Question: Last week at the 1st International XMRV Conference at NIH headquarters the Whittemore Peterson Institute and Cerus corporation reported they developed a system to inactivate XMRV and other MLV-related viruses in donated blood. Dr. Lily Lin at Cerus claimed the INTERCEPT system inactivates pathogens by crosslinking their DNA or RNA, which blocks their ability to replicate and prevents transmission of the infection. This mechanism of action is designed to provide prospective protection against emerging threats like XMRV and its genetic variants." Any idea how this might be done? Would it harm the blood? Might something like this technology ever be used to treat infected people? Reply: The Intercept System patented by the Cerus Corporation works by photo-inactivation of blood and blood products by adding a photo-activated crosslinker, Amotosalen, which in the presence of ultraviolet A (UVA) light crosslinks DNA and inactivates a broad range of bacteria, viruses, protozoa, and leukocytes in platelet and plasma components. Upon UVA illumination a small fraction of Amotosalen reacts with the nucleic acid of contaminating pathogens and residual white blood cells and the remaining fraction undergoes photo-degradation into defined photoproducts. The levels of amotosalen and photoproducts can also be accurately quantified so that the levels of contamination can be estimated. The procedure will only harm the white blood cells and pathogens that are hit by the UVA light. This procedure is more applicable to stored blood and blood products than to patients who need their white blood cells intact to fight infection. If used in patients, blood would have to be removed and then returned to the venous blood supply after Amotosalen and UVA treatment, which would destroy all the white blood cells (and their immunity) but not the red blood cells (because they don’t have a nucleus and don’t contain DNA) during the process.