Hal Baker, senior vice president of Pall Medical, reviewed the latest study results that validate the filter's removal of infectious prions from red cell concentrates, the most widely transfused blood component. He reported that the filter's innovative surface modification technology provides the dual benefit of concurrently reducing leukocytes (log 5) and infectious prions (below the limit of detection of the Western blot assay). Roughly 40 percent of prion infectivity in blood resides in leukocytes (cell-associated) and 60 percent in plasma (non-cell associated). The new filter removes 99 percent of vCJD infectious agent, both cell- and non-cell associated, and also removes all types of prions including aggregated, denatured and normal.
He also presented results from a battery of in vitro and in vivo studies demonstrating the safety and efficacy of the filter for use with red blood cells. The filter does not damage red cells and does not impact their therapeutic value based on parameters of purity, efficacy and 42 days stability.
Transfusion medicine professionals and the public perceive the risk of developing vCJD from a blood transfusion as a growing, not a declining, threat to public safety. Public health officials believe that the problem is not limited to the UK, where a majority of the early cases of vCJD have been identified, or to Europe, but is a potential global threat that includes the U.S. and Canada.
"Due to worldwide public health concern about whether outbreaks of mad cow disease (Bovine Spongiform Encephalopathy or BSE) will result in the large-scale spread of the infection to humans, there is a need to consider new methods to safeguard the blood supply from the risk of transmission of infectious prions," Baker said. Animal studies demonstrate that the agent that causes vCJD can be transmitted through blood transfusion. The United Kingdom confirmed that a patient who received donor blood during an operation in 1997 developed vCJD and died six years later. The latest scientific findings show that vCJD is not confined to a single genotype, thereby placing a majority, not a minority, of the population at risk. The existence of asymptomatic prion carriers means that there may be many more cases of undetected prion infections lying dormant. Combined with the unknown time interval between exposure and onset of symptoms, estimating the true size of a second wave of transmission or a vCJD epidemic is increasingly complex.
"Equally important, there is a serious need to determine whether the current measures to prevent the disease are sufficient," added Baker. "We need to balance the efficacy of these measures against the safety and availability of life-saving blood components." Baker explained how donor deferral policies have a reverberating impact on blood availability. A loss of one percent of donors involves approximately 75,000 to 85,000 individuals in the first year, not to mention their future potential donations. There is currently a ban on blood donations from people who lived in countries with BSE-infected cattle.
In addition to deferral policies, Baker addressed the myriad difficulties associated with testing human blood for prions, specifically the potential impact on donors who are subjected to it. Although no human blood test is available, he explained that any new prion test, regardless of its makeup, raises ethical concerns. These tests must have the absolute highest sensitivity and specificity performance to minimize false positive results when applied to an always-fatal neurodegenerative disease. He also noted that since prions lack nucleic acid, they can not be inactivated by pathogen inactivation procedures that exist today or in development.
"The Leukotrap Affinity Prion Reduction Filter represents the first of a new generation of proprietary "Smart" filters that will concurrently reduce leukocytes and infectious prions to minimize the risk of transmission of variant CJD through blood transfusion," said Baker. "Smart" filters can selectively capture and remove target contaminants or components while allowing the desired components to pass through even those of equal size.
He explained the advantages of targeted removal of prions through affinity filtration. Filtration is more cost effective than molecular biology testing, more efficacious than inactivation technology and is a widely applicable process that can be easily scaleable and efficiently integrated with current blood handling logistics and good manufacturing practices.
"Pall's approach to improving the safety of the global blood supply grows out of our core competency in material science engineering and proprietary surface modification technology combined with our legacy of leadership in blood filtrations technology," Baker added. "We are uniquely positioned to introduce novel "Smart" filter technology as a key element in a new blood safety paradigm.
Pall Corporation expects to introduce the Leukotrap Affinity Prion Reduction Filter commercially in Europe this spring followed by submission to regulatory agencies in both Canada and the U.S. The Company is also studying the filter as a device to aid in the detection of BSE in cattle before entering the food supply.
Source: Pall Corporation