Cancer immunotherapy, or immuno-oncology, is an approach to treat cancer by stimulating the body's immune system to combat cancer cells. The major categories of immunotherapy include cytokine therapies, cancer vaccines, oncolytic virus therapies, immune checkpoint inhibitors, and adoptive cell transfer -which includes chimeric antigen receptor-T (CAR-T) cell therapy and natural killer (NK) cell therapy. One of the most promising applications of CRISPR/Cas-9 mediated genome editing is the generation of CAR-T cells. To create CAR-T cells, autologous T cells are collected and genetically engineered to attack cancer antigens ex vivo. These cells are then transferred back into the patient. Zych et al. reported that CRISPR/Cas9 system could be able to improve CAR-T cell function via interrupting the genes that code T cell inhibitory receptors or signaling molecules. CRISPR/Cas9 can also be used to create allogenic CAR-T cells, which can overcome the major limitation of autologous CAR-T cells, which is mismatch of HLA typing. Various studies have attempted to create allogenic CAR-T cells by knocking out genes like beta-2 microglobulin (B2M), T cell receptor α subunit constant (TRAC), and programmed-death 1 (PD-1). Using such approach, it will be possible to create universal CAR-T cells derived from healthy donors and use for multiple patients. This will also reduce the overall cost and time required to generate CAR-T based cell therapies.