Anti-CD19 chimeric antigen receptor (CAR) T-cell therapy represents a breakthrough in the treatment of relapsed and refractory B-cell malignancies, such as chronic lymphocytic leukemia (CLL), inducing long-term, sometimes curative, responses. However, fewer than 30% of CLL patients achieve such outcomes. It has been shown that a smaller subset of T cells capable of expansion and persistence is crucial for treatment effectiveness. Notably, a pre-existing mutation in the epigenetic regulator TET2, combined with CAR vector-induced disruption of the other intact allele, significantly enhanced the potency of the CAR-engineered T-cell clone in one CLL patient. This finding aligns with independent research, suggesting that the CAR gene's genomic insertion site influences tumor-targeting capability. Thus, it is plausible that vector-induced gene disruptions affect CAR T-cell function. This review synthesizes existing knowledge on vector integration into the host genome and its impact on clinical outcomes in CAR T-cell therapy patients. Our aim is to inform the development of improved therapies and enhance their overall efficacy.