Advancement in the Development of ASFV Vaccine Technology for Emergency Vaccination

Scientific Abstract

As a result of the alarming spread of the African swine fever virus (ASFV) in several parts of the world, research efforts on this virus have increased, including the development of several genetically engineered vaccine candidates. Although different continuous cell lines have been proposed for ASFV vaccine production, only one of them, the porcine macrophage ZMAC-4 cell line, has been approved by the USDA-CVB for commercial vaccine production. In this study, we examined ZMAC-4 cell line for its ability to support the replication of two ASF gene-deleted recombinant modified live virus (MLV) vaccine candidates, the ASFV-G-Δ9GL/ΔUK and ASFV-G-ΔMGF. As expected, because the natural host cell for ASFV consists of macrophages and monocytes, both viruses were able to readily replicate to high titers in ZMAC-4 cells without the need of adaptation. Further, sequence analysis of the virus genome after 5 and 10 serial passages of the ASFV-G-Δ9GL/ΔUK in the ZMAC-4 cell line showed no genomic changes, indicating that the ZMAC-4 cell line supports the replication of this vaccine candidate without the need for viral mutations to optimally replicate in this host cell. In addition, we optimized the scale-up virus culture conditions consisting of 1,500 ml volume capable of yielding a high titer of infectious virus in ZMAC-4 cells suitable for vaccine production. Accordingly, we obtained a titer close to 10⁷ HAD₅₀/ml of the ASFV-G-Δ9GL/ΔUK, which by simply increasing the number of 2 L containers used for virus culture can produce several million doses of ASFV vaccine per 150 L batch. Our results confirm previous studies and demonstrate the value of the ZMAC-4 cell line for the stable propagation and production of ASFV MLV vaccine candidates. Based on these observations, the ZMAC-4 cell line provides a sensible choice for ASFV commercial vaccine production. A major deliverable of this project is the development of suitable methods to use the ZMAC-4 cell line as the substrate to grow a leading ASFV vaccine candidate to produce a stockpile of emergency vaccine doses.