ATTENUATED, LIVE VACCINE FOR DELAWARE STRAIN IBDV

Abstract: Live, attenuated Delaware infectious bursal disease viruses are screened for effectiveness by a monoclonal antibody specific for said Delaware strain. Those which are not bound by the antibody are not or may not be as effective in conferring protection against homologous wild type infectious bursal disease infection. Currently available live, attenuated vaccines do not include a virus having the binding site specified. A monoclonal antibody specific for the Delaware strain also provides a vaccine for passive immunization.

Description: Description Attenuated, Live Vaccine for Delaware Strain IBDV Technical Field The invention pertains to a vaccine prepared from a live, but attenuated virus of the Delaware strain inducing infectious bursal disease in chickens. Specifically, a vaccine is prepared by screening potential attenuated virus candidates with a non-neutralizing specific monoclonal antibody. Further, a highly specific neutralizing monoclonal antibody is provided as an alternative, effective vaccine. Background Art In the inventors' related applications, including U.S. Patent Application Serial No. 07/423,752, entitled MONOCLONAL ANTIBODIES FOR INFECTIOUS BURSAL DISEASE, VACCINES AND ASSAYS FOR USE THEREWITH, which in turn is a CIP application of U.S. Application Serial No. 07/061,083, now U.S. Patent 4,956,452 and U.S. Application Serial No. 07/227,311, now U.S. Patent 5,064,464 the development and study of a large number of monoclonal antibodies (Mab) specific for various strains of infectious bursal disease is discussed. As related in the above-cited U.S. Application Serial No. 07/423,752, the entire content of which is incorporated herein by reference, a panel of antibodies has been developed, each specific to a particular type of infectious bursal disease virus. That virus has been, by means of antibody assays, categorized into three separate classifications, classic, Delaware and GLS. At the time of filing of this application, the Delaware strain, of all pure strains, appears to be the dominant infectious bursal disease virus in the Eastern United States. Certainly, it is a substantial and continuing threat to the U.S. poultry industry. Wild-type Delaware IBDV have been known for some time, and are commercially available. There are a number of vaccines for this Delaware-type IBDV commercially available, including both "killed" and "live" vaccines. A killed vaccine is prepared by culturing the virus itself, in e.g., chicken eggs and the like, and subsequently "killing" the virus by heat, chemical treatment and the like. In a live vaccine, the virus is present in a living form, but has been attenuated to reduce or eliminate its virulency, by serial passage through cell culturing and the like. Thus, the "virus" component of a live vaccine is attenuated. Methods for preparation thereof are known in the art, and do not constitute, per se, an aspect of this invention. No currently available vaccine for wild-type Delaware IBDV is based on or comprises a non-virus active element, such as a monoclonal antibody. During the analysis and categorization of IBDV in the United States, all commercially available live, attenuated Delaware strain vaccines were assayed. One of the monoclonal antibodies used in that assay is designated B 9, and is expressed by the hybridomal cell line deposited at the ATCC under deposit number HB-10157. It is apparent that in order to provide adequate coverage and protection against the Delaware strain infection, a live, attenuated vaccine must contain a virus that will produce antibodies recognizing the wild-type Delaware IBDV. That is, in the process of attenuation, the marker characteristics of the wild-type Delaware virus strain must not be lost. Surprisingly, in the course of testing commercially available vaccines, not one was demonstrated to bear the BK9 Mab marker, and thus not truly wild-type. Vaccines employing this type of virus will not, in fact, generate antibodies providing effective protection against wild-type Delaware IBDV infection. Thus, it remains a pressing need in the industry to provide a live, attenuated vaccine for Delaware IBDV. Alternatively, it is known that for certain IBDV, vaccines can be prepared from monoclonal antibodies (Mab) which neutralize the virus. See, in particular, U.S. Patent 4,956,452. It is a continuing goal to provide such Mab which neutralize the Delaware strain IBDV, and provide a vaccine based thereon. Disclosure of the Invention The above goal, and others made clear by the invention disclosure set forth below, has been met by identification of the fact that the wild-type Delaware virus does not replicate well in serial cell culturing. Thus, live, attenuated viruses obtained by serial passaging of the wild-type Delaware strain IBDV frequently lose the IBDV characteristics desirable or necessary to induce the production of effective antibodies against the parental virus. A Delaware virus which lacks the BK9 Mab marker, i.e., to which that monoclonal antibody will not bind, will not or may not confer as effective protection, in a vaccine against the wild type. When attenuating a wild-type Delaware IBDV, it is highly unlikely that any given adapt (the result of serial passaging) will retain the BK9 marker, and so provide effective coverage. The odds, in fact, on successful passaging are quite small. Therefore, adapts, as produced, must be screened for retention of the Delaware marker, by antigen capture enzyme linked immunosorbent assay (AC- ELISA) assay using the BK9 marker. As reflected in copending application, Attorney Docket Number 2284-018-0 CIP, the binding of the BK9 marker is a positive indication of the presence of the wild type Delaware strain. A neutralizing Mab has been developed against the wild-type Delaware strain of IBDV. The antibody has been deposited and extensively mapped. Brief Description of the Drawings Figure 1-le is a rendering of the complete nucleotide and deduced amino acid sequence of the Delaware IBDV structural protein(s) that is recognized by the Monoclonal Antibody 67. Best Mode for Carrying Out the Invention Six different cell culture adapted (i.e., chicken embryo fibroblast and the like) attenuated viruses were prepared from wild-type Delaware IBDV. Each was prepared by serial passaging through cell culture processes, conventional in the industry. Alternate methods of producing attenuated viruses, including cloning of the virus with deletion of nucleic acid sequences and site- directed mutagenesis, are also known, and are embraced in the invention. Of the six adapts prepared, five, when tested with the monoclonal antibody expressed by HB-10157 yielded negative results, that is, that had lost the BK9 antibody marker. Such viruses, although attenuated, will not or may not induce the production of antibodies effective in preventing Delaware IBDV infection. The sixth adapt did indeed react positively with the BK9 monoclonal antibody, thus indicating that this attenuated virus still maintained an essential characteristics of a wild-type Delaware IBDV, and as prepared in a vaccine, should induce the production of antibody effective against wild-type Delaware IBDV infection. This sixth adapt is currently available from the University of Maryland or Intervet America and can be continuously monitored and maintained in chicken origin or vero cell lines located at Avrum Gudelsky Center, College of Veterinary Medicine, University of Maryland. However, it should be noted that access to this virus or these cell lines is not necessary to practice the invention. Specifically, the adapts retaining the BK9 marker, and thus providing effective vaccines, occur randomly, with a low probability for the given adapt, as discussed above. There appears to be a portion of the wild-type Delaware IBDV genomic population which does not replicate well during serial passage. However, the odds on successful reproduction of an attenuated virus, given appropriate screening measures is quite high, if a large enough family of adapts is made. Thus, one of ordinary skill in the art, practicing a plurality of serial passages, need only screen the results with the BK9 Mab, available from the deposit, made under Budapest Treaty conditions, in order to practice this invention. Identification of the virus presence and confirmation of its virulence, is conducted in a fashion identical to that set forth in the copending application U.S. Application Serial No. 07/423,752, incorporated herein by reference. Given the monoclonal antibody, these procedures are routine. The vaccines themselves may be prepared by simple incorporation of the selected virus, confirmed by screening, and suspending or mixing it in a carrier. Appropriate dosage values can be determined through team trial and error techniques, sampling for the production of antibodies in the treated poultry individual. In general, dosage ranges will vary in a physiologically acceptable carrier, such as buffered saline, cell culture medium, Mareti's virus vaccine diluent, etc. The dosage is determined by the ability of the virus to replicate in the chicken and provide effective immunity with minimal pathologic damage. Applicants have also developed a Mab, designated Mab 67, which neutralizes the wild-type Delaware strain IBDV. The murine monoclonal antibody is specific only for the Delaware-type virus, and does not neutralize or bind to other recognized IBDV viruses. Mab 67 does not bind to, or neutralize any of the currently available live or live- attenuated vaccine viruses which are licensed or currently available, intended to confer protection against Delaware- type IBDV. This further confirms the inadequacy of existing virus-based vaccines to confer protection against Delaware-type infection. The monoclonal antibody was developed according to the method set forth in U.S. Patent 4,956,452. Specifically, hybridoma cell lines were prepared according to standard procedure beginning with BALB/c mice, immunized with the Delaware virus strain, after purification. Hybridomas were prepared therefrom, and the resulting cell lines were assayed, through an enzyme-linked immunosorbent assay (ELISA) to identify those lines secreting an antibody that binds to at least one strain. The resulting cell line was cloned again, and injected into pristane primed mice, to produce ascitic fluid with higher titre values. Specific details as to the propagation of the IBDV strains used, production of the hybridomas, the ELISA employed, and the virus neutralization tests are set forth in U.S. Patent 4,956,452, beginning at column 3, line 64 and continuing on to column 5, line 68. The disclosure of this patent is incorporated herein by reference. The hybridoma cell line expressing Mab 67 has been deposited under Accession No. ATCC-HB11122, deposited at the ATCC by David Snyder on September 14, 1992. Further, the cell lines are continuously available from Avrum Gudelsky Center, College of Veterinary Medicine, University of Maryland. This Mab can be used not only as an assay to determine the presence of the Delaware-type IBDV, but in addition to the virus- based vaccine disclosed above, can be employed to prepare a vaccine conferring challenge protection against Delaware- type IBDV. To achieve temporary passive immunization at a uniform, standardized level, and to augment any maternally derived levels against Delaware-type IBDV field infection, one-day old chicks should be vaccinated with a vaccine comprising a pharmacologically acceptable carrier such as a phosphate buffered saline, cell culture medium, Mareti's virus vaccine diluent, etc., in which is present an amount of Mab 67 effective to provide enhanced protection for a period of time which allows the chicks to become more immunologically competent (about two-three weeks) . The necessary level of protection can be conferred by a single dose of the vaccine administered to day-old chicks having a Mab concentration of between 1 icrograin and 1 illigrain, or repeated vaccinations having a smaller effective dose, but carried out over time. If repeated vaccinations are used, the dosage level should range within 10 micrograins to 1 milligrain. The concentration level needed to vaccinate older chickens is expected to increase with the weight of the bird. Other administration protocols can be developed by those of skill in the art without the exercise of inventive skill. It should be noted that in general, the pharmacologically acceptable carriers to be used with the virus-based vaccine discussed above can also be used in conjunction with the Mab-based vaccine addressed herein. Figures 1-1E contains a full recitation of the nucleotide sequence for the gene responsible for the expression of Delaware IBDV structural protein(s) recognized by Mab 67. Presented together with this information in Figures 1-1E is the a ino acid sequence for the Delaware IBDV protein(s) which will be recognized by Mab 67. As noted above, it is apparent that the virus quickly loses, in serial passage, its identifying characteristics, and accordingly, wholesale modification of the Mab, from a synthetic or site-specific mutagenesis aspect, may impair or destroy the antibody's ability to neutralize the virus. Nonetheless, based on the length of the amino acid required for the binding of the antibody, and studies applied to similar materials, it is expected that up to 10 percent of the amino acids of the structure can be modified or deleted, and up to 25 percent of the nucleotide sequence replaced or modified, particularly at the ends of the sequence, without loss of the binding and neutralizing ability of Mab 67. In particular, small modifications which do not affect conformal (quaternary) structure will not impede binding. Such modifications are clearly contemplated as one aspect of this invention. Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be alternatively described or practiced otherwise than as specifically described herein.

Claims: Claims 1. A live, attenuated virus capable of inducing the production of antibodies to wild-type Delaware infectious bursal disease virus in poultry, when administered thereto, but sufficiently attenuated so as not to induce infectious bursal disease in said treated poultry. 2. The virus of Claim 1, wherein a monoclonal antibody having the binding characteristics of the antibody expressed by HB-10157 will bind. 3. A vaccine, comprising the live, attenuated virus of Claim 1, and a pharmaceutically acceptable carrier. 4. A vaccine comprising the live, attenuated virus of Claim 2, and a pharmaceutically acceptable carrier. 5. A method of vaccinating poultry against wild-type Delaware infectious bursal disease comprising administering to said poultry the vaccine of Claim 3, the virus thereof. 6. A monoclonal antibody which neutralizes Delaware strain infectious bursal disease viruses (DIBDV) . 7. The monoclonal antibody of Claim 6, which recognizes substantially the amino acid sequence of Figures 1-1E. 8. The monoclonal antibody of Claim 7, wherein the amino acid sequence varies from that of Figures 1-1E by at most 10 percent. 9. A purified preparation comprising a gene comprising substantially the nucleotide sequence of Figures 1-1E. 10. The purified preparation of Claim 9, wherein said nucleotide sequence varies from that of Figures 1-1E by at most 25 percent. 11. A reco binant expression vehicle which expresses the amino acid sequence recognized by the antibody of Claim 6. 12. The expression vehicle of Claim 11, wherein said expression vehicle comprises a gene comprising substantially the nucleotide sequence of Figures 1-1E.

Inventors: LUETTICKEN HEINRICH DIETER, SNYDER DAVID B, VAKHARIA VIKRAM, LUETTICKEN, HEINRICH, DIETER, SNYDER, DAVID, B., VAKHARIA, VIKRAM
Applicants: UNIV MARYLAND, UNIVERSITY OF MARYLAND COLLEGE PARK
Application year: 1993
Main classification: A61K39
IPC codes: A61K38, A61K39, A61P31, C07K14, C07K16, C12N7, C12N15, C12P21