Purification and characterization of recombinant human interleukin 4. Biological activities, receptor binding and the generation of monoclonal antibodies

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.

Plant-made pharmaceuticals for the prevention and treatment of autoimmune diseases: where are we?

Molecular farming in plants or plant cell cultures represents a viable alternative technology that holds great promise for the low-cost and large-scale production of recombinant proteins. The particular case of plant-based vaccines for the prevention of autoimmune diseases is addressed here, presenting a comprehensive overview of the different molecules and expression technologies that have been investigated so far in both academia and industry. The potential of plants not only as bioreactors but also as delivery systems for pharmaceuticals is discussed, and the advantages of oral delivery of autoantigens for the induction of immune tolerance are highlighted.

Production of biologically active human interleukin-4 in transgenic tobacco and potato

Interleukin-4 (IL-4) is a pleiotropic cytokine that plays a key regulatory role in the immune system. Recombinant human IL-4 (rhIL-4) offers great potential for the treatment of cancer, viral and autoimmune diseases. Unfortunately, the high production cost of IL-4 associated with conventional expression systems has, until now, limited broader clinical testing, particularly with regard to the more convenient and safer oral delivery of IL-4 as opposed to parenteral injection in patients. In this study, we investigated the feasibility of transgenic plants for the cost-effective production of rhIL-4. IL-4 expression vectors with different modifications under the control of a constitutive cauliflower mosaic virus 35S (CaMV 35S) promoter were introduced into tobacco by Agrobacterium-mediated transformation. Transgenic tobaccos expressing various levels of rhIL-4 protein were generated. Higher expression was achieved through IL-4 retention in the endoplasmic reticulum (ER), with the maximal accumulation being approximately 0.1% of total soluble protein (TSP) in the leaves. No improvement in expression was further achieved by replacing the native signal peptide of IL-4 with the plant signal peptide. The best rhIL-4-expressing vector shown in tobacco was selected and further transferred into potato plants. The analysis of transgenic tubers also revealed various levels of rhIL-4, with the highest being 0.08% of TSP. Sensitive in vitro T-cell proliferation assays showed that plant-derived rhIL-4 retained full biological activity. These results suggest that plants can be used to produce biologically active rhIL-4 and probably many other mammalian proteins of medical significance. Moreover, the production of plants expressing rhIL-4 will enable the testing of plant rhIL-4 by oral delivery for the treatment of clinical diseases.

Functional characterization of equine dendritic cells propagated ex vivo using recombinant human GM-CSF and recombinant equine IL-4

Naive T cells can be activated both in vivo and in vitro by specialized antigen presenting cells, dendritic cells (DC), with potent antigen-specific, immunostimulatory activity. Indeed, DC can provide an extremely powerful and important immunological tool by which to potentiate the immune response for specific recognition of foreign antigens. Until recently, the direct isolation of DC from PBMC required laborious procedures with extremely poor yields (<0.1%). Methods have been developed for the human, lower primate, and murine model systems to propagate large numbers of DC from PBMC or bone marrow ex vivo with various cytokines. However, all other model systems, including equine, still require the laborious isolation procedures to obtain DC. In this study, we have adapted the methods developed for the human system to generate large numbers of equine DC from PBMC precursors using recombinant human GM-CSF and recombinant equine IL-4. Our report is the first documentation of ex vivo generated DC from PBMC in a domesticated animal model system. Equine DC derived from PBMC were rigorously characterized by analyzing morphological, phenotypic, and functional properties and were determined to have similar attributes as DC generated from human PBMC. Equine DC appeared stellate with large projectiles and veils and had cell surface antigens at similar levels as those defined on human and murine DC. Furthermore, functional attributes of the DC included rapidly capturing antigens by pinocytosis, receptor-mediated endocytosis, and phagocytosis, activating naive T cells in a mixed leukocyte reaction to a much greater extent than macrophage or lymphoblasts, presenting soluble and particulate antigen 10-100 fold more effectively to T cells on a per cell basis than macrophage or lymphoblasts, and presenting soluble and particulate antigen to both CD4+ and CD8+ T cells. Taken together, our study provides a framework by which equine DC can now be readily produced from PBMC precursors and presents an impetus for and model by which DC can be simply generated in other animal model systems.

Optimized gene synthesis, high level expression, isotopic enrichment, and refolding of human interleukin-5

Structural studies on soluble proteins using nuclear magnetic resonance (NMR) spectroscopy and other structural methods in general require large quantities of isotopically enriched proteins. Human interleukin-5 is a disulfide-linked homodimeric cytokine implicated in asthmatic response. The development of a high yield overexpression system for human interleukin-5 is an important prerequisite to using modern multidimensional NMR in the characterization of the solution structure of the protein and to characterize interactions with a soluble receptor domain. Significant amounts of the protein were expressed using an optimized synthetic gene in a high yield expression system. Gene synthesis was accomplished through the ligation of six oligonucleotides composed of optimized codons. The ligated fragments were further amplified by a polymerase chain reaction and then subcloned into the T7 RNA polymerase based overexpression vector pET11a. However, the induced protein accumulated in the form of inclusion bodies. Initially, the protein was solubilized under denaturing conditions and purified in these denaturing conditions by passage through a single S-200 HR sizing column. Finally, protein refolding was initiated in the presence of 2 M urea followed by dialysis. This protocol yielded 40 mg of biologically active, isotope-enriched protein from 4 liters of minimal medium thus facilitating structural studies by NMR. The strategy described may be of immense value in the production of significant quantities of recombinant, eukaryotic proteins for structural and other studies.

Phenotypic and immunoregulatory analysis of intestinal T-cells in patients with inflammatory bowel disease: evaluation of an in vitro model

Although a disturbed immune response to constituents of the gut mucosa has been implicated in the pathogenesis of inflammatory bowel disease, the mechanisms are still unclear. Intestinal T-cells derived from gut biopsies were propagated in vitro as single and co-cultures under different experimental conditions prior to flow cytometry. Intestinal T-cell lines from inflamed mucosa (n = 69) showed a significant (P < 0.001) decrease in CD4+ T-cells compared to T-cells from normal (n = 49) and uninflamed (n = 29) tissue specimens. Co-culturing of inflamed and uninflamed mucosa led to a normalization of CD4+ T-cells in cultures derived from inflamed mucosa. Analysis of supernatants revealed a significantly (P < 0.001) increased secretion of IL-4 under co-culture conditions. Moreover, stimulation of cultures derived from inflamed mucosa with rIL-4 led to a significant (P < 0.001) increase in CD4+ T-cells, whereas anti-IL-4 antibodies or IFN-gamma supplementation of T-cells derived from uninflamed mucosa significantly (P < 0.001) reduced the CD4+ subset. Treatment with IFN-gamma and anti-IL-4 antibodies did not affect the phenotype of T-cells derived from inflamed mucosa. These data suggest that IL-4 might play a key role in the intestinal immune response. Furthermore, this in vitro system allows the investigation of mucosal immune mechanisms in more detail under standardized conditions.

Receptor binding properties of four-helix-bundle growth factors deduced from electrostatic analysis

Hormones of the hematopoietin class mediate signal transduction by binding to specific transmembrane receptors. Structural data show that the human growth hormone (hGH) forms a complex with a homodimeric receptor and that hGH is a member of a class of hematopoietins possessing an antiparallel 4-alpha-helix bundle fold. Mutagenesis experiments suggest that electrostatic interactions may have an important influence on hormone-receptor recognition. In order to examine the specificity of hormone-receptor complexation, an analysis was made of the electrostatic potentials of hGH, interleukin-2 (IL-2), interleukin-4 (IL-4), granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), and the hGH and IL-4 receptors. The binding surfaces of hGH and its receptor, and of IL-4 and its receptor, show complementary electrostatic potentials. The potentials of the hGH and its receptor display approximately 2-fold rotational symmetry because the receptor subunits are identical. In contrast, the potentials of GM-CSF and IL-2 lack such symmetry, consistent with their known high affinity for hetero-oligomeric receptors. Analysis of the electrostatic potentials supports a recently proposed hetero-oligomeric model for a high-affinity IL-4 receptor and suggests a possible new receptor binding mode for G-CSF; it also provides valuable information for guiding structural and mutagenesis studies of signal-transducing proteins and their receptors.

Neutralizing monoclonal antibodies define two different functional sites in human interleukin-4

Human interleukin-4 (IL-4) is a small four-helix-bundle protein which is essential for organizing defense reactions against macroparasites, in particular helminths. Human IL-4 also appears to exert a pathophysiological role during various IgE-mediated allergic diseases. Seven different monoclonal antibodies neutralizing the activity of human IL-4 were studied in order to identify functionally important epitopes. A collection of 41 purified IL-4 variants was used to analyse how defined amino acid replacements affect binding affinity for each individual mAb. Specific amino acid positions could be assigned to four different epitopes. mAbs recognizing epitopes on helix A and/or C interfered with IL-4 receptor binding and thus inhibited IL-4 function. However, other mAbs also inhibiting IL-4 function recognized an epitope on helix D of IL-4 and did not inhibit IL-4 binding to the receptor protein. One mAb, recognizing N-terminal and C-terminal residues, partially competed for binding to the receptor. The results of these mAb epitope analyses confirm and extend previous data on the functional consequences of the amino acid replacements which showed that amino acid residues in helices A and C of IL-4 provide a binding site for the cloned IL-4 receptor and that a signalling site in helix D interacts with a further receptor protein.

T cells from atopic individuals produce IgE-inducing activity incompletely blocked by anti-interleukin-4 antibody

We investigated peripheral blood B and T lymphocyte functions in atopic individuals. B cells were co-cultured with mutant EL4 thymoma cells in the presence of a standard T cell supernatant (T-SN) with or without exogenous interleukin (IL)-4. IgE secretion in this assay was found to be IL-4 dependent, but not significantly different for atopic patients (n = 25) vs. normal controls (n = 25). Phytohemagglutinin plus phorbol 12-myristate 13-acetate (PHA+PMA)- induced T-SN from patients or controls was tested on normal B cells in the same assay system (in the absence of exogenous IL-4). Compared to the controls, the IgE-inducing activity was significantly increased for patients with asthma or allergic rhinitis (n = 12; p less than 0.005) but not for patients with atopic dermatitis (n = 13). The difference between the asthma or allergic rhinitis vs. the atopic dermatitis groups was significant (p greater than 0.05). Since the assay was not inhibited by interferon (IFN)-gamma, this difference can not be attributed to IFN-gamma concentrations. Other T cell activities may be different between the patient groups or atopic T cells from the respiratory mucosa may recirculate more than those from the skin. In any case, the T cells rather than the B cells were found to be abnormal in atopic individuals. If atopic T cells were stimulated with PHA+PMA not as immediately but after a resting period of 48 h in culture medium alone, the IgE-inducing activity, but not the total Ig-inducing activity or the IL-2 secretion, disappeared. In addition, a mean of 37% of the IgE-inducing activity (range of 13% to 79% for five very active T-SN) was not inhibited by an anti-IL-4 antibody which neutralized exogenous IL-4, indicating a participation of factors capable of bypassing the requirement for IL-4 for the IgE response.

Site-directed mutagenesis reveals the importance of disulfide bridges and aromatic residues for structure and proliferative activity of human interleukin-4

Mutant proteins (muteins) of human Interleukin-4 (IL4) were constructed by means of in vitro mutagenesis. The muteins were expressed in E. coli, submitted to a renaturation and purification protocol and analysed for biological activity. Exchange of the cysteines at either position 46 or 99 which form one of the three disulfide bridges resulted in a nearly complete loss of biological activity and an unstable protein. The exchange of tyrosine 124 also inactivated the protein, while a mutation of tyrosine 56 left some residual activity. Exchange of the other four cysteines or of the single tryptophane had smaller effects.

In vitro and in vivo studies with purified recombinant human interleukin 5

The functional activities of highly purified recombinant human IL 5 (hIL 5) have been characterized on a number of cell types in vitro and in BALB/c mice in vivo. In vitro, hIL 5 could induce the differentiation of eosinophils from precursors in both human and mouse bone marrow with approximately the same efficiency. A mouse IL 5/3-dependent B cell line, LyH7.B13, was found to proliferate in response to hIL 5 but not human interleukin 1 (IL 1), interleukin 2 (IL 2), interleukin 3 (IL 3), interleukin 4 (IL 4), interleukin 6 (IL 6), interferon-gamma (IFN-gamma), or granulocyte macrophage-colony stimulating factor (GM-CSF) and was at least 10-fold more sensitive than BCL1 mouse lymphoma cells. We have successfully used this cell line to demonstrate the production of IL 5 by human T cell clones. In marked contrast to its effects on murine B cell lines, hIL 5 had no demonstrable activity on CD23 expression, anti-mu costimulated proliferation or IgM, IgG, or IgE production by tonsillar B cells and did not influence such responses triggered by IL 4. BALB/c mice injected with hIL 5 for 7 consecutive days were shown to develop an eosinophilia comparable to that induced by infection with the parasite Mesocestoid corti.