Systemic circulation of poly(L-lysine)/DNA vectors is influenced by polycation molecular weight and type of DNA: differential circulation in mice andrats and the implications for human gene therapy

Effective gene therapy for diseases of the circulation requires vectors cap able of systemic delivery. The molecular weight of poly(L-lysine) (pLL) has a significant effect on the circulation of pLL/DNA complexes in mice, with pLL(211)/DNA complexes displaying up to 20 times greater levels in the blo od after 30 minutes compared with pLL(20)/DNA. It is shown that pLL(20)/DNA complexes fix mouse complement C3 in vitro, independent of immunoglobulin binding; are less soluble in the blood in vivo; bind erythrocytes; are rapi dly removed by the liver, where they associate predominantly with Kupffer c ells; and result in a rapid increase in hepatic leukocytes expressing high levels of complement receptor 3 (CR3). The circulation properties of these complexes are also dependent on the type of DNA used, with circular plasmid DNA complexes exhibiting increased circulation compared with linear DNA. P LL211/DNA complexes bind erythrocytes and associate with Kupffer cells but, in contrast, do not fix mouse complement in vitro and are unaffected by th e type of DNA used. In rats, both types of complexes produce hematuria and are rapidly removed from the circulation. Correlation of in vivo and in vit ro results suggests that the solubility of complexes in physiological salin e and species-matched complement fixation and erythrocyte lysis may correla te with systemic circulation. Analysis using human blood in vitro shows no hemolysis, but both types of complexes fix complement and bind IgG, suggest ing that pLL/DNA complexes may be rapidly cleared from the human circulatio n. (Blood, 2001;97:2221-2229) (C) 2001 by The American Society of Hematolog y.