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Title:  Recombinant immunogens for the generation of antivenoms to the venom of scorpions of the genus Centruroides
United States Patent: 
7,335,759
Issued: 
February 26, 2008

Inventors: 
Corona Villegas; Miguel (Cuernavaca City, MX), Garcia Rodriguez; Ma Consuelo (Cuernavaca City, MX), Gurrola Briones; Georgina (Cuernavaca City, MX), Valdez Cruz; Norma Adriana (Cuernavaca City, MX), Becerril Lujan; Baltazar (Cuernavaca City, MX), Possani Postay; Lourival Domingos (Cuernavaca City, MX)
Assignee: 
Universidad Nacional Autonoma de Mexica (UNAM) (MX)
Appl. No.:  10/721,793
Filed: 
November 26, 2003


 

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Abstract

The invention concerns genes and fusion of genes that code for scorpion toxins and the corresponding polypeptides. The invention also concerns the use of the polypeptides as immunogens for the generation of antibodies that can recognize and neutralize components of scorpion venom as well as for vaccines to prevent envenomation from stings of scorpions of the genus Centruroides, and to immunogenic matrices for the purification of specific immunoglobulins.

Description of the Invention

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to the isolated genes that code for scorpion toxins (particularly, toxins that affect the sodium and Erg type potassium channels), to fusions of said genes with fragments of genes from other proteins, to the genetic constructions they comprise, to the isolated recombinant fusion proteins and recombinant peptides that comprise the primary sequence of the toxins in question, to their use as immunogens or antigens for the generation of antibodies that can recognize and neutralize components of the scorpion venom from which the toxin genes were obtained, to their use as vaccines to prevent envenomation from stings of scorpions of the genus Centruroides, and to their use as part of an immunogenic matrix for the purification of specific immunoglobulins.

Scorpion venom is a complex mixture of peptides, which can be classified in two groups based on the number of amino acids: long chain toxins with 60-76 amino acids (Possani, L. D., et al., Eur. J. Biochem. 264:287-300 (1999)), which block the Na+ channels of excitable cells and short chain toxins with 29-41 amino acids that affect the K.sup.+ channels (Possani, L. D., et al., Biochemie 82:861-868 (2000)), including the Erg type channels (Ether a go go).

The toxins that modify the Na.sup.+ channels are, in turn, classified as a and .beta. toxins (Couraud, F., et al., Toxicon 20:9-16 (1982)). The .alpha.-toxins mainly modify the inactivation mechanism of the Na.sup.+ channels, while the .beta.-toxins preferentially modify their activation mechanism (Strichartz, G., et al., Annu. Rev. Neurosci 10:237-267 (1987)).

Scorpion venom is composed of several peptides that can be toxic for a large variety of animals, some are toxic for mammals, others for insects, others for crustaceans, etc. (Possani, L. D., et al., Eur. J. Biochem. 264:287-300 (1999)).

There are approximately 221 species and subspecies of scorpions in Mexico, but only eight are medically important and are those that belong to the genus Centruroides, of which the species Centruroides noxius Hoffmann, C. limpidus limpidus Krash, C. elegans and C. sculpturatus are some of the most dangerous (Calderon-Aranda, et al., Toxicon 31:327-337 (1993)). From 1981 to 1990, approximately 250,000 cases of stings in humans were reported, with some 300 deaths (Calderon-Aranda, E. S., et al., Vaccine 13:1198-1206 (1995)), while from 1996-1998, of the cases that were reported among the population covered by the Mexican Social Security Institute, there were 429,561 cases of intoxication caused by scorpion stings (Esteba Maraboto, J. A., and Turrubiate Guillen, N. (1999). Panorama epidemiologico de las intoxicaciones causadas por animales ponzonosos en la poblacion derechohabiente del IMSS 1990-1998.5.sup.a Reunion de expertos en Envenenamiento por Animales Ponzofonosos. Instituto de Biotecnologia/UNAM Cuernavaca, Morelos, Mexico, 17 Feb., 1999). Hence scorpionism is considered to be a public health problem in Mexico.

In the United States, although the incidence of scorpion stings is much lower than in Mexico, there is a health problem caused by the scorpion C. sculpturatus of Arizona. This low incidence of cases of envenomation from this scorpion means a very small potential market, which has discouraged the large pharmaceutical companies from developing and producing efficacious antivenoms, and therefore cases are usually attended with intensive therapy, that is, relieving the symptoms caused by means of intensive care. In general, symptoms following a scorpion sting include: pain, cough, hypersensitivity, hyperexcitability, excessive salivation and vomiting. When two or more of these symptoms are present, antiscorpion serum is administered to counteract the effects, since cases of severe envenomation can cause heart and/or lung failure (Normer, W., Adv. Cytopharmacol. 3:345-351 (1979)), which can cause the death of the individual who has been stung.

Perhaps the most successful strategy in treating scorpion envenomation is the use of hyperimmune sera or monoclonal antibodies that can neutralize or delay the toxic effect of the scorpion toxins (serotherapy). In this sense, serotherapy studies have been conducted with polyclonal antibodies (Dehesa-Davila, M., and Possani, L. D., Toxicon 32: 1015-1018 (1994)) and monoclonal antibodies (Dehesa-Davila, M., et al., "Cinical toxicology of scorpion stings." In: Handbook of Clinical Toxicology of Animal Venoms and Poisons, pp. 201-238 (Meier, J. and White, J. Eds.). New York, CRC Press (1995); Zamudio, F., et al., Eur. J. Biochem. 204:281-292 (1992)); similarly, there are products on the market obtained from hyperimmune anti-scorpion horse sera, that after being fractionated, are enzymatically digested to obtain the F(ab).sub.2 fragment (for example, the one prepared by Instituto Bioclon S. A., in Mexico). However, these sera are prepared by immunizing horses with the macerated telson of a large number of scorpions. Once this maceration has been prepared, it is centrifuged and the horse is inoculated with the soluble part. This procedure is carried out by macerating a mixture of telsons from several scorpion species, such as C. noxius, C. limpidus limpidus and C. suffusus suffusus (in Mexico) (Dehesa-Davila, M., and Possani, L. D., Toxicon 32: 1015-1018 (1994)).

After several immunizations, the horse serum is obtained and whole immunoglobulins of the horse are purified. The antibodies are subsequently digested with pepsin to obtain the immunoglobulin fragments, F(ab).sub.2, responsible for neutralizing the venom.

The preparation described above has the disadvantage of containing a mixture of very varied antibodies, since, as mentioned earlier, scorpion venom is composed of dozens of peptides, only a few of which are active against mammals. Hence, the antibodies directed against these toxins are found in a very small proportion with respect to the total population of antibodies, meaning that it is necessary to apply a high dose of the preparation in order to be able to neutralize the effect of the toxins. Since this is an exogenous protein, the larger the amount the greater the risk of provoking an anaphylactic shock or serum sickness in patients, and the greater the possibility of provoking secondary effects in persons to whom this neutralizing preparation is applied on more than one occasion.

Due to the above, there is a need to remove the immunoglobulins not associated with the neutralizing effect of these sera, since their administration can produce an undesirable immune response (crossed autoimmunity, for example), induce nephrotoxicity, serum sickness and, in serious cases, anaphylactic shock.

In the case of the use of monoclonal antibodies, there are other disadvantages such as the presence of pollutants in the culture mediums that contain antibodies expressed by a hybridoma of interest, such as cells or nucleic acids. In the same way, antibody aggregates can also act as immunogens and cause an undesirable immune response in the organism receiving the therapy.

Together with the failed attempts to generate a reliable vaccine, and until more adequate, safe peptides for vaccination are determined, the most viable alternative with greatest purity, at least in the short term, for protection from scorpion stings is the use of anti-scorpion fabotherapics.

Furthermore, independent of whether or not adequate vaccines are produced to prevent intoxication from scorpion venom, there will be the constant need to have an effective reagent (anti-scorpion antiserum or purified anti-scorpion antibodies) for administration to non-vaccinated, intoxicated individuals available for immediate use in the field, since the time in which the venom exerts its toxic effect and can even provoke death in the affected organism is very short (0.33 hrs. in mice) (Zamudio, F., et al., Eur. J. Biochem. 204:281-292 (1992)).

For this reason, there is interest in constantly improving the production of the anti-scorpion antivenoms to be administered in order to neutralize the toxic activity of the scorpion venom in affected individuals.

Legros et al. (2002) published a report in which clones of mammal specific toxins I, II and III of Androctonus australis were used to produce recombinant peptides fused to the maltose binding protein (MBP). The fusion proteins were subsequently employed to generate antibodies in rabbits and proved to have a neutralizing effect on the toxic fraction (for mammals) that was separated from the scorpion venom, producing a sustained response. Hence, it is suggested that these recombinant peptides can even be used as a vaccine against the sting of this scorpion.

DETAILED DESCRIPTION OF THE INVENTION

One way of improving the antivenoms being currently produced is to enrich the mixtures of scorpion venoms that are used as immunogens or antigens with selected toxins whose effect is known as being especially toxic for mammals. To this end, it would be necessary to purify large amounts of toxins from large amounts of venom. One interesting alternative is to substitute these native toxins with synthetic peptides or peptides produced using recombinant DNA techniques. Although feasible, chemical synthesis of the peptide is not economically recommendable on a large scale, while to be able to produce said recombinant peptides it is necessary to have the nucleotide sequences coding for these toxins.

It may prove even better to prepare a chemical composition consisting of a mixture of those toxins specific for mammals or alternatively a mixture of synthetic or recombinant peptides that have the same primary sequence as said toxins for use as an immunogen instead of the whole venoms for the generation of antibodies in mammals. It is postulated that said mixture of antibodies would have a clear advantage over those currently produced, since it would have been generated only against mammal specific toxins and would have greater venom neutralizing activity per milligram of exogenous protein administered to the organism affected by the venom.

Another way of improving the antivenoms currently produced is to separate those antibodies or their fragments that really participate in the neutralization of mammal specific toxins. To this end, it would be useful to have an antigenic matrix to which those antibodies against said toxins are specifically bound (immunoaffinity). This can be achieved by binding said isolated toxins to an inert material by way of support. Again, it is necessary to have sufficient amounts of said toxins or, alternatively, recombinant or synthetic peptides with the same primary sequence as the toxins in question.

In order to be able to have sufficient amounts of peptides with the same primary sequence as the toxins that are potentially specific for mammals, which can be used to improve the antivenoms currently produced as mentioned in the paragraphs above, the inventors of the present invention decided to isolate and sequence several cDNA clones of toxins from different scorpions of potential interest to health in several regions, such as Centruroides exilicauda, C. limpidus limpidus Karsh, C. noxius Hoffman, C. elegans and C. gracilis from Mexico and C. sculpturatus Ewing from the United States. The isolation and cloning of these genes is described in detail in examples 1 to 7. As shown in Table 1 (see Original Patent), it was possible to isolate and clone a total of 71 clones of toxins from 6 species of scorpions of the genus Centruroides, 49 of which are specific for sodium channels and 22 for Erg type potassium channels.

Naturally occurring toxins in the scorpion venom will raise specific antibodies in a stung individual In certain embodiments of the invention, the antibodies are specific against only a particular polypeptide and/or the toxin from a particular Centruroides species. Such polypeptides may be used as part of a composition, where the polypeptide is bound covalently or through hydrophobic or hydrophilic interaction to a substrate. The substrate may then be used as part of a diagnostic device.

Another embodiment of the invention comprises a device using the substrate described in the previous paragraph. Such a device may be used to detect the presence of species-specific antibodies in an individual stung by a species of Centruroides scorpion. A method to dianose whether the scorpion that stunag an individual belongs to a particular species of Centruroides scoprion comprises contacting such a diagnostic device with a sample from a stung individual, and detecting the presence of antibodies from the individual that had been stung by the scorpion. If present, the antibodies raised against a particular naturally occurring toxin will bind to the polypeptides of the device. The bound antibodies can then be detected by methods and optical detecting systems well-known to those of ordinary skill in the art. Such methods and devices may for example, be based on immuno-enzymatic, immuno-fluorescenct or immuno-chromatographic techniques.

A significant amount of toxins and their genes including the respective signal peptide are now known. From comparative analyses of the nucleotide and/or amino acid sequences, it can be seen that there are some highly conserved regions, like those equivalent to the first 6 amino acids of the signal peptide and part of the 3' uncoding region (UTR). Based on the foregoing, it is possible to design degenerate oligonucleotides corresponding to the amino ends of the signal peptide and the carboxyl end of the toxin, which can be amplified by PCR using the messenger RNA present in the telson of the scorpion in question. The sequences that hybridize with said oligos generate clones that comprise the coding sequence of the toxin and its peptide signal. These are cloned in a useful vector for rapid identification, as is the case of the vector PKS- (Stratagene, La Jolla, Calif., USA) that has Beta galactosidase as marker in such a way that when X-gal is present in the solid culture medium the colonies that received inserts (clones) lose Beta galactosidase activity and grow with a white color, while this enzyme remains intact in the colonies that received no insert and generates blue colonies. The white colonies are cultivated in order to amplify their plasmid DNA (that presumably comprises some of the clones of interest) which is subsequently sequenced to determine the nucleotide sequence and the deduced amino acid sequence.

Another alternative for oligonucleotide design is to purify some of the toxins present in the scorpion venom in question and obtain the amino acid sequence of the amino region (at least the first 8 amino acids) and use them to design specific oligonucleotides with which to try to obtain, in particular, the clones of these toxins, or rather, based on the homology between the amino acid sequences obtained, design a degenerate oligonucleotide to try to obtain the clones present in the telson that are homologous to the oligonucleotide that has been designed. In both cases, the clones obtained will comprise the coding sequence of the just the toxin without the signal peptide.

Another strategy to be used should there be no further information on the possible expected clones consists of using, instead of an oligonucleotide corresponding to the 3' region of the clone, a poly T oligonucleotide that should hybridize with the PolyA site present in all cDNAs independently of the direct oligo used, the one from the amino region of the signal peptide or of the mature peptide.

The choice of the strategy to be followed in each case will depend on the elements available such as the knowledge of the total or partial amino acid sequence of the toxins of interest or an analysis by mass spectrometry of one or more toxins of the venom of the scorpion in question, the sequence of other toxins from the same scorpion or from other related scorpions, the information on the signal peptide toxin sequence of the same scorpion or other related scorpions, to name but a few.

The peptide or toxin purification procedures using raw venoms from the different scorpions can begin with chromatographic columns that separate fractions based on screening of molecular mass, followed by ion exchange resins and HPLC using reverse phase columns. At present, most laboratories use direct separations of peptides by HPLC or use it directly after a simple separation by molecular mass of the soluble venoms (Possani, L. D., et al., Eur. J. Biochem. 264:287-300 (1999)). To this end, the whole venom of the scorpion in question is obtained by electrostimulation of the telson and is subsequently centrifuged before beginning the purification processes.

It is known that some of the polypeptide precursors of the toxins suffer postranslational modifications in both the amino and carboxyl ends: in the amino end a signal peptide of 18 to 21 amino acids is normally eliminated by means of a signal peptidase. In the carboxyl end, the extra basic amino acids (Arg and/or Lys) are processed by a carboxypeptidase. Several mechanisms have been discovered for the postranslational processing of the carboxyl end, typically the basic residue(s) of the end are removed. When a glycine residue precedes one or two basic residues of the amino group of the glycine residue, it is used to amidate to the amino acid residue that precedes it. If a glycine precedes a group of three basic residues, the basic triad is removed without there being any amidation (Possani, L. D., et al., Eur. J. Biochem. 264:287-300 (1999)). It will therefore be appropriate if the recombinant peptides being produced have a primary sequence the most similar possible to the mature toxin, that is, without the signal peptide and without the amino acids of the carboxyl end that are eliminated when the toxin is processed, when this is the case.

In order for the genes or clones of the present invention to be used in the generation of better antivenoms, they should first be expressed in a heterologue system, as for example Escherichia coli, Pichia pastoris, Baculovirus or others, for either the corresponding recombinant peptide or a fusion protein comprising said peptide to then be used as immunogen (antigen) or component of an immunogen for the production of antibodies in mammals.

It is clear that in order to be expressed in a heterologue system, the genes or clones of the present invention should be introduced in genetic constructions that are compatible with the expression in said systems. Some examples of these could be the Protein Expression and Purification System of New England Biolabs where plasmid pMal-C is used in E. coli to express the proteins of interest as fusion proteins bound to the maltose binding protein. Another system could be the one used by Legros' group (Legros, C., et al., Vaccine 20:934-942 (2002)), pMal-p from the same supplier.

Before inserting the genes or clones of the present invention in said genetic constructions, it is necessary to edit them to eliminate any fragment of 3' and 5' uncoding regions (UTR). In order to edit the genes or clones of the present invention, it is necessary to synthesize oligonucleotides that, for the direct oligonucleotide, comprise the first amino acids (from 6 to 9) of the amino terminal region to be expressed, either the signal peptide, if it is to be included in the expressed protein, or the mature peptide if the signal peptide is to be excluded and, for the reverse oligonucleotide, the last 6-9 amino acids of the carboxyl terminal region of the mature peptide. In the cases of those toxins that are known to be postranslationally processed, it will be convenient for the reverse oligo to be designed leaving out the amino acid residue(s) that are known to be eliminated with the processing. Subsequently, using both oligonucleotides as primers and the clone or gene of interest as template, a PCR amplification reaction is performed to obtain the DNA that codes only for the mature peptide or for the mature peptide plus the signal peptide. It can also be recommendable to take advantage of the direct oligo to include a methionine residue just before the first amino acid This, at some moment, will permit cleavage of the recombinant peptide once the fusion protein has been expressed through the application of cyanogen bromide (Possani, L. D., et al., Biochem. J. 229:739-750 (1985))

In order to demonstrate the feasibility of using any of the genes or clones isolated from scorpions of the genus Centruroides, including those of the present invention, for industrial production of the recombinant peptide whose primary sequence is identical to that of the encoded toxin, that is, the native toxin, either in free form or fused with part of other proteins producing a larger polypeptide, the inventors of the present invention carried out a construction (shown in FIG. 1 (see Original Patent)) using clone CngtII (Becerril, B., et al., Gene 128:165-171 (1993)), that codes for a well-known, characterized toxin of Centruroides noxius Hoffmann, Cn5 (Garcia, C., et al., Com. Biochem. Physiol. 116B (3):315-322 (1997)), in which this clone was fused to the maltose binding protein. This is illustrated in detail in examples 8 and 9. The fusion protein expressed was used to generate antibodies in mammals as can be seen in example 10, while in example 11 the use is illustrated of said antibodies in the neutralization in vivo of a known toxin specific for mammals whose amino acid sequence is similar to that of Cn5 and which has proved to be one of the most important in its toxic effect, Cn2 (Zamudio, F., et al., Eur. J. Biochem. 204:281-292 (1992); Garcia, C., et al., Com. Biochem. Physiol. 116B (3):315-322 (1997)).

Any of the clones of the present invention can, like CngtII, be edited by designing specific oligos which, as mentioned earlier, can be used for the insertion of some methionine or some other sequence that permits its purification, for example, by amplifying them by PCR using the clone of choice as template, obtaining DNA fragments that comprise the corresponding sequence reported in column D, Table 1. Constructions can be made with said fragments in commercial systems, such as plasmids pMalC and pMal-p of the Protein Expression and Purification System (New England Biolabs), or in manufactured expression systems that comprise said DNA fragments fused to heterologue protein coding fragments or fragments of the same, transforming hosts into bacteria such as the CMK strain of Escherichia coli or any other expression host for which the selected expression system is appropriate.

On cultivating said cells of the recombinant host, these cells will express (after induction) the fusion protein that will comprise the corresponding sequence reported in column E, Table 1.

It is known that the genetic code is degenerate, that is, that for one same amino acid there is generally more than one encoding codon. The difference between these codons is the third of the bases. It is obvious to an expert in the state of the technique that it is possible to substitute some bases in the encoding nucleotide sequence of the clones of the present invention referred to in column B or in the edited sequences of column D, Table 1, that encode exactly the same amino acid sequences as those referred to in column E, Table 1. This may be particularly useful when it is wished to express said peptides of the present invention in different recombinant hosts, for it is known that different types of hosts have a "preference" of use towards certain codons for determined amino acids. Such "silent mutations" fall within the scope of the present invention, since the products of their expression are again the peptides referred to in column E, Table 1, of the present invention.

Recombinant peptides for the present invention shall be understood to be those peptides obtained by recombinant methods that comprise the primary sequence reported in column E, Table 1.

Thus, the present invention also refers to the use of the recombinant peptides of the present invention, either free or as part of fusion proteins, as vaccines to prevent envenomation from the venom of scorpions of the genus Centruroides and the pharmaceutical preparations of said vaccine. Administration of the peptides may be by intravenous, subcutaneous, intramuscular, intravaginal, intraperitoneal, intranasal, oral or other mucous routes. Additionally, the hyperimmune sera or antibodies (obtained following injection of the polypeptides of the invention) that can neutralize or delay the toxic effect of the scorpion toxins can be used to treat envenomation (serotherapy).

The vaccines of the present invention comprise one or more of the recombinant peptides of the present invention, either free or as fusion proteins that, in turn, comprise the primary sequence of the peptides of the present invention. Since the folding of the recombinant peptides expressed in heterologue hosts is not the same as that of the native toxin, said vaccine is also sufficiently innocuous to be administered without danger of intoxication, it is stable and compatible with vaccine carriers.

An effective amount of the vaccine should be administered that is capable of producing an immune response in a mammal, where "effective amount" is defined as an amount of recombinant peptides from the present invention or any fusion protein comprising the same. The necessary amount will vary depending on whether the peptides of the present invention are used or fusion proteins comprising these peptides and on the antigenicity of said fusion protein and on the species and weight of the subject to be vaccinated, but it can be estimated by standard techniques.

Pharmaceutically useful compositions can be formulated as vaccines that comprise one or more of the recombinant peptides of the present invention or any fusion protein including said peptides, according to known methods such as the addition of a pharmaceutically acceptable carrier. In order to form a pharmaceutically acceptable composition suitable for effective administration, said composition shall contain an effective amount of one or more of the recombinant peptides of the present invention or any fusion protein including said recombinant peptides.

The pharmaceutical compositions of the vaccines of the present invention can include a pharmaceutically acceptable adjuvant such as aluminum or calcium gels, modified muramyl dipeptides, monophosphorylated lipids, liposomes, delayed release capsules, polyglycolic acids and polyamino acids. Polyglycolic and polyamino acids are also useful for the oral administration of vaccines. Some examples of aluminum gels useful as adjuvants include precipitated aluminum salts such as aluminum phosphate and hydroxide. Some preservatives such as thimerosal, dextrane and glycerine can be added to stabilize the final vaccine. If it is wished to have the vaccines in injectable form, immunologically acceptable diluents or carriers can be included.

The vaccine of the present invention or the pharmaceutical compositions of the same can be administered to mammals locally and/or systemically through the conventional routes such as the intravenous, subcutaneous, intramuscular, intravaginal, intraperitoneal, intranasal, oral or other mucous routes to arouse an efficacious immune response to protect against the venom of scorpions of the genus Centruroides. The vaccine can be optionally administered in sole or multiple doses with the object of sustaining antibody levels.

The pharmaceutic compositions of the vaccines of the present invention should be administered to an individual in such amounts that they contain effective amounts of the vaccine of the present invention. The effective amount will vary according to a variety of factors such as species, condition, weight, sex and age of the individual to be treated. Another factor includes the administration route used.

Another scope of the present invention is based on the fact that the recombinant peptides of the present invention, either free or as fusion proteins, can also be used to generate an immunogenic matrix when bound either covalently or through hydrophobic or hydrophilic interactions to some substrate like polyacrylamide, polyvinyl, activated aldehyde agarose (U.S. Pat. Nos. 5,904,922 and 5,443,976), sepharose, carboxymethyl cellulose or some other, in such a way that the matrix is capable of specifically binding either antibodies (raised against the whole venom of scorpions of the genus Centruroides or against the same venoms enriched with some of the recombinant peptides of the present invention, or against mixtures of recombinant peptides of the present invention) or the F(ab) or F(ab)2 fragments obtained from hydrolysis of said antibodies, and is useful in the purification by immunoaffinity of said antibodies or F(ab) or F(ab).sub.2 fragments, which is why said use in the antigenic matrix and said antigenic matrix are included in the scope of the present invention.
 

Claim 1 of 20 Claims

1. An isolated nucleic acid comprising the sequence of SEQ ID NO:115.
 

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