Liposome Mediated Gene Transfer into Vascular Cells

Mechanism of calcium ion induced multilamellar vesicle-DNA interaction

The effect of Ca2+ on the DNA interaction with anionic and neutral multilamellar vesicles (MLV) has been investigated. DNA from wheat (Triticum aestivum L. Gerek) was introduced to a suspension of MLV, composed of phosphatidylcholine (PC):dicetylphosphate (DCP):cholesterol (CHOL) at different molar ratios, to which Ca2+ (5-75 mM) was subsequently added. Indication of aggregation and/or fusion was obtained via light-scattering examination following the addition of Ca2+ and DNA to the MLV medium. Using a UV spectrophotometric assay, it was observed that although DNA alone has no effect on negatively charged MLV, it enhances liposomal interaction in the presence of calcium ions. The minimal Ca2+ concentration required to promote the interaction was detected to be 10 mM, and the highest level of interaction was observed at 75 mM. The aggregation/fusion of vesicles was detected for uncharged MLV (with no DCP in their structure), as well as for the anionic ones containing c. 10% CHOL, but not for anionic MLV containing 40% CHOL. This is explained in terms of cholesterol decreasing the membrane fluidity (above the Tc of components) as a result of which more rigid vesicles become less prone to aggregation/fusion interactions.

Microencapsulation--an alternative approach to gene therapy

Non-autologous somatic gene therapy' is a novel approach to gene therapy which does not depend on genetic modification of the patient's own cells. Recombinant cell lines secreting a desired therapeutic gene product can be implanted into different patients requiring the same product replacement. Graft rejection is avoided by enclosing these cells in immuno-isolation devices whose permeability excludes the host's immune mediators but permits the transit of nutrients and recombinant gene products. The feasibility of this strategy is demonstrated by expression of recombinant human enzymes, hormones and coagulation factors from fibroblasts or myoblasts enclosed within alginate-poly-L-lysine-alginate microcapsules. Its clinical efficacy is demonstrated by the correction of pathological phenotypes in murine models of human endocrine and lysosomal storage diseases. Hence, this approach may lead to a potentially cost-effective method of gene-based therapy.