Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or... – Involving antigen-antibody binding – specific binding protein...
Reexamination Certificate
1998-07-21
2003-10-14
Duffy, Patricia A. (Department: 1645)
Chemistry: molecular biology and microbiology
Measuring or testing process involving enzymes or...
Involving antigen-antibody binding, specific binding protein...
C435S007320, C435S007340, C435S007940, C435S007950, C435S018000, C435S019000, C435S195000, C435S196000, C436S517000, C436S518000, C436S536000
Reexamination Certificate
active
06632614
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is directed to recombinant DNase B derived from the pathogenic bacterium
Streptococcus pyogenes
, methods for its production, and methods for its use.
Despite advances in the prevention and treatment of bacterial infection, a number of bacterial pathogens remain serious problems in medical practice and continue to cause severe, even fatal disease. One of these pathogens is
S. pyogenes
. Among the diseases caused by
S. pyogenes
are streptococcal pharyngitis (“strep throat”), scarlet fever, and their suppurative complications, including cervical adenitis, otitis media, mastoiditis, peritonsillar abscesses, meningitis, pneumonitis, pneumonia, puerperal sepsis, cellulitis of the skin, impetigo, lymphangitis, erysipelas, acute glomerulonephritis, and rheumatic fever.
Such infections often occur in hospitals (nosocomial infection), particularly in patients whose normal immune system functioning is suppressed. The latter category includes patients with AIDS, patients taking immunosuppressive drugs for cancer or to prevent transplant rejection, and patients having poor circulation, e.g., patients with diabetes.
Because these diseases require rapid and effective treatment to eradicate the suppurative lesions and prevent sequelae caused by immunological reactions to persisting suppurative lesions, prompt diagnosis of the presence of
S. pyogenes
is essential in patients in whom such infections are suspected. Failure to diagnose
S. pyogenes
promptly can greatly complicate treatment or even make it impossible.
Although detection methods for
S. pyogenes
are currently available, these methods have defects, particularly in clinical applications.
Among the methods of detection of
S. pyogenes
is the detection of the presence of antibodies against DNase B, a DNA-degrading enzyme produced by
S. pyogenes
. This enzyme, which is excreted from
S. pyogenes
during infection, initiates development of substantial titers of antibody in patients who go on to develop acute rheumatic fever and acute glomerulonephritis.
Although other serum-based diagnostic tests for these rheumatic fever and glomerulonephritis are available, including the detection of antibodies to streptolysin O, and to hyaluronidase, assays for anti-DNase B antibodies offer certain advantages, because DNase B is found among nearly all strains of group A beta-hemolytic streptococci, and because high DNase B titers are found in patients with infections of the skin and pharynx.
Although a number of commercially-available tests exist for the assay of anti-DNase B antibody, these tests have defects. As indicated above, an improved test is greatly needed.
The commercially-available tests fall into three categories: (1) a DNase B inhibition-based assay using the ability of the antibody to inhibit enzymatic activity; (2) a latex agglutination assay for antibody against a variety of
S. pyogenes
antigens; and (3) a turbidimetric inhibition assay. ELISA assays have also been used in the research laboratory, but, as detailed below, they have not yet proven suitable for routine clinical application.
The DNase B inhibition assay is very slow, and typically requires about 4-8 hours to perform. Thus, in situations in which confirmation of anti-DNase B antibody is required rapidly so the treatment can be started as soon as possible should the presence of
S. pyogenes
be confirmed, the enzyme inhibition assay is not particularly useful.
The latex agglutination assay is designed to detect antibodies to five
S. pyogenes
antigens. However, test results indicate poor agreement between the latex agglutination assay and a specific anti-DNase B tests. In one study, G. C. Klein & W. L. Jones, “Comparison of the Streptozyme Test with the Antistreptolysin O, Antideoxyribonuclease B, and Antihyaluronidase Tests,”
App. Microbiol.
21:257-259 (1971), 12 out of 80 patients that tested negatively in the latex agglutination assay were, in fact, positive for anti-DNase B antibody. This high level of false negative results means that the test is undesirable for clinical use.
The turbidimetric inhibition assay depends on the inhibition of agglutination of latex particles coated with anti-DNase B antibody by a limiting quantity of a crude preparation of DNase B in the presence of serum containing anti-DNase B antibody, which competes for the antibody on the latex particles. This assay, which is described in U.S. Pat. No. 5,055,395, incorporated herein by this reference, is relatively insensitive. Therefore, it is not suitable for use in the early stages of
S. pyogenes
infection, and it is precisely this period when accurate detection of the anti-DNase B antibody is most important. Additionally, the reagents used in the turbidimetric inhibition assay are difficult to manufacture.
ELISA-based assays for anti-DNase B antibody are reported in M. A. Gerber et al., “Enzyme-Linked Immunosorbent Assay of Antibodies in Human Sera to Streptococcal DNase B,”
J. Lab. Clin. Med.
95:258-265 (1980). Although these assays have proven effective as research tools, their scale-up for commercial use, particularly in clinical practice, has been impractical. This is because such scale-up would require production and purification of the DNase B enzyme of
Streptococcus pyogenes
, which is, as detailed above, a serious pathogen. Not only would extremely costly containment methods be required for growth of this pathogenic bacterium in the quantity required to produce sufficient enzyme for commercialization of the ELISA assay, the media required for the growth of
S. pyogenes
is very complex and expensive. These concerns have seriously hampered development of a commercial version of the ELISA assay for anti-DNase B antibody.
Therefore, there exists a need for an improved, rapid, and specific assay for anti-DNase B antibody. Preferably, such an assay would be usable by a physician in his office and would require minimal equipment. This is because patients with diseases such as strep throat or scarlet fever typically see their family physician prior to hospitalization, and accurate diagnosis of
S. pyogenes
infection at that point would be preferable to a subsequent diagnosis made only when the patient has been hospitalized.
The development of such an improved assay is dependent on the availability of large quantities of DNase B enzyme itself. Therefore, there is also a need for a method for the production of
S. pyogenes
DNase B enzyme using a procedure that can be scaled up to produce commercial quantities of the enzyme without requiring complex, unwieldy, and expensive containment measures.
SUMMARY
We have cloned and expressed the gene for
S. pyogenes
DNase B in
Escherichia coli
, allowing convenient and efficient production of the DNase B enzyme without requiring the growth of
S. pyogenes.
This cloning procedure results in substantially purified DNA encoding an amino acid sequence selected from the group consisting of the amino acid sequence of: (i)
Streptococcus pyogenes
DNase B enzyme as shown in
FIG. 4
, below, which enzyme includes at its amino terminus an arginine (R) residue derived from a leader peptide and absent in the natural DNase B enzyme; and (ii) a sequence encoding a functional equivalent of
S. pyogenes
DNase B enzyme, optionally including at least one residue of the leader peptide. The DNA is substantially free of DNA other than DNA encoding the
S. pyogenes
DNase B sequence of
FIG. 4
, DNA encoding a functional equivalent of
S. pyogenes
DNase B enzyme, and DNA encoding the leader peptide.
Preferably, the DNA further comprises a DNA sequence coding for a leader peptide fused to the amino terminus of
S. pyogenes
DNase B enzyme.
Most preferably, the DNA cloned is the DNA whose sequence is given in
FIG. 3
, including the DNA coding for the entire amino acid sequence of
S. pyogenes
DNase B enzyme and the leader peptide.
Another aspect of the invention is expression vectors for
Streptococcus pyogenes
DNase B enzyme comprising the DNA sequences described above operatively linked to at least one con
Adams Craig W.
Belei C. Marina
Pang Patty P. Y.
Beckman Coulter Inc.
Duffy Patricia A.
Gates & Cooper
Hill D. David
May William H.
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