Porcine reproductive and respiratory syndrome virus (PRRSV) is a persistent threat of economically significant influence to the swine industry worldwide. Recombinant DNA technology coupled with tissue culture technology is a viable alternative for the inexpensive production of heterologous proteins in planta. Embryogenic cells of banana cv. ‘Pei chiao’ (AAA) have been transformed with the ORF5 gene of PRRSV envelope glycoprotein (GP5) using Agrobacterium-mediated transformation and have been confirmed. Recombinant GP5 protein levels in the transgenic banana leaves were detected and ranged from 0.021%–0.037% of total soluble protein. Pigs were immunized with recombinant GP5 protein by orally feeding transgenic banana leaves for three consecutive doses at a 2-week interval and challenged with PRRSV at 7 weeks postinitial immunization. A vaccination-dependent gradational increase in the elicitation of serum and saliva anti-PRRSV IgG and IgA was observed. Furthermore, significantly lower viraemia and tissue viral load were recorded when compared with the pigs fed with untransformed banana leaves. The results suggest that transgenic banana leaves expressing recombinant GP5 protein can be an effective strategy for oral delivery of recombinant subunit vaccines in pigs and can open new avenues for the production of vaccines against PRRSV.
Yah. Um. Well. OK, the study actually showed results indicating that feeding piglets with transgenic banana leaf material containing PRRSV GP5 protein is an effective strategy to prevent disease after viral challenge, and to significantly decrease viral load. Even if the expression levels were very low, and the amount of antigen per feed was of the order of 10 ug/dose – which, for a piglet, is VERY low for an oral dose! So – a qualified success, then, which could doubtless be improved upon in terms of expression and dose and response.
But it’s back to the days of "a banana a day, keeps the vaccinator away".
Which, although it is a noble sentiment, simply is not practical for the reasons advanced – which have to do with the fact that bananas can be cultivated near where pigs are raised, and it is easy to include fresh leaves in food.
All of which ignores the fact that vaccines have to (a) be given in controlled doses, (b) the fresh material containing the doses has to be assayed to determine what the dose is. All of which is a little difficult for a pig famer in a developing country, I would surmise.
All in all, however, the authors have shown that their vaccine is protective, and the concept has promise. But just maybe they should look at using formulated extracts as a food additive, with a higher-yielding expression system.
See on onlinelibrary.wiley.com