suppressed state.6 Sunitinib is a small molecule RTKI that was approved by the FDA for the treatment of advanced clear cell renal cell carcinoma (ccRCC) and gastrointestinal stromal tumors (GIST) in 2006.7 Sunitinib treatment induces both antiangiogenic and antitumor activity. In contrast to sorafenib, sunitinib decreases the population Opaganib order of regulatory T cells (Tregs) and circulating myeloid-derived suppressor cells (MDSCs), and has no detectable negative effects on DCs.6 Recent work demonstrates that sunitinib-induced immune activation is associated with STAT3 inhibition.8 Ablating STAT3 in tumor-associated myeloid cells increases the activation of DCs and CD8+ T cells while reducing the activity of tumor-associated Tregs.9 These findings indicate

that sunitinib may play a role in activating the immune response in addition to its role in direct tumor killing. However, the tumor antigen-specific effects of sunitinib treatment in HCC remain unclear. Although early analysis of a recent Phase III trial suggests that sorafenib may be more effective Lumacaftor purchase than sunitinib as a monotherapy for HCC,10 in this study we sought to evaluate the efficacy and mechanisms of sunitinib in combination with immunotherapy for this deadly

disease. To facilitate mechanistic evaluation of HCC tumorigenesis and treatment, distinct HCC mouse models, including xenograft tumors, chemical carcinogen-induced tumors, viral carcinogen-induced tumors, and genetically engineered tumors,11 have been established. However, a practical and reproducible model using immunocompetent mice is needed for testing immune therapies. Transgenic MTD2 mice express SV40 Amino acid T antigen (Tag) under control of the major urinary protein (Mup) promoter,12 and consistently develop hepatic dysplasia leading to frank HCC by 8-10 weeks of age.13 However, these mice uniformly express Tag in the entire population of hepatocytes from an early age, leading to an overwhelming hepatic tumor burden and profound immune tolerance toward Tag. Here we developed an orthotopic model of HCC through seeding a small number of tumorigenic hepatocytes from MTD2 mice into the livers of syngeneic immunocompetent C57BL/6 mice. In this novel model, an average of 2.3 tumor nodules per mouse develop in a background of normal liver parenchyma.