Lentiviral vector integration in the human genome induces alternative splicing and generates aberrant transcripts

Abstract

Retroviral vectors integrate in genes and

Gene therapy: too much splice can spoil the dish

“…Through highly sensitive yet very specific techniques, these chimeric ("read-through") transcripts were systematically detected in populations of transduced cells. While neither study could claim a strong quantitative power, the examination by Mavilio and colleagues of a limited set of integrants revealed read-through transcripts for more than half of the targeted genes in all cell types tested (13).…”

“…However, in about 10% of cases, read-through mRNAs matched their physiological counterparts in abundance (13), which, considering that retroviral integration is monoallelic, suggests complete subversion of transcripts produced by the targeted locus.…”

“…In this issue of the JCI, the teams of Fulvio Mavilio and Eugenio Montini, who have had a long-standing interest in assessing the genotoxicity of integrating vectors, follow up on this observation by reporting large-scale explorations of provirus-induced aberrant splicing (13,14). Both studies were performed using lentiviral vectors and human cells, notably HSCs and primary T lymphocytes.…”

“…The risk of aberrant splicing can only be predicted for a given vector to an extent through the types of in vitro analyses described in this issue of the JCI (13,14). However, observations collected so far point to the frequent use of noncanonical cryptic splice donor or acceptor sites, in some cases generated by reverse transcription-induced mutations, and to the critical influence of integrated locus-specific elements (3,13,14). Nevertheless, the finding that in most cases levels of viral-cellular fusion transcripts are low, whether due to weak rates of aberrant splicing or to missensemediated RNA degradation, is reassuring, as many growth-promoting factors only…”

The Committee for Advanced Therapies' of the European Medicines Agency Reflection Paper on Management of Clinical Risks Deriving from Insertional Mutagenesis

“…A study in mice harboring a truncated form of HMGA2 showed that overexpression of the transcript could result in benign hematopoietic stem/progenitor cell expansion (Ikeda et al, 2011). Following these observations, several groups have now shown that the generation of aberrant transcripts could indeed alter the cellular transcriptome, potentially leading to haplo insufficiency of a tumor suppressor gene (Cesana et al, 2012;Heckl et al, 2012;Moiani et al, 2012). The clinical significance of these mutagenic events, however, remains uncertain.…”