Plant-based vaccine production with foreign protein expression is a multistep procedure involves with the integration of transgene into the plant cells. As the first step, a gene coding for the antigen that would stimulate serum or mucosal antibody production against the selected pathogen has to be identified and isolated.
Next, this target sequence of the selected antigen has to be integrated into a plant expression vector. This is usually a vector suitable for plant transformation. Basically transformation vector should contain a strong plant tissue specific or constitutive promoter that controls antigen sequence expression within the plant, as well as marker genes such as an antibiotic resistance marker for selection of transformed plant tissue (Hansen, 1997). Transgene can be expressed in the plants either through a stable transformation system or through transient transformation system, depending on the location where the transgene has been inserted in the cells. Stable transformation system can be achieved either through the nuclear genome integration or the plastid genome integration.
It is called stable or permanent due to the permanent changes occurring in recipient cells’ genetics as the target transgene is integrated into the genome of host plant cells. Biolistic and genetically modified Agrobacterium strain can lead to the formation of stable transfection. Transient transformation system involves the production of desired protein or antigen soon after the heterologous gene resides transiently in the host cells(Altpeter et al., 2005). It does not depend on chromosomal integration of heterologous DNA so is a relatively simple and can lead to high levels of transgene expression.
Thus transient gene expression provides a rapid and facile alternative to the generation of stably transformed plants (Hansen, 1997). Two most commonly used methods that would achieve transient expression of a desired protein in plants are the Agrobacterium-mediated transformation and particle bombardment (Altpeter et al., 2005)
