Preventing secondary primary malignancies (SPMs) in CAR-T cell therapy through site-specific transgene integration into genomic safe harbors (GSHs)

Chimeric antigen receptor (CAR)-T cell therapy has revolutionized oncology by achieving durable remissions in refractory hematologic malignancies. However, emerging reports link this therapy to second primary malignancies, including CAR+ lymphomas and leukemias, driven by insertional mutagenesis from semi-random viral vector integration near oncogenes or tumor suppressor loci. These rare but serious complications underscore the dual challenge of eradicating primary tumors while mitigating delayed genotoxic risks. Conventional CAR-T cell manufacturing, reliant on gamma-retroviral or lentiviral vectors, introduces genomic instability through integration into fragile sites or transcriptionally active regions. CRISPR/Cas9-mediated genome editing further amplifies risks via off-target double-strand breaks and chromosomal rearrangements. This review evaluates genomic safe harbors (GSHs)-such as AAVS1, TRAC, CCR5, ROSA26 and CLYBL-as loci validated for stable, high-level CAR transgene expression without oncogenic disruption. GSHs meet stringent criteria: distal from cancer-related genes, resistant to epigenetic silencing, and transcriptionally permissive. Preclinical studies demonstrate that site-directed CAR integration into GSHs preserves antitumor efficacy while eliminating malignant transformation risks. Challenges persist in optimizing homology-directed repair efficiency, mitigating residual dsDNA toxicity, and standardizing regulatory frameworks for long-term genomic surveillance. Emerging technologies-base/prime editing, hybrid nucleases, and rigorous monitoring-promise enhanced precision and safety. By reconciling therapeutic innovation with genomic integrity, GSH-engineered CAR-T cells herald a paradigm shift toward precision immunotherapies, offering curative potential while preempting secondary oncogenesis. Collaborative efforts to refine manufacturing, harmonize global standards, and prioritize patient-specific risk stratification will be critical to advancing this transformative approach.