The objective of the study is to provide long term expression of Factor IX in subjects with severe hemophilia B. SB-FIX is a therapeutic for ZFN-mediated genome editing which will be delivered by adeno-associated virus (AAV)-derived vectors. SB-FIX is intended to function by placement of a corrective copy of the Factor IX transgene into the genome of the subject's own hepatocytes, under the control of the highly expressed endogenous albumin locus, and is expected to provide permanent, liver-specific expression of Factor IX for the lifetime of a hemophilia B subject.