If I understand this correctly (my biomedical engineering undergrad finally coming to use!):
1. Cancer cells present antigens that are specific to cancer cells and do not occur in healthy cells.
2. CRISPR allows us to genetically engineer someone's existing T cells to target those antigens.
3. When re-introduced, these T-cells target the cancer cells and destroy the tumor.
4. Because they are T-cells, they're effectively distributed through blood to the entire body and are able to affect cancerous cells that may be too small to observe or detect.
5. They become inactive and stowaway in the lymphatic system but if the cancer comes out of remission, an "immunity" type response brings them back.
This is amazing. This feels like science fiction from my childhood and the life changing possibilities unlocked by CRISPR that I was taught in my undergrad classes.