Other cell associated viruses and safety considerations Mouse/human hybridomas can be established by fusing human EBV transformed lymphoblastoid cells with mouse plasmacytomas. As these cells were EBV transformed, the hybridoma cells are potential EBV producers. Cells transformed by EBV are potential EBV producers (e.g. Namalva), and the downstream processing protocol as well as the safety testing have to take this fact into account (Cartwright, 1994; Robertson, 1996) (see Section on 'Process validation -downstream -processing -viral clearance').