Upstream Development of a Viral Vectored Vaccine

The Problem

The upstream process for a viral vectored vaccine needed to circumvent the dependency on an avian embryo production system which posed a risk due to egg supply limitations and operational difficulties. The vaccine was produced in a roller bottle-based process, which lack scalability and include difficulty in controlling critical process parameters. To meet demands for clinical supply a targeted upstream development approach was required.

The Breakthrough

The process required adaption to a more scalable, commercially viable format to facilitate clinical demands. An approach investigating cell line selection, growth condition optimisation, vessel selection and infection optimisation was undertaken to determine to develop an upstream process.

The Impact

Using this process development approach, target titres were achieved and successful scale up to pilot scale was accomplished in time to meet clinical supply demands.

Background

Vaccine development has traditionally been a long, complex process often taking up to 15 years. The COVID-19 pandemic has fuelled the need for the rapid development of vaccine processes with the flexibility and scalability required to respond to new pathogens. Viral vector vaccines use a modified virus as a vector to deliver the genetic material encoding for a disease-specific antigen into host cells. To support the increased global demand for vaccines APC leverages its BioAchieve® platform to accelerate development of robust, scalable and cost-effective vaccine processes.

 Multiple factors are considered for this upstream process development approach for viral vector vaccines. Early in upstream process development cell line selection involves the screening of biologically suitable cell lines. Traditionally, viral vector processes utilise adherent cell lines which require surface attachment to grow. Adherent cells are difficult to scale up and involve labour intensive steps which are avoided with suspension modes of operation. However, it is a well-known fact that a bioreactor provides a more controlled culture environment than flasks, with minimal batch-to-batch variability, low contamination rate and lower operation costs.

Suspension cells grow free-floating, suspended in the culture medium. Suspended cell cultures don’t require surface detachment and are more easily scaled. An important consideration early in development is the adaption to a suspension cell line or the development of a microcarrier bead process (microcarrier beads increase surface area for adherent cells and can be used with suspension modes of operation i.e., stirred tank bioreactors).

Growth conditions including media selection, supplementation, nutrient feeding and media exchange strategies can be explored to optimize cell growth and improve product titres. Nutrient requirements and optimal process conditions must be investigated for both the cell growth phase (pre infection of cells with a virus seed stock) and viral replication phase (post infection).

Vessel selection largely depends on whether the process utilises an adherent (T-flasks, HYPERflasks) or suspension cell line (Erlenmeyer shake flask, stirred tank bioreactor). Single use technology (the use of single-use disposable bags in process steps typically operated using stainless steel equipment) presents a cost-effective option suitable for the rapidly changing demand for vaccines.

Infection parameters including the MOI (the ratio of viral particles added per cell), TOI (cell density at the time of infection) and TOH (time of harvest) must be determined at the optimisation stage. Different harvest strategies can be explored (Batch mode & Perfusion mode) to maximise the yield.

Once optimised at bench scale, the upstream process must be scaled up. APC can design a production road map and thus help you in avoiding stumbling blocks. Overall, up-scaling should be a carefully designed and well-documented process. Our process development team provides the knowledge base and means for GMP production. The use of Design of Experiments (DoE) at an early stage is a fundamental element for the identification of your Critical Quality Attributes (CQAs), which in turn support a Quality by Design (QBD) approach to your process development and validation.

APC, to meet clinical supply, developed an approach using Computational Fluid Dynamics (CFD) to simulate the current mixing environment and identify process conditions to replicate the process across different scales. The result: a scalable, robust upstream process suitable to support clinical demands and lay the groundwork for the pathway to regulatory approval.