32 research outputs found
Antiviral Activity of Influenza A Virus Defective Interfering Particles against SARS-CoV-2 Replication In Vitro through Stimulation of Innate Immunity
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causing coronavirus disease 2019 (COVID-19) emerged in late 2019 and resulted in a devastating pandemic. Although the first approved vaccines were already administered by the end of 2020, worldwide vaccine availability is still limited. Moreover, immune escape variants of the virus are emerging against which the current vaccines may confer only limited protection. Further, existing antivirals and treatment options against COVID-19 show only limited efficacy. Influenza A virus (IAV) defective interfering particles (DIPs) were previously proposed not only for antiviral treatment of the influenza disease but also for pan-specific treatment of interferon (IFN)-sensitive respiratory virus infections. To investigate the applicability of IAV DIPs as an antiviral for the treatment of COVID-19, we conducted in vitro co-infection experiments with cell culture-derived DIPs and the IFN-sensitive SARS-CoV-2 in human lung cells. We show that treatment with IAV DIPs leads to complete abrogation of SARS-CoV-2 replication. Moreover, this inhibitory effect was dependent on janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling. Further, our results suggest boosting of IFN-induced antiviral activity by IAV DIPs as a major contributor in suppressing SARS-CoV-2 replication. Thus, we propose IAV DIPs as an effective antiviral agent for treatment of COVID-19, and potentially also for suppressing the replication of new variants of SARS-CoV-2
Influenza A virus-derived defective interfering particles for antiviral treatment
Here, we report on genetically engineered, propagation-incompetent influenza A virus (IAV) particles, so-called defective interfering particles (DIPs) that have been suggested as a promising novel antiviral agent. Typically, IAV DIPs harbor a large internal deletion in one of their eight genomic viral RNA (vRNA) segments. Further, DIPs are capable of hijacking cellular and viral resources upon co-infection with fully infectious standard virus (STV), resulting in an antiviral effect. Besides this replication interference, DIP infection also stimulates innate immunity, adding to the antiviral efficacy.
So far, DIPs were produced in embryonated chicken eggs. To improve scalability and flexibility of processes as well as to increase product quality, we established a cell culture-based DIP production system [1,2]. This includes the development of a genetically engineered virus-cell propagation system that allows production of DIPs without the need to add infectious STV to complement missing gene functions of DIPs. Specifically, the MDCK suspension cell line generated expresses the PB2 protein [2], encoded by segment 1 (S1) of IAV, which is not expressed by “DI244” - a prototypic, well-characterized DIP harboring a deletion in S1. Using this cell culture-based production process in batch [2,3] and perfusion mode [4] at laboratory scale, we show that we can achieve very high DI244 titers of up to 2.6E+11 DIPs/mL. Infections of mice demonstrated that intranasal administration of the produced DI244 material resulted in no apparent toxic effects and in a full rescue of mice co-treated with an otherwise lethal dose of IAV [2].
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Chromatographic purification of biological macromolecules by their capture on hydrophilic surfaces with the aid of non-ionic polymers
Viral vaccines are considered to be amongst the most successful achievements in health
science. Also, the use of viral vectors for gene therapies has shown the promise to become
the next medical revolution for combating a wide variety of currently untreatable diseases.
The wide range of viruses and their production methods make it extremely difficult to
standardize viral vaccine manufacturing. Purification processes require several steps and
are typically tailored to each particular virus species and how it is produced, making
process development time-consuming and potentially delaying time to market. Even for
the same product, purification processes might differ almost in their totality between
a small laboratory and a commercial manufacturing facility. Due to scalability, costs,
efficiency, and capacity constraints, industrial purification methods are mostly limited to
chromatography and filtration operations.
This work presents the development of steric exclusion chromatography (SXC) as a
new platform purification method for large biomolecules such as virus particles. In SXC,
an unpurified sample is mixed with a non-ionic polymer — in this case polyethylene
glycol (PEG) — and fed onto a device made of a porous hydrophilic stationary phase.
The target product is captured without a direct chemical interaction by a thermodynamic
effect caused by the presence of the PEG. Smaller impurities such as media components
and proteins are unaffected by the PEG and washed away. The bigger the target product,
the lesser size and/or concentration of PEG is needed for its capture. Finally, the purified
product is recovered by flushing the device with a solution not containing PEG.
SXC was used for the purification of 14 different cell-based virus strains and serotypes
— influenza virus, yellow fever virus, adeno-associated virus (AAV), and Modified Vaccinia
Ankara (MVA) — with a wide variety of sizes (20–250 nm) and from several production
processes. Likewise, extracellular vesicles (EVs) of 160–230 nm from Madin-Darby canine
kidney (MDCK), baby hamster kidney (BHK), and human embryonic kidney (HEK) cells
were purified.
A number of stationary phases were tested, including hydroxylated monoliths (1–2 μm
pore size), cellulose membranes (1–1.2 μm pore size), and 3D-printed cellulose monoliths
(400–500 μm pore size). Devices packed with regenerated cellulose membranes of 1.0 μm
pore size were the most efficient in terms of product yield as were concentrations of 8–10%
PEG-6000 for sample loading. Four different strains of influenza virus produced in suspension MDCK cells in batch
systems showed product recoveries >98%. The highest measured productivity for influenza
virus A/Puerto Rico/8/34 H1N1 in terms of the hemagglutinin protein antigen was around
69 000 ÎĽg per square meter per hour (4600 monovalent doses per square meter per hour).
In the case of yellow fever virus, two strains used for commercial vaccine manufacture
were produced separately in adherent Vero cells. Virtually full yield of infectious titer was
observed and residual DNA and protein levels were below regulatory requirements. As
many as 6 Ă— 109 plaque forming units (equivalent to more than 100 000 vaccine doses)
were purified from around one liter of cell culture with a productivity of more than 5
million doses per square meter per hour.
For adeno-associated virus (AAV), several wild-type and recombinant variants were
produced in adherent HEK cells by triple transfection and purified from both cell lysates
and cell supernatants; no product losses were detected during SXC and the purified AAV
(up to 2 Ă— 1014 viral genomes per liter) successfully induced either gene expression or
gene knockdown in transduced cells both in vitro and ex vivo.
Exploratory results with Modified Vaccinia Ankara (MVA) virus produced in avian
cells showed virtually full yield with a TCID50 titer of 3.7 Ă— 109 virions. The virus, however,
seemed susceptible to aggregation upon addition of PEG as evidenced by particle size
distribution analysis. Adding sucrose or sorbitol (8% of either) to the PEG-conditioned
virus seemed to lower the amount of aggregates observed compared to the PEG-conditioned
sample without stabilizers. Regardless, the SXC-purified MVA virus showed a distinct
monomer peak of around 220 nm without visible aggregation.
It was observed that EVs from the host cells were often co-purified with the target
virus particles. This was attributed to the very similar characteristics between both.
Preliminary results for the capture of EVs present in cell supernatants showed particle
recoveries of around 40% and concentrations close to 8 Ă— 1010 particles per mL. Further
studies should continue to evaluate SXC for the preparative purification of EVs.
Clearance of protein and DNA with SXC were typically >85% and >75%, respectively,
depending on the virus and the experimental setup (e.g., placing a DNA digestion step
before SXC). In all cases, it was advantageous to have a nuclease treatment before SXC
to achieve lower amounts of residual DNA.
SXC with 3D-printed cellulose monoliths with channel diameters of 400 ÎĽm and 500
ÎĽm was inefficient in terms of product yield (around 40% for influenza A virus) compared
to the 1.0 ÎĽm regenerated cellulose membranes, however, their use is interesting for future
work, e.g., as an alternative to expanded-bed chromatography.
The ability to load and recover the product at physiological pH and conductivity as
well as the conformation stabilizing properties of PEG are relevant advantages during
the purification of labile biopharmaceuticals. The high product recoveries achieved so far
with SXC make it possible to allow for subsequent polishing operations for improving purity without risking unacceptably low process yields. The narrow operational range of
SXC permits the purification of viruses with a high probability of success (e.g., testing
8% PEG-6000 as a starting point) and the low cost of the membranes allows single-use
operation (which avoids expensive and time-consuming cleaning and sanitization steps).
Scale-up of SXC is simple, as it requires only a linear increase in membrane surface,
and the use of devices of up to 20 square meters would enable industrial-scale virus
purification.
As a capture step, SXC seems to be comparable or better than most chromatography
methods available in terms of product yield, ease of use, and scalability. However, estimating
capacities is challenging since there is no direct chemical bond involved. Recovery was
highly dependent on certain quality attributes of the starting material, such as residual
cell debris and/or aggregated product.
The results shown here are the basis for further optimization and application of this
technology and they indicate that membrane-based SXC has the potential for becoming
a platform technology for both viral vaccine and gene therapy applications