Developments in biological standardization最新文献

Since 1993, consistent with its statutory responsibility to ensure that regulated products are safe, pure, and free of << extraneous organisms, >> the United States Food and Drug Administration (FDA) has requested that, with certain exceptions, bovine-derived materials from animals born in or residing in countries where bovine spongiform encephalopathy has occurred, should not be used to manufacture products intended for humans. FDA's Center for Biologics Evaluation and Research (CBER) has specifically recommended that serum used to produce biologicals be obtained from sources << certified to be free from contaminants and adventitious agents, such as the agent responsible for the production of Bovine Spongiform Encephalopathy. >> The United States Department of Agriculture (USDA) has prohibited importation of such serum for use in products. FDA staff are aware that bovine blood, including foetal blood, and placental tissues and fluids that might contaminate foetal serum have not been found to contain the infectious agent of BSE, and that those tissues are considered by most authorities to have little risk for transmitting disease to humans or animals. However, studies of BSE have been limited in size and sensitivity, and several experimental studies of scrapie and CJD in rodents found their blood to be infectious. In addition, a recent unpublished study of BSE (requiring confirmation) reported finding infectivity in the bone marrow of cattle. Possible transmission of BSE from cows to calves, although unlikely to constitute a major mode for maintaining the BSE outbreak, has also not been rigorously ruled out. Considering the special nature of biological products, especially of vaccines intended for widespread use in children, it seems prudent for U.S. regulatory authorities to continue current conservative policies that discourage or prohibit the use of bovine serum from countries with BSE.

I firmly believe that we should use animal-based studies only when there is no satisfactory alternative. However, the development of meaningful alternatives requires good science. Regrettably, all too often, we can see examples of potency tests which have not been properly developed and validated and are therefore incapable of providing us with the information that they should be designed to provide.

With increasing frequency new methods are being developed for the assessment of the quality of biological products. Before these methods can be considered for regulatory acceptance, their relevance and reliability must be established in a formal validation study. Such a study should be tailor-made, depending on the particular purpose and goal of the new method. However, a set of general principles can be given, according to which a validation study should be conducted. Essential ingredients in a validation study are the three Cs for Common sense, Commitment and Communication. Common sense in the design of the study, Commitment of the participating laboratories and Communication between the parties involved. An overview will be given of the various stages of a validation study, the time period needed (Table 1) and a number of problems that can be encountered will be discussed.

Regulatory agencies responsible for protecting public health must be concerned with reducing or preventing opportunities for exposure of humans and animals to the agents of transmissible spongiform encephalopathies (TSEs), especially bovine spongiform encephalopathy and Creutzfeldt-Jakob disease. The United States Food and Drug Administration (FDA) has taken precautionary actions to assure that regulated products are free of such infectious agents, from both animal and human sources, including the issuing of a regulation and a number of guidance documents. With regard to TSEs, the materials of greatest concern to FDA's Center for Biologics Evaluation and Research have been bovine gelatin, tallow derivatives and serum, as well as human-derived products and excipients including blood, blood components and plasma derivatives. A number of newer issues regarding TSEs now confront agencies responsible for protecting public health. It would be of great help to have standard reference materials available to assist in the diagnosis of the diseases and to detect the infectious agents.

Removal of virus infectivity from blood and biopharmaceutical products prepared from blood is an issue of considerable importance. Irrespective of the methods that are chosen it is vital that the biological activity of the product is not impaired. For blood and unfractionated plasma or serum, the problem is even more challenging. Selective inactivation of the genome is the key step in the preparation of killed virus vaccines. Imines have been used for more than 30 years for the preparation of inactivated foot-and-mouth disease virus vaccines without any evidence of survival of virus infectivity. Moreover, the immunogenicity of the virus is unimpaired. Viruses belonging to all the recognised families can be inactivated by imines. The biological properties of several proteins, including the cell growth-promoting factors in calf serum, are not impaired using conditions which ensure the inactivation of > 10(15) infectious units of poliovirus and foot-and-mouth disease virus (FMDV). Moreover, both viruses can be inactivated by imines at 4 degrees C, thus providing a method for removing infectivity from protein preparations which are unstable at higher temperatures. The mechanism by which FMDV is inactivated has been studied. We found that the RNA extracted from the virus after inactivation at 4 degrees C was not degraded and contained no hidden breaks but nevertheless was non-infectious. However, it could be amplified by PCR using primers corresponding to the gene coding for a portion of the viral RNA polymerase, but not from that coding for VP1, one of the structural proteins, showing that alteration of a base or bases had occurred in that region.

To quantify the biological activity of different cytokine preparations with different specific activities by bioassay, mass units cannot be used and biological activity has to be expressed as << biological potency units >>. The biological unit requires definition by a standard that is assay-independent (especially when measuring a particular type of biological activity). Once the unit is defined, it can be used in any laboratory, thus providing a means of ensuring uniformity throughout the world in the designation of potency of different biological preparations. The World Health Organisation (WHO) standardization programme involves the production of biologically stable, well-characterised potency and immunoassay standards that are available world-wide using a single international unitage. These international standards have been used to reduce dramatically the variation in estimates of cytokine preparations within and between laboratories for immunoassays and bioassays.