# Patent

## Title
IL-7 fusion proteins

## Abstract

The invention is directed to a fusion protein which includes a first portion including an immunoglobulin (Ig) chain and a second portion including interleukin-7 (IL-7).

## Background
RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser. No. 11/027,446, filed Dec. 30, 2004, which claims priority to and the benefit of U.S. Provisional Application No. 60/533,406, filed Dec. 30, 2003, the entire disclosures of each of which are incorporated herein by reference.


FIELD OF THE INVENTION
The invention relates to interleukin-7 (IL-7) fusion proteins, methods of their production and uses thereof. The proteins of the invention are particularly useful in treating disorders accompanied by immune deficiencies and particularly diseases which involve T-cell deficiencies.
BACKGROUND OF THE INVENTION
A variety of disorders and therapies involve a deficiency of immune cells. For example, HIV infection results in a loss of CD4+ T-cells, while therapies such as chemotherapy and radiation therapy generally result in a loss of a wide variety of blood cells. Attempts have been made to provide specific protein drugs that can replenish specific types of immune cells that are lost as a result of a disease or therapy. For example, in cancer chemotherapy, erythropoietin is used to replenish red blood cells, granulocyte colony-stimulating factor (G-CSF) is used to replenish neutrophils, and granulocyte macrophage colony stimulating factor (GM-CSF) is used to replenish granulocytes and macrophages. These protein drugs, although beneficial, have relatively short serum half-lives such that immune cell replenishment is often insufficient. Moreover, no specific treatment is currently in clinical use to specifically stimulate T or B-cell development, even though loss of these cells as a result of disease or after certain myeloablative treatments is know to be particularly deleterious to a patient's health. Thus, there exists a need in the art to develop immune system stimulators and restoratives, particularly of lymphocytes, that have extended serum half-lives.
SUMMARY OF THE INVENTION
The present invention is directed to interleukin-7 (IL-7) fusion proteins which have improved biological properties compared to corresponding wild-type IL-7 proteins. Moreover, the present invention is based, in part, on the finding that IL-7 fusion proteins having particular structural features have improved biological properties compared to wild-type recombinant IL-7.
Accordingly, in one aspect, the invention features a fusion protein including a first portion comprising an immunoglobulin (Ig) chain and a second portion comprising interleukin-7 (IL-7), wherein the IL-7 fusion protein has an increased biological activity, such as an extended-serum half-life or in promoting the survival or expansion of immune cells, as compared to wild-type IL-7.
In one embodiment, the invention features a fusion protein including a first portion including an Ig chain and a second portion including IL-7, wherein the amino acid residues at positions 70 and 91 of IL-7 are glycosylated and the amino acid residue at position 116 of IL-7 is non-glycosylated. Throughout this document, amino acid positions of IL-7 refer to the corresponding positions in the mature, human IL-7 sequence. In one embodiment, the amino acid residue at position 116 of IL-7 is asparagine. In another embodiment, the amino acid residue at position 116 of IL-7 is altered such that it does not serve as a glycosylation site. In one embodiment, the IL-7 moiety comprises disulfide bonds between Cys2 and Cys92, Cys34 and Cys129, and Cys47 and Cys141 of IL-7.
In another embodiment, the invention includes a fusion protein including a first portion including an Ig chain and a second portion including IL-7, wherein the IL-7 comprises disulfide bonding between Cys2 and Cys92, Cys34 and Cys129, and Cys47 and Cys141 of IL-7. In one embodiment, the amino acid residue at position 116 of IL-7 is non-glycosylated. In another embodiment, the amino acid residue at position 116 of IL-7 is asparagine or is altered such that it does not serve as a glycosylation site. In another embodiment, the amino acid residues at positions 70 and 91 of IL-7 are glycosylated.
The Ig chain is generally an intact antibody or portion thereof, such as an Fc region. The Ig chain of the IL-7 fusion protein can be derived from any known Ig isotype and can include at least a portion of one or more constant domains. For example the constant domain can be selected from the group consisting of a CH1 region, a hinge region, a CH2 region, and a CH3 region. In one embodiment, the Ig moiety includes a hinge region, a CH2 region and a CH3 region. The Ig chain is optionally connected to the IL-7 portion by a linker.
Ig moieties of a single antibody isotype, such as IgG1 or IgG2, and hybrid Ig moieties are permitted in the present invention. For example, in one embodiment, the Ig moiety includes a hinge region derived from one isotype (i.e. IgG2) and a CH region from another isotype (i.e. IgG1). An Ig chain including an Fc portion of IgG1 can advantageously be modified to include the mutations Asn297Gln and Tyr296Ala. Furthermore, an Ig chain including an Fc portion of IgG2 can be advantageously modified to include the mutations Asn297Gln and Phe296Ala.
The IL-7 portion of the IL-7 fusion protein described above may comprise the mature portion of the IL-7 portion. In one embodiment, the IL-7 portion can further include a deletion, such as an internal deletion. In one example, IL-7 can include an eighteen amino acid deletion of amino acids 96 to 114 of SEQ ID NO:1.
In other embodiments, the invention includes purified nucleic acids encoding the IL-7 fusion proteins described above and cultured host cells including these nucleic acids.
In another aspect, the invention includes a method of preparing an IL-7 fusion protein including expressing in a host cell the nucleic acid described above and harvesting the fusion protein.
In another aspect, the invention includes a composition such as a pharmaceutical composition which includes the fusion protein described above.
In another aspect, the invention includes a method of treating a patient by administering Fc-IL-7 fusion proteins.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts the amino acid sequence of human IL-7 (SEQ ID NO:1). The signal sequence is shown in bold. Also depicted in bold and italics is a stretch of eighteen amino acids which can be deleted from the IL-7 sequence.
FIG. 2 depicts the amino acid sequence of cow IL-7 (SEQ ID NO:2). The signal sequence is shown in bold.
FIG. 3 depicts the amino acid sequence of sheep IL-7 (SEQ ID NO:3). The signal sequence is shown in bold.
FIG. 4 is the nucleic acid sequence for the Fc region of human Fcγ2(h) (FN>AQ)-IL-7 (SEQ ID NO:19).
FIG. 5 is a graphical representation of the pharmacokinetic profile of recombinant human IL-7 (open squares) and the fusion protein Fcγ2(h)(FN>AQ)-IL-7 (open diamonds) of Example 7. The serum concentration of the administered IL-7 fusion proteins (in ng/ml) was measured over time (in hours).
FIG. 6 is a graphical representation of B-cell reconstitution in irradiated, bone marrow transplanted mice treated with recombinant human IL-7 (open symbols), human Fc-IL-7 (filled symbols) or PBS (X). Proteins were administered every other day (squares) or once a week (triangles). The stippled line represents B-cell concentration in donor mice.
FIG. 7 is a graphical representation of T-cell reconstitution in irradiated, bone marrow transplanted mice treated with recombinant human IL-7 (open symbols), human Fc-IL-7 (filled symbols) or PBS (X). Proteins were administered every other day (squares) or once a week (triangles). The stippled line represents T-cell concentration in donor mice.
FIG. 8 is a dot plot representing lymphocyte populations of samples from the blood (top row) and spleen (bottom row) of irradiated, bone marrow transplanted mice treated with huFcγ2(h)(FN>AQ)-IL-7 (first two columns), and untreated controls (last column). The first column represents reconstituted endogenous lymphocytes (CD45.2+), and the second column represents reconstituted donor lymphocytes (CD45.1+). T-lymphocytes were detected as CD3 positive cells shown in the lower right quadrant. B-lymphocytes were detected as B220 positive cells, shown in the upper left quadrant.



DETAILED DESCRIPTION OF THE INVENTION
The invention provides IL-7 fusion proteins that have enhanced biological activity compared to wild-type IL-7 proteins. In particular, the invention provides IL-7 fusion proteins that include an immunoglobulin (Ig) portion. These Ig-IL-7 fusion proteins have enhanced biological activity such as extended serum half-life as compared to the wild type IL-7 proteins, which makes them suitable for use in the treatment of conditions accompanied by immune cell deficiencies such as lymphocyte deficiencies.
The invention is further based in part on the finding that IL-7 fusion proteins that have particular structural characteristics also have enhanced biological properties. While the amino acid sequence of mammalian IL-7 is well known, information about the structure of eukaryotically derived IL-7 proteins, including, for example, how the protein folds and the effects of its predicted N-linked glycosylation sites on its biological activity, remain ill-defined. For example, human IL-7 protein has a cysteine at positions 2, 34, 47, 92, 129, and 141 of the mature protein and three potential N-linked glycosylation sites at positions asparagine (Asn)70, Asn91, and Asn116. However, the precise structure of IL-7 synthesized under eukaryotic conditions is unknown.
The present invention includes IL-7 fusion proteins having particular structural forms and enhanced biological activity. For example, IL-7 fusion proteins having the disulfide bonding pattern of Cys2-Cys92, Cys34-Cys129 and Cys47-141 are more active in vivo than a wild-type recombinant IL-7 protein.
Moreover, the invention provides a form of an IL-7 fusion protein in which only two of the three potential N-linked glycosylation sites of IL-7 are glycosylated. Specifically, Asn70 and Asn91 of the mature protein are glycosylated, while the predicted N-linked glycosylation site at IL-7 Asn116 is not glycosylated. Such an IL-7 fusion protein is more active in vivo than a wild-type recombinant IL-7.
The invention also includes IL-7 fusion proteins wherein the IL-7 moiety contains a deletion and which retain comparable activity compared to the corresponding unmodified IL-7 fusion proteins. For example, the invention provides a form of Ig-IL-7 in which the IL-7 moiety contains an eighteen amino acid internal deletion corresponding to the sequence VKGRKPAALGEAQPTKSL (SEQ ID NO:9).
Interleukin-7 Fusion Proteins
Typically, the IL-7 protein portion is fused to a carrier protein. In one embodiment, the carrier protein is disposed towards the N-terminus of the fusion protein and the IL-7 protein is disposed towards the C-terminus. In another embodiment, the IL-7 fusion protein is disposed towards the N-terminus of the fusion protein and the carrier protein is disposed towards the C-terminus.
As used herein, the term “interleukin-7” or “IL-7” mean IL-7 polypeptides and derivatives and analogs thereof having substantial amino acid sequence identity to wild-type mature mammalian IL-7s and substantially equivalent biological activity, e.g., in standard bioassays or assays of IL-7 receptor binding affinity. For example, IL-7 refers to an amino acid sequence of a recombinant or non-recombinant polypeptide having an amino acid sequence of: i) a native or naturally-occurring allelic variant of an IL-7 polypeptide, ii) a biologically active fragment of an IL-7 polypeptide, iii) a biologically active polypeptide analog of an IL-7 polypeptide, or iv) a biologically active variant of an IL-7 polypeptide. IL-7 polypeptides of the invention can be obtained from any species, e.g., human, cow or sheep. IL-7 nucleic acid and amino acid sequences are well known in the art. For example, the human IL-7 amino acid sequence has a Genbank accession number of NM 000880 (SEQ ID NO:11) and is shown in FIG. 1; the mouse IL-7 amino acid sequence has a Genbank accession number of NM 008371; the rat IL-7 amino acid sequence has a Genbank accession number of AF 367210; the cow IL-7 amino acid sequence has a Genbank accession number of NM 173924 (SEQ ID NO:2) and is shown in FIG. 2; and the sheep IL-7 amino acid sequence has a Genbank accession number of U10089 (SEQ ID NO:3) and is shown in FIG. 3. The signal sequence for each of the polypeptide species is shown in bold in each of the figures and is typically not included where the IL-7 portion is fused C-terminal to the carrier protein.
A “variant” of an IL-7 protein is defined as an amino acid sequence that is altered by one or more amino acids. The variant can have “conservative” changes, wherein a substituted amino acid has similar structural or chemical properties, e.g., replacement of leucine with isoleucine. More rarely, a variant can have “nonconservative” changes, e.g., replacement of a glycine with a tryptophan. Similar minor variations can also include amino acid deletions or insertions, or both. Guidance in determining which and how many amino acid residues may be substituted, inserted or deleted without abolishing biological activity can be found using computer programs well known, in the art, for example software for molecular modeling or for producing alignments. The variant IL-7 proteins included within the invention include IL-7 proteins that retain IL-7 activity. IL-7 polypeptides which also include additions, substitutions or deletions are also included within the invention as long as the proteins retain substantially equivalent biological IL-7 activity. For example, truncations of IL-7 which retain comparable biological activity as the full length form of the IL-7 protein are included within the invention. The activity of the IL-7 protein can be measured using in vitro cellular proliferation assays such as described in Example 6 below. The activity of IL-7 variants of the invention maintain biological activity of at least 10%, 20%, 40%, 60%, but more preferably 80%, 90%, 95% and even more preferably 99% as compared to wild type IL-7.
Variant IL-7 proteins also include polypeptides that have at least about 70%, 75%, 80%, 85%, 90%, 92%, 95%, 96%, 97%, 98%, 99%, or more sequence identity with wild-type IL-7. To determine the percent identity of two amino acid sequences or of two nucleic acids, the sequences are aligned for optimal comparison purposes (e.g., gaps can be introduced in the sequence of a first amino acid or nucleic acid sequence for optimal alignment with a second amino acid or nucleic acid sequence). The percent identity between the two sequences is a function of the number of identical positions shared by the sequences (i.e., % homology=# of identical positions/total # of positions.times.100). The determination of percent homology between two sequences can be accomplished using a mathematical algorithm. A preferred, non-limiting example of a mathematical algorithm utilized for the comparison of two sequences is the algorithm of Karlin and Altschul (1990) Proc. Natl. Acad. Sci. USA 87:2264-68, modified as in Karlin and Altschul (1993) Proc. Natl. Acad. Sci. USA 90:5873-77. Such an algorithm is incorporated into the NBLAST and XBLAST programs of Altschul, et al. (1990) J. Mol. Biol. 215:403-10. BLAST nucleotide searches can be performed with the NBLAST program, score=100, wordlength=12. BLAST protein searches can be performed with the XBLAST program, score=50, wordlength=3. To obtain gapped alignments for comparison purposes, Gapped BLAST can be utilized as described in Altschul et al., (1997) Nucleic Acids Research 25 (17):3389-3402. When utilizing BLAST and Gapped BLAST programs, the default parameters of the respective programs (e.g. XBLAST and NBLAST) can be used.
Potential T-cell or B-cell epitopes in the IL-7 moiety can be removed or modified in the Fc-IL-7 fusion proteins of the invention. Exemplary deimmunized IL-7 moieties are disclosed in U.S. Provisional Patent Application No. 60/634,470 .
Carrier Protein
The carrier protein can be any moiety covalently fused to the IL-7 protein. In one embodiment, the carrier protein is albumin, for example, human serum albumin. In another embodiment, the carrier protein is an immunoglobulin (Ig) moiety, such as an Ig heavy chain. The Ig chain may be derived from IgA, IgD, IgE, IgG, or IgM. According to the invention, the Ig moiety may form an intact antibody and may direct the IL-7 fusion protein to specific target sites in the body. Fusion proteins making use of antibody targeting are known to those in the art. In another embodiment, the carrier Ig moiety further comprises an Ig light chain.
In one embodiment, the Ig moiety comprises an Fc region. As used herein, “Fc portion” encompasses domains derived from the constant region of an immunoglobulin, preferably a human immunoglobulin, including a fragment, analog, variant, mutant or derivative of the constant region. Suitable immunoglobulins include IgG1, IgG2, IgG3, IgG4, and other classes. The constant region of an immunoglobulin is defined as a naturally-occurring or synthetically-produced polypeptide homologous to the immunoglobulin C-terminal region, and can include a CH1 domain, a hinge, a CH2 domain, a CH3 domain, or a CH4 domain, separately or in any combination. In the present invention, the Fc portion typically includes at least a CH2 domain. For example, the Fc portion can include hinge-CH2-CH3. Alternatively, the Fc portion can include all or a portion of the hinge region, the CH2 domain and/or the CH3 domain and or the CH4 domain.
The constant region of an immunoglobulin is responsible for many important antibody functions including Fc receptor (FcR) binding and complement fixation. There are five major classes of heavy chain constant region, classified as IgA, IgG, IgD, IgE, and IgM. For example, IgG is separated into four γ subclasses: γ1, γ2, γ3, and γ4, also known as IgG1, IgG2, IgG3, and IgG4, respectively.
IgG molecules interact with multiple classes of cellular receptors including three classes of Fcγ receptors (FcγR) specific for the IgG class of antibody, namely FcγRI, FcγRII, and FcγRIII. The important sequences for the binding of IgG to the FCγR receptors have been reported to be located in the CH2 and CH3 domains. The serum half-life of an antibody is influenced by the ability of that antibody to bind to an Fc receptor (FcR). Similarly, the serum half-life of immunoglobulin fusion proteins is also influenced by the ability to bind to such receptors (Gillies et al., (1999) Cancer Res. 59:2159-66). Compared to those of IgG1, CH2 and CH3 domains of IgG2 and IgG4 have biochemically undetectable or reduced binding affinity to Fc receptors. It has been reported that immunoglobulin fusion proteins containing CH2 and CH3 domains of IgG2 or IgG4 had longer serum half-lives compared to the corresponding fusion proteins containing CH2 and CH3 domains of IgG1 (U.S. Pat. No. 5,541,087; Lo et al., (1998) Protein Engineering, 11:495-500). Accordingly, in certain embodiments of the invention, preferred CH2 and CH3 domains are derived from an antibody isotype with reduced receptor binding affinity and effector functions, such as, for example, IgG2 or IgG4. More preferred CH2 and CH3 domains are derived from IgG2.
The hinge region is normally located C-terminal to the CH1 domain of the heavy chain constant region. In the IgG isotypes, disulfide bonds typically occur within this hinge region, permitting the final tetrameric antibody molecule to form. This region is dominated by prolines, serines and threonines. When included in the present invention, the hinge region is typically at least homologous to the naturally-occurring immunoglobulin region that includes the cysteine residues to form disulfide bonds linking the two Fc moieties. Representative sequences of hinge regions for human and mouse immunoglobulins are known in the art and can be found in Borrebaeck, ed., (1992) Antibody Engineering, A Practical Guide, W. H. Freeman and Co. Suitable hinge regions for the present invention can be derived from IgG1, IgG2, IgG3, IgG4, and other immunoglobulin classes.
The IgG1 hinge region has three cysteines, the second and third of which are involved in disulfide bonds between the two heavy chains of the immunoglobulin. These same two cysteines permit efficient and consistent disulfide bonding of an Fc portion. Therefore, a preferred hinge region of the present invention is derived from IgG1, more preferably from human IgG1 wherein the first cysteine is preferably mutated to another amino acid, preferably serine.
The IgG2 isotype hinge region has four disulfide bonds that tend to promote oligomerization and possibly incorrect disulfide bonding during secretion in recombinant systems. A suitable hinge region can be derived from an IgG2 hinge; the first two cysteines are each preferably mutated to another amino acid.
The hinge region of IgG4 is known to form interchain disulfide bonds inefficiently. However, a suitable hinge region for the present invention can be derived from the IgG4 hinge region, preferably containing a mutation that enhances correct formation of disulfide bonds between heavy chain-derived moieties (Angal et al. (1993) Mol. Immunol., 30:105-8).
In accordance with the present invention, the Fc portion can contain CH2 and/or CH3 and/or CH4 domains and a hinge region that are derived from different antibody isotypes, i.e., a hybrid Fc portion. For example, in one embodiment, the Fc portion contains CH2 and/or CH3 domains derived from IgG2 or IgG4 and a mutant hinge region derived from IgG1. As used in this application, Fcγ2(h) refers to an embodiment wherein the hinge is derived from IgG1 and the remaining constant domains are from IgG2. Alternatively, a mutant hinge region from another IgG subclass is used in a hybrid Fc portion. For example, a mutant form of the IgG4 hinge that allows efficient disulfide bonding between the two heavy chains can be used. A mutant hinge can also be derived from an IgG2 hinge in which the first two cysteines are each mutated to another amino acid. Such hybrid Fc portions facilitate high-level expression and improve the correct assembly of the Fc-IL-7 fusion proteins. Assembly of such hybrid Fc portions is known in the art and has been described in U.S. Published Patent Application No. 2003-0044423.
In some embodiments, the Fc portion contains amino acid modifications that generally extend the serum half-life of an Fc fusion protein. Such amino acid modifications include mutations substantially decreasing or eliminating Fc receptor binding or complement fixing activity. For example, the glycosylation site within the Fc portion of an immunoglobulin heavy chain can be removed. In IgG1, the glycosylation site is Asn297 within the amino acid sequence Gln-Tyr-Asn-Ser (SEQ ID NO:30). In other immunoglobulin isotypes, the gylycosylation site corresponds to Asn297 of IgG1. For example, in IgG2 and IgG4, the glycosylation site is the asparagine within the amino acid sequence Gln-Phe-Asn-Ser (SEQ ID NO:29). Accordingly, a mutation of Asn297 of IgG1 removes the glycosylation site in an Fc portion derived from IgG1. In one embodiment, Asn297 is replaced with Gln. In other embodiments, the tyrosine within the amino acid sequence Gln-Tyr-Asn-Ser (SEQ ID NO:30) is further mutated to eliminate a potential non-self T-cell epitope resulting from asparagine mutation. As used herein, a T-cell epitope is a polypeptide sequence in a protein that interacts with or binds an MHC class II molecule. For example, the amino acid sequence Gln-Tyr-Asn-Ser (SEQ ID NO:30) within an IgG1 heavy chain can be replaced with a Gln-Ala-Gln-Ser (SEQ ID NO:28) amino acid sequence. Similarly, in IgG2 or IgG4, a mutation of asparagine within the amino acid sequence Gln-Phe-Asn-Ser (SEQ ID NO:29) removes the glycosylation site in an Fc portion derived from IgG2 or IgG4 heavy chain. In one embodiment, the asparagine is replaced with a glutamine. In other embodiments, the phenylalanine within the amino acid sequence Gln-Phe-Asn-Ser (SEQ ID NO:29) is further mutated to eliminate a potential non-self T-cell epitope resulting from asparagine mutation. For example, the amino acid sequence Gln-Phe-Asn-Ser (SEQ ID NO:29) within an IgG2 or IgG4 heavy chain can be replaced with a Gln-Ala-Gln-Ser (SEQ ID NO:28) amino acid sequence.
It has also been observed that alteration of amino acids near the junction of the Fc portion and the non-Fc portion can dramatically increase the serum half-life of the Fc fusion protein. (U.S. Published patent application Ser. No. 2002-0147311). Accordingly, the junction region of an Fc-IL-7 or IL-7-Fc fusion protein of the present invention can contain alterations that, relative to the naturally-occurring sequences of an immunoglobulin heavy chain and IL-7, preferably lie within about 10 amino acids of the junction point. These amino acid changes can cause an increase in hydrophobicity by, for example, changing the C-terminal lysine of the Fc portion to a hydrophobic amino acid such as alanine or leucine. In yet another embodiment of the invention, the C-terminal lysine and preceding glycine of the Fc portion is deleted.
In other embodiments, the Fc portion contains amino acid alterations of the Leu-Ser-Leu-Ser segment near the C-terminus of the Fc portion of an immunoglobulin heavy chain. The amino acid substitutions of the Leu-Ser-Leu-Ser (SEQ ID NO:27) segment eliminate potential junctional T-cell epitopes. In one embodiment, the Leu-Ser-Leu-Ser (SEQ ID NO:27) amino acid sequence near the C-terminus of the Fc portion is replaced with an Ala-Thr-Ala-Thr (SEQ ID NO:26) amino acid sequence. In other embodiments, the amino acids within the Leu-Ser-Leu-Ser (SEQ ID NO:27) segment are replaced with other amino acids such as glycine or proline. Detailed methods of generating amino acid substitutions of the Leu-Ser-Leu-Ser (SEQ ID NO:27) segment near the C-terminus of an IgG1, IgG2, IgG3, IgG4, or other immunoglobulin class molecules, as well as other exemplary modifications for altering junctional T-cell epitopes, have been described in U.S. Published patent application Ser. No. 2003-0166877.
Spacer
In one embodiment, a spacer or linker peptide is inserted between the carrier protein and the IL-7 fusion protein. For example, the spacer is placed immediately C-terminal to the last amino acid of an Ig constant region. The spacer or linker peptide is preferably non-charged and more preferably non-polar or hydrophobic. The length of a spacer or linker peptide is preferably between 1 and about 100 amino acids, more preferably between 1 and about 50 amino acids, or between 1 and about 25 amino acids, and even more preferably between 1 and about 15 amino acids, and even more preferably less than 10 amino acids. In one embodiment, the spacer contains a sequence (G4S)n, where n is less than 5. In a preferred embodiment, the spacer contains the sequence G4SG4 (SEQ ID NO:25). In yet another embodiment, the spacer contains a motif that is recognized as an N-linked glycosylation site. In yet another embodiment, the spacer contains a motif that is recognized by a site specific cleavage agent. In an alternative embodiment of the invention, the carrier protein and IL-7 fusion protein are separated by a synthetic spacer, for example a PNA spacer, that is preferably non-charged, and more preferably non-polar or hydrophobic.
Production of IL-7 Fusion Proteins
Non-limiting methods for synthesizing useful embodiments of the invention are described in the Examples herein, as well as assays useful for testing the in vitro properties, and pharmacokinetic and in vivo activities in animal models.
The IL-7 fusion proteins of the invention can be produced using recombinant expression vectors known in the art. The term “expression vector” refers to a replicable DNA construct used to express DNA which encodes the desired IL-7 fusion protein and which includes a transcriptional unit comprising an assembly of (1) genetic element(s) having a regulatory role in gene expression, for example, promoters, operators, or enhancers, operatively linked to (2) a DNA sequence encoding the desired IL-7 fusion protein which is transcribed into mRNA and translated into protein, and (3) appropriate transcription and translation initiation and termination sequences. The choice of promoter and other regulatory elements generally varies according to the intended host cell. A preferred expression vector of the invention is an Fc expression vector derived from the PdCs-huFc expression vector described in Lo et al., Protein Engineering (1998) 11:495.
In a preferred example, the nucleic acid encoding the IL-7 fusion protein is transfected into a host cell using recombinant DNA techniques. In the context of the present invention, the foreign DNA includes a sequence encoding the inventive proteins. Suitable host cells include prokaryotic, yeast or higher eukaryotic cells. Preferred host cells are eukaryotic cells.
The recombinant IL-7 fusion proteins can be expressed in yeast hosts, preferably from Saccharomyces species, such as S. cerevisiae. Yeast of other genera such as Pichia or Kluyveromyces may also be employed. Yeast vectors will generally contain an origin of replication from a yeast plasmid or an autonomously replicating sequence (ARS), a promoter, DNA encoding the IL-7 fusion protein, sequences for polyadenylation and transcription termination and a selection gene. Suitable promoter sequences in yeast vectors include the promoters for metallothionein, 3-phosphoglycerate kinase or other glycolytic enzymes, such as enolase, glyceraldehyde-3-phosphate dehydrogenase, hexokinase, pyruvate decarboxylase, phosphofructokinase, glucose-4-phosphate isomerase, 3-phosphoglycerate mutase, pyruvate kinase, triosephosphate isomerase, phosphoglucose isomerase and glucokinase.
Various mammalian or insect cell culture systems can be employed to express recombinant protein. Baculovirus systems for production of proteins in insect cells are well known in the art. Examples of suitable mammalian host cell lines include NS/0 cells, L cells, C127, 3T3, Chinese hamster ovary (CHO), HeLa, and BHK cell lines. Additional suitable mammalian host cells include CV-1 cells (ATCC CCL70) and COS-7 cells both derived from monkey kidney. Another suitable monkey kidney cell line, CV-1/EBNA, was derived by transfection of the CV-1 cell line with a gene encoding Epstein-Barr virus nuclear antigen-1 (EBNA-1) and with a vector containing CMV regulatory sequences (McMahan et al., (1991) EMBO J. 10:2821). The EBNA-1 gene allows for episomal replication of expression vectors, such as HAV-EO or pDC406, that contain the EBV origin of replication.
Mammalian expression vectors may comprise non-transcribed elements such as an origin of replication, a suitable promoter and enhancer linked to the gene to be expressed, and other 5′ or 3′ flanking nontranscribed sequences, and 5′ or 3′ nontranslated sequences, such as necessary ribosome binding sites, a poly-adenylation site, splice donor and acceptor sites, and transcriptional termination sequences. Commonly used promoters and enhancers are derived from Polyoma, Adenovirus 2, Simian Virus 40 (SV40), and human cytomegalovirus. DNA sequences derived from the SV40 viral genome, for example, SV40 origin, early and late promoter, enhancer, splice, and polyadenylation sites may be used to provide the other genetic elements required for expression of a heterologous DNA sequence.
For secretion of the IL-7 fusion protein from the host cell, the expression vector comprises DNA encoding a signal or leader peptide. In the present invention, DNA encoding the native signal sequence of IL-7 can be used, or alternatively, a DNA encoding a heterologous signal sequence may be used, such as the signal sequence from another, interleukin or from a secreted Ig molecule.
The present invention also provides a process for preparing the recombinant proteins of the present invention including culturing a host cell transformed with an expression vector comprising a DNA sequence that encodes the IL-7 fusion protein under conditions that promote expression. The desired protein is then purified from culture media or cell extracts. For example, supernatants from expression systems that secrete recombinant protein into the culture medium can be first concentrated using a commercially available protein concentration filter, for example, an Amicon or Millipore Pellicon ultrafiltration unit. Following the concentration step, the concentrate can be applied to a suitable purification matrix, as known in the art. For example, Fc-IL-7 fusion proteins are conveniently captured using a matrix coupled to Protein A.
An “isolated” or “purified” IL-7 fusion protein or biologically active portion thereof is substantially free of cellular material or other contaminating proteins from the cell or tissue source from which the IL-7 fusion protein is derived, or substantially free from chemical precursors or other chemicals when chemically synthesized. The language “substantially free of cellular material” includes preparations of IL-7 fusion protein in which the protein is separated from cellular components of the cells from which it is isolated or recombinantly produced. In one embodiment, the language “substantially free of cellular material” includes preparations of IL-7 fusion protein having less than about 30% (by dry weight) of non-IL-7 fusion protein (also referred to herein as a “contaminating protein”), more preferably less than about 20% of non-IL-7 fusion protein, still more preferably less than about 10% of non-IL-7 fusion protein, and most preferably less than about 5% non-IL-7 fusion protein. When the IL-7 fusion protein or biologically active portion thereof is purified from a recombinant source, it is also preferably substantially free of culture medium, i.e., culture medium represents less than about 20%, more preferably less than about 10%, and most preferably less than about 5% of the volume of the protein preparation.
The term “substantially pure Ig-IL-7 fusion protein” refers to a preparation in which the Ig-IL-7 fusion protein constitutes at least 60%, 70%, 80%, 90%, 95% or 99% of the proteins in the preparation. In one embodiment, the invention includes substantially pure preparations of Ig-IL-7 fusion proteins having a disulfide bonding pattern between Cys2 and Cys92, Cys34 and Cys129, and Cys47 and Cys141. In another embodiment, the invention features substantially pure preparations of Ig-IL-7 fusion proteins where Asn116 is non-glycosylated but Asn70 and Asn91 are glycosylated.
Methods of Treatment Using Fc-IL-7 Proteins
The IL-7 fusion proteins of the invention are useful in treating immune deficiencies and in accelerating the natural reconstitution of the immune system that occurs, for example, after diseases or treatments that are immunosuppressive in nature. For example, IL-7 fusion proteins can be used to treat infectious pathogens, immune disorders, and to enhance the growth (including proliferation) of specific immune cell types. Moreover, the IL-7 fusion proteins can be used in the treatment of cancers such as bladder cancer, lung cancer, brain cancer, breast cancer, skin cancer, and prostate cancer. In one example, it is useful to treat patients who have undergone one or more cycles of chemotherapy with IL-7 fusion proteins as described above to help their immune cells replenish. Alternatively, IL-7 fusion proteins are useful in adoptive T-cell transplantations. For example, IL-7 fusion proteins may be administered to facilitate the expansion and survival of transplanted T-cells, or to expand isolated T-cell populations ex vivo. Alternatively, it is also useful to administer the IL-7 fusion proteins described above to patients with HIV, the elderly, patients receiving a transplant or other patients with suppressed immune system function.
Administration
The IL-7 fusion proteins of the invention can be incorporated into a pharmaceutical composition suitable for administration. Such compositions typically comprise the IL-7 fusion protein and a pharmaceutically-acceptable carrier. As used herein the language “pharmaceutically-acceptable carrier” is intended to include any and all solvents, dispersion media, coatings antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like, compatible with pharmaceutical administration. The use of such media and agents for pharmaceutically active substances is well known in the art.
A pharmaceutical composition of the invention is formulated to be compatible with its intended route of administration. Examples of routes of administration include parenteral, e.g., intravenous, intradermal, subcutaneous, oral (e.g., inhalation), transdermal (topical), transmucosal, and rectal administration. Solutions or suspensions used for parenteral, intradermal, or subcutaneous application can include the following components: a sterile diluent such as water for injection, saline solution, fixed oils, polyethylene glycols, glycerine, propylene glycol or other synthetic solvents; antibacterial agents such as benzyl alcohol or methyl parabens; antioxidants such as ascorbic acid or sodium bisulfite; chelating agents such as ethylenediaminetetraacetic acid; buffers such as acetates, citrates or phosphates and agents for the adjustment of tonicity such as sodium chloride or dextrose. pH can be adjusted with acids or bases, such as hydrochloric acid or sodium hydroxide. The parenteral preparation can be enclosed in ampoules, disposable syringes or multiple dose vials made of glass or plastic.
Medicaments that contain the IL-7 fusion proteins of the invention can have a concentration of 0.01 to 100% (w/w), though the amount varies according to the dosage form of the medicaments.
Administration dose depends on the body weight of the patients, the seriousness of the disease, and the doctor's opinion. However, it is generally advisable to administer about 0.01 to about 10 mg/kg body weight a day, preferably about 0.02 to about 2 mg/kg, and more preferably about 0.5 mg/kg in case of injection. The dose can be administered once or several times daily according to the seriousness of the disease and the doctor's opinion.
Compositions of the invention are useful when co-administered with one or more other therapeutic agents, for example, a molecule also known to be useful to replenish blood cells. For example, the molecule may be erythropoietin which is known to be used to replenish red blood cells G-CSF which is used to replenish neutrophils or GM-CSF which is used to replenish granulocytes and macrophages.
EXAMPLE 1
Cloning of Human (hu) Fc-IL-7 and huFc-IL-7 Variants
The nucleic acid encoding the mature form of human IL-7 (i.e. lacking its N-terminal signal sequence) is amplified by Polymerase Chain Reaction (PCR), using forward and reverse primers that incorporated the restriction sites for Sma I and Xho I, respectively. The amplified PCR product is cloned into a pCRII vector (Invitrogen, Carlsbad, Calif.), and its sequence verified. The amino acid sequence of mature IL-7 is shown as SEQ ID NO:1. The Sma I/Xho I digested IL-7 fragment is transferred into a likewise treated pdCs-huFc derived expression vector, resulting in a chimeric sequence between huFc and IL-7, with IL-7 placed in-frame, directly downstream of the sequence encoding a CH3 moiety of Fc (see Lo et al., Protein Engineering (1998) 11:495).
A series of expression vectors are derived from the pdCs-huFc vector which encodes an Fc fragment that generally includes a hinge, a CH2 domain, and a CH3 domain of Ig, and which have been engineered to incorporate specific alterations in the Fc region. Thus, by shuttling the IL-7 fragment between these vectors, a series of huFc-IL-7 fusion proteins were generated which differ in their Fc backbone. In order to create the various backbones, the appropriate mutations can first be introduced into the Fc sequence by methods known in the art. Since the Fc region of the pdCs-huFc derived vector is flanked by an AflII restriction site and a Smal restriction site, by subjecting the nucleic acid of the appropriately modified backbone to PCR using primers that incorporate the restriction sites for AflII and SmaI respectively, the resultant Fc encoding nucleic acid fragment can then be substituted into the pdCs-huFc derived vector as an AflII to SmaI fragment. The AflII sequence CTTAAGC (SEQ ID NO:24) is upstream of the Fc sequence beginning GAGCCCAAA (SEQ ID NO:23), which represents the beginning of a hinge region. The SmaI site CCCGGGT (SEQ ID NO:17) is towards the end of the CH3 region as shown by the underlined nucleic acids in FIG. 4 and encodes the Pro-Gly amino acids proceeding the alanine residue from the lysine to alanine mutation at the end of the CH3 region.
For example, huFcγl-IL-7 is constructed having the hinge region, the CH2 and the CH3 domains derived from the IgGγ1 subclass. In the context of an Fc fusion protein, the IgGγ1 hinge region in addition contains a mutation substituting the first cysteine for serine. The sequence of the encoded fusion protein is depicted in SEQ ID NO:4, while the sequence in SEQ ID NO:22 encodes the mature huFcγ1 backbone of the vector.
In addition, Fcγ1-IL-7 fusion proteins were generated that included the dipeptide mutation YN to AQ to eliminate the glycosylation site on Fc (corresponding to N297 in IgGγ1) as well as a potential immunogenic T-cell epitope, according to the methods described above. The mature Fc backbone sequence for huFcγ1(YN>AQ) is disclosed in SEQ ID NO:21. The substitution of alanine and glycine in place of tyrosine and asparagine was accomplished by first introducing mutations into the Fc backbone by an overlap PCR approach. Two overlapping complementary mutagenic primers were used to generate two PCR fragments, which were used as the template in a second round of amplification to produce a single fragment containing the appropriate codon substitutions. The mutagenic primer in the sense direction was 5′-AGCAGGCCCAGAG CACGTACCGTGTGGT-3′ (mutation underlined) (SEQ ID NO:36). The complementary strand was 5′-GTACGTGCTCTGGGCCTGCTCCTCCCGC-3′ (SEQ ID NO:37). The flanking forward primer was 5′-CTCTCTGCAGAGCCCAAA TCT-3′ (SEQ ID NO:38), which also contains a PstI site. In the antisense direction, the flanking reverse primer was 5′CAGGGTGTACACCTGTGGTTC-3′ (SEQ ID NO:33), which also contains a BsrGI site. After amplification, the sequence was verified through standard methods and was subject to restriction by BsrGI and PstI. The resultant fragment was then substituted for the non-mutant fragment of the Fc region.
The huFcγ2(h)(FN>AQ)-IL-7 was also constructed using the techniques previously described. This fusion protein includes an altered hinge region which was derived from IgGγ1 subclass, while the CH2 and CH3 domains were derived from IgGγ2 subclass. Additionally, the dipeptide mutation FN to AQ was included to eliminate the glycosylation site on Fc (corresponding to N297 in IgGγ1) as well as a potential immunogenic T-cell epitope. The sequence of the encoded fusion protein is depicted in SEQ ID NO:5. The sequence of the mature Fc backbone huFcγ2(h)(FN>AQ) is shown in SEQ ID NO:19.
In addition, Fc-IL-7 fusion proteins were generated which included a flexible linker sequence between the Fc moiety and the IL-7 moiety. For example, a linker polypeptide with the sequence GGGGSGGGGSGGGGS (linker1, SEQ ID NO:34) was inserted. To generate huFcγ1(linker1)-IL-7, a synthetic oligonucleotide duplex of the sequence 5′-G GGT GCA GGG GGC GGG GGC AGC GGG GGC GGA GGA TCC GGC GGG GGC TC-3′ (SEQ ID NO:18) was inserted by blunt-end ligation at the unique SmaI site of the expression vector pdCs-huFc-IL-7 and the orientation of the duplex was verified. The forward primer was designed such that the amino acid residues Pro-Gly encoded by the codons spanning the Smal site (C CCG GGT) (SEQ ID NO:17), and the ensuing Ala residue (resulting from the encoded lysine to alanine substitution) of the CH3 region, were maintained. The amino acid sequence of the encoded fusion protein is shown in SEQ ID NO:6.
Additional Fc-IL-7 fusion proteins were constructed that included a shorter linker polypeptide with the sequence GGGGSGGGG (linker2, SEQ ID NO:25). To generate huFcγ1(YN>AQ)(linker2)-IL-7, an amplified PCR product, obtained from the primer pair 5′-CCCGGGCGCCGGCGGTGGAGGATCAGGTGGTGGCGGTGATTGTGA TATTGAAGGTAAAGATG-3′ (containing the encoded linker sequence, SEQ ID NO:15) and 5′-ATCATGTCTGGATCCCTCGA-3′ (SEQ ID NO:14) on an appropriate pdCs-Fc-IL-7 template plasmid, was cloned into a pCRII vector (Invitrogen, Carlsbad, CA), and its sequence verified. A Xma I/Xho I digested fragment encoding linker2/IL-7 was then transferred into a likewise treated pdCs-huFc derived expression vector. The vector was modified to contain the mature Fc backbone huFcγ1(YN>AQ) of SEQ ID NO:21. The amino acid sequence of the encoded fusion protein is shown in SEQ ID NO:7.
Similarly, huFcγ1(YN>AQ,d)(linker2)-IL-7 was generated, using the primer pair 5′-CCCGGGCGGTGGAGGATCAGGTGGTGGCGGTGATTGTGATAT TGAAGGTAAAGATG-3′ (SEQ ID No:16) and 5′-ATCATGTCTGGATCCCTCGA-3′ (SEQ ID NO:12). huFcγ1(YN>AQ,d)(linker2)-IL-7 differs from the preceding fusion protein huFcγ1(YN>AQ)(linker2)-IL-7 in that it lacks the terminal two amino acid residues of the Fc portion of the fusion protein. Specifically, rather than terminating in with the sequence . . . ATATPGA (SEQ ID NO:11), the Fc portion ends with the sequence . . . ATATP (SEQ ID NO:10). The amino acid sequence of the encoded fusion protein is shown in SEQ ID NO:8.
EXAMPLE 2
Transfection and Expression of Fc-IL-7 Fusion Proteins
Electroporation was used to introduce the DNA encoding the IL-7 fusion proteins described above into a mouse myeloma NS/0 cell line. To perform electroporation NS/0 cells were grown in Dulbecco's modified Eagle's medium supplemented with 10% heat-inactivated fetal bovine serum, 2 mM glutamine and penicillin/streptomycin. About 5×106 cells were washed once with PBS and resuspended in 0.5 ml PBS. 10 μg of linearized plasmid DNA for huFcγ1-IL-7 was then incubated with the cells in a Gene Pulser Cuvette (0.4 cm electrode gap, BioRad) on ice for 10 min. Electroporation was performed using a Gene Pulser (BioRad, Hercules, Calif.) with settings at 0.25 V and 500 μF. Cells were allowed to recover for 10 min on ice, after which they were resuspended in growth medium and plated onto two 96 well plates.
Stably transfected clones were selected by their growth in the presence of 100 nM methotrexate (MTX), which was added to the growth medium two days post-transfection. The cells were fed every 3 days for two to three more times, and MTX-resistant clones appeared in 2 to 3 weeks. Supernatants from clones were assayed by anti-Fc ELISA to identify clones that produced high amounts of the IL-7 fusion proteins. High producing clones were isolated and propagated in growth medium containing 100 nM MTX. Typically a serum-free growth medium, such as H-SFM or CD medium (Life Technologies), was used.
EXAMPLE 3
Biochemical Analysis of huFc-IL-7 Fusion Proteins
Routine SDS-PAGE characterization was used to assess the integrity of the fusion proteins. Differences between the huFc-IL-7 variants huFcγ1-IL-7. huFcγ2(h)(FN>AQ)-IL-7, huFcγ1(linker1)-IL-7, huFcγ1(YN>AQ)(linker2)-IL-7 and huFcγ1(YN>AQ,d)-IL-7 were investigated. The huFc-IL-7 fusion proteins, expressed from NS/0 cells, were captured on Protein A Sepharose beads (Repligen, Needham Mass.) from the tissue culture medium into which they were secreted, and were eluted by boiling in protein sample buffer, with or without a reducing agent such as β-mercaptoethanol. The samples were separated by SDS-PAGE and the protein bands were visualized by Coomassie staining. By SDS-PAGE the tested huFc-IL-7 fusion proteins were generally well expressed, as they were present substantially as a single band on the gel; it was found that in samples of huFc-IL-7 variants that included a linker, secondary bands, which may represent clipped material, were noticeably reduced.
Purified huFc-IL-7 fusion proteins were also analyzed by size exclusion chromatography (SEC) to assess the extent to which the huFc-IL-7 variants were aggregated. Briefly, the cell culture supernatant was loaded onto a pre-equilibrated Fast-Flow Protein A Sepharose column, the column was washed extensively in a physiological buffer (such as 100 mM Sodium Phosphate, 150 mM NaCl at neutral pH), and the bound protein was eluted at about pH 2.5 to 3 in same salt buffer as above. Fractions were immediately neutralized.
It was found that for each of the fusion proteins tested at least 50% of the product was monomeric, and generally more than 65%. “Monomeric,” as used herein, refers to non-aggregated proteins. It is understood that proteins with an Fc portion normally form a disulfide-bonded complex which normally include two polypeptide chains (unless the two Fc portions are present within the same polypeptide) and may be thought of as a “unit-dimer”. “Monomeric” is not intended to exclude such disulfide-bonded species, but only to connote that the proteins are non-aggregated. To obtain a virtually monomeric huFc-IL-7 fusion protein preparation (around 98%), the eluate from a Sepharose-Protein A purification was loaded onto a preparative SEC column (Superdex) and the monomeric peak fraction was collected. Typically, the concentration of the recovered protein was around 1 mg/ml. If required, the sample was concentrated, for example by spin dialysis (e.g. VivaSpin) with a molecular weight cut-off of 10-30 kDa.
Disulfide Bonding
IL-7 contains six Cys residues which could make disulfide bonds, at positions Cys2, Cys34, Cys47, Cys92, Cys129 and Cys141 of the mature IL-7 protein sequence. The folding of huFcγ1-IL-7 was assessed by determining the pattern of disulfide bonds present in the IL-7 moiety of the fusion protein. Briefly, peptide maps of huFcγ1-IL-7 were generated from trypsinized material and analyzed for the presence of signature peptide fragments. huFcγ1-IL-7 protein was trypsinized either in a native form or after reduction and alkylation. To account for peptide fragments that may be glycosylated, samples of the native and denatured proteins were additionally treated with PNGaseF to remove glycosyl chains prior to tryptic digestion. Peptide fragments were fractionated by HPLC, and their mass was determined by mass spectroscopy.
In the context of Fcγ1-IL-7, a peptide fragment containing the disulfide bond Cys47-Cys141 (“3-6”) would be predicted to have a mass of 1447.6, whereas a peptide fragment containing the disulfide bond Cys2-Cys141 (“1-6”) would be predicted to have a mass of 1426.6. Similarly, a peptide fragment containing the disulfide bond Cys34-Cys129 (“2-5”) would be predicted to have a mass of 2738.3. Indeed, peptide fragments of a mass of 1447.6 (“3-6”) and of 2738.3 (“2-5”) were identified in samples derived from the native Fc-IL-7 protein regardless of whether the samples were treated with PNGaseF or not, but not in samples from reduced Fc-IL-7. Conversely, the peptide fragment of a mass of 1426.6 (“1-6”) was not found in any sample. Thus, Fcγ1-IL-7 contained the disulfide bonds Cys47-Cys141 and Cys34-Cys129, but not Cys2-Cys141. It was noted that a peptide fragment of the predicted mass of 2439.2, corresponding to a fragment containing Cys2-Cys92 (“1-4”) was identified only in the sample from the native fusion protein treated with PNGaseF. In fact, Cys92 lies within the tripeptide motif Asn91Cys92Thr93, indicating that Asn91 was glycosylated in huFcγ1-IL-7. Thus, in huFcγ1-IL-7 the disulfide bonding pattern was consistent with Cys2-Cys92. Cys34-Cys129, and Cys47-Cys141. This experimentally determined configuration of disulfide bonds of Fc-IL-7 stands in contrast to the experimentally determined configuration reported for bacterially produced and re-folded IL-7 (Cosenza et al. (1997) JBC 272:32995).
N-Linked Glycosylation Sites
Human IL-7 contains three potential glycosylation sites, at positions Asn70, Asn91 and Asn116 of the mature IL-7 protein sequence. Peptide maps of huFcγ1-IL-7 (reduced/alkylated) were analyzed for the presence of signature peptide fragments. If glycosylated, these signature fragments would only be revealed in samples treated with PNGaseF. Masses of 1489.7, 1719.9 and 718.3 would be predicted for tryptic peptide fragments containing the unmodified residues for Asn70, Asn91, and Asn116, respectively.
Indeed, peptide fragments of a mass of 1489.7 and of 1719.9 were identified in samples that had been treated with PNGaseF, but were absent in the untreated sample, indicating that Asn70 (contained in the sequence . . . MNSTG . . . ) (SEQ ID NO:31), and Asn91 (contained in the sequence . . . LNCTG . . . ) (SEQ ID NO:32), were indeed glycosylated. Surprisingly, a tryptic fragment of a mass of 718.3, corresponding to SLEENK (SEQ ID NO:35), was identified in both the PNGaseF treated sample and the untreated sample, indicating that Asn116 was not glycosylated. This was not expected because Asn116 in the human IL-7 sequence . . . PTKSLEENKSLKE . . . (SEQ ID NO:13) (see SEQ ID NO:1) is predicted to be an N-linked glycosylation site. The NKS putative glycosylation site is conserved in sheep and cows as well as humans.
The analysis of disulfide bonding patterns and N-linked glycosylation sites, repeated with samples of Fcγ1-(linker1)-IL-7 and of Fcγ2h(FN>AQ)-IL-7, gives similar results.
EXAMPLE 4
ELISA Procedures
The concentrations or protein products in the supernatants of MTX-resistant clones and other test samples was determined by anti-huFc ELISA, as described in detail below. ELISA plates were coated with AffiniPure Goat anti-Human IgG (H+L) (Jackson Immuno Research Laboratories. West Grove, Pa.) at 5 μg/mL in PBS and 100 μL/well in 96-well plates. Coated plates were covered and incubated at 4° C. overnight. Plates were washed 4 times with 0.05% Tween (Tween 20) in PBS, and blocked with 1% BSA/1% goat serum in PBS, 200 μL/well. After incubation with the blocking buffer at 37° C. for 2 hrs, the plates were washed 4 times with 0.05% Tween in PBS and tapped dry. Test samples were diluted as appropriate in sample buffer (1% BSA/1% goat serum/0.05% Tween in PBS). A standard curve was prepared using a chimeric antibody (with a human Fc) of known concentration. To prepare a standard curve, serial dilutions were made in the sample buffer to give a standard curve ranging from 125 ng/mL to 3.9 ng/mL. The diluted samples and standards were added to the plate, 100 μL/well and the plate incubated at 37° C. for 2 hr. After incubation, the plate was washed 8 times with 0.05% Tween in PBS. To each well 100 μL of the secondary antibody horseradish peroxidase-conjugated anti-human IgG was added, diluted to around 1:120,000 in sample buffer. The exact dilution of the secondary antibody was determined for each lot of the HRP-conjugated anti-human IgG. After incubation at 37° C. for 2 hr, the plate was washed 8 times with 0.05% Tween in PBS.
The substrate solution was added to the plate at 100 μL/well. This solution was prepared by dissolving 30 mg of OPD (o-phenylenedianmine dihydrochloride (OPD), (1 tablet) into 15 mL of 0.025 M citric acid/0.05 M Na2HPO4 buffer, pH 5, which contained 0.03% of freshly added hydrogen peroxide. The color was allowed to develop for about 30 minutes at room temperature in the dark. The reaction was stopped by adding 4N sulfuric acid, 100 μL/well. The plate was read by a plate reader, which was set at both 490 and 650 nm and programmed to subtract the background OD at 650 nm from the OD at 490 nm.
The concentration of human IL-7 in serum samples of animals treated with huFc-IL-7 fusion proteins or recombinant human IL-7 was determined by ELISA, essentially as described above. Human IL-7 was captured via a mouse anti-human IL-7 antibody (R&D Systems, Minneapolis, Minn.) and detected with a goat anti-human IL-7 biotin antibody (R&D Systems. Minneapolis, Minn.).
EXAMPLE 5
Purification of huFc-IL-7 Proteins
A standard purification of Fc-containing fusion proteins was performed based on the affinity of the Fc protein moiety for Protein A. Briefly, NS/0 cells expressing the appropriate fusion protein, were grown in tissue culture medium and the supernatant containing the expressed protein was collected and loaded onto a pre-equilibrated Past Flow Protein A Sepharose column. The column was then washed extensively with buffer (such as 100 in M Sodium Phosphate, 150 mM NaCl at neutral pH). Bound protein was eluted at a low pH (pH 2.5-3) in same buffer as above and fractions were immediately neutralized.
To obtain a non-aggregated huFc-IL-7 fusion protein preparation (around 98% monomer), the eluate was loaded onto a preparative SEC column (Superdex) and the monomeric peak fraction was collected. Typically, the concentration of the recovered protein was around 0.5 mg/ml to 2 mg/ml, and where appropriate the sample was concentrated by spin dialysis (e.g. Viva Spin with a molecular weight cut-off of 30 kDa).
EXAMPLE 6
In Vitro Activity of huFc-IL-7 Proteins
The cytokine activity of the purified huFc-IL-7 fusion proteins was determined in vitro in a cellular proliferation bioassay. Human PBMC (Peripheral Blood Mononuclear Cells) were activated by PHA-P to produce cells which were responsive to IL-7. Proliferation was measured in a standard thymidine incorporation assay. Briefly, PBMC's were first incubated for five days with 10 microgram/ml PHA-P, cells were washed and then incubated in a medium supplemented with the huFc-IL-7 fusion proteins, in a dilution series, for a total of 48 hours. During the final 12 hours, the samples were pulsed with 0.3 μCi of [methyl-3H]thymidine (Dupont-NEN-027). Cells were then washed extensively, harvested and lysed into glass filters. 3H-thymidine incorporated into DNA was measured in a scintillation counter. As a standard, wild type huIL-7 protein, obtained from R&D Systems (Minneapolis, Minn.), or obtained from the National Institute for Biological Standards and Control (NIBSC), was assayed.
An ED50 value of cell proliferation for huFc-IL-7 fusion proteins was obtained from plotting a dose response curve according to standard techniques, and determining the protein concentration that resulted in half-maximal response. The fusion proteins huFcγ1-IL-7, huFcγ2(h)(FN>AQ)-IL-7, and huFcγ1(linker1)-IL-7 were evaluated. The ED50 values of the fusion proteins were fairly similar to one another, falling within a 3-fold range from one another. Therefore, it was found that these alterations in the Fc moiety have little influence on IL-7 activity of the fusion protein.
In addition, it was found that the ED50 values of these fusion proteins were about 3- to 10-fold higher than the ED50 value obtained for huIL-7 commercially available from R&D Systems. Since this commercial preparation is produced in bacteria and is not glycosylated, enzymatically deglycosylated huFcγ1-IL-7 protein, by treatment with PNGaseF, was evaluated. It was found to have similar activity to the untreated form. Without wishing to be bound by theory, the somewhat decreased activity of the fusion proteins may have been due not to glycosylation of the IL-7 moiety but instead to a steric effect resulting from a constrained N-terminus of the IL-7 moiety.
EXAMPLE 7
Pharmacokinetics of huFc-IL-7 Proteins
The pharmacokinetic (PK) profiles of an huFc-IL-7 fusion protein and of recombinant human IL-7 (Peprotech, Rocky Hill, NJ) were evaluated, and the results are depicted in FIG. 5. A single subcutaneous injection of equimolar amounts of huFcγ2(h)(FN>AQ)-IL-7 or of recombinant human IL-7 (50 micrograms) was administered to groups of C57BL6/J mice. Blood samples were obtained by retro-orbital bleeding at injection (i.e., at t=0 min), and at 30 min, 1 hr, 2 hrs, 4 hrs, 8 hrs, 24, 48, 72, 96, 120 and 144 hrs post-injection. Samples were collected in heparin-tubes to prevent clotting, and cells were removed by centrifugation in a high-speed Eppendorf microcentrifuge for 4 min at 12,500 g. PK values were calculated with the PK solutions 2.0TM. software package (Summit Research Services, Montrose, CO).
The concentration of administered IL-7 was determined in quadruplicate plasma samples at each time point by an ELISA specific for human IL-7. It was found that the pharmacokinetic behavior of the huFc-IL-7 and recombinant IL-7 differed dramatically. For recombinant human IL-7, the maximum concentration (Cmax) was 23.5 ng/ml at 2.0 hours post injection (Tmax), whereas for huFc-IL-7 Cmax was 1588.7 ng/ml 24 hours post injection. In addition, while recombinant human IL-7 was absorbed more rapidly than huFc-IL-7 (α-phase half-life 0.9 hours vs. 12.4 hours), huFc-IL-7 was eliminated approximately 9-fold more slowly from circulation during the β-phase. Thus, in tends of AUC (area under the curve) as a measure of total drug exposure, mice receiving huFc-IL-7 had a 572-fold higher exposure to the administered protein than mice receiving recombinant human IL-7. These data demonstrate a significant improvement of huFc-IL-7 fusion proteins relative to free recombinant human IL-7 with regards to their PK. It was further found that the PK profiles of huFc-IL-7 fusion proteins, such as huFcγ1-IL-7 and huFcγ2(h)(FN>AQ)-IL-7, huFcγ1(YN>AQ)(linker2)-IL-7, and huFcγ1(YN>AQ,d)(linker2)-IL-7, which were administered to the mice by intravenous injection, were similar to one another.
EXAMPLE 8
Efficacy of huFc-IL-7 in Lymphopenic Mice after Bone Marrow (BM) Transplantation
The efficacy of huFc-IL-7 fusion proteins compared to recombinant human IL-7 was evaluated in vivo. For example, huFcγ2(h)(FN>AQ)-IL-7 or recombinant human IL-7 (Peprotech, Rocky Hill, N.J.) was administered to lymphopenic mice after transplantation of T-cell-depleted bone marrow (BM), and the recovery of immune cell populations was assessed.
Essentially, recipient mice were lethally irradiated prior to BM transplantation with two doses of 600 cGy total body irradiation at a 4 hr interval, and BM cells re-suspended in PBS were infused into tail veins of recipient mice. At regular intervals from Day 5 onwards, an equimolar amount of huFc-IL-7 (7 μg) or recombinant human IL-7 (2.5 μg) (Peprotech, Rocky Hill, N.J.) was administered subcutaneously to the recipient mice. Over the course of the experiment, recipient mouse blood samples were taken, and lymphocyte cell concentrations in the samples were measured.
For BM cell transplantations, BM cells were obtained aseptically from femurs and tibias of BL/6.SJL (H2b, CD45.1) mice (Jackson Labs, Bar Harbor, Me.) and depleted of T-cells by removing magnetically labeled T-cells over MACS® columns (Miltenyi Biotec, Auburn, Calif.). The degree of T-cell depletion was monitored by FACS analysis with fluorescently labeled antibodies against CD45, αβ-TCR (T-cells) and 7-Amino Actinomycin D (7-AAD, apoptotic cells) (Calbiochem, X). 10×106 live (7-AAD-negative) BM cells (containing less than 1% T-cells) were used per recipient mouse. In congeneic BM transplantations, B6 (H2b, CD45.2) mice were used as the recipient mouse strain, and in allogeneic BM transplantations B6C3F1 (H2b/k, CD45.2) mice were chosen.
Lymphocyte cell concentrations (as presented in Table 1) were measured essentially as described by Brocklebank and Sparrow (Brocklebank and Sparrow (2001) Cytometry 46:254). Briefly, fluorescent beads (TruCOUNTTM Tubes, BD Biosciences, San Jose, Calif.) were dissolved in 40 μl of PBS containing a mixture of lymphocyte-specific antibodies. Subsequently, 10 μl of anti-coagulated blood was added, mixed and incubated for 30 minutes in the dark at room temperature. Red blood cells were lysed in 450 μl of Red Blood Cell lysis solution (BD Biosciences, San Jose, Calif.) and samples were analyzed by flow cytometry (BD FACSCaliburTM, BD Biosciences, San Jose, Calif.). The concentration of a particular lymphocyte population (e.g. B-cells, T-cells or total leukocytes) was determined by creating separate gates around lymphocytes and fluorescent beads and reading the number of events within each gate. The number of gated lymphocytes per microliter was calculated by dividing the number of events in a gated lymphocyte region by the number of events in the gated bead region. This number was multiplied by the fraction of the number of beads per TruCOUNTTM tube (provided by the supplier) over the sample volume and finally multiplied by the sample dilution factor.
In one experiment, lymphocyte reconstitution was assessed in a congeneic BM transplantation setting, using materials and methods specified above. Recipient mice were injected with huFcγ2(h)(FN>AQ)-IL-7 at a dose of 7 μg (125 μg IL-7/kg body weight), and lymphocyte cells were measured as described. Donor lymphocytes were detected as CD45.1 positive cells, whereas endogenous lymphocytes of the recipient mice were detected as CD45.2 positive cells. Lymphocyte B-cells and T-cells were identified using B220 and CD3 lymphocyte markers respectively. It was found that by Day 49, donor lymphocytes (CD45.1 positive cells) had repopulated the recipient mice to levels comparable to non-irradiated control mice, while endogenous lymphocytes (CD45.2 positive cells) had not significantly expanded. In addition, the treatment with the huFc-IL-7 fusion protein did not cause significant toxicity. These results demonstrated the efficacy of the fusion protein in expanding adoptively transferred lymphocyte populations. These results are depicted in FIG. 8.
In another experiment, an allogeneic BM transplantation model, which may better simulate a clinical transplantation setting, was used to compare a huFc-IL-7 fusion protein to recombinant human IL-7, and the results are shown in Table 1. Again, methods and materials described above were used. huFcγ2(h)(FN>AQ)-IL-7 and human IL-7 (equivalent of 125 μg IL-7/kg body weight) were administered either every other day (q2 d) or once a week (q7 d) from Day 5 to Day 56 after transplantation. PBS-treated donor mice and irradiated, bone marrow recipient mice treated with PBS served as controls.
In recipient mice treated with the fusion protein, donor-derived B-cells (CD45.1+, B220+, CD19+) reached baseline levels (as defined by the blood concentration of B-cells in donor control mice) 14 or 16 days after transplantation, when given q2d or q7d, respectively. In contrast, in recipient mice treated with recombinant human IL-7, neither dosing regimen had an effect; B-cell numbers in PBS-treated and human IL-7-treated recipient mice required about the same time to reach baseline levels, about 28 days. In addition to accelerated B-cell reconstitution, huFc-IL-7 treatment promoted the continuous expansion of B-cells until Day 33: huFc-IL-7 administered q2d resulted in a 7-fold increase, whereas administered q7d resulted in a 2.5-fold increase in B-cell numbers compared to control mice. After Day 33, B-cell numbers declined, but were still approximately 2-fold higher than in control mice. Also, after Day 33, levels of administered IL-7 proteins declined in the blood, which partially may be due to the formation of neutralizing antibodies to the human fusion protein. FIG. 6 represents these results of B-cell reconstitution in irradiated, bone marrow transplanted mice treated with recombinant human IL-7 and huFC-IL-7.
A similar result was observed regarding donor-derived T-cells (CD45.130 , CD3+, TCRαβ+. Treatment with the huFc-IL-7 fusion protein resulted in accelerated T-cell reconstitution, whereas treatment with recombinant human IL-7 did not. Maximum T-cell levels were reached around Day 49. However, T-cell numbers above baseline (i.e., blood concentration of T-cells in donor mice) were only achieved with a q2d dosing schedule of the huFc-IL-7 fusion protein, reaching about 1.5 fold the number of T-cells in the control mice. FIG. 7 represents these results of T-cell reconstitution in irradiated bone marrow transplanted mice treated with recombinant human IL-7 and huFc-IL-7.
Despite the transiently high numbers of donor B-cells and T-cells in the recipient mice under certain conditions, none of the experimental mice showed any signs of morbidity during the course of the experiment. Analysis of internal organs at Day 55 did not reveal pathological abnormalities in liver, kidney, lung, spleen, thymus, lymph nodes, stomach, small intestine and colon. Thus, this allogeneic transplantation experiment demonstrated that the huFc-IL-7 fusion protein was significantly superior in vivo over recombinant human IL-7 in reconstituting lymphocytes after myeloablative conditioning.







TABLE 1







Effect of huFc-IL-7 fusion protein on immune cell reconstitution.









Number of cells per microliter of blood



Day


















Treatment

7
13
19
27
33
41
47
55





















I. Donor Derived












Leukocytes (CD45.1+)


a.) Allogeneic
PBS
AVG
580.8
3576.8
4384.0
16805.6
20732.8
16395.2
21462.4
20329.6


BMT into B6C3

SEM
324.5
1717.0
1474.2
8367.6
10065.3
7997.3
11230.2
9693.2


mice
huFc-IL-7,
AVG
248.8
26597.0
130253.6
148048.0
194266.4
168794.0
127848.0
79175.2



q2d
SEM
89.3
4786.2
25106.8
18786.3
17131.1
25949.9
981.0
10740.2



huFc-IL-7,
AVG
278.4
5848.8
32308.0
64256.0
74103.2
69042.4
55989.6
58519.2



q7d
SEM
106.3
762.9
2786.3
6081.4
8345.9
14497.4
5989.8
6583.8



human IL-
AVG
270.7
6020.0
6922.7
24278.7
37353.3
42166.7
33570.7
38138.7



7, q7d
SEM
84.9
1229.2
1089.7
5235.3
2697.0
4691.4
764.5
3273.6



human IL-
AVG
229.0
4603.0
4963.0
27443.0
27027.0
27797.0
32675.0
33205.0



7, q7d
SEM
31.9
435.6
654.1
2513.8
1813.4
4084.6
6307.8
4894.7


b.) B6.SJL
PBS
AVG
30744.5


Control mice

SEM
3018.6


II. Donor Derived B-cells


(CD45.1+ CD19+B220+)


a.) Allogeneic
PBS
AVG
32.0
1013.3
4257.3
19294.7
22549.3
17842.7
23841.3
22296.0


BMT into B6C3

SEM
5.7
25.7
661.1
2858.5
2625.4
1691.6
3783.7
1474.5


mice
huFc-IL-7,
AVG
16.0
17830.0
122122.4
131862.4
169745.6
142972.0
98571.0
58661.6



q2d
SEM
5.7
3755.4
24028.4
16974.5
15413.6
22834.6
2599.1
9352.9



huFc-IL-7,
AVG
14.4
2559.0
28124.0
53573.6
59999.2
52932.8
41489.6
42899.2



q7d
SEM
6.5
408.9
2464.1
4911.5
6337.2
10998.2
4821.1
5013.0



human IL-
AVG
5.3
1550.7
4316.0
17802.7
28061.3
30177.3
24720.0
26104.0



7, q7d
SEM
3.5
403.5
542.7
3689.5
1484.5
2861.6
633.8
2085.3



human IL-
AVG
4.0
748.0
3179.0
19303.0
19203.0
17930.0
22460.0
21473.0



7, q7d
SEM
1.6
56.1
443.3
1666.1
1429.5
2511.6
4458.6
3199.5


b.) B6.SJL
PBS
AVG
15572.6


Control mice

SEM
1631.4


III. Donor Derived T-


cells


(CD45.1−CD3+abTCR+)


a.) Allogeneic
PBS
AVG
0.0
206.7
192.0
1808.0
3928.0
4453.3
6178.7
5622.7


BMT into B6C3

SEM
0.0
121.6
46.2
245.0
546.7
533.0
538.1
210.0


mice
huFc-IL-7,
AVG
0.0
124.0
839.0
5260.8
12252.8
15204.8
16628.0
13365.6



q2d
SEM
0.0
24.9
155.5
1183.1
1734.8
1641.2
1524.5
1423.9



huFc-IL-7,
AVG
0.0
38.4
228.0
2428.0
5492.0
9988.0
9252.8
8598.4



q7d
SEM
0.0
6.1
38.5
326.2
918.1
2475.8
2748.6
1185.9



human IL-
AVG
0.0
56.0
144.0
1057.3
3068.0
5368.0
5081.3
7112.0



7, q7d
SEM
0.0
3.3
42.5
160.1
154.0
645.5
113.7
409.9



human IL-
AVG
0.0
41.0
88.0
1493.0
2579.0
3918.0
5021.0
6043.0



7, q7d
SEM
0.0
2.5
20.2
187.5
238.0
694.6
724.2
1013.1


b.) B6.SJL
PBS
AVG
10832.0


Control mice

SEM
1500.4









EXAMPLE 9
Efficacy of huFc-IL-7 on T-Cell Transplantations in Lymphopenic Mice
The efficacy of huFc-IL-7 fusion proteins was also evaluated in a T-cell transplantation model. In essence, a homogeneous (clonal) population of T-cells was transferred into immunodeficient, irradiated mice, the recipient mice were administered the huFc-IL-7 fusion protein, and the degree of T-cell reconstitution and, eventually, T-cell function, was assessed.
To obtain a homogeneous population of T-cells, splenocytes were taken from P14 TCR-tg/RAG mice (Charles River Laboratories, Wilmington, Mass.), which are devoid of B-cells. In addition, all T-cells of these mice express the transgenic T-cell receptor (TCR), P14, which is specific for a viral epitope (gp33 of LCMV).
Single cell suspensions of splenocytes were injected intravenously into the tails of RAG Cγ−/− immunodeficient mice (Charles River Laboratories) that had been irradiated once with 650 Rads (sub-lethal dose) 4 has prior to transplantation. On alternate days starting at Day 2, recipient mice were administered 7 μg of the fusion protein huFcγ2(h)(FN>AQ)-IL-7. A control group of recipient mice were administered PBS. The degree of T-cell reconstitution in response to the huFc-IL-7 fusion protein or PBS was determined by measuring the presence of P14 T-cells (CD8+Vβ8.1+Vα2+ cells) in the blood by flow cytometry.
It was found that at Day 35, mice that were administered the huFc-IL-7 fusion protein had a 17-fold increase in T-cell numbers (35,000 cells/μl) compared to control mice (2,000 cells/μl). Indeed, the levels of T-cell reconstitution exceeded those seen in untreated P14 TCR mice (23,000 cells/μl). In addition, in these huFc-IL-7-treated mice a significant fraction of reconstituted T-cells had up-regulated the IL-2Rα receptor subunit, CD25, on the cell surface. Thus, not only was the huFc-IL-7 fusion protein useful in expanding transplanted T-cells, but in addition may have preconditioned the transferred T-cells to be responsive to cytokines, such as IL-2.
EXAMPLE 10
huFc-IL-7 Adjuvant Therapy for Immunocompromised Patients
Numerous clinical settings are envisaged in which patients may benefit from huFc-IL-7 adjuvant therapy. For example, new treatment modalities are being developed for pediatric patients with malignant disease such as lymphoblastic or myeloid leukemias, who, following a myeloablative therapy, are treated by allogeneic hematopoietic stem cell transplantation to reconstitute the immune system.
To increase markedly the potential donor pool for these patients, it has been found that G-CSF mobilized peripheral blood stem cells (PBSCs) from matched unrelated donors or haplo-identical donors with 1-3 HLA loci mismatches may be a source of cells, provided that the transplant is depleted of T-cells (see Handgretinger et al. (2001) Annals NY Acad. Sciences 938:340-357). This depletion drastically reduced the occurrence of acute graft-to-host transplant rejection (GvHD); however, it is believed that because of the low concentration of T-cells, there was a significant delay in immunoreconstitution. Patients were at high risk of viral infections for at least the first 6 month post transplant, and T-cells did not return to normal levels for a year (Handgretinger et al, (2001) Annals NY Acad. Sciences 938:340-357; Lang et al., (2003) Blood 101: 1630-6). Therefore, it would be advantageous to increase the rate of repopulation of T-cells and of other immune cells in these patients.
Patients that will benefit huFc-IL-7 therapy include patients with a childhood leukemia, such as a lymphoblastic leukemia or a myeloid leukemia. Children having this disorder will first undergo a myeloablative conditioning therapy which may be based either on the chemotherapeutic agent busulfan or total body irradiation combined with chemotherapy. For instance, according to the patient's diagnosis and age, the patient is treated with total body irradiation (typically 6 treatments of 2 Gy each), rabbit anti-thymocyte globulin (10 mg/kg daily for 3 days), etoposide (40 mg/kg) and cyclophosphamide (120 mg/kg).
To obtain, CD34 positive (pos) stem cells for transplant, peripheral blood stem cells (PBSCs) of a histocompatible (allogeneic) donor are mobilized with a daily dose of 10 micrograms/kg of G-CSF for 6 days, and are harvested by leukapharesis on days 5 and 6. Generally, about 20×106 kg CD34 pos stem cells are obtained and transplanted. CD34 pos stem cells are purified from the PBSCs by positive selection with an antiCD34 antibody in a SuperMACS system (Magnetic activated cell sorting, Miltenyi Biotec) and eluted. T-cell depletion is typically around 5 logs, to about 10×103 cells/kg. Aggregates and other debris are excluded from the graft by FACS sorting. The cell suspension is infused into the patient via a central venous catheter. Optionally, the graft may include purified populations of other immune cells, such as haploidenitical NK cells, DCs, monocytes, as well as CD34neg stem cells.
To assess engraftment, an absolute neutrophil count is performed. Engraftment is considered successful once neutrophil levels remain above 50 cells/microliter. Reconstitution of immune cells is monitored by FACS analysis, weekly at first and, once T-cell recovery begins, every 3 months.
To augment immunoreconstitution, the patient is treated with a huFc-IL-7 fusion protein such as huFcγ2h(FN>AQ)-IL-7 or huFcγ1(YN>AQ)(linker2)-IL-7. Approximately 3 weeks after transplant (or after engraftment is established), the patient receives a subcutaneous administration of huFcγ2h(FN>AQ)-IL-7 or huFcγ1 (YN>AQ)(linker2)-IL-7 at a dose of about 1.5 mg/m2 (or a dose in the range of 0.15 mg/m2 to 15 mg/m2), about 2 times a week for 6 months-12 months, until T-cell counts reach 50% of normal levels. It is found that the prognosis of the patient is improved due to lowered risk of viral infection, one of the main post-transplant complications. It is further found that this treatment does not significantly increase the risk of acute GvHD.
In addition to administration of huFc-IL-7 protein, other medications are optimally given prophylactically. These include, for example, acyclovir, metronidazole, flucanazole and co-trimoxazole. For the first three months, the patient may receive weekly administration of immunoglobulins, as well as of G-CSF.
Equivalents
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting on the invention described herein. Scope of the invention is thus indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.

## Claims

1. A fusion protein comprising:
a first portion comprising an immunoglobulin chain; and
a second portion comprising a polypeptide comprising an amino acid sequence at least 85% identical to mature human interleukin-7 (IL-7), wherein the mature human IL-7 comprises amino acid residues 26-177 of SEQ ID NO:1, and wherein the polypeptide comprises disulfide bonding between residues corresponding to positions Cys2 and Cys92, Cys34 and Cys 129, and Cys47 and Cys141 of mature human IL-7.

2. The fusion protein of claim 1, wherein the second portion polypeptide further comprises a deletion comprising an eighteen amino acid deletion from amino acid 96 to amino acid 114 of mature human IL-7.

3. The fusion protein of claim 1, wherein the amino acid residue at position 116 of mature human IL-7 is non-glycosylated.

4. The fusion protein of claim 1, wherein the amino acid residue at position 116 of mature human IL-7 is asparagine.

5. The fusion protein of claim 1, wherein the amino acid residue at position 116 of mature human IL-7 is altered such that it does not serve as a glycosylation site.

6. The fusion protein of claim 1, wherein the amino acid residues at positions 70 and 91 of mature human IL-7 are glycosylated.

7. The fusion protein of claim 1, wherein the immunoglobulin chain comprises at least a portion of one or more constant domains.

8. The fusion protein of claim 7, wherein the constant domain is selected from the group consisting of CH1, CH2, and CH3.

9. The fusion protein of claim 1, further comprising a linker between the first portion and the second portion.

10. The fusion protein of claim 7, wherein the constant domain is an IgG1 constant domain.

11. The fusion protein of claim 10, wherein Asn297 of the constant domain is modified.

12. The fusion protein of claim 11, wherein the Asn297 modification is Asn297G1n.

13. The fusion protein of claim 11, further comprising a modification at Tyr296.

14. The fusion protein of claim 13, wherein the Tyr296 modification is Tyr296Ala.

15. The fusion protein of claim 7, wherein the constant domain is an IgG2 constant domain.

16. The fusion protein of claim 7, wherein the immunoglobulin chain further comprises an IgG1 hinge.

17. The fusion protein of claim 16, wherein Asn297 is modified.

18. The fusion protein of claim 17, wherein the Asn297 modification is Asn297G1n.

19. The fusion protein of claim 16, further comprising a modification at Phe296.

20. The fusion protein of claim 19, wherein the Phe296 modification is Phe296Ala.