Hydrodynamics-based delivery of plasmid DNA encoding CTLA4-Ig prolonged cardiac allograft survival in rats

Although gene therapy using plasmid vectors is thought to be safer compared with viral vectors, poor efficacy of gene transfer is the obstacle preventing wide application of plasmid vectors. However, high levels of foreign gene expression have been achieved by rapid tail vein injection of a large volume of a plasmid DNA solution into rats. Using this technique, we examined the effect of rat CTLA4-Ig gene transfer on prevention of cardiac allograft rejection in this animal model.

Recipient Lewis rats were injected with either plasmid pCAGGS-CTLA4-Ig-Glu-tag as a treatment vector or plasmid pCAGGS-signal peptide (SP)-Ig as a control vector by hydrodynamics-based delivery technique on the day before heart transplantation. Hearts from Brown Norway donors were transplanted into the neck of Lewis recipients and graft survival was assessed.

The plasma level of CTLA4-Ig reached a peak of nearly 5 microg/mL 1 day after injection, and then slowly decreased but still remained above 0.9 microg/mL until 100 days after injection. The recipient rats treated with the control vector and untreated rats rejected cardiac allografts within 7 days. On the other hand, the median survival time of the grafts treated with pCAGGS-CTLA4Ig-Glu-tag was more than 100 days. Histological examination revealed that long-term survival allografts contained fewer infiltrating lymphocytes. The serum from recipients with long-term survival allograft suppressed allogenic mixed lymphocyte reaction.

CTLA4-Ig gene transfer by means of tail vein injection of plasmid DNA into a recipient rat resulted in remarkable prolongation of cardiac allograft survival with persistent plasma level of CTLA4-Ig protein.