WHAT IS PIRBRIGHT DOING? Traditional methods for performing such modifications are time consuming and unreliable. At Pirbright, COMBATTING Mosquito-borne diseases researchers are now using the CRISPR/Cas9 system for vaccine development which makes the process Mosquitoes have the ability to carry and transmit quick, simple and efficient. This technique also allows DISEASE many deadly diseases that are responsible for millions multiple genes from different to be inserted of deaths and billions of pounds of economic losses into a single vaccine to provide protection against every year, particularly in developing countries. USING multiple diseases. Pirbright carries out research to understand how genetically Immunogenetics modified mosquitoes can Immunogenetics explores the link between the be used for the control of and an animal’s genes. Understanding mosquito populations to the genes that control livestock immune responses can prevent diseases of both help us improve their resistance to disease. livestock and people. Experts at Pirbright have been working to understand

One of the most promising Female Aedes aegypti the genes that control natural killer (NK) cells; one control techniques is known mosquito feeding of the first lines of defence against viral infection. as a gene drive. This is where the mosquito NK cells detect the presence of a using special is modified to decrease their ability to breed or receptor proteins on their surface. These attach to carry infections, and this modification is favourably signalling proteins on cells that have become infected, spread into a population at a faster rate than normal triggering the NK cell to kill the infected cell and inheritance. As these modified mosquitoes mate activate other arms of the immune system. with the wild population, up to 100% of the next generation inherit the modification whereas normal Our scientists have been researching the genetics inheritance would give only up to 50%. This means behind this system and in doing so hope to improve the number of modified mosquitoes that need to the resistance of cattle to disease, either by informing be released to make an effective change to the breeding practices to help improve their innate population is much lower than other strategies. resistance, or by designing and selecting vaccines that trigger NK cell functions. Researchers at Pirbright are particularly interested in developing safe, reversible gene drive designs that will modify a target mosquito population but remain local in their effects.

Vaccine development Genetic modification can be employed to help develop new vaccines. For example, we can use to take genes from a virus that causes disease and insert them in to a safe virus such as vaccinia. When a host is injected with the modified vaccinia virus it will then develop against the disease causing virus, without risk of infection. www.pirbright.ac.uk/genetic-engineering Preventing and controlling viral disease GENETICS - KEY FACTS

DNA provides instructions The information in DNA is The structure of The first example of genetic The newly developed gene editing CRISPR is an abbreviation on how to build living stored as a code made up of DNA was originally engineering, a direct transfer tool called the CRISPR/Cas9 of Clustered Regularly organisms and is found four chemical letters: guanine determined in 1953 of DNA from one organism to system was originally discovered Interspaced Short in most cells. It stands (G), cytosine (C), adenine (A) and by James Watson another, was demonstrated in in . It forms part of their Palindromic Repeats. for deoxyribonucleic acid thymine (T). These pair together and Francis Crick 1972 by Herbert Boyer and Stanley defence mechanism against viral Cas9 is a protein used in and it takes the form of a like rungs on a ladder down at the University Cohen when they transferred DNA infection, and we now use it as a the CRISPR system that double helix. the length of the DNA helix. of Cambridge. from one bacterial cell to another. powerful tool in . actually cuts the DNA.

GENOME EDITING USING CRISPR TO EDIT GENES Each organism has a unique which is Genome editing can be achieved in a determined by the sequence of the DNA chemical variety of ways, but one of the most promising Cas9 Protein letters, C, G, A and T. A section of code that is newer technologies is the CRISPR/Cas9 system, responsible for a specific characteristic is known as which has been likened to the ‘find and replace’ a gene. These sections of code can vary from a few function used in document editing. hundred letters to over a million depending on the gene. Cas9 is an enzyme that has the Genome editing is the process of changing the genetic ability to cut DNA, which is often Guide RNA code of an organism by inserting, deleting, modifying likened to ‘molecular scissors’. or replacing sections of DNA. Genome editing uses It is guided to the correct place by specialised tools to cut away a section of DNA at a ‘guide RNA’, which is similar to specific site and sometimes insert a new section. DNA, and has the ability to stick to a section of DNA if its genetic code This can be employed to mend DNA by correcting is complementary. By designing DNA that cause disease, to insert entirely new the guide RNA to stick to a gene bits of DNA giving an organism new characteristics, of interest we can guide Cas9 to or to discover the function of specific genes. cut the DNA only at that site.

Gene editing has already been performed on After the DNA strand is cut we animals, plants, bacteria and even humans, but it is can use the natural DNA repair still in its infancy. However, recent discoveries, such mechanisms of the cell to insert as CRISPR/Cas9, have made it cheaper, quicker and a new gene or reconnect the DNA more accurate. where a gene has been removed.

The CRISPR/Cas9 system enables cheap and rapid editing of genes with greater accuracy than previous methods.

A diagram of the CRISPR/Cas9 complex processing DNA.