Introduction We have previously described upregulation of TLR9, which is mainly located in the endosomes, in human HCC and cell lines. Their inhibition or stimulation was associated with alteration in tumour growth. As TLR7 is also expressed on the endosomes we hypothesised that its expression may also be altered in HCC. The aim of the study was to determine whether TLR7 is expressed in human HCC and whether its modulation alters tumour growth.

Methods Study 1. Human tissue array platforms which included 102 cores of liver tissue (including 9 normal livers, 26 Hepatitis B and C, 25 HBV and HCV cirrhosis and 42 HCC) and liver tissue obtained from a DEN/NMORE model of HCC were stained for TLR7. The scoring was performed in a blinded fashion by two individual pathologists TLR7 was scored 2 when found in ≥1/3 of hepatocyte nucleus and 1 in <1/3. Study 2. Human HCC cell lines (HepG2 and Huh7) were tested for the localisation of TLR7 receptors using immunoflurocense antibody, confocal microscopy and response to stimulation was tested in the presence of a specific TLR7 agonist (Imiqumoid, Invivogen) and promega proliferation assay technique.

Results Study 1. TLR7 was expressed in the nucleus of hepatocytes in 34/42 HCC's with intense staining in 24; four out 25 positive in cirrhosis only one showed intense staining. In HBV and HCV, 5/26 were positive and 0/9 in normal [p<0.001]. In rat tissues, TLR7 was found in all HCC tumour cells only while the background either normal, dysplastic or cirrhotic was negative. Study 2. Using confocal microscopy, TLR7 was found in the cytoplasm and the nucleus of both HepG2 and Huh7 and with stimulation of TLR7 agonist the cellular proliferation significantly increased compared to control p<0.05.

Conclusion The data show that TLR7 is highly expressed in human HCC's, animal model of HCC and in cell lines. Importantly, the background cirrhotic liver does not express TLR7. Their stimulation is associated with marked increase in proliferation. These data suggest that TLR7 may be a future target of therapy in HCC.

Competing interests None declared.