T-Cells are remarkable tricky to grow in-vitro. Most of them only grow after presented the particular antigen (for the non-biologists: the part of the virus/bacteria which they recognise) which they are keyed to. I haven't looked at the actual proposals, but I figure they'll take T-Cells, use CRISPR on those directly, clean them off (so you don't accidentally CRISPRize other cells in the body) and re-inject them directly so they won't die off.
You could sequence part of them before insertion, if you manage not to kill the rest of the T-Cells with the wildly differing in vitro environment, but by that point you're playing a numbers game. The non-specific CRISPR action (called off-target mutagenesis in the literature) is a low probability event, but if you sequence part of the T-Cells, you could easily miss one with a bad (read: non-lethal) off-target mutation.
You could sequence part of them before insertion, if you manage not to kill the rest of the T-Cells with the wildly differing in vitro environment, but by that point you're playing a numbers game. The non-specific CRISPR action (called off-target mutagenesis in the literature) is a low probability event, but if you sequence part of the T-Cells, you could easily miss one with a bad (read: non-lethal) off-target mutation.