Lepidopteran cells, an alternative for the production of recombinant antibodies?

Development of a Bispecific IgG1 Antibody Targeting BCMA and PDL1

We designed, produced, and purified a novel IgG1-like, bispecific antibody (bsAb) directed against B-cell maturation antigen (BCMA), expressed by multiple myeloma (MM) cells, and an immune checkpoint inhibitor (ICI), PDL1, expressed in the MM microenvironment. The BCMA×PDL1 bsAb was fully characterized in vitro. BCMA×PDL1 bound specifically and simultaneously, with nM affinity, to both native membrane-bound antigens and to the recombinant soluble antigen fragments, as shown by immunophenotyping analyses and surface plasmon resonance (SPR), respectively. The binding affinity of bsAb for PDL1 and BCMA was similar to each other, but PDL1 affinity was about 10-fold lower in the bsAb compared to parent mAb, probably due to the steric hindrance associated with the more internal anti-PDL1 Fab. The bsAb was also able to functionally block both antigen targets with IC50 in the nM range. The bsAb Fc was functional, inducing human-complement-dependent cytotoxicity as well as ADCC by NK cells in 24 h killing assays. Finally, BCMA×PDL1 was effective in 7-day killing assays with peripheral blood mononuclear cells as effectors, inducing up to 75% of target MM cell line killing at a physiologically attainable, 6 nM, concentration. These data provide the necessary basis for future optimization and in vivo testing of this novel bsAb.

Comparative analysis of protein expression systems and PTM landscape in the study of transcription factor ELK-1

Post-translational modifications (PTMs) are important for protein folding and activity, and the ability to recreate physiologically relevant PTM profiles on recombinantly-expressed proteins is vital for meaningful functional analysis. The ETS transcription factor ELK-1 serves as a paradigm for cellular responses to mitogens and can synergise with androgen receptor to promote prostate cancer progression, although in vitro protein function analyses to date have largely overlooked its complex PTM landscapes. We expressed and purified human ELK-1 using mammalian (HEK293T), insect (Sf9) and bacterial (E. coli) systems in parallel and compared PTMs imparted upon purified proteins, along with their performance in DNA and protein interaction assays. Phosphorylation of ELK-1 within its transactivation domain, known to promote DNA binding, was most apparent in protein isolated from human cells and accordingly conferred the strongest DNA binding in vitro, while protein expressed in insect cells bound most efficiently to the androgen receptor. We observed lysine acetylation, a hitherto unreported PTM of ELK-1, which appeared highest in insect cell-derived ELK-1 but was also present in HEK293T-derived ELK-1. Acetylation of ELK-1 was enhanced in HEK293T cells following starvation and mitogen stimulation, and modified lysines showed overlap with previously identified regulatory SUMOylation and ubiquitination sites. Our data demonstrate that the choice of recombinant expression system can be tailored to suit biochemical application rather than to maximise soluble protein production and suggest the potential for crosstalk and antagonism between different PTMs of ELK-1.

BL-01, an Fc-bearing, tetravalent CD20 × CD5 bispecific antibody, redirects multiple immune cells to kill tumors in vitro and in vivo

BACKGROUND AIMS

The authors describe here a novel therapeutic strategy combining a bispecific antibody (bsAb) with cytokine-induced killer (CIK) cells.

METHODS

The authors have designed, produced and purified a novel tetravalent IgG1-like CD20 × CD5 bsAb called BL-01. The bsAb is composed of a fused heavy chain and two free light chains that pair correctly to the heavy chain sequences thanks to complementary mutations in the monoclonal antibody 2 CH1/CL sequences.

RESULTS

The authors show that BL-01 can bind specifically to CD20 and CD5 with an affinity of 4-6 nM, demonstrating correct pairing of two light chains to the fused heavy chain. The CD20 × CD5 BL-01 bsAb has a functional human IgG1 Fc and can induce up to 65% complement-dependent cytotoxicity of a CD20⁺ lymphoma cell line in the presence of human complement, similar to anti-CD20 rituximab. The bsAb also induces significant natural killer cell activation and antibody-dependent cytotoxicity of up to 25% as well as up to 65% phagocytosis by human macrophages in the presence of CD20⁺ tumor cells. The BL-01 bsAb binds to CD20 and CD5 simultaneously and can redirect CIK cells in vitro to kill CD20⁺ targets, increasing the cytotoxicity of CIK cells by about 3-fold. The authors finally show that the CD20 × CD5 BL-01 bsAb synergizes with CIK cells in vivo in controlling tumor growth and prolonging survival of nonobese diabetic/severe combined immunodeficiency mice inoculated with a patient-derived, aggressive diffuse large B-cell lymphoma xenograft.

CONCLUSIONS

The authors suggest that the efficacy of bsAb in vivo is due to the combined activation of innate immunity by Fc and redirection of CIK cells to kill the tumor target.

Expressing of Recombinant VEGFR2-specific Nanobody in Baculovirus Expression System

Background

Baculovirus expression system, introduced more than 20 years ago, is considered as a useful tool for large and complex eukaryotic recombinant protein production. A baculovirus expression vector is a recombinant virus which desired foreign protein coding sequences is under control of the virus gene promoter. Baculovirus only infects insect cells and do not normally infect vertebrates therefore, they possess no risk of biological risks for human.

Objectives

The aim of this study was to recombinant expression of vascular endothelial growth factor (VEGF) reseptor-2 specific Nanobody in the baculovirus expression system.

Materials and Methods

Gene of specific Nanobody against the VEGF reseptor-2 that called 3VGR19 was cloned and expressed in baculovirus system.

Results

3VGR19 Nanobody gene was amplified by Polymerase Chain Reaction (PCR) using the specific primers, and was cloned in pFastBac HTA plasmid. DH10Bac bacteria was transformed with resulted donor plasmid. The cultured Sf9 insect cell line was transfected with recombinant bacmid, and finally, the expression and purification of 3VGR19 was confirmed in insect cells.

Conclusions

In conclusion, Transient infection of insect cells with baculovirus can be a promising technology for expression of antibody fragments.

Virus-based SELEX (viro-SELEX) allows development of aptamers targeting knotty proteins

It has been 100 years since the worst flu (Spanish flu) mankind has ever experienced. Rapid, accurate diagnosis and subtyping of flu are still an urgent unmet medical need. By using surrogate virus-based SELEX (viro-SELEX), we report here multiple advances incorporated into the field of flu diagnostics: (i) aptamers that can bind to the native virus well even though they cannot bind strongly to a recombinant protein (hemagglutinin); (ii) a couple of aptamers that can target a broad range of strains belonging to the H1N1 subtype and detect only the H1N1 subtype and nothing else; (iii) a highly sensitive lateral flow assay system (limit of detection is 0.08 HAU) using fluorescence-tagged aptamers. The viro-SELEX method of aptamer selection in conjunction with a fluorescent tag on aptamers is a very useful approach to develop highly sensitive, specific, portable, rapid, and quantitative point-of-care testing diagnostic tools for the future.

One-pot N-glycosylation remodeling of IgG with non-natural sialylglycopeptides enables glycosite-specific and dual-payload antibody-drug conjugates

Chemoenzymatic transglycosylation catalyzed by endo-S mutants is a powerful tool for in vitro glycoengineering of therapeutic antibodies. In this paper, we report a one-pot chemoenzymatic synthesis of glycoengineered Herceptin using an egg-yolk sialylglycopeptide (SGP) substrate. Combining this one-pot strategy with novel non-natural SGP derivatives carrying azido or alkyne tags, glycosite-specific conjugation was enabled for the development of new antibody-drug conjugates (ADCs). The site-specific ADCs and semi-site-specific dual-drug ADCs were successfully achieved and characterized with SDS-PAGE, intact antibody or ADC mass spectrometry analysis, and PNGase-F digestion analysis. Cancer cell cytotoxicity assay revealed that small-molecule drug release of these ADCs relied on the cleavable Val-Cit linker fragment embedded in the structure. These results represent a new approach for glycosite-specific and dual-drug ADC design and rapid synthesis, and also provide the structural requirement for their biologic activities.

Antibody production using a ciliate generates unusual antibody glycoforms displaying enhanced cell-killing activity

Antibody glycosylation is a key parameter in the optimization of antibody therapeutics. Here, we describe the production of the anti-cancer monoclonal antibody rituximab in the unicellular ciliate, Tetrahymena thermophila. The resulting antibody demonstrated enhanced antibody-dependent cell-mediated cytotoxicity, which we attribute to unusual N-linked glycosylation. Detailed chromatographic and mass spectrometric analysis revealed afucosylated, oligomannose-type glycans, which, as a whole, displayed isomeric structures that deviate from the typical human counterparts, but whose branches were equivalent to fragments of metabolic intermediates observed in human glycoproteins. From the analysis of deposited crystal structures, we predict that the ciliate glycans adopt protein-carbohydrate interactions with the Fc domain that closely mimic those of native complex-type glycans. In addition, terminal glucose structures were identified that match biosynthetic precursors of human glycosylation. Our results suggest that ciliate-based expression systems offer a route to large-scale production of monoclonal antibodies exhibiting glycosylation that imparts enhanced cell killing activity.

Design and Validation of a Novel Generic Platform for the Production of Tetravalent IgG1-like Bispecific Antibodies

We have designed and validated a novel generic platform for production of tetravalent IgG1-like chimeric bispecific Abs. The VH-CH1-hinge domains of mAb2 are fused through a peptidic linker to the N terminus of mAb1 H chain, and paired mutations at the CH1-CL interface mAb1 are introduced that force the correct pairing of the two different free L chains. Two different sets of these CH1-CL interface mutations, called CR3 and MUT4, were designed and tested, and prototypic bispecific Abs directed against CD5 and HLA-DR were produced (CD5xDR). Two different hinge sequences between mAb1 and mAb2 were also tested in the CD5xDR-CR3 or -MUT4 background, leading to bispecific Ab (BsAbs) with a more rigid or flexible structure. All four Abs produced bound with good specificity and affinity to CD5 and HLA-DR present either on the same target or on different cells. Indeed, the BsAbs were able to efficiently redirect killing of HLA-DR(+) leukemic cells by human CD5(+) cytokine-induced killer T cells. Finally, all BsAbs had a functional Fc, as shown by their capacity to activate human complement and NK cells and to mediate phagocytosis. CD5xDR-CR3 was chosen as the best format because it had overall the highest functional activity and was very stable in vitro in both neutral buffer and in serum. In vivo, CD5xDR-CR3 was shown to have significant therapeutic activity in a xenograft model of human leukemia.

Monomeric IgA can be produced in planta as efficient as IgG, yet receives different N-glycans

The unique features of IgA, such as the ability to recruit neutrophils and suppress the inflammatory responses mediated by IgG and IgE, make it a promising antibody isotype for several therapeutic applications. However, in contrast to IgG, reports on plant production of IgA are scarce. We produced IgA1κ and IgG1κ versions of three therapeutic antibodies directed against pro-inflammatory cytokines in Nicotiana benthamiana: Infliximab and Adalimumab, directed against TNF-α, and Ustekinumab, directed against the interleukin-12p40 subunit. We evaluated antibody yield, quality and N-glycosylation. All six antibodies had comparable levels of expression between 3.5 and 9% of total soluble protein content and were shown to have neutralizing activity in a cell-based assay. However, IgA1κ-based Adalimumab and Ustekinumab were poorly secreted compared to their IgG counterparts. Infliximab was poorly secreted regardless of isotype backbone. This corresponded with the observation that both IgA1κ- and IgG1κ-based Infliximab were enriched in oligomannose-type N-glycan structures. For IgG1κ-based Ustekinumab and Adalimumab, the major N-glycan type was the typical plant complex N-glycan, biantennary with terminal N-acetylglucosamine, β1,2-xylose and core α1,3-fucose. In contrast, the major N-glycan on the IgA-based antibodies was xylosylated, but lacked core α1,3-fucose and one terminal N-acetylglucosamine. This type of N-glycan occurs usually in marginal percentages in plants and was never shown to be the main fraction of a plant-produced recombinant protein. Our data demonstrate that the antibody isotype may have a profound influence on the type of N-glycan an antibody receives.

Significant productivity improvement of the baculovirus expression vector system by engineering a novel expression cassette

Here we describe the development of a baculovirus vector expression cassette containing rearranged baculovirus-derived genetic regulatory elements. This newly designed expression cassette conferred significant production improvements to the baculovirus expression vector system (BEVS), including prolonged cell integrity after infection, improved protein integrity, and around 4-fold increase in recombinant protein production yields in insect cells with respect to a standard baculovirus vector. The expression cassette consisted of a cDNA encoding for the baculovirus transactivation factors IE1 and IE0, expressed under the control of the polyhedrin promoter, and a homologous repeated transcription enhancer sequence operatively cis-linked to the p10 promoter or to chimeric promoters containing p10. The prolonged cell integrity observed in cells infected by baculoviruses harbouring the novel expression cassette reduced the characteristic proteolysis and aberrant forms frequently found in baculovirus-derived recombinant proteins. The new expression cassette developed here has the potential to significantly improve the productivity of the BEVS.

A novel baculovirus vector for the production of nonfucosylated recombinant glycoproteins in insect cells

Glycosylation is an important attribute of baculovirus-insect cell expression systems, but some insect cell lines produce core α1,3-fucosylated N-glycans, which are highly immunogenic and render recombinant glycoproteins unsuitable for human use. To address this problem, we exploited a bacterial enzyme, guanosine-5'-diphospho (GDP)-4-dehydro-6-deoxy-d-mannose reductase (Rmd), which consumes the GDP-l-fucose precursor. We expected this enzyme to block glycoprotein fucosylation by blocking the production of GDP-l-fucose, the donor substrate required for this process. Initially, we engineered two different insect cell lines to constitutively express Rmd and isolated subclones with fucosylation-negative phenotypes. However, we found the fucosylation-negative phenotypes induced by Rmd expression were unstable, indicating that this host cell engineering approach is ineffective in insect systems. Thus, we constructed a baculovirus vector designed to express Rmd immediately after infection and facilitate the insertion of genes encoding any glycoprotein of interest for expression later after infection. We used this vector to produce a daughter encoding rituximab and found, in contrast to an Rmd-negative control, that insect cells infected with this virus produced a nonfucosylated form of this therapeutic antibody. These results indicate that our Rmd(+) baculoviral vector can be used to solve the immunogenic core α1,3-fucosylation problem associated with the baculovirus-insect cell system. In conjunction with existing glycoengineered insect cell lines, this vector extends the utility of the baculovirus-insect cell system to include therapeutic glycoprotein production. This new vector also extends the utility of the baculovirus-insect cell system to include the production of recombinant antibodies with enhanced effector functions, due to its ability to block core α1,6-fucosylation.

Lessons for the clinic from rituximab pharmacokinetics and pharmacodynamics

The anti-CD20 antibody rituximab (RTX; Rituxan®, MabThera®) was the first anti-cancer antibody approved by the US Food and Drug Administration in 1997 and it is now the most-studied unconjugated therapeutic antibody. The knowledge gained over the past 15 y on the pharmacodynamics (PD) of this antibody has led to the development of a new generation of anti-CD20 antibodies with enhanced efficacy in vitro. Studies on the pharmacokinetics (PK) properties and the effect of factors such as tumor load and localization, antibody concentration in the circulation and gender on both PK and clinical response has allowed the design of optimized schedules and novel routes of RTX administration. Although clinical results using newer anti-CD20 antibodies, such as ofatumumab and obinutuzumab, and novel administration schedules for RTX are still being evaluated, the knowledge gained so far on RTX PK and PD should also be relevant for other unconjugated monoclonal antibody therapeutics, and will be critically reviewed here.

Engineering the baculovirus genome to produce galactosylated antibodies in lepidopteran cells

Nowadays, recombinant proteins are used with great success for the treatment of a variety of medical conditions, such as cancer, autoimmune, and infectious diseases. Several expression systems have been developed to produce human proteins, but one of their most critical limitations is the addition of truncated or nonhuman glycans to the recombinant molecules. The presence of such glycans can be deleterious as they may alter the protein physicochemical properties (e.g., solubility, aggregation), its half-life, and its immunogenicity due to the unmasking of epitopes.The baculovirus expression system has long been used to produce recombinant proteins for research. Thanks to recent methodological advances, this cost-effective technology is now considered a very promising alternative for the production of recombinant therapeutics, especially vaccines. Studies on the lepidopteran cell metabolism have shown that these cells can perform most of the posttranslational modifications, including N- and O-glycosylation. However, these glycan structures are shorter compared to those present in mammalian proteins. Lepidopteran N-glycans are essentially of the oligomannose and paucimannose type with no complex glycan identified in both infected and uninfected cells. The presence of short N-glycan structures is explained by the low level of N-acetylglucosaminyltransferase I (GNT-I) activity and the absence of several other glycosyltransferases, such as GNT-II and β1,4-galactosyltransferase I (β1,4GalTI), and of sialyltransferases.In this chapter, we show that the glycosylation pathway of a lepidopteran cell line can be modified via infection with an engineered baculovirus to "humanize" the glycosylation pattern of a recombinant protein. This engineering has been performed by introducing in the baculovirus genome the cDNAs that encode three mammalian glycosyltransferases (GNT-I, GNT-II, and β1,4GalTI). The efficiency of this approach is illustrated with the construction of a recombinant virus that can produce a galactosylated antibody.

Marketing approval of mogamulizumab: a triumph for glyco-engineering

Therapeutic properties of antibodies strongly depend on the composition of their glycans. Most of the currently approved antibodies are produced in mammalian cell lines, which yield mixtures of different glycoforms that are close to those of humans, but not fully identical. Glyco-engineering is being developed as a method to control the composition of carbohydrates and to enhance the pharmacological properties of mAbs. The recent approval in Japan of mogamulizumab (POTELIGEO^®), the first glyco-engineered antibody to reach the market, is a landmark in the field of therapeutic antibodies. Mogamulizumab is a humanized mAb derived from Kyowa Hakko Kirin’s POTELLIGENT^® technology, which produces antibodies with enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) activity. The approval was granted April 30, 2012 by the Japanese Ministry of Health, Labour and Welfare for patients with relapsed or refractory CCR4-positive adult T-cell leukemia-lymphoma.