TET2 and B-cell chronic lymphocytic leukemia: REGASE-1 knock-out T cells demonstrated improved accumulation and persistence in an adoptive cell therapy model in vivo.89 In another case report, Fraietta et al. discovered unintended disruption of the methylcytosine dioxygenase TET2 gene by CAR lentiviral integration in a CAR T cell administrated into a chronic lymphocytic leukemia (CLL) patient, in addition to a hypomorphic variant in the other TET2 allele.90