To insert the gene, you use lentiviral transfection. The gene can wind up inserted in the wrong location of the genome, causing a mutation. Worst of all, natur

To insert the gene, you use lentiviral transfection. The gene can wind up inserted in the wrong location of the genome, causing a mutation. Worst of all, natural selection can happen where landing in a region of the genome that promotes growth (i.e. cancer) will give those off target cells a selective advantage. Inside the petri dish, Darwinian natural selection means the most cancery cells are the fittest. There are ways of mitigating this. Like through selecting and screening monoclonal populations, but right now that process is painstaking and expensive. Alternatively (and concurrently), we could invest into gene insertion technologies with lower probability of off-target effects. Just one of the many reasons a treatment like this is expensive. You need to screen clones from every single patient because the treatment is unique to every single patient.