Genome Editing

Question 1

How is prime editing done?

Answer 1

1. Cas9 nicking of protospacer adjacent motif (PAM) strand
2. hybridisation of primer-binding site to PAM strand
3. Reverse transcription
4. hybridisation of DNA strands and flap cleavage, enables editing
5. ligation and mismatch repair, incorporating edit

Question 2

Exa-cel

Answer 2

• targets BCL11A to prevent repression of HbF
• study 121 : VF12 response >20% seen in 29 of 31 subjects; SAE observed in 45% of subjects with SCD
• study 111 : 91.4% of subjects acheived sustained transfusion independence, median trnasfusion-free status 20.4 months, no resumption of transfusion observed, 32.7% of subjects with TDT suffered from SAE
• overall safety comparable to autologous transplants

no chromosomal aberrations or off-target editing observed, but only certain loci tested

Question 3

EDIT101

Answer 3

correction of CEP290 protein in LCA10 photoreceptor to rescue protein, to restore to full length protein and rebuild outer segment, via subretinal injection
- trials halted as homozygous condition very rare, and only 8% of heteroyzgous condition are responders

Question 4

Examples of genome-edited products

Answer 4

• MSTN KO pork for increased lean meat and low fat, greater productivity and profit
• meatier red sea bream in japan
• eggXYt for birth control of male chicks
• high oleic acid oil from soybean, trans fat free by editing FAD2 gene which converts oleic acid to linoleic acid
• herbicide-resistant plants by adenine base editing in plastid DNA
• GABA-enriched tomato
• bigger, more nutritious yams developed in Ghana