Cell-line screening and process development for a fusogenic oncolytic virus in small-scale suspension cultures

Oncolytic viruses (OVs) represent a novel class of immunotherapeutics under development for the treatment of cancers. OVs that express a cognate or transgenic fusion protein is particularly promising as their enhanced intratumoral spread via syncytia formation can be a potent mechanism for tumor lysis and induction of antitumor immune responses. Rapid and efficient fusion of infected cells results in cell death before high titers are reached. Although this is an attractive safety feature, it also presents unique challenges for large-scale clinical-grade manufacture of OVs. Here we evaluate the use of four different suspension cell lines for the production of a novel fusogenic hybrid of vesicular stomatitis virus and Newcastle disease virus (rVSV-NDV). The candidate cell lines were screened for growth, metabolism, and virus productivity. Permissivity was evaluated based on extracellular infectious virus titers and cell-specific virus yields (CSVYs). For additional process optimizations, virus adaptation and multiplicity of infection (MOI) screenings were performed and confirmed in a 1 L bioreactor. BHK-21 and HEK293SF cells infected at concentrations of 2 × 10⁶ cells/mL were identified as promising candidates for rVSV-NDV production, leading to infectious titers of 3.0 × 10⁸ TCID₅₀/mL and 7.5 × 10⁷ TCID₅₀/mL, and CSVYs of 153 and 9, respectively. Compared to the AGE1.CR.pIX reference produced in adherent cultures, oncolytic potency was not affected by production in suspension cultures and possibly even increased in cultures of HEK293SF and AGE1.CR.pIX. Our study describes promising suspension cell-based processes for efficient large-scale manufacturing of rVSV-NDV. KEY POINTS: • Cell contact-dependent oncolytic virus (OV) replicates in suspension cells. • Oncolytic potency is not encompassed during suspension cultivation. • Media composition, cell line, and MOI are critical process parameters for OV production. • The designed process is scalable and shows great promise for manufacturing clinical-grade material.