Drug – bio-affecting and body treating compositions – Antigen – epitope – or other immunospecific immunoeffector – Virus or component thereof
Reexamination Certificate
1994-05-26
2001-08-14
Allen, Marianne P. (Department: 1631)
Drug, bio-affecting and body treating compositions
Antigen, epitope, or other immunospecific immunoeffector
Virus or component thereof
C424S185100, C424S204100, C435S005000, C435S069300, C435S069900, C530S350000, C530S395000, C530S826000
Reexamination Certificate
active
06274148
ABSTRACT:
DESCRIPTION
1. Technical Field
This invention relates to the general fields of recombinant protein expression and virology. More particularly, the invention relates to glycoproteins useful for diagnosis, treatment, and prophylaxis of Hepatitis C virus (HCV) infection, and methods for producing such glycoproteins.
2. Background of the Invention
Non-A, Non-B hepatitis (NANBH) is a transmissible disease (or family of diseases) that is believed to be virally induced, and is distinguishable from other forms of virus-associated liver disease, such as those caused by hepatitis A virus (HAV), hepatitis B virus (HBV), delta hepatitis virus (HDV), cytomegalovirus (CMV) or Epstein-Barr virus (EBV). Epidemiologic evidence suggests that there may be three types of NANBH: the water-borne epidemic type; the blood or needle associated type; and the sporadically occurring community acquired type. The number of causative agents is unknown. However, a new viral species, hepatitis C virus (HCV) has recently been identified as the primary (if not only) cause of blood-borne NANBH (BB-NANBH). See for example PCT WO89/046699 and U.S. patent application Ser. No. 07/355,002, filed May 18, 1989 now abandoned. Hepatitis C appears to be the major form of transfusion-associated hepatitis in a number of countries or regions, including the United States, Europe, and Japan. There is also evidence implicating HCV in induction of hepatocellular carcinoma. Thus, a need exists for an effective method for preventing and treating HCV infection.
The demand for sensitive, specific methods for screening and identifying carriers of HCV and HCV-contaminated blood or blood products is significant. Post-trans-fusion hepatitis (PTH) occurs in approximately 10% of transfused patients, and HCV accounts for up to 90% of these cases. The major problem in this disease is the frequent progression to chronic liver damage (25-55%).
Patient care, as well as the prevention of transmission of HCV by blood and blood products or by close personal contact, requires reliable diagnostic and prognostic tools to detect nucleic acids, antigens and antibodies related to HCV. In addition, there is also a need for effective vaccines and immunotherapeutic therapeutic agents for the prevention and/or treatment of the disease.
HCV appears in the blood of infected individuals at very low rates relative to other infectious viruses, which makes the virus very difficult to detect. The low viral burden is probably the primary reason that the causative agent of NANB hepatitis went so long undetected. Even though it has now been cloned, HCV still proves difficult to culture and propagate. Accordingly, there is a strong need for recombinant means of producing diagnostic/therapeutic/prophylactic HCV proteins.
DISCLOSURE OF THE INVENTION
It has been found that two HCV proteins, E1 and E2, appear to be membrane associated asialoglycoproteins when expressed in recombinant systems. This is surprising because glycoproteins do not usually remain in mannose-terminated form in mammals, but are further modified with other carbohydrates: the mannose-terminated form is typically only transient. In the case of E1 and E2 (as expressed in our systems), the asialoglycoprotein appears to be the final form. E1 (envelope protein 1) is a glycoprotein having a molecular weight of about 35 kD which is translated from the predicted E1 region of the HCV genome. E2 (envelope protein 2) is a glycoprotein having a molecular weight of about 72 kD which is translated from the predicted NSl (non-structural protein 1) region of the HCV genome, based on the flaviviral model of HCV. As viral glycoproteins are often highly immunogenic, E1 and E2 are prime candidates for use in immunoassays and therapeutic/prophylactic vaccines.
The discovery that E1 and E2 are not sialylated is significant. The particular form of a protein often dictates which cells may serve as suitable hosts for recombinant expression. Prokaryotes such as
E. coli
do not glycosylate proteins, and are generally not suitable for production of glycoproteins for use as antigens because glycosylation is often important for full antigenicity, solubility, and stability of the protein. Lower eukaryotes such as yeast and fungi glycosylate proteins, but are generally unable to add terminal sialic acid residues to the carbohydrate complexes. Thus, yeast-derived proteins may be antigenically distinct from their natural (non-recombinant) counterparts. Expression in mammalian cells is preferred for applications in which the antigenicity of the product is important, as the glycosylation of the recombinant protein should closely resemble that of the wild viral proteins.
New evidence indicates that the HCV virus may gain entry to host cells during infection through either the asialoglycoprotein receptor found on hepatocytes, or through the mannose receptor found on hepatic endothelial cells and macrophages (particularly Kupffer cells). Surprisingly, it has been found that the bulk of natural E1 and E2 do not contain terminal sialic acid residues, but are only core-glycosylated. A small fraction additionally contains terminal N-acetylglucosamine. Accordingly, it is an object of the present invention to provide HCV envelope glycoproteins lacking all or substantially all terminal sialic acid residues.
Another aspect of the invention is a method for producing asialo-E1 or E2, under conditions inhibiting addition of terminal sialic acid, e.g., by expression in yeast or by expression in mammalian cells using antibiotics to facilitate secretion or release.
Another aspect of the invention is a method for purifying E1 or E2 by affinity to lectins which bind terminal mannose residues or terminal N-acetylglucosamine residues.
Another aspect of the invention is an immunogenic composition comprising a recombinant asialoglycoprotein selected from the group consisting of HCV E1 and E2 in combination with a pharmaceutically acceptable vehicle. One may optionally include an immunological adjuvant, if desired.
Another aspect of the invention is an immunoassay reagent, comprising a recombinant asialoglycoprotein selected from the group consisting of HCV E1 and E2 in combination with a suitable support. Another immunoassay reagent of the invention comprises a recombinant asialoglycoprotein selected from the group consisting of HCV E1 and E2 in combination with a suitable detectable label.
Another aspect of the invention concerns dimers and higher-order aggregates of E1 and/or E2. One species of the invention is an E2 complex. Another species of the invention is an E1:E2 heterodimer.
Another aspect of the invention is an HCV vaccine composition comprising E1:E2 aggregates and a pharmaceutically acceptable carrier.
Another aspect of the invention is a method for purifying E1:E2 complexes.
MODES OF CARRYING OUT THE INVENTION
A. DEFINITIONS
The term “asialoglycoprotein” refers to a glycosylated protein which is substantially free of sialic acid moieties. Asialoglycoproteins may be prepared recombinantly, or by purification from cell culture or natural sources. Presently preferred asialoglycoproteins are derived from HCV, preferably the glycoproteins E1 and E2, most preferably recombinant E1 and E2 (rE1 and rE2). A protein is “substantially free” of sialic acid within the scope of this definition if the amount of sialic acid residues does not substantially interfere with binding of the glycoprotein to mannose-binding proteins such as GNA. This degree of sialylation will generally be obtained where less than about 40% of the total N-linked carbohydrate is sialic acid, more preferably less than about 30%, more preferably less than about 20%, more preferably less than about 10%, more preferably less than about 5%, and most preferably less than about 2%.
The term “E1” as used herein refers to a protein or polypeptide expressed within the first 400 amino acids of an HCV polyprotein, sometimes referred to as the E or S protein. In its natural form it is a 35 kD glycoprotein which is found strongly membrane-associated. In most natural HCV strains, the E1 protein is
Berger Kim M.
Choo Qui-Lim
Gervase Barbara A.
Hall John A.
Houghton Michael
Allen Marianne P.
Blackburn Robert P.
Chiron Corporation
Harbin Alisa A.
Robins Roberta L.
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