The WHO recommends complete withdrawal of the oral polio vaccine (OPV) by April 2016 globally and replacing with at least one dose of inactivated poliovirus vaccine (IPV). However, high-cost, limited supply of IPV, persistent circulating vaccine-derived poliovirus transmission and need for subsequent boosters remain unresolved.  Now, a study from researchers led by the University of Pennsylvania develops an oral vaccine booster by manipulating plants to express a protein found in the polio virus; tests with sera from immunized mice show that the booster confers immunity against all three serotypes of polio.  The team states that their findings have the potential to provide a timely solution to deal with polio outbreaks and eradication around the globe.  The opensource study is published in the Plant Biotechnology Journal.

Previous studies show that two vaccines, bivalent oral poliovirus vaccine, or bOPV, and the inactivated poliovirus vaccine, IPV, are currently used throughout the world to protect against polio. Even though persons immunized with IPV are completely protected against paralysis, they could be infected with poliovirus and transmit it to their contacts. Additionally, poliovirus can live in an infected person’s faeces for many weeks and can also contaminate food and water in unsanitary conditions.  While mucosal immunity caused by OPV is significantly more effective, it rapidly wanes, but can be boosted by either OPV or IPV.  This suggests that there is a need for booster vaccine that could be used in previously immunized individuals to induce immunity.  The current study provides evidence that oral-boosting with a plant-derived viral protein 1 (VP1) provides immunity against different PV serotypes.

The current study coaxed plants to grow the biomolecule of interest by bombarding the leaves with the appropriate gene until it is taken up by chloroplasts. The plant then produces the associated protein in its leaves, which can then be freeze-dried and encapsulated for oral administration.  To induce immunity against polio, the lab decided to target VP1, a structural protein present in all three serotypes of polio. They fused it to carrier protein cholera toxin subunit B, which enables the protein to cross mucosal surfaces.  Next they fed the freeze-dried plant material expressing the fused protein to mice to see if it could induce an immune response in mice that had already been primed with an IPV vaccination.

Results show that the vaccine, when formulated with adjuvants, induced high levels of mucosal and systemic immunity in the mice, corresponding to IgA and IgG antibody responses, respectively.  Data findings that it could neutralize all three serotypes of polio virus.

The team surmise that their findings provide a novel strategy of a low-cost, cold chain-free, plant-made oral booster vaccine.  For the future, the researchers hope to pursue FDA approval to conduct clinical studies in humans with this virus-free vaccine, which could be produced relatively inexpensively and does not require refrigeration or special handling and could therefore eventually contribute to a polio-free world.

Source: University of Pennsylvania