US biotech firm Gilead Sciences announced plans Monday to acquire rival Pharmasset, a group specializing in treatments for AIDS and hepatitis, for $11 billion. The deal at $137 per share \"represents an important and exciting opportunity to accelerate Gilead\'s effort to change the treatment paradigm for HCV (hepatitis C virus) infected patients by developing all-oral regimens for the treatment of the disease regardless of viral genotype,\" California-based Gilead said.