Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or... – Involving antigen-antibody binding – specific binding protein...
Reexamination Certificate
1999-01-20
2001-04-24
Marschel, Ardin H. (Department: 1631)
Chemistry: molecular biology and microbiology
Measuring or testing process involving enzymes or...
Involving antigen-antibody binding, specific binding protein...
C424S520000, C436S525000
Reexamination Certificate
active
06221614
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to methods of purifying samples and particularly to methods of removing prions from blood and blood products.
BACKGROUND OF THE INVENTION
Prions are infectious pathogens that cause central nervous system spongiform encephalopathies in humans and animals. Prions are distinct from bacteria, viruses and viroids. The predominant hypothesis at present is that no nucleic acid component is necessary for infectivity of prion protein. Further, a prion which infects one species of animal (e.g., a human) will not infect another (e.g., a mouse).
A major step in the study of prions and the diseases that they cause was the discovery and purification of a protein designated prion protein (“PrP”) [Bolton et al.,
Science
218:1309-11 (1982); Prusiner et al.,
Biochemistry
21:6942-50 (1982); McKinley et al.,
Cell
35:57-62 (1983)]. Complete prion protein-encoding genes have since been cloned, sequenced and expressed in transgenic animals. PrP
C
is encoded by a single-copy host gene [Basler et al.,
Cell
46:417-28 (1986)] and is normally found at the outer surface of neurons. A leading hypothesis is that prion diseases result from conversion of PrP
C
into a modified form called PrP
Sc
.
It appears that the scrapie isoform of the prion protein (PrP
Sc
) is necessary for both the transmission and pathogenesis of the transmissible neurodegenerative diseases of animals and humans. See Prusiner, S. B., “Molecular biology of prion disease,”
Science
252:1515-1522 (1991). The most common prion diseases of animals are scrapie of sheep and goats and bovine spongiform encephalopathy (BSE) of cattle [Wilesmith, J. and Wells,
Microbiol. Immunol
. 172:21-38 (1991)]. Four prion diseases of humans have been identified: (1) kuru, (2) Creutzfeldt-Jakob Disease (CJD), (3) Gerstmann-Strassler-Scheinker Disease (GSS), and (4) fatal familial insomnia (FFI) [Gajdusek, D.C.,
Science
197:943-960 (1977); Medori et al.,
N. Engl. J. Med
. 326:444-449 (1992)]. The presentation of human prion diseases as sporadic, genetic and infectious illnesses initially posed a conundrum which has been explained by the cellular genetic origin of PrP.
Most CJD cases are sporadic, but about 10-15% are inherited as autosomal dominant disorders that are caused by mutations in the human PrP gene [Hsiao et al.,
Neurology
40:1820-1827 (1990); Goldfarb et al.,
Science
258:806-808 (1992); Kitamoto et al.,
Proc. R. Soc. Lond
. 343:391-398. Iatrogenic CJD has been caused by human growth hormone derived from cadaveric pituitaries as well as dura mater grafts [Brown et al.,
Lancet
340:24-27 (1992)]. Despite numerous attempts to link CJD to an infectious source such as the consumption of scrapie infected sheep meat, none has been identified to date [Harries-Jones et al.,
J. Neurol. Neurosurg. Psychiatry
51:1113-1119 (1988)] except in cases of iatrogenically induced disease. On the other hand, kuru, which for many decades devastated the Fore and neighboring tribes of the New Guinea highlands, is believed to have been spread by infection during ritualistic cannibalism [Alpers, M. P.,
Slow Transmissible Diseases of the Nervous System
, Vol. 1, S. B. Prusiner and W. J. Hadlow, eds. (New York: Academic Press), pp. 66-90 (1979)].
The initial transmission of CJD to experimental primates has a rich history beginning with William Hadlow's recognition of the similarity between kuru and scrapie. In 1959, Hadlow suggested that extracts prepared from patients dying of kuru be inoculated into nonhuman primates and that the animals be observed for disease that was predicted to occur after a prolonged incubation period [Hadlow, W. J.,
Lancet
2:289-290 (1959)]. Seven years later, Gajdusek, Gibbs and Alpers demonstrated the transmissibility of kuru to chimpanzees after incubation periods ranging form 18 to 21 months [Gajdusek et al.,
Nature
209:794-796 (1966)]. The similarity of the neuropathology of kuru with that of CJD [Klatzo et al.,
Lab Invest
. 8:799-847 (1959)] prompted similar experiments with chimpanzees and transmissions of disease were reported in 1968 [Gibbs, Jr. et al.,
Science
161:388-389 (1968)]. Over the last 25 years, about 300 cases of CJD, kuru and GSS have been transmitted to a variety of apes and monkeys.
The expense, scarcity and often perceived inhumanity of such experiments have restricted this work and thus limited the accumulation of knowledge. While the most reliable transmission data has been said to emanate from studies using nonhuman primates, some cases of human prion disease have been transmitted to rodents but apparently with less regularity [Gibbs, Jr. et al.,
Slow Transmissible Diseases of the Nervous System
, Vol. 2, S. B. Prusiner and W. J. Hadlow, eds. (New York: Academic Press), pp. 87-110 (1979); Tateishi et al.,
Prion Diseases of Humans and Animals
, Prusiner et al., eds. (London: Ellis Horwood), pp. 129-134 (1992)].
The infrequent transmission of human prion disease to rodents has been cited as an example of the “species barrier” first described by Pattison in his studies of passaging the scrapie agent between sheep and rodents [Pattison, I. H.,
NINDB Monograph
2, D. C. Gajdusek, C. J. Gibbs Jr. and M. P. Alpers, eds. (Washington, D.C.: U.S. Government Printing), pp. 249-257 (1965)]. In those investigations, the initial passage of prions from one species to another was associated with a prolonged incubation time with only a few animals developing illness. Subsequent passage in the same species was characterized by all the animals becoming ill after greatly shortened incubation times.
The molecular basis for the species barrier between Syrian hamster (SHa) and mouse was shown to reside in the sequence of the PrP gene using transgenic (Tg) mice [Scott et al.,
Cell
59:847-857 (1989)]. SHaPrP differs from MoPrP at 16 positions out of 254 amino acid residues [Basler et al.,
Cell
46:417-428 (1986); Locht et al.,
Proc. Natl. Acad. Sci. USA
83:6372-6376 (1986)]. Tg(SHaPrP) mice expressing SHaPrP had abbreviated incubation times when inoculated with SHa prions. When similar studies were performed with mice expressing the human, or ovine PrP transgenes, the species barrier was not abrogated, i.e., the percentage of animals which became infected were unacceptably low and the incubation times were unacceptably long. Thus, it has not been possible, for example in the case of human prions, to use transgenic animals (such as mice containing a PrP gene of another species) to reliably test a sample to determine if that sample is infected with prions. The seriousness of the health risk resulting from the lack of such a test is exemplified below.
More than 45 young adults previously treated with HGH derived from human pituitaries have developed CJD [Koch et al.,
N. Engl. J. Med
. 313:731-733 (1985); Brown et al.,
Lancet
340:24-27 (1992); Fradkin et al.,
JAMA
265:880-884 (1991); Buchanan et al.,
Br. Med. J
. 302:824-828 (1991)]. Fortunately, recombinant HGH is now used, although the seemingly remote possibility has been raised that increased expression of wtPrP
C
stimulated by high HGH might induce prion disease [Lasmezas et al.,
Biochem. Biophys. Res. Commun
. 196:1163-1169 (1993)]. That the HGH prepared from pituitaries was contaminated with prions is supported by the transmission of prion disease to a monkey 66 months after inoculation with a suspect lot of HGH [Gibbs, Jr. et al.,
N. Engl. J. Med
. 328:358-359 (1993)]. The long incubation times associated with prion diseases will not reveal the full extent of iatrogenic CJD for decades in thousands of people treated with HGH worldwide. Iatrogenic CJD also appears to have developed in four infertile women treated with contaminated human pituitary-derived gonadotrophin hormone [Healy et al.,
Br. J. Med
. 307:517-518 (1993); Cochius et al.,
Aust. N.Z. J. Med
. 20:592-593 (1990); Cochius et al.,
J. Neur
Prusiner Stanley B.
Safar Jiri G.
Bozicevic Karl
Bozicevic Field & Francis LLP
Marschel Ardin H.
Ogihara Nancy
The Regents of the University of California
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