Viral vector-based therapeutics have revolutionised modern medicine, enabling precise gene delivery for treating genetic disorders, cancers, and infectious diseases. These therapies rely on the safe and efficient expression of a therapeutic transgene within target cells. However, a critical challenge in the development and regulatory approval of viral vector therapeutics is ensuring that the transgene product is correctly expressed, and functions as intended.
Regulatory agencies, including the FDA, EMA and MHRA, require detailed characterisation of transgene expression as part of the approval process for gene therapies and viral vector-based vaccines. The absence of a validated transgene expression method has previously been a significant regulatory barrier, as seen during the COVID-19 pandemic.
This column explores the essential aspects of transgene expression analysis, discusses the challenges associated and highlights why robust analytical strategies are critical for the successful development and approval of viral vector therapeutics.
Why Transgene Expression Matters
In viral vector-based therapies, the genetic material of the virus is modified to remove its ability to replicate. Instead, a therapeutic transgene is inserted, which is expressed in target cells after the vector infects them. The therapeutic effect of the treatment depends on the correct expression of this transgene, making it essential to confirm and characterise its production.
Regulatory authorities expect developers to demonstrate that their viral vector reliably produces the intended transgenic protein. Failure to do so could delay approvals, as seen with the EMA’s initial assessment of the Vaxzevria COVID-19 vaccine. A major objection during the approval process was that at the time of submission a validated method to measure transgene expression was not available. While the issue was eventually resolved, it underscored the importance of having a validated transgene expression method in place when submitting viral vector-based therapeutics for approval.
