>For people who are involved in dealing with CRISPR/Cas9, what is the effective rate of gene editing done in vitro vs. in vivo? Difficult question. CRISPR is i

>For people who are involved in dealing with CRISPR/Cas9, what is the effective rate of gene editing done in vitro vs. in vivo? Difficult question. CRISPR is ironclad in vitro, but in vivo it's not well understood. For reference, other methods of gene transfer/editing are almost exclusively for in vitro use, with the exception of lentiviral vector-based transduction. >Would the molecular machinery of CRISPR/Cas9 encounter any natural defense mechanism of the human immune system when attempting to mutate target sites on T-cells in say, lymph nodes of adult humans (contrasting to changing DNA in the germ-lines of bacteria or even human embryo's)? Yes. The cell membrane, the nuclear envelope within the cell, and the chromatin/chromosomal structure of the genetic material within the nuclear envelope are huge barriers that can't be skipped across easily when in vivo because many of the convenient work-arounds aren't suitable for in vivo use. Bacteria are always much easier.