The rapid emergence and spread of novel infectious diseases such as COVID-19 caused by the SARS-CoV-2 virus has highlighted the need for innovative protein expression solutions to support rapid and comprehensive virus characterization, serological testing, therapeutic antibody and vaccine development to mitigate these threats to global health. A recent white paper published by Thermo Fisher Scientific entitled Advancing the development of therapeutics against infectious diseases with optimized protein expression systems highlights how their comprehensive portfolio of mammalian and insect transient protein expression systems can accelerate and streamline infectious disease research and meet high-yield bioproduction requirements for the development of diagnostics and therapeutics that can mitigate virus spread.
In order to gain timely insight into the structure and function of novel viruses, transient protein expression can be employed to rapidly produce antigens for crystallization and cryo-electron microscopy (cryo-EM) experiments. The Gibco™ Expi293™ Expression System, now with additional cell lines and products for glycan modulation, inducible expression, and methionine labeling, enables high-yield expression of recombinant viral capsid proteins for a variety of structural analysis applications and bioproduction strategies.
One example provided in the white paper, shared how researchers were able to use the Expi293 Expression System to determine the crystal structure of the neutralizing antibody CR3022 bound to the receptor-binding-domain (RBD) of the SARS-CoV-2 S protein, thus permitting researchers to identify a conserved epitope that enables cross-reactive binding between SARS-CoV-2 and SARS-CoV. This structural analysis provides molecular insights into antibody recognition that could aide in the development of not only a SARS-CoV-2 vaccine but also a universal coronavirus vaccine. These types of structural analyses enabled by Gibco expression systems can provided much needed insight into SARS-CoV-2 antigenicity, antibody recognition, and therapeutics research.
Serological testing has been used for decades in medicine to diagnose and monitor viral infection and has been useful for SARS-CoV-2 to better understand its spread and pathogenicity within the population. Serological assays identify antibodies and antigens in a patient’s blood that indicate current or previous exposure to a virus. The white paper detailed work by researchers who used the Gibco Expi293 system to produce S and RBD proteins for the development of a sensitive ELISA-based serological test for SARS-CoV-2.
Spike (S) protein yield is often a limiting factor for serological testing, but optimizing expression parameters in the Expi293 system increased protein yield sufficiently to support an NIH-led SARS-CoV-2 serosurvey, conducted to better understand antibody responses mounted against the virus to aid in vaccine and therapeutic treatment research.
Antibodies are a critical part of an immune response to neutralize pathogenic viruses by either blocking virus attachment or by presenting the viral antigens to effector cells to activate target cell killing. Anti-viral monoclonal antibodies (mAbs) are, therefore, an important therapeutic strategy to combat emerging viruses. The white paper highlights the research by Pan et al., who leveraged the Gibco™ ExpiCHO™ Expression System to reliably produce large quantities of the SARS-CoV-2 S RBD protein for a broad range of experiments from receptor blockade assays, virus neutralization tests, and biomolecular interaction analyses to rapidly identify an effective antibody targeting SARS-CoV-2 virus.
Researchers have also used the Expi293 Expression System to generate anti-HA stem antibodies that can synergize with NA inhibitors to enhance protection against existing diseases like influenza over current neutralizing antibodies strategies, as described in detail in the white paper.
Utilizing high-yield transient protein expression systems offers a viable alternative to stable producer cell lines, which can take a long time to develop and optimize, to accelerate vaccine development timelines, critical for both emerging and existing virus outbreaks. However, expression systems are protein- and application-dependent. The white paper summarizes results where the production of HIV-1 envelope glycoprotein trimers in Gibco ExpiCHO-S cells resulted in higher yield, purity, and antigenicity compared to its expression in Expi293F cells, which helped to streamline HIV-1 vaccine development work.
Another group found that using human cell-based Expi293F-expression of the HA protein from H1N1pdm09 influenza virus induced cross-protection against the highly pathogenic avian influenza H5N1 virus in mice not observed with HA produced in embryonated chicken eggs, which could represent a novel influenza vaccine strategy.
Together, the research summarized in the white paper underscores the need for robust and flexible transient protein production systems to support the rapid pace of infectious disease research, where optimized workflows to generate high-quality viral proteins can fuel research to better our understanding of viral pathogenicity and spread in efforts to produce effective therapeutic strategies.