Expression in CHO cells of a bacterial biosynthetic pathway producing a small non-ribosomal peptide aldehyde prevents proteolysis of recombinant proteins

A significant problem during recombinant protein production is proteolysis. One of the most common preventive strategies is the addition of protease inhibitors, which has drawbacks, such as their short half-life and high cost, and their limited prevention of extracellular proteolysis. Actinomycetes produce the most commonly used inhibitors, which are non-ribosomal small aldehydic peptides. Previously, an unprecedented biosynthetic route involving a condensation-minus non-ribosomal peptide synthetase (NRPSs) and a tRNA utilizing enzyme (tRUE) was shown to direct the synthesis of one of these inhibitor peptides, livipeptin. Here, we show that expression of the livipeptin biosynthetic pathway encoded by the lvp genes in CHO cells resulted in the production of this metabolite with cysteine protease inhibitory activity, implying that mammalian tRNAs were recruited by the lvp system. CHO cells transiently expressing the biosynthetic pathway produced livipeptin without affecting cell growth or viability. Expression of the lvp system in CHO cells producing two model proteins, secreted alkaline phosphatase (hSeAP) and a monoclonal antibody, resulted in higher specific productivity with reduced proteolysis. We show for the first time that the expression of a bacterial biosynthetic pathway is functional in CHO cells, resulting in the efficient, low-cost synthesis of a protease inhibitor without adverse effects on CHO cells. This expands the field of metabolic engineering of mammalian cells by expressing the overwhelming diversity of actinomycetes biosynthetic pathways and opens a new option for proteolysis inhibition in bioprocess engineering.

One-Step Purification Strategy for Cowpea Chlorotic Mottle Virus-Like Particles Produced by the IC-BEVS

Virus-like particles (VLP) of the cowpea chlorotic mottle virus (CCMV), a plant virus, have been shown to be safe and noncytotoxic vehicles for delivering various cargos, including nucleic acids and peptides, and as scaffolds for presenting epitopes. Thus, CCMV-VLP have acquired increasing attention to be used in fields such as gene therapy, drug delivery, and vaccine development. Regardless of their production method, most reports purify CCMV-VLP through a series of ultracentrifugation steps using sucrose density gradient ultracentrifugation, which is a complex and time-consuming process. Here, the use of anion exchange chromatography is described as a one-step protocol for purification of CCMV-VLP produced by the insect cell-baculovirus expression vector system (IC-BEVS).

Extraction of Modified Adeno-Associated Virus-Like Particles Displaying Peptides on Their Surface

Virus-like particles (VLPs) of the adeno-associated virus (AAV) can be produced using the baculovirus expression vector system. Insertion of small peptides on the surface of the AAV or AAV VLPs has been used to redirect the AAV to different target tissues and for vaccine development. Usually, the VLPs self-assemble intracellularly, and an extraction step must be performed before purification. Here, we describe the method we have used to extract AAV VLPs from insect cells successfully with peptide insertions on their surface.

Construction of Recombinant Baculoviruses

The success of using the insect cell-baculovirus expression technology (BEST) relies on the efficient construction of recombinant baculovirus with genetic stability and high productivity, ideally within a short time period. Generation of recombinant baculoviruses requires the transfection of insect cells, harvesting of recombinant baculovirus pools, isolation of plaques, and the expansion of baculovirus stocks for their use for recombinant protein production. Moreover, many options exist for selecting the genetic elements to be present in the recombinant baculovirus. This chapter describes the most commonly used homologous recombination systems for the production of recombinant baculoviruses, as well as strategies to maximize generation efficiency and recombinant protein or baculovirus production. The key steps for generating baculovirus stocks and troubleshooting strategies are described.

Longitudinal anti-SARS-CoV-2 antibody immune response in acute and convalescent patients

Despite global efforts to assess the early response and persistence of SARS-CoV-2 antibodies in patients infected with or recovered from COVID-19, our understanding of the factors affecting its dynamics remains limited. This work aimed to evaluate the early and convalescent immunity of outpatients infected with SARS-CoV-2 and to determine the factors that affect the dynamics and persistence of the IgM and IgG antibody response. Seropositivity of volunteers from Mexico City and the State of Mexico, Mexico, was evaluated by ELISA using the recombinant receptor-binding domain (RBD) of the SARS-CoV-2 Spike protein for 90 days, at different time points (1, 15, 45, 60, and 90 days) after molecular diagnosis (RT-qPCR). Gender, age range, body mass index (BMI), comorbidities, and clinical spectrum of disease were analyzed to determine associations with the dynamics of anti-SARS-CoV-2 antibodies. On 90 days post-infection, individuals with moderate and asymptomatic disease presented the lowest levels of IgM, while for IgG, at the same time, the highest levels occurred with mild and moderate disease. The IgM and IgG levels were related to the clinical spectrum of disease, BMI, and the presence/absence of comorbidities through regression trees. The results suggest that the dynamics of anti-SARS-CoV-2 IgM and IgG antibodies in outpatients could be influenced by the clinical spectrum of the disease. In addition, the persistence of antibodies against SARS-CoV-2 could be related to the clinical spectrum of the disease, BMI, and the presence/absence of comorbidities.

Mimotope discovery as a tool to design a vaccine against Zika and dengue viruses

Vaccine development against dengue virus is challenging because of the antibody-dependent enhancement of infection (ADE), which causes severe disease. Consecutive infections by Zika (ZIKV) and/or dengue viruses (DENV), or vaccination can predispose to ADE. Current vaccines and vaccine candidates contain the complete envelope viral protein, with epitopes that can raise antibodies causing ADE. We used the envelope dimer epitope (EDE), which induces neutralizing antibodies that do not elicit ADE, to design a vaccine against both flaviviruses. However, EDE is a discontinuous quaternary epitope that cannot be isolated from the E protein without other epitopes. Utilizing phage display, we selected three peptides that mimic the EDE. Free mimotopes were disordered and did not elicit an immune response. After their display on adeno-associated virus (AAV) capsids (VLP), they recovered their structure and were recognized by an EDE-specific antibody. Characterization by cryo-EM and enzyme-linked immunosorbent assay confirmed the correct display of a mimotope on the surface of the AAV VLP and its recognition by the specific antibody. Immunization with the AAV VLP displaying one of the mimotopes induced antibodies that recognized ZIKV and DENV. This work provides the basis for developing a Zika and dengue virus vaccine candidate that will not induce ADE.

A Novel Formulation of Asparaginase Encapsulated into Virus-like Particles of Brome Mosaic Virus: In Vitro and In Vivo Evidence

The interest in plant-derived virus-like particles (pVLPs) for the design of a new generation of nanocarriers is based on their lack of infection for humans, their immunostimulatory properties to fight cancer cells, and their capability to contain and release cargo molecules. Asparaginase (ASNase) is an FDA-approved drug to treat acute lymphoblastic leukemia (LLA); however, it exhibits high immunogenicity which often leads to discontinuation of treatment. In previous work, we encapsulated ASNase into bacteriophage P22-based VLPs through genetic-directed design to form the ASNase-P22 nanobioreactors. In this work, a commercial ASNase was encapsulated into brome mosaic virus-like particles (BMV-VLPs) to form stable ASNase-BMV nanobioreactors. According to our results, we observed that ASNase-BMV nanobioreactors had similar cytotoxicity against MOLT-4 and Reh cells as the commercial drug. In vivo assays showed a higher specific anti-ASNase IgG response in BALB/c mice immunized with ASNase encapsulated into BMV-VLPs compared with those immunized with free ASNase. Nevertheless, we also detected a high and specific IgG response against BMV capsids on both ASNase-filled capsids (ASNase-BMV) and empty BMV capsids. Despite the fact that our in vivo studies showed that the BMV-VLPs stimulate the immune response either empty or with cargo proteins, the specific cytotoxicity against leukemic cells allows us to propose ASNase-BMV as a potential novel formulation for LLA treatment where in vitro and in vivo evidence of functionality is provided.

Baculovirus-mediated expression of a Helicobacter pylori protein-based multiepitope hybrid gene induces a potent B cell response in mice

Helicobacter pylori is a gram-negative bacterium that is present in over half of the world's population. The colonization of the stomach́s gastric mucosa by H. pylori is related to the onset of chronic gastritis, peptic ulcer, and cancer. The estimated deaths from gastric cancer caused by this bacterial infection are in the 15,000-150,000 range. Current treatment for controlling the colonization of H. pylori includes the administration of two to four antibiotics and a gastric ATPase proton pump inhibitor. Nevertheless, the bacterium has shown increased resistance to antibiotics. Despite an extensive list of attempts to develop a vaccine, no approved vaccine against H. pylori is available. Recombinant viruses are a novel alternative for the control of primary pathogenic agents. In this work, we employed a baculovirus that carries a Thp1 transgene coding for nine H. pylori epitopes, some from the literature, and others were selected in silico from the sequence of H. pylori proteins (carbonic anhydrase, urease B subunit, gamma-glutamyl transpeptidase, Lpp20, Cag7, and CagL). We verified the expression of this hybrid multiepitopic protein in HeLa cells. Mice were inoculated with the recombinant baculovirus Bac-Thp1 using various administration routes: intranasal, intragastric, intramuscular, and a combination of intranasal and intragastric. We identified a strong adjuvant-independent IgG-antibody response in the serum of recombinant baculovirus-Thp1 inoculated mice, which was specific for a strain of H. pylori isolated from a human patient. The bacterium-specific IgG-antibodies were present in sera 125 days after the first vaccine administration. Also, H. pylori-specific IgA-antibodies were found in feces at 82 days after the first inoculation. A baculovirus-based vaccine for H. pylori is promising for controlling this pathogen in humans.

A pseudovirus-based platform to measure neutralizing antibodies in Mexico using SARS-CoV-2 as proof-of-concept

The gold-standard method to evaluate a functional antiviral immune response is to titer neutralizing antibodies (NAbs) against a viral pathogen. This is historically performed using an in vitro assay of virus-mediated infection, which requires BSL-3 facilities. As these are insufficient in Latin American countries, including Mexico, scant information is obtained locally about viral pathogens NAb, using a functional assay. An alternative solution to using a BSL-3 assay with live virus is to use a BSL-2-safe assay with a non-replicative pseudovirus. Pseudoviral particles can be engineered to display a selected pathogen's entry protein on their surface, and to deliver a reporter gene into target cells upon transduction. Here we comprehensively describe the first development of a BSL-2 safe NAbs-measuring functional assay in Mexico, based on the production of pseudotyped lentiviral particles. As proof-of-concept, the assay is based on Nanoluc luciferase-mediated luminescence measurements from target cells transduced with SARS-CoV-2 Spike-pseudotyped lentiviral particles. We applied the optimized assay in a BSL-2 facility to measure NAbs in 65 serum samples, which evidenced the assay with 100% sensitivity, 86.6% specificity and 96% accuracy. Overall, this is the first report of a BSL-2 safe pseudovirus-based functional assay developed in Mexico to measure NAbs, and a cornerstone methodology necessary to measure NAbs with a functional assay in limited resources settings.

Comparable diagnostic accuracy of SARS-CoV-2 Spike RBD and N-specific IgG tests to determine pre-vaccination nation-wide baseline seroprevalence in Mexico

A major challenge for developing countries during the COVID-19 pandemic is affordable and adequate monitoring of disease progression and population exposure as the primary source relevant epidemiological indicators. Serology testing enables assessing population exposure and to guide vaccination strategies but requires rigorous accuracy validation before population-wide implementation. We adapted a two-step ELISA protocol as a single-step protocol for detection of IgG against the Receptor Binding Domain (RBD) of SARS-CoV-2 spike protein and compared its diagnostic accuracy with a commercial immunoassay anti-nucleoprotein IgG. Both methods yielded adequate and comparable diagnostic accuracy after 3 weeks post-symptom onset and were implemented in a nation-wide population based serological survey during August-November 2020. Anti-RBD National seroprevalence was 23.6%, 1.3% lower, but not significantly, than for anti-N. Double positive seroprevalence was 19.7%. Anti-N single-positive seroprevalence was 3.72% and anti-RBD single-positive seroprevalence was 1.98%. Discrepancies in the positivity to either single marker may be due to different kinetics of each antibody marker as well as the heterogeneity of the sampling time in regards to local epidemic waves. Baseline single positivity prevalence will be useful to assess the serological impact of vaccination and natural infection in further serosurveillance efforts.

Effect of sericin, a silk derived protein, on the amplification of Zika virus in insect and mammalian cell cultures

Sericin, a silk-derived non-immunogenic protein, has been used to improve cell culture performance by increasing viability, cell concentration, and promoting adherence of several cell lines. Here, we hypothesized that the properties of sericin can enhance the amplification of flaviviruses in cell cultures. The propagation of flavivirus is inefficient and limits scientific research. Zika virus (ZIKV) is an important human pathogen that has been widely studied because of its high impact on public health. There is a need to amplify Zika virus both for research and vaccine development. In this work, we show that sericin improves ZIKV amplification in insect (C6/36) and mammalian (Vero) cell cultures, and that it has a cryoprotectant capacity. Supplementation of cell culture media with sericin at 80 µg/mL resulted in a significant increase of 1 log in the concentration of ZIKV infectious particles produced from both cell lines. Furthermore, final virus yields increased between 5 and 10-fold in Vero cells and between 7 and 23-fold in C6/36 cells when sericin was supplemented, compared to control conditions. These results show that sericin is an effective supplement to increase ZIKV production by Vero and C6/36 cells. Additionally, sericin was a suitable cryoprotective agent, and hence an alternative to FBS and DMSO, for the cryopreservation of C6/36 cells but not for Vero cells.

Flavivirus vaccines: Virus-like particles and single-round infectious particles as promising alternatives

The genus flavivirus of the Flaviridae family includes several human pathogens, like dengue, Zika, Japanese encephalitis, and yellow fever virus. These viruses continue to be a significant threat to human health. Vaccination remains the most useful approach to reduce the impact of flavivirus fever. However, currently available vaccines can induce severe side effects or have low effectiveness. An alternative is the use of recombinant vaccines, of which virus-like particles (VLP) and single-round infectious particles (SRIP) are of especial interest. VLP consist of the virus structural proteins produced in a heterologous system that self-assemble in a structure almost identical to the native virus. They are highly immunogenic and have been effective vaccines for other viruses for over 30 years. SRIP are promising vaccine candidates, as they induce both cellular and humoral responses, as viral proteins are expressed. Here, the state of the art to produce both types of particles and their use as vaccines against flaviviruses are discussed. We summarize the different approaches used for the design and production of flavivirus VLP and SRIP, the evidence for their safety and efficacy, and the main challenges for their use as commercial vaccines.

A novel method for the in vitro assembly of virus-like particles and multimeric proteins

OBJECTIVE

To develop a method for the efficient assembly of viral or multimeric proteins into virus-like particles (VLP) or other macro structures.

RESULTS

Protein monomers were assembled by eliminating calcium ions through precipitation. The model protein, rotavirus VP6, assembled into stable, long nanotubes with better quality than the assemblies obtained directly from cell culture. Nanotube length was directly proportional to the initial concentration of VP6 monomers, in accordance with the classic nucleation theory of capsid assembly. The quality of the obtained assemblies was confirmed when the nanotubes were functionalized with metals, yielding unique nanobiomaterials. Assembly efficiency was improved in comparison with other previously proposed methods.

CONCLUSIONS

The novel method presented here is simpler and faster than other reported methods for the assembly and disassembly of viral proteins, a step needed for most applications.

Dynamic Modeling of CHO Cell Metabolism Using the Hybrid Cybernetic Approach With a Novel Elementary Mode Analysis Strategy

Chinese hamster ovary (CHO) cell culture has a major importance on the production of biopharmaceuticals, including recombinant therapeutic proteins such as monoclonal antibodies (MAb). Mathematical modeling of biological systems can successfully assess metabolism complexity while providing logical and systematic methods for relevant genetic target and culture parameter identification toward cell growth and productivity improvements. Most modeling approaches on CHO cells have been performed under stationary constraints, and only a few dynamic models have been presented on simplified reaction sets, due to substantial overparameterization problems. The hybrid cybernetic modeling (HCM) approach has been recently used to describe the dynamic behavior by incorporating regulation between different metabolic states by elementary mode participation control, with sets of equations evaluated by objective functions. However, as metabolic networks evaluated are constructed toward a genomic scale, and cell compartmentalization is considered, identification of the active set becomes more difficult as EM number exponentially grows. Thus, the development of robust approaches for EM active set selection and analysis with smaller computational requirements is required to impulse the use of cybernetic modeling on larger up to genome-scale networks. In this report, a novel elementary mode selection strategy, based on a polar representation of the convex solution space is presented and coupled to a cybernetic approach to model the dynamic physiologic and metabolic behavior of CHO-S cell cultures. The proposed Polar Space Yield Analysis (PSYA) was compared to other reported elementary mode selection approaches derived from Common Metabolic Objective Analysis (CMOA) used in Flux Balance Analysis (FBA), Yield Space Analysis (YSA), and Lumped Yield Space Analysis (LYSA). For this purpose, exponential growth phase dynamic metabolic models were calculated using kinetic rate equations based on previously modeled growth parameters. Finally, complete culture dynamic metabolic flux models were constructed using the HCM approach with selected elementary mode sets. The yield space elementary mode- and the polar space elementary mode- hybrid cybernetic models presented the best fits and performances. Also, a flux reaction perturbation prediction approach based on the polar yield solution space resulted useful for metabolic network flux distribution capability analysis and identification of potential genetic modifications targets.

Understanding cellular interactions with nanomaterials: towards a rational design of medical nanodevices

Biomedical applications increasingly require fully characterized new nanomaterials. There is strong evidence showing that nanomaterials not only interact with cells passively but also actively, mediating essential molecular processes for the regulation of cellular functions, but we are only starting to understand the mechanisms of those interactions. Systematic studies about cell behavior as a response to specific nanoparticle properties are scarce in the literature even when they are necessary for the rational design of medical nanodevices. Information in the literature shows that the physicochemical properties determine the bioactivity, biocompatibility, and safety of nanomaterials. The information available regarding the interaction and responses of cells to nanomaterials has not been analyzed and discussed in a single document. Hence, in this review, we present the latest advances about cellular responses to nanomaterials and integrate the available information into concrete considerations for the development of innovative, efficient, specific and, more importantly, safe biomedical nanodevices. We focus on how physicochemical nanoparticle properties (size, chemical surface, shape, charge, and topography) influence cell behavior in a first attempt to provide a practical guide for designing medical nanodevices, avoiding common experimental omissions that may lead to data misinterpretation. Finally, we emphasize the importance of the systematic study of nano-bio interactions to acquire sufficient reproducible information that allows accurate control of cell behavior based on tuning of nanomaterial properties. This information is useful to guide the design of specific nanodevices and nanomaterials to elicit desired cell responses, like targeting, drug delivery, cell attachment, differentiation, etc, or to avoid undesired side effects.

Defining the multiplicity and time of infection for the production of Zaire Ebola virus-like particles in the insect cell-baculovirus expression system

The Ebola virus disease is a public health challenge. To date, the only available treatments are medical support or the emergency administration of experimental drugs. The absence of licensed vaccines against Ebola virus impedes the prevention of infection. Vaccines based on recombinant virus-like particles (VLP) are a promising alternative. The Zaire Ebola virus serotype (ZEBOV) is the most aggressive with the highest mortality rates. Production of ZEBOV-VLP has been accomplished in mammalian and insect cells by the recombinant coexpression of three structural proteins, the glycoprotein (GP), the matrix structural protein VP40, and the nucleocapsid protein (NP). However, specific conditions to manipulate protein concentrations and improve assembly into VLP have not been determined to date. Here, we used a design of experiments (DoE) approach to determine the best MOI and TOI for three recombinant baculoviruses: bac-GP, bac-VP40 and bac-NP, each coding for one of the main structural proteins of ZEBOV. We identified two conditions where the simultaneous expression of the three recombinant proteins was observed. Interestingly, a temporal and stoichiometric interplay between the three structural proteins was observed. VP40 was required for the correct assembly of ZEBOV-VLP. High NP concentrations reduced the accumulation of GP, which has been reported to be necessary for inducing a protective immune response. Electron microscopy showed that the ZEBOV-VLP produced were morphologically similar to the native virus micrographs previously reported in the literature. A strategy for producing ZEBOV in insect cells, which consists in using a high MOI of bac-VP40 and bac-GP, and reducing expression of NP, either by delaying infection or reducing the MOI of bac-NP, was the most adequate for the production of VLP.

Gene Therapy for Treatment of Chronic Hyperammonemia in a Rat Model of Hepatic Encephalopathy

INTRODUCTION AND AIM

Hepatic encephalopathy (HE), caused by hyperammonemia resulting from liver disease, is a spectrum of neuropsychiatric and motor disorders that can lead to death. Existing therapies are deficient and alternative treatments are needed. We have shown that gene therapy with a baculovirus vector containing the glutamine synthetase (Bac-GS) gene is efficient for reducing ammonia levels in an acute hyperammonemia rat model. However, the most common condition resulting from liver disease is chronic hyperammonemia. In this work, Bac-GS was evaluated in bile-duct ligated rats, a chronic liver disease model with hyperammonemia and some characteristics of Type C HE.

MATERIAL AND METHODS

Bac-GS was tested for mediating GS overexpression in HeLa cells and H9C2 myotubes. For determining the utility of Bac-GS for the reduction of ammonia levels in a chronic hyperammonemia animal model, four groups of rats were treated: control, sham, ligated with Bac-GS and ligated with Bac-GFP. Baculoviruses were injected i.m. 18 days post-surgery. Blood was drawn 2, 3 and 4 weeks post-surgery and plasma ammonia concentrations were quantified.

RESULTS

In protein lysates of cells and myotubes transduced with Bac-GS, a 44 kDa band corresponding to GS was detected. Significant results were obtained in the hyperammonemic bile-duct ligated rat model, as plasma ammonia was reduced to normal levels 3 days after treatment with Bac-GS. Furthermore, a transitory effect of Bac-GS was observed.

CONCLUSION

Our results show that gene therapy by delivering GS is a promising alternative for treatment of hyperammonemia in acute-on-chronic liver failure patients with HE.

Immune responses elicited against rotavirus middle layer protein VP6 inhibit viral replication in vitro and in vivo

Rotavirus (RV) is a common cause of severe gastroenteritis (GE) in children worldwide. Live oral RV vaccines protect against severe RVGE, but the immune correlates of protection are not yet clearly defined. Inner capsid VP6 protein is a highly conserved, abundant, and immunogenic RV protein, and VP6-specific mucosal antibodies, especially IgA, have been implicated to protect against viral challenge in mice. In the present study systemic and mucosal IgG and IgA responses were induced by immunizing BALB/c mice intranasally with a combination of recombinant RV VP6 protein (subgroup II [SGII]) and norovirus (NoV) virus-like particles (VLPs) used in a candidate vaccine. Following immunization mice were challenged orally with murine RV strain EDIMwt (SG non-I-non-II, G3P10[16]). In order to determine neutralizing activity of fecal samples, sera, and vaginal washes (VW) against human Wa RV (SGII, G1P1A[8]) and rhesus RV (SGI, G3P5B[3]), the RV antigen production was measured with an ELISA-based antigen reduction neutralization assay. Only VWs of immunized mice inhibited replication of both RVs, indicating heterotypic protection of induced antibodies. IgA antibody depletion and blocking experiments using recombinant VP6 confirmed that neutralization was mediated by anti-VP6 IgA antibodies. Most importantly, after the RV challenge significant reduction in viral shedding was observed in feces of immunized mice. These results suggest a significant role for mucosal RV VP6-specific IgA for the inhibition of RV replication in vitro and in vivo. In addition, these results underline the importance of non-serotype-specific immunity induced by the conserved subgroup-specific RV antigen VP6 in clearance of RV infection.