Scientists at the International Livestock Research Institute (ILRI) have been working to develop a vaccine for African swine fever, a lethal and contagious haemorrhagic viral disease in domestic pigs caused by the African swine fever virus (ASFV). Currently there are no vaccines on the market, but several are under development. Scientists at ILRI are applying the cutting-edge Nobel Prize-winning genome editing technology known as CRISPR technology to fast-track rational development of live-attenuated ASFV vaccine candidates. CRISPR stands for ‘clustered regularly interspaced short palindromic repeats’, and the technology was adapted from natural defense mechanisms of bacteria. In order to protect themselves, bacteria essentially chop up and destroy the building blocks (DNA) from foreign invaders.
Jennifer Doudna, a UC Berkely professor, and Emmanuelle Charpentier, director of the Max Planck Institute for Infection Biology, won the 2020 Nobel Prize for Chemistry for their co-development of the CRISPR-Cas9 tool, that allows scientists to remove genes or change them quickly with precision. In the lab they used the protein Cas9 which act like a pair of molecular scissors which cut through DNA.
In the past, a technique known as a homologous recombination was applied to generate genetically modified ASFV vaccine candidates. This process involved transferring of genetic material to cause a change in the genome. But this approach is hampered by low efficiency of incorporation of the plasmid, a molecular vehicle that aids in modification of the DNA of interest, into the viral genome.
In addition to these challenges, there is a need for extensive screening to isolate the mutated virus from the parental strains through a method that could further alter the mutant virus in an undesired way. To circumvent these challenges, scientists have introduced precise genome modification in different organisms ranging from tiny microbes to plants and mammals with speed, simplicity, and efficiency. Thus, this powerful approach eliminates the random recombination, deployed in the old methods. The tool increases the fraction of changed viruses and makes it easier to isolate the mutants. Using this approach, ILRI scientists have generated 10 ASFV vaccine candidates due to be tested for their safety and efficacy beginning the first quarter of 2021. It takes approximately six months to get single mutant using the older method, which implies the team would have taken 5 years to make 10 vaccine candidates. CRISPR technology reduced that time a little over a year.
Lucilla Steinaa, principal scientist at ILRI, who is leading the vaccine research against African swine fever, says ‘the CRISPR-Cas9 gene editing system is a quick and easy way to achieve the mutants we want as vaccine candidates. Steinaa adds, ‘Based on the successes of editing the African swine fever virus, we are looking into the use of this technology to generate live attenuated vaccines for other pathogens.’
Hussein Abkallo, a postdoctoral scientist at ILRI and technical lead of the CRISPR-Cas9 work in ASFV vaccine research says, ‘besides accelerating ASFV vaccine development effort, CRISPR technology has significant potential for making vaccines for other livestock pathogens such as, Theileria parva, a parasite that causes East Coast fever, a fatal cattle disease.’ Abkallo added, ‘this technology has also proven useful for improving livestock breeds and developing extremely sensitive multiplex diagnostics for both human and veterinary pathogens.’ He is keen on applying the full potential of the CRISPR-Cas9 technology to improve lives through livestock in developing countries.
Steinaa added, ‘We recently received funding from the United States Agency for International Development (USAID) to apply the CRISPR-Cas9 technology for attenuation of the Theileria parva parasite. This is indeed a very exciting project and is part of a larger consortium, led by Washington State University (U.S.A).’
This project has been funded through the International Development Research Centre (IDRC) and partners on this project include J. Craig Venture Institute (U.S) and the Friedrich Loeffler Institute (FLI).
Learn more about ILRI's work on African swine fever
Presentation by Lucilla Steinaa, ‘Towards a vaccine for African swine fever’