A new study suggests that CRISPR might not work in humans. The Cas9 snipper proteins come from bacterial species to which humans have extensive immunity. The study found immunity levels of 79% and 65% against the two most widely used homologs for Cas9.
This means that gene-therapies currently in developement that use CRISPR in its current form may not work.
As the paper's abstract states, "The CRISPR-Cas9 system has proven to be a powerful tool for genome editing allowing for the precise modification of specific DNA sequences within a cell. Many efforts are currently underway to use the CRISPR-Cas9 system for the therapeutic correction of human genetic diseases."
Clinical trials will need to adapt to take this factor into account.