Large double copy vectors are functional but show a size-dependent decline in transduction efficiency

Area of Science:

• Gene therapy vector development
• Molecular and cellular biology

Background:

• Self-inactivating lentivectors (SIN-lentivectors) enable double copy vectors (DCV) by replacing 3' LTR deletions with functional sequences.
• Previous studies indicated size-dependent impairment of DCV transduction efficiency with large insulator inserts.

Purpose of the Study:

• To investigate the impact of increasing 3' LTR insert size on DCV transduction efficiency and transgene functionality.
• To determine if promoter-transgene inserts in DCV are affected similarly to insulator sequences.

Main Methods:

• Designed a series of DCV with varying 3' LTR sizes containing different promoter-transgene combinations.
• Transduced cells were analyzed for transduction efficiency and insert functionality.
• Compared transduction efficiencies across different insert sizes.

Main Results:

• Transduction efficiency of DCV decreased in a size-dependent manner with increasing 3' LTR insert size.
• Inserts below 1 kb showed a linear decrease in efficiency, while inserts between 1-2 kb reduced efficiency to a minimum of 5% of empty SIN-vectors.
• No insert size completely abolished transduction, and all tested inserts remained functional post-integration.

Conclusions:

• DCV retain functionality even with large inserts in the 3' LTR.
• Transduction efficiencies are significantly compromised with inserts exceeding 1 kb.
• DCV technology offers a viable platform for gene delivery, with careful consideration of insert size for optimal efficiency.