Long-term safety of lentiviral or gammaretroviral gene-modified T cell therapies

Abstract

Long-term risks of gene therapy are not fully understood. In this study, we evaluated safety outcomes in 783 patients over more than 2,200 total patient-years of observation from 38 T cell therapy trials. The trials employed integrating gammaretroviral or lentiviral vectors to deliver engineered receptors to target HIV-1 infection or cancer. Eighteen patients (2.3%) developed secondary malignancies after treatment, with a median onset of 1.94 years (range: 51 d to 14 years). Where possible, incident tumor samples were analyzed for vector copy number, revealing no evidence of high-level marking or other indications of insertional mutagenesis. One T cell lymphoma was detected, but malignant T cells were not marked by vector integration. Analysis of vector integration sites in 176 patients revealed no pathological insertions linked to secondary malignancies, although, in some cases, integration in or near specific genes, including tumor suppressor genes, was associated with modest clonal expansion and sustained T cell persistence. These findings highlight the safety of engineered T cell therapies.