B lymphocytes repress hepatic tumorigenesis but not development in Hras12V transgenic mice

Increasing reports show noninflammation underlying HCC, challenging our understanding of the roles of the immune system in hepatocarcinogenesis. By exploring a mouse model of hepatic tumor induced by hepatocyte-specific expression of the Hras12V oncogene without obvious inflammation, we found that the proportion of B cells, but not T cells, progressively and significantly decreased in 3, 5-month-old transgenic mice (Tg) compared with non-transgenic mice. Notably, the proportions of total and activated B and T cells all significantly decreased in 9-month-old Tg with multiple massive hepatic tumors. Together with the decreased B cell proportion, serum IgG1/2 also significantly decreased in 5, 9-month-old Tg. Interestingly, homozygous Tg showed significantly higher B cell proportion and IgG2 levels, accompanied by significantly lower incidences of liver nodules but not adenomas and carcinomas compared with heterozygous Tg. Treatment of Tg with PCI-32765, a potent Bruton's tyrosine kinase (BTK) inhibitor for suppressing B cell proliferation and activation, significantly decreased the B cell proportion and IgG2 levels, accompanied by a significantly higher incidence of liver nodules, but had no effects on adenoma and carcinoma. Treatment of Tg with insulin-like growth factor 1 (IGF-1) significantly increased the B cell proportion and IgG2 levels, accompanied by a significantly lower incidence of liver nodules and carcinoma, but had no effects on adenoma. Conclusively, B cells and IgG2 may play important roles in suppressing hepatic tumorigenesis, but not development. In addition, hepatocyte-specific expression of the ras oncogene may play roles in suppressing B cells, while developed hepatic tumors suppress both B and T cells.