Modified factor viii   

This application is a continuation of U.S. patent application Ser. No. 11/550,366, filed Oct. 16, 2006, which is a continuation-in-part of U.S. patent application Ser. No. 10/938,414, filed Sep. 10, 2004, now U.S. Pat. No. 7,122,634; which is divisional application of U.S. patent application Ser. No. 10/187,319 filed Jun. 28, 2002; which is a continuation-in-part of U.S. patent application Ser. No. 09/523,656 filed Mar. 10, 2000, now U.S. Pat. No. 6,458,563; which is a continuation-in-part of U.S. patent application Ser. No. 09/037,601 filed Mar. 10, 1998, which issued as U.S. Pat. No. 6,180,371; which is a continuation-in-part of U.S. patent application Ser. No. 08/670,707 filed Jun. 26, 1996, which issued as U.S. Pat. No. 5,859,204; and of International Patent Application No. PCT/US97/11155 filed Jun. 26, 1997. All of the foregoing priority applications are incorporated herein by reference to the extent there is no inconsistency with the present disclosure.

The government has rights in this invention arising from National Institutes of Health Grant Nos. HL40921, HL46215, and HL36094 that partially funded the research leading to this invention.

BACKGROUND OF THE INVENTION

This invention relates generally to a hybrid factor VIII having human and animal factor VIII amino acid sequence or having human factor VIII and non-factor VIII amino acid sequence and methods of preparation and use thereof.

Blood clotting begins when platelets adhere to the cut wall of an injured blood vessel at a lesion site. Subsequently, in a cascade of enzymatically regulated reactions, soluble fibrinogen molecules are converted by the enzyme thrombin to insoluble strands of fibrin that hold the platelets together in a thrombus. At each step in the cascade, a protein precursor is converted to a protease that cleaves the next protein precursor in the series. Cofactors are required at most of the steps.

Factor VIII circulates as an inactive precursor in blood, bound tightly and non-covalently to von Willebrand factor. Factor VIII is proteolytically activated by thrombin or factor Xa, which dissociates it from von Willebrand factor and activates its procoagulant function in the cascade. In its active form, the protein factor VIIIa is a cofactor that increases the catalytic efficiency of factor IXa toward factor X activation by several orders of magnitude.

People with deficiencies in factor VIII or antibodies against factor VIII who are not treated with factor VIII suffer uncontrolled internal bleeding that may cause a range of serious symptoms, from inflammatory reactions in joints to early death. Severe hemophiliacs, who number about 10,000 in the United States, can be treated with infusion of human factor VIII, which will restore the blood\'s normal clotting ability if administered with sufficient frequency and concentration. The classic definition of factor VIII, in fact, is that substance present in normal blood plasma that corrects the clotting defect in plasma derived from individuals with hemophilia A.

The development of antibodies (“inhibitors” or “inhibitory antibodies”) that inhibit the activity of factor VIII is a serious complication in the management of patients with hemophilia. Autoantibodies develop in approximately 20% of patients with hemophilia A in response to therapeutic infusions of factor VIII. In previously untreated patients with hemophilia A who develop inhibitors, the inhibitor usually develops within one year of treatment. Additionally, autoantibodies that inactivate factor VIII occasionally develop in individuals with previously normal factor VIII levels. If the inhibitor titer is low enough, patients can be managed by increasing the dose of factor VIII. However, often the inhibitor titer is so high that it cannot be overwhelmed by factor VIII. An alternative strategy is to bypass the need for factor VIII during normal hemostasis using factor IX complex preparations (for example, KONYNE™, Proplex™) or recombinant human factor VIIIa. Additionally, since porcine factor VIII usually has substantially less reactivity with inhibitors than human factor VIII, a partially purified porcine factor VIII preparation (HYATE:C7) is used. Many patients who have developed inhibitory antibodies to human factor VIII have been successfully treated with porcine factor VIII and have tolerated such treatment for long periods of time. However, administration of porcine factor VIII is not a complete solution because inhibitors may develop to porcine factor VIII after one or more infusions.

Several preparations of human plasma-derived factor VIII of varying degrees of purity are available commercially for the treatment of hemophilia A. These include a partially-purified factor VIII derived from the pooled blood of many donors that is heat- and detergent-treated for viruses but contain a significant level of antigenic proteins; a monoclonal antibody-purified factor VIII that has lower levels of antigenic impurities and viral contamination; and recombinant human factor VIII, clinical trials for which are underway. Unfortunately, human factor VIII is unstable at physiologic concentrations and pH, is present in blood at an extremely low concentration (0.2 μg/ml plasma), and has low specific clotting activity.

Hemophiliacs require daily replacement of factor VIII to prevent bleeding and the resulting deforming hemophilic arthropathy. However, supplies have been inadequate and problems in therapeutic use occur due to difficulty in isolation and purification, immunogenicity, and the necessity of removing the AIDS and hepatitis infectivity risk. The use of recombinant human factor VIII or partially-purified porcine factor VIII will not resolve all the problems.

The problems associated with the commonly used, commercially available, plasma-derived factor VIII have stimulated significant interest in the development of a better factor VIII product. There is a need for a more potent factor VIII molecule so that more units of clotting activity can be delivered per molecule; a factor VIII molecule that is stable at a selected pH and physiologic concentration; a factor VIII molecule that is less apt to cause production of inhibitory antibodies; and a factor VIII molecule that evades immune detection in patients who have already acquired antibodies to human factor VIII.

It is therefore an object of the present invention to provide a factor VIII that corrects hemophilia in a patient deficient in factor VIII or having inhibitors to factor VIII.

It is a further object of the present invention to provide methods for treatment of hemophiliacs.

It is still another object of the present invention to provide a factor VIII that is stable at a selected pH and physiologic concentration.

It is yet another object of the present invention to provide a factor VIII that has greater coagulant activity than human factor VIII.

It is an additional object of the present invention to provide a factor VIII against which less antibody is produced.

SUMMARY

The present invention provides isolated, purified, hybrid factor VIII molecules and fragments thereof with coagulant activity including hybrid factor VIII having factor VIII amino acid sequence derived from human and pig or other non-human mammal (together referred to herein as “animal”); or in a second embodiment including a hybrid equivalent factor VIII having factor VIII amino acid sequence derived from human or animal or both and amino acid sequence having no known sequence identity to factor VIII (“non-factor VIII amino acid sequence”), preferably substituted in an antigenic and/or immunogenic region of the factor VIII, is described. One skilled in the art will realize that numerous hybrid factor VIII constructs can be prepared including, but not limited to, human/animal factor VIII having greater coagulant activity than human factor VIII (“superior coagulant activity”); non-immunogenic human/equivalent factor VIII; non-antigenic human/equivalent or human/animal factor VIII; non-immunogenic human/animal or human/equivalent factor VII having superior coagulant activity; non-antigenic human/animal or human/animal/equivalent factor VIII having superior coagulant activity; non-immunogenic, non-antigenic human/equivalent or human/equivalent/animal factor VIII; and non-immunogenic, non-antigenic human/animal/equivalent factor VIII having superior coagulant activity.

The hybrid factor VIII molecule is produced by isolation and recombination of human and animal factor VIII subunits or domains; or by genetic engineering of the human and animal factor VIII genes.

In a preferred embodiment, recombinant DNA methods are used to substitute elements of animal factor VIII for the corresponding elements of human factor VIII, resulting in hybrid human/animal factor VIII molecules. In a second preferred embodiment, recombinant DNA methods are used to replace one or more amino acids in the human or animal factor VIII or in a hybrid human/animal factor VIII with amino acids that have no known sequence identity to factor VIII, preferably a sequence of amino acids that has less immunoreactivity with naturally occurring inhibitory antibodies to factor VIII (“nonantigenic amino acid sequence”) and/or is less apt to elicit the production of antibodies to factor VIII (“non-immunogenic amino acid sequence”) than human factor VIII. An example of an amino acid sequence that can be used to replace immunogenic or antigenic sequence is a sequence of alanine residues.

In another embodiment, subunits of factor VIII are isolated and purified from human or animal plasma, and hybrid human/animal factor VIII is produced either by mixture of animal heavy chain subunits with human light chain subunits or by mixture of human heavy chain subunits with animal light chain subunits, thereby producing human light chain/animal heavy chain and human heavy chain/animal light chain hybrid molecules. These hybrid molecules are isolated by ion exchange chromatography.

Alternatively, one or more domains or partial domains of factor VIII are isolated and purified from human or animal plasma, and hybrid human/animal factor VIII is produced by mixture of domains or partial domains from one species with domains or partial domains of the second species. Hybrid molecules can be isolated by ion exchange chromatography.

Methods for preparing highly purified hybrid factor VIII are described having the steps of: (a) isolation of subunits of plasma-derived human factor VIII and subunits of plasma-derived animal factor VIII, followed by reconstitution of coagulant activity by mixture of human and animal subunits, followed by isolation of hybrid human/animal factor VIII by ion exchange chromatography; (b) isolation of domains or partial domains of plasma-derived human factor VIII and domains or partial domains of plasma-derived animal factor VIII, followed by reconstitution of coagulant activity by mixture of human and animal domains, followed by isolation of hybrid human/animal factor VIII by ion exchange chromatography; (c) construction of domains or partial domains of animal factor VIII by recombinant DNA technology, and recombinant exchange of domains of animal and human factor VIII to produce hybrid human/animal factor VIII with coagulant activity; (d) creation of hybrid human/animal factor VIII by replacement of specific amino acid residues of the factor VII of one species with the corresponding unique amino acid residues of the factor VIII of the other species; or (e) creation of a hybrid equivalent factor VIII molecule having human or animal amino acid sequence or both, in which specific amino acid residues of the factor VIII are replaced with amino acid residues having no known sequence identity to factor VIII by site-directed mutagenesis. A preferred factor VIII is POL1212, which is derived from porcine factor VIII and lacks most of the B-domain.

The determination of the entire DNA sequence encoding porcine factor VIII has enabled the synthesis of full-length porcine factor VIII by expressing the DNA encoding porcine factor VIII in a suitable host cell. Purified recombinant porcine factor VIII is therefore an aspect of the present invention. The DNA encoding each domain of porcine factor VIII as well as any specified fragment thereof, can be similarly expressed, either by itself or in combination with DNA encoding human factor VIII to make the hybrid human/porcine factor VIII described herein. Furthermore, porcine factor VIII having all or part of the B domain deleted (B-domainless or substantially B-domainless porcine fvIII) is made available as part of the present invention, by expression DNA encoding porcine fVIII having a deletion of one or more codons of the B-domain.

Some embodiments of hybrid or hybrid equivalent factor VIII have specific activity greater than that of human factor VIII and equal to or greater than that of porcine factor VIII. Some embodiments of hybrid or hybrid equivalent factor VIII have equal or less immunoreactivity with inhibitory antibodies to factor VIII and/or less immunogenicity in humans or animals, compared to human or porcine factor VIII.

Also provided are pharmaceutical compositions and methods for treating patients having factor VIII deficiency comprising administering the hybrid or hybrid equivalent factor VIII, especially the POL1212 protein, the amino acid sequence of the protein after the removal of the signal peptide is provided herein as SEQ ID NO:49.

A specific, preferred embodiment of the present invention is a substantially B-domainless porcine factor VIII protein, called POL1212 or OBI-1. See SEQ ID NOs:48 and 49. Also within the scope of the present invention are pharmaceutical compositions comprising the OBI-1 protein, and optionally a lyoprotectant and/or a pharmaceutically acceptable carrier or excipient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1H taken together provide an aligned sequence comparison of the human, pig and mouse factor VIII amino acid sequences. FIG. 1A compares signal peptide regions (human, SEQ ID NO:40; porcine, SEQ ID NO:37, amino acids 1-19; murine, SEQ ID NO:6, amino acids 1-19). Note that the amino acids in FIGS. 1A-1H are numbered at the first Alanine of the mature protein as number 1, with amino acids of the signal peptide assigned negative numbers. The Human fvIII sequence in SEQ ID NO:2 also begins with the first Alanine of the mature protein as amino acid number 1. In the amino acid sequences of mouse fvIII (SEQ ID NO:6) and porcine fvIII (SEQ ID No:37), the first amino acid (alanine) of the mature sequence is amino acid number 20. FIGS. 1A-1H show an alignment of the corresponding sequences of human, mouse and pig fVIII, such that the regions of greatest amino acid identity are juxtaposed. The amino acid numbers in FIGS. 1A-1H apply to human fVIII only. FIG. 1B gives the amino acid sequences for the A1 domain of human (SEQ ID NO:2, amino acids 1-372), porcine (SEQ ID NO:37, amino acids 20-391), and murine (SEQ ID NO:6, amino acids 20-391). FIG. 1C provides amino acid sequences for the factor VIII A2 domains from human (SEQ ID NO:2, amino acids 373-740), pig (SEQ ID NO:37, amino acids 392-759) and mouse (SEQ ID NO:6, amino acids 392-759). FIGS. 1D and 1D-1 provide the amino acid sequences of B domains of human factor VIII (SEQ ID NO:2, amino acids 741-1648), pig (SEQ ID NO:37, amino acids 760-1449) and mouse (SEQ ID NO:6, amino acids 760-1640). FIG. 1E compares the amino acid sequences of factor VIII light chain activation peptides of human, pig and mouse (SEQ ID NO:2, amino acids 1649-1689; SEQ ID NO:37, amino acids 1450-1490; and SEQ ID NO:6, amino acids 1641-1678, respectively). FIG. 1F provides the sequence comparison for human, pig and mouse factor VIII A3 domains (SEQ ID NO:2, amino acids 1690-2019; SEQ ID NO:37, amino acids 1491-1820; and SEQ ID NO:6, amino acids 1679-2006, respectively. FIG. 1G provides the amino acid sequences of the factor VIII C1 domains of human, pig and mouse (SEQ ID NO:2, amino acids 2020-2172; SEQ ID NO:37, amino acids 1821-1973; and SEQ ID NO:6, amino acids 2007-2159, respectively). FIG. 1H provides sequence data for the C2 domains of the factor VIII C2 domains of human, pig and mouse (SEQ ID NO:2, amino acids 2173-2332; SEQ ID NO:37, amino acids 1974-2133; and SEQ ID NO:6, amino acids 2160-2319, respectively).

DETAILED DESCRIPTION

Unless otherwise specified or indicated, as used herein, “factor VIII” denotes any functional factor VIII protein molecule from any animal, any hybrid factor VIII or modified factor VIII, “hybrid factor VIII” or “hybrid protein” denotes any functional factor VIII protein molecule or fragment thereof comprising factor VIII amino acid sequence from human, porcine, and/or non-human, non-porcine mammalian species. Such combinations include, but are not limited to, any or all of the following hybrid factor VIII molecules or fragments thereof: (1) human/porcine; (2) human/non-human, non-porcine mammalian, such as human/mouse; (3) porcine/non-human, non-porcine mammalian, such as mouse/dog. Such combinations also include hybrid factor VIII equivalent molecules or fragments thereof, as further defined below, comprising factor VIII amino acid sequence of hybrid, human, porcine, or non-human, non-porcine mammalian origin in which amino acid sequence having no known sequence identity to factor VIII is substituted. Such hybrid combinations also include hybrid factor VIII amino sequence derived from more than two species, such as human/pig/mouse, or from two or more species in which amino acid sequence having no known sequence identity to factor VIII is substituted. Unless otherwise indicated, “hybrid factor VIII” includes fragments of the hybrid factor VIII, which can be used, as described below in one exemplary embodiment, as probes for research purposes or as diagnostic reagents.

As used herein, “mammalian factor VIII” includes factor VIII with amino acid sequence derived from any non-human mammal, unless otherwise specified. “Animal”, as used herein, refers to pig and other non-human mammals.

A “fusion protein” or “fusion factor VIII or fragment thereof”, as used herein, is the product of a hybrid gene in which the coding sequence for one protein is extensively altered, for example, by fusing part of it to the coding sequence for a second protein from a different gene to produce a hybrid gene that encodes the fusion protein. As used herein, a fusion protein is a subset of the hybrid factor VIII protein described in this application.

A “corresponding” nucleic acid or amino acid or sequence of either, as used herein, is one present at a site in a factor VIII or hybrid factor VIII molecule or fragment thereof that has the same structure and/or function as a site in the factor VIII molecule of another species, although the nucleic acid or amino acid number may not be identical. A sequence “corresponding to” another factor VIII sequence substantially corresponds to such sequence, and hybridizes to the sequence of the designated SEQ ID NO. under stringent conditions. A sequence “corresponding to” another factor VIII sequence also includes a sequence that results in the expression of a factor VIII or claimed procoagulant hybrid factor VIII or fragment thereof and would hybridize to a nucleic molecule of the designated SEQ ID NO. but for the redundancy of the genetic code.

A “unique” amino acid residue or sequence, as used herein, refers to an amino acid sequence or residue in the factor VIII molecule of one species that is different from the homologous residue or sequence in the factor VIII molecule of another species.

“Specific activity,” as used herein, refers to the activity that will correct the coagulation defect of human factor VIII-deficient plasma. Specific activity is measured in units of clotting activity per milligram total factor VIII protein in a standard assay in which the clotting time of human factor VIII deficient plasma is compared to that of normal human plasma. One unit of factor VIII activity is the activity present in one milliliter of normal human plasma. In the assay, the shorter the time for clot formation, the greater the activity of the factor VIII being assayed. Hybrid human/porcine factor VIII has coagulation activity in a human factor VIII assay. This activity, as well as that of other hybrid or hybrid equivalent factor VIII molecules or fragments thereof, may be less than, equal to, or greater than that of either plasma-derived or recombinant human factor VIII.

The human factor VIII cDNA nucleotide and predicted amino acid sequences are shown in SEQ ID NOs:1 and 2, respectively. Factor VIII is synthesized as an approximately 300 kDa single chain protein with internal sequence homology that defines the “domain” sequence NH2-A1-A2-B-A3-CI-C2-COOH. In a factor VIII molecule, a “domain”, as used herein, is a continuous sequence of amino acids that is defined by internal amino acid sequence identity and sites of proteolytic cleavage by thrombin. Unless otherwise specified, factor VIII domains include the following amino acid residues, when the sequences are aligned with the human amino acid sequence (SEQ ID NO:2): A1, residues Ala1-Arg372; A2, residues Ser373-Arg740; B, residues Ser741-Arg1648; A3, residues Ser1690-Ile2032; C1, residues Arg2033-Asn2172; C2, residues Ser2173-Tyr2332. The A3-CI-C2 sequence includes residues Ser1690-Tyr2332. The remaining sequence, residues Glu1649-Arg1689, is usually referred to as the factor VIII light chain activation peptide. Factor VIII is proteolytically activated by thrombin or factor Xa, which dissociates it from von Willebrand factor, forming factor VIIIa, which has procoagulant function. The biological function of factor VIIIa is to increase the catalytic efficiency of factor IXa toward factor X activation by several orders of magnitude. Thrombin-activated factor VIIIa is a 160 kDa A1/A2/A3-C1-C2 heterotrimer that forms a complex with factor IXa and factor X on the surface of platelets or monocytes. A “partial domain” as used herein is a continuous sequence of amino acids forming part of a domain.

“Subunits” of human or animal factor VIII, as used herein, are the heavy and light chains of the protein. The heavy chain of factor VIII contains three domains, A1, A2, and B. The light chain of factor VIII also contains three domains, A3, C1, and C2.

The hybrid factor VIII or fragment thereof can be made (1) by substitution of isolated, plasma-derived animal subunits or human subunits (heavy or light chains) for corresponding human subunits or animal subunits; (2) by substitution of human domains or animal domains (A1, A2, A3, B, C1, and C2) for corresponding animal domains or human domains; (3) by substitution of parts of human domains or animal domains for parts of animal domains or human domains; (4) by substitution of at least one specific sequence including one or more unique human or animal amino acid(s) for the corresponding animal or human amino acid(s); or (5) by substitution of amino acid sequence that has no known sequence identity to factor VIII for at least one sequence including one or more specific amino acid residue(s) in human, animal, or hybrid factor VIII or fragments thereof. A “B-domainless” hybrid factor VIII, hybrid equivalent factor VIII, or fragment of either, as used herein, refers to any one of the hybrid factor VIII constructs described herein that lacks the B domain.

The terms “epitope”, “antigenic site”, and “antigenic determinant”, as used herein, are used synonymously and are defined as a portion of the human, animal, hybrid, or hybrid equivalent factor VIII or fragment thereof that is specifically recognized by an antibody. It can consist of any number of amino acid residues, and it can be dependent upon the primary, secondary, or tertiary structure of the protein. In accordance with this disclosure, a hybrid factor VIII, hybrid factor VIII equivalent, or fragment of either that includes at least one epitope may be used as a reagent in the diagnostic assays described below. In some embodiments, the hybrid or hybrid equivalent factor VIII or fragment thereof is not cross-reactive or is less cross-reactive with all naturally occurring inhibitory factor VIII antibodies than human or porcine factor VIII.

The term “immunogenic site”, as used herein, is defined as a region of the human or animal factor VIII, hybrid or hybrid equivalent factor VIII, or fragment thereof that specifically elicits the production of antibody to the factor VIII, hybrid, hybrid equivalent, or fragment in a human or animal, as measured by routine protocols, such as immunoassay, e.g. ELISA, or the Bethesda assay, described herein. It can consist of any number of amino acid residues, and it can be dependent upon the primary, secondary, or tertiary structure of the protein. In some embodiments, the hybrid or hybrid equivalent factor VIII or fragment thereof is nonimmunogenic or less immunogenic in an animal or human than human or porcine factor VIII.

As used herein, a “hybrid factor VIII equivalent molecule or fragment thereof” or “hybrid equivalent factor VIII or fragment thereof” is an active factor VIII or hybrid factor VIII molecule or fragment thereof comprising at least one sequence including one or more amino acid residues that have no known identity to human or animal factor VIII sequence substituted for at least one sequence including one or more specific amino acid residues in the human, animal, or hybrid factor VIII or fragment thereof. The sequence of one or more amino acid residues that have no known identity to human or animal factor VIII sequence is also referred to herein as “non-factor VIII amino acid sequence”. In a preferred embodiment, the amino acid(s) having no known sequence identity to factor VIII sequence are alanine residues. In another preferred embodiment, the specific factor VIII sequence for which the amino acid(s) having no known sequence identity to factor VIII sequence are substituted includes an antigenic site that is immunoreactive with naturally occurring factor VIII inhibitory antibodies, such that the resulting hybrid factor VIII equivalent molecule or fragment thereof is less immunoreactive or not immunoreactive with factor VIII inhibitory antibodies. In yet another preferred embodiment, the specific hybrid factor VIII sequence for which the amino acid(s) having no known sequence identity to factor VIII sequence are substituted includes an immunogenic site that elicits the formation of factor VIII inhibitory antibodies in an animal or human, such that the resulting hybrid factor VIII equivalent molecule or fragment thereof is less immunogenic.

“Factor VIII deficiency,” as used herein, includes deficiency in clotting activity caused by production of defective factor VIII, by inadequate or no production of factor VIII, or by partial or total inhibition of factor VIII by inhibitors. Hemophilia A is a type of factor VIII deficiency resulting from a defect in an X-linked gene and the absence or deficiency of the factor VIII protein it encodes.

As used herein, “diagnostic assays” include assays that in some manner utilize the antigen-antibody interaction to detect and/or quantify the amount of a particular antibody that is present in a test sample to assist in the selection of medical therapies. There are many such assays known to those of skill in the art. As used herein, however, the hybrid or hybrid equivalent factor VIII DNA or fragment thereof and protein expressed therefrom, in whole or in part, can be substituted for the corresponding reagents in the otherwise known assays, whereby the modified assays may be used to detect and/or quantify antibodies to factor VIII. It is the use of these reagents, the hybrid or hybrid equivalent factor VIII DNA or fragment thereof or protein expressed therefrom, that permits modification of known assays for detection of antibodies to human or animal factor VIII or to hybrid human/animal factor VIII. Such assays include, but are not limited to ELISAs, immunodiffusion assays, and immunoblots. Suitable methods for practicing any of these assays are known to those of skill in the art. As used herein, the hybrid or hybrid equivalent factor VIII or fragment thereof that includes at least one epitope of the protein can be used as the diagnostic reagent. Examples of other assays in which the hybrid or hybrid equivalent factor VIII or fragment thereof can be used include the Bethesda assay and anticoagulation assays.

U.S. Pat. No. 5,364,771 described the discovery of hybrid human/porcine factor VIII molecules having coagulant activity, in which elements of the factor VIII molecule of human or pig are substituted for corresponding elements of the factor VIII molecule of the other species. U.S. Pat. No. 5,663,060 and PCT/US94/13200 describe procoagulant hybrid human/animal and hybrid equivalent factor VIII molecules, in which elements of the factor VIII molecule of one species are substituted for corresponding elements of the factor VIII molecule of the other species.

The present invention provides hybrid human/animal, animal/animal, and equivalent factor VIII molecules and fragments thereof, and the nucleic acid sequences encoding such hybrids, some of which have greater coagulant activity in a standard clotting assay when compared to highly-purified human factor VIII; and/or are less immunoreactive to inhibitory antibodies to human or porcine factor VIII than human or porcine factor VIII; and/or are less immunogenic in a human or animal than human or porcine factor VIII. These hybrid factor VIII molecules can be constructed as follows.

At least five types of active hybrid human/porcine or hybrid equivalent factor VIII molecules or fragments thereof, the nucleic acid sequences encoding these hybrid factor VIII molecules, and the methods for preparing them are disclosed herein: those obtained (1) by substituting a human or porcine subunit (i.e., heavy chain or light chain) for the corresponding porcine or human subunit; (2) by substituting one or more human or porcine domain(s) (i.e., A1, A2, A3, B, C1, and C2) for the corresponding porcine or human domain(s); (3) by substituting a continuous part of one or more human or porcine domain(s) for the corresponding part of one or more porcine or human domain(s); (4) by substituting at least one specific sequence including one or more unique amino acid residue(s) in human or porcine factor VIII for the corresponding porcine or human sequence; and (5) by substituting at least one sequence including one or more amino acid residue(s) having no known sequence identity to factor VIII (“non-factor VIII amino acid sequence”) for at least one specific sequence of one or more amino acids in human, porcine, or hybrid human/porcine factor VIII.

At least five types of active hybrid human/non-human, non-porcine mammalian or hybrid equivalent factor VIII molecules or fragments thereof, and the nucleic acid sequences encoding them, can also be prepared by the same methods: those obtained (1) by substituting a human or non-human, non-porcine mammalian subunit (i.e., heavy chain or light chain) for the corresponding non-human, non-porcine mammalian or human subunit; (2) by substituting one or more human or non-human, non-porcine mammalian domain(s) (i.e., A1, A2, A3, B, C1 and C2) for the corresponding non-human, non-porcine mammalian or human domain(s); (3) by substituting a continuous part of one or more human or non-human, non-porcine mammalian domain(s) for the corresponding part of one or more non-human, non-porcine mammalian or human domain(s); (4) by substituting at least one specific sequence including one or more unique amino acid residue(s) in human or non-human, non-porcine mammalian factor VIII for the corresponding non-human, non-porcine mammalian or human sequence; and (5) by substituting at least one sequence including one or more amino acid residue(s) having no known sequence identity to factor VIII (“non-factor VIII amino acid sequence”) for at least one specific sequence of one or more amino acids in human, non-human, non-porcine mammalian, or hybrid human/non-human, non-porcine mammalian factor VIII.

Further, one skilled in the art will readily recognize that the same methods can be used to prepare at least five types of active hybrid factor VIII molecules or fragments thereof, corresponding to types (1)-(5) in the previous two paragraphs, comprising factor VIII amino acid sequence from two or more non-human mammals, such as porcine/mouse, and further comprising non-factor VIII amino acid sequence.

Hybrid human/animal, animal/animal, and equivalent factor VIII proteins or fragments thereof listed above under groups (1)-(3) are made by isolation of subunits, domains, or continuous parts of domains of plasma-derived factor VIII, followed by reconstitution and purification. Hybrid human/animal, animal/animal, and equivalent factor VIII proteins or fragments thereof described under groups (3)-(5) above are made by recombinant DNA methods. The hybrid molecule may contain a greater or lesser percentage of human than animal sequence, depending on the origin of the various regions, as described in more detail below.

Since current information indicates that the B domain has no inhibitory epitope and has no known effect on factor VIII function, in some embodiments the B domain is deleted in the active hybrid or hybrid equivalent factor VIII molecules or fragments thereof (“B(−) factor VIII”) prepared by any of the methods described herein.

It is shown in Example 4 that hybrid human/porcine factor VIII comprising porcine heavy chain and human light chain and corresponding to the first type of hybrid listed above has greater specific coagulant activity in a standard clotting assay compared to human factor VIII. The hybrid human/animal or equivalent factor VIII with coagulant activity, whether the activity is higher, equal to, or lower than that of human factor VIII, can be useful in treating patients with inhibitors, since these inhibitors can react less with hybrid human/animal or equivalent factor VIII than with either human or porcine factor VIII.

Preparation of Hybrid Factor VIII Molecules from Isolated Human and Animal Factor VIII Subunits by Reconstitution

The present invention provides hybrid human/animal factor VIII molecules or fragments thereof, with subunit substitutions, the nucleic acid sequences encoding these hybrids, methods for preparing and isolating them, and methods for characterizing their procoagulant activity. One method, modified from procedures reported by Fay, P. J. et al. (1990) J. Biol. Chem. 265:6197; and Lollar, J. S. et al. (1988) J. Biol. Chem. 263:10451, involves the isolation of subunits (heavy and light chains) of human and animal factor VIII, followed by recombination of human heavy chain and animal light chain or by recombination of human light chain and animal heavy chain.

Isolation of both human and animal individual subunits involves dissociation of the light chain/heavy chain dimer. This is accomplished, for example, by chelation of calcium with ethylenediaminetetraacetic acid (EDTA), followed by MonoS™ HPLC (Pharmacia-LKB, Piscataway, N.J.). Hybrid human/animal factor VIII molecules are reconstituted from isolated subunits in the presence of calcium. Hybrid human light chain/animal heavy chain or animal light chain/human heavy chain factor VIII is isolated from unreacted heavy chains by MonoS™ HPLC by procedures for the isolation of porcine factor VIII, such as described by Lollar, J. S. et al. (1988) Blood 71:137-143.

These methods, used in one embodiment to prepare active hybrid human/porcine factor VIII, described in detail in the examples below, result in hybrid human light chain/porcine heavy chain molecules with greater than six times the procoagulant activity of human factor VIII.

Other hybrid human/non-human, non-porcine mammalian factor VIII molecules can be prepared, isolated, and characterized for activity by the same methods. One skilled in the art will readily recognize that these methods can also be used to prepare, isolate, and characterize for activity hybrid animal/animal factor VIII, such as porcine/mouse, comprising the light or heavy chain or one species is combined with the heavy or light chain of the other species.

Preparation of Hybrid Factor VIII Molecules from Isolated Human and Animal Factor VIII Domains by Reconstitution

The present invention provides hybrid human/animal factor VIII molecules or fragments thereof with domain substitutions, the nucleic acid sequences encoding them, methods for preparing and isolating them, and methods for characterizing their procoagulant activity. One method involves the isolation of one or more domains of human and one or more domains of animal factor VIII, followed by recombination of human and animal domains to form hybrid human/animal factor VIII with coagulant activity, as described by Lollar, P. et al. (1992) J. Biol. Chem. 267(33):23652-23657, for hybrid human/porcine factor VIII.

Specifically provided is a hybrid human/porcine factor VIII with substitution of the porcine A2 domain for the human A2 domain, which embodiment illustrates a method by which domain-substituted hybrid human/non-human, non-porcine mammalian factor VIII can be constructed. Plasma-derived non-human, non-porcine mammalian and human A1/A3-C1-C2 dimers are isolated by dissociation of the A2 domain from factor VIIIa. This is accomplished, for example, in the presence of NaOH, after which the mixture is diluted and the dimer is eluted using MonoS™ HPLC (Pharmacia-LKB, Piscataway, N.J.). The A2 domain is isolated from factor VIIIa as a minor component in the MonoS™ HPLC. Hybrid human/animal factor VIII molecules are reconstituted by mixing equal volumes of the A2 domain of one species and the A1/A3-C1-C2 dimer of the other species.

Hybrid human/animal factor VIII or fragments thereof with one or more domain substitutions is isolated from the mixture of unreacted dimers and A2 by MonoS™ HPLC by procedures for the isolation of porcine factor VIII, as described by Lollar, J. S. et al. (1988) Blood 71:137-143. Routine methods can also be used to prepare and isolate the A1, A3, C1, C2, and B domains of the factor VIII of one species, any one or more of which can be substituted for the corresponding domain in the factor VIII of the other species. One skilled in the art will readily recognize that these methods can also be used to prepare, isolate, and characterize for activity domain-substituted hybrid animal/animal factor VIII, such as porcine/mouse.

These methods, described in detail in the examples below, result in hybrid factor VIII molecules with procoagulant activity.

The present invention provides active, recombinant hybrid human/animal and hybrid equivalent factor VIII molecules and fragments thereof with subunit, domain, and amino acid sequence substitutions, the nucleic acid sequences encoding these hybrids, methods for preparing and isolating them, and methods for characterizing their coagulant, immunoreactive, and immunogenic properties.

The human factor VIII gene was isolated and expressed in mammalian cells, as reported by Toole, J. J. et al. (1984) Nature 312:342-347 (Genetics Institute); Gitschier, J. et al. (1984) Nature 312:326-330 (Genentech); Wood, W. I. et al. (1984) Nature 312:330-337 (Genentech); Vehar, G. A. et al. (1984) Nature 312:337-342 (Genentech); WO 87/04187; WO 88/08035; WO 88/03558; U.S. Pat. No. 4,757,006, and the amino acid sequence was deduced from cDNA. U.S. Pat. No. 4,965,199 to Capon et al. discloses a recombinant DNA method for producing factor VIII in mammalian host cells and purification of human factor VIII. Human factor VIII expression on CHO (Chinese hamster ovary) cells and BHKC (baby hamster kidney cells) has been reported. Human factor VIII has been modified to delete part or all of the B domain (U.S. Pat. No. 4,868,112), and replacement of the human factor VIII B domain with the human factor V B domain has been attempted (U.S. Pat. No. 5,004,803). The cDNA sequence encoding human factor VIII and predicted amino acid sequence are shown in SEQ ID NOs:1 and 2, respectively.

Porcine factor VIII has been isolated and purified from plasma (Fass, D. N. et al. (1982) Blood 59:594). Partial amino acid sequence of porcine factor VIII corresponding to portions of the N-terminal light chain sequence having homology to ceruloplasmin and coagulation factor V and largely incorrectly located were described by Church et al. (1984) Proc. Nat. Acad. Sci. USA 81:6934. Toole, J. J. et al. (1984) Nature 312:342-347 described the partial sequencing of the N-terminal end of four amino acid fragments of porcine factor VIII but did not characterize the fragments as to their positions in the factor VIII molecule. The amino acid sequence of the B and part of the A2 domains of porcine factor VIII were reported by Toole, J. J. et al. (1986) Proc. Nat. Acad. Sci. USA 83:5939-5942. The cDNA sequence encoding the complete A2 domain of porcine factor VIII and predicted amino acid sequence and hybrid human/porcine factor VIII having substitutions of all domains, all subunits, and specific amino acid sequences were disclosed in U.S. Pat. No. 5,364,771 and in WO 93/20093. The cDNA sequence encoding the A2 domain of porcine factor VIII having sequence identity to residues 373-740 in mature human factor VIII, as shown in SEQ ID NO:1, and the predicted amino acid sequence are shown in SEQ ID NOs:3 and 4, respectively. More recently, the nucleotide and corresponding amino acid sequences of the A1 and A2 domains of porcine factor VIII and a chimeric factor VIII with porcine A1 and/or A2 domains substituted for the corresponding human domains were reported in WO 94/11503.

Both porcine and human factor VIII are isolated from plasma as a two subunit protein. The subunits, known as the heavy chain and light chain, are held together by a non-covalent bond that requires calcium or other divalent metal ions. The heavy chain of factor VIII contains three domains, A1, A2, and B, which are linked covalently. The light chain of factor VIII also contains three domains, designated A3, C1, and C2. The B domain has no known biological function and can be removed from the molecule proteolytically or by recombinant DNA technology methods without significant alteration in any measurable parameter of factor VIII. Human recombinant factor VIII has a similar structure and function to plasma-derived factor VIII, though it is not glycosylated unless expressed in mammalian cells.

Both human and porcine activated factor VIII (“factor VIIIa”) have three subunits due to cleavage of the heavy chain between the A1 and A2 domains. This structure is designated A1/A2/A3-C1-C2. Human factor VIIIa is not stable under the conditions that stabilize porcine factor VIIIa, presumably because of the weaker association of the A2 subunit of human factor VIIIa. Dissociation of the A2 subunit of human and porcine factor VIIIa is associated with loss of activity in the factor VIIIa molecule.

Using as probes the known sequence of parts of the porcine factor VIII molecule, the domains of the porcine factor VIII molecule that have not been sequenced to date can be sequenced by standard, established cloning techniques, such as those described in Weis, J. H., “Construction of recombinant DNA libraries,” in Current Protocols in Molecular Biology, F. M. Ausubel et al., eds. (1991); and Sambrook, J. (1989), et al., Molecular Cloning, A Laboratory Manual, so that full length hybrids can be constructed.

Specifically provided as an exemplary and a preferred embodiment is active recombinant hybrid human/porcine factor VIII having substituted A2 domain, the nucleic acid sequence encoding it, and the methods for preparing, isolating, and characterizing its activity. The methods by which this hybrid construct is prepared can also be used to prepare active recombinant hybrid human/porcine factor VIII or fragments thereof having substitution of subunits, continuous parts of domains, or domains other than A2. One skilled in the art will recognize that these methods also demonstrate how other recombinant hybrid human/non-human, non-porcine mammalian or animal/animal hybrid factor VIII molecules or fragments thereof can be prepared in which subunits, domains, or continuous parts of domains are substituted.

Recombinant hybrid human/porcine factor VIII is prepared starting with human cDNA (Biogen, Inc.) or porcine cDNA (described herein) encoding the relevant factor VIII sequence. In a preferred embodiment, the factor VIII encoded by the cDNA includes domains A1-A2-A3-C1-C2, lacking the entire B domain, and corresponds to amino acid residues 1-740 and 1649-2332 of single chain human factor VIII (see SEQ ID NO:2), according to the numbering system of Wood et al. (1984) Nature 312:330-337.

Individual subunits, domains, or continuous parts of domains of porcine or human factor VIII cDNA can be and have been cloned and substituted for the corresponding human or porcine subunits, domains, or parts of domains by established mutagenesis techniques. For example, Lubin, I. M. et al. (1994) J. Biol. Chem. 269(12):8639-8641 describes techniques for substituting the porcine A2 domain for the human domain using convenient restriction sites. Other methods for substituting any arbitrary region of the factor VIII cDNA of one species for the factor VIII cDNA of another species include splicing by overlap extension (“SOE”), as described by Horton, R. M. et al. (1993) Meth. Enzymol 217:270-279.

The hybrid factor VIII cDNA encoding subunits, domains, or parts of domains or the entire hybrid cDNA molecules are cloned into expression vectors for ultimate expression of active hybrid human/porcine factor VIII protein molecules in cultured cells by established techniques, as described by Selden, R. F., “Introduction of DNA into mammalian cells,” in Current Protocols in Molecular Biology, F. M. Ausubel et al., eds (1991).

In an embodiment, a hybrid human/porcine cDNA encoding factor VIII, in which the porcine sequence encodes a domain or part domain, such as the A2 domain or part domain, is inserted in a mammalian expression vector, such as ReNeo, to form a hybrid factor VIII construct. Preliminary characterization of the hybrid factor VIII is accomplished by insertion of the hybrid cDNA into the ReNeo mammalian expression vector and transient expression of the hybrid protein in COS-7 cells. A determination of whether active hybrid protein is expressed can then be made. The expression vector construct is used further to stably transfect cells in culture, such as baby hamster kidney cells, using methods that are routine in the art, such as liposome-mediated transfection (LipofectinJ, Life Technologies, Inc.). Expression of recombinant hybrid factor VIII protein can be confirmed, for example, by sequencing, Northern and Western blotting, or polymerase chain reaction (PCR). Hybrid factor VIII protein in the culture media in which the transfected cells stably expressing the protein are maintained can be precipitated, pelleted, washed, and resuspended in an appropriate buffer, and the recombinant hybrid factor VIII protein purified by standard techniques, including immunoaffinity chromatography using, for example, monoclonal anti-A2-Sepharose™.

In a further embodiment, the hybrid factor VIII comprising subunit, domain, or amino acid sequence substitutions is expressed as a fusion protein from a recombinant molecule in which sequence encoding a protein or peptide that enhances, for example, stability, secretion, detection, isolation, or the like is inserted in place adjacent to the factor VIII encoding sequence. Established protocols for use of homologous or heterologous species expression control sequences including, for example, promoters, operators, and regulators, in the preparation of fusion proteins are known and routinely used in the art. See Current Protocols in Molecular Biology (Ausubel, F. M., et al., eds), Wiley Interscience, N.Y.

The purified hybrid factor VIII or fragment thereof can be assayed for immunoreactivity and coagulation activity by standard assays including, for example, the plasma-free factor VIII assay, the one-stage clotting assay, and the enzyme-linked immunosorbent assay using purified recombinant human factor VIII as a standard.

Other vectors, including both plasmid and eukaryotic viral vectors, may be used to express a recombinant gene construct in eukaryotic cells depending on the preference and judgment of the skilled practitioner (see, for example, Sambrook et al., Chapter 16). Other vectors and expression systems, including bacterial, yeast, and insect cell systems, can be used but are not preferred due to differences in, or lack of, glycosylation.

Recombinant hybrid or other modified factor VIII protein can be expressed in a variety of cells commonly used for culture and recombinant mammalian protein expression. In particular, a number of rodent cell lines have been found to be especially useful hosts for expression of large proteins. Preferred cell lines, available from the American Type Culture Collection, Manassas, Va., include baby hamster kidney cells, and Chinese hamster ovary (CHO) cells which are cultured using routine procedures and media.

The same methods employed for preparing hybrid human/porcine factor VIII having subunit, domain, or amino acid sequence substitution can be used to prepare other recombinant hybrid factor VIII protein and fragments thereof and the nucleic acid sequences encoding these hybrids, such as human/non-human, non-porcine mammalian or animal/animal. Starting with primers from the known human DNA sequence, the murine and part of the porcine factor VIII cDNA have been cloned. Factor VIII sequences of other species for use in preparing a hybrid human/animal or animal/animal factor VIII molecule can be obtained using the known human and porcine DNA sequences as a starting point. Other techniques that can be employed include PCR amplification methods with animal tissue DNA, and use of a cDNA library from the animal to clone out the factor VIII sequence.

As an exemplary embodiment, hybrid human/mouse factor VIII protein can be made as follows. DNA clones corresponding to the mouse homolog of the human factor VIII gene have been isolated and sequenced and the amino acid sequence of mouse factor VIII protein predicted, as described in Elder, G., et al. (1993) Genomics 16(2):374-379, which also includes a comparison of the predicted amino acid sequences of mouse, human, and part of porcine factor VIII molecules. The mouse factor VIII cDNA sequence and predicted amino acid sequence are shown in SEQ ID NO:5 and SEQ ID NO:8, respectively. In a preferred embodiment, the RNA amplification with transcript sequencing (RAWTS) methods described in Sarkar, G. et al. (1989) Science 244:331-334, can be used. Briefly, the steps are (1) cDNA synthesis with oligo(dT) or an mRNA-specific oligonucleotide primer; (2) polymerase chain reaction (PCR) in which one or both oligonucleotides contains a phage promoter attached to a sequence complementary to the region to be amplified; (3) transcription with a phage promoter; and (4) reverse transcriptase-mediated dideoxy sequencing of the transcript, which is primed with a nested (internal) oligonucleotide. In addition to revealing sequence information, this method can generate an in vitro translation product by incorporating a translation initiation signal into the appropriate PCR primer: and can be used to obtain novel mRNA sequence information from other species.

The present invention provides active recombinant hybrid human/animal and animal/animal factor VIII molecules or fragments thereof comprising at least one sequence including one or more unique amino acids of one species substituted for the corresponding amino acid sequence of the other species or fragments thereof, nucleic acid sequences encoding these hybrids, methods for preparing and isolating them, and methods for characterizing their coagulant, immunogenic and immunoreactive properties.

The A2 domain is necessary for the procoagulant activity of the factor VIII molecule. Studies show that porcine factor VIII has six-fold greater procoagulant activity than human factor VIII (Lollar, P. et al. (1991) J. Biol. Chem. 266:12481-12486, and that the difference in coagulant activity between human and porcine factor VIII appears to be based on a difference in amino acid sequence between one or more residues in the human and porcine A2 domains (Lollar, P. et al. (1992) J. Biol. Chem. 267:23652-23657. Further, the A2 and C2 domains and possibly a third light chain region in the human factor VIII molecule are thought to harbor the epitopes to which most, if not all, inhibitory antibodies react, according to Hoyer (1994) Semin. Hematol. 31:1-5.

Recombinant hybrid human/animal, animal/animal, or equivalent factor VIII molecules or fragments thereof can be made by substitution of at least one specific sequence including one or more unique amino acids from the A2, C2, and/or other domains of the factor VIII of one species for the corresponding sequence of the other species, wherein the amino acid sequences differ, as illustrated in more detail below, between the molecules of the two species. In an exemplary preferred embodiment described herein, the present invention provides active recombinant hybrid human/porcine factor VIII comprising porcine amino acid sequence substituted for corresponding human amino acid sequence that includes an epitope, wherein the hybrid factor VIII has decreased or no immunoreactivity with inhibitory antibodies to factor VIII. In a further embodiment, active recombinant hybrid factor VIII molecules can also be made comprising amino acid sequence from more than one species substituted for the corresponding sequence in a third species. Recombinant hybrid equivalent molecules can also be made, comprising human, animal, or hybrid factor VIII including at least one sequence including one or more amino acids that have no known sequence identity to factor VIII, as further described below.

Any hybrid factor VIII construct having specific amino acid substitution as described can be assayed by standard procedures for coagulant activity and for reactivity with inhibitory antibodies to factor VIII for identification of hybrid factor VIII molecules with enhanced coagulant activity and/or decreased antibody immunoreactivity. Hybrid molecules may also be identified that have reduced coagulant activity compared to human or porcine factor VIII but also have decreased antibody reactivity. One skilled in the art will recognize that hybrid factor VIII molecules or fragments thereof having less, equal, or greater coagulant activity, compared to human or porcine factor VIII, is useful for treating patients who have a factor VIII deficiency. The methods described herein to prepare active recombinant hybrid human/porcine factor VIII with substitution of specific amino acids can be used to prepare active recombinant hybrid human/non-human, non-porcine mammalian factor VIII protein, hybrid animal-1/animal-2 factor VIII, and hybrid equivalent factor VIII or fragments thereof.

Hybrid Factor VIII Molecules with Altered Coagulant Activity

The present invention provides procoagulant recombinant hybrid human/animal, animal/animal, or equivalent factor VIII molecules or fragments thereof comprising at least one specific sequence including one or more unique amino acids having procoagulant activity in the factor VIII of one species substituted for the corresponding amino acid sequence of the factor VIII of the other species, using established site-directed mutagenesis techniques as described herein. The specific sequences to be used in the substitution are selected and the hybrid constructs are prepared and assayed for coagulant activity, as follows. Specifically provided as a preferred and exemplary embodiment is a hybrid human/porcine factor VIII comprising amino acid substitutions in the A2 domain. It is understood that one skilled in the art can use these methods to prepare other hybrid human/animal, animal/animal, and equivalent factor VIII molecules or fragments thereof having altered coagulant activity, preferably increased coagulant activity compared to human factor VIII.

The basis for the greater coagulant activity in porcine factor VIII appears to be the more rapid spontaneous dissociation of the A2 subunit of human factor VIIIa than porcine factor VIIIa, which leads to loss of activity, according to Lollar, P. et al. (1990) J. Biol. Chem. 265:1688-1692; Lollar, P. et al. (1992) J. Biol. Chem. 267:23652-23657; Fay, P. J. et al. (1992) J. Biol. Chem. 267:13246-13250.

A comparison of the alignment of the amino acid sequences of the human and porcine factor VIII A2 domains (residue numbering starts at position 373 with respect to the full length amino acid sequence of human factor VIII, SEQ ID NO:2) is shown in FIG. 1C. For preparation of a hybrid human/porcine factor VIII molecule with altered coagulant activity, the initial target candidates for mutagenesis, which were revealed upon comparison of the human and porcine A2 amino acid sequences (SEQ ID NOs: 2 and 6, respectively) within the human A2 domain, are shown in Table I.

TABLE I HUMAN AMINO ACID SEQUENCE TARGET CANDIDATES FOR MUTAGENESIS (SEQ ID NO: 2) Sequence Changes Residues Mismatches Charge 398-403 6 4 1 434-444 10 4 3 484-496 13 7 3 598-603 6 4 2 536-541 6 4 0 713-722 10 6 2 727-737 11 6 2

Table I and the bold letters of FIGS. 1A-1B illustrate seven sequences in the human and pig A2 domain amino acid sequences (SEQ ID NOs:2 and 4, respectively) that constitute only 17 percent of the A2 domain but include 70 percent of the sequence differences between human and porcine A2 domains.

A recombinant hybrid human/porcine construct is described in which amino acids Ser373-Glu604 in the A2 domain (Ser373-Arg740) of human factor VIII have been replaced with the homologous porcine sequence. This construct does not react with A2 inhibitors and has the same coagulant activity as human B(−) factor VIII. A plasma-derived hybrid molecule is described that comprises a complete porcine A2 domain substitution in the human factor VIII that has increased coagulant activity compared to human factor VIII. Comparison of these constructs indicates that a region between residues Asp605 and Arg740 is responsible for the difference in activity between human and porcine factor VIII. This region can be defined more specifically by systematically making recombinant hybrid human/porcine factor VIII molecules with porcine substitutions in the region between Asp605 and Arg740 by using established site-directed mutagenesis techniques, for example, the “splicing by overlap extension” (SOE) method that has been used extensively to make hybrid factor VIII molecules containing porcine substitutions in the NH2-terminal region of A2. These molecules can be expressed in COS-7 cells and baby hamster kidney cells as described above. They can be purified to homogeneity using methods known in the art, such as heparin-Sepharose™ and immunoaffinity chromatography. Protein concentration can be estimated by absorption of ultraviolet light at A280, and the specific activity of the constructs can be determined by dividing coagulant activity (measured in units per ml by single stage clotting assay) by A280. Human factor VIII has a specific activity of approximately 3000-4000 U/A280, whereas porcine factor VIII has a specific activity of approximately 20,000 U/A280. In a preferred embodiment, the procoagulant recombinant hybrid human/porcine factor VIII has a specific activity of 20,000 U/A280 and contains a minimal amount of porcine substitution in the A2 domain.

As described herein, site-directed mutagenesis techniques are used to identify hybrid protein with coagulant activity that can be enhanced, equal to, or reduced, compared to human factor VIII, but preferably is enhanced. In the hybrid human/porcine embodiment, specific human sequences are replaced with porcine sequences, preferably using the splicing by overlap extension method (SOE), as described by Ho, S, N., et al., (1994) Gene 77:51-59, and in Examples 7 and 8. Oligonucleotide-directed mutagenesis can also be used, as was done to loop out the amino acid sequence for part of the human A2 domain (see Example 7). As functional analysis of the hybrids reveals coagulant activity, the sequence can be further dissected and mapped for procoagulant sequence by standard point mutation analysis techniques.

The present invention contemplates that hybrid factor VIII cDNA and protein can be characterized by methods that are established and routine, such as DNA sequencing, coagulant activity assays, mass by ELISA and by UV absorbance at 280 nm of purified hybrid factor VIII, specific coagulant activity (U/mg), SDS-PAGE of purified hybrid factor VIII, and the like. Other known methods of testing for clinical effectiveness may be required, such as amino acid, carbohydrate, sulfate, or metal ion analysis.

A recombinant hybrid factor VII having superior coagulant activity, compared to human factor VIII, may be less expensive to make than plasma-derived factor VIII and may decrease the amount of factor VIII required for effective treatment of factor VIII deficiency.

Hybrid Factor VIII Molecules with Reduced Immunoreactivity

Epitopes that are immunoreactive with antibodies that inhibit the coagulant activity of factor VIII (“inhibitors” or “inhibitory antibodies”) have been characterized based on known structure-function relationships in factor VIII. Presumably, inhibitors could act by disrupting any of the macromolecular interactions associated with the domain structure of factor VIII or its associations with von Willebrand factor, thrombin, factor Xa, factor IXa, or factor X. However, over 90 percent of inhibitory antibodies to human factor VIII act by binding to epitopes located in the 40 kDa A2 domain or 20 kDa C2 domain of factor VIII, disrupting specific functions associated with these domains, as described by Fulcher et al. (1985) Proc. Nat. Acad. Sci. USA 82:7728-7732; and Scandella et al. (1988) Proc. Nat. Acad. Sci. USA 85:6152-6156. In addition to the A2 and C2 epitopes, there may be a third epitope in the A3 or C1 domain of the light chain of factor VIII, according to Scandella et al. (1993) Blood 82:1767-1775. The significance of this putative third epitope is unknown, but it appears to account for a minor fraction of the epitope reactivity in factor VIII.

Anti-A2 antibodies block factor X activation, as shown by Lollar et al. (1994) J. Clin. Invest. 93:2497-2504. Previous mapping studies by deletion mutagenesis described by Ware et al. (1992) Blood Coagul. Fibrinolysis 3:703-716, located the A2 epitope to within a 20 kDa region of the NH2-terminal end of the 40 kDa A2 domain. Competition immunoradiometric assays have indicated that A2 inhibitors recognize either a common epitope or narrowly clustered epitopes, as described by Scandella et al. (1992) Throm. Haemostas 67:665-671, and as demonstrated in Example 8.

The present invention provides active recombinant hybrid and hybrid equivalent factor VIII molecules or fragments thereof, the nucleic acid sequences encoding these hybrids, methods of preparing and isolating them, and methods for characterizing them. These hybrids comprise human/animal, animal/animal, or equivalent hybrid factor VIII molecules, further comprising at least one specific amino acid sequence including one or more unique amino acids of the factor VIII of one species substituted for the corresponding amino acid sequence of the factor VIII of the other species; or comprises at least one sequence including one or more amino acids having no known sequence identity to factor VIII substituted for specific amino acid sequence in human, animal, or hybrid factor VIII. The resulting hybrid factor VIII has reduced or no immunoreactivity to factor VIII inhibitory antibodies, compared to human or porcine factor VIII.

Using the approach described in the previous section for substitution of amino acids in the factor VIII molecule, mutational analysis is employed to select corresponding factor VIII amino acid sequence of one species, preferably porcine, which is substituted for at least one sequence including one or more amino acids in the factor VIII of another species, preferably human, or for amino acid sequence of a hybrid equivalent factor VIII molecule, that includes one or more critical region(s) in the A2, C2, or any other domain to which inhibitory antibodies are directed. The methods are described in more detail below. The resulting procoagulant recombinant hybrid construct has reduced or no immunoreactivity to inhibitory antibodies, compared to human factor VIII, using standard assays. Through systematic substitution of increasingly smaller amino acid sequences followed by assay of the hybrid construct for immunoreactivity, as described below, the epitope in any domain of a factor VIII molecule is mapped, substituted by amino acid sequence having less or no immunoreactivity, and a hybrid factor VIII is prepared.

It is understood that one skilled in the art can use this approach combining epitope mapping, construction of hybrid factor VIII molecules, and mutational analysis of the constructs to identify and replace at least one sequence including one or more amino acids comprising an epitope in the A2, C2, and/or other domains to which inhibitory antibodies are directed and to construct procoagulant recombinant hybrid human/animal, animal/animal, or equivalent factor VIII or fragments thereof having decreased or no immunoreactivity compared to human or porcine factor VIII. This approach is used, as described in Example 8, to prepare a recombinant procoagulant hybrid human/porcine factor VIII having porcine amino acid substitutions in the human A2 domain and no antigenicity to anti-factor VIII antibodies as an exemplary embodiment.

Usually, porcine factor VIII has limited or no reaction with inhibitory antibodies to human factor VIII. The recombinant hybrid human/porcine factor VIII molecules having decreased or no reactivity with inhibitory antibodies based on amino acid substitution in the A2 domain are prepared, as an example of how hybrid factor VIII can be prepared using the factor VIII of other species and substitutions in domains other than A2, as follows. The porcine A2 domain is cloned by standard cloning techniques, such as those described above and in Examples 6, 7, and 8, and then cut and spliced within the A2 domain using routine procedures, such as using restriction sites to cut the cDNA or splicing by overlap extension (SOE). The resulting porcine amino acid sequence is substituted into the human A2 domain to form a hybrid factor VIII construct, which is inserted into a mammalian expression vector, preferably ReNeo, stably transfected into cultured cells, preferably baby hamster kidney cells, and expressed, as described above. The hybrid factor VIII is assayed for immunoreactivity, for example with anti-A2 antibodies by the routine Bethesda assay or by plasma-free chromogenic substrate assay. The Bethesda unit (BU) is the standard method for measuring inhibitor titers. If the Bethesda titer is not measurable (<0.7 BU/mg IgG) in the hybrid, then a human A2 epitope was eliminated in the region of substituted corresponding porcine sequence. The epitope is progressively narrowed, and the specific A2 epitope can thus be determined to produce a hybrid human/porcine molecule with as little porcine sequence as possible. As described herein, a 25-residue sequence corresponding to amino acids Arg484-Ile508 that is critical for inhibitory immunoreactivity has been identified and substituted in the human A2 domain. Within this sequence are only nine differences between human and porcine factor VIII. This region can be further analyzed and substituted.

Hybrid human/porcine factor VIII molecules having decreased or no reactivity with inhibitory antibodies based on substitution of amino acid sequence in the C1, C2 or other domain, with or without substitution in the A2 domain, can also be prepared. The C2 epitope, for example can be mapped using the homolog scanning approach combined with site-directed mutagenesis. More specifically, the procedures can be the same or similar to those described herein for amino acids substitution in the A2 domain, including cloning the porcine C2 or other domain, for example by using RT-PCR or by probing a porcine liver cDNA library with human C2 or other domain DNA; restriction site techniques and/or successive SOE to map and simultaneously replace epitopes in the C2 or other domain; substitution for the human C2 or other domain in B(−) factor VIII; insertion into an expression vector, such as pBluescript; expression in cultured cells; and routine assay for immunoreactivity. For the assays, the reactivity of C2 hybrid factor VIII with a C2-specific inhibitor, MR (Scandella et al. (1992) Thromb. Haemostasis 67:665-671 and Lubin et al. (1994)), and/or other C2 specific antibodies prepared by affinity chromatography can be performed.

The C2 domain consists of amino acid residues 2173-2332 (SEQ ID NO:2). Within this 154 amino acid region, inhibitor activity appears to be directed to a 65 amino acid region between residues 2248 and 2312, according to Shima, M. et al. (1993) Thromb. Haemostasis 69:240-246. If the C2 sequence of human and porcine factor VIII is approximately 85 percent identical in this region, as it is elsewhere in the functionally active regions of factor VIII, there will be approximately ten differences between human and porcine factor VIII C2 amino acid sequence, which can be used as initial targets to construct hybrids with substituted C2 sequence.

It is likely that clinically significant factor VIII epitopes are confined to the A2 and C2 domains. However, if antibodies to other regions (A1, A3, B, or C1 domains) of factor VIII are identified, the epitopes can be mapped and eliminated by using the approach described herein for the nonantigenic hybrid human/porcine factor VIII molecules.

More specifically, mapping of the putative second light chain epitope and/or any other epitope in any other animal or human factor VIII domain can also be accomplished. Initially, determination of the presence of a third inhibitor epitope in the A3 or C1 domains can be made as follows. Using human (“H”) and porcine (“p”) factor VIII amino acid sequences as a model, A1p-A2p-A3p-C1H-C2p and A1p-A2p-A3H-C1p-C2p B-domainless hybrids will be constructed. Inhibitor IgG from approximately 20 patient plasmas (from Dr. Dorothea Scandella, American Red Cross) who have low or undetectable titers against porcine factor VIII will be tested against the hybrids. If the third epitope is in the A3 domain, inhibitory IgG is expected to react with A1p-A2p-A3H-C1p-C2p but not A1p-A2p-A3p-C1H-C2p. Conversely, if the third epitope is in the C1 domain, then inhibitory IgG is expected to react with A1p-A2p-A3p-C1H-C2p but not A1p-A2p-A3H-C1p-C2p. If a third epitope is identified it will be characterized by the procedures described herein for the A2 and C2 epitopes.

For example, antibodies specific for the C1 or A3 domain epitope can be isolated from total patient IgG by affinity chromatography using the A1p-A2p-A3H-C1p-C2p and A1p-A2p-A3p-C1H-C2p hybrids, and by elimination of C2 specific antibodies by passage over recombinant factor VIII C2-Sepharaose™. The putative third epitope will be identified by SOE constructs in which, in a preferred embodiment, portions of the human factor VIII A3 or C1 domain are systematically replaced with porcine sequence.

Hybrid Factor VIII Molecules with Reduced Immunogenicity:

A molecule is immunogenic when it can induce the production of antibodies in human or animal. The present invention provides a procoagulant recombinant hybrid human/animal or animal/animal factor VIII molecule, hybrid factor VIII equivalent molecule, or fragment of either that is less immunogenic than wild-type human porcine factor VIII in human or animal, comprising at least one specific amino acid sequence including one or more unique amino acids of the factor VIII of one species substituted for the corresponding amino acid sequence that has immunogenic activity of the factor VIII of the other species; or at least one amino acid sequence including one or more amino acids having no known identity to factor VIII substituted for amino acid sequence of the human, animal, or hybrid factor. This hybrid can be used to lower the incidence of inhibitor development in an animal or human and to treat factor VIII deficiency, and would be preferred in treating previously untreated patients with hemophilia. In a preferred embodiment, the hybrid factor VIII comprises human factor VIII amino acid sequence, further comprising one or more alanine residues substituted for human amino acid sequence having immunogenic activity, resulting in a procoagulant recombinant hybrid equivalent molecule or fragment thereof having reduced or no immunogenicity in human or animal.

The process described herein of epitope mapping and mutational analysis combined with substitution of non-antigenic amino acid sequence in a factor VIII molecule, using hybrid human/porcine factor VIII, produces hybrid molecules with low antigenicity. Using this model and the associated methods, any of the hybrid constructs described herein can be altered by site-directed mutagenesis techniques to remove as much of any functional epitope as possible to minimize the ability of the immune system to recognize the hybrid factor VIII, thereby decreasing its immunogenicity.

One method that can be used to further reduce the antigenicity and to construct a less immunogenic hybrid factor VIII is alanine scanning mutagenesis, described by Cunningham, B. C. et al. (1989) Science 244:1081-1085, of selected specific amino acid sequences in human, animal, or hybrid equivalent factor VIII. In alanine scanning mutagenesis, amino acid side chains that are putatively involved in an epitope are replaced by alanine residues by using site-directed mutagenesis. By comparing antibody binding of alanine mutants to wild-type protein, the relative contribution of individual side chains to the binding interaction can be determined. Alanine substitutions are likely to be especially useful, since side chain contributions to antibody binding are eliminated beyond the β carbon, but, unlike glycine substitution, main chain conformation is not usually altered. Alanine substitution does not impose major steric, hydrophobic or electrostatic effects that dominate protein-protein interactions.

In protein antigen-antibody interactions, there usually are about 15-20 antigen side chains in contact with the antibody. Side chain interactions, as opposed to main chain interactions, dominate protein-protein interactions. Recent studies have suggested that only a few (approximately 3 to 5) of these side chain interactions contribute most of the binding energy. See Clackson, T. et al. (1995) Science 267:383-386. An extensive analysis of growth hormone epitopes for several murine monoclonal antibodies revealed the following hierarchy for side chain contributions to the binding energy: Arg>Pro>Glu-Asp-Phe-Ile, with Trp, Ala, Gly, and Cys not tested (Jin, L. et al. (1992) J. Mol. Biol. 226:851-865). Results with the A2 epitope described herein are consistent with this, since twelve of the 25 residues in the 484-508 A2 segment contain these side chains (Table 1).

The finding that certain amino acid residues are particularly well recognized by antibodies, indicates that elimination of these residues from a known epitope can decrease the ability of the immune system to recognize these epitopes, i.e., can make a molecule less immunogenic. In the case of the A2 epitope, immunogenic residues can be replaced without loss of factor VIII coagulant activity. For example, in HP9, Arg484 is replaced by Ser, Pro485 is replaced by Ala, Arg489 is replaced by Gly, Pro492 is replaced by Leu, and Phe501 is replaced by Met. Further, results from the patient plasmas used to test immunoreactivity in hybrid human/porcine factor VIII constructs, described in Example 8, indicate that antibodies from different patients recognize the same or a very similar structural region in the A2 domain and that the residues in the A2 domain that participate in binding A2 inhibitors appear to show little variation. Thus, the A2 epitope included in human factor VIII residues 484-508 is an immunodominant epitope in that it is recognized by the human immune system better than other structural regions of factor VIII. Replacing this structure by nonantigenic factor VIII sequence from another species or by non-factor VIII amino acid sequence, while retaining full procoagulant activity, is expected to alter recognition of hybrid or hybrid equivalent factor VIII by the immune system.

It is anticipated that site-directed mutagenesis to replace bulky and/or charged residues that tend to dominate epitopes with small, neutral side chains (e.g., alanine) may produce a less immunogenic region. It is expected that a molecule containing a few of these substitutions at each significant inhibitor epitope will be difficult for the immune system to fit by the lock-and-key mechanism that is typical of antigen-antibody interactions. Because of its low antigenicity, such a hybrid molecule could be useful in treating factor VIII deficiency patients with inhibitors, and because of its low immunogenicity, it could be useful in treating previously untreated patients with hemophilia A. The POL1212 protein expression product of DNA comprising SEQ ID NO:48 is especially useful in treatment of hemophilia A patients.

A general result is that mutation of one of a few key residues is sufficient to decrease the binding constant for a given protein-protein interaction by several orders of magnitude. Thus, it appears likely that all factor VIII epitopes contain a limited number of amino acids that are critical for inhibitor development. For each epitope in factor VIII, alanine substitutions for at least one sequence including one or more specific amino acids having immunogenic activity, may produce an active molecule that is less immunogenic than wild-type factor VIII. In a preferred embodiment, the porcine factor VIII is B-domainless.

The methods for preparing active recombinant hybrid or hybrid equivalent factor VIII with substitution of amino acid sequence having little or no immunogenic activity for amino acid sequence in the factor VIII having immunogenic activity are as follows, using hybrid human/porcine factor VIII with amino acid substitutions in the A2 domain as an exemplary embodiment. There are 25 residues in the human factor VIII region 484-508. Site-directed mutagenesis can be used to make single mutants in which any of these residues is replaced by any of the other 19 amino acids for a total of 475 mutants. Furthermore, hybrid molecules having more than one mutation can be constructed.

The hybrid constructs can be assayed for antigenicity by measuring the binding constant for inhibitor antibodies, as described by Friguet, B. et al. (1985) J. Immunol. Methods 77:305-319 (1985). In a preferred embodiment, the binding constant will be reduced by at least three orders of magnitude, which would lower the Bethesda titer to a level that is clinically insignificant. For example, the IC50 (a crude measure of the binding constant) of inhibition by A2 antibodies was reduced in hybrid human/porcine factor VIII constructs HP2, HP4, HP5, HP7, and HP9, described in Example 8, and this was associated with a reduction in Bethesda titer to an unmeasurable level. It is anticipated, for example, that a double or triple alanine mutant of human factor VIII (e.g., a human factor VIII Arg484->Ala, Arg489->Ala, Phe501->Ala triple mutant) will produce a molecule with sufficiently low antigenicity for therapeutic use. Similar mutations can be made in the C2 epitope and the putative third epitope. An embodiment comprises two or three alanine substitutions into two or three factor VIII epitopes. Other substitutions into these regions can also be done.

In an embodiment of the invention, hybrid equivalent factor VIII molecules will be identified that are less antigenic and/or immunogenic in human and animal than either human or porcine factor VIII. Such hybrid equivalent constructs can be tested in animals for their reduced antigenicity and/or immunogenicity. For example, control and factor VIII deficient rabbits, pigs, dogs, mice, primates, and other mammals can be used as animal models. In one experimental protocol, the hybrid or hybrid equivalent factor VIII can be administered systematically over a period of six months to one year to the animal, preferably by intravenous infusion, and in a dosage range between 5 and 50 Units/kg body weight, preferably 10-50 Units/kg, and most preferably 40 Units/kg body weight. Antibodies can be measured in plasma samples taken at intervals after the infusions over the duration of the testing period by routine methods, including immunoassay and the Bethesda assay. Coagulant activity can also be measured in samples with routine procedures, including a one-stage coagulation assay.

The hybrid equivalent factor VIII molecules can be tested in humans for their reduced antigenicity and/or immunogenicity in at least two types of clinical trials. In one type of trial, designed to determine whether the hybrid or hybrid equivalent factor VIII is immunoreactive with inhibitory antibodies, hybrid or hybrid equivalent factor VIII is administered, preferably by intravenous infusion, to approximately 25 patients having factor VIII deficiency who have antibodies to factor VIII that inhibit the coagulant activity of therapeutic human or porcine factor VIII. The dosage of the hybrid or hybrid equivalent factor VIII is in a range between 5 and 50 Units/kg body weight, preferably 10-50 Units/kg, and most preferably 40 Units/kg body weight. Approximately 1 hour after each administration, the recovery of factor VIII from blood samples is measured in a one-stage coagulation assay. Samples are taken again approximately 5 hours after infusion, and recovery is measured. Total recovery and the rate of disappearance of factor VIII from the samples is predictive of the antibody titer and inhibitory activity. If the antibody titer is high, factor VIII recovery usually cannot be measured. The recovery results are compared to the recovery of recovery results in patients treated with plasma-derived human factor VIII, recombinant human factor VIII, porcine factor VIII, and other commonly used therapeutic forms of factor VIII or factor VIII substitutes.

In a second type of clinical trial, designed to determine whether the hybrid or hybrid equivalent factor VIII is immunogenic, i.e., whether patients will develop inhibitory antibodies, hybrid or hybrid equivalent factor VIII is administered, as described in the preceding paragraph, to approximately 100 previously untreated hemophiliac patients who have not developed antibodies to factor VIII. Treatments are given approximately every 2 weeks over a period of 6 months to 1 year. At 1 to 3 month intervals during this period, blood samples are drawn and Bethesda assays or other antibody assays are performed to determine the presence of inhibitory antibodies. Recovery assays can also be done, as described above, after each infusion. Results are compared to hemophiliac patients who receive plasma-derived human factor VIII, recombinant human factor VIII, porcine factor VIII, or other commonly used therapeutic forms of factor VIII or factor VIII substitutes.