Expression vectors for eukaryotic expression systems
The invention provides expression vectors for expressing recombinant proteins (e.g., biologics) in mammalian cells. Also provided are host cells comprising the expression vectors, methods of producing the recombinant proteins, and methods of propagating the expression vectors.
1. An expression vector comprising:
(a) a first expression cassette comprising the following elements in the order of upstream to downstream: a promoter operably linked to an insertion site for a gene of interest (GOI), an internal ribosome entry site (IRES), wherein the IRES consists of a polynucleotide sequence of SEQ ID NO: 3, a polynucleotide encoding a eukaryotic selectable marker, and a polyadenylation (polyA) signal;
(b) a second expression cassette comprising a polynucleotide encoding a bacterial selectable marker; and
(c) a bacterial plasmid origin of replication;
wherein optionally the first expression cassette further comprises one or more regulatory element; and
wherein optionally the regulatory element is an enhancer, an insulator, a locus control region (LCR), a matrix attachment region (MAR), a scaffold attachment region (SAR), an expression augmenting sequence element (EASE), an adenovirus tripartite leader (TPL), or a ubiquitous chromatin opening element (UCOE).
2. The expression vector of claim 1 , further comprising two inverted terminal repeat (ITR) sequences flanking the first expression cassette.
3. The expression vector of claim 2 , wherein
(a) the eukaryotic selectable marker is a neomycin phosphotransferase, a histidinol dehydrogenase, a hygromycin B phosphotransferase, a xanthine-guanine phosphoribosyltransferase, a dihydrofolate reductase, a tryptophan synthetase, a puromycin N-acetyl-transferase, a thymidine kinase, an adenine phosphoribosyl transferase, a glutamine synthetase, an adenosine deaminase, or metallothionein-1; wherein optionally the eukaryotic selectable marker is a glutamine synthetase or a neomycin phosphotransferase;
(b) the promoter is a human cytomegalovirus (CMV) immediate-early promoter, a human elongation factor 1 alpha (EF1a) promoter, a SV40 promoter, a phosphoglycerate kinase 1 (PGK1) promoter, a human ubiquitin C (Ubc) promoter, a human β-actin promoter, a CAG promoter, a yeast transcription elongation factor 1 (TEF1) promoter, a yeast glyceraldehyde 3-phosphate dehydrogenase (GAPDH) promoter, or a yeast alcohol dehydrogenase 1 (ADH1) promoter; wherein optionally the promoter is a human CMV immediate-early promoter;
(c) the enhancer is a CMV immediate-early enhancer; and/or
(d) the insulator is HS4.
4. An expression vector comprising:
(a) a first expression cassette comprising the following elements in the order of upstream to downstream: a first insulator, an EASE, a promoter, a TPL, an insertion site for a GOI, an IRES, a polynucleotide encoding a eukaryotic selectable marker, a polyA signal, and a second insulator;
(b) two ITR sequences flanking the first expression cassette;
(c) a second expression cassette comprising a polynucleotide encoding a bacterial selectable marker; and
(d) a bacterial plasmid origin of replication;
wherein optionally the first expression cassette further comprises an enhancer;
wherein optionally the enhancer is located between the EASE and the promoter;
wherein optionally the enhancer is a human CMV immediate-early enhancer;
wherein optionally the promoter is a human CMV immediate-early promoter;
wherein optionally the first and the second insulators are HS4;
wherein optionally the eukaryotic selectable marker is a glutamine synthetase or a neomycin phosphotransferase; and
wherein the IRES consists of a polynucleotide sequence of SEQ ID NO: 3.
5. An expression vector,
(a) comprising a polynucleotide sequence of SEQ ID NO: 6 or 8;
(b) consisting of a polynucleotide sequence of SEQ ID NO: 6 or 8; or
(c) consisting essentially of a polynucleotide sequence of SEQ ID NO: 6 or 8.
6. The expression vector of claim 5 , wherein the polynucleotide sequence is SEQ ID NO:8.
7. The expression vector of claim 4 , wherein the first expression cassette further comprises the GOI encoding
(a) a therapeutic or prophylactic protein;
(b) a light chain of a monoclonal antibody; or
(c) a heavy chain of a monoclonal antibody.
8. An isolated host cell comprising the expression vector of claim 7 , wherein optionally the host cell is a mammalian host cell or a bacterial host cell; wherein optionally the mammalian host cell is a CHO cell; and wherein optionally the endogenous glutamine synthetase gene of the CHO cell is knocked out.
9. A method of producing a polypeptide encoded by a GOI, comprising culturing the host cell of claim 8 in vitro under conditions in which the polypeptide is expressed, wherein the expression vector comprises the GOI encoding the polypeptide; and wherein the method further comprises recovering the polypeptide from the culture.
10. A method of propagating an expression vector, comprising culturing the host cell of claim 8 in vitro under conditions in which the expression vector is replicated; and wherein optionally the method further comprises recovering the expression vector from the culture.
11. An isolated host cell comprising a first expression vector of claim 4 and a second expression vector of claim 4 , wherein the first expression vector further comprises a first GOI encoding a light chain of a monoclonal antibody or fragments thereof; wherein the second expression vector further comprises a second GOI encoding a heavy chain of the monoclonal antibody or fragments thereof; and wherein the eukaryotic selectable marker of the first expression vector is different from the eukaryotic selectable marker of the second expression vector.
12. A method of producing a monoclonal antibody, comprising culturing the host cell of claim 11 in vitro under conditions in which the light chain of the monoclonal antibody and the heavy chain of the monoclonal antibody are expressed; and wherein optionally the method further comprises recovering the monoclonal antibody from the culture.