Table 1.

A comparison of gene editing technologies used in T cell engineering

DNA-binding protein	Binding unit	Binding-site restrictions	Nuclease	Successful use in primary T cells?	Commercially available?
ZFN	Each finger binds 3 bp of DNA	Two different adjacent sites separated by a spacer, guanine-rich; binding is context dependent, and limited specificities are available	FokI dimer	Yes	Yes
TALEN	Each TALE repeat binds 1 bp of DNA	Two different adjacent sites separated by a spacer, T at the 5′ end of target sequences	FokI dimer	Yes	Yes
MegaTAL	Combination of TALE repeats and meganuclease	Meganuclease target site must be present	Meganuclease	Yes	No
Cas9	20 bp of a RNA-DNA hybrid	3 bp of PAM immediately following the target site	Cas9	Yes	Yes

Abbreviations: Cas9, clustered regularly interspaced short palindromic repeats associated protein 9; megaTAL, a synthetic protein that is a combination of TALE DNA binding domains and a meganuclease; PAM, protospacer-adjacent motif; TALE, transcription activator-like effector; TALEN, transcription activator-like effector nuclease; ZFN, zinc finger nuclease.