FIX output and liver VCN were overlapping in hemophilia B mice treated with LV‐FIX‐Padua produced in B2M‐positive or B2M‐negative cells by transient transfection, or by the most productive clone of the B2M‐negative producer cell line, further confirming comparable liver gene transfer by LV produced by either cells and methods (Fig 4E and F). The gene discussed is B2M; the disease is hemophilia.