Making blood safe: A filtration technology for removing infectious prions from red-cell concentrates

is tolerant to normal prions that are produced constitutively by the host. CJD is the most common form of human TSE, and although usually sporadic (sCJD), it has been transmitted from person to person through medical instruments and transplant of tissues or organs. In the latter instances, it has been referred to as iatrogenic (iCJD)3,4. A variant of CJD (vCJD) appeared in the UK in 1995, as a result of the consumption of tissue or meat products from cattle infected with BSE. This variant form of CJD has been shown to have significant involvement of the lymphoid organs, as demonstrated by the presence of abnormal prion (PrPSc) and infectivity in lymphoreticular organs, such as spleen, tonsils and appendix, all of which are interactive with circulating blood5–7. Recent animal data, together with the reported cases Since the first case of vCJD in 1995, 164 people worldwide have died from the disease, which is believed to have emerged as a result of the consumption of meat from cattle infected with BSE. A new filtration technology that removes prions from red cell concentrates (RCCs), the most widely transfused blood component, has been developed and is available commercially in Europe this summer. The technical approaches used in developing this filtration technology, along with the proposed mechanisms for removal of prions by the device, are discussed in this article. Prion diseases are believed to be caused by proteinaceous infectious agents called prions1,2. Unlike viruses, bacteria, fungi and parasites, prions do not contain DNA or RNA and are therefore not destroyed by chemicals that target nucleic acids. In contrast with viruses, prions are non-immunogenic; that is, they do not elicit an immune response, because the host of probable transmission of vCJD in humans from transfused blood products, have raised the concerns about the transmission of the causative agent through transfusion of blood products8–11. In addition, PrPSc has also been found to be present in the spleen and muscles of patients with classical CJD and in the blood of affected mice and hamsters12,13, raising the possibility that this disease too may be transmitted through blood transfusion. There are no diagnostic tests for the detection of infectious prions in the blood of potential blood donors who are asymptomatic for the disease, nor can infectious prions be inactivated or destroyed by currently available technologies without destroying the essential therapeutic product. To deal with these challenges, several precautionary measures