The only connection that I can find between the 2 companies is that Sigma-Aldrich have equity stakes in both Oxford Biomedica and Benitec dating back to 2005 with agreements with both of them for exclusive access etc to areas of their intellectual property. Benitec's technology is based on an "adeno-associated viral" (AAV) vector and Oxford's on lentivector technology.
Oxford and Benitec don't appear to have any direct connection that I can find and are, in fact, competitors in the same area of technology!