Table 2.

Summary of in vivo epigenetic editing studies. The epigenome editor used, genes modified, target tissues/cells, disease, and delivery mechanisms are listed.

Epigenome Editor	Gene	Target	Disease or Condition	Delivery Form	Delivery Route	Comments	Reference
TALE-KRAB	c-Kit, PU.1 (Spi1)	Bone Marrow (BM)	BM transplantation	Cell implantation	Intravenous injection	Combined BM transplantation with a multicolor TALE-KRAB expression vector to knock down two targets genes in hematopoietic compartment in vivo. A technology for investigating functional roles of multiple gene targets.	[19]
dCas9-eGFP, dCas9-VP64	Trp53, Mgmt	B-cell lymphoma, B-ALL leukemia	Lymphoma	Cell implantation	Intravenous injection	Showed dCas9-mediated gene level perturbation for modeling cancer progression and therapeutic relapse both in vitro and in mouse models.	[20]
dCas9-Tet1	FMR1	iPSC-derived neurons	Fragile X	Cell implantation	Intracranial injection/Neonatal engrafting	Showed sustained reactivation of FMR1 in the methylation edited FXS cells when injected into the P1 mouse brain for subsequent analysis one- or three-month post transplantation.	[21]
ZF-VP64	GDNF	Glial cells	Parkinson’s disease	AAV2	Striatum injection with convection-enhanced delivery	Demonstrated that the activation of endogenous GDNF is sufficient to protect against 6-OHDA lesion in rat, and, additionally, showed that the ZF-vp64 activates the endogenous human GDNF gene.	[31]
dCas9 expressing mice with MS2-P65-HSF1	Fst, Il10, klotho, Pdx1, Utrn	Liver, Muscle and Kidney	Diabetes, muscular dystrophy, and acute kidney disease	AAV2/9	Intravenous Intramuscular Intracranial	The authors showed that this system can activate genes by modulating histone marks rather than editing DNA sequences and claimed that it can be used to express genes to compensate for disease-associated genetic mutations, or to overexpress long non-coding RNAs, and GC-rich genes which has been difficult until now.	[32]
dSaCas9-KRAB	Pcsk9	Liver	High cholesterol diseases	AAV8	Intravenous	Authors discuss that one potential improvement of dSaCas9-KRAB system is that they need to deliver two components (the Cas9 and gRNA), which minimizes additional recruitment and potential immune response.	[33]
TALE-VP64 or TALE-SunTag VP64	FXN	Liver, Heart, Muscle, Brain	Friedreich’s ataxia	AAV9	Intraperitoneal injection	Authors discuss that the delivery of AAV9 could be improved with intracranial and intravenous injections in future studies. The delivery of AAV9 intraperitoneal ly is suboptimal if the target organ is also the brain.	[34], [35]
dCas9-KRAB, dCas9-VP64-Rta	Cd81, Afp, Nrl	Liver, Retina	Retinitis pigmentosa	AAV8, AAV2-Y444F	Intravenous, Subretinal	Utilized split-Cas9 system and showed up to 80% transcriptional repression and up to 6-fold transcriptional activation and showed efficacy of using AAV-KRAB-Cas9 in the context of gene therapy in a mouse model for retinitis pigmentosa.	[36]
ZF-KRAB	Ube3a	Brain	Angelman Syndrome	Protein	Intraperitoneal, Subcutaneous	A transient activation of Ube3a gene in the brain by using a ZF protein which when injected subcutaneous crosses the blood-brain barrier.	[46]
dCas9	cmyc	T cells	N.A.	Transgenesis Retrovirus	N.A.	The generated transgenic animals represent a useful tool for enChIP analysis in primary mouse cells.	[47]
dCas9-eGFP KRAB	telomeres Trf1	Liver	N.A.	Transgenesis, DNA	Microinject ion for the generation of the animals in mouse zygotes and hydrodynamic tail vein (intravenous) injection	The generated dCas9-EGFP knock-in mouse provides a useful tool to dissect genome functions, including chromatin dynamics in live animals.	[48]
dCas9-SunTag-P65-HSF1	Ascl1, Neurog2, Neurod1, Dkk1, Hbb, many	Brain, Astrocytes, Fibroblasts	N.A.	Transgenesis, AAV8 and Lentivirus	Intracranial, Intravenous	The generated transgenic mouse model allows for a flexible screening for studying complex gene networks, including long noncoding RNAs and gain-of-function phenotypes in the nervous system.	[49]
dCas9-SunTag VP64	Myc, Tnfrsf1a, Slc7a11, Tp53	Liver	Liver injury and tumorigenesis	Transgenesis, and AAV8	Intravenous	The authors envision that their system CRISPRa system will be useful for performing additional tissue‐ specific genetic screens as dCas9 can be activated in any tissue of interest. They showed hepatocyte specificity with an AAV- Cre virus, but viruses with other cell type–specific tropisms could be used to target other tissues.	[50]