Secretory production of bioactive recombinant human granulocyte-macrophage colony-stimulating factor by a baculovirus expression system

Current status, and the developments of hosts and expression systems for the production of recombinant human cytokines

Cytokines consist of peptides, proteins and glycoproteins, which are biological signaling molecules, and boost cell-cell communication in immune reactions to stimulate cellular movements in the place of trauma, inflammation and infection. Recombinant cytokines are designed in such a way that they have generalized immunostimulation action or stimulate specific immune cells when the body encounters immunosuppressive signals from exogenous pathogens or other tumor microenvironments. Recombinant cytokines have improved the treatment processes for numerous diseases. They are also beneficial against novel toxicities that arise due to pharmacologic immunostimulators that lead to an imbalance in the regulation of cytokine. So, the production and use of recombinant human cytokines as therapeutic proteins are significant for medical treatment purposes. For the improved production of recombinant human cytokines, the development of host cells such as bacteria, yeast, fungi, insect, mammal and transgenic plants, and the specific expression systems for individual hosts is necessary. The recent advancements in the field of genetic engineering are beneficial for easy and efficient genetic manipulations for hosts as well as expression cassettes. The use of metabolic engineering and systems biology approaches have tremendous applications in recombinant protein production by generating mathematical models, and analyzing complex biological networks and metabolic pathways via simulations to understand the interconnections between metabolites and genetic behaviors. Further, the bioprocess developments and the optimization of cell culture conditions would enhance recombinant cytokines productivity on large scales.

Expression and purification of biologically active human granulocyte-macrophage colony stimulating factor (hGM-CSF) using silkworm-baculovirus expression vector system

Human granulocyte-macrophage colony stimulating factor (hGM-CSF) is a hematopoietic growth factor. It is widely employed as a therapeutic agent targeting neutropenia in cancer patients undergoing chemotherapy and in patients with AIDS or after bone marrow transplantation. In this study, we constructed the recombinant baculoviruses for the expression of recombinant hGM-CSF (rhGM-CSF) with two small affinity tags (His-tag and Strep-tag) at the N or C-terminus. Compared to N-tagged rhGM-CSF, C-tagged rhGM-CSF was highly recovered from silkworm hemolymph. The purified rhGM-CSF proteins migrated as a diffuse band and were confirmed to hold N-glycosylations. A comparable activity was achieved when commercial hGM-CSF was tested as a control. Considering the high price of hGM-CSF in the market, our results and strategies using silkworm-baculovirus system can become a great reference for mass production of the active rhGM-CSF at a lower cost.

Cloning and expression of recombinant human GMCSF from Pichia pastoris GS115--a progressive strategy for economic production

Human granulocyte-macrophage colony-stimulating factor (hGMCSF) is a proinflammatory cytokine and hematopoietic growth factor. Recombinant human granulocyte-macrophage colony-stimulating factor (rhGMCSF) serves as a biotherapeutic agent in bone marrow stimulations, vaccine development, gene therapy approaches, and stem cell mobilization. The objective of the present study includes construction of rhGMCSF having N-terminal intein tag, expression of protein both extracellularly and intracellularly from yeast expression system followed by its purification in a single step by affinity chromatography. The soluble and biologically active rhGMCSF was obtained from Pichia pastoris GS115. About 122 g DCW/L of final yield was obtained for both cytosolic and secretory expression of Pichia GS115 strain. Purified intracellular hGMCSF was 420 mg/L with a specific activity of 2.1×10⁸ IU/mg, and the purified extracellular recombinant protein was 360 mg/L with a specific activity of 1.9×10⁸ IU/mg. The data presented here indicate the possibilities of exploring the economic ways of producing the rhGMCSF.

Enhancing toxic protein expression in Escherichia coli fed-batch culture using kinetic parameters: Human granulocyte-macrophage colony-stimulating factor as a model system

The kinetics of recombinant human granulocyte-macrophage colony-stimulating factor (hGM-CSF) expression was studied under the strong T7 promoter in continuous culture of Escherichia coli using complex medium to design an optimum feeding strategy for high cell density cultivation. Continuous culture studies were done at different dilution rates and the growth and product formation profiles were monitored post-induction. Recombinant protein expression was in the form of inclusion bodies with a maximum specific product formation rate (q(p)) of 63.5 mg g(-1) DCW h(-1) at a dilution rate (D) of 0.3 h(-1). The maximum volumetric product concentration achieved at this dilution rate was 474 mg l(-1), which translated a ~1.4 and ~1.75 folds increase than the values obtained at dilution rates of 0.2 h(-1) and 0.4 h(-1) respectively. The specific product yield (Y(P/x)) peaked at 138 mg g(-1) DCW, demonstrating a ~1.6 folds increase in the values obtained at other dilution rates. A drop in q(p) was observed within 5-6 h of induction at all the dilution rates, possibly due to protein toxicity and metabolic stress associated with protein expression. The data from the continuous culture studies allowed us to design an optimal feeding strategy and induction time in fed-batch cultures which resulted in a maximum product concentration of 3.95 g l(-1) with a specific hGM-CSF yield (Y(P/x)) of 107 mg g(-1) DCW.

Attempts to express the A1-GMCSF immunotoxin in the baculovirus expression vector system

Immunotoxins are fusion proteins consisting of two elements, a targeting and a toxin moiety, and are designed for specific elimination of tumor cells. Previously we expressed a recombinant fusion protein consisting of the toxic fragment of Shiga toxin (A1) and GMCSF (A1-GMCSF) in Escherichia coli, and evaluated its cytotoxic properties in acute myeloid leukemia and colon carcinoma cell lines. In view of the specific cytotoxic effects of this immunotoxin, further detailed in-vitro and preclinical studies were undertaken. Large amounts of the recombinant protein of high purity and free of unwanted side products, such as lipopolysaccharides (LPS), were required. Since GMCSF is of mammalian origin and it requires proper disulfide bond formation, we intended to use the baculovirus expression vector system (BEVS) for the expression of the recombinant fusion protein. However, despite previous reports on the expression of several other immunotoxins by this system, the A1 derived fusion proteins revealed an inhibitory effect on baculoviral particle formation and even caused cell death in insect cells. This observation was further pursued and confirmed by the use of other baculoviral specific promoters. The salient features of this finding are described below.

Optimization of human granulocyte macrophage-colony stimulating factor (hGM-CSF) expression using asparaginase and xylanase gene's signal sequences in Escherichia coli

The toxicity of the recombinant protein towards the expression host remains a significant deterrent for bioprocess development. In this study, the expression of human granulocyte macrophage-colony stimulating factor (hGM-CSF), which is known to be toxic to its host, was enhanced many folds using a combination of genetic and bioprocess strategies in Escherichia coli. The N terminus attachment of endoxylanase and asparaginase signal sequences from Bacillus subtilis and E. coli, respectively, in combination with and without His-tag, considerably improved expression levels. Induction and media optimization studies in shake flask cultures resulted in a maximal hGM-CSF concentration of 365 mg/L in the form of inclusion bodies (IBs) with a specific product yield (Y (P/X)) of 120 mg/g dry cell weight in case of the asparaginase signal. Culturing the cells in nutrient rich Terrific broth maintained the specific product yields (Y (P/X)) while a 6.6-fold higher volumetric concentration of both product and biomass was obtained. The purification and refolding steps were optimized resulting in a 95% pure protein with a fairly high refolding yield of 45%. The biological activity of the refolded protein was confirmed by a cell proliferation assay on hGM-CSF dependent human erythroleukemia TF-1 cells. This study demonstrated that this indeed is a viable route for the efficient production of hGM-CSF.

Construction of intein-mediated hGMCSF expression vector and its purification in Pichia pastoris

As a novel attempt for the intracellular recombinant protein over expression and easy purification from Pichia pastoris, the therapeutic cytokine human granulocyte macrophage colony stimulating factor (hGMCSF) gene was fused to an intein-chitin-binding domain (gene from pTYB11 vector) fusion tag by overlap extension PCR and inserted into pPICZB vector, allowing for the purification of a native recombinant protein without the need for enzymatic cleavage. The fusion protein under the AOX1 promoter was integrated into the P. pastoris genome (SMD 1168) and the recombinant Pichia clones were screened for multicopy integrants. Expression of hGMCSF was done using glycerol and methanol based synthetic medium by three stage cultivation in a bioreactor. Purification of the expressed hGMCSF fusion protein was done after cell disruption and binding of the solubilized fusion protein to chitin affinity column, followed by DTT induced on column cleavage of hGMCSF from the intein tag. In this study, final biomass of 89 g dry cell weight/l and purified hGMCSF of 120 mg/l having a specific activity of 0.657 x 10(7) IU/mg was obtained. This strategy has an edge over the other--His or--GST based fusion protein purification where non-specific protein binding, expensive enzymatic cleavage and further purification of the enzyme is required. It distinguishes itself from all other purification systems by its ability to purify, in a single chromatographic step.

Production and purification of recombinant human granulocyte–macrophage colony stimulating factor (GM-CSF) from high cell density cultures of Pichia pastoris

Granulocyte-macrophage colony stimulating factor (GM-CSF) is a hematopoietic growth factor, which has been used as a therapeutic agent in clinical cases like neutropenia. In this study, we report the production of recombinant human GM-CSF in the methylotrophic yeast Pichia pastoris through secretory expression using the inducible AOX1 promoter. Recombinant P. pastoris GS115 cells were grown in fed batch cultures to obtain a biomass density of 55.6 gDCW L(-1) and a high volumetric activity of 131 mg L(-1) of GM-CSF. The protein migrated as a diffuse band on SDS-PAGE at the range of 28-35 kDa indicating differential glycosylation. The secreted protein was purified to 95% in two steps using cation exchange and size exclusion chromatography.

Process optimization of constitutive human granulocyte-macrophage colony-stimulating factor (hGM-CSF) expression in Pichia pastoris fed-batch culture

Human granulocyte-macrophage colony-stimulating factor (hGM-CSF) is a therapeutically important cytokine that is poorly expressed because of its toxic effects on the host cells. Extracellular expression of hGM-CSF was obtained by cloning its gene in Pichia pastoris under the constitutive glyceraldehyde-3-phosphate dehydrogenase (GAP) promoter with an N-terminal alpha peptide sequence for its extracellular production. The clones obtained were screened for a hyper producer following which media and cultivation conditions were optimized in shake flasks. Batch and fed-batch studies were performed in a bioreactor where different feed compositions were fed exponentially to obtain high biomass concentrations. Feeding of complex media allowed us to maintain a high specific growth rate of 0.2 h(-1) for the longest time period, and a final biomass of 98 g DCW/l was obtained in 34 h. Product formation was found to be growth associated, and the product yield with respect to biomass (Y (P/X)) was approximately 2.5 mg/g DCW. The above fed-batch strategy allowed us to obtain fairly pure glycosylated hGM-CSF at a final product concentration of 250 mg/l in the culture supernatant with a high volumetric productivity of 7.35 mg l(-1) h(-1).

Porcine interleukin 18: cloning, characterization of the cDNA and expression with the baculovirus system

We have isolated and sequenced a cDNA that contains the coding sequence of porcine interleukin 18 (IL-18) and the recombinant protein of porcine IL-18 was expressed using the baculovirus system. The open reading frame (ORF) of the porcine IL-18 cDNA is 579 base pairs (bp) in length and encodes 192 amino acids. The predicted amino acid sequence is 76.7%, 64.7% and 61.6% homologous to the predicted human, murine and rat amino acid sequences, respectively. The porcine precursor and mature IL-18 protein were expressed respectively in Trichoplusia ni -derived (Tn5) cells using the baculovirus Autografha californica nuclear polyhedorosis virus (AcNPV) as a vector. Tn5 cells infected with recombinant virus containing a whole IL-18 protein coding region sequence secreted porcine precursor IL-18 into the culture medium. On the other hand, Tn5 cells infected with recombinant virus containing a mature IL-18 protein coding region sequence expressed several proteins in the cell lysates, but did not secrete mature protein into the culture medium efficiently. Immunoblotting analysis of recombinant protein showed cross-reactivity with anti-human IL-18 polyclonal antibody. The mature form of porcine IL-18 protein induced IFN-gamma production in suboptimal doses of anti-CD3 antibody and concanavalin A- (ConA) stimulated porcine peripheral blood mononuclear cells (PBMC), but the precursor form had little effect.

Production of recombinant DTctGMCSF fusion toxin in a baculovirus expression vector system for biotherapy of GMCSF-receptor positive hematologic malignancies

The fusion toxin DTctGMCSF has been constructed by genetically replacing the native receptor-binding domain of diphtheria toxin (DT) with human granulocyte-macrophage colony stimulating factor (GMCSF). This recombinant fusion toxin preserves the catalytic (c) and membrane translocation (t) domains of DT and includes a sterically neutral peptide linker separating the toxin and growth factor domains. Previous work using DTctGMCSF produced in Escherichia coli has shown that this chimeric toxin is selectively cytotoxic to GMCSF receptor (R)-positive acute myeloid leukemia (AML) cells both in vitro and in vivo. Its clinical development has been hampered due to very low expression levels, requirements for solubilization with guanidine hydrochloride and subsequent refolding, and concerns about bacterial endotoxin contamination. These difficulties prompted us to investigate the utility of a baculovirus/insect cell expression system for the production of DTctGMCSF. Here, we report that a soluble form of DTctGMCSF can be produced in the baculovirus expression vector system (BEVS) and purified to homogeneity by column chromatography. The BEVS-derived DTctGMCSF fusion toxin caused apoptotic death in GMCSF-R-positive human AML cells at nanomolar concentrations. In contrast to the 100 microg/L yields of purified DTctGMCSF obtained from E. coli, the BEVS allows us to routinely generate 8-10 mg/L of purified DTctGMCSF. This increased capacity provided by the BEVS for the production of DTctGMCSF makes it now possible to obtain sufficient quantities to carry out preclinical and clinical trials. To our knowledge, this is the first report of the successful utilization of the BEVS for producing a therapeutic fusion toxin.