11.3.2.4

Production Process of VSV Vector

The manufacturing process of the rVSV vaccine starts with cell-line expansion in

shake flasks. Then, the cells are seeded in a bioreactor. Fewer papers have fo-

cused on the bioreactor operation modes. Currently, single-use bioreactors are

used more commonly in process development and large-scale production. Once

harvested, the viral stock is subjected to enzyme treatment, essentially

Benzonase. Then, the supernatant is transferred to purification processes and

concentration. A critical step after purification is the formulation step, which has

a significant effect on transport and storage (Figure 11.4). Two parameters,

genomic viral particles and infectious viral titer, are usually used as the char-

acterization of rVSV production. The genomic viral particles that can be mea-

sured by ddPCR are equivalent to the total particles. The infectious viral titer can

be measured by TCID50, which can give us the infectivity or functionality of the

viruses. Although people calculate the dose based on the infectious unit, the load

that is injected to the patient in terms of total particles matters since too much

virus particles can result in a cytokine storm.

11.3.3

EXAMPLE OF VSV-BASED VACCINES

11.3.3.1

VSV-Based Ebola Vaccine

The Ebola virus (EBOV) outbreak in West Africa from 2013 to 2016 accelerated

the development of several antivirals and vaccine candidates that have been

evaluated in clinical trials. Among those, a replication-competent VSV-based

vaccine which expresses the glycoprotein of Ebola was developed and tested in

animal models and in phase 1–3 clinical trials in Europe, North America, and Africa

[74–76]. Although some side effects were still observed in vaccination, the results

of clinical trials for rVSV-ZEBOV demonstrated safety and strong immunogenicity

in humans [61]. In 2019, rVSV-ZEBOV was approved by FDA for emergency use

in individuals at risk for Ebola virus disease. In the rVSV-ZEBOV vaccine, the

glycoprotein (GP) of the EBOV is inserted into a VSV vector in which the G open

reading frame is deleted. The rVSV was generated as a replication-competent virus

particle expressing EBOV GP on its surface.

FIGURE 11.4 Schematic representation of the bioprocesses for VSV viral vector production.

Vectored vaccines

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